JP2013137231A - Vibration sensor system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration sensor system in which a synchronous detection reference signal is easily obtained, the effects of a disturbing wave is reduced, and the occurrence of malfunction is prevented.SOLUTION: An interrogator 1 generates an electrical signal having frequency higher than the resonance frequency of a vibration sensor 2 as a modulation signal, modulates an electrical signal of resonance frequency of a surface elastic wave resonator with a modulation signal to acquire a carrier wave 5, converts a reflection wave 6 to frequency of the modulation signal, and performs narrow-band limitation to acquire a synchronous detection signal, and uses the synchronous detection signal for synchronous detection.

Description

  The present invention relates to a vibration sensor system that detects a vibration phenomenon of an object.

  Conventionally, vibration sensors have been used for seismic diagnosis of buildings, glass breakage detection devices for crime prevention security, and abnormal vibration detection of equipment and machine tools.

  Patent Document 1 discloses a conventional vibration sensor and interrogator. In Patent Document 1, a vibration sensor system is constructed by using a batteryless vibration sensor having a single-port surface acoustic wave resonator and an interrogator. Further, since the signal processing for vibration detection is executed on the interrogator side, it is not necessary to provide a signal processing unit in the vibration sensor, and the vibration sensor can be downsized.

Japanese Patent Laid-Open No. 2007-232708

  In Patent Document 1, a carrier wave is transmitted from an interrogator to a vibration sensor, a reflected wave from the vibration sensor is monitored, and based on a change in the reflected wave due to mechanical vibration of the vibration sensor accompanying the vibration of the object, It is configured to detect the vibration of an object. That is, when vibration occurs, a reflected wave modulated by the resonance frequency of the vibration sensor is transmitted from the vibration sensor.

  However, if an interference wave with a frequency approximate to the reflected wave modulated by the resonance frequency of the vibration sensor is input to the interrogator, the vibration signal due to the vibration of the object cannot be distinguished from the interference wave, causing a malfunction. There is a possibility.

  On the other hand, a synchronous detection method has been conventionally used in order to detect a response (vibration) of an object without being affected by an external interference wave. For synchronous detection, an input signal to be input to the synchronous detection circuit and a reference signal having the same frequency and phase as those of the input signal are required. However, when this synchronous detection method is applied to a vibration sensor system that communicates wirelessly and used in a high frequency band, the phase of the input signal (carrier wave) is short and the phase is likely to change. Has a problem that a special circuit is required.

  Therefore, an object of the present invention is to provide a vibration sensor system in which a reference signal for synchronous detection can be easily obtained, the influence of an interference wave is reduced, and the occurrence of malfunction is suppressed.

  According to the present invention, the surface acoustic wave resonator includes a vibration sensor attached to an object, and a carrier wave is transmitted to the vibration sensor, while a reflected wave from the surface acoustic wave resonator is monitored, A vibration sensor system comprising: an interrogator that detects the vibration phenomenon based on a change that occurs in the reflected wave according to a mechanical vibration applied to the vibration sensor in accordance with a vibration phenomenon of an object, the interrogator Generates an electric signal having a frequency higher than the resonance frequency of the vibration sensor as a modulation signal, and modulates the electric signal of the resonance frequency of the surface acoustic wave resonator with the modulation signal to obtain the carrier wave, A vibration sensor system is obtained, wherein a reflected wave is converted into a frequency of the modulation signal, a narrow band is limited to obtain a synchronous detection signal, and synchronous detection is performed using the synchronous detection signal. That.

  In the vibration sensor system of the present invention, it is preferable that the modulation signal has a frequency that is 10 times or more the resonance frequency of the vibration sensor.

  The vibration sensor and the interrogator preferably each include an antenna.

  In addition, the surface acoustic wave resonator may include a piezoelectric substrate and a comb electrode formed on the piezoelectric substrate.

  In the present invention, the carrier wave transmitted to the vibration sensor is modulated with a modulation signal having a frequency higher than the resonance frequency of the vibration sensor, and the reflected wave from the surface acoustic wave resonator is converted into the modulation signal frequency (down-converted). By performing narrow band limitation, an input signal for synchronous detection is obtained, and a reference signal for synchronous detection whose frequency and phase coincide with each other can be easily obtained. Further, by performing synchronous detection using the synchronous detection signal composed of the input signal and the reference signal, the influence of the interference wave can be reduced.

  That is, according to the present invention, it is possible to provide a vibration sensor system that can easily obtain a reference signal for synchronous detection, reduce the influence of an interference wave, and suppress the occurrence of malfunction.

The block diagram of the interrogator which concerns on embodiment of this invention. Schematic which shows the structure of the vibration sensor system of this invention. 1 is a schematic perspective view of a vibration sensor according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 2 is a schematic diagram showing the configuration of the vibration sensor system of the present invention. As shown in FIG. 2, the vibration sensor system of the present invention includes an interrogator 1 and a vibration sensor 2. The interrogator 1 and the vibration sensor 2 are provided with an antenna 3 and an antenna 4, respectively. The vibration sensor 2 is attached to an object for detecting vibration and is configured without a battery. While transmitting the carrier wave 5 from the interrogator 1 to the surface acoustic wave resonator provided in the vibration sensor 2, the reflected wave 6 from the vibration sensor 2 is monitored to detect the vibration of the object. In the present embodiment, a vibration sensor for detecting a mechanical vibration phenomenon of glass is used as an example of a vibration sensor.

  FIG. 3 is a schematic perspective view of the vibration sensor according to the embodiment of the present invention. The vibration sensor 2 includes a surface acoustic wave resonator having a piezoelectric substrate 7 and a comb electrode 8 formed on the piezoelectric substrate 7, a support substrate 9 that supports the piezoelectric substrate 7, and a comb electrode 8. It consists of a connected antenna 4.

  When vibration is applied to the piezoelectric substrate 7 from the outside of the vibration sensor 2, a distortion occurs, the distance between the comb electrodes 8 changes, and the impedance of the surface acoustic wave resonator also changes simultaneously. That is, when the vibration sensor 2 detects a vibration signal from the outside, the reflected wave transmitted from the vibration sensor 2 uses the resonance frequency of the surface acoustic wave resonator having the same frequency as the carrier wave as the vibration sensor 2 (piezoelectric substrate). The signal is modulated at the resonance frequency of 7). Note that the piezoelectric substrate 7 according to the present embodiment has a vibration shape selected so that the resonance frequency belongs to a characteristic frequency band in the mechanical vibration of the target object to be detected.

  In the present embodiment, the piezoelectric substrate 7 has a cantilever shape, and a quartz ST-cut substrate having an overhang length of 2 mm, a width of 1 mm, and a thickness of 0.25 mm is used. At this time, the resonance frequency of the bending vibration mode in the thickness direction of the cantilever is approximately 60 kHz. That is, the resonance frequency of the vibration sensor of the present embodiment is 60 kHz. The interval between the comb-teeth electrodes 8 was set to 0.35 μm so that the resonance frequency of the surface acoustic wave resonator was in the 2.45 GHz band. The comb electrode 8 is disposed in the vicinity of the support portion so that the distortion of the piezoelectric substrate 7 is maximized with respect to external vibration. In addition, the antenna 4 is a 2.45 GHz band half-wave dipole antenna in accordance with the resonance frequency of the surface acoustic wave resonator. The quality factor of the piezoelectric substrate 7 was about 100. The quality factor can be adjusted to about 50 to 3000 by a fixing method with the support substrate 9 or the like.

  FIG. 1 is a block diagram of an interrogator according to an embodiment of the present invention. In the interrogator 1, an output signal of 2.45 GHz is first generated by the oscillator 11 and input to the distributor (DIV) 12. The output signal of the distributor 12 is branched into two, one being distributed to the mixer 13 as a transmission signal and the other being distributed to the mixer 17 as a local oscillation signal.

  The transmission signal is modulated with a modulation signal having a frequency of 600 kHz output from the oscillator 16 by the mixer 13, and is vibrated several m away from the antenna 3 with a desired power amount via the power amplifier (PA) 14 and the circulator 15. It is transmitted as a carrier wave 5 to the sensor 2. At this time, by modulating with a modulation signal having a frequency of 10 times or more with respect to the resonance frequency 60 kHz of the vibration sensor, a synchronous detection signal can be easily obtained at the time of synchronous detection, which will be described later. Can be detected.

  As described above, the modulation signal needs to be sufficiently higher than the resonance frequency of the vibration sensor, and preferably 10 times or more in consideration of reproducibility and practicality. Furthermore, it is preferable that the modulation signal has a frequency having a wavelength of 10 times or more with respect to the propagation distance between the interrogator and the vibration sensor. This is because the modulation signal has such a magnitude that the phase change of the carrier wave and the reflected wave can be ignored with respect to the propagation distance. In this embodiment, the propagation distance between the interrogator and the vibration sensor is assumed to be several meters, the wavelength of 600 kHz is approximately 500 m, which is 10 times or more of the propagation distance, and a modulation signal that can ignore the phase change. Yes.

  The antenna 4 of the vibration sensor 2 receives the carrier wave 5 transmitted from the antenna 3 and re-radiates the reflected wave 6 according to the impedance change of the surface acoustic wave resonator from the antenna 4. That is, the reflected wave 6 re-radiated at this time includes a signal obtained by modulating the carrier wave 5 transmitted from the antenna 3 with an external vibration signal. In the present embodiment, when external vibration is applied to the vibration sensor, the reflected wave 6 obtained by further modulating the carrier wave 5 obtained by modulating 2.45 GHz at 600 kHz is further modulated at 60 kHz which is the resonance frequency of the vibration sensor 2. can get. The reflected wave 6 is received by the antenna 3, passes through the circulator 15, is mixed with the local oscillation signal of 2.45 GHz by the mixer 17, and is converted (down-converted) into a signal having a frequency of 600 kHz band.

  The output signal of the mixer 17 is input to a band-pass filter (BPF) 18 and an amplifier circuit (AMP) 19, and is band-limited to a narrow band (600 kHz ± 60 kHz) and amplified. The output signal of the amplifier circuit 19 branches into two and is input to the mixer 20 and the mixer 21. The output signal of the amplifier circuit 19 becomes an input signal used for synchronous detection. Therefore, a synchronous detection reference signal can be easily obtained from the output signal of the oscillator 16.

  A reflected wave demodulation method using synchronous detection, that is, a vibration detection method will be described below.

  In the mixer 20, the output signal of the amplifier circuit 19 (synchronous detection input signal) and the output signal of the oscillator 16 (synchronous detection reference signal) are multiplied and down-converted to a signal having a frequency of 60 kHz band. Then, the band is limited by the band pass filter (BPF) 23, and a 60 kHz signal is obtained. Similarly, the mixer 21 multiplies the output signal of the amplification circuit 19 (synchronous detection input signal) and the signal output by the phase shift circuit 22 by 90 ° from the output signal of the oscillator 16 (synchronous detection reference signal). Processed and down-converted to a signal with a frequency in the 60 kHz band. Then, the band is limited by the band pass filter (BPF) 24, and the phase is shifted by 90 ° by the phase shift circuit 25.

  The output signal of the bandpass filter 23 and the output signal of the phase shift circuit 25 are input to the subtraction circuit 26 and the addition circuit 27, respectively. By the signal processing in the subtracting circuit 26 and the adding circuit 27, a signal obtained by separating the reflected wave 6 into a USB (upper side band) component and an LSB (lower side band wave) component is obtained. Further, the two signal components including the USB component and the LSB component are rectified into DC signals by the amplitude detection circuit 28 and the amplitude detection circuit 29, respectively, and input to the comparator 30 and the comparator 31.

  The comparator 30 and the comparator 31 set a desired threshold value in advance, and are turned on when vibration is detected by the vibration sensor 2. Further, the output signals of the comparator 30 and the comparator 31 are input to the AND circuit 32. Only when the output signals of the comparator 30 and the comparator 31 are simultaneously turned ON, the output signal of the AND circuit 32 is turned ON to notify the user that the vibration sensor 2 has detected vibration.

  By performing signal processing in this way, when an interference wave is mixed into the LSB band or the USB band, only the comparator corresponding to one of them is turned on, and the AND circuit 32 is turned off, so that no false alarm is generated. Therefore, the influence of the interference wave can be reduced and the occurrence of malfunction can be suppressed.

  In this embodiment, a carrier wave to be transmitted to the vibration sensor is modulated with a modulation signal having a frequency 10 times or more the resonance frequency of the vibration sensor, and the reflected wave from the surface acoustic wave resonator is down-converted to the frequency of the modulation signal. By obtaining the synchronous detection signal by limiting the band, the influence of the interference wave can be reduced.

  That is, according to the present invention, it is possible to provide a vibration sensor system that can easily obtain a reference signal for synchronous detection, reduce the influence of an interference wave, and suppress the occurrence of malfunction.

DESCRIPTION OF SYMBOLS 1 Interrogator 2 Vibration sensor 3, 4 Antenna 5 Carrier wave 6 Reflected wave 7 Piezoelectric substrate 8 Comb electrode 9 Support substrate 11, 16 Oscillator 12 Distributor 13, 17, 20, 21 Mixer 14 Power amplifier 15 Circulator 18, 23, 24 Band-pass filter 19 Amplifier circuit 22, 25 Phase shift circuit 26 Subtractor circuit 27 Adder circuit 28, 29 Amplitude detector circuit 30, 31 Comparator 32 AND circuit

Claims (4)

A vibration sensor including a surface acoustic wave resonator and attached to an object;
While transmitting a carrier wave to the vibration sensor, the reflected wave from the surface acoustic wave resonator is monitored, and the reflected wave according to the mechanical vibration applied to the vibration sensor in accordance with the vibration phenomenon of the object. A vibration sensor system comprising an interrogator for detecting the vibration phenomenon based on a change occurring in
The interrogator is
Generating an electrical signal having a frequency higher than the resonance frequency of the vibration sensor as a modulation signal;
An electric signal having a resonance frequency of the surface acoustic wave resonator is modulated with the modulation signal to obtain the carrier wave,
The reflected wave is converted to the frequency of the modulation signal, and a synchronous detection signal is obtained by narrow-band limiting,
A vibration sensor system that performs synchronous detection using the synchronous detection signal.   The vibration sensor system according to claim 1, wherein the modulation signal has a frequency that is 10 times or more the resonance frequency of the vibration sensor.   The vibration sensor system according to claim 1, wherein each of the vibration sensor and the interrogator includes an antenna.   4. The vibration sensor according to claim 1, wherein the surface acoustic wave resonator includes a piezoelectric substrate and a comb electrode formed on the piezoelectric substrate. 5. system.

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