NL2036150B1

NL2036150B1 - Smart aggregate for monitoring of concrete structures: design of embedded ultrasonic tomography system

Info

Publication number: NL2036150B1
Application number: NL2036150A
Authority: NL
Inventors: Van Beek Cornelis; Cheng Hao; Yang Yuguang
Original assignee: Univ Delft Tech
Priority date: 2023-10-30
Filing date: 2023-10-30
Publication date: 2025-05-13
Also published as: WO2025095774A1

Abstract

5 1 The invention provides a monitoring system (1000) for monitoring a concrete structure (1), the monitoring system (1000) comprising 11 sensing arrangements (500), an electrical grounding element (700), a pulser (400), an ampliﬁer (200), and a control system (300), wherein n Z 4, wherein: (A) each sensing arrangement (500) comprises a sensor element (10), a ﬁrst switch (510), a second switch (520), and a spacing wire (530), wherein the spacing wire (530) is conﬁgured to separate the ﬁrst switch (510) from the second switch (520) by a spacing distance (ds) of at least 0.5 cm, wherein the sensing arrangement (500) has 10 a ﬁrst conﬁguration and a second conﬁguration, wherein in the ﬁrst conﬁguration the sensor element (10) is conﬁgured electrically coupled to the pulser (400) via the ﬁrst switch (510), the spacing wire (530), and the second switch (520), and wherein in the second conﬁguration (i) the spacing wire (530) is conﬁgured electrically coupled to the electrical grounding element (700) via the ﬁrst switch (510) and (ii) the sensor element (10) is conﬁgured 15 electrically coupled to the ampliﬁer (200) via the second switch (520), (B) the sensor elements (10) of the n sensing arrangements (500) are conﬁgured to be embedded in the concrete structure (1) in a sensing grid arrangement (110), wherein each sensor element (10) is separated from at least two neighboring sensor elements (10) in the sensing grid arrangement (110) by distances independently selected from the range of 20-150 cm, (C) the 20 monitoring system (1000) has an operational mode comprising an actuation stage and a sensing stage, wherein: (a) in the actuation stage a ﬁrst sensing arrangement (501) comprising a ﬁrst sensor element (11) is in the ﬁrst conﬁguration, wherein the pulser (400) is conﬁgured to provide an electrical pulse to the ﬁrst sensor element (11), and wherein the ﬁrst sensor element (11) is conﬁgured to provide an actuation signal in response to the electrical 25 pulse, and (b) in the sensing stage a second sensing arrangement (502) comprising a second sensor element (12) is in the second conﬁguration, wherein the second sensor element (12) is conﬁgured to detect the actuation signal and to provide a related sensor signal to the control system (300) via the ampliﬁer (200), (D) the ampliﬁer (200) is conﬁgured to (i) receive the sensor signal, (ii) amplify the sensor signal, and (iii) provide an ampliﬁed sensor signal to the 30 control system (300), and (E) the control system (300) is conﬁgured to determine a structurerelated parameter of the concrete structure (1) based on a difference between the ampliﬁed sensor signal and a reference signal. Fig. 2

Description

Smart aggregate for monitoring of concrete structures: design of embedded ultrasonic tomography system

FIELD OF THE INVENTION

The invention relates to a monitoring system for monitoring a concrete structure.

The invention further relates to a method for monitoring of a concrete structure. Additionally, the invention relates to a system comprising the monitoring system. Further, the invention relates to a data carrier.

BACKGROUND OF THE INVENTION

Systems for testing concrete are known in the art. For instance, US2023083616 (A1) describes a system for non-destructive testing of a bond condition of concrete beams reinforced by steel rods. The system includes a transducing transmitter, a transducing receiver, and an ultrasonic pulse generator configured to generate drive signals for the transducing transmitter and receive a plurality vibrational waves at the transducing receiver. The system further includes a computing device including a measurement circuit configured to record a transit time for each vibrational wave and divide a distance between the transducing transmitter and the transducing receiver by the transit time to determine a pulse velocity of each vibrational wave, a comparison circuit configured to identify a highest pulse velocity of the vibrational waves and compare each highest pulse velocity to a first reference pulse velocity, and a decision circuit including an artificial neural network configured to identify a compromised bond condition around a steel rod.

SUMMARY OF THE INVENTION

The maintenance of existing concrete structures (e.g. bridges and/or tunnels) may be relevant for the safety of people near said structures. In the case of bridges and/or tunnels, old structures (e.g., structures constructed more than 30 years ago) may degrade faster than originally anticipated due to the increased frequency and weight of the traffic passing over/through them compared to when they were initially constructed. To determine the safety and degradation of concrete structures, the structures may need to be inspected regularly.

Inspection of a concrete structure may be performed visually, which may be labor intensive, and may not expose all defects in the structure, as defects may be located embedded in the concrete. Alternatively, inspection of a concrete structure may be performed using equipment,

which may similarly be labor intensive and require suitable infrastructure (e.g. scaffolding).

Further, due to the heterogeneous and dense structure of concrete, equipment may have a limited penetration depth into the concrete. Additionally, inspection of a concrete structure may be performed using (electrical) pulses. Such electrical pulses may create an electromotive force in the measuring equipment, reducing the sensitivity and/or accuracy of the measurement.

As such, defects in the center of the structure may go undetected.

Hence, it is an aspect of the invention to provide an alternative monitoring system for monitoring a concrete structure, which preferably further at least partly obviates one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

According to a first aspect, the invention provides a monitoring system for monitoring a concrete structure. The monitoring system may comprise n sensing arrangements, an electrical grounding element, a pulser, an amplifier, and a control system. Especially, in embodiments, n > 4. In embodiments, each sensing arrangement may comprise a sensor element, a first switch, a second switch, and a spacing wire. The spacing wire may be configured to separate the first switch from the second switch by a spacing distance ds. In embodiments, ds may be at least 0.5 cm. Further, (each of) the sensing arrangement(s) may have a first configuration and a second configuration. In the first configuration, the sensor element may in embodiments be configured electrically coupled to the pulser via the first switch, the spacing wire, and the second switch. Conversely, in the second configuration, the sensor element may be configured electrically coupled to the amplifier via the second switch.

Additionally, in the second configuration, the spacing wire may be configured electrically coupled to the electrical grounding element via the first switch. In embodiments, the sensor elements of the n sensing arrangements may be configured to be embedded in the concrete structure in a sensing grid arrangement. In such embodiments, each sensor element (in the sensing grid arrangement) may be separated from at least two neighboring sensor elements in the sensing grid arrangement by distances independently selected from the range of 20-150 cm.

Further, the monitoring system (especially the control system) may have an operational mode comprising an actuation stage and a sensing stage. In the actuation stage, a first sensing arrangement comprising a first sensor element may be in the first configuration (i.e., the first sensor element may be configured electrically coupled to the pulser). Further, the pulser may be configured to provide an electrical pulse to the first sensor element. Consequently, the first sensor element may be configured to provide an actuation signal in response to the electrical pulse. Further, in the sensing stage, a second sensing arrangement comprising a second sensor element may be in the second configuration (i.e., the second sensor element may be configured electrically coupled to the amplifier via the second switch). In embodiments, the second sensor element may especially be configured to detect the actuation signal and to provide a related sensor signal (or “electrical signal”) to the control system via the amplifier. In embodiments, the amplifier may be configured to receive the sensor signal (from the second sensor element).

Additionally, the amplifier may be configured to amplify the sensor signal, 1.e., to amplify the (received) sensor signal to provide an amplified sensor signal. Further, the amplifier may be configured to provide an amplified sensor signal to the control system. The control system may be configured to determine a structure-related parameter of the concrete structure based on a difference between the amplified sensor signal and a reference signal.

Hence, in specific embodiments, the invention provides a monitoring system for monitoring a concrete structure, the monitoring system comprising n sensing arrangements, an electrical grounding element, a pulser, an amplifier, and a control system, wherein n > 4, wherein: (A) each sensing arrangement comprises a sensor element, a first switch, a second switch, and a spacing wire, wherein the spacing wire is configured to separate the first switch from the second switch by a spacing distance (ds) of at least 0.5 cm, wherein the sensing arrangement has a first configuration and a second configuration, wherein in the first configuration the sensor element is configured electrically coupled to the pulser via the first switch, the spacing wire, and the second switch, and wherein in the second configuration (1) the spacing wire is configured electrically coupled to the electrical grounding element via the first switch and (ii) the sensor element is configured electrically coupled to the amplifier via the second switch; (B) the sensor elements of the n sensing arrangements are configured to be embedded in the concrete structure in a sensing grid arrangement, wherein each sensor element is separated from at least two neighboring sensor elements in the sensing grid arrangement by distances independently selected from the range of 20-150 cm; (C) the monitoring system has an operational mode comprising an actuation stage and a sensing stage, wherein: (a) in the actuation stage a first sensing arrangement comprising a first sensor element is in the first configuration, wherein the pulser is configured to provide an electrical pulse to the first sensor element, and wherein the first sensor element is configured to provide an actuation signal in response to the electrical pulse; and (b) in the sensing stage a second sensing arrangement comprising a second sensor element is in the second configuration, wherein the second sensor element 1s configured to detect the actuation signal and to provide a related sensor signal to the control system via the amplifier; (D) the amplifier is configured to (i) receive the sensor signal, (ii) amplify the sensor signal, and (iii) provide an amplified sensor signal to the control system;

and (E) the control system is configured to determine a structure-related parameter of the concrete structure based on a difference between the amplified sensor signal and a reference signal.

With such a system, damage (or: “defects”) within the concrete structure may be sensed, before said damage may be visible from the outside of the concrete structure.

Further, as the sensor elements may be configured embedded, interference from signals external to the concrete may be reduced. As such, the monitoring system, especially the sensor elements, may be — compared to monitoring equipment and/or sensor elements configured external to the concrete structure — relatively more sensitive to local changes in the concrete structure, e.g. as a result of damage such as a microcrack, a hole, corrosion, a change of strain, and/or a change of stress (e.g., loss of a prestressing force). Further, the monitoring system of the present invention may be relatively easily installed into existing and new concrete structures. Especially for installation into new concrete structures, the monitoring system may facilitate (remote) monitoring of the concrete structure over the full lifetime of said concrete structure, especially without requiring additional materials, equipment, and/or infrastructure (e.g. scaffolding) for each measurement.

In embodiments, the monitoring system may be configured for monitoring a concrete structure. In embodiments, the concrete structure may be any concrete structure known in the art. For instance, in further embodiments, the concrete structure may comprise a building (e.g. an office building, factory, parking garage, warehouse, stadium, etc. ), a bridge, a tunnel, a dam, a dock (also “wharf” and/or “quay”), a pipe, a wall, a pillar (including a piling, a post, a pier, a column, etc.), flooring (e.g. a floor, a road, a deck, a curb, etc.), a statue, a river bed and/or bank, a pool base, a (pound) lock, etc.. However, other concrete structures are herein not excluded.

Further, in embodiments, the monitoring system may comprise n sensing arrangements, an electrical grounding element, a pulser, an amplifier, and a control system.

Each of these features will be further discussed below.

The monitoring system may comprise sensing arrangements. Especially, the monitoring system may comprise n sensing arrangements. In embodiments, n may be selected from the range of > 2, such as > 4, especially > 6. Further, n may be selected from the range of < 64, such as <32, especially < 16. In embodiments, the n sensing arrangement may (together) comprise n sensor elements. In embodiments, the n sensor elements may be configured to convert electrical energy into a mechanical displacement. Further, in embodiments, the sensor elements may comprise ultrasonic wave transducers. Ultrasonic wave transducers may further be referred to herein as “piezoelectric transducers”. A smart aggregate (or “piezoelectric-based embedded sensor”) may be a specialized piezoelectric transducer especially designed for integration within a concrete structure. Hence, in specific embodiments, the sensor element may be a piezoelectric transducer, especially a smart aggregate. In embodiments, the 5 piezoelectric transducer (or smart aggregate) may comprise a layer of piezoelectric material configured between two layers of support material, such as (natural or artificial) rock (e.g. marble), a ceramic, a polymeric material, or concrete. Especially, the support material may be configured to support and/or protect the piezoelectric material. Further, the support material may have an (average) acoustic impedance selected from the range of 80-120%, such as from the range of 85-115%, especially from the range of 90-110%, of an (average) acoustic impedance of (the concrete of) the concrete structure. A support material having such an (average) acoustic impedance may facilitate minimizing the distortion of the actuation signal upon propagating from the concrete (of the concrete structure) to the support material (and the piezoelectric material). In embodiments, the piezoelectric material may comprise one or more of lead zirconate titanate (PZT), barium titanate, lead titanate, gallium nitride, gallium phosphate, lanthanum gallium silicate (langasite), zinc oxide, quartz, tourmaline, Rochelle salt, lead magnesium niobate-lead titanate (PMN-PT), lithium sulfate, ethylene diamine tartrate, a piezoelectric polymer (such as polyvinylidene difluoride (PVDF)), bismuth layer-structured ferroelectrics (BLSF), sodium bismuth titanate (BNT), bismuth potassium titanate (BKT), potassium sodium niobate, and a ceramic-polymer composite. Especially, the piezoelectric material may comprise lead zirconate titanate (PZT), such as (essentially) consist of lead zirconate titanate. Further, in embodiments, the sensor element, especially the piezoelectric transducer, may comprise an electrical connection, configured to electrically couple the piezoelectric transducer, especially the piezoelectric material, to the second switch of the sensing arrangement comprising said sensor element.

In embodiments, the n sensor elements may be configured to be embedded in the concrete structure. Hence, in embodiments, the sensor elements may be arranged inside a mold, after which (fresh) concrete is poured into the mold, thereby covering (and thus embedding) the sensor elements. Alternatively, in embodiments, holes may be drilled in an (existing) concrete structure, after which the sensor elements may be embedded in the holes.

Optionally, the holes may subsequently be filled with fresh concrete to provide improved contact between the concrete structure and the sensor element. In embodiments, the sensor elements may be configured embedded in the concrete structure at a depth selected from the range of 2-200 cm, such as from the range of 3-175 cm, especially from the range of 5-150 cm,

wherein the depth may be defined as the shortest distance between a surface of the concrete structure and a surface of the sensor element.

Further, the sensor elements may be configured in a sensing grid arrangement (especially after being embedded in the concrete structure). In embodiments, the sensor elements may be arranged in an irregular array in the sensing grid arrangement. Alternatively, in embodiments, the sensor elements may be arranged in a regular array in the sensing gnd arrangement. The regular array may e.g. be an x*y*z array, wherein x, y, and z may be individually selected from the range of 1 — 8, such as from the range of 2 — 6, especially from the range of 2 — 4. Further, in embodiments, any two sensor elements (of the n sensor elements)

IO may have a center-to-center distance selected from the range of > 10 cm, such as from the range of > 15 cm, especially from the range of > 20 cm. Additionally, in embodiments, any two sensor elements (of the n sensor elements) may have a center-to-center distance selected from the range of < 200 cm, such as from the range of < 175 cm, especially from the range of < 150 cm. Hence, in embodiments, any two sensor elements (of the n sensor elements) may have a center-to-center distance selected from the range of 10-200 cm, such as from the range of 15-175 cm, especially from the range of 20-150 cm, like from the range of 20-100 cm.

Additionally or alternatively, the piezoelectric materials comprised by any two sensor elements (of the n sensor elements) may have a smallest center-to-center distance dmin determined by formula (I): 3 dmin = is * 5 Mm wherein vp denotes the P-wave velocity in concrete (~4500 m/s), vs denotes the S-wave velocity in concrete (~2745 m/s), and Xs denotes the total scattering cross-section from P- to S-wave (in mt), which is related to the conversion probability from P-wave to S-wave in concrete. P- waves may be characterized by an alternating compression and expansion of material particles in the direction of wave propagation. Conversely, S-waves may be characterized by a side-to- side or up-and-down motion perpendicular to the direction of wave propagation. The total scattering cross-section ps can be calculated numerically through formula (IT): 2 dg Gpeg] >

Vp 1 H202 H2w2 H202 (Ey) wherein H denotes the characteristic coarse aggregate distance in the concrete of the concrete structure, ¢. is the volume fraction of coarse aggregate in said concrete, © is the angular frequency of the elastic wave (comprising the P-wave and S-wave), and y is the cosine of the angle between the incident wave vector and the scattered wave vector during the collision.

Hence, here, x may especially be the cosine of the angle between the wave vector of the (incoming) actuation signal and the wave vector of the (scattered) actuation signal after collision with a coarse aggregate. In embodiments, such a smallest distance dmin may facilitate equilibrating the energy of the actuation signal (comprising the P-wave and the S-wave), thereby providing an actuation signal (to the second sensor element) that approximates a model actuation signal, such that the sensor signal provided by the second sensor element may be relatively reliably analyzed using calculations and/or models assuming (such) an equilibrated actuation signal in the processing unit, thus increasing the precision of the acquired structure- related parameter.

Further, in embodiments, the piezoelectric materials comprised by any two sensor elements (of the n sensor elements) may have a largest center-to-center distance dmax determined by formula (III): dmax =U *T (IT) wherein T represents the characteristic dissipation time for energy (in a concrete structure). In embodiments, such a largest center-to-center distance may facilitate providing an actuation signal having a signal-to-noise ratio selected from the range of > 2, such as from the range of > 3, especially from the range of > 4.

In embodiments, especially in a regular array configuration, each sensor element in the sensing grid arrangement may be separated from at least two neighboring sensor elements by distances independently selected from the range of 10-200 cm, such as from the range of 20-150 cm. Additionally or alternatively, each sensor element in the sensing grid arrangement may be separated from at least two neighboring sensor elements by distances independently selected from the range of dmin — dmax. In embodiments, the range din — dmax may correspond to a range of 10-200 cm, such as especially to the range of 20-150 cm. In specific embodiments, each sensor element in the sensing grid arrangement may be separated from all of the other sensor elements (in the sensing grid arrangement) by distances independently selected from the range of 10-200 cm and/or from the range of dmin — dmax. Yet, in embodiment, at least two of the sensor elements in the sensing grid arrangement may be separated by a distance > 200 cm and/or > dmax. In such embodiments, a first of said at least two sensor elements may not be designated as the second sensor element when a second of said at least two sensor elements is designated as the first sensor element, and vice versa.

A monitoring system may comprise a switch, configured to electrically couple a sensor element to a pulser or a processing unit. Further, a monitoring system may comprise a plurality of sensor elements and switches, wherein each switch may be configured to electrically couple one sensor element to a pulser or a processing unit. That is, each switch may have three connection points for the pulser, the sensor element, and the processing unit, respectively. Upon transmission of an electrical pulse by the pulser, an electromotive force may be generated in each of the plurality of switches, such as especially in the connection point for the pulser in each of the plurality of switches not having an electrical connection between the pulser and the sensor element. Said generated electromotive force may cause a formation and/or increase of (electrical) noise in the switch, such as especially in the connection points for the sensor elements and the processing unit. Hence, when the sensor element connected to

IO said switch transmits a sensor signal to the processing unit (through said switch having (increased) electrical noise), the sensor signal may be corrupted by the (electrical) noise 1n the connection points of the sensor element and the processing unit. As such, the sensitivity and accuracy of the measurement performed with such a sensor element (and such a system) may be reduced. Further, a monitoring system may comprise two switches per sensor element, wherein the two switches are located close together (< 0.5 cm apart). In such systems, one switch may be configured to electrically couple the sensor element to the pulser, and the other (second) switch may be configured to electrically couple the sensor element to the processing unit. In such systems, the electromotive force generated in the first switch (upon transmission of an electrical pulse by the pulser) may affect the second switch due to their close proximity.

Hence, in such systems, the sensitivity and accuracy of the measurements performed may still be reduced.

Hence, in embodiments, the n sensing arrangements of the present invention, especially of the present monitoring system, may (each) comprise a first switch, a second switch, and a (electrically conductive) spacing wire. The spacing wire may especially be configured to separate the first switch from the second switch. In embodiments, the spacing wire may comprise (such as consist of) any type of electrical wiring known to the skilled person, such as e.g. copper wire (insulated with a polymeric coating). Additionally or alternatively, the spacing wire may comprise an electrically conductive track, such as a coating of electrically conductive material applied and/or printed on an (electrically-insulating) polymeric coating. Further, the spacing wire may be configured to separate the first switch from the second switch by a spacing distance ds. The spacing distance ds may correspond to a length of the spacing wire, though this need not be the case; e.g., the spacing wire may comprise loops or bends, such that a length of the spacing wire may be larger than the separation distance ds. In embodiments, the spacing distance ds may be selected from the range of > 0.5 cm, such as from the range of > 0.8 cm, especially from the range of > | cm. Further, in embodiments, the spacing distance ds may be selected from the range of < 100 cm, such as from the range of < 75 cm, especially from the range of < 50 cm. Hence, in embodiments, the spacing distance ds may be selected from the range of 0.5-100 cm, such as from the range of 0.8-75 cm, especially from the range of 1-50 cm. With such a spacing distance ds, an electromotive force generated in the first switch may not affect the second switch, and thus not reduce the sensitivity and accuracy of the measurements performed with the present monitoring system.

Further, in embodiments, the first switch and the second switch may be selected from the group of mechanical switches. Especially, in embodiments, the first switch and the second switch may be mechanical switches. Mechanical switches may provide the benefit of generating very little (electrical) noise upon switching from a first configuration to a second configuration. Hence, in embodiments, the first switch and/or the second switch may (each) be configured to generate < 500 nV of noise over a frequency range of 0.1-200 kHz. Additionally, in embodiments, the first switch and/or the second switch may be able to transmit an electrical signal having a voltage selected from the range of > 150 V, such as from the range of > 175 V, especially from the range of > 200 V, without damaging the first switch and/or the second switch. Further, in embodiments, the first switch and/or the second switch may have a coupling capacitance between open (i.e. non-connected) contacts selected from the range of < 30 pF, such as from the range of < 25 pF, especially from the range of < 20 pF, like from the range of < 15 pF, wherein the coupling capacitance may especially be a measure for the amount of electrical energy and/or electromotive force transmitted and/or generated in a neighboring contact upon providing a current and/or electrical signal to a first contact. Further, the first switch and/or the second switch may have a first switching time ts 1, wherein the first switching time ts; may be the time needed for the (first and/or second) switch to switch from a first configuration (comprising a first electrical connection) to a second configuration (comprising a second electrical connection). In embodiments, the first switching time ts; may be selected from the range of 0.1-50 ms, such as from the range of 0.5-30 ms, especially from the range of 1-20 ms. In embodiments, the n sensing arrangements may be partially comprised by a first multiplexor. Especially, in embodiments, the first switches, second switches, and spacing wires of the n sensing arrangements may be comprised by a first multiplexor. Hence, in embodiments, the monitoring system may comprise a first multiplexor, wherein the first multiplexor may comprise at least part of the n sensing arrangements.

In embodiments, during the actuation stage, the first sensing arrangement may be configured in the first configuration. In the first configuration, the (first) sensor element may be configured electrically coupled to the pulser via the first switch, the spacing wire, and the second switch. That is, in the first configuration the pulser may be configured electrically coupled to the first switch, the first switch may (further) be configured electrically coupled to the spacing wire, the spacing wire may (on the opposite end of the spacing wire) be configured electrically coupled to the second switch, and the second switch may (further) be configured electrically coupled to the sensor element. Hence, in the first configuration, the first switch may be configured to electrically couple the pulser to the spacing wire, and the second switch may be configured to electrically couple the spacing wire to the sensor element. Hence, in embodiments, the monitoring system may comprise the pulser. The pulser may be configured to provide an electrical pulse to a sensor element, especially to the first sensor element (comprised by the first sensing arrangement). In embodiments, the electrical pulse may comprise one or more waveforms. The one or more waveforms may be selected from the group comprising an exponentially decaying wave, a gaussian wave, a triangular wave, a sinusoidal wave, a square wave, a bi-concave wave, a bi-sigmoidal wave, a zeta wave, a bell wave, etc..

Especially, the electrical pulse may comprise a square wave. The square wave may be selected from the group comprising a monopolar square wave, a symmetric bipolar square wave, an asymmetric bipolar square wave, and a balanced asymmetric bipolar square wave, such as especially an asymmetric bipolar square wave. Further, in embodiments, the electrical pulse may comprise <3 (asymmetric bipolar) square waves, such as < 2 (asymmetric bipolar) square waves, such as especially 1 (asymmetric bipolar) square wave. Further, in embodiments, the electrical pulse (especially the square wave) may have a pulse duration tp. In embodiments, the pulse duration t, may especially be the time period between the start of the electrical pulse and the end of the electrical pulse. In embodiments, the pulse duration t, may be selected from the range of 2-500 us, such as from the range of 4-350 us, especially from the range of 6-200 us.

Hence, in specific embodiments, the pulser may be configured to provide an electrical pulse comprising a square wave, wherein the electrical pulse has a pulse duration tp selected from the range of 6-200 us. A square wave may have sharp transitions from a maximum intensity to a minimum intensity and vice versa. Consequently, a square wave may facilitate generating a well-defined actuation signal in the first sensor element. Further, the square wave may (essentially) not interfere with the actuation signal. Hence, the square wave may facilitate a more accurate determination of the structure-related parameter than, e.g., a gaussian wave.

Further, in embodiments, the electrical pulse, especially the square wave, may have an electrical pulse amplitude. In embodiments, the electrical pulse amplitude may be selected from the range of 20-300 V, such as from the range of 25-250 V, especially from the range of 50-200 V. Similarly, in embodiments, the electrical pulse, especially the square wave, may comprise an electrical current. Especially, the electrical pulse may have a peak current (i.e., a maximum value of the current over the whole electrical pulse) selected from the range of > 1.5 A, such as from the range of > 1.75 A, especially from the range of > 2 A, like from the range of > 2.25 A. Additionally, in embodiments, the electrical pulse may have a center frequency fc. The term “center frequency fs” may herein refer to the reciprocal of the time duration of one cycle of the electrical pulse, especially of the square wave. In embodiments, the center frequency fc may be selected from the range of 70-90 kHz, such as from the range of 72-88 kHz, especially from the range of 75-85 kHz, such as from the range of 77-83 kHz, especially from the range of 79-81 kHz.

In embodiments, at least for the duration of the electrical pulse, the spacing wires comprised by one or more of the n sensing arrangements not designated as the first sensing arrangement may be electrically coupled to the electrical grounding element.

Especially, at least for the duration of the electrical pulse, the one or more of the n sensing arrangements not designated as the first sensing arrangement may be configured in the second configuration. In the second configuration, the spacing wire of the sensing arrangement may be configured electrically coupled to the electrical grounding element via the first switch. That is, the electrical grounding element may be configured electrically coupled to the first switch, wherein the first switch is further configured electrically coupled to the spacing wire. Further, in the second configuration, the second switch may especially not be configured electrically coupled to the spacing wire. Instead, in the second configuration, the second switch may be configured electrically coupled to the sensor element and the amplifier. Hence, the monitoring system may comprise the electrical grounding element (or “grounding element”). The grounding element may especially be configured to electrically ground the spacing wire(s) (comprised by one or more of the n sensing arrangements not designated as the first sensing arrangement) via the (corresponding) first switch, i.e, the grounding element may be configured to direct (excess) electrical energy from said spacing wires (and/or said first switches) into an electric sink, i.e, a ground. Hence, in embodiments, the grounding element may comprise an electrically conductive material. The electrically conductive material may especially be selected from the group comprising a metal (e.g. copper, steel, iron, etc.), a conductive polymer, graphite, an ionic liquid, and a conductive ceramic. Further, in embodiments, the grounding element may be electrically coupled to the electric sink (or “ground”) at a grounding contact point, wherein the grounding contact point may be configured external to the sensing grid arrangement. Especially, in embodiments, the grounding contact point may be configured at least 10 cm, such as at least 20 cm, especially at least 50 cm from any sensor element (and outside of the sensing grid arrangement). In embodiments, the grounding contact point may be configured comprised by the first multiplexor, i.e., the first multiplexor may comprise the grounding contact point. A grounding contact point may facilitate (fully) dissipating the electrical energy (via the ground), such that (essentially) none of the (excess) electrical energy may reach (any of) the sensor elements in the sensing grid arrangement. In embodiments, the grounding element may comprise a plurality of grounding structures, such as 2-n grounding structures, wherein n corresponds to the total number of sensing arrangements in the monitoring system. In such embodiments, the plurality of grounding structures may be configured to be electrically coupled to one or more of the n sensing arrangements (such as especially to the one or more of the sensing arrangements not designated as the first sensing arrangement). Further, in embodiments wherein the monitoring system comprises n grounding structures, each of the n grounding structures may be configured to be electrically coupled to one respective sensing arrangement (of the n sensing arrangements). In embodiments, electrically coupling the spacing wire and the first switch to the grounding element may facilitate dissipating (in the ground) the majority of the electromotive force and/or electrical charge generated in said spacing wire and/or first switch, such as at least 70%, especially at least 80%, like at least 90%, of the electromotive force and/or electrical charge.

In embodiments, the sensor signal provided by the second sensing arrangement, especially by the second sensor element, may have a small amplitude. In such embodiments, the effect of interference on said sensor signal (having said small amplitude) may be relatively large. Therefore, it may be desirable to increase the amplitude of the sensor signal, especially prior to transfer to the control system. Hence, in embodiments, the monitoring system may comprise an amplifier. The amplifier may be any amplifier known in the art, and it will be obvious to a person skilled in the art to select a suitable amplifier. Especially, the amplifier may be an analog amplifier. In embodiments, the amplifier may be configured to receive the sensor signal. Especially, the amplifier may be (electrically and/or spatially) configured between the (second) sensing arrangement and the control system, i.e., the second sensing arrangement (especially the second sensor element) may provide the sensor signal to the amplifier (via the second switch) before the (amplified) signal is transmitted to the control system. Further, the amplifier may be configured to amplify the sensor signal. In embodiments, the amplifier may be configured to amplify the sensor signal by at least 20 dB, such as by at least 40 dB, especially by at least 60 dB. Further, in embodiments, the amplifier may be configured to amplify the sensor signal with an amplification factor selected from the range of 10-1000, such as from the range of 20-500, especially from the range of 30-200. Hence, the amplifier may be configured to provide an amplified sensor signal, especially to the control system (such as more especially to the second multiplexor and/or the processing unit (see below)). A monitoring system comprising an amplifier may facilitate increasing the amplitude of the sensor signal, especially prior to transmission to the control system. In embodiments, an amplified sensor signal (i.e., a sensor signal having a larger amplitude) may be less affected by interference of external influences, as the amplitude of such interference may be smaller than the amplitude of the amplified sensor signal. Hence, a monitoring system comprising an amplifier may facilitate increasing the sensitivity and/or accuracy of the measurement system, especially of the measurements. In embodiments, the monitoring system may further comprise a plurality of amplifiers, such as 2 —n amplifiers, especially n amplifiers. In such embodiments, each of the n sensing arrangements may be configured to be electrically coupled to one respective amplifier.

In embodiments, as indicated above, the monitoring system may comprise a control system. The control system may be configured to receive an (amplified) sensor signal from the second sensing arrangement (especially from the second sensor element), especially via the amplifier. Further, the control system may be configured to determine a structure- related parameter, such as a change in elastic modulus (see further below), of the concrete structure based on the (amplified) sensor signal, especially based on a difference between said (amplified) sensor signal and a reference signal. Hence, in embodiments, the monitoring system, especially the control system, may comprise a processing unit, wherein the processing unit may be configured to determine the structure-related parameter of the concrete structure.

Further, the processing unit may be configured to combine (and/or average) multiple (amplified) sensor signals, especially multiple (amplified) sensor signals originating from the same sensing arrangement (especially the same sensor element), to provide a combined sensor signal (see below). Additionally, in embodiments, the processing unit may comprise a user interface, configured to facilitate adjusting one or more settings of the control system (by a user). Further, in embodiments, the control system may comprise a second multiplexor. The second multiplexor may in embodiments be configured to transmit the amplified sensor signal (from the amplifier) to the processing unit. Hence, in embodiments, the second multiplexor may be configured in the vicinity of the sensing grid arrangement, like within 10 m, such as within 5 m, especially within 3 m of the sensing grid arrangement. Further, in embodiments, the processing unit may be configured distant from the second multiplexor, especially from the sensing grid arrangement. For example, the sensing grid arrangement may be configured embedded in the deck of a bridge, and the processing unit may be configured on an end of the bridge. In embodiments, a signal transmission distance between the second multiplexor and the processing unit may be selected from the range of < 750 m, such as from the range of < 500 m, especially from the range of < 250 m. A monitoring system having such a signal transmission distance may facilitate placing the processing unit (and optionally the user interface) at a location where access to said processing unit (and optionally the user interface) may be relatively good. In such embodiments, extracting information from and/or adjusting settings of the monitoring system, especially from and/or of the control system, may be relatively easy, and may not require additional infrastructure (e.g. scaffolding).

The (combined and/or amplified) sensor signal may be susceptible to corruption from (electrical) noise during transport of the (combined and/or amplified) sensor signal from the second multiplexor to the processing unit. To mitigate (and/or prevent) said corruption, the monitoring system, especially the control system, may comprise a differential line driver. In embodiments, the differential line driver may be configured to convert the (amplified) sensor signal into a related pair of differential signals with opposite polarity. Additionally or alternatively, the differential line driver may be configured to convert the combined sensor signal into a related pair of differential signals with opposite polarity. In embodiments, the pair of differential signals may have equal amplitude, yet opposite signs, i.e., when a first signal (of the pair of differential signals) has a positive amplitude, the second signal may have a negative amplitude, and vice versa. In embodiments, the differential line driver may comprise twisted pair cabling (i.e., two cables configured twisting about each other), wherein one of the cables (comprised by the twisted pair cabling) is configured to transport a first differential signal having a first polarity, and the other of the cables (comprised by the twisted pair cabling) is configured to transport a second differential signal having a second polarity, wherein the first differential signal and the second differential signal together provide the related pair of differential signals, and especially wherein the first polarity is opposite to the second polarity.

In embodiments, the twisted pair cabling may have a cable length related to the signal transmission distance. Especially, the twisted pair cabling may have a cable length selected from the range of < 750 m, such as from the range of < 500 m, especially from the range of < 250 m. Hence, the differential line driver may be configured to transport the (amplified) sensor signal (as a pair of differential signals) over a distance selected from the range of < 750 m, such as from the range of < 500 m, especially from the range of < 250 m. In further embodiments, the cable length may be selected from the range of > 10 m, such as from the range of > 50 m, especially from the range of > 100 m.

Hence, the differential line driver may be configured to transport the (amplified) sensor signal (as a pair of differential signals) over a distance selected from the range of > 10 m, such as from the range of > 50 m, especially from the range of > 100 m.

Further, in embodiments, the differential line driver may be configured to provide the related pair of differential signals to the processing unit.

In such embodiments, the processing unit may be configured to determine a difference between the pair of differential signals to provide a reconstituted sensor signal.

In embodiments, as indicated, the processing unit may be configured to combine multiple (especially k) sensor signals (see below). Said combining of multiple (or k) signals may in embodiments occur after transmitting the respective signals (one-by-one) through the differential line driver.

Hence, in embodiments, the processing unit may further be configured to combine multiple (especially k) reconstituted sensor signals to provide the combined sensor signal.

Alternatively, the k sensor signals may be combined prior to transmission through the differential line driver.

In such embodiments,

the reconstituted sensor signal may comprise the combined sensor signal.

Further, in such embodiments, the processing unit may comprise a primary processing unit and a secondary processing unit, wherein the primary processing unit is configured between the amplifier (and/or second multiplexor) and the differential line driver, and the secondary processing unit is configured after the differential line driver.

The primary processing unit may in such embodiments be configured to combine the k sensor signals (prior to transmission through the differential line driver). Further, the (secondary) processing unit may be configured to determine the structure-related parameter of the concrete structure based on a difference between the reconstituted (and/or combined) sensor signal and the reference signal.

Hence, in specific embodiments, the control system may comprise a differential line driver and a processing unit, wherein: (a) the differential line driver may be configured to convert one or more of the amplified sensor signal and the combined sensor signal into a related pair of differential signals with opposite polarity; (b) the differential line driver may be configured to provide the related pair of differential signals to the processing unit; and (¢) the processing unit may be configured to determine a difterence between the pair of differential signals to provide a reconstituted sensor signal; wherein the processing unit may be configured to determine a structure-related parameter of the concrete structure based on a difference between the reconstituted sensor signal and the reference signal.

As indicated, a control system comprising a differential line driver may facilitate mitigating corruption (by electrical noise) of the (combined and/or amplified) sensor signal during transport of the (combined and/or amplified) sensor signal.

Further, such a control system may facilitate placing the processing unit remote from the sensing grid arrangement, especially up to a signal transmission distance. As such, the monitoring system, especially the control system, may facilitate (upon installation of the monitoring system) placing the processing unit at any desired location within a radius from the sensing grid arrangement determined by the signal transmission distance. In embodiments, the control system may comprise a plurality of differential line drivers, such as especially 2-n differential line drivers (with n corresponding to the total number of sensing arrangements). In such embodiments, each of the plurality of differential line drivers may in embodiments be configured to receive an (amplified) sensor signal from one of the (second) sensing arrangements (especially from one of the (second) sensor elements). Further, in such embodiments, each of the plurality of differential line drivers may be configured electrically coupled to the same processing unit. Alternatively, each of the plurality of differential line drivers may be configured electrically coupled to another processing unit, i.e., the control system may in embodiments comprise a plurality of processing units.

In embodiments, the amplified sensor signal may be an analog signal. Hence, in embodiments, the differential line driver may be an analog differential line driver, providing an analog pair of differential signals to the processing unit. In such embodiments, the processing unit may be configured to convert the (analog) pair of differential signals and/or the reconstituted sensor signal into digital data. Especially, the processing unit may be configured to convert the (analog) pair of differential signals into digital data. In embodiments, the digital data may comprise numerical data. Further, in embodiments, the combining of the plurality of (k) pairs of differential signals and/or (k) reconstituted sensor signals (by the processing unit) may occur after conversion of the pairs of differential signals and/or reconstituted sensor signal into digital data. Further, in embodiments, the (primary) processing unit may be configured to convert the analog (amplified) sensor signal into digital data. In such embodiments, the combining of the plurality of (k) amplified sensor signals (by the primary processing unit) may occur after conversion of the (k) amplified sensor signal into digital data. In embodiments wherein the (primary) processing unit provides a digital combined sensor signal to the differential line driver, the differential line driver may especially be a digital differential line driver. In such embodiments, the secondary processing unit may (directly) reconstitute the (combined) sensor signal and compare this reconstituted signal to the reference signal. Hence, in embodiments, the reference signal may be provided by the processing unit as digital data.

Especially, the reference signal may be converted into digital data (and stored as digital data in the processing unit). Hence, in embodiments, the processing unit may be configured to determine the structure-related parameter of the concrete structure based on a difference between the digital data encoding the reconstituted and/or combined sensor signal and the digital data encoding the reference signal.

The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein “controlling” and similar terms may e.g. refer to imposing behavior to the element (determining the behavior or supervising the running of an element), etc., such as e.g. measuring, displaying, actuating, opening, shifting, changing temperature, etc.. Beyond that, the term “controlling” and similar terms may additionally include monitoring. Hence, the term “controlling” and similar terms may include imposing behavior on an element and also imposing behavior on an element and

IO monitoring the element. The controlling of the element can be done with a control system, which may also be indicated as “controller”. The control system and the element may thus at least temporarily, or permanently, functionally be coupled. The element may comprise the control system. In embodiments, the control system and element may not be physically coupled. Control can be done via wired and/or wireless control. The term “control system” may also refer to a plurality of different control systems, which especially are functionally coupled, and of which e.g. one control system may be a master control system and one or more others may be slave control systems. A control system may comprise or may be functionally coupled to a user interface.

The control system may also be configured to receive and execute instructions from a remote control. In embodiments, the control system may be controlled via an App on a device, such as a portable device, like a Smartphone or I-phone, a tablet, etc.. The device is thus not necessarily coupled to the monitoring system, but may be (temporarily) functionally coupled to the monitoring system.

Hence, in embodiments the control system may (also) be configured to be controlled by an App on a remote device. In such embodiments the control system of the monitoring system may be a slave control system or control in a slave mode. For instance, the monitoring system may be identifiable with a code, especially a unique code for the respective monitoring system. The control system of the monitoring system may be configured to be controlled by an external control system which has access to the monitoring system on the basis of knowledge (input by a user interface of with an optical sensor (e.g. QR code reader) of the (unique) code. The monitoring system may also comprise means for communicating with other systems or devices, such as on the basis of Bluetooth, Thread, WIFI, LiFi, ZigBee,

BLE or WiMAX, or another wireless technology.

The system, or apparatus, or device may execute an action in a “mode” or “operation mode” or “mode of operation” or “operational mode”. The term “operational mode may also be indicated as “controlling mode”. Likewise, in a method an action or stage, or step may be executed in a “mode” or “operation mode” or “mode of operation” or “operational mode”. This does not exclude that the system, or apparatus, or device may also be adapted for providing another controlling mode, or a plurality of other controlling modes. Likewise, this may not exclude that before executing the mode and/or after executing the mode one or more other modes may be executed.

However, in embodiments a control system may be available, that is adapted to

IO provide at least the controlling mode. Would other modes be available, the choice of such modes may especially be executed via a user interface, though other options, like executing a mode in dependence of a sensor signal or a (time) scheme, may also be possible. The operation mode may in embodiments also refer to a system, or apparatus, or device, that can only operate in a single operation mode (i.e. “on”, without further tunability).

In embodiments, the monitoring system, especially the control system, may thus have an operational mode. The operational mode may especially comprise an actuation stage and a sensing stage. The term “stage” and similar terms used herein may refer to a (time) period (also “phase”) of a method and/or an operational mode. The different stages may (partially) overlap (in time). For example, the actuation stage may, in general, be initiated prior to the sensing stage, but may partially overlap in time therewith. However, for example, the actuation stage may typically be completed prior to the sensing stage. It will be clear to the person skilled in the art how the stages may be beneficially arranged in time.

In embodiments, in the actuation stage, the pulser may be configured electrically coupled to the first sensing arrangement (of the n sensing arrangements) comprising a first sensor element. In embodiments, any of the n sensing arrangements may be (designated as) the first sensing arrangement. Hence, the n sensor elements comprised by the n sensing arrangements may in embodiments especially be transceivers. Further, the same sensing arrangement (of the n sensing arrangements) may not permanently be the first sensing arrangement, i.e., one of the n sensing arrangements may be the first sensing arrangement for a first time period, and another of the n sensing arrangements may be the first sensing arrangement for a second time period, wherein in specific embodiments the first time period and the second time period may be temporally separated. In embodiments, the control system may be configured to designate a sensing arrangement as the first sensing arrangement. In specific embodiments, the control system may be configured to change the configuration of the (first) sensing arrangement (e.g. from the second configuration to the first configuration or vice versa). Especially, the control system may be configured to control the first switch and the second switch comprised by the (first) sensing arrangement. Hence, the control system may be configured to control the first switch and the second switch of the (first) sensing arrangement to configure said sensing arrangement (according to and/or) in the first configuration and to establish an electrical connection between the pulser and the sensor element (comprised by said sensing arrangement), thereby designating this sensor element as the first sensor element (and thus this sensing arrangement as the first sensing arrangement).

In embodiments, in the actuation stage, the pulser may be configured to provide an electrical pulse to the first sensor element (comprised by the first sensing arrangement).

Especially, the pulser may be configured to provide the electrical pulse after the first switch and second switch of the first sensing arrangement are configured according to the first configuration. Hence, in embodiments, the pulser may be configured to provide the electrical pulse after a first switching time ts ;. In embodiments, the control system may be configured to control the pulser, such that the pulser provides the electrical pulse at the desired time, such as e.g. after a first switching time tsi. Alternatively, in embodiments, the control system may be configured to control the pulser based on a time scheme or an input signal from a user interface.

Hence, in embodiments, the control system may control in dependence of one or more of an input signal of a user interface, a sensor signal (of a sensor), and a timer. The term “timer” may refer to a clock and/or a predetermined time scheme.

In embodiments, as indicated, during the actuation stage, the remaining sensing arrangements, 1.e., the sensing arrangements not designated as the first sensing arrangement, may be configured in the second configuration. Hence, in embodiments, the configuration of said remaining sensing arrangements may not change throughout the actuation stage and sensing stage.

In embodiments, the first sensor element (of the first sensing arrangement) may be configured to provide an actuation signal in response to the electrical pulse. Hence, the first sensor element may be referred to as an “actuator”. Further, in embodiments, the first sensor element (or “the actuator”) may be configured to provide an (exponentially decaying) mechanical vibration in response to the electrical pulse. Hence, in embodiments, the actuation signal may comprise the mechanical vibration. Especially, the actuation signal may comprise one or more seismic waves generated (in the concrete structure) by the mechanical vibration.

Further, in embodiments, the one or more seismic waves may comprise the P-wave and/or the

S-wave, such as especially the P-wave and the S-wave. In embodiments, the actuation signal,

especially the mechanical vibration, may have an actuation frequency fa selected from the range of fc-75 <f, <fc+75 kHz, such as from the range of f.-60 < fà < f-+60 kHz, especially from the range of f:-50 < fa < {+50 kHz. Further, in embodiments, the actuation signal, especially the mechanical vibration, may have an actuation frequency fa selected from the range of f<-40 < fa <f-+40 kHz, such as from the range of f-25 < fa < f:+25 kHz, especially from the range of fc- 15 < fa < f-+15 kHz. Hence, in specific embodiments, the actuation frequency fa may be determined by the center frequency fe of the electrical pulse. Such a relation between the center frequency f: of the electrical pulse and the actuation frequency fa may have as advantage that the frequency of the actuation signal may be tuned by changing the center frequency fe, without the need to change the (first) sensor element. Further, such an actuation frequency fa may have as advantage that the wavelength of the one or more seismic waves related to (such as generated by) such an actuation frequency f may be larger than the size of the coarse aggregates in the concrete structure. As such, the one or more seismic waves may interact with the coarse aggregates, and may especially scatter upon contact with one or more of the coarse aggregates, cracks, and defects in the concrete. The (extent of) scattering of the one or more seismic waves may thus be a measure for the structure-related parameter of the concrete structure. Further, in embodiments, the actuation signal, especially the mechanical vibration, may have an actuation duration ta selected from the range of t,-30 < ta <t,+30 us, such as from the range of tp-20 <t, <tp+20 us, especially from the range of t,-10 <t, <tp+10 us. Hence, in specific embodiments, the actuation duration ta may be determined by the pulse duration t of the electrical pulse.

In embodiments, the operational mode of the monitoring system, especially of the control system, may (further) comprise a sensing stage. In embodiments, in the sensing stage, a second sensing arrangement (of the n sensing arrangements) comprising a second sensor element may be configured electrically coupled to the control system via the amplifier.

Similarly to the first sensing arrangement, the second sensing arrangement may be any of the n sensing arrangements (provided the sensor element of said sensing arrangement has a distance < dmax and/or < 200 cm from the first sensor element). Further, the same sensing arrangement (of the n sensing arrangements) may not permanently be the second sensing arrangement, i.e, one of the n sensing arrangements may be the second sensing arrangement for a first time period, and another of the n sensing arrangements may be the second sensing arrangement for a second time period, wherein the first time period and the second time period may in embodiments overlap. In embodiments, the control system, especially the second multiplexor, may be configured to designate a sensing arrangement as the second sensing arrangement. Especially, in embodiments, the control system, especially the second multiplexor, may be configured to electrically couple the control system, especially the processing unit and/or differential line driver, to a sensing arrangement (selected from the sensing arrangements not designated as the first sensing arrangement), thereby designating this sensing arrangement as the second sensing arrangement, and the corresponding sensor element as the second sensor element. More especially, the control system, especially the second multiplexor, may comprise a plurality of (electrical and/or mechanical) third switches, configured to establish an electrical connection between the control system (especially the processing unit and/or differential line driver) and a sensing arrangement. In embodiments, the plurality of third switches may have a second switching time ts (i.e, a time needed to switch from a first configuration to a second configuration) selected from the range of < 50 ns, such as from the range of < 30 ns, especially from the range of < 20 ns. Further, in embodiments, the plurality of third switches may be configured to generate < 1000 nV, such as < 750 nV, especially < 500 nV, like < 350 nV, of noise over a frequency range of 1kHz to 200 kHz. In embodiments, the control system, especially the second multiplexor, may be configured to control (the respective positions of) the plurality of third switches, and may thus be configured to designate a sensing arrangement as the second sensing arrangement.

In embodiments, the sensing stage may (directly) follow the actuation stage.

Especially, the sensing stage may start after the pulser has provided the electrical pulse to the first sensing arrangement, such as especially to the first sensor element. Hence, in embodiments, the sensing stage may temporally overlap the actuation stage. Specifically, the sensing stage may temporally overlap the actuation stage for the duration required for the electrical pulse to travel to the first sensor element, and the duration required for the first sensor element to provide an actuation signal in response to the electrical pulse. Alternatively, in embodiments, the sensing stage may not temporally overlap the actuation stage, i.e, the sensing stage may start after the first sensor element has provided the actuation signal.

In embodiments, the n sensing arrangements may be in the same (respective) configuration in both the actuation stage and the sensing stage, i.e, the n sensing arrangements may maintain their respective (first or second) configurations throughout (at least part of) the actuation stage and the sensing stage. In embodiments, the sensing stage may have a sensing stage duration. The sensing stage duration may especially be selected from the range of 0.5%*z — 5%t, such as from the range of 0.75%r — 3*r, especially from the range of 7 — 2*r, wherein 7 represent the characteristic dissipation time after which the energy of the actuation signal (in the concrete structure) has decreased by around 63% compared to the energy of the actuation signal as generated by the actuator (directly after the electrical pulse). Hence, in embodiments,

the sensing stage may start when the pulser has provided the electrical pulse, and may end after a time of 0.5*7 — 5*z. Further, in embodiments, the second sensor element may not provide the sensor signal at the start of the sensing stage, that is, the actuation signal may not have reached the second sensor signal at the start of the sensing stage. Hence, the sensing stage may start before the generation of a sensor signal in the second sensor element. In embodiments, the actuation signal may (thus) have a travelling time t:.2 to propagate from the first sensor element to the second sensor element. The travelling time t12 may be determined by di.2/vp, wherein di. 2 denotes the (shortest) distance between the first sensor element and the second sensor element in meters, and wherein vp is as defined above. Additionally, the travelling time t1-2 may be selected from the range of 10-500 us, such as from the range of 20-400 pus, especially from the range of 40-350 us.

In embodiments, one or more of the sensing arrangements not designated as the first sensing arrangement may be configured electrically coupled to the control system during the sensing stage. Hence, in embodiments, one or more of the sensing arrangements not designated as the first sensing arrangement may be designated as a second sensing arrangement in the sensing stage. Especially, in embodiments, 1 — n-1 sensing arrangements may be designated as second sensing arrangements in the sensing stage, such as > 2 sensing arrangements, especially > 3 sensing arrangements. Yet, in embodiments, only one sensing arrangement may be designated as the second sensing arrangement in the sensing stage. The second sensing arrangement, especially the second sensor element, may be configured to detect (or receive) the actuation signal (provided by the first sensing arrangement, especially by the first sensor element). Hence, in embodiments, the second sensor element may especially be referred to as a “receiver”. Further, the second sensing arrangement, especially the second sensor element, may be configured to, after detecting the actuation signal, provide a related sensor signal to the control system, especially via the amplifier (and the second switch). The term “related sensor signal” may herein refer to a signal that is related to the detected actuation signal. In particular, the related sensor signal may comprise raw and/or processed data related to the (detected) actuation signal.

In embodiments, the actuation signal may comprise seismic waves. Further, in embodiments, the second sensor element may be configured to detect said seismic waves, and to consequently vibrate with a frequency related to the frequency of said seismic waves. Further yet, the second sensor element may be configured to convert the mechanical vibration (of the second sensor element) into an (exponentially decaying) electrical signal, i.e, the related sensor signal. In embodiments, the related sensor signal may comprise a frequency and a waveform, wherein the waveform of the sensor signal may be different from the waveform of the electrical pulse. Further, in embodiments, the waveform of the sensor signal may be at least partially determined by (a magnitude of) the structure-related parameter. Hence, in embodiments, comparing the waveform of the sensor signal to the waveform of a reference signal may provide information regarding (the magnitude of) the structure-related parameter.

Especially, determining a difference between the sensor signal and the reference signal may facilitate determining (the magnitude of) the structure-related parameter. In embodiments, the reference signal may comprise a simulated version of the sensor signal. Additionally or alternatively, the reference signal may comprise a previously recorded (amplified) sensor signal. Further, in embodiments, the reference signal may comprise an (amplified) sensor signal recorded in a model system, using a similar type of concrete and distance between the first and second sensor element. Yet, in embodiments, the reference signal may especially comprise (a simulated version of) a previously recorded (and amplified) sensor signal, wherein the previously recorded sensor signal may especially be recorded prior to any damage to and/or strain on the concrete structure. Hence, in specific embodiments, the reference signal may comprise (a simulated version of) a previously recorded and amplified sensor signal. In particular, the reference signal may reflect a “healthy” state of the concrete structure, i.e., the reference signal may have been measured before the concrete was damaged and/or experienced a substantial (change in) strain. For newly created concrete structures, the reference signal may be an initial measurement, for instance measured prior to or soon after the concrete structure was taken into use. For existing concrete structures, the reference signal may, alternatively, be a simulated signal corresponding to an initial (undamaged) state of the concrete structure.

Comparing the sensor signal to a reference signal comprising a previously-recorded sensor signal may facilitate determining a relative structure-related parameter, 1.e., a difference in the structure-related parameter of the current situation with the structure-related parameter of a previous situation. Comparing the sensor signal to a reference signal comprising (1) a sensor signal recorded in a model system, and/or (ii) a simulated version of the sensor signal, may facilitate determining an (absolute) structure-related parameter of an (existing) concrete structure, wherein the concrete structure may already have an altered structure-related parameter compared to a freshly-constructed concrete structure.

As indicated, in embodiments, the structure-related parameter may thus affect the waveform of the sensor signal. Further, in embodiments, the structure-related parameter may affect a travelling time t; of the actuation signal. In embodiments, the travelling time t; may be the time needed for the actuation signal to travel from the first sensor element to the second sensor element, i.e, the time between the generation (and/or transmission) of the actuation signal and the time a sensor signal is generated (and/or provided) by the second sensor element. In embodiments, the travelling time tt may be determined by: (1) the distance between the first sensor element and the second sensor element; (ii) the characteristics of the concrete (comprised by the concrete structure) between said first sensor element and second sensor element; and (111) the (magnitude of the) structure-related parameter. Hence, comparing the travelling time t; to a reference travelling time tir may provide (further) information regarding the structure-related parameter of the concrete structure.

In embodiments, the structure-related parameter (of the concrete structure) may be selected from the group comprising a number of cracks, a crack size, a crack position, an elastic modulus, a stress, a strain, a density, a porosity, and an average particle size. Especially, in embodiments, the structure-related parameter may be selected from the group comprising a crack position, an elastic modulus, a stress, and a strain. Hence, in embodiments, the structure- related parameter may be a measure for the number and size of cracks in the concrete structure, especially in the space between the first sensor element and the second sensor element.

Additionally, the structure-related parameter may be a measure for deformation of the concrete structure, especially in the space between the first sensor element and the second sensor element. For example, a change in the travelling time t: may indicate the formation of a crack (in the space between the first sensor element and the second sensor element), or a deformation of the concrete structure causing an increase in the distance between the first and second sensor element. Alternatively, a change in the waveform of the sensor signal may indicate an increase in scattering of the actuation signal, e.g. due to (micro)cracks partially reflecting and/or scattering the actuation signal.

In embodiments, the monitoring system, especially the control system, may have a first operational mode. The first operational mode may especially comprise a sensing operation. Further, in embodiments, the sensing operation may comprise k repetitions of (a chronological sequence comprising) the actuation stage as defined above and the sensing stage as defined above. Hence, in embodiments, the sensing operation may comprise k repetitions of the sequence: (1) providing an electrical pulse to the first sensing arrangement, especially to the first sensor element (with the pulser), (ii) electrically coupling (at least) the second sensing arrangement comprising the second sensor element to the control system via the amplifier, and (iii) providing a sensor signal (related to the actuation signal) to the control system via the amplifier. In embodiments, k may be selected from the range of > 2, such as from the range of > 10, especially from the range of > 20. Further, k may be selected from the range of < 1500,

such as from the range of < 1250, especially from the range of < 1000. Hence, in embodiments, k may be selected from the range of 2-1500, such as from the range of 10-1250, especially from the range of 20-1000. In embodiments, in each of the k repetitions, i.e., during the (full) sensing operation, the same sensing arrangements may be designated as first sensing arrangement and second sensing arrangement, respectively. Hence, in embodiments, in each of the k repetitions, i.e., during the (full) sensing operation, the same sensor elements may be designated as first sensor element and second sensor element, respectively. Especially, the same sensor element may be the first sensor element during each of the k repetitions.

Additionally, the same sensor element may be the second sensor element during each of the k repetitions. Further, in the sensing operation, the control system, especially the processing unit, may in embodiments be configured to combine (and/or average) the amplified sensor signals provided by the second sensor element (via the amplifier) in the k repetitions. Hence, in embodiments, the control system, especially the processing unit, may be configured to combine (and/or average) k amplified sensor signals provided by the second sensor element in the sensing operation. Further, the control system, especially the processing unit, may thus be configured to provide a combined sensor signal. Further yet, the control system may be configured to determine a structure-related parameter of the concrete structure based on a difference between the combined sensor signal and the reference signal. Hence, in specific embodiments, the monitoring system may have a first operational mode comprising a sensing operation, wherein the sensing operation comprises k repetitions of a chronological sequence comprising the actuation stage and the sensing stage, wherein k is selected from the range of 2-1000; and wherein the control system may be configured to combine k amplified sensor signals provided by the second sensor element in the sensing operation to provide a combined sensor signal, wherein the control system may be configured to determine a structure-related parameter of the concrete structure based on a difference between the combined sensor signal and the reference signal. Combining (and/or averaging) k amplified sensor signals may facilitate increasing the signal-to-noise ratio of the (combined and amplified) sensor signal.

Especially, the amplified sensor signal may have the same phase (e.g., positive or negative) in each of the k repetitions, whereas the noise may have an independently selected phase in each of the k repetitions. As such, combining the k amplified sensor signals may facilitate providing (a) destructive interference for the part of the sensor signal originating from noise, and (b) constructive interference for the part of the sensor signal generated by the second sensor element in response to the actuation signal. Hence, the signal-to-noise ratio may be increased.

In specific embodiments, the combined sensor signal may have a signal-to-noise ratio selected from the range of > 3, such as from the range of > 5, especially from the range of > 10.

In embodiments, the first operational mode may further comprise a monitoring stage. The monitoring stage may comprise (successively) executing m sensing operations.

Hence, in embodiments, the monitoring stage may comprise executing a first sensing operation, subsequently executing a second sensing operation, optionally followed by a third sensing operation, etc., until m sensing operations have been executed. Especially, in embodiments, the m sensing operations may be temporally separated. In embodiments, at least two of the m sensing operations may differ in the sensing arrangement, especially the sensor element, electrically coupled to the control system via the amplifier (and the second switch) in the sensing stage, 1.e., at least two of the m sensing operations may differ in which sensor element is designated as the second sensor element. Further, in embodiments, in each (of the m) sensing operation(s), a different sensing arrangement, such as especially a different sensor element, may be configured electrically coupled to the control system via the amplifier in the sensing stage. That is, in each of the m sensing operations, a different sensor element may be designated as the second sensor element. Further, in each of the m sensing operations, the same sensing arrangement, especially the same sensor element, may be designated as the first sensor element.

In embodiments, m may be selected from the range of 1 —n-1, such as from the range of 2 — n- 1, especially from the range of 3 — n-1. Hence, in specific embodiments, in the monitoring stage, each of the sensor elements (not designated as the first sensor element) may be designated as the second sensor element in one of the m sensing operations. Further, in embodiments, m <n-1. Further yet, in embodiments, k may be independently selected for each sensing operation. For example, for a first sensing operation (of the m sensing operations comprised by the monitoring stage,) k may be 5, while for a second sensing operation (of the m sensing operations comprised by the monitoring stage.) k may be 10. Hence, in specific embodiments, the first operational mode may comprise a monitoring stage, wherein the monitoring stage may comprise executing m sensing operations, wherein m < n-1, wherein in each sensing operation a different sensor element may be configured electrically coupled to the control system via the amplifier in the sensing stage. A control system having a first operational mode comprising a monitoring stage may facilitate determining the structure-related parameter in a wider area of the concrete structure, especially compared to a first operational mode (only) comprising a (single) sensing operation. Further, a monitoring stage may provide additional quality control; an incorrect value for the structure-related parameter (obtained from one of the m sensing operations) due to a defect in the respective (second) sensor element may be filtered out based on the structure-related parameters obtained from the other m-1 sensing operations.

In embodiments, one or more (of the m) sensing operations may temporally overlap, such as especially be executed simultaneously. In such embodiments, the sensor elements (or sensing arrangements) designated as the second sensor element (or second sensing arrangements) in said one or more (of the m) sensing operations may be (1) configured electrically coupled to the control system (via the amplifier) in the sensing stage, (ii) configured to detect the (same) actuation signal, and (ii1) configured to provide a related sensor signal to the control system (via the amplifier). Hence, the second sensor elements of the one or more

IO sensing operations may all detect the same actuation signal, and, based on their respective distance from the first sensor element, provide a related sensor signal to the control system (via the amplifier) with a delay depending on said respective distance from the first sensor element.

In such embodiments, the control system may be configured to (simultaneously or consecutively) determine a separate structure-related parameter for each of the second sensor elements (of the one or more (of the m) sensing operations). Further, in such embodiments, the control system may be configured not comprising the second multiplexor, i.e., the amplifier may be (optionally via a differential line driver) directly electrically coupled to the processing unit. In specific embodiments, when one or more (of the m) sensing operations in the monitoring stage temporally overlap, the control system may comprise a plurality of differential line drivers (see above), such that the second sensing arrangements, especially the second sensor elements, from each of the one or more overlapping sensing operations may all be electrically coupled to a different differential line driver. Further, in such specific embodiments, the control system may comprise one or a plurality of processing units, configured to simultaneously determine a structure-related parameter for each of the one or more overlapping sensing operations. In embodiments, in the monitoring stage, the number of sensing operations temporally overlapping(, especially executed simultaneously,) may be selected from the range of 2 — m, such as from the range of 3 — m. A monitoring stage comprising simultaneously executing (and determining a structure-related parameter for) 2 — m sensing operations may facilitate reducing the total time required for the monitoring stage, compared to a monitoring stage comprising successively executing m sensing operations.

In embodiments, the monitoring stage may provide a distribution of the structure-related parameter in the area between the first sensor element and the m second sensor elements (of the m sensing operations). In such embodiments, the distribution of the structure- related parameter in areas between the m second sensor elements (of the m sensing operations)

may not be known. To resolve this, in embodiments, the first operational mode may comprise (successively) executing a plurality of monitoring stages. Hence, in embodiments, the first operational mode may comprise executing a first monitoring stage, subsequently executing a second monitoring stage, optionally followed by a third monitoring stage, etc., until the plurality of monitoring stages have been executed. Especially, in embodiments, the plurality of monitoring stages may not temporally overlap. In embodiments, at least two of the plurality of monitoring stage may differ in the sensing arrangement, especially the sensor element, configured electrically coupled to the pulser in the actuation stage, i.e., at least two of the plurality of monitoring stages may differ in the sensor element (or sensing arrangement) being designated as the first sensor element (or as the first sensing arrangement). Further, in embodiments, in each (of the plurality of) monitoring stage(s) a different sensor element may be configured electrically coupled (via the first switch, spacing wire, and second switch) to the pulser in the actuation stage. That is, in each (of the plurality of) monitoring stage(s), a different sensor element may be designated as the first sensor element. In embodiments, the plurality of monitoring stages may comprise z monitoring stages. In embodiments, z may be selected from the range of 2 — n, such as from the range of 3 — n, especially from the range of 4 — n. Hence, in specific embodiments, in the first operational mode, each of the sensor elements may be designated as the first sensor element in one of the z (or plurality of) monitoring stages. Further, in specific embodiments, the first operational mode may comprise executing a plurality of monitoring stages, wherein in each monitoring stage a different sensor element may be configured electrically coupled to the pulser in the actuation stage. A first operational mode comprising executing a plurality of monitoring stages may facilitate (precisely) determining a distribution of the structure-related parameter in the (entire) area defined by the n sensor elements (i.e., the sensing grid arrangement). Hence, in embodiments, the location of defects in the concrete structure (e.g. cracks) may be determined with high accuracy. This may provide the benefit that potential repairs may be performed efficiently and effectively, as the location and extent of the damage may be (precisely) known before starting the repair. Further, in such embodiments, if a sensor element designated as the first sensor element in one of the monitoring stages is or becomes defective, such a first operational mode may still provide reliable information from the other monitoring stages.

In embodiments, the monitoring system as defined herein may be used to determine a structure-related parameter of a concrete structure. Hence, the invention may provide a method for monitoring of a concrete structure using the monitoring system as described herein.

Further, according to another aspect, the invention provides a method for monitoring of a concrete structure, especially using n sensing arrangements. In embodiments, each (of the n) sensing arrangements (of the method) may comprise a sensor element, a first switch, a second switch, and a spacing wire. The spacing wire may especially be configured to separate the first switch (of the respective sensing arrangement) from the second switch (of the respective sensing arrangement) by a spacing distance (ds) of at least 0.5 cm. Further, in embodiments, n may be as defined above. Additionally or alternatively, in embodiments, n > 4. In embodiments, the sensor elements of the n sensing arrangements may be embedded in the concrete structure in a sensing grid arrangement. Further, in embodiments, each sensor element in the sensing grid arrangement may be separated from at least two neighboring sensor elements in the sensing grid arrangement by distances independently selected from the range of 20-150 cm. Further, in embodiments, each sensor element in the sensing grid arrangement may be separated from at least two neighboring sensor elements in the sensing grid arrangement by distances independently selected from the range of duin — dmx. In embodiments, the method may comprise an actuation stage, wherein the actuation stage may comprise providing an electrical pulse to a first sensor element comprised by a first sensing arrangement, especially via the first switch, the spacing wire, and the second switch (of said first sensing arrangement). In embodiments, the first sensor element may generate an actuation signal in response to the electrical pulse. Further, in embodiments, the method may comprise a sensing stage, wherein the sensing stage may comprise detecting the actuation signal with a second sensor element comprised by a second sensing arrangement. Further, the sensing stage may comprise providing (with the second sensor element) a related sensor signal (to the control system) via the second switch. In embodiments, the sensing stage may further comprise grounding the spacing wire of the second sensing arrangement via the first switch. Further, in embodiments, the method may comprise amplifying the sensor signal (using an amplifier) to provide an amplified sensor signal. Additionally, the method may comprise determining a structure-related parameter of the concrete structure based on a difference between the amplified sensor signal and a reference signal.

Hence, in specific embodiments, the invention provides a method for monitoring of a concrete structure using n sensing arrangements, wherein each sensing arrangement comprises a sensor element, a first switch, a second switch, and a spacing wire, wherein the spacing wire is configured to separate the first switch from the second switch by a spacing distance (ds) of at least 0.5 cm, wherein n > 4, wherein the sensor elements of the n sensing arrangements are embedded in the concrete structure in a sensing grid arrangement,

wherein each sensor element in the sensing grid arrangement is separated from at least two neighboring sensor elements in the sensing grid arrangement by distances independently selected from the range of 20-150 cm, wherein the method comprises: (1) an actuation stage comprising providing an electrical pulse to a first sensor element comprised by a first sensing arrangement via the first switch, the spacing wire, and the second switch, with the first sensor element generating an actuation signal in response to the electrical pulse; and (ii) a sensing stage comprising detecting the actuation signal with a second sensor element comprised by a second sensing arrangement, and providing a related sensor signal via the second switch, wherein the sensing stage comprises grounding the spacing wire of the second sensing arrangement via the first switch; and wherein the method comprises (a) amplifying the sensor signal to provide an amplified sensor signal, and (b) determining a structure-related parameter of the concrete structure based on a difference between the amplified sensor signal and a reference signal. Such a method using an embedded sensing grid arrangement may, for example, facilitate detecting damage within a concrete structure before said damage is visible from the outside of the concrete structure. Further, small changes in the structure-related parameter may have a relatively large effect on the sensor signal. As such, a method comprising determining a structure-related parameter of the concrete structure based on a difference between the (amplified) sensor signal and a reference signal may be relatively sensitive to local changes in the structure-related parameter, such as local changes due to the opening of micro cracks or the change of strain.

In embodiments, the method of the invention may especially be executed using the monitoring system as defined herein. Hence, all embodiments relating to the monitoring system may further be applied to the method, and vice versa. For instance, in embodiments of the system, the system, especially the control system, may be configured to execute the method of the invention. Further, in embodiments, the actuation stage of the method may essentially correspond to the actuation stage in the operational mode of the monitoring system. That is, during the actuation stage of the method, the monitoring system as defined herein may especially be configured to execute the actuation stage (in the operational mode). Conversely, the sensing stage may (essentially) correspond to the sensing stage in the operational mode of the monitoring system. Yet, the method of the invention may (also) be executed using any suitable system. Therefore, in embodiments, the method of the invention may not be limited to embodiments involving the system of the invention.

In embodiments, the method may comprise a sensing operation, wherein the sensing operation may comprise executing k repetitions of a chronological sequence comprising the actuation stage and the sensing stage. Hence, in embodiments, the sensing operation may comprise k repetitions of the sequence: (i) providing an electrical pulse to the first sensor element (via the first switch, spacing wire, and second switch) to generate an actuation signal, (it) detecting the actuation signal with the second sensor element, and (111) providing a (related) sensor signal (to the control system) via the second switch. In embodiments, k may be selected from the range of > 2, such as from the range of > 10, especially from the range of > 20. Further, k may be selected from the range of < 1500, such as from the range of < 1250, especially from the range of < 1000. Hence, in embodiments, k may be selected from the range of 2-1500, such as from the range of 10-1250, especially from the range of 20-1000. In embodiments, in each of the k repetitions, i.e, during the (full) sensing operation, the same sensor elements (or sensing arrangements) may be designated as first sensor element (or first sensing arrangement) and second sensor element (or second sensing arrangement), respectively. Especially, the same sensor element may be the first sensor element during each of the k repetitions. Additionally, the same sensor element may be the second sensor element during each of the k repetitions. Further, in embodiments, the method may comprise combining (and/or averaging) the k amplified sensor signals provided by the second sensor element (via the amplifier and the second switch) in the sensing operation to provide a combined sensor signal. Further yet, in embodiments, the method may comprise determining the structure-related parameter of the concrete structure based on a difference between the combined sensor signal and the reference signal. Hence, in specific embodiments, the sensing operation may comprise executing k repetitions of a chronological sequence comprising the actuation stage and the sensing stage, wherein k may be selected from the range of 2-1000, the method comprising combining k amplified sensor signals provided by the second sensor element in the sensing operation to provide a combined sensor signal, and determining a structure-related parameter of the concrete structure based on a difference between the combined sensor signal and the reference signal. A method comprising combining (and/or averaging) k amplified sensor signals may facilitate increasing the signal-to-noise ratio of the (combined) sensor signal. Hence, such a method may provide a structure-related parameter with a decreased error margin.

In embodiments, the method may comprise multiple sensing operations.

Especially, in embodiments, the method may comprise a monitoring stage, wherein the monitoring stage comprises successively executing m sensing operations. In embodiments, the monitoring stage of the method may correspond to the monitoring stage in the first operational mode of the monitoring system. Further, in embodiments, m may be selected from the range of 1 —n-1, such as from the range of 2 — n-1, especially from the range of 3 — n-1. Especially, in embodiments, m <n-1. In embodiments, each (of the m) sensing operation(s) may comprise detecting the actuation signal with a different sensor element (comprised by a different sensing arrangement). Hence, in each of the m sensing operations, a different sensor element may be designated as the second sensor element (by the control system). Further, in embodiments, each (of the m) sensing operation(s) may comprise providing the electrical pulse to the same sensor element, i.e., the same sensor element (or sensing arrangement) may be designated as the first sensor element (or first sensing arrangement) in each (of the m) sensing operation(s). In embodiments, k may be independently selected for each sensing operation. Hence, in specific embodiments, the method may comprise a monitoring stage, wherein the monitoring stage may comprise successively executing m sensing operations, wherein m <n-1, wherein each sensing operation may comprise detecting the actuation signal with a different sensor element. A method comprising a monitoring stage may facilitate determining the structure-related parameter in a wider area of the concrete structure, especially in areas between the single first sensor element and the m second sensor elements. In embodiments, as indicated above, one or more of the m sensing operations may temporally overlap. Especially, in embodiments, one or more of the m sensing operations may be executed simultaneously.

In embodiments, in the monitoring stage, the same sensor element may be designated as the first sensor element for each of the m sensing operations. Yet, in embodiments, it may be beneficial to alternate which of the sensor elements (or which of the sensing arrangements) is designated as the first sensor element (or as the first sensing arrangement). Especially, it may be desired to repeat the monitoring stage, yet designate a different sensor element as the first sensor element. Hence, in specific embodiments, the method may comprise successively executing a plurality of monitoring stages, wherein each monitoring stage comprises providing the electrical pulse to a different sensor element. Such a method comprising a plurality of monitoring stages may facilitate (precisely) determining a distribution of the structure-related parameter in the (entire) area defined by the sensing grid arrangement. As such, in embodiments, the location of defects in the concrete structure (e.g. cracks) may be determined with high accuracy. This may provide the benefit that potential repairs may be performed efficiently and effectively, as the location and extent of the damage may be (precisely) known before starting the repair. In embodiments, the method may comprise executing z monitoring stages, wherein z may be selected from the range of 2 —n, such as from the range of 3 — n, especially from the range of 4 -n.

In embodiments, the structure-related parameter may be determined at a location remote from the sensing grid arrangement. For example, the structure-related parameter may be determined in a processing unit, wherein the structure-related parameter may e.g. be displayed on a user interface comprised by said processing unit. In such embodiments, the processing unit may be placed at a location where access to the processing unit may be relatively easy, to facilitate monitoring of the structure-related parameter and/or optionally adjusting one or more settings of the method. Hence, in embodiments, it may be needed to transport the amplified sensor signal over a longer distance, such as over a signal transmission distance. In embodiments, to protect the amplified sensor signal from interference and/or

IO corruption by external (electrical) noise, the amplified sensor signal may be converted into a related pair of differential signals with opposite polarity. Especially, one or more of the amplified sensor signal and the combined sensor signal may be converted into a related pair of differential signals with opposite polarity. Such conversion (into a related pair of differential signals with opposite polarity) of the amplified sensor signal and/or the combined sensor signal may especially be performed in a differential line driver (see above). In embodiments, the related pair of differential signals may (subsequently) be provided to the (remote) processing unit. Further, in embodiments, the method may comprise determining (with the processing unit) a difference between the pair of differential signals to provide a reconstituted sensor signal. In embodiments, the method may (further) comprise transmitting the k amplified sensor signals obtained in a (single) sensing operation through the differential line driver before combining said k (amplified) sensor signals (in the processing unit). Hence, the method may comprise combining k reconstituted sensor signals to provide the combined sensor signal.

Further, the method may comprise (subsequently) determining a structure-related parameter of the concrete structure based on a difference between the reconstituted (and/or combined) sensor signal and the reference signal. Alternatively, the method may comprise (directly) determining a structure-related parameter of the concrete structure based on the pair of differential signals and the reference signal, i.e., the method may not comprise reconstituting the sensor signal before determining the structure-related parameter. Hence, in specific embodiments, the method may comprise: (1) converting one or more of the amplified sensor signal and the combined sensor signal into a related pair of differential signals with opposite polarity; (ii) providing the related pair of differential signals to a processing unit; (iii) determining a difference between the pair of differential signals to provide a reconstituted sensor signal; and (iv) determining a structure-related parameter of the concrete structure based on a difference between the reconstituted sensor signal and the reference signal. Such a method may facilitate transporting the amplified sensor signal (and/or the combined sensor signal) over (relatively) long distances, especially without the (combined and/or amplified) sensor signal becoming corrupted and/or distorted due to interference from (electrical) noise. As such, such a method may facilitate determining the structure-related parameter at a location remote from the sensing grid arrangement, such as at the foot of a pillar, or the side of a bridge.

In embodiments, one or more of the sensing grid arrangement of the monitoring system as defined herein and the sensing grid arrangement of the method as defined herein may be embedded in a concrete structure. Embedding the sensing grid arrangement (according to the monitoring system as defined herein and/or the method as defined herein) may be done after construction of the concrete structure, for example by drilling holes in said concrete structure and fixating the sensor elements (comprised by the sensing grid arrangement) in said holes. Alternatively, in embodiments, the sensing grid arrangement (according to the monitoring system as defined herein and/or the method as defined herein) may be embedded in the concrete structure during construction of said concrete structure, such as e.g. during pouring of the concrete.

Hence, in another aspect, the invention provides a system comprising a concrete structure and the monitoring system as defined herein. Especially, the system may comprise the monitoring system as described herein, or the (monitoring) system of the method as described herein. In embodiments, the sensor elements (comprised by the system) may be arranged in a sensing grid arrangement inside of the concrete structure. Hence, in specific embodiments, the invention provides a system comprising a concrete structure and the monitoring system as defined herein, wherein the sensor elements are arranged in a sensing grid arrangement inside of the concrete structure. Such a system may provide the benefit that the sensor elements may be fully integrated into the concrete structure, such as especially during construction of said concrete structure. Hence, the contact between the concrete structure and the sensor elements may be improved compared to sensor elements installed (by e.g. drilling) into an already existing concrete structure. Improved contact between the sensor elements and the concrete structure may provide the benefit of increasing the sensitivity of the monitoring system, as the sensor signal may not be (as much) distorted and/or weakened at the interface between the concrete structure and the sensor element (hole).

In embodiments, the concrete structure of the system may be selected from the group comprising a building (e.g. an office building, factory, parking garage, warehouse, stadium, etc.), a bridge, a tunnel, a dam, a dock (also “wharf” and/or “quay”), a pipe, a wall, a pillar (including a piling, a post, a pier, a column, etc.), flooring (e.g. a floor, a road, a deck, a curb, etc.), a statue, a river bed and/or bank, a pool base, a (pound) lock, etc. Further, in embodiments, e.g. especially for larger concrete structures, the system may comprise a plurality of monitoring systems. In embodiments, the system may comprise > 2 monitoring systems, such as > 3 monitoring systems, especially > 4 monitoring systems. Further, in embodiments, the system may comprise < 15 monitoring systems, such as < 12 monitoring systems, especially < 10 monitoring systems. In embodiments, the plurality of monitoring systems may be separated by a distance dum. Especially, the distance du may be the shortest distance between any two sensor elements (each) comprised by different sensing grid arrangements, wherein said different sensing grid arrangements are each comprised by different monitoring systems (of the plurality of monitoring systems). In embodiments, the distance du may be selected from the range of > 2 m, such as from the range of > 4 m, especially from the range of > 6 m. Further, in embodiments, the distance dm may be selected from the range of < 200 m, such as from the range of < 150 m, especially from the range of < 100 m. In embodiments, each of the plurality of monitoring systems may comprise (respectively) n sensing arrangements (each comprising a sensor element, see above), an electrical grounding element, a pulser, an amplifier, and a control system, wherein the sensor elements of the n sensing arrangements may be configured (embedded in the concrete structure) in a sensing grid arrangement. Yet, in embodiments, one or more of the plurality of monitoring systems may share at least (part of at least) the control system. Further, in embodiments, the plurality of monitoring systems may share (at least part of) the control system. Especially, in embodiments, the plurality of monitoring systems may share the processing unit. Hence, in specific embodiments, the system may comprise a plurality of monitoring systems, wherein the plurality of monitoring systems share the control system. Such a system comprising a plurality of monitoring systems sharing a control system may be more cost effective than a system comprising a plurality of control systems (such as especially a plurality of processing units).

Further, as the structure-related parameters from all monitoring systems may be provided to the same control system, especially to the same processing unit, such a system may facilitate comparing, on e.g. one user interface, the structure-related parameter determined by all monitoring systems. Further yet, such a system may facilitate changing the settings of all monitoring systems from one central control system, thus simplifying maintenance of the system.

In embodiments, the control system may be configured to execute in a controlling mode the method according to the invention. The control system may especially receive program instructions from a data carrier such that the control system executes the method according to the invention. Hence, in a further aspect, the invention may provide a data carrier having stored thereon program instructions. Such program instructions when executed by the system described above may cause the system to execute the method described above.

Hence, in specific embodiments, the invention may provide a data carrier carrying thereupon program instructions which, when carried out by the system described herein may cause the system to carry out the method as described herein. Thus, the data carrier may facilitate the execution of pre-programmed operational modes of the system. This may increase user convenience and adherence to standard use of the system. Further, the data carrier may comprise the reference signal that may be used in determining the structure-related parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: Fig. 1A-B schematically depict embodiments of the monitoring system 1000; and Fig. 2 schematically depicts an embodiment of the system 3000. The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1A (I) and Fig. 1A (II) schematically depict embodiments of the monitoring system 1000 for monitoring a concrete structure 1. In embodiments, the monitoring system 1000 may comprise n sensing arrangements 500, an electrical grounding element 700, a pulser 400, an amplifier 200, and a control system 300. In embodiments, n may be selected from the range of > 2. Additionally or alternatively, n may be selected from the range of < 12. In specific embodiments, n > 4 (in Fig. 1A, embodiments with n = 4 are depicted). In embodiments, each sensing arrangement 500 may comprise a sensor element 10, a first switch 510, a second switch 520, and a spacing wire 530. The sensor element 10 may especially be a piezoelectric transducer. Further, the first switches 510, second switches 520, and spacing wires 530 of the n sensing arrangements 500 may in embodiments be comprised by a multiplexor, such as especially a first multiplexor 311 (as depicted in Fig. 1 A). Further, in embodiments, the spacing wire 530 may be configured to separate the first switch 510 from the second switch 520 by a spacing distance ds of at least 0.5 cm. In embodiments, the sensing arrangement 500 has a first configuration and a second configuration. In the first configuration, the sensor element 10 may be configured electrically coupled to the pulser 400 via the first switch 510, the spacing wire 530, and the second switch 520. An example of the first configuration is depicted for the bottom sensing arrangement 500 in Fig. 1A (I). Meanwhile, in the second configuration the spacing wire 530 may be configured electrically coupled to the electrical grounding element 700 via the first switch 510. Additionally, in the second configuration, the sensor element 10 may be configured electrically coupled to the amplifier 200 via the second switch 520. An example of the second configuration is depicted for the top three sensing arrangements in Fig. 1A (I). In embodiments, the sensor elements 10 of the n sensing arrangements S00 may be configured to be embedded in the concrete structure 1 in a sensing grid arrangement 110 (depicted in Fig.

IB). In such embodiments, each sensor element 10 (in the sensing grid arrangement 110) may be separated from at least two neighboring sensor elements 10 in the sensing grid arrangement 110 by distances independently selected from the range of 20-150 cm. Further, in embodiments, each sensor element 10 (in the sensing grid arrangement 110) may be separated from at least two neighboring sensor elements 10 in the sensing grid arrangement 110 by (center-to-center) distances independently selected from the range of dmin — dma. During operation, the monitoring system 1000 (especially the control system 300) may have an operational mode comprising an actuation stage and a sensing stage. In the actuation stage, a first sensing arrangement 501 (of the n sensing arrangements 500) comprising a first sensor element 11 (of the sensor elements 10) may be in the first configuration. Especially, in embodiments, the control system 300 may be configured to control the first switch 510 and the second switch 520 of the first sensing arrangement 501, thereby moving the switches 510,520 into the first configuration, thereby electrically coupling the pulser 400 to a sensor element 10, and thereby designating this sensor element 10 as the first sensor element 11. In the embodiments depicted in Fig. 1A (I), the bottom sensor element 10 is designated as the first sensor element 11, while in Fig. 1A (II), the top sensor element 10 is designated as the first sensor element 11. It should however be noted that any of the n sensor elements 10 (and any ofthe sensing arrangements 500) may in embodiments be designated as the first sensor element 11 (and the first sensing arrangement 501). In embodiments, the pulser 400 may be configured to provide an electrical pulse to the first sensor element 11. In embodiments, the pulser 400 may be configured to provide an electrical pulse comprising a square wave. Further, the electrical pulse may have a pulse duration tp selected from the range of 6-200 us. In embodiments, the first sensor element 11 may be configured to (in the actuation stage) provide an actuation signal in response to the electrical pulse.

Further, in the sensing stage, a second sensing arrangement 502 (of the n sensing arrangements 500) comprising a second sensor element 12 (of the sensor elements 10) may be in the second configuration. In embodiments, the second sensor element 12 may especially be configured to detect the actuation signal and to provide a related sensor signal to the control system 300 via the amplifier 200. Further, in the sensing stage, the spacing wires 530 of the sensing arrangements 500 not designated as the first sensing arrangement 501 may be configured electrically coupled to the grounding element 700 via the respective first switches 510. In embodiments, the grounding element 700 may comprise up to n grounding structures 710. Further, in embodiments, each of the up to n grounding structures 710 may be configured to be electrically coupled to one or more sensing arrangements 500, such as especially to one or more spacing wires 530 (via the respective first switches 510). Depicted here is an embodiment with four grounding structures 710, wherein each of the grounding structures 710 is configured to be electrically coupled to one respective sensing arrangement 500. In embodiments, the first multiplexor 311 may comprise the grounding element 700.

In embodiments, all of the sensing arrangements S00 not designated as the first sensing arrangement 501, including the second sensing arrangement 502, may be configured in the second configuration during the sensing stage. Yet, only the second sensing arrangement 502 may be configured electrically coupled to the control system 300 (via the amplifier 200).

Hence, in embodiments, only the sensing arrangement 500 electrically coupled to the control system 300 may provide a sensor signal to the control system 300 (via the amplifier 200), thereby designating this sensing arrangement 500 as the second sensing arrangement 502. In the embodiment depicted in Fig. 1A (I), the top sensing arrangement 500 is configured electrically coupled to the control system 300 (via the amplifier 200), and may thus be the second sensing arrangement 502. Especially, the second sensing arrangement 502 may be electrically coupled to a second multiplexor 312 comprised by the control system 300. In embodiments, the second multiplexor 312 may designate a sensing arrangement 500 (and the corresponding sensor element 10) as the second sensing arrangement 502 (and the second sensor element 12) by establishing an electrical connection between said sensing arrangement 500 (or sensor element 10) and the processing unit 320 (optionally via a differential line driver 321). In Fig. 1A (I), an electrical connection is established between the top sensor element 10 and the processing unit 320, thereby designating this top sensor element 10 as the second sensor element 12, and the corresponding sensing arrangement 500 as the second sensing arrangement 502. In embodiments, the sensing arrangements 500, especially the sensor elements 10, configured not electrically coupled to the control system 300 may be configured to detect the actuation signal, yet may be configured not to provide a related sensor signal to the control system 300, especially to the processing unit 320 (via the second multiplexor 312 and differential line driver 321). That is, the control system 300, especially the processing unit 320,

may be configured to (only) receive related sensor signals from sensor elements 10 designated as second sensor elements 12. In embodiments, the monitoring system 1000 may comprise an amplifier 200. The amplifier 200 may especially be configured to (in the sensing stage) (i) receive the sensor signal (from the sensor elements 10 not designated as the first sensor element 11, and via their respective second switches 520), (ii) amplify the sensor signal, and (iii) provide an amplified sensor signal to (the second multiplexor 312 and/or the processing unit 320 of) the control system 300 (but only for the sensor element(s) 10 designated as second sensor element(s) 12). In embodiments, the monitoring system 1000 may comprise a plurality of amplifiers 200, such as especially n amplifiers 200. Alternatively, the monitoring system

IO 1000 may comprise a single amplifier 200 comprising a plurality of amplifier ports (this is schematically depicted in Fig. 1B). Further, in embodiments, the control system 300 may be configured to determine a structure-related parameter of the concrete structure 1 based on a difference between the (amplified) sensor signal and a reference signal. The structure-related parameter may especially be selected from the group comprising a number of cracks, an (average) crack size, a crack position, a (change in) elastic modulus, a (change in) the stress, a (change in) the strain, a density, a porosity, and an average particle size. Further, the reference signal may comprise one or more of (i) a simulated version of the sensor signal, (ii) a previously recorded sensor signal, and (iii) a sensor signal recorded in a model system using a similar type of concrete and distance between the first sensor element 11 and second sensor element 12.

In embodiments, the monitoring system 1000(, especially the control system 300,) may have a first operational mode. The first operational mode may comprise a sensing operation. Further, the sensing operation may comprise k repetitions of a chronological sequence comprising the actuation stage and the sensing stage. In embodiments, k may be selected from the range of 2-1000. Further, in embodiments, the same sensor element 10 may be designated as the first sensor element 11 for each of the k repetitions. Hence, the same sensing arrangement 500 may be designated as the first sensing arrangement 501 for each of the k repetitions. Additionally, in embodiments, the same sensor element 10 may be designated as the second sensor element 12 for each of the k repetitions. Hence, the same sensing arrangement 500 may be designated as the second sensing arrangement 502 for each of the k repetitions. In embodiments, the control system 300 may be configured to combine (and/or average) k (amplified) sensor signals provided by the second sensor element 12 in the sensing operation to provide a combined sensor signal. Further, the control system 300 may be configured to determine a structure-related parameter of the concrete structure 1 based on a difference between the combined sensor signal and the reference signal.

The first operational mode may further comprise a monitoring stage. In embodiments, the monitoring stage may comprise (successively) executing m sensing operations. In embodiments, m < n-1. Further, in each sensing operation, a different sensor element 10 may be configured electrically coupled to the control system 300 (via the amplifier 200) in the sensing stage. That is, in each sensing operation, a different sensor element 10 may be designated as the second sensor element 12. Similarly, that is, in each sensing operation, a different sensing arrangement 500 may be designated as the second sensing arrangement 502.

Further, in embodiments, k may be independently selected for each sensing operation. In embodiments, one or more of the m sensing operations may temporally overlap, such as be executed simultaneously. Hence, multiple (of the n) sensor elements 10 (and thus the corresponding sensing arrangements 500) may be designated as second sensor element 12 (and second sensing arrangement 502) simultaneously. Such an embodiment is schematically depicted in Fig. 1A (II). Here, the bottom three sensing arrangements 500 (comprising sensor elements 10) are all designated as second sensing arrangements 502 (and second sensor elements 12) simultaneously. In embodiments wherein one or more sensing operations temporally overlap, the control system 300 may be configured not comprising a second multiplexor 312. Further, in such embodiments, the control system 300 may comprise a plurality of differential line drivers 321. In embodiments, as depicted in Fig. 1A (II), each of the plurality of differential line drivers 321 may be configured to be electrically coupled to one sensing arrangement S00 (via the amplifier 200). Further, each of the plurality of differential line drivers 321 may be configured to be electrically coupled to the same or a different processing unit 320. As such, the (amplified) sensor signals from the second sensor element 12 of each of the overlapping sensing operations may be simultaneously transmitted to the processing unit(s) 320. As such, in embodiments, the control system 300 may be configured to simultaneously or consecutively determine a structure-related parameter for each of the one or more (overlapping) sensing operations in the monitoring stage.

In embodiments, the first operational mode may comprise (successively) executing a plurality of monitoring stages. Especially, in such embodiments, in each monitoring stage a different sensor element 10 may be configured electrically coupled to the pulser 400 in the actuation stage. That is, in each monitoring stage, a different sensor element 10 may be designated as the first sensor element 11. Further, that is, in each monitoring stage, a different sensing arrangement 500 may be in the first configuration, and may thus be designated as the first sensing arrangement 501.

Further, (the monitoring system 1000, especially) the control system 300 may comprise a differential line driver 321 and a processing unit 320. The differential line driver 321 may be configured to convert one or more of the (amplified) sensor signal and the combined sensor signal into a related pair of differential signals with opposite polarity. Further, the differential line driver 321 may be configured to provide the related pair of differential signals to the processing unit 320. The processing unit 320 may in embodiments especially be configured to determine a difference between the pair of differential signals to provide a reconstituted sensor signal. Further, the processing unit 320 may be configured to combine k reconstituted sensor signals to provide the combined sensor signal. Further yet, the processing

IO unit 320 may be configured to determine a structure-related parameter of the concrete structure 1 based on a difference between the reconstituted (and/or combined) sensor signal and the reference signal.

Fig. 1B schematically depicts a further embodiment of the monitoring system 1000. Further, Fig. 1B schematically depicts an embodiment of the method of the invention.

The invention may provide a method for monitoring of a concrete structure 1 using n sensing arrangements 500. In embodiments, each sensing arrangement 500 (of the n sensing arrangements 500) may comprise a sensor element 10, a first switch 510, a second switch 520, and a spacing wire 530. The spacing wire 530 may be configured to separate the first switch 510 from the second switch 520, especially by a spacing distance ds of at least 0.5 cm. In embodiments, n > 4 (i.e., the method may comprise using at least four sensing arrangements 500). Further, the sensor elements 10 of the n sensing arrangements 500 may especially be embedded in the concrete structure 1 in a sensing grid arrangement 110. In embodiments, each sensor element 10 in the sensing grid arrangement 110 may be separated from at least two neighboring sensor elements 10 in the sensing grid arrangement 110 by (center-to-center) distances independently selected from the range of 20-150 cm. Further, in embodiments, each sensor element 10 in the sensing grid arrangement 110 may be separated from at least two neighboring sensor elements 10 in the sensing grid arrangement 110 by (center-to-center) distances independently selected from the range of dmin — dma. Here, the center-to-center distance between the first sensor element 11 and a or the second sensor element 12 is indicated by diz, wherein di 2 may be selected from the range of 20-150 cm and/or from the range of dmin — dmax. In embodiments, the method may comprise an actuation stage, wherein the actuation stage may comprise providing an electrical pulse to a first sensor element 11 comprised by a first sensing arrangement S01, especially via the first switch 510, the spacing wire 530, and the second switch 520 (of the respective first sensing arrangement 501). In embodiments, the first sensor element 11 may generate an actuation signal in response to the electrical pulse. Further, in embodiments, the method may comprise a sensing stage, wherein the sensing stage may comprise detecting the actuation signal with a second sensor element 12 comprised by a second sensing arrangement 502. Further, the sensing stage may comprise providing (with the second sensor element 12) a related sensor signal (to the control system 300) via the (respective) second switch 520. In embodiments, the sensing stage may (further) comprise grounding the spacing wire 530 of the second sensing arrangement 502 via the first switch 510. Further, in embodiments, the method may comprise amplifying the sensor signal to provide an amplified sensor signal. Additionally, the method may comprise determining a structure-related parameter of the concrete structure 1 based on a difference between the amplified sensor signal and a reference signal.

In embodiments, the method may comprise a sensing operation. The sensing operation may comprise executing k repetitions of a chronological sequence comprising the actuation stage and the sensing stage. In embodiments, k may especially be selected from the range of 2-1000. Further, the method may comprise combining (and/or averaging) k amplified sensor signals provided (by the second sensing arrangement 502, especially) by the second sensor element 12 in the sensing operation to provide a combined sensor signal. Further, the method may comprise determining a structure-related parameter of the concrete structure 1 based on a difference between the combined sensor signal and the reference signal.

Additionally, the method may comprise a monitoring stage. The monitoring stage may especially comprise successively executing m sensing operations. In embodiments, m < n-1. Further, in such embodiments, each (of the m) sensing operation(s) may comprise detecting the actuation signal with a different sensor element 10. That is, in each (of the m) sensing operation(s), a different sensor element 10 may be designated as the second sensor element 12. Further, that is, in each (of the m) sensing operation(s), a different sensing arrangement 500 may be designated as the second sensing arrangement 502 (especially by the control system 300 establishing an electrical connection between the control system 300 and a sensing arrangement 500 in the second configuration). Further, in embodiments, one or more of the m sensing operations may temporally overlap, such as be executed simultaneously. In embodiments, the method may further comprise successively executing a plurality of monitoring stages. In embodiments, each (of the plurality of) monitoring stage(s) may comprise providing the electrical pulse to a different sensor element 10. That is, in each (of the plurality of) monitoring stage(s), a different sensor element 10 may be designated as the first sensor element 11. Especially, that is, in each (of the plurality of) monitoring stage(s), a different sensing arrangement S00 may be in the first configuration, thereby designated this sensing arrangement 500 as the first sensing arrangement 501, and the corresponding sensor element 10 as the first sensor element 11.

In embodiments, the processing unit 320 may be configured remote from the sensing grid arrangement 110. Hence, the method may comprise converting one or more of the amplified sensor signal and the combined sensor signal into a related pair of differential signals with opposite polarity (in a differential line driver 321). Further, the method may comprise providing the related pair of differential signals to a processing unit 320. Additionally, the method may comprise determining a difference between the pair of differential signals to provide a reconstituted sensor signal. In embodiments, the method may comprise combining k reconstituted sensor signals to provide the combined sensor signal. Further, the method may comprise determining a structure-related parameter of the concrete structure 1 based on a difference between the reconstituted (and/or combined) sensor signal and the reference signal.

Fig. 1B further schematically depicts an embodiment of the data carrier 4000.

In embodiments, the invention may provide a data carrier 4000 carrying thereupon program instructions which, when carried out by a system 1000 as described herein, cause the system 1000 to carry out the method as described herein.

Further, Fig. 1B depicts a schematic embodiment of the system 3000. The system 3000 may comprise a concrete structure 1 (depicted in cross-sectional view) and the monitoring system 1000 as described herein, wherein the sensor elements 10 may be arranged in a sensing grid arrangement 110 inside of the concrete structure 1.

Fig. 2 schematically depicts a further embodiment of the system 3000. The system 3000 may comprise a plurality of monitoring systems 1000. In the embodiment of the system 3000 depicted here, the concrete structure 1 is a bridge, and the system 3000 comprises three monitoring systems 1000. In embodiments, the plurality of monitoring systems 1000 may share (at least part of) the control system 300. Especially, the plurality of monitoring systems 1000 may share the processing unit 320. In such embodiments, the (central) processing unit 320 may be electrically coupled to each of the sensing grid arrangements 110 (and/or each of the n sensing arrangements 500) of the plurality of monitoring systems 1000 via a plurality of respective differential line drivers 321 (and/or a plurality of respective second multiplexors 312). This way, a single processing unit 320 may be used to control all of the plurality of monitoring systems 1000. Further, the structure-related parameters determined for each of the plurality of monitoring systems 1000 may in such embodiments be viewed and/or processed using the same processing unit 320.

The term “plurality” refers to two or more. The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%.

The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases

IO may relate to one or more of item 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of" but may in another embodiment also refer to "containing at least the defined species and optionally one or more other species". The term “comprise” thus also includes embodiments wherein the term “comprises” means “consists of”.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. In yet a further aspect, the invention (thus) provides a software product, which, when running on a computer is capable of bringing about (one or more embodiments of) the method as described herein.

The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and/or shown 1n the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

Claims

Conclusions

1. A monitoring system (1000) for monitoring a concrete structure (1), the monitoring system (1000) comprising n sensor devices (500), an electrical grounding element (700), a pulser (400), an amplifier (200), and a control system (300), wherein n > 4, wherein: - each sensor device (500) comprises a sensor element (10), a first switch (510), a second switch (520), and a spacing wire (530), wherein the spacing wire (530) is configured to separate the first switch (510) from the second switch (520) by a distance (ds) of at least 0.5 cm, the sensor device (500) having a first configuration and a second configuration, wherein in the first configuration the sensor element (10) is electrically coupled via the first switch (510), the spacing wire (530), and the second switch (520); configured to the pulser (400), and wherein in the second configuration (1) the spacing wire (530) is configured to be electrically coupled to the electrical grounding element (700) via the first switch (510) and (ii) the sensor element (10) is configured to be electrically coupled to the amplifier (200) via the second switch (520); - the sensor elements (10) of the n sensor devices (500) are configured to be embedded in a sensor grid device (110) in the concrete structure (1), each sensor element (10) being separated by distances independently selected from the range of 20-150 cm from at least two adjacent sensor elements (10) in the sensor grid device (110); - the monitoring system (1000) has an operational mode comprising an actuation phase and a detection phase, wherein: (a) in the actuation phase, a first sensor device (501) comprising a first sensor element (11) is in the first configuration, the pulser (400) being configured to provide an electrical pulse to the first sensor element (11), and the first sensor element (11) being configured to provide an actuation signal in response to the electrical pulse; and

(b) in the detection phase, a second sensor device (502) comprising a second sensor element (12) is in the second configuration, the second sensor element (12) being configured to detect the drive signal and to provide a related sensor signal to the control system (300) via the amplifier (200); - the amplifier (200) being configured to (i) receive the sensor signal, (ii) amplify the sensor signal, and (iii) provide an amplified sensor signal to the control system (300); and - the control system (300) being configured to determine a structure-related parameter of the concrete structure (1) based on a difference between the amplified sensor signal and a reference signal.

The monitoring system (1000) of claim 1, wherein the pulser (400) is configured to provide an electrical pulse comprising a square wave, the electrical pulse having a pulse duration t selected from the range of 6-200 ps.

The monitoring system (1000) according to any one of the preceding claims, wherein: - the monitoring system (1000) has a first operational mode comprising a sensing operation, the sensing operation comprising k repetitions of a chronological sequence comprising the actuation phase and the sensing phase, k being selected from the range of 2-1000; - the control system (300) is configured to combine k amplified sensor signals provided by the second sensor element (12) in the sensing operation to provide a combined sensor signal, the control system (300) being configured to determine a structure-related parameter of the concrete structure (1) based on a difference between the combined sensor signal and the reference signal.

The monitoring system (1000) of claim 3, wherein the first operational mode comprises a monitoring phase, the monitoring phase comprising performing m sensing operations, where m < n-1, wherein in each sensing operation a different sensor element (10) is configured in the sensing phase electrically coupled to the control system (300) via the amplifier (200).

The monitoring system (1000) of claim 5, wherein the first operational mode comprises performing multiple monitoring phases, each monitoring phase having a different sensor element (10) in the drive phase electrically coupled to the pulser (400).

The monitoring system (1000) of any preceding claim, wherein the control system (300) comprises a differential line driver (321) and a processing unit (320), wherein: - the differential line driver (321) is configured to convert one or more of the amplified sensor signal and the combined sensor signal as defined in claim 3 into a related pair of differential signals of opposite polarity; - the differential line driver (321) is configured to provide the related pair of differential signals to the processing unit (320); and - the processing unit (320) is configured to determine a difference between the pair of differential signals to provide a reconstructed sensor signal; wherein the processing unit (320) is configured to determine the structure-related parameter of the concrete structure (1) based on a difference between the reconstructed sensor signal and the reference signal.

7. The monitoring system (1000) according to any one of the preceding claims, wherein one or more of the following applies: - the sensor element (10) is a piezoelectric transducer; and - the structure-related parameter is selected from the group consisting of a number of cracks, a crack size, a crack position, an elastic modulus, a stress, a strain, a density, a porosity, and an average particle size; and

- the reference signal includes a previously recorded and amplified sensor signal.

8. A method for monitoring a concrete structure (1) by means of n sensor devices (500), each sensor device (500) comprising a sensor element (10), a first switch (510), a second switch (520), and a spacing wire (530), the spacing wire (530) configured to separate the first switch (510) from the second switch (520) by a distance (ds) of at least 0.5 cm, wherein n > 4, the sensor elements (10) of the n sensor devices (500) being embedded in a sensor grid device (110) in the concrete structure (1), each sensor element (10) in the sensor grid device (110) being separated by distances independently selected from the range of 20-150 cm from at least two adjacent sensor elements (10) in the sensor grid device (110), the method comprising: - an actuating phase comprising providing an electrical pulse to a first sensor element (11) via the first switch (510), the spacing wire (530), and the second switch (520), the first sensor element (11) generating an actuation signal in response to the electrical pulse; and - a detection step comprising detecting the actuation signal with a second sensor element (12) comprised by a second sensor device (502), and providing a related sensor signal via the second switch (520), the detection step comprising grounding the spacing wire (530) of the second detection device (502) via the first switch (510); and wherein the method comprises (a) amplifying the sensor signal to provide an amplified sensor signal, and (b) determining a structure-related parameter of the concrete structure (1) based on a difference between the amplified sensor signal and a reference signal.

9. The method according to claim 8, wherein the method comprises a sensing operation, the sensing operation comprising performing k repetitions of a chronological sequence including the actuating phase and the sensing phase, k being selected from the range of 2-1000, the method comprising combining k amplified sensor signals provided by the second sensor element (12) in the sensing operation to provide a combined sensor signal, and determining the structure-related parameter of the concrete structure (1) based on a difference between the combined sensor signal and the reference signal.

10. The method according to any of claims 8 to 9, wherein the method comprises a monitoring phase, the monitoring phase comprising sequentially performing m sensing operations, where m < n-1, each sensing operation comprising detecting the drive signal with a different sensor element (10).

11. The method of claim 10, wherein the method comprises sequentially performing multiple monitoring phases, each monitoring phase comprising delivering the electrical pulse to a different sensor element (10).

The method according to any of claims 8 to 11, comprising: - converting one or more of the amplified sensor signal and the combined sensor signal as defined in claim 9 into a related pair of differential signals of opposite polarity; - providing the related pair of differential signals to a processing unit (320); - determining a difference between the pair of differential signals to provide a reconstructed sensor signal; and - determining the structure-related parameter of the concrete structure (1) based on a difference between the reconstructed sensor signal and the reference signal.

A system (3000) comprising a concrete structure (1) and the monitoring system (1000) according to any one of the preceding claims 1-7, wherein the sensor elements (10) are arranged in a sensor grid arrangement (110) within the concrete structure (1).

14. The system (3000) of claim 13, wherein the system (3000) comprises a plurality of monitoring systems (1000), the plurality of monitoring systems (1000) sharing the control system (300).

15. A data carrier (4000) carrying thereon program instructions which, when executed by a system (1000) according to any one of the preceding claims 1 to 7, cause the system (1000) to perform the method according to any one of the preceding claims 8 to 12.