KR101904254B1 - Wireless temperature measument system - Google Patents

Abstract

A wireless temperature measurement system according to an embodiment of the present invention includes a sensor unit 100 for measuring a temperature and generating a response signal 20 according to temperature, And a reader unit (200) for transmitting a driving signal (10) to the sensor unit (100) and receiving a response signal (20) A piezoelectric substrate 120 for propagating the generated surface acoustic waves, an interdigital transducer 130 for generating surface acoustic waves through the driving signal 10, And a delay line 150 for propagating a surface acoustic wave between the IDT 130 and the reflection plate 140. The reflection plate 140 includes a reflection plate 140 and a reflection plate 140. The reflection plate 140 reflects the IDT 130, And the driving signal 10 of the sensor unit 100 and the reader unit 200 in a wireless manner, The transmission and reception of the response signal 20 is characterized in that is carried out.

Description

[0001] WIRELESS TEMPERATURE MEASUREMENT SYSTEM [0002]

The present invention relates to a wireless temperature measurement system. More particularly, the present invention relates to a wireless temperature measurement system capable of measuring the temperature of a structure wirelessly, non-powered, or unmanned, for structural health monitoring of a structure with limited human accessibility.

Surface acoustic wave (SAW) devices are devices that produce surface acoustic waves (IDTs) on a piezoelectric substrate, generate surface acoustic waves, reflect the surface acoustic waves on reflectors, and then convert them into electrical signals. It was developed by White and Voltmer and has been used mainly in the field of signal processing until now. SAW devices can be used as ultra-small, light-weight, high-performance sensors that respond sensitively to changes in the surrounding environment by changing the frequency characteristics according to changes in the surrounding environment.

Recently, researches are being actively carried out to develop a high-performance, compact and light-weight wireless sensor used for structural health monitoring of structures with limited human access, among which sensors using SAW devices are in the spotlight. SAW sensors require no external power supply, can select a high frequency band, can be applied wirelessly, can be mass-produced, have a fast response time, have relatively high accuracy and reliability.

The propagation energy of the surface acoustic wave generated from the IDT of the SAW sensor is sensitive to the physical change of the surface of the piezoelectric body because the energy of the surface acoustic wave propagates more than 90% of the energy at a depth within 1 to 1.5 times the wavelength from the surface. It is necessary to develop a SAW temperature sensor that utilizes the change of the resonance frequency of the surface acoustic wave generated through the IDT as the physical properties of the piezoelectric body change with external temperature change by using such characteristics.

In order to apply the SAW temperature sensor to structural health monitoring, it is necessary to acquire the resonance frequency change caused by the SAW temperature sensor. In order to apply the SAW temperature sensor to the wireless communication, the surface acoustic wave generated from the IDT is reflected from the reflection plate, Should be able to.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wireless temperature measurement system capable of maximizing the size of a signal generated in a SAW temperature sensor, in order to solve various problems including the above problems.

It is another object of the present invention to provide a wireless temperature measurement system having a bidirectional propagation structure capable of wireless communication by maximizing a signal size. However, these problems are exemplary and do not limit the scope of the present invention.

According to an aspect of the present invention, there is provided a wireless communication system including a sensor unit for measuring a temperature and generating a response signal according to temperature, and a reader unit for transmitting a drive signal to the sensor unit and receiving the response signal. A temperature measuring system, comprising: a first antenna for receiving the driving signal; A piezoelectric substrate for propagating the generated surface acoustic wave; An IDT (Inter Digital Transducer) formed on the piezoelectric substrate and generating surface acoustic waves through the driving signal; A reflection plate that reflects the propagated surface acoustic wave and propagates to the IDT; And a delay line for propagating the surface acoustic wave between the IDT and the reflection plate, wherein a pair of the reflection plates are disposed on both sides of the IDT, and the reader unit and the sensor unit And a transmission and reception of the response signal are performed.

Also, according to an embodiment of the present invention, the IDT and the reflection plate may have a comb-like structure.

Also, according to an embodiment of the present invention, the electrode width of the IDT and the strip width of the reflection plate may be 2.25 mu m to 2.45 mu m.

Also, according to an embodiment of the present invention, the reader unit may sequentially transmit a plurality of driving signals having different center frequencies to the sensor unit through a second antenna.

According to an embodiment of the present invention, the surface acoustic waves traveling between the IDT and the reflection plate overlap each other to form a standing wave.

According to an embodiment of the present invention, a reflected wave is formed when a center frequency of the driving signal is equal to a resonance frequency of the response signal, and a measurement object temperature can be determined to a maximum value of the reflected wave.

Also, according to an embodiment of the present invention, the resonance frequency may be designed to be 425 MHz.

Further, according to an embodiment of the present invention, the resonance frequency can be lowered by at least 30 kHz when the temperature of the object to be measured is 1 DEG C higher in a temperature range of -20 DEG C to 80 DEG C.

Also, according to an embodiment of the present invention, the piezoelectric substrate may be 128 ° YX-LiNbO ₃ .

According to an embodiment of the present invention, the length of the delay line may be 10 times the wavelength of the surface acoustic wave.

According to the embodiment of the present invention as described above, it is possible to maximize the size of the signal generated by the SAW temperature sensor.

According to another aspect of the present invention, there is provided a wireless temperature measurement system having a bidirectional propagation structure capable of wireless communication by maximizing a signal size.

1 is a schematic diagram showing a configuration of a wireless temperature measurement system according to an embodiment of the present invention.
2 is a graph illustrating the shape of a reflected wave according to whether a resonance frequency of a drive signal and a response signal coincides with each other according to an exemplary embodiment of the present invention.
3 is a SEM (Scanning Electron Microscope) photograph showing a comb-shaped IDT manufactured according to an embodiment of the present invention.
4 is a schematic view showing a configuration of a wire temperature measuring system according to a comparative example of the present invention.
5 is a graph showing the results of wire and wireless temperature experiments according to an embodiment of the present invention.
6 is a graph illustrating the frequency-temperature relationship of the wire and wireless temperature experiment according to an embodiment of the present invention.

The following detailed description of the invention refers to the accompanying drawings, which illustrate, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the present invention are different, but need not be mutually exclusive. For example, certain features, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in connection with an embodiment. It is also to be understood that the position or arrangement of the individual components within each disclosed embodiment may be varied without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is to be limited only by the appended claims, along with the full scope of equivalents to which such claims are entitled, if properly explained. In the drawings, like reference numerals refer to the same or similar functions throughout the several views, and length and area, thickness, and the like may be exaggerated for convenience.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily carry out the present invention.

1 is a schematic diagram showing a configuration of a wireless temperature measurement system according to an embodiment of the present invention.

Referring to FIG. 1, the wireless temperature measurement system may include a sensor unit 100 and a reader unit 200.

The sensor unit 100 may measure the temperature and generate a response signal 20 according to the temperature, which corresponds to a surface acoustic wave (SAW) sensor. The sensor unit 100 may include a first antenna 110, a piezoelectric substrate 120, an interdigital transducer 130, a reflector 140, and a delay line 150.

The reader unit 200 can transmit the driving signal 10 to the sensor unit 100 and receive the response signal 20. The reader unit 200 may include a second antenna 210 and a processing unit 220. The reader unit 200 may analyze the drive signal 10 and the response signal 20 by itself and may also analyze the drive signal 10 using an analyzer (not shown) such as a computer connected to the reader unit 200. [ ) And the response signal (20).

The first antenna 110 may receive the driving signal 10 wirelessly transmitted from the reader unit 200 through the second antenna 210. [

The sensor unit 100 may transmit the driving signal 10 received through the first antenna 110 to the IDT 130. The IDT 130 has an electrode shape of a comb-like structure and may be formed on the piezoelectric substrate 120. The IDT 130 can convert the received driving signal 10 into a surface acoustic wave according to an inverse piezoelectric effect. The generated surface acoustic wave can propagate along the delay line 150 at the surface of the piezoelectric substrate 120.

The IDT 130 is formed at the center of the sensor unit 100 (or the piezoelectric substrate 120), and the reflection plate 140 is disposed outside the sensor unit 100 (or the piezoelectric substrate 120) . The reflection plate 140 may reflect the surface acoustic wave propagated along the delay line 150 and propagate to the IDT 130 again.

In order to maximize the size of the reflected wave to be suitable for wireless communication, a pair of reflection plates 140 may be disposed on both sides of the IDT 130 (or both ends of the sensor unit 100) 150 may be set as short as possible.

The processing unit 220 according to an embodiment of the present invention sequentially generates a plurality of driving signals 10 having different center frequencies (from the first frequency to the second frequency) and sequentially outputs the driving signals 10 through the second antenna 210 1 < / RTI > The surface acoustic wave can propagate along the surface of the piezoelectric substrate 120 by the vibration of the piezoelectric substrate 120 by the drive signal 10 inputted to the IDT 130. At this time, depending on the temperature of the sensor unit 100, , Phase, propagation speed, delay time, and the like. The surface acoustic wave can be reflected by the reflection plate 140 and converted into the response signal 20 again according to the piezoelectric effect in the IDT 130 via the delay line 150. [ The first antenna 110 can wirelessly transmit the converted response signal 20 to the reader unit 200. The processing unit 220 can measure the temperature of the measurement object by calculating a change between the response signal 20 and the drive signal 10 received through the second antenna 210. [

2 is a graph showing the shape of a reflected wave according to whether the resonance frequency of the drive signal 10 and the response signal 20 coincide with each other according to an embodiment of the present invention. 2A shows a case in which the resonance frequencies of the drive signal 10 and the response signal 20 coincide with each other and FIG.2B shows a case where the resonance frequency of the drive signal 10 and the response signal 20 is Indicates inconsistency. 2 (a) and 2 (b), the section a represents the driving signal 10, and the section b represents the reflected wave when the reflected wave is formed.

The reader unit 200 can transmit the driving signal 10 to the sensor unit 100 at regular intervals in a predetermined frequency band. The reader unit 200 can receive the response signal 20 generated by the sensor unit 100 after changing the drive signal 10 of f _{0 to} the receive mode after transmission. In this order, the transmission and reception of the signals 10 and 20 can be repeated at regular intervals from f ₀ to f _n .

The surface acoustic waves traveling between the IDT 130 and the reflection plate 140 in the sensor unit 100 may overlap each other to form a stinging wave. The frequency of the standing wave may reflect the temperature of the sensor unit 100. The standing wave may be transmitted to the reader unit 200 as the response signal 20.

When the center frequency of the driving signal 10 coincides with the resonance frequency of the response signal 20, a reflected wave can be formed (section b of FIG. 2A) The temperature can be determined. When the center frequency of the driving signal 10 and the resonance frequency of the response signal 20 do not coincide with each other, a reflected wave will not be formed (section b in FIG.

(Experimental Example)

Hereinafter, a temperature measurement result of the wireless temperature measurement system according to the experimental example of the present invention will be described.

The main parameters for selecting the piezoelectric substrate 120 in the wireless temperature measurement system are an electromechanical coupling coefficient ( k ² ) indicating the efficiency at which the electrical energy changes into mechanical energy, a TCD Temperature Cofficient of Delay, and piezoelectric characteristics. The piezoelectric substrates mainly used are LiNbO ₃ , LiTaO ₃ , and Quartz. Among them, LiNbO ₃ was selected considering the electro-mechanical coupling coefficient and TCD.

In addition, among the LiNbO ₃ substrates, the characteristics differ depending on the cross-sectional angle and the propagation direction after the piezoelectric element growth, and the number of the temperature coefficients should be the largest. As shown in the following Table 1, the piezoelectric substrates suitable for the sensor unit 100 are 128 ° YX-LiNbO ₃ and YZ-LiNbO ₃ , and SSBW (128 ° YX-LiNbO _3), in which surface acoustic waves are radiated into the piezoelectric substrate, Surface Skimming Bulk Wave) was relatively small, and finally, 128 ° YX-LiNbO ₃ was selected.

[Table 1]

The IDT 130 plays a key role in converting electrical energy into mechanical energy. When an AC voltage V (t) = V ₀ exp (jwt) is applied to the IDT 130, a mechanical deformation occurs in the piezoelectric substrate 120 and the voltage is moved to the next electrode at a speed of v _R. In the case of a single IDT structure, the structure is simple and the electrode width is relatively wide, so that the photolithography process for the electrode implementation is simple. In order to maintain the same surface wave in the single electrode structure, the width d of the individual comb electrodes of the IDT (or the interval of the individual comb electrodes) should be 1/4 of the surface acoustic wave wavelength as shown in Equation (1). The frequency f ₀ on the same phase is expressed by Equation (2).

[Equation 1]

 &Quot; (2) "

In this case, the efficiency of converting electrical energy (driving signal) into mechanical energy (surface acoustic wave) is maximized.

The number of the individual interdigital electrodes of the IDT 130 is proportional to the intensity of the surface acoustic wave by the principle of superposition. In this experiment, about 40 pairs were designed. The resonant frequency is designed to resonate at 425 MHz, which is in compliance with the industrial scientific medical (ISM) band, which is available in industrial, scientific and medical fields. Thus, according to Equations (1) and (2), the width d of the individual interdigital electrodes of the IDT at the propagation velocity (3996 m / s) of the piezoelectric substrate 120 was determined to be 2.35 mu m. 3 is a SEM (Scanning Electron Microscope) photograph showing the IDT 130 of the comb type structure manufactured according to an embodiment of the present invention. In the semiconductor etching process, a slight error may occur in the distance and width (d) of the individual comb electrodes of the IDT, and d may be about 2.25 탆 to 2.45 탆.

In order to determine the characteristics of the reflector 140, the reflection power, the reflection bandwidth, and the shape of the reflector should be considered. The reflection power is proportional to the strip (finger) of the reflection plate, and the reflection coefficient (R) is expressed by Equation (3). r means the reflection force of the individual strip (finger).

&Quot; (3) "

The reflection plate 140 may have a closed type, an open type in which a strip end is opened, and an IDT-type (or a comb type) in a combination of a closed type and an open type. Since the reflector 140 and the IDT 130 are different from each other in terms of voltage application and basically have the same concept of propagating the surface acoustic wave, the IDT 130 has a comb-like structure similar to that of the IDT 130, (d) of 2.35 mu m. In order to maximize the size of the reflected waves, the reflection plates are disposed on both sides of the IDT 130 as shown in FIG.

In order to reduce the loss of the response signal 20 (or the reflected signal), the delay line 150 is set to 10? As short as possible.

4 is a schematic view showing a configuration of a wire temperature measuring system according to a comparative example of the present invention.

4, a sensor unit 100 is connected to a connection port 310 of a network analyzer 300 by a wire system 301 to constitute a wire temperature measuring system, (TEMI850, SJ Science, Korea) and the temperature was changed from -20 to 80 DEG C to measure the frequency change pattern through the processing unit 320. [

As an experimental example of the present invention, a first antenna 110 having a bandwidth of 410 to 480 MHz is attached to the sensor unit 100 and a second antenna 210, which is the same as the first antenna 110, (Same as in the reader unit 200), and a wireless temperature measurement system (same as FIG. 1) was constructed, and the frequency change pattern was measured by changing the temperature in the same manner as in the comparative example.

FIG. 5 is a graph showing the temperature experiment results of the wired (FIG. 5 (a)) and wireless (FIG. 5 (b)) according to an embodiment of the present invention. 6 is a graph illustrating the frequency-temperature relationship of the wire and wireless temperature experiment according to an embodiment of the present invention.

The measured value is an average value of 10 data measured for 5 minutes at 10 intervals in the range of -20 to 80 ° C, and the sampling rate is 1500 per temperature. The insertion loss averages for cable and wireless temperature experiments were about -11 dB and -17 dB, respectively. When the temperature is increased by 1, the resonance frequency is lowered by about 30 kHz in both experiments. The resonance frequencies of the oil and radio sensor unit 100 were measured at about 425.4 and 425.3 MHz at room temperature (about 20), respectively. It is confirmed that the transition of the resonant frequency according to the temperature is the same in both wire and wireless. As the temperature changes, the resonant frequency changes as well. Therefore, it can be analyzed that accurate temperature measurement is possible using the wireless temperature measurement system of the present invention.

As described above, according to the present invention, the reflectors 140 are arranged on both sides of the IDT 130, and the IDT 130 and the reflector 140 have the same structure to maximize the size of the signal generated by the SAW temperature sensor . Since the plurality of drive signals having different center frequencies are sequentially applied and the measurement target temperature is determined as the maximum value of the reflected wave formed when the center frequency of the drive signal and the resonance frequency of the response signal coincide with each other, It is possible to implement a wireless temperature measurement system having a bi-directional propagation structure capable of maximizing and communicating wirelessly.

The wireless temperature measurement system of the present invention can be utilized in a field where measurement is required in a noncontact manner in a field where a separate power source for driving the sensor is not required and the access is difficult or dangerous. For example, it can be applied to various fields requiring temperature measurement such as structural structure monitoring of a human-restricted structure, high-voltage transformer, temperature distribution monitoring in the workplace, environment field, and food manufacturing process.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken in conjunction with the present invention. Variations and changes are possible. Such variations and modifications are to be considered as falling within the scope of the invention and the appended claims.

10: drive signal
20: response signal
100:
110: first antenna
120: piezoelectric substrate
130: Inter Digital Transducer (IDT)
140: Reflector
150: Delay Line
200:
210: second antenna
220:

Claims (10)

A wireless temperature measurement system comprising: a sensor section for measuring a temperature and generating a response signal according to temperature; and a reader section for transmitting a drive signal to the sensor section and receiving the response signal,
The sensor unit includes:
A first antenna for receiving the driving signal;
A piezoelectric substrate for propagating the generated surface acoustic wave;
An IDT (Inter Digital Transducer) formed on the piezoelectric substrate and generating surface acoustic waves through the driving signal;
A reflection plate that reflects the propagated surface acoustic wave and propagates to the IDT; And
A delay line propagating the surface acoustic wave between the IDT and the reflection plate,
/ RTI >
Wherein the pair of reflection plates are disposed on both sides of the IDT, and transmission and reception of the drive signal and the response signal of the reader unit and the sensor unit are performed in a wireless manner. The method according to claim 1,
Wherein the IDT and the reflector are comb-like structures. The method according to claim 1,
Wherein an electrode width of the IDT and a strip width of the reflector are 2.25 mu m to 2.45 mu m. The method according to claim 1,
Wherein the reader unit sequentially transmits a plurality of drive signals having different center frequencies to the sensor unit via a second antenna. 5. The method of claim 4,
And the surface acoustic waves traveling between the IDT and the reflection plate overlap each other to form a standing wave. The method according to claim 1,
Wherein a reflected wave is formed when a center frequency of the drive signal is equal to a resonance frequency of the response signal and a measurement object temperature is determined to be a maximum value of the reflected wave. The method according to claim 6,
Wherein the resonant frequency is designed to be 425 MHz. The method according to claim 6,
Wherein the resonant frequency is lowered by at least 30 kHz when the temperature of the object under measurement is increased by 1 占 폚 in the temperature range of -20 占 폚 to 80 占 폚. The method according to claim 1,
It said piezoelectric substrate is a 128 ° YX-LiNbO ₃ is, the wireless temperature measurement system. The method according to claim 1,
Wherein the length of the delay line is ten times the wavelength of the surface acoustic wave.

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