WO2024160869A1

WO2024160869A1 - Printed sensor

Info

Publication number: WO2024160869A1
Application number: PCT/EP2024/052326
Authority: WO
Inventors: Johannes Zimmermann
Original assignee: Innovationlab GmbH
Current assignee: Innovationlab GmbH
Priority date: 2023-01-31
Filing date: 2024-01-31
Publication date: 2024-08-08
Anticipated expiration: 2025-07-31
Also published as: CN120615185A; KR20250135304A; LU503405B1

Abstract

A method for manufacturing a printed sensor, a method for detecting a pressure using a printed sensor and a printed sensor are disclosed. The printed sensor comprises a first substrate comprising at least one electrode unit, a second substrate opposite to the first substrate, the second substrate comprising a plurality of counter-electrodes. The electrode unit comprises a connection electrode, a first electrode and a second electrode, wherein said connection electrode extends between said first electrode and said second electrode. The plurality of counter-electrodes is distributed on the second substrate and wherein more than one of the plurality of counter-electrodes faces the opposite connection electrode.

Description

Description Title: Printed Sensor

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Luxemburg Patent Application LU503405, filed on 31 January 2023. The entire disclosure of Luxemburg Patent Application LU503405 is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The field of the invention relates to a printed sensor, a method for manufacturing a printed sensor and a method for detecting a pressure using a printed sensor.

BACKGROUND OF THE INVENTION

[0003] Printed sensors, created by printing conductive materials onto a flexible substrate, which detect and respond to a physical input and convert the input into an electrical signal that can be processed, stored, or transmitted, are well known in the art.

[0004] Document WO 2014/037016 Al discloses for example a sensing device, which comprises a substrate, a sensor ink printed onto the substrate, a conductive polymer ink printed onto the sensor ink, a conductive carbon paste formed on the polymer ink, and a conductive silver ink printed on the conductive carbon paste.

[0005] Document WO 1997/004294 Al discloses a force sensor employing a segmental electrode construction, with a portion of one of its pair of electrodes being printed on a first backing sheet and another portion of the one electrode being printed on a second sheet. When they are juxtaposed, they form a continuous electrode. The other of the pair of electrodes is also formed on the first backing sheet and cooperates with the first electrode to indicate when a load is applied to a zone in which the pair of electrodes overlie one another.

[0006] Document US 7 073 387 B2 discloses implantable pressure sensors and methods for making and using the same. A feature of at least some of the subject pressure sensors is that they are low-drift sensors. Additional features of representable pressure sensors include the presence of a compliant member mounted on a substrate in a manner such that the compliant member has first and second opposing exposed surfaces and is positioned at least proximal to the said pressure sensor's neutral plane. The subject pressure sensors find use in a variety of applications.

[0007] WO 2022/084308 Al discloses a sensor measuring forces, a method for manufacturing a sensor and a method for measuring a force. The sensor comprises a first substrate and a second substrate arranged at a distance in a planar manner from each other. A plurality of first electrodes is disposed apart from each other at a first distance on an inner side of the first substrate and a plurality of force-sensitive elements arranged on the inner side of the first substrate and covers at least a part of individual ones of the plurality of first electrodes. A second electrode is arranged on an inner side of the second substrate and extends across at least ones of the plurality of the force-sensitive elements. The second electrode of the second substrate is thereby in direct contact with the plurality of forcesensitive elements of the first substrate. The principle of the sensor corresponds to the common model of a shunt-mode sensor. The document describes that pressure or force is detected by a change in resistance generated by the compression of a material, which thereby changes its electrical conductivity. Here, the direction of current flow through the material to be compressed is parallel to the direction of the applied pressure. Thereby, the zero resistance without pressure load is infinitely high. Only in this manner can a sufficiently large change in electrical resistance be achieved. Moreover, both sides of the substrates must be precisely matched to each other that the force-sensitive elements match the electrodes.

[0008] EP 3 748 320 Al discloses a sensor with a time-sharing regional shielding function and a robot. The sensor comprises a plurality of sensor units, each of which comprises regions contained in four multifunctional layers. Four parallel-plate capacitors are contained in the multifunctional layers. The multifunctional layers realize the regional shielding function through the time-sharing switching of analog switches and the control of a bus.

[0009] EP 3 726 191 Al discloses a pressure sensor, comprising at least two adjacent electrically conductive leads disposed in a pattern on a face of a first elastomeric carrier; and an electrically resistive layer formed of an electrically resistive composite material for shunting the at least two adjacent electrically conductive leads, said electrically conducting layer disposed on a face of a second elastomeric carrier. The document describes that pressure or force is detected by a change in resistance generated by the compression of a material, which thereby changes its electrical conductivity. Here, the direction of current flow through the material to be compressed is again parallel to the direction of the applied pressure. Thereby, the zero resistance without pressure load is infinitely high. Only in this manner can a sufficiently large change in electrical resistance be achieved.

[0010] The substrates of the sensors must be precisely aligned for the sensor to detect the applied pressure. In the manufacture of sensors, the alignment of the two substrates is often fully automated using camera systems and specialised production units. Alternatively, the two substrates are aligned manually, which is subjective, inefficient, and expensive. If the sensors are small, production failures increase which lead to waste.

[0011] For the sensing, the sensors can be configured in thru-mode or shunt-mode. The thru-mode in sensors refers to a mode of operation where the sensor is used to measure the transmission of a signal through a material, rather than measuring its reflection. The main advantage of thru-mode sensing is that it provides a direct measurement of the material's properties, rather than relying on indirect measurements made from reflected signals. Thru- mode sensors can be designed using various technologies, including ultrasound, microwave, and optical sensors.

[0012] The shunt-mode in sensors refers to a mode of operation where the sensor is used to measure the current passing through a material, rather than measuring the voltage across it. This mode is useful for detecting changes in the material's electrical resistance, which can indicate changes in its physical properties such as temperature, strain, or pressure. Shuntmode sensors can be designed using various technologies, including resistive, inductive, and capacitive sensors.

[0013] Sensors in both modes (and in general) are subject to two common errors, hysteresis, and drift, which affect the accuracy and repeatability.

[0014] Hysteresis in a printed sensor refers to a difference in output readings of the sensor for the same input value when the input value is approached from different directions. For example, the output readings of a pressure sensor may be different for the same applied pressure when the pressure is increasing compared to when the pressure is decreasing. This phenomenon occurs because the deformation of the sensor material (e.g., polymer, ink) is not instantaneous and depends on its past history of deformation. This results in a difference between the sensor's output under increasing and decreasing input, creating a hysteresis loop. [0015] Drift in a printed pressure sensor refers to a gradual change in the sensor's output over time. Drift in printed sensors can be characterized as the normalized resistance over time, which refers to the change in the sensor's output relative to its initial value. This value can be represented as a percentage or ratio, and it indicates how much the sensor's output has changed over a certain time period. A high level of drift would mean a significant change in the normalized resistance, which would affect the accuracy and stability of the sensor's readings. A low level of drift, on the other hand, would indicate good stability and reliability of the sensor's performance over time.

[0016] Figures 1A and IB illustrate the hysteresis of two common sensor, on in thru-mode (Fig. 1A) and the other in shunt-mode (Fig. IB). Thereby, both sensors have approximately the same area and were measured with the same measurement protocol, where the sensors were measured from 0 N/cm2 to 500 N/cm2 and back to 0 N/cm2. In Figures 1 A and IB the hysteresis is summarised for the pressures 1 N/cm2, 10 N/cm2 and 100 N/cm2. The hysteresis was calculated by determining the standard deviation and the mean value of the resistance in the up and down passage at the respective pressure. Hysteresis is presented as the ratio of standard deviation to mean value, expressed as a percentage of the mean value. The results are presented in table 1 :

Table 1 : Hysteresis of the sensor in thru-mode vs shunt-mode

[0017] Based on the measures in table 1, the sensor in shunt-mode has a better hysteresis behaviour than the sensor in thru-mode. However, in both cases there is a difference between the resistance values when the pressure is increased and decreased, resulting in the shown hysteresis loops.

[0018] Figures 2A and 2B illustrate the drift behaviour at constant pressures of 1 N/cm2, 10 N/cm2 and 100 N/cm2 applied to the sensor in thru-mode (Fig. 2A) and the sensor in shunt-mode (Fig. 2B). The drift illustrated in these figures is presented as percentage change between the start and end value of the resistance for different measurement periods. The results are presented in table 2:

Table 2: Drift of the sensor in thru-mode vs shunt-mode [0019] Based on the measures in table 2, the drift changes in both sensor types over time. The drift is higher in the beginning and lower at a later time, which is because a higher initial drift may occur as the sensing material adjusts to the applied pressure and the environment, but it may decrease over time as the material stabilizes.

[0020] Repeatability is a term used to describe the precision of a sensor in measuring the same input repeatedly over time. Repeatability is a measure of the ability of a sensor to produce consistent readings for the same input and thus how accurately a sensor delivers the same signal with the same input. For this purpose, the above sensors were each loaded 20 times for 10 seconds at pressures 1 N/cm2, 10 N/cm2 and 100 N/cm2. The standard deviation of the cycles at the same pressure was measured and set in relation to the mean value. This ratio (repeatability) is expressed in table 3 as a percentage.

Table 3: Repeatability of the sensor in thru-mode vs shunt-mode

[0021] The objective of the present invention is to provide a printed sensor in which performance over time and repeatability are improved. A further objective of the present invention is to provide a sensor in which the alignment of the substrates can be omitted which leads to a more cost-effective and easier-to-manufacture sensor.

SUMMARY OF THE INVENTION

[0022] The above-mentioned objective is solved by a printed sensor comprising a first substrate, comprising at least one electrode unit and a second substrate, opposite to the first substrate, comprising a plurality of counter-electrodes. The electrode unit comprises a connection electrode, a first electrode and a second electrode, wherein said connection electrode extends between said first electrode and said second electrode. The plurality of counter-electrodes is distributed on the second substrate and more than one of the plurality of counter-electrodes faces the opposite connection electrode. Thus, the two substrates do not need to be aligned to form the printed sensor.

[0023] In one aspect a distance between two adjacent electrode units is greater than a size of a single one of the plurality of counter-electrodes. Thus, a single one of the plurality of counter-electrodes is not able to short-circuit two adjacent electrode units, because the distance is greater than the size. The manufacture of the sensor becomes more cost-effective and easier because an alignment of the first substrate to the second substrate is not needed anymore.

[0024] In another aspect the size of a single one of the plurality of counter-electrodes is smaller than a distance between the first and the second electrode. Thus, more than one of the plurality of counter-electrodes can face the opposite connection electrode to cause at least one short-circuit which influences a measurable total unit electrical resistance when a pressure is applied to the printed sensor. The manufacture of the sensor becomes more cost- effective and easier because an alignment of the first substrate to the second substrate is not needed anymore.

[0025] In another aspect the plurality of counter-electrodes is periodically distributed on the second substrate. A periodically distribution of the counter-electrodes on the second substrate enhances the ability to not require alignment with the first substrate to form the printed sensor.

[0026] In another aspect the counter-electrode comprises an electrode core made of a different material than the counter-electrode. A combination of dissimilar materials of the counter-electrode increases the conductivity of the printed sensor.

[0027] The above objective is further solved by a method for manufacturing a printed sensor having a first substrate and a second substrate disposed opposite to the first substrate. The method comprises the steps of printing the first substrate with at least one electrode unit, printing a second substrate with a plurality of counter-electrodes, and positioning the second substrate on the first substrate, wherein the positioning of the second substrate is performed without alignment on the first substrate, and wherein the at least one electrode unit faces more than one of the plurality of counter-electrodes. Thus, the two substrates does not need to be aligned to form the printed sensor.

[0028] In one aspect, the printing of the first substrate and the printing of the second substrate are performed at separate times. This allows that the printed first substrate and the printed second substrate may be manufactured and stored separately. The printed sensor can thus be formed out of the printed first substrate and the printed second substrate at a time, when the printed sensor is needed and formed dependent on the application. The ability to not require alignment between the printed first substrate and the printed second substrate increases cost-efficiency of manufacture and makes the manufacture and logistics easier.

[0029] In another aspect the printing of the plurality of counter-electrodes is configured such that the size of each one of the plurality of counter-electrodes is smaller than a distance of at least two adjacent electrode units at the first printing. Each one of the plurality of counter-electrodes is not able to short-circuit two adjacent electrode units when the printed sensor is formed. The ability to not require alignment when forming the printed sensor by positioning the second printed substrate on the first printed substrate becomes possible. The manufacture of the sensor becomes more cost-effective and easier because an alignment of the first substrate to the second substrate is not needed anymore.

[0030] In another aspect, the printing of the plurality of counter-electrodes is configured such that the size of a single one of the plurality of counter-electrodes is smaller than a distance between the first and the second electrode. Thus, at least one counter-electrode faces the opposite connection electrode to cause a short-circuit which influences a measurable change of the total unit electrical resistance of the pressure sensor. The ability to not have to align the first substrate and the second substrate to form the printed sensor is improved. The manufacture of the sensor becomes more cost-effective and easier because the alignment is not needed anymore.

[0031] The above objective is further solved by a method for detecting the pressure using the printed sensor. The method comprises applying pressure to at least one region of the sensor, contacting at least one counter-electrode with the connection electrode of the printed sensor at the at least one region, generating at least one electronic circuit at the at least one region, changing the total unit electrical resistance of the sensor between the first electrode and the second electrode in accordance of the pressure, and measuring the change in total unit electrical resistance indicative of the applied pressure to the sensor. Thereby each of the at least one electric circuits comprises a counter-resistance of the counter-electrode, a contact resistance and a second section-resistance.

[0032] In one aspect, the changing of the total unit electrical resistance is dependent on the number of electric circuits and an amount of first section-resistances.

DESCRIPTION OF THE FIGURES [0033] Fig. 1 A is a pressure-resistance diagram of a known thru-mode sensor illustrating a hysteresis.

[0034] Fig. IB is a pressure-resistance diagram of a known shunt-mode sensor illustrating a hysteresis.

[0035] Fig. 2A shows a drift diagram of a drift behaviour of the known thru-mode sensor of Fig. 1A.

[0036] Fig. 2B shows a drift diagram of a drift behaviour of the known shunt-mode sensor of Fig. IB.

[0037] Fig. 3 is a schematic cross-view of a first region of a printed sensor of a first embodiment.

[0038] Fig. 4 is a schematic cross-view of a second region of the printed sensor ofFig. 3.

[0039] Fig. 5 is a schematic view of a section of a printed sensor according to a second embodiment.

[0040] Fig. 6A is a schematic illustration of the printed sensor ofFig. 3 when no pressure is applied.

[0041] Fig. 6B is a schematic illustration of resistances of the printed sensor ofFig. 6A.

[0042] Fig. 7A is a schematic illustration of the printed sensor ofFig. 3 when a pressure is applied.

[0043] Fig. 7B is a schematic illustration of resistances of the printed sensor ofFig. 7A.

[0044] Fig. 8 is a schematic top-view of the first region of the printed sensor.

[0045] Fig. 9 is a schematic top-view of the second region of the printed sensor.

[0046] Fig. 10A is a pressure-resistance diagram of the printed sensor.

[0047] Fig. 10B is a drift diagram of the printed sensor.

[0048] Fig. 11 is a flow diagram of a method for manufacturing the printed sensor.

[0049] Fig. 12 is a flow diagram of a method for detecting the pressure using the printed sensor.

DETAILED DESCRIPTION OF THE INVENTION

[0050] The invention will now be described on the basis of the figures. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and/or embodiments of the invention.

[0051] Fig. 3 shows a schematic cross-view of a first region of a printed sensor 100. The first region is a region of the sensor 100 which comprises one electrode unit 7. The printed sensor 100 comprises a first substrate 1, a second substrate 2, an electrode unit 7 and a plurality of counter-electrodes 5. The plurality of counter-electrodes 5 is deposited by printing on the second electrode 2 and spaced from each other. The plurality of counterelectrodes 5 are not electrically connected with each other. The electrode unit 7 comprises a first electrode 3a, a second electrode 3b and a connection electrode 4. The connection electrode 4 extends between the first electrode 3a and the second electrode 3b and is electrically connected to the first and second electrode 3 a, 3b. The first electrode 3a and the second electrode 3b are printed electrodes for determining a total unit electrical resistance Ru. The first electrode 3a, the second electrode 3b and the connection electrode 4 can be made of any electrically conductive material, such as but not limited to silver-, copper- or carbon-ink. Between the first and second electrodes 3a, 3b the total unit electrical resistance Ru is determined as a measurand for pressure measurement.

[0052] The electrode unit 7 is deposited by printing on the first substrate 1. The second substrate 2 is positioned on the first substrate 1 such that the plurality of counter-electrodes 5 faces the electrode unit 7. For the first substrate 1 and the second substrate 2 any material can be used onto which electrode materials can be deposited. Such materials are for example Polyethylennaphthalate- (PEN), Polyethylenterephthalate- (PET) or Polyimide- (PI) foils, which however are not limiting of the invention. The printed sensor 100 is formed by positioning the printed second substrate 2 on the printed first substrate 1.

[0053] Fig. 4 shows a schematic cross-view of a second region of the printed sensor 100. The second region is a region of the sensor 100 which comprises a plurality of electrode units 7. A plurality of electrode units 7 is provided on the first substrate 1, wherein two adjacent electrode units 7 are spaced from each other by a distance 71. Every single one of the plurality of counter-electrodes 5 has a size 51. In one example, in which the counterelectrode 5 has a circular shape, the size 51 indicates a radius of the counter-electrode 5. In another example, in which the counter-electrode 5 has a rectangular shape, the size 51 indicates an edge length of the counter-electrode 5. The size 51 is smaller than the distance 71. Thus, more than one of the plurality of counter-electrodes 5 will face the opposite connection electrode 4 and not a single one of the plurality of counter-electrodes 5 will be able to contact two of the plurality of electrode units 7 at the same time.

[0054] In one example one of the plurality of counter-electrodes 5 and at least part of a second one of the plurality of counter-electrodes 5 face the opposite connection electrode 4. Thus, at least one short-circuit between the counter-electrodes 5 through the opposite connection electrode 4 is caused. This short-circuit influences the measurable total unit electrical resistance Ru when a pressure P is applied to the printed sensor 100. Further, the size 51 of a single one of the plurality of counter-electrodes 5 is smaller than a distance between the first and the second electrode 3a, 3b resulting in that more than one of the plurality of counter-electrodes 5 will face the opposite connection electrode 4. In other words, a width of the electrode units 7, defined from the first electrode 3a to the second electrode 3b is greater than the width of more than one of the plurality of counter-electrodes 5. Thus, a positioning SI 03 of the second substrate 2 on the first substrate 1 can be performed without alignment between the two substrates.

[0055] The second substrate 2 is positioned to the first substrate 1 such that the plurality of counter-electrodes 5 faces the plurality of electrode units 7. Thereby the distance 71 between two adjacent electrode units 7 is greater than the size 51 of a single one of the plurality of counter-electrodes 5. This prevents two adjacent electrode units 7 from being short-circuited by one of the counter-electrodes 5 when the pressure P is applied to the printed sensor 100, because the distance 71 is greater than the size 51.

[0056] In one aspect, the single ones of the plurality of counter-electrodes 5 can have differing sizes 51. In one aspect, the plurality of counter-electrodes 5 is printed and/or distributed periodically on the second substrate 2, as illustrated in Figs. 8 and 9. In another aspect, the plurality of counter-electrodes 5 can be printed and/or distributed randomly on the second substrate 2.

[0057] As shown in Fig. 5, in a second embodiment of the printed sensor 100 a combination of dissimilar materials can be used for the counter-electrodes 5 to increase the conductivity. The counter-electrodes 5 of the printed sensor 100 of the second embodiment comprise an electrode core 6 which can be overprinted with any electrically conductive material, such as but not limited to silver-, copper- or carbon-ink. The electrode core 6 can be made of any electrically conductive material, such as for a non-limiting example silver-, copper- or carbon-ink as long as it differentiates from the overprinted conductive layer. In one example, the electrode core 6 can be made of silver which is coated by carbon to produce one of the plurality of counter-electrodes 5.

[0058] Figures 6A and 6B illustrate the printed sensor 100 when pressure P is not applied. In a first embodiment, the first substrate 1 and the second substrate 2 are spaced from each other such that the plurality of counter-electrodes 5 and the connection electrodes 4 do not contact. In this embodiment, there is no short-circuit between the plurality of counterelectrodes 5 and the connection electrodes 4 as long as no pressure P is applied. In another embodiment, the first substrate 1 and the second substrate 2 are spaced from each other such that the plurality of counter-electrodes 5 and the connection electrodes 4 contact each other. In this embodiment, short-circuits appear between the plurality of counter-electrodes 5 and the connection electrodes 4 which can be zero-calibrated in order to detect a later applied pressure P.

[0059] As illustrated in Fig. 6B the printed sensor 100 is shown as a resistance diagram. A resistance R4 represent a single connection electrode 4. A plurality of counter-resistances R5 represent the plurality of counter-electrodes 5, wherein every single counter-resistance R5 represents one of the counter-electrodes 5. When no pressure P is applied to the printed sensor 100, the total unit electrical resistance Ru measured between the first and second electrodes 3a, 3b is equal to the resistance R4.

[0060] Figures 7A and 7B illustrate a region of the printed sensor 100 where pressure P is applied. At this region as well as at any other region of the printed sensor 100 where pressure P is applied, the plurality of counter-electrodes 5 and the connection electrodes 4 contact each other generating a plurality of local short-circuits therebetween which are illustrated as electric circuits S in Fig. 7B.

[0061] As illustrated in Fig. 7B the printed sensor 100 is shown as a resistance diagram wherein three counter-electrodes 5 contact the connection electrode 4 resulting in three electric circuits S. The initial resistance R4 (as shown in Fig. 6B) is divided into at least one first section-resistances R4* between every electric circuit S and a second section-resistance R**. Each of the electric circuits S comprise one counter-resistance R5 of one counterelectrode 5, one contact resistance RK and the second section-resistance R4**. The value of the contact resistance RK changes with the strength/amount of the applied pressure P and has a direct influence on the total unit electrical resistance Ru which is thus changed. When pressure P is applied to the printed sensor 100, the total unit electrical resistance Ru measured between the first and second electrodes 3a, 3b is equal to the sum of resistances of each electric circuit S and the first section-resistances R* therebetween.

[0062] The higher the pressure P more counter-electrodes 5 will contact the connection electrode 4 of the electrode unit 7 and generate electric circuits S resulting in a change of the total unit electrical resistance Ru. The total unit electrical resistance Ru is consequently directly proportional to the applied pressure P. A measurement of a change in total unit electrical resistance Ru is thus indicative of the pressure P applied to the printed sensor 100. [0063] Fig. 8 shows a schematic top-view of the first region of the printed sensor 100 wherein the first substrate 1 is positioned against the second substrate 2. The plurality of counter-electrodes 5 is printed and/or distributed periodically on the second substrate 2. The electrode unit 7 is contacted by the plurality of counter-electrodes 5. The design of the printed sensor 100, where at least one counter-electrode 5 contacts the connection electrode 4 of the electrode unit 7 allows that a positioning SI 03 of the second substrate 2 can be performed without alignment on the first substrate 1 when the printed sensor 100 is manufactured.

[0064] Fig. 9 shows a schematic top-view of the second region of the printed sensor 100 wherein the first substrate 1 is positioned against the second substrate 2. The plurality of counter-electrodes 5 is printed and/or distributed periodically on the second substrate 2. The plurality of electrode units 7 is printed and/or distributed periodically on the first substrate 1. The plurality of counter-electrodes 5 is thereby distributed such that every of the plurality of electrode units 7 is contacted by at least one counter-electrode 5. This allows that the printed sensor 100 can be manufactured by printing a theoretically endless sheet of substrate

1 with the plurality of counter-electrodes 5 and printing a theoretically endless sheet of substrate 2 with the plurality of electrode units 7. After positioning SI 03 the second substrate

2 on the first substrate 1 a sensor matrix is obtained, wherein the first and second substrates 1, 2 do not need to be aligned to each other. In an example, a plurality of single printed sensors 100 can be cut out of the sensor matrix, wherein every single printed sensor 100 may comprise an individual amount of electrode units 7. In another example, the first substrate 1 with the plurality of electrode units 7 and the second substrate 2 with the plurality of counterelectrodes 5 can be manufactured separately and stored for a later use, wherein the desired size can be obtained individually. [0065] As illustrated in Figs. 10A and 10B, the same measurement protocol for hysteresis and drift was applied to the printed sensor 100 as was used for the previously described thru- mode and shunt-mode sensors.

[0066] Fig. 10A illustrates the hysteresis of the printed sensor 100, where the sensor 100 was measured from 0 N/cm2 to 500 N/cm2 and back to 0 N/cm2. In Fig. 10A the hysteresis is summarised for the pressures 1 N/cm2, 10 N/cm2 and 100 N/cm2. The hysteresis illustrated in Fig. 10A was calculated by determining the standard deviation and the mean value of the resistance in the up and down passage at the respective pressure. The hysteresis is presented in table 4 as the ratio of standard deviation to mean value, expressed as a percentage of the mean value:

Table 4: Hysteresis of the printed sensor 100

[0067] Based on the measures in table 4 and, in comparison with the measures of table 1, the printed sensor 100 exhibits a clearly better hysteresis behaviour than the sensors in thru- and shunt-mode.

[0068] Fig. 10B illustrates the drift at constant pressures of 1 N/cm2, 10 N/cm2 and 100 N/cm2 applied to the printed sensor 100. The drift illustrated in Fig. 10B is presented as percentage change between the start and end value of the resistance for different measurement periods in table 5.

Table 5: Drift of the printed sensor 100

[0069] Based on the measures in table 5 and, in comparison with the measures of table 2, the printed sensor 100 exhibits a clearly better drift than the sensors in thru- and shunt-mode. [0070] Because of the clearly better hysteresis and drift behaviour of the printed sensor 100 in comparison with the two sensors in thru- and shift-mode, also the repeatability is clearly better. The printed sensors 100 was loaded 20 times for 10 seconds at pressures 1 N/cm2, 10 N/cm2 and 100 N/cm2. The standard deviation of the cycles at the same pressure was measured and set in relation to the mean value. This ratio (repeatability) is expressed in table 6 as a percentage.

Table 6: Repeatability of the printed sensor 100

[0071] Based on the performed measures it is demonstrated that the printed sensor 100 has a clearly improved hysteresis and drift behaviour. The two common errors, hysteresis, and drift and thus the accuracy and repeatability of the printed sensor are improved in comparison to the known sensors in thru- and shunt-mode. Consequently, the printed sensor 100 results in consistent and reliable readings.

[0072] Fig. 11 illustrates a flow diagram of a method for manufacturing the printed sensor 100. Printing S101 the first substrate 1 with at least one electrode unit 7 is performed in a first step. Printing S102 the second substrate 2 with the plurality of counter-electrodes 5 is performed in a second step. Positioning S103 the second substrate 2 on the first substrate 1 is performed as third step, wherein the positioning SI 03 of the second substrate 2 is performed without alignment on the first substrate 1, and wherein the at least one electrode unit 7 faces the plurality of counter-electrodes 5.

[0073] The printing S101 of the first substrate 1 and the printing S102 of the second substrate 2 can be performed at separate times. This allows that the printed first substrate 1 and the printed second substrate 2 may be manufactured and stored separately. The printed sensor 100 can thus be formed out of the printed first substrate 1 and the printed second substrate 2 at that time, when the printed sensor 100 is needed and formed dependent on the application.

[0074] The printing S102 of the plurality of counter-electrodes 5 can be configured such that the size 51 of each one of the plurality of counter-electrodes 5 will be smaller than the distance 71 of at least two electrode units 7 at the first printing SI. Further, the printing SI 02 of the plurality of counter-electrodes 5 can be configured such that the size 51 of a single one of the plurality of counter-electrodes 5 will be smaller than a distance between the first and the second electrode 3a, 3b of one electrode unit 7. The method for manufacturing the printed sensor 100 becomes thus faster, cheaper, and flexible to the needs of consumers, wherein the manufactured printed sensor 100 comprises a high accuracy and repeatability.

[0075] Fig. 12 illustrates a flow diagram of a method for detecting the pressure P using the printed sensor 100. In a first step pressure P is applied S201 to at least one region of the printed sensor 100. The application of the pressure P causes at least one counter-electrode 5 to contact S202 with a connection electrode 4 at the at least one region. Because of the contacting S202 at least one electric circuit S is generated S203 at the at least one region. A total unit electrical resistance Ru is changed S204 because of the at least one electric circuit S. The change in total unit electrical resistance Ru is measured S205 wherein the change S204 in total unit electrical resistance Ru is indicative of the applied pressure P to the sensor 100. The change S204 of the total unit electrical resistance Ru is dependent on the number of electric circuits S and an amount of first section-resistances R4*. The change S204 of the total unit electrical resistance Ru is thus dependent on the number of counter-resistances R5, contact resistances RK and second section-resistance R4** comprised in each electric circuit S, and the amount of first section-resistances R4* (see Fig. 7B). Measuring S205 the changing S204 of the total unit electrical resistance Ru is thus indicative of the pressure P applied to the printed sensor 100. With the printed sensor 100 the applied pressure P can be detected with high accuracy and repeatability.

Reference numerals

100 printed sensor

1 first substrate

2 second substrate

3a first electrode

3b second electrode

4 connection electrode

5 counter-electrode

51 size

6 electrode core

7 electrode unit

71 distance

P pressure

R4 resistance

R4* first section-resistance

R4** second section-resistance

R5 counter-resistance

RK contact resistance

Ru total unit electrical resistance

S electric circuits

Claims

1. A printed sensor (100) compri sing : a first substrate (1) comprising at least one electrode unit (7); a second substrate (2) opposite to the first substrate (1), the second substrate (2) comprising a plurality of counter-electrodes (5), wherein said electrode unit (7) comprises a connection electrode (4), a first electrode (3a) and a second electrode (3b), and said connection electrode (4) extends between said first electrode (3a) and said second electrode (3b), and wherein the plurality of counter-electrodes (5) is distributed on the second substrate (2) and wherein more than one of the plurality of counter-electrodes (5) faces the opposite connection electrode (4).

2. The sensor (100) according to claim 1, wherein a distance (71) between two adjacent electrode units (7) is greater than a size (51) of a single one of the plurality of counter-electrodes (5).

3. The sensor (100) according to claim 1 or 2, wherein a size (51) of a single one of the plurality of counter-electrodes (5) is smaller than a distance between the first and the second electrode (3a, 3b).

4. The sensor (100) according to one of claims 1 to 3, wherein the plurality of counter-electrodes (5) is periodically distributed on the second substrate (2).

5. The sensor (100) according to one of claims 1 to 4, wherein the counter-electrode (5) comprises an electrode core (6) made of a different material than the counter-electrode (5).

6. A method for manufacturing a printed sensor (100) having a first substrate (1) and a second substrate (2) opposite to the first substrate (1), the method comprising: a. Printing (S 101) the first substrate (1) with at least one electrode unit (7); b. Printing (S102) the second substrate (2) with a plurality of counterelectrodes (5); c. Positioning (S103) the second substrate (2) on the first substrate (1), wherein the positioning (SI 03) of the second substrate (2) is performed without alignment on the first substrate (1), and wherein the at least one electrode unit (7) faces more than one of the plurality of counter-electrodes (5).

7. The method according to claim 6, wherein the printing (SI 02) of the plurality of counter-electrodes (5) is configured such that the size (51) of each one of the plurality of counter-electrodes (5) is smaller than a distance (71) of at least two electrode units (7) at the first printing (SI).

8. The method according to one of the claims 6 or 7, wherein the printing (SI 02) of the plurality of counter-electrodes (5) is configured such that the size (51) of a single one of the plurality of counter-electrodes (5) is smaller than a distance between the first and the second electrode (3a, 3b).

9. A method for detecting a pressure (P) using a printed sensor (100) according to claims 1 to 5, the method comprising: a. Applying (S201) pressure (P) to at least one region of the sensor (100); b. Contacting (S202) at least one counter-electrode (5) with a connection electrode (4) of the printed sensor (100) at the at least one region; c. Generating (S203) at least one electronic circuit (S) at the at least one region; d. Changing (S204) a total unit electrical resistance (Ru) of the sensor (100) between a first electrode (3a) and a second electrode (3b) in accordance of the pressure (P); e. Measuring (S205) the change in total unit electrical resistance (Ru) indicative of the applied pressure (P) to the sensor (100); wherein each of the at least one electric circuits (S) comprise a counter-resistance (R5) of the counter-electrode (5), a contact resistance (RK) and a second sectionresistance (R4**).

10. The method according to claim 9, wherein the changing (S204) of the total unit electrical resistance (Ru) is dependent on the number of electric circuits (S) and an amount of first section-resistances (R4*).