JP2008175678A - Dynamic quantity sensor system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic quantity sensor system capable of discrimination of existence of a sensor or an individual body, normal operation diagnosis, compensation to a temperature change, and management of a plurality of sensors, concerning a dynamic quantity sensor system requiring continuous sensing. <P>SOLUTION: A sensor element 101 comprising a surface elastic wave resonator having an interdigital electrode and a reflector formed on a piezoelectric substrate, and a vibration sensor 102 comprising an antenna 120 are installed on a measuring object in a measuring domain, and an interrogator 103 for transmitting by radio a carrier wave signal to the vibration sensor 102 and monitoring a reflected wave from the vibration sensor 102 is installed. The interrogator 103 comprises a reference signal generation part 104 for generating a signal having a carrier wave frequency used as a reference, a frequency modulation part 105 for generating a signal whose frequency is changed continuously and periodically around the reference frequency of the carrier wave signal, an antenna 108, a signal receiving part 109, a signal processing part 110, and a determination output part 111. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mechanical quantity sensor system using a passive mechanical quantity sensor capable of wireless communication using surface acoustic waves (SAW), and in particular, a mechanical quantity sensor capable of constantly monitoring a mechanical quantity sensor that needs to be continuously monitored. About the system.

  Many sensors use the fact that the resonance frequency of surface acoustic wave resonators obtained by forming comb electrodes and reflectors on a piezoelectric substrate changes depending on external mechanical quantities such as temperature, pressure, acceleration, and vibration. It has been developed and is disclosed in Patent Document 1 and the like.

  Patent Document 2 discloses an apparatus in which an antenna is installed on the sensor element and the sensor can be driven and sensing results can be received by supplying energy from a wireless radio wave from the outside. In this apparatus, the reflector installation position is changed for each sensor element, and the sensor element is identified from the delay time.

  Patent Document 3 shows a car tire pressure sensor as a specific application, which is configured to measure and output a difference from a standard pressure cavity, and further configured to generate an individual reflection identification pulse train. The sensor element can be identified.

  However, the sensor elements of Patent Documents 2 and 3 above are called acoustic emission (AE) waves, and are intended to capture vibrations caused by cracks in structures at a frequency higher than the audible range and a very short duration. As a sensor, sufficient performance cannot be obtained.

  Therefore, the inventors of the present application invented a vibration detection system aiming at a sensor that is small in size and sufficiently sensitive to AE waves, and filed a patent application (Japanese Patent Application No. 2006-197678).

  The configuration of the vibration detection system of this earlier application is shown in FIG. 6, the cross-sectional structure of the sensor element used in this system is shown in FIG. 7, the comb-tooth electrode of the SAW resonator formed on the piezoelectric substrate in the sensor element, and The arrangement of the reflectors is shown in FIG.

  As shown in FIG. 6, the vibration detection system includes a vibration sensor 100 including an antenna 10 and a sensor element 20, and an interrogator 200 that drives the vibration sensor 100 with a radio wave and receives a sensing result. The vibration sensor 100 is a passive mechanical quantity sensor that can be miniaturized by applying RFID (Radio Frequency Identification) technology.

  As shown in FIG. 7, the SAW resonator 30 in the sensor element 20 includes a plate-like piezoelectric substrate 32, comb-shaped electrodes 34 formed on the piezoelectric substrate 32, and both sides of the SAW propagation direction. Reflectors 37 and 38 provided close to each other, and one end of the piezoelectric substrate 32 is supported by the support substrate 22 so as to be able to vibrate within a housing composed of the support substrate 22 and the lid member 23. Yes. That is, as shown in FIG. 7, the piezoelectric substrate 32 of the SAW resonator 30 is supported in a cantilever shape by the support substrate 22, and the comb electrode 34 is located near the base of the support portion. Therefore, the vibration of the vibration part of the piezoelectric substrate 32 can be efficiently concentrated near the comb electrode 34.

  The connecting portions 35 and 36 (FIG. 8) drawn from the comb-teeth electrode 34 of the SAW resonator 30 are connected to a pattern (not shown) on the support substrate 22 via the solder bumps 25 and 26, and further the support substrate. 22 is connected to the terminal 27 through a via hole (not shown) formed in the inside. The terminal 27 is connected to the antenna unit.

  The received wave received by the antenna 10 is supplied to the comb electrode 34 inside the sensor element 20 through the electrical path described above. Since the antenna 10 and the comb electrode 34 are impedance matched including the path between them, all received waves received by the antenna 10 are supplied to the comb electrode 34. Here, the reflectors 37 and 38 constitute reception wave confining means for confining the reception wave received via the antenna unit 10 in the comb electrode 34 and in the vicinity of the comb electrode 34. The reflectors 37 and 38 are for increasing energy efficiency, and when there is a margin in the intensity of the reflected wave, either one or both can be omitted.

  When the frequency of the received radio wave coincides with the resonance frequency of the SAW resonator, energy is confined in the SAW resonator 30 so that the reflected wave is reflected and returns to the antenna 10 again, but the frequency is shifted. The reflected intensity increases accordingly and the light is reflected and reflected from the antenna unit 10 to the outside of the vibration sensor 100 as a reflected wave. When vibration is applied to the piezoelectric substrate 32, the resonance frequency of the SAW resonator 30 changes, so that a side lobe corresponding to the vibration frequency is generated in the reflected wave, and the side lobe in the reflected wave is detected by the interrogator 200. By detecting, vibration is detected.

  The piezoelectric substrate 32 has a vibrator shape selected so that the resonance frequency belongs to a characteristic frequency band in the mechanical vibration of the target object to be detected. For example, in the case of the piezoelectric substrate 32 having a certain thickness, the length of the vibrating portion of the cantilever is selected to an appropriate value, and the resonance frequency of the piezoelectric substrate 32 is set to the “characteristic frequency band”. Can be adapted to Thereby, the vibration of the detection target is amplified by the piezoelectric substrate 32 and continued. For example, in the case of application to vibration detection associated with the glass breaking phenomenon, the vibration itself accompanying the glass breaking phenomenon lasts only for about 2 ms, whereas in a frequency band characteristic of the vibration accompanying glass breaking. By combining the frequency that belongs to the resonance frequency in the piezoelectric substrate 32, the vibration of the piezoelectric substrate 32 can be sustained for longer than 2 ms even after the vibration associated with the glass breakage itself stops. The accuracy of vibration detection is improved.

  Furthermore, if a plurality of vibration sensors 100 are used and the resonance frequencies of the SAW resonators 30 of the vibration sensors 100 are different from each other, the vibration sensors can be identified individually. That is, when the vibration detection determination process is performed by the interrogator 200, it is possible to identify which vibration sensor 100 has detected the vibration based on the difference in frequency characteristics.

JP-A-8-166302 JP-A-9-147284 JP 2005-55444 A

  As described above, the vibration detection system of the previous application has an excellent function, but also has the following problems.

  As described above, when the sensor is used as a sensor that detects vibrations caused by cracks in the structure, the waves need to detect vibrations having a very short duration. Therefore, since monitoring may occur frequently if monitoring is performed at regular intervals, monitoring is performed using continuous waves. However, as described above, the detection system of the previous application transmits a continuous wave of a constant frequency and detects the side lobe of the reflected wave when the vibration of the detection target occurs, so when the vibration does not occur The presence / absence of the sensor, sensor identification, and failure diagnosis cannot be performed. In addition, the resonance frequency of a mechanical quantity sensor using SAW generally varies depending on temperature. As a compensation method, a method of correcting the carrier wave frequency by measuring the temperature with a temperature sensor placed near the sensor element is performed, but the sensor becomes complicated. In addition, when transmitting a plurality of continuous waves for sensor identification, there is a problem that reflected waves interfere with each other.

  The present invention has been made to solve the above-described problems, and its technical problem is that in a mechanical quantity sensor system that requires continuous sensing, the presence / absence of the sensor, individual identification, normal operation diagnosis, and temperature change It is an object of the present invention to provide a mechanical quantity sensor system that enables compensation and management of a plurality of sensors.

  In order to solve the above-described problems, a mechanical quantity sensor system of the present invention includes at least one surface acoustic wave resonator having a comb-shaped electrode formed on a piezoelectric substrate and an antenna, and is installed on an object to be measured in a measurement region. In a mechanical quantity sensor system comprising two passive mechanical quantity sensors and an interrogator that wirelessly transmits a carrier wave signal to the passive mechanical quantity sensor and monitors a reflected wave from the sensor, the carrier signal has a reference frequency. The interrogator detects the information of the passive mechanical quantity sensor from the reflected wave. The interrogator detects the information of the passive mechanical quantity sensor from the reflected wave.

  Here, the information of the passive mechanical quantity sensor includes the presence or absence of the passive mechanical quantity sensor in the measurement region, the presence or absence of failure of the passive mechanical quantity sensor, or the resonance frequency of the surface acoustic wave resonator. Alternatively, one or more pieces of information may be included among a temperature change of the surface acoustic wave resonator or a load applied to the surface acoustic wave resonator.

  Further, a plurality of passive mechanical quantity sensors may be provided, and information of the plurality of passive mechanical quantity sensors may be separately classified and detected.

  As described above, in the present invention, the reflection characteristic of the sensor within a wide frequency range is obtained by making the carrier signal from the interrogator a signal whose frequency is changed continuously and periodically around the reference frequency. By receiving and analyzing the output signal according to the interrogator, the state of the sensor can be constantly monitored regardless of the presence or absence of a mechanical quantity applied to the sensor that is the detection target. That is, it is possible to constantly monitor information such as whether the sensor is present in the area covered by the interrogator, whether it is operating normally, and the resonance frequency of the sensor. In addition, when the resonance frequency of the sensor changes depending on the temperature and load, the temperature and load can be constantly monitored. Even when there are a plurality of sensors, individual identification of the sensors is possible from the frequency characteristics of the reflected waves.

  As described above, according to the present invention, in a mechanical quantity sensor that requires continuous sensing, the presence / absence of the sensor, individual identification, normal operation diagnosis, compensation for temperature change, and management of a plurality of sensors can be performed. A quantity sensor system is obtained.

  Embodiments of a mechanical quantity sensor system according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of a vibration detection system which is a first embodiment of a mechanical quantity sensor system according to the present invention. In FIG. 1, a sensor element 101 including a surface acoustic wave resonator having a comb-like electrode formed on a piezoelectric substrate similar to the SAW resonator 30 of FIG. An interrogator 103 that is installed on the object to be measured and that monitors a reflected wave from the vibration sensor 102 by wirelessly transmitting a carrier wave signal to the vibration sensor 102 is installed. The interrogator 103 includes a reference signal generation unit 104 that generates a signal having a reference carrier frequency, a frequency modulation unit 105 that generates a signal whose frequency is continuously and periodically changed around the reference frequency of the carrier signal, A transmission output unit 106 that amplifies and outputs the signal, a circulator 107 that separates transmission and reception signals, an antenna 108, a signal reception unit 109 that receives a signal detected by the antenna 108, a signal processing unit 110 that processes the reception signal, A determination output unit 111 that determines vibration detection from the processing result and outputs the result.

  FIG. 2 is a diagram illustrating an example of a signal whose frequency is continuously and periodically changed around the reference frequency transmitted from the interrogator 103, where the horizontal axis represents time and the vertical axis represents frequency. 2 (a) shows an example in which the frequency is changed trigonometrically, and FIG. 2 (b) shows an example in which the frequency is changed in a sawtooth manner. In this case, the center frequency is 2450 MHz close to the resonance frequency of the SAW resonator, the frequency change width Δf is ± several MHz, and the temporal repetition period is about several KHz or more because the oscillation time to be observed is about 2 ms. Is possible.

  FIG. 3A schematically shows a time waveform of a carrier signal transmitted from the antenna 108 of the interrogator 103 (FIG. 1) and a reflected signal reflected from the vibration sensor 102 and transmitted from the antenna 120 in this embodiment. FIG. 3B is a diagram showing the reflection output characteristics of the vibration sensor 102. In FIG. 3A, a carrier wave signal 11 transmitted from the interrogator 103 is a signal obtained when the frequency f1 is changed from the frequency f1 to the frequency f3. As shown in FIG. 3 (b), the power output as a wave is minimized at the frequency f2, which is the resonance frequency, and therefore, the amplitude of the frequency f2 component is minimized as in the reflected signal 13 of FIG. 3 (a). Become. By receiving and analyzing such a reflected wave signal by the interrogator 103, even when the vibration sensor 102 is in a resonance state, the reflected output is small, and there is no vibration of the vibration sensor 102 and no side lobe is generated. It becomes possible to always monitor the response from the vibration sensor 102.

  This monitoring makes it possible to determine whether or not there is a vibration sensor in the space that can be monitored by the interrogator 103. Further, it can be determined whether or not the vibration sensor has failed by comparing the record of the state in which the vibration sensor is operating normally and the received signal of the vibration sensor when monitored. An alarm can also be issued when a signal other than a vibration sensor is intentionally received.

  When the resonance frequency of the vibration sensor changes with temperature, the change in resonance frequency can be converted into temperature by measuring the resonance frequency at each temperature in advance. Even when a load is applied to a piezoelectric substrate or the like, the load can be similarly detected by grasping the relationship between the load and the resonance frequency in advance.

  In order to confirm the effect of this example, the vibration detection system of FIG. 1 was actually configured and vibration detection was performed. As the sensor element 101, an aluminum tooth electrode and a reflector were formed on a lithium tantalate single crystal substrate to form a SAW resonator. When the reflection output characteristic was measured, the resonance frequency was around 2450 MHz. The single crystal substrate was processed into a shape that detects vibration of 50 kHz, and the vibration sensor 102 was configured by attaching an antenna. The vibration sensor 102 was attached to a 50 kHz vibrator. The interrogator 103 generates and transmits a signal such as the carrier signal 11 in FIG. 3 in which the frequency is continuously and periodically changed by applying a 1 MHz FM modulation signal to the 2450 MHz reference carrier signal, and the vibration sensor 102. The received signal from was measured with a spectrum analyzer. As a waveform of the received signal when there was no vibration, a modulated waveform like the reflected signal 13 in FIG. 3 was confirmed. The frequency spectrum of the carrier signal from the interrogator 103 was symmetric about the center frequency of 2450 Hz, whereas the frequency spectrum of the received signal from the vibration sensor 102 was asymmetrical. This is because the actual resonance frequency of the SAW resonator is slightly deviated from 2450 MHz.

  Next, when the vibration sensor 102 was vibrated at 50 kHz, a 50 kHz modulation signal due to vibration could be confirmed in the received signal, and a 50 kHz side lobe could also be confirmed in the frequency spectrum. It was also confirmed that the 50 kHz signal could not be obtained when the wiring in the vibration sensor 102 was cut or when the vibration sensor 102 was removed.

  Next, the change in the resonance frequency of the sensor element 101 due to temperature was measured. When the temperature characteristics of the sensor element 101 from −20 ° C. to 80 ° C. were measured in advance, the resonance frequency decreased linearly with respect to the temperature, and was −35 ppm / ° C. A temperature sensor was attached to a temperature measurement object at room temperature, an FM modulation signal of 10 MHz was applied to a reference carrier signal of 2450 MHz from the interrogator and continuously transmitted, and an output signal from the sensor was taken into a spectrum analyzer. Next, when the sensor element 101 was heated to 65 ° C., a change in the resonance frequency from the frequency characteristic of the received signal to 2447 MHz was confirmed, and the corresponding temperature could be measured.

  FIG. 4 is a configuration diagram of a vibration detection system which is a second embodiment of the mechanical quantity sensor system according to the present invention. The basic configuration of this embodiment is the same as that of the first embodiment shown in FIG. 1 except that the two vibration sensors 201 and 202 are provided.

  FIG. 5A is a diagram schematically showing a time waveform of a carrier signal transmitted from the antenna 108 of the interrogator 103 and a reflected signal reflected from the vibration sensors 201 and 202 and transmitted from the antenna in this embodiment. FIG. 5B is a diagram showing the reflection output characteristics of the vibration sensors 201 and 202. In FIG. 5A, the carrier signal 131 transmitted from the interrogator 103 is a signal when changed from the frequency f1 to the frequency f3. The reflected output characteristic 135 of the vibration sensor 201 is minimized at the resonance frequency f3 as shown in FIG. 5B, so that the reflected wave from the vibration sensor 201 is like a reflected signal 133 in FIG. 5A. The amplitude of the f3 component is minimized. On the other hand, the reflected output characteristic 136 of the vibration sensor 202 is minimized at the resonance frequency f2 as shown in FIG. 5B, and therefore the reflected wave from the vibration sensor 202 is reflected by the reflected signal 134 in FIG. As shown, the amplitude of the f2 component is minimized.

  The signal received by the interrogator 3 is a composite wave of the reflected signals 133 and 134, and the frequency spectrum thereof is an envelope shape in which the reflected output characteristics 135 and 136 of FIG. By analyzing the frequency of the received signal in this way, the resonance frequency of the vibration sensor in the reception range can be detected, and a plurality of sensors can be identified by the difference in the resonance frequency. When a vibration is applied to each vibration sensor, a side lobe corresponding to the vibration frequency is generated at the resonance vibration frequency, so that it can be detected in which vibration sensor the vibration is generated.

  Similarly to the first embodiment, the temperature, load, presence / absence of failure, etc. can be detected from the change in the resonance frequency of each vibration sensor.

  In order to confirm the effect of this example, the vibration detection system of FIG. 4 was actually configured and vibration detection was performed. As the sensor elements 203 and 204, aluminum tooth electrodes and reflectors were formed on a lithium tantalate single crystal substrate to prepare two types of SAW resonators. When the reflection output characteristics were measured, the respective resonance frequencies were 2450 MHz and 2451 MHz. Both the single crystal substrates were processed into a shape for detecting vibration of 50 kHz, and an antenna was attached to constitute vibration sensors 201 and 202, which were attached to a 50 kHz vibrator.

  The interrogator 103 generates and transmits a signal such as the carrier signal 131 of FIG. 5 in which the frequency is continuously and periodically changed by applying a 2 MHz FM modulation signal to the 2450 MHz reference carrier signal, and the vibration sensor 201. And the received signal from 202 was measured with the spectrum analyzer. Two resonance frequencies corresponding to the above two vibration sensors can be measured as shown in FIG. 5B, and when a vibration is applied to each vibration sensor at 50 KHz, a side lobe of 50 kHz is generated at each resonance frequency. I was able to confirm.

  Next, a load sensor system which is a third embodiment of the mechanical quantity sensor system according to the present invention will be described. The interrogator of this embodiment is the same as that of Embodiment 1, but the structure of the sensor element used for the sensor is different. In this embodiment, the piezoelectric substrate on which the SAW resonator is installed has a diaphragm structure so that a load is applied uniformly. An antenna was attached to this sensor element to produce a load sensor. The resonance frequency of the SAW resonator is 2450 MHz. When the resonance frequency change due to the load of this sensor was measured in advance, the resonance frequency decreased linearly with respect to the load and was −50 ppm / kgf. A load sensor was attached to a measurement object at room temperature, and an FM modulation signal of 10 MHz was applied to a carrier wave signal of 2450 MHz from the interrogator and continuously transmitted, and an output signal from the sensor was taken into a spectrum analyzer. A reception signal due to resonance at 2450 MHz was obtained. Next, when a load of 10 kgf was applied to the measurement object, the resonance frequency of the received signal was 2449 MHz, and the detection of the load could be confirmed.

  As described above, according to the present invention, in a mechanical quantity sensor system such as a vibration sensor or a load sensor that requires continuous sensing, the presence / absence of the sensor, individual identification, normal operation diagnosis, compensation for temperature change, multiple A mechanical quantity sensor system capable of managing the sensors can be obtained.

  Needless to say, the present invention is not limited to the above-described embodiments. For example, the detection target may be any object that affects the characteristics of the sensor element due to the surface acoustic wave, such as acceleration and impact. It is also possible to detect the mechanical quantity. The resonance frequency of the SAW resonator, the frequency modulation width of the carrier signal from the interrogator, and the like can be designed according to the purpose.

The block diagram of the vibration detection system which is a 1st Example of the mechanical quantity sensor system of this invention. It is a figure which shows the example of the signal which changed the frequency continuously and periodically centering | focusing on the reference | standard frequency transmitted from an interrogator, Fig.2 (a) is a figure when a frequency is changed trigonometrically. FIG. 2B is a diagram illustrating an example in which the frequency is changed in a sawtooth manner. The figure explaining operation | movement of the vibration detection system of Example 1 of this invention. FIG. 3A is a diagram schematically illustrating a time waveform of a carrier wave signal transmitted from an interrogator antenna and a reception signal reflected from a vibration sensor and received by the antenna in the first embodiment. FIG. 3B is a diagram illustrating the reflection output characteristics of the vibration sensor according to the first embodiment. The block diagram of the vibration detection system which is the 2nd Example of the mechanical quantity sensor system of this invention. The figure explaining operation | movement of the vibration detection system of Example 2 of this invention. FIG. 5A is a diagram schematically illustrating a time waveform of a carrier signal transmitted from the antenna of the interrogator and a received signal reflected from the vibration sensor and received by the antenna in the second embodiment. FIG. 5B is a diagram illustrating the reflection output characteristics of the vibration sensor according to the second embodiment. The figure which shows the structure of the vibration detection system of a previous application. The figure which shows the cross-section of a sensor element. The arrangement figure of the comb-tooth electrode and reflector of a SAW resonator.

Explanation of symbols

10, 108, 120 Antenna 11, 131 Carrier signal 13, 133, 134 Reflected signal 20, 101, 203, 204 Sensor element 22 Support substrate 23 Cover member 25, 26 Solder bump 27 Terminal 30 SAW resonator 32 Piezoelectric substrate 34 Comb Tooth electrode 35, 36 Connection unit 37, 38 Reflector 100, 102, 201, 202 Vibration sensor 104 Reference signal generation unit 105 Frequency modulation unit 106 Transmission output unit 107 Circulator 109 Signal reception unit 110 Signal processing unit 111 Determination output unit 135, 136 Reflected output characteristics 200, 103 Interrogator

Claims (7)

  At least one passive mechanical quantity sensor comprising a surface acoustic wave resonator having a comb-like electrode formed on a piezoelectric substrate and an antenna, and placed on a measurement object in a measurement region, and a carrier wave is provided to the passive mechanical quantity sensor. In a mechanical quantity sensor system comprising an interrogator for wirelessly transmitting a signal and monitoring a reflected wave from the sensor, the carrier signal is a signal whose frequency is changed continuously and periodically around a reference frequency. The interrogator detects information of the passive mechanical quantity sensor from the reflected wave.   The mechanical quantity sensor system according to claim 1, wherein the information of the passive dynamic quantity sensor includes the presence or absence of the passive dynamic quantity sensor in the measurement region.   2. The mechanical quantity sensor system according to claim 1, wherein the information of the passive type mechanical quantity sensor includes the presence or absence of a failure of the passive type mechanical quantity sensor.   2. The mechanical quantity sensor system according to claim 1, wherein the information of the passive mechanical quantity sensor includes a resonance frequency of the surface acoustic wave resonator.   The mechanical quantity sensor system according to claim 1, wherein the information of the passive mechanical quantity sensor includes a temperature change of the surface acoustic wave resonator.   2. The mechanical quantity sensor system according to claim 1, wherein the information of the passive mechanical quantity sensor includes a load applied to the surface acoustic wave resonator.   7. The apparatus according to claim 1, wherein a plurality of passive mechanical quantity sensors are provided in the measurement region, and information of the plurality of passive mechanical quantity sensors is separately classified and detected. The described mechanical quantity sensor system.

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