JP7226275B2 - Wireless measurement system for physical quantities - Google Patents

Description

The present invention relates to a wireless measurement system that uses a surface acoustic wave device to measure physical quantities such as temperature and pressure acting on an object to be sensed by wireless communication.

2. Description of the Related Art Conventionally, various sensors and measuring devices for measuring physical quantities such as temperature and pressure are provided by taking advantage of changes in the propagation characteristics of surface acoustic waves (SAWs) due to physical quantities such as temperature and pressure.
For example, the pressure sensor and pressure measuring device described in Patent Document 1 are driven from a computer as a master device via a reading device and an antenna to a pressure sensor that is a wireless parasitic sensor installed on a detection target. A signal is transmitted wirelessly, a reading device receives a response signal from the pressure sensor, and a computer detects the gas pressure (air pressure) applied to the object to be detected.

In the above-described prior art, the comb-teeth electrode in the pressure sensor receives a drive signal from a computer and excites a surface acoustic wave. As it is reflected, the comb electrodes convert the signal from the reflective electrode into a response signal and send it back to the computer via the antenna and reader.
Here, when the pressure applied to the object to be detected changes, the propagation speed of the surface acoustic wave in the pressure sensor changes, and this changes the phase of the response signal. The pressure applied to the object to be detected can be detected based on the time difference).

In addition, the surface acoustic wave sensor described in Patent Document 2 is used to detect the strain and temperature of the object to be detected by utilizing the fact that the surface acoustic wave phase changes based on the same principle as in Patent Document 1. It is

Since the conventional technologies disclosed in the above-mentioned Patent Documents 1 and 2 both detect the phase change and measure the physical quantity, the signal processing method is the drive signal transmitted from the master device to the sensor. and the response signal from the sensor to analyze the phase and frequency.

Japanese Patent No. 5101356 (paragraphs [0033] to [0050] etc.) Japanese Patent No. 5333538 (paragraphs [0059] to [0062] etc.)

In the conventional techniques described in Patent Documents 1 and 2, when noise (unnecessary radio waves) in the same frequency band is mixed at the same timing as the response signal from the sensor, the phase information included in the response signal is disturbed, and the physical quantity is measured. is difficult.
In order to reduce the effect of the above-mentioned noise, it is conceivable that the master device averages the response signals. cannot be grasped quickly.

Therefore, the problem to be solved by the present invention is wireless measurement of physical quantities that can measure physical quantities with high accuracy and speed by distinguishing only normal response signals even in an environment where noise is mixed in the response signal from the sensor. It is to provide a system.

In order to solve the above-mentioned problems, the invention according to claim 1 excites a surface acoustic wave in a surface acoustic wave element by a drive signal transmitted from a master device, and modulates the propagation characteristics according to the physical quantity acting on the object to be detected. with a sensor that produces a response signal,
In a wireless measurement system in which the master device includes transmission/reception means for transmitting the drive signal and receiving the response signal, and calculation means for calculating the physical quantity from the change in the propagation characteristic detected from the response signal,
The calculation means is
successively comparing a difference signal, which is a difference between the drive signal and the response signal, with a pre-stored template signal, and when the difference between the difference signal and the template signal exceeds a predetermined threshold; A response signal corresponding to a signal is determined to be a noise-containing signal, and the physical quantity is calculated using the response signal excluding the noise-containing signal.

The invention according to claim 2 is the physical quantity wireless measurement system according to claim 1,
The calculating means is characterized in that, when the difference between the amplitude of the differential signal and the amplitude of the template signal exceeds a predetermined threshold, the response signal corresponding to the differential signal is determined as the noise mixed signal.

The invention according to claim 3 is the physical quantity wireless measurement system according to claim 1 or 2,
The physical quantity is temperature, and the calculation means selects a template signal corresponding to the ambient temperature at the time of measurement from among a plurality of the template signals stored in advance according to the ambient temperature, and compares the template signal with the difference signal. It is characterized by using

According to the present invention, the difference signal between the drive signal sent from the center device to the sensor and the response signal from the sensor is sequentially compared with the reference template signal, and the difference between the two is calculated and compared with a predetermined threshold value. By doing so, it is possible to distinguish a normal response signal even in a high noise environment and accurately measure the physical quantity acting on the object to be detected. Moreover, since a high SN ratio (signal-to-noise ratio) of the response signal can be ensured without performing averaging processing or the like, the physical quantity can be measured almost in real time.

1 is an overall configuration diagram of a radio measurement system according to an embodiment of the present invention; FIG. FIG. 2 is a schematic diagram showing the configuration of the surface acoustic wave device in FIG. 1; FIG. 4 is a waveform diagram showing an example of the amplitude of a difference signal and the intensity of a response signal; FIG. 4 is a waveform diagram showing an example of the amplitude of a differential signal and the intensity of a response signal when noise is mixed; FIG. 4 is a waveform diagram showing an example of amplitude of a template signal used in the embodiment of the present invention; It is a flow chart which shows the operation of the embodiment of the present invention.

An embodiment of the present invention will be described below with reference to the drawings. This embodiment relates to a wireless measurement system that measures the temperature of a sensing target using a surface acoustic wave device.
FIG. 1 is an overall configuration diagram of a wireless measurement system according to this embodiment, and FIG. 2 is a schematic diagram showing the configuration of a surface acoustic wave device in FIG. The configurations of the wireless measurement system and the surface acoustic wave device are not limited to the illustrated examples, and can be changed as appropriate without departing from the gist of the present invention.

The wireless measurement system shown in FIG. 1 includes a master device 10 such as a microcomputer, a temperature-measuring wireless parasitic sensor (hereinafter simply referred to as a sensor) 20 having a surface acoustic wave element 22, and radio waves between them. and antennas 11 and 21 for transmitting and receiving. It should be noted that the sensor 20 is installed on a detection object whose temperature is to be detected.

The master device 10 includes a drive circuit 12, an amplifier circuit 13, and a calculation circuit .
The drive circuit 12 oscillates a high-frequency drive signal with transmission timing of a constant period, and this drive signal is received by the surface acoustic wave element 22 in the sensor 20 via the antennas 11 and 21 .
The amplifier circuit 13 amplifies the difference signal between the drive signal transmitted from the drive circuit 12 via the antenna 11 and the response signal received from the sensor 20 via the antennas 21 and 11 , and outputs the difference signal to the calculation circuit 14 .

The calculation circuit 14 measures the temperature of the object to be detected based on the input amplified difference signal.
The difference signal reflects the propagation characteristics of the surface acoustic waves generated by the surface acoustic wave element 22, and changes in the propagation characteristics depend on temperature changes of the object to be detected. can measure the temperature of the object to be detected. As the propagation characteristics, speed, phase, frequency, delay time, etc. may be used in addition to the difference signal between the drive signal and the response signal.

Various operations in the drive circuit 12, the amplifier circuit 13, and the calculation circuit 14 are executed by a processor, memory, or the like. The memory is composed of one or a plurality of storage media such as ROM (Read Only Memory) and RAM (Random Access Memory) depending on the application. These memories store a plurality of template signals for determining the presence or absence of noise as described later, various parameters indicating the propagation characteristics used as references when calculating the propagation characteristics of the response signal, and the propagation characteristics of the response signal. and the temperature of the object to be detected may be stored as a database.

As shown in FIG. 2, the surface acoustic wave element 22 in the sensor 20 includes an IDT (Interdigital Transducer) electrode 222 and a reflective electrode 223 placed at a predetermined interval on the surface of a piezoelectric substrate 221 capable of propagating surface acoustic waves. It is configured by arranging The piezoelectric substrate 221 is not limited to a surface acoustic wave that generates a Rayleigh wave that vibrates perpendicularly to the substrate surface, and a surface acoustic wave that generates an SH wave that vibrates perpendicularly to the traveling direction along the substrate surface is used. may

As the material of the piezoelectric substrate 221, for example, lithium compounds such as lithium tantalate (LiTaO3), lithium niobate (LiNbO3), lithium tetraborate (Li2B4O7), and quartz can be used.
The IDT electrode 222 has a structure in which a pair of comb-teeth electrodes 222a and 222b face each other, and an electrode piece of the other comb-teeth electrode 222b is arranged between electrode pieces of one comb-teeth electrode 222a. The electrode 222a is connected to the antenna 21, and the other comb tooth electrode 222b is grounded. As a material of the IDT electrode 222, for example, aluminum, titanium, chromium, gold, platinum, or the like is used. The number and width of the individual electrode pieces of the comb-teeth electrodes 222a and 222b, the pitch between the electrode pieces, and the like are not particularly limited, and can be appropriately changed in consideration of the excitation efficiency.
When a drive signal from the master device 10 is input to the IDT electrodes 222 via the antenna 21 , surface acoustic waves are excited at the IDT electrodes 222 .

The reflective electrode 223 is constructed by arranging a plurality of electrode pieces in parallel with the electrode pieces of the comb-teeth electrodes 222a and 222b. The reflective electrode 223 has a function of reflecting the surface acoustic wave propagating from the IDT electrode 222 through the surface of the piezoelectric substrate 221 toward the IDT electrode 222 . During the propagation of the surface acoustic wave, the propagation characteristics such as the propagation speed of the surface acoustic wave change according to the state of the object to be detected, for example, the temperature, and the surface acoustic wave reflected by the reflective electrode 223 is input to the IDT electrode 222 . Thereby, a response signal to be transmitted from the sensor 20 to the master device 10 is generated.
The number and width of individual electrode pieces of the reflective electrode 223, the pitch between the electrode pieces, and the like are not particularly limited, and can be changed as appropriate in consideration of the reflection efficiency. 222 can be used.

Next, referring to FIGS. 3 to 6, even in an environment where the response signal from the sensor 20 to the master device 10 contains noise, the temperature of the object to be detected can be accurately measured without being affected by this noise. I will explain the procedure to do.
FIG. 3 is a waveform diagram showing the amplitude of the difference signal amplified by the amplifier circuit 13 and the strength of the response signal calculated by the calculation circuit 14 based on this difference signal. FIG. FIG. 5 is a waveform diagram showing the amplitude of the difference signal and the strength of the response signal based on this difference signal, FIG. 5 is a waveform diagram showing the amplitude of the template signal used by the calculation circuit 14, and FIG. be.

First, a response signal from the sensor 20 to the drive signal transmitted from the drive circuit 12 of the master device 10 is read into the calculation circuit 14 (step S1 in FIG. 6). Next, if the maximum amplitude of the response signal exceeds the first threshold (S2 NO), the response signal is excluded and the process returns to step S1 to sample the response signal again.
If the maximum amplitude of the response signal is equal to or less than the first threshold (S2 YES), for example, a template signal selected from a plurality of template signals in the memory according to the ambient temperature at that time is read into the calculation circuit 14 (S3a ).

Next, the calculation circuit 14 obtains the difference between the drive signal and the response signal, calculates the difference or moving standard deviation between this difference signal and the template signal, and analog-digital converts the result at a predetermined sampling frequency (S3 ).
Here, if the difference signal when noise is not mixed in the response signal is, for example, time-series data as shown in FIG. It has almost the same waveform as the signal (an example is shown in FIG. 5). Further, the intensity of the response signal calculated based on the difference signal at this time has a large SN ratio as shown in FIG. becomes small.

On the other hand, in a noise environment in which unwanted radio waves in the same frequency band as the radio waves used by the wireless temperature measurement system are mixed, the difference signal becomes, for example, as shown in FIG. The intensity of the signal is also as shown in FIG. 4(b).
That is, the SN ratio of the response signal is reduced due to the influence of noise, and variations in extracted phase information and the like, and thus variations in temperature measurement values, increase. In order to accurately measure the temperature of the object to be sensed, it is necessary to remove the differential signal mixed with noise, in other words, the response signal.

Therefore, in the present embodiment, the difference or moving standard deviation calculated in step S3 described above is compared with a second threshold, and if it exceeds the second threshold (S4 NO), noise is mixed in the response signal. Then, the process returns to step S1, and sampling of the response signal is performed again. It was decided to use it for temperature measurement (S4 YES).

The calculation circuit 14 searches for the peak of the response signal by arithmetic processing such as FFT (Fast Fourier Transform) and calculates its intensity (S5) for the response signal that is free of noise. Wave propagation time, propagation phase information, etc. are extracted (S6). Using this information and various parameters stored in the memory, the temperature of the detection object detected by the sensor 20 is calculated (S7).

It should be noted that the present invention can measure not only the temperature of the object to be detected, but also the pressure, strain, etc. acting on the object to be detected.

10: Master Device 11: Antenna 12: Drive Circuit 13: Amplifier Circuit 14: Calculation Circuit 20: Sensor 21: Antenna 22: Surface Acoustic Wave Element 221: Piezoelectric Substrate 222: IDT Electrodes 222a, 222b: Comb-toothed Electrode 223: Reflective Electrode

Claims (3)

a sensor for generating a response signal having a propagation characteristic corresponding to a physical quantity acting on an object to be sensed by exciting a surface acoustic wave from a surface acoustic wave element in response to a drive signal transmitted from the master device;
A physical quantity wireless measurement system in which the master device includes a transmitting/receiving means for transmitting the driving signal and receiving the response signal, and a calculating means for calculating the physical quantity from the change in the propagation characteristic detected from the response signal. in
The calculation means is
successively comparing a difference signal, which is a difference between the drive signal and the response signal, with a pre-stored template signal, and when the difference between the difference signal and the template signal exceeds a predetermined threshold; A physical quantity wireless measurement system, wherein a response signal corresponding to a signal is determined as a noise-containing signal, and the physical quantity is calculated using the response signal excluding the noise-containing signal. In the physical quantity wireless measurement system according to claim 1,
wherein the calculating means determines a response signal corresponding to the difference signal when the difference between the amplitude of the difference signal and the amplitude of the template signal exceeds a predetermined threshold as a noise-containing signal. Radio measurement system. In the physical quantity wireless measurement system according to claim 1 or 2,
the physical quantity is temperature;
The physical quantity, wherein the calculating means selects a template signal corresponding to the ambient temperature at the time of measurement from among the plurality of template signals stored in advance according to the ambient temperature, and uses the template signal for comparison with the difference signal. radio measurement system.

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