JP2021032676A - Recognition signal generation element and element recognition system - Google Patents

Abstract

To enable accurate identification between a plurality of elements, without complicating a configuration.SOLUTION: A SAW sensor 2 includes a piezoelectric substrate 3 which has a planar shape, an excitation electrode 4 which is formed on the surface 3a of the piezoelectric substrate 3 and is for exciting an elastic surface wave on the surface 3a according to an AC signal of a prescribed frequency, an antenna 8 which is electrically connected to the excitation electrode 4, receives the AC signal, and transmits a reflection signal with respect to the elastic surface wave to the outside, a first reflection electrode 5 which is formed on the surface 3a separately from the excitation electrode 4 and reflects the elastic surface wave toward the excitation electrode 4, a mass load film 7 which is formed between the excitation electrode 4 and the first reflection electrode 5 on the surface 3a and generates a mass load effect, and a second reflection electrode 6 which is electrically connected to a sensor element 10, is formed on the surface 3a separately from the excitation electrode 4, and reflects the elastic surface wave toward the excitation electrode 4.SELECTED DRAWING: Figure 2

Description

The embodiment relates to a recognition signal generation element using surface acoustic waves and an element recognition method.

In recent years, a sensing technology using surface acoustic wave (SAW) has been developed, and a passive SAW sensor that does not require a power supply is known as a device using the technology. Unlike semiconductor devices, this passive SAW sensor does not require a DC bias and can be driven only by a high frequency signal of a desired frequency. On the other hand, when sensing is performed simultaneously using a plurality of passive SAW sensors, how to identify each sensor becomes a problem.

For example, the SAW sensor described in Patent Document 1 below has a surface acoustic wave element for identification that excites a surface acoustic wave for identification in addition to a surface acoustic wave for detection on a piezoelectric substrate. This surface acoustic wave element for identification enables identification of a SAW sensor by changing the frequency characteristic of reflection of the surface acoustic wave for identification with respect to the identification frequency and changing the propagation distance of the surface acoustic wave for identification.

Further, in the SAW sensor described in Non-Patent Document 1 below, an excitation electrode provided on the piezoelectric substrate and exciting a surface acoustic wave based on a high frequency signal received via an antenna, and an excitation electrode thereof on the piezoelectric substrate. A plurality of reflective electrodes arranged separately from the above at a specific distance are used. With such a configuration, since the reflected signal corresponding to the arrangement pattern of the plurality of reflecting electrodes is received via the antenna, the SAW sensor can be identified.

JP-A-2019-66206

LeonhardReindl et al., “Theory and Application of Passive SAW Radio Transponders as Sensors”, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROLL, September 1998, Vol. 45, No. 5, p. 1281-1292

Recently, an antenna is provided in the SAW sensor, a high-frequency signal is wirelessly transmitted from an external transmitter / receiver to a plurality of SAW sensors, and the transmitter / receiver wirelessly receives signals from the plurality of SAW sensors. There is. However, in the configuration of the SAW sensor described in Non-Patent Document 1 described above, multiple reflections occur between a plurality of reflecting electrodes, so that the actual reflected signal includes a dummy signal due to the multiple reflections. As a result, the SAW sensor The accuracy of identification may decrease.

Further, even in the configuration of the SAW sensor described in Patent Document 1 described above, in order to enable discrimination among many SAW sensors, various frequency characteristics of the reflective electrode provided on the surface acoustic wave element for identification may be set. , It is necessary to set various positions of the reflecting electrode or the impedance connected to the reflecting electrode in the surface acoustic wave element for identification. As a result, in order to make many SAW sensors distinguishable, the element structure for identification tends to be complicated.

Therefore, the embodiment has been made in view of the above problems, and provides a recognition signal generation element and an element recognition method that enable highly accurate identification between a plurality of elements without complicating the configuration. With the goal.

In order to solve the above problems, the recognition signal generation element according to one aspect of the present invention is formed on the surface of the piezoelectric body having a planar shape and the surface of the piezoelectric body, and responds to an AC signal of a predetermined frequency received from the outside. It is electrically connected to an excitation electrode for exciting surface acoustic waves above, and at least to the excitation electrode, receives an AC signal to generate a surface acoustic wave, and transmits a signal generated in response to the surface acoustic wave to the outside. At least one antenna, a first electrode formed on the surface separately from the excitation electrode and receiving a surface acoustic wave to generate a signal, and formed on the surface between the excitation electrode and the first electrode. A thin film and a second electrode which is an electrode electrically connected to the sensor and is formed on the surface separately from the excitation electrode and receives a surface acoustic wave from the excitation electrode to generate a signal. ..

According to the recognition signal generation element of the above embodiment, a surface acoustic wave is excited from the excitation electrode on the piezoelectric body by applying an AC signal of a predetermined frequency from the outside to the excitation electrode on the piezoelectric body via an antenna. The surface acoustic wave is propagated on the piezoelectric body toward the first electrode and the second electrode. Then, the first electrode receives the surface acoustic wave to generate the first signal, and the first signal is transmitted to the outside via the antenna, while the second electrode receives the surface acoustic wave. A second signal is generated at, and the second signal is transmitted to the outside via the excitation electrode and the antenna. Since the sensor is electrically connected to the second electrode, an external transmitter / receiver that receives the second signal enables sensing of a desired measurement variable using the second signal. In addition, since the thin film is provided on the piezoelectric body between the excitation electrode and the first electrode, the external transmitter / receiver may receive the first signal with a delay time according to the characteristics of the thin film. It is possible to identify the sensor element based on the delay time in the external transmission / reception device. As a result, highly accurate identification between a plurality of sensor elements can be realized without complicating the configuration for generating an elastic surface wave for identification.

Here, the first electrode may reflect the surface acoustic wave toward the excitation electrode, and at least one antenna may transmit the reflected signal generated at the excitation electrode by the reflected surface acoustic wave to the outside. .. With such a configuration, the surface acoustic wave is reflected by the first electrode to generate a reflected signal, and the reflected signal is transmitted to the outside as a first signal via the excitation electrode and the antenna. In this case as well, the sensor elements can be identified based on the delay time of the first signal in the external transmission / reception device, the number of antennas can be reduced, and the configuration can be simplified.

Further, the thin film may have a rectangular shape along the arrangement direction of the excitation electrode and the first electrode. By doing so, the mass loading effect can be stably given to the surface acoustic wave generated from the excitation electrode and propagated toward the first electrode, and the identification of the sensor element by the external device is stabilized.

Further, the excitation electrode has two comb-shaped electrodes arranged in mesh with each other, and the thin film meshes the two comb-shaped electrodes in a direction perpendicular to the arrangement direction of the excitation electrode and the first electrode. It may be formed so as to be wider than the mating portion. In this case, the mass loading effect can be efficiently given to the surface acoustic wave generated from the excitation electrode and propagated toward the first electrode, and the accuracy of identification of the sensor element by the external device can be further improved. it can.

Further, the thin film may contain a metal or a dielectric material. In this case, the mass load effect of the thin film can be stabilized, and the identification of the sensor element by the external device can be stabilized.

Further, the thin film may contain an alloy of gold, silver, copper, aluminum, platinum, or any of gold, silver, copper, aluminum, and platinum. In this case, a thin film can be easily formed on the piezoelectric body.

Alternatively, the element recognition system of another aspect of the present invention transmits an AC signal to the above-mentioned recognition signal generation element and the recognition signal generation element, and the first electrode and the second electrode correspond to the surface acoustic wave. Each of the first signal and the second signal generated by the above is received via at least one antenna, and the recognition signal generating element is identified based on the phase difference or time difference between the AC signal and the first signal. , A transmission / reception device for sensing using a second signal.

According to the element recognition system of the above-described embodiment, the external transmission / reception device that has received the second signal enables sensing of a desired measurement variable using the second signal. In addition, an external transmitter / receiver can receive the first signal with a delay time according to the characteristics of the thin film, and the external transmitter / receiver can make a phase difference or time difference between the AC signal and the first signal. Based on this, the delay time of the first signal can be evaluated. Then, in the external transmission / reception device, each recognition signal generation element can be identified based on the evaluation result of the delay time. As a result, highly accurate identification between a plurality of sensor elements can be realized without complicating the configuration for generating an elastic surface wave for identification.

Here, the transmitter / receiver determines the material of the thin film, the length of the thin film in the arrangement direction of the excitation electrode and the first electrode, the thickness of the thin film, and the excitation frequency of the surface acoustic wave based on the phase difference or the time difference. It is preferable to identify the recognition signal generating element by determining any of them. According to such a configuration, when sensing is performed using a plurality of recognition signal generation elements in which any of the thin film material, length, thickness, or excitation frequency in the recognition signal generation element is set variously, a plurality of recognition signal generation elements are used. The recognition signal generation element can be identified with high accuracy. In addition, a thin film having desired characteristics can be easily processed in the recognition signal generation element.

Further, the element recognition system of the above embodiment includes a plurality of recognition signal generation elements, and among the plurality of recognition signal generation elements, any value of the thin film material, the thin film length, the thin film thickness, and the excitation frequency. Are different, it is also preferable. As described above, according to the configuration including a plurality of recognition signal generation elements having various surface acoustic wave propagation characteristics, the plurality of recognition signal generation elements can be identified more accurately.

According to the embodiment, it enables highly accurate identification between a plurality of elements without complicating the configuration.

It is a figure which shows the schematic structure of the sensing system 100 which concerns on a preferred embodiment. It is a top view which looked at the SAW sensor 2 of FIG. 1 from the surface side of the piezoelectric substrate. FIG. 3 is a cross-sectional view taken along the line III-III of the SAW sensor 2 of FIG. It is a graph which shows the image of the time waveform WF0, WF1 of the reference signal and the reflection signal detected by the transmission / reception device 1 of FIG. FIG. 5 is a plan view of the SAW sensor 2A according to the modified example as viewed from the surface side of the piezoelectric substrate. FIG. 5 is a plan view of the SAW sensor 2B according to the modified example as viewed from the surface side of the piezoelectric substrate. FIG. 5 is a plan view of the SAW sensor 2C according to the modified example as viewed from the surface side of the piezoelectric substrate. It is a graph which shows the image of the time waveform WF22 and WF3 of the reflection signal detected from the SAW sensor 2C of FIG. FIG. 5 is a plan view of the SAW sensor 2D according to the modified example as viewed from the surface side of the piezoelectric substrate.

Hereinafter, preferred embodiments of the recognition signal generation element and the element recognition system according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted. In addition, each drawing is created for the purpose of explanation, and is drawn so as to particularly emphasize the target part of the explanation. Therefore, the dimensional ratio of each member in the drawing does not always match the actual one.

The SAW sensor 2, which is a surface acoustic wave device included in the sensing system 100 according to the embodiment, is a device for detecting a predetermined measurement parameter (measurement variable) by using a surface acoustic wave (SAW). .. This measurement parameter includes a numerical value indicating a tilted state, a numerical value indicating a vibration state, temperature, humidity, pressure, and the like, but is not limited to a specific parameter. Here, the surface acoustic wave is a wave composed of a longitudinal wave and a transverse wave propagating on the surface of the elastic body.

FIG. 1 shows a schematic configuration of a sensing system 100, which is an element recognition system according to the present embodiment. As shown in the figure, the sensing system 100 receives a transmission / reception device 1 configured to wirelessly transmit and receive an AC signal having a predetermined frequency to and from the SAW sensor 2, and an AC signal transmitted from the transmission / reception device 1. , A plurality of SAW sensors 2 configured to generate a reflected signal in response to the AC signal and transmit the reflected signal to the transmission / reception device 1 are included. The reflected signal is an AC signal having the same frequency as the AC signal transmitted from the transmission / reception device 1. The frequency of the AC signal transmitted / received between the transmission / reception device 1 and the SAW sensor 2 is not limited to a specific frequency, but is set to, for example, a frequency in the 920 MHz band of the specific low power band. Each of these plurality of SAW sensors 2 constitutes a recognition signal generation element according to the present embodiment. According to such a sensing system 100, since the transmission / reception device 1 and the plurality of SAW sensors 2 are wirelessly connected, it is possible to perform sensing at a plurality of locations where it is difficult to connect by wire. To. The sensing system 100 is used not only in the fields of architecture, civil engineering, and disaster prevention, which require sensing of various states such as bridges, tunnels, highway slopes, and buildings, but also in the fields of environmental sensors in vehicles and indoors. Can be mentioned.

Next, the configuration of the SAW sensor 2 will be described. FIG. 2 is a plan view of the SAW sensor 2 as viewed from the surface side of the piezoelectric substrate, and FIG. 3 is a cross-sectional view of the SAW sensor 2 of FIG. 2 along lines III-III. The SAW sensor 2 includes a piezoelectric substrate (piezoelectric body) 3 formed in a rectangular flat plate shape (planar shape), an excitation electrode 4 formed on the surface 3a of the piezoelectric substrate 3, and a first reflective electrode (first electrode). 5. A second reflective electrode (second electrode) 6, a mass load film (thin film) 7, and an antenna 8 are provided. Here, the surface 3a of the piezoelectric substrate 3 indicates a propagation surface on which surface acoustic waves propagate.

The piezoelectric substrate 3 is composed of crystals that generate surface acoustic waves due to the piezoelectric effect, for example, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), quartz, langasite-based materials, and the like. The piezoelectric substrate 3 is a substrate that generates elastic waves including longitudinal waves, for example, a piezoelectric ceramic such as PZT, or a piezoelectric thin film made of zinc oxide (ZnO), aluminum nitride (AlN), or the like from glass, silicon, or the like. It may be entirely or partially laminated on the surface of the substrate. Further, the piezoelectric substrate 3 may be a polymer substrate that produces a piezoelectric effect. The piezoelectric effect is a phenomenon in which when a force or an electric field is applied to a crystal such as quartz, a voltage or distortion is generated according to the force or the electric field.

The excitation electrode 4 is a pair of electrode members provided at the center between one end (left end in FIG. 2) and the other end (right end in FIG. 2) on the surface 3a of the piezoelectric substrate 3. is there. The excitation electrode 4 is an electrode for exciting a surface acoustic wave on the piezoelectric substrate 3, and is composed of two comb-shaped interdigital transducers (IDTs) 4a and 4b. Specifically, the two electrode-shaped electrodes 4a and 4b each extend linearly along a direction perpendicular to one end of the piezoelectric substrate 3 and parallel to each other in a direction orthogonal to the base. The two electrode-shaped electrodes 4a and 4b have a plurality of electrode fingers so that one electrode finger and the other electrode finger are alternately arranged in a direction perpendicular to one end of the piezoelectric substrate 3. Have been placed. In other words, the two blind electrodes 4a and 4b are formed in a meshed state. The excitation electrode 4 is made of a single metal such as Al, Au, Cu, Cr, Ti, Pt, or an alloy thereof, and is formed on the surface 3a of the piezoelectric substrate 3 by photolithography, sputtering, or the like. Further, one of the blind electrodes 4a of the excitation electrode 4 is electrically connected to the antenna 8, and the other blind electrode 4b is grounded. The excitation electrode 4 having such a configuration excites a surface acoustic wave on the surface 3a in response to an AC signal applied by the antenna 8. The frequency (excitation frequency) of the AC signal that can be excited by the excitation electrode 4 is limited to a predetermined frequency range by the shapes of the two blind electrodes 4a and 4b. That is, the excitation electrode 4 generates surface acoustic waves propagating in two directions, one is from the center of the surface 3a toward one end and the other is from the center of the surface 3a toward the other end. ..

The antenna 8 is electrically connected to one of the blind electrodes 4a of the excitation electrode 4, receives an AC signal wirelessly from the transmission / reception device 1, converts the AC signal into an electric signal, and applies the AC signal to the excitation electrode 4. Further, the antenna 8 receives a reflected signal for the surface acoustic wave generated based on the AC signal as an electric signal via the excitation electrode 4, converts the reflected signal into a radio signal, and transmits the reflected signal to the transmission / reception device 1. ..

The first reflective electrode 5 is a conductive member formed separately from the excitation electrode 4 so as to face the excitation electrode 4 at the other end (right end in FIG. 2) on the surface 3a of the piezoelectric substrate 3. , Has the role of a reflector for receiving the surface acoustic wave generated by the excitation electrode 4 and generating a reflected wave for it. Specifically, the first reflective electrode 5 is a short-circuit type electrode having a plurality of linear portions 5a extending in parallel along the other end portion on the surface 3a and integrated with each other. These linear portions 5a are formed so that the formation ranges in the direction along the other end portion on the surface 3a overlap with the electrode fingers of the two blind electrodes 4a and 4b constituting the excitation electrode 4. There is. The first reflective electrode 5 may be composed of two blind electrodes as in the excitation electrode 4. The first reflecting electrode 5 is made of a metal simple substance or an alloy similar to that of the excitation electrode 4, and is formed by a forming method similar to that of the excitation electrode 4.

The mass-loaded film 7 is a rectangular film member (thin film) formed on the surface 3a between the excitation electrode 4 and the first reflection electrode 5 separated from the excitation electrode 4 and the first reflection electrode 5. .. Specifically, the mass loading film 7 extends along the arrangement direction of the excitation electrode 4 and the first reflection electrode 5 (direction perpendicular to the other end on the surface 3a), and is perpendicular to the arrangement direction. The formation range in the direction is formed so as to be wider than the meshing portion (overlapping portion of the electrode fingers) R1 of the two electrode-shaped electrodes 4a and 4b of the excitation electrode 4. The mass loading film 7 is formed of a material capable of generating a mass loading effect on the piezoelectric substrate 3, and includes gold (Au), silver (Ag), copper (Au), aluminum (Al), platinum (Pt), and the like. , An alloy containing any of these metals, or a dielectric material such as a polymer material typified by _{silicon dioxide (SiO 2) or polymethyl methacrylate resin (PMMA).} The "mass load effect" referred to here refers to the property of reducing the natural vibration frequency of the piezoelectric substrate 3 in proportion to the mass of the substance adhering to the piezoelectric substrate 3.

The second reflective electrode 6 is an electrode member formed separately from the excitation electrode 4 so as to face the excitation electrode 4 at one end (left end in FIG. 2) on the surface 3a of the piezoelectric substrate 3. , Has the role of a reflector for generating a reflected wave with respect to the surface acoustic wave generated by the excitation electrode 4. Specifically, the second reflective electrode 6 has the same configuration as the excitation electrode 4, and has two blind electrodes 6a and 6b. These stagnation electrodes 6a and 6b have electrode fingers extending in the same direction as the electrode fingers of the two stagnation electrodes 4a and 4b constituting the excitation electrode 4, and are oriented along one end on the surface 3a. The formation range of the electrode finger in the above is formed so as to overlap with the excitation electrode 4. The second reflective electrode 6 is made of a metal simple substance or an alloy similar to that of the excitation electrode 4, and is formed by a formation method similar to that of the excitation electrode 4.

Further, both ends of the impedance change type sensor element 10 are electrically connected to these blind electrodes 6a and 6b. The sensor element 10 is an element that detects predetermined measurement parameters such as an inclination amount, a vibration amount, a humidity, a temperature, and a pressure, and has a property that an impedance changes according to a change in the measurement parameters. For example, the sensor element 10 for detecting the amount of vibration includes a vibration power generation element and a variable diode whose impedance is changed according to the output of the vibration power generation element. The sensor element 10 is not limited to the impedance change type sensor, and may be a voltage change type, a current change type, or a magnetic change type sensor.

In the SAW sensor 2 having the above configuration, the recognition propagation path MP1 for identifying one SAW sensor 2 from the plurality of SAW sensors 2 and the measurement propagation path MP2 for measuring the measurement parameters Is configured. That is, a recognition propagation path MP1 is formed between the excitation electrode 4 on the surface 3a of the piezoelectric substrate 3 and the first reflection electrode 5, and the excitation electrode 4 and the second reflection electrode 6 on the surface 3a of the piezoelectric substrate 3 are formed. A propagation path MP2 for measurement is formed between the two.

Next, the identification function of the SAW sensor 2 and the detection function of the measurement parameters in the sensing system 100 will be described. The transmission / reception device 1 has a function of identifying the SAW sensor 2 and a function of detecting measurement parameters based on the reflected signal transmitted from the SAW sensor 2.

First, the identification function of the SAW sensor 2 by the transmission / reception device 1 will be described.

The transmission / reception device 1 transmits an AC signal from the transmission / reception device 1 to the SAW sensor 2 at a predetermined timing triggered by a user's instruction or the like. As a result, surface acoustic waves are excited by the excitation electrode 4 of the SAW sensor 2 in both the recognition propagation path MP1 and the measurement propagation path MP2. On the other hand, a reflected wave (first signal) is generated from the first reflecting electrode 5 toward the excitation electrode 4, but the surface acoustic wave in the recognition propagation path MP1 and the propagation velocity of the reflected wave are mass-loaded. It changes depending on the difference in the mass loading effect caused by the film 7.

Here, when the material of the piezoelectric substrate 3 _{is assumed to be lithium tantalate (128YX-LiTaO 3} ), the amount of change due to the mass loading effect of the propagation velocity of the surface acoustic wave is given by the following equation (1).

上記式（１）中、ΔＶ／Ｖは速度変化率、Ｖは非摂動時の弾性表面波の伝搬速度、ｈは質量負荷膜の厚さ、Ｐは圧電結晶の単位幅当たりのパワーフロー、ρ’は質量負荷膜の密度、λ’、μ’はラメの定数、ν_１は弾性表面波の伝搬方向の粒子速度、ν_３は弾性表面波の伝搬方向と伝搬面に垂直な方向の粒子速度である。圧電基板３の材料がタンタル酸リチウム（１２８ＹＸ−ＬｉＴａＯ_３）であり、励振の角周波数がωの場合には、
Ｖ＝３８８４．４ｍ／ｓ、
ν_１／ｓｑｒｔ（Ｐ）＝２．２０６５Ｅ−０６×ｓｑｒｔ（ω）、
ν_３／ｓｑｒｔ（Ｐ）＝２．９４６８Ｅ−０６×ｓｑｒｔ（ω）
で与えられるので、質量負荷膜の材料定数に対して速度変化ΔＶを計算することができる。さらに、その速度変化ΔＶを基に、質量負荷膜７の伝搬方向（励振電極４と第１反射電極５の配列方向）の長さＬを考慮すれば、励振電極４と第１反射電極５との間を往復する反射波の伝搬時間差Δｔを計算することができる。

In the above equation (1), ΔV / V is the rate of change in velocity, V is the propagation velocity of surface acoustic waves when not perturbed, h is the thickness of the mass-loaded film, P is the power flow per unit width of the piezoelectric crystal, and ρ. 'Is the density of the mass-loaded film, λ'and μ'are the constants of lame, ν ₁ is the particle velocity in the _{surface acoustic wave propagation direction, and ν 3} is the particle velocity in the surface acoustic wave propagation direction and the direction perpendicular to the propagation plane. Is. When the material of the piezoelectric substrate 3 is lithium tantalate (128YX-LiTaO ₃ ) and the angular frequency of excitation is ω,
V = 3884.4 m / s,
ν _{1 /} square (P) = 2.2065E-06 × square (ω),
ν _{3 /} square (P) = 2.9468E-06 × square (ω)
Since it is given by, the velocity change ΔV can be calculated with respect to the material constant of the mass-loaded membrane. Further, if the length L in the propagation direction of the mass load film 7 (arrangement direction of the excitation electrode 4 and the first reflection electrode 5) is taken into consideration based on the velocity change ΔV, the excitation electrode 4 and the first reflection electrode 5 The propagation time difference Δt of the reflected wave reciprocating between the two can be calculated.

For example, when the length L of the mass-loaded membrane 7 is 100 μm, the material of the mass-loaded membrane 7 is Au, and the thickness h of the mass-loaded membrane 7 is variously changed, the propagation time difference Δt for each excitation frequency is shown in the table below. It can be calculated as 1.

また、上記の場合に対して質量負荷膜７の長さＬ＝５００μｍに変更した場合には、各励振周波数に対する伝搬時間差Δｔは、下記の表２のように計算できる。

Further, when the length L of the mass loading film 7 is changed to 500 μm with respect to the above case, the propagation time difference Δt for each excitation frequency can be calculated as shown in Table 2 below.

さらに、表１の場合に対して質量負荷膜７の材料をＡｌに変更した場合、各励振周波数に対する伝搬時間差Δｔは、下記の表３のように計算でき、表２の場合に対して質量負荷膜７の材料をＡｌに変更した場合、各励振周波数に対する伝搬時間差Δｔは、下記の表４のように計算できる。

Further, when the material of the mass loading film 7 is changed to Al as compared with the case of Table 1, the propagation time difference Δt for each excitation frequency can be calculated as shown in Table 3 below, and the mass loading with respect to the case of Table 2 can be calculated. When the material of the film 7 is changed to Al, the propagation time difference Δt for each excitation frequency can be calculated as shown in Table 4 below.

表１〜表４の計算結果に示すように、同じ励振周波数であっても質量負荷膜７の膜厚ｈあるいは材料を変えると伝搬時間差Δｔが異なる。

As shown in the calculation results of Tables 1 to 4, the propagation time difference Δt is different when the film thickness h or the material of the mass loading film 7 is changed even if the excitation frequency is the same.

Using the calculation result of the above theoretical formula (1), the transmission / reception device 1 can identify each SAW sensor 2 from the plurality of SAW sensors 2. That is, if a plurality of SAW sensors 2 having the same thickness h and length L but different materials are formed and have the same surface acoustic wave excitation frequency, each SAW sensor 2 can be targeted. The material of the mass-loaded membrane 7 can be determined from the propagation time difference Δt detected in the above, and each SAW sensor can be identified from the determination result. Specifically, if three SAW sensors 2 having no film, material A, and material B having a mass load film 7 formed therein are prepared, the three SAW sensors 2 can be identified. Further, even if a plurality of SAW sensors 2 having the same thickness h and different lengths L are formed of the same material and have the same excitation frequency, the length L is determined for each of the SAW sensors 2. The SAW sensor 2 can be identified. Further, even if a plurality of SAW sensors 2 having the same length L and materials having different thicknesses h are formed and a plurality of SAW sensors 2 having the same excitation frequency are prepared, each of them is determined by determining the thickness h. The SAW sensor 2 can be identified. Further, even if a plurality of SAW sensors 2 having the same length L, the same material, and the same thickness h are formed and have different excitation frequencies, each SAW sensor 2 is prepared while changing the frequency of the AC signal. Each SAW sensor 2 can be identified by determining the excitation frequency. Further, if a plurality of SAW sensors 2 configured by combining a plurality of parameters of these materials, length L, thickness h, and excitation frequency so that the values of any of the parameters differ among the sensors, further A large number of SAW sensors 2 can be identified.

Specifically, when the transmission / reception device 1 identifies the SAW sensor 2, the time waveform of the reference signal that is the basis of the AC signal transmitted to the SAW sensor 2 and the propagation path for recognition from the SAW sensor 2 The phase difference between the reflected signal received via MP1 and the time waveform is detected. FIG. 4 shows images of the time waveforms WF0 and WF1 of the reference signal and the reflected signal detected by the transmission / reception device 1. The transmission / reception device 1 refers to the value of the propagation time difference Δt calculated by the theoretical formula (1), and obtains the propagation time difference calculated from the phase difference between the reference signal and the reflected signal detected for the plurality of SAW sensors 2. Each SAW sensor 2 can be identified by relative comparison.

Next, the processing procedure of the measurement parameter detection function by the transmission / reception device 1 will be described. In the transmission / reception device 1, the reflected signal (second signal) from the SAW sensor 2 identified as described above via the measurement propagation path MP2 is received. In this reflected signal, the reflectance changes according to the impedance change due to the change in the measurement parameter of the sensor element 10. Using such a property, the transmission / reception device 1 can detect the measurement parameter by detecting the change in the amplitude of the reflected signal.

The action and effect of this embodiment will be described.

According to the sensing system 100 of the present embodiment, the transmission / reception device 1 that receives the reflected signal from the SAW sensor 2 enables sensing of a desired measurement parameter using the reflected signal that has passed through the measurement propagation path MP2. In addition, the transmission / reception device 1 can receive the reflected signal via the recognition propagation path MP1 having a propagation time difference Δt according to the characteristics of the mass load film 7, and the transmission / reception device 1 is the basis of the AC signal. The delay time of the reflected signal can be evaluated based on the phase difference between the reference signal and the reflected signal. Then, in the transmission / reception device 1, the individual SAW sensors 2 can be identified by relatively comparing the evaluation results of the delay time. As a result, highly accurate identification between the plurality of SAW sensors 2 can be realized without complicating the configuration for generating the surface acoustic wave for identification.

Here, the transmission / reception device 1 is based on the material of the mass load film 7, the length L of the mass load film 7 in the arrangement direction of the excitation electrode 4 and the first reflection electrode 5, and the thickness h of the mass load film 7. The SAW sensor 2 is identified based on the calculated value of the propagation time difference Δt calculated and the phase difference between the reference signal and the reflected signal. With such a function, when sensing is performed using a plurality of SAW sensors 2 in which any of the material, the length L, and the thickness h of the mass loading film 7 is set variously, the plurality of SAW sensors 2 can be used. It can be identified accurately. In addition, the SAW sensor 2 can easily process the mass loading film 7 having desired characteristics.

According to the configuration of the SAW sensor 2 of the present embodiment, an AC signal of a predetermined frequency is applied to the excitation electrode 4 on the piezoelectric substrate 3 from the outside via the antenna 8, so that the excitation electrode 4 on the piezoelectric substrate 3 A surface acoustic wave is excited, and the surface acoustic wave is propagated on the piezoelectric substrate 3 toward the first reflecting electrode 5 and the second reflecting electrode 6. Then, the elastic surface wave is reflected by the first reflection electrode 5 to generate a reflected signal, and the reflected signal is transmitted to the outside as a radio signal via the excitation electrode 4 and the antenna 8, while the elastic surface wave is the first. 2 Reflected by the reflecting electrode 6, a reflected signal is generated, and the reflected signal is transmitted to the outside as a radio signal via the excitation electrode 4 and the antenna 8. Since the impedance change type sensor element 10 is electrically connected to the second reflecting electrode 6, the transmission / reception device 1 that has received the reflected signal enables sensing of a desired measurement parameter using the reflected signal. .. In addition, since the mass load film 7 is provided on the piezoelectric substrate 3 between the excitation electrode 4 and the first reflection electrode 5, the transmission / reception device 1 reflects the delay time according to the characteristics of the mass load film 7. The signal can be received, and the SAW sensor 2 can be identified based on the delay time of the transmission / reception device 1. As a result, highly accurate identification between the plurality of SAW sensors 2 can be realized without complicating the configuration for generating the surface acoustic wave for identification.

Here, since the mass loading film 7 has a rectangular shape along the propagation direction of the surface acoustic wave, the mass is relative to the surface acoustic wave generated from the excitation electrode 4 and propagated toward the first reflecting electrode 5. The load effect can be stably given, and the identification of the SAW sensor 2 by the external device is stabilized. Further, since the mass loading film 7 is formed of a metal or a dielectric material, the mass loading effect of the mass loading film 7 can be stabilized. In particular, when the mass loading film 7 is formed of a metal such as gold, silver, copper, aluminum, or platinum, the mass loading film 7 can be easily formed on the piezoelectric substrate 3.

Further, the excitation electrode 4 has two comb-shaped blind electrodes 4a and 4b arranged in mesh with each other, and the mass loading film 7 is perpendicular to the arrangement direction of the excitation electrode 4 and the first reflection electrode 5. In the direction, it is formed so as to be wider than the meshing portion R1 of the two blind electrodes 4a and 4b. With such a configuration, the mass load effect can be efficiently given to the surface acoustic wave generated from the excitation electrode 4 and propagated toward the first reflection electrode 5, and the accuracy of identification of the sensor element by the external device can be obtained. Can be further enhanced.

As the conventional configuration of the sensor element that enables identification, a configuration in which the number of reflecting electrodes is changed and a configuration in which the distance of the reflecting electrode from the excitation electrode is changed have been used. However, in this conventional configuration, the amplitude of the reflected signal is detected for identification. Therefore, when the distance between the transmitter / receiver and the sensor element changes, the propagation distance of the radio wave changes, and as a result, the amplitude of the reflected signal changes, so that the accuracy of identification decreases. In addition, multiple reflections between the reflecting electrodes are also included, so that the accuracy of identification is lowered. On the other hand, in the present embodiment, the phase difference is used and multiple reflections do not occur, so that the identification accuracy does not deteriorate. As another conventional recognition method, the use of the orthogonal frequency method has also been proposed. In this case, by inputting a wide band signal to the chirp-type blind electrode and utilizing the frequency characteristics of the reflecting electrode, it is possible to distinguish between the position and frequency of the reflecting electrode. However, in the orthogonal frequency method, it is necessary to use a wide band signal, which cannot be realized by using a specific low power band having a narrow bandwidth. In addition, the function of the transmitter / receiver becomes complicated, and the power consumption also increases. On the other hand, in the present embodiment, it is not necessary to use a wideband signal and it can be used in a specific low power band, and it can be realized by a simple configuration with low power consumption. For example, even when only a signal having a narrow bandwidth such as a specific low power band (920 MHz) can be used and only one excitation frequency can be used, it is possible to identify a large number of elements.

The present invention is not limited to the above-described embodiments.

In the SAW sensor 2 according to the above embodiment, the mass load film 7 is formed on the piezoelectric substrate 3 separately from the excitation electrode 4 and the first reflection electrode 5, but the mass load film 7 is formed of a dielectric material. If so, it may be formed in contact with the excitation electrode 4 or the first reflection electrode 5. FIG. 5 is a plan view of the SAW sensor 2A according to the modified example as viewed from the surface 3a side of the piezoelectric substrate 3. In this way, the mass loading film 7 may be formed so as to be in contact with the excitation electrode 4 and cover the first reflection electrode 5. In this modification, when evaluating the propagation time difference Δt, the distance between the excitation electrode 4 and the first reflecting electrode 5 is used as the length L of the mass loading film 7.

Further, the recognition propagation path MP1 and the measurement propagation path MP2 may be arranged in parallel as in the SAW sensor 2B according to the modification shown in FIG. Specifically, the excitation electrode 24 is formed at one end (left end in FIG. 6) on the surface 3a of the piezoelectric substrate 3, and two sets of blind electrode pairs 24a and 24b connected to the antenna 8 are on the surface. It has an integrated configuration on the central side of 3a. The second reflective electrode 6 is formed at the other end (right end in FIG. 6) on the surface 3a so as to face one blind electrode pair 24a, and the one blind electrode pair 24a and the second reflective electrode 6 are formed. A propagation path MP2 for measurement is formed between 6 and 6. The first reflective electrode 5 is formed at the other end on the surface 3a so as to face the other blind electrode pair 24b, and is used for measurement between the other blind electrode pair 24b and the first reflective electrode 5. The recognition propagation path MP1 is formed in parallel with the propagation path MP2.

Further, in the SAW sensor 2 according to the above embodiment, the positions of the excitation electrode 4, the first reflecting electrode 5, and the second reflecting electrode 6 may be interchanged. For example, the positions of the excitation electrode 4 and the second reflection electrode 6 may be exchanged as in the SAW sensor 2C according to the modification shown in FIG. In the case of such a configuration, the measurement propagation path MP2 and the recognition propagation path MP1 are partially formed in the same range on the surface 3a. FIG. 8 shows an image of the time waveforms WF2 and WF3 of the reflected signal detected by using the SAW sensor 2C. When an AC signal that is a burst wave is transmitted from the transmission / reception device 1, the time of the reflected signal passing through the recognition propagation path MP1 after the time waveform WF2 of the reflected signal passing through the measurement propagation path MP2 is detected. Waveform WF3 is detected. Also in this modification, the transmission / reception device 1 can identify the SAW sensor by using the time waveform WF0 of the reference signal and the time waveform WF3 of the reflected signal. However, when a burst signal is used as the AC signal, each SAW sensor 2 can be identified by relatively comparing the rising time difference between the time waveform WF0 of the reflected signal and the time waveform WF3 of the reflected signal. it can.

Further, the shapes of the first reflecting electrode 5 and the second reflecting electrode 6 in the above embodiment and the above modified example are the shape of a blind electrode or the shape of a short circuit, and a plurality of linear electrodes are arranged in parallel. The shape may be a parallel line type (shape of an open electrode).

Further, the shape of the mass loading film 7 in the above embodiment and the above modified example is not limited to a rectangular shape, and may be various shapes within a range in which surface acoustic waves are transmitted. Further, the mass loading film 7 does not have to have a uniform thickness within the range in which the surface acoustic wave propagates, and may have a configuration in which the propagation velocity changes by changing the thickness. Further, the mass loading film 7 may be formed by stacking a plurality of layers, and in that case, the material of each layer has a different structure (a structure having a dielectric layer and a metal layer, and having two types of metal layers. Configuration, etc.).

Further, in the above embodiment and the above modification, the signal frequency for measurement and the signal frequency for recognition may be different. In this case, an antenna for transmitting and receiving the measurement signal and an antenna for transmitting and receiving the recognition signal may be provided separately.

As the sensor element 10 used in the above embodiment and the above modification, a sensor capable of various sensing can be used. For example, a pressure sensor, a strain sensor, a temperature sensor, a humidity sensor, a twist sensor, a chemical sensor, a biosensor and the like can be used.

Further, in the above-described embodiment and the above-described modification, a reflected wave is generated by the first reflecting electrode 5 in response to the surface acoustic wave propagating from the excitation electrode 4 on the piezoelectric substrate 3 in the recognition propagation path MP1, and propagated for measurement. In the path MP2, the second reflecting electrode 6 generates a reflected wave according to the surface acoustic wave. On the other hand, in the recognition propagation path MP1, the surface acoustic wave may be directly received by the electrode, converted into an electric signal, and the wireless signal is transmitted to the outside via the antenna, or the measurement propagation path MP2 may be used. The surface acoustic wave may be directly received by the electrode, converted into an electric signal, and transmitted to the outside via the antenna. Both the recognition propagation path MP1 and the measurement propagation path MP2 may be configured to directly transmit a radio signal to the outside, or only one of them may be configured as such. FIG. 9 shows the configuration of the SAW sensor 2D according to the modified example. In this SAW sensor 2D, instead of the first reflection electrode 5, an electrode (first electrode) 105 that directly receives an elastic surface wave excited by the excitation electrode 4 on the recognition propagation path MP1 and generates an electric signal. Is provided, and the electrode 105 is electrically connected to an antenna 108a that converts the electric signal into a radio signal and transmits the electric signal to the transmission / reception device 1. The electrode 105 has a structure similar to that of the excitation electrode 4, for example. Further, in the SAW sensor 2D, the electrode (second electrode) 6 is configured to directly receive a surface acoustic wave to generate an electric signal, and the electrode 6 converts the electric signal into a radio signal for transmission and reception. The antenna 108b to be transmitted to the device 1 is electrically connected.

The sensing system 100 including a plurality of SAW sensors 2D of the above-described modification has the following SAW sensor 2 identification function. That is, each design value of the mass loading membrane 7 and the propagation time difference Δt for each excitation frequency are calculated in advance as a one-way propagation time difference between the excitation electrode 4 and the electrode 105, and are held as data in the transmission / reception device 1. .. Then, the transmission / reception device 1 can identify the SAW sensor 2D by determining the characteristics of the material or the like of the mass load film 7 of the SAW sensor 2D or the excitation frequency of the SAW sensor 2D based on the propagation time difference Δt.

1 ... Transmitter / receiver, 2,2A, 2B, 2C, 2D ... SAW sensor (recognition signal generation element), 3 ... piezoelectric substrate (piezoelectric material), 3a ... surface, 4,24 ... excitation electrode, 4a, 4b ... Electrodes, 5 ... 1st reflective electrode (1st electrode), 105 ... Electrode (1st electrode) 6 ... 2nd reflective electrode (2nd electrode), 7 ... Mass loading film (thin film), 8 ... Antenna, 10 ... sensor element (sensor), 100 ... sensing system (element recognition system), R1 ... meshing portion.

Claims (9)

Piezoelectric material with a planar shape and
An excitation electrode formed on the surface of the piezoelectric body and for exciting a surface acoustic wave on the surface in response to an AC signal having a predetermined frequency received from the outside,
At least one antenna that is electrically connected to the excitation electrode, receives the AC signal to generate the surface acoustic wave, and transmits a signal generated in response to the surface acoustic wave to the outside.
A first electrode formed on the surface separately from the excitation electrode and receiving the surface acoustic wave to generate the signal,
A thin film formed on the surface between the excitation electrode and the first electrode,
A second electrode electrically connected to the sensor, which is formed on the surface of the surface separately from the excitation electrode and receives the surface acoustic wave from the excitation electrode to generate the signal.
A recognition signal generation element comprising. The first electrode reflects the surface acoustic wave toward the excitation electrode.
The at least one antenna transmits a reflected signal generated by the excitation electrode by the reflected surface acoustic wave to the outside.
The recognition signal generation element according to claim 1. The thin film has a rectangular shape along the arrangement direction of the excitation electrode and the first electrode.
The recognition signal generation element according to claim 1 or 2. The excitation electrode has two comb-shaped electrodes arranged in mesh with each other.
The thin film is formed so as to be wider than the meshing portion of the two comb-shaped electrodes in a direction perpendicular to the arrangement direction of the excitation electrode and the first electrode.
The recognition signal generation element according to any one of claims 1 to 3. The thin film comprises a metal or dielectric material.
The recognition signal generation element according to any one of claims 1 to 4. The thin film comprises an alloy of gold, silver, copper, aluminum, platinum, or any of gold, silver, copper, aluminum, and platinum.
The recognition signal generation element according to claim 5. The recognition signal generation element according to any one of claims 1 to 6,
The AC signal is transmitted to the recognition signal generation element, and each of the first signal and the second signal generated by the first electrode and the second electrode according to the surface acoustic wave is at least one. A transmitter / receiver that receives via two antennas, identifies the recognition signal generating element based on the phase difference or time difference between the AC signal and the first signal, and senses using the second signal. When,
Element recognition system with. The transmitter / receiver is based on the phase difference or the time difference, the material of the thin film, the length of the thin film in the arrangement direction of the excitation electrode and the first electrode, the thickness of the thin film, and the elasticity of the thin film. The recognition signal generation element is identified by determining one of the excitation frequencies of the surface wave.
The element recognition system according to claim 7. A plurality of the recognition signal generating elements are provided, and the material of the thin film, the length of the thin film, the thickness of the thin film, and the excitation frequency are different among the plurality of recognition signal generating elements. ,
The element recognition system according to claim 8.

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