Sensor Device

Abstract

To reduce the influence from a factor different from a sensing object in a no-power supply wireless using an IDT.SOLUTION: A first IDT 110 is electrically connected to a first antenna 112. The first IDT 110 is positioned on a first piezoelectric substrate 100. A second IDT 120 is electrically connected to a first sensor 122. The first sensor 122 has an impedance that changes depending on the physical quantity from the outside. The second IDT 120 is positioned on the first piezoelectric substrate 100 while being opposite to the first IDT 110 with a first distance D1 therebetween. A third IDT 210 is electrically connected to a second antenna 212. The third IDT 210 is positioned on a second piezoelectric substrate 200. A fourth IDT 220 is positioned on the second piezoelectric substrate 200 while being opposite to the third IDT 210 with a second distance D2 therebetween. The second distance D2 is different from the first distance D1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sensor device, and more particularly to a non-powered wireless sensor using an interdigital transducer (IDT). [Background technology]

[0002] In a non-powered wireless sensor, an IDT is used. The IDT has a pair of comb-shaped electrodes and can convert between a surface acoustic wave (SAW) and an electrical signal.

[0003] Patent Document 1 describes an example of a non-powered wireless sensor using an IDT. The sensor device of Patent Document 1 includes a piezoelectric substrate, a first interdigital transducer (IDT), and a second IDT. The first IDT and the second IDT are located on the piezoelectric substrate facing each other. The first IDT is electrically connected to an antenna that transmits and receives radio waves to and from an external antenna. The second IDT is electrically connected to a sensor having an impedance that changes according to a physical quantity from the outside. The first IDT generates a SAW on the piezoelectric substrate in response to radio waves from the external antenna. The SAW generated by the first IDT is reflected by the second IDT. The reflectance of the second IDT varies depending on the impedance of the sensor.

[0004] Non-Patent Document 1 describes an example of a temperature measurement method using a SAW temperature sensor. In this example, a method is considered in which a rough temperature is obtained from a delay time difference, and a detailed temperature is obtained from a phase difference. According to Non-Patent Document 1, a necessary condition for temperature calculation in this method is that the temperature width per 2π obtained from the phase difference is larger than the temperature fluctuation obtained from the delay time difference. With two reflectors, the temperature width per 2π obtained from the phase difference cannot be made larger than the temperature fluctuation obtained from the delay time difference. In contrast, by using three reflectors, the temperature width per 2π obtained from the phase difference can be made larger than the temperature fluctuation obtained from the delay time difference. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-255706 A [Non-patent literature]

[0006] [Non-Patent Document 1] Takahiro Kudo, Takuya Furuichi, Michio Kadota, Shuji Tanaka, Akira Morita, "Passive Wireless SAW Temperature Sensor System for Specified Low Power Radio Stations", IEEJ Transactions on Sensors and Micromachines, Vol. 139, No. 5, pp. 103-108 Summary of the Invention [Problem to be solved by the invention]

[0007] For example, sensing by the sensor device described in Patent Document 1 may be affected by various factors different from the sensing target, such as the distance between the antenna and an external antenna, other external environments, etc. The present inventors have investigated reducing the influence of factors different from the sensing target in a non-powered wireless system using an IDT.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to reduce the influence of factors other than the sensing target in a non-powered wireless sensor using an IDT. [Means for solving the problem]

[0009] The sensor device according to the present invention includes a first piezoelectric substrate, a first IDT, a second IDT, a second piezoelectric substrate, a third IDT, and a fourth IDT. The first IDT is electrically connected to a first antenna for transmitting and receiving radio waves to and from an external antenna. The first IDT is located on the first piezoelectric substrate. The second IDT is electrically connected to a first sensor having an impedance that changes according to a physical quantity from the outside. The second IDT is located on the first piezoelectric substrate, facing the first IDT at a first distance. The third IDT is electrically connected to a second antenna for transmitting and receiving radio waves to and from the external antenna. The third IDT is located on the second piezoelectric substrate. The fourth IDT is located on the second piezoelectric substrate, facing the third IDT at a second distance different from the first distance. Effect of the Invention

[0010] According to the present invention, it is possible to reduce the influence of factors different from the sensing target in a non-powered wireless sensor using an IDT. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a sensor device according to a first embodiment. [Diagram 2] FIG. 11 is a diagram showing a sensor device according to a second embodiment. [Diagram 3] FIG. 11 is a diagram showing a sensor device according to a third embodiment. [Figure 4] 4 is a graph showing signals generated by FMCW (frequency modulated continuous wave) from radio waves transmitted from an external antenna and radio waves received by the external antenna in the sensor device shown in FIG. 3. [Diagram 5] FIG. 13 is a diagram showing a sensor device according to a fourth embodiment. [Figure 6] 6 is a graph showing signals generated by FMCW (frequency modulated continuous wave) from radio waves transmitted from an external antenna and radio waves received by the external antenna in the sensor device shown in FIG. 5. [Figure 7]FIG. 13 is a diagram showing a sensor device according to a fifth embodiment. [Figure 8] 10 is a graph showing an example of a schematic relationship between the impedance connected to a second IDT and the level of a signal generated by the second IDT. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0013] (Embodiment 1) FIG. 1 is a diagram showing a sensor device 10 according to the first embodiment.

[0014] The sensor device 10 includes a first piezoelectric substrate 100, a first interdigital transducer (IDT) 110, a second IDT 120, a second piezoelectric substrate 200, a third IDT 210, a fourth IDT 220, and a host device 300. The host device 300 includes a measuring device 302 and an external antenna 312.

[0015] An overview of the sensor device 10 will be described with reference to FIG. 1. The first IDT 110 is electrically connected to the first antenna 112. The first antenna 112 is for transmitting and receiving radio waves to and from the external antenna 312. The first IDT 110 is located on the first piezoelectric substrate 100. The second IDT 120 is electrically connected to the first sensor 122. The first sensor 122 has an impedance that changes depending on a physical quantity from the outside. The second IDT 120 is located on the first piezoelectric substrate 100, facing the first IDT 110 at a first distance D1. The third IDT 210 is electrically connected to the second antenna 212. The second antenna 212 is for transmitting and receiving radio waves to and from the external antenna 312. The third IDT 210 is located on the second piezoelectric substrate 200. The fourth IDT 220 is located on the second piezoelectric substrate 200, facing the third IDT 210 at a second distance D2. The second distance D2 is different from the first distance D1. In this embodiment, the fourth IDT 220 is electrically connected to the second sensor 222. The second sensor 222 has an impedance that changes depending on a physical quantity from the outside. However, the fourth IDT 220 does not have to be electrically connected to the second sensor 222.

[0016] The sensor device 10 will be described in detail with reference to FIG.

[0017] The first piezoelectric substrate 100 generates a surface acoustic wave (SAW) by the piezoelectric effect and propagates the generated SAW. The first piezoelectric substrate 100 is made of a material that is capable of generating and propagating a SAW.

[0018] The first piezoelectric substrate 100 has a parallelogram shape and has a first side 102a, a second side 102b, a third side 102c, and a fourth side 102d. The second side 102b is on the opposite side to the first side 102a. The third side 102c is oblique to the first side 102a and the second side 102b. The fourth side 102d is on the opposite side to the third side 102c. The SAW in the first piezoelectric substrate 100 propagates along the extension direction of the first side 102a or the second side 102b. The sides oblique to the propagation direction of the SAW (i.e., the third side 102c and the fourth side 102d in the example shown in FIG. 1) can function as anti-reflection portions. The inclination θ1 of the third side 102c and the fourth side 102d relative to the first side 102a and the second side 102b (the angle of the acute angle among the four corners of the parallelogram of the first piezoelectric substrate 100) can be, for example, 60°.

[0019] The shape of the first piezoelectric substrate 100 is not limited to the example shown in FIG. 1. For example, the first piezoelectric substrate 100 may have a rectangular shape. In this case, the first IDT 110 and the second IDT 120 can be arranged diagonally with respect to the extension direction of a pair of opposing sides (for example, sides corresponding to the first side 102a and the second side 102b in FIG. 1) among the four sides of the rectangle. In this way, two opposing corners of the rectangle and their surroundings can function as an anti-reflection portion. Furthermore, a pair of opposing sides among the four sides of the rectangle may have an uneven shape. In this case, by arranging the first IDT 110 and the second IDT 120 between the pair of opposing sides having an uneven shape, the pair of opposing sides having an uneven shape can function as an anti-reflection portion.

[0020] The above-mentioned points regarding the first piezoelectric substrate 100 are also applicable to the second piezoelectric substrate 200. For example, the fifth side 202a, the sixth side 202b, the seventh side 202c, the eighth side 202d, and the inclination θ2 of the second piezoelectric substrate 200 correspond to the first side 102a, the second side 102b, the third side 102c, the fourth side 102d, and the inclination θ1 of the first piezoelectric substrate 100, respectively. In this embodiment, the shape and material of the second piezoelectric substrate 200 are the same as those of the first piezoelectric substrate 100, respectively. However, at least one of the shape and material of the second piezoelectric substrate 200 may be different from those of the first piezoelectric substrate 100, respectively.

[0021] The first piezoelectric substrate 100 and the second piezoelectric substrate 200 are disposed apart from each other. In the example shown in FIG. 1, the first piezoelectric substrate 100 and the second piezoelectric substrate 200 are disposed side by side, and the first side 102a and the second side 102b of the first piezoelectric substrate 100 are parallel to the fifth side 202a and the sixth side 202b of the second piezoelectric substrate 200. However, the arrangement of the first piezoelectric substrate 100 and the second piezoelectric substrate 200 is not limited to the example shown in FIG. 1. For example, the first side 102a and the second side 102b of the first piezoelectric substrate 100 may not be parallel to the fifth side 202a and the sixth side 202b of the second piezoelectric substrate 200. Alternatively, the first piezoelectric substrate 100 and the second piezoelectric substrate 200 may overlap each other in the thickness direction of the first piezoelectric substrate 100 or the second piezoelectric substrate 200. In other words, as long as radio waves can reach between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100, and between the external antenna 312 of the host device 300 and the second antenna 212 of the second piezoelectric substrate 200, the arrangement of the first piezoelectric substrate 100 and the second piezoelectric substrate 200 is not particularly limited.

[0022] The first IDT 110 has a pair of comb-shaped electrodes, one of which is electrically connected to the first antenna 112, and the other of which is grounded.

[0023] The second IDT 120 has a pair of comb-shaped electrodes. The second IDT 120 (the pair of comb-shaped electrodes) is electrically connected to the first sensor 122.

[0024] The first sensor 122 has an impedance that changes depending on a physical quantity from the outside. The first sensor 122 can detect the physical quantity from the outside by the change in impedance. For example, the first sensor 122 can be a thermistor. In this example, the impedance of the first sensor 122 changes depending on the temperature. The physical quantity detected by the first sensor 122 may be not only temperature but also other physical quantities, for example, light, sound, ultrasound (vibration), pressure, humidity, gas, electric field, or magnetic field.

[0025] 1, the second IDT 120 faces the first IDT 110 in the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100. Therefore, a SAW can be propagated between the first IDT 110 and the second IDT 120 along the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100.

[0026] The points described above regarding the first IDT 110, the first antenna 112, the second IDT 120, and the first sensor 122 of the first piezoelectric substrate 100 are also applicable to the third IDT 210, the second antenna 212, the fourth IDT 220, and the second sensor 222 of the second piezoelectric substrate 200, respectively.

[0027] A second distance D2 between the third IDT 210 and the fourth IDT 220 of the second piezoelectric substrate 200 in the propagation direction of the SAW between them (in the example shown in FIG. 1, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) is longer than a first distance D1 between the first IDT 110 and the second IDT 120 of the first piezoelectric substrate 100 in the propagation direction of the SAW between them (in the example shown in FIG. 1, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100). However, the second distance D2 may be shorter than the first distance D1. In this embodiment, the first distance D1 is the distance between the center of the multiple comb-tooth portions of the first IDT 110 (in the example shown in FIG. 1, six comb-tooth portions of a pair of comb-tooth electrodes of the first IDT 110) in the propagation direction of the SAW between the first IDT 110 and the second IDT 120 (in the example shown in FIG. 1, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) and the center of the multiple comb-tooth portions of the second IDT 120 (in the example shown in FIG. 1, six comb-tooth portions of a pair of comb-tooth electrodes of the second IDT 120) in the propagation direction of the SAW between the first IDT 110 and the second IDT 120 (in the example shown in FIG. 1, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) (the distance in the propagation direction of the SAW between the first IDT 110 and the second IDT 120). The second distance D2 is the distance between the center of the multiple comb-tooth portions of the third IDT 210 (in the example shown in FIG. 1, six comb-tooth portions of a pair of comb-tooth electrodes of the third IDT 210) in the propagation direction of the SAW between the third IDT 210 and the fourth IDT 220 (in the example shown in FIG. 1, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) and the center of the multiple comb-tooth portions of the fourth IDT 220 (in the example shown in FIG. 1, six comb-tooth portions of a pair of comb-tooth electrodes of the fourth IDT 220) in the propagation direction of the SAW between the third IDT 210 and the fourth IDT 220 (in the example shown in FIG. 1, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) (the distance in the propagation direction of the SAW between the third IDT 210 and the fourth IDT 220).

[0028] The host device 300 is located away from both the first piezoelectric substrate 100 and the second piezoelectric substrate 200. The distance between the first antenna 112 of the first piezoelectric substrate 100 and the external antenna 312 of the host device 300 and the distance between the second antenna 212 of the second piezoelectric substrate 200 and the external antenna 312 of the host device 300 may be equal to or different from the distance between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100 and the distance between the external antenna 312 of the host device 300 and the second antenna 212 of the second piezoelectric substrate 200 may be within a range where radio waves can reach.

[0029] An example of the operation of the sensor device 10 will be described with reference to FIG.

[0030] The external antenna 312 of the host device 300 transmits radio waves to the first antenna 112 of the first piezoelectric substrate 100. The first antenna 112 generates a high-frequency signal corresponding to the radio waves transmitted from the external antenna 312. The first IDT 110 generates a SAW in the first piezoelectric substrate 100 corresponding to the high-frequency signal generated by the external antenna 312. The SAW generated by the first IDT 110 propagates through the first piezoelectric substrate 100 and is reflected by the second IDT 120. The reflectance of the second IDT 120 varies depending on the impedance of the first sensor 122. Therefore, the SAW reflected from the second IDT 120 corresponds to the impedance of the first sensor 122. The first IDT 110 generates a high-frequency signal corresponding to the SAW reflected from the second IDT 120. The first antenna 112 transmits radio waves corresponding to the high-frequency signal generated by the first IDT 110 to the external antenna 312 of the host device 300. The host device 300 analyzes the radio waves received by the external antenna 312 .

[0031] The external antenna 312 of the host device 300 transmits radio waves to the second antenna 212 of the second piezoelectric substrate 200. The second antenna 212 generates a high-frequency signal corresponding to the radio waves transmitted from the external antenna 312. The third IDT 210 generates a SAW in the second piezoelectric substrate 200 corresponding to the high-frequency signal generated by the external antenna 312. The SAW generated by the third IDT 210 propagates through the second piezoelectric substrate 200 and is reflected by the fourth IDT 220. The reflectance of the fourth IDT 220 varies depending on the impedance of the second sensor 222. Therefore, the SAW reflected from the fourth IDT 220 corresponds to the impedance of the second sensor 222. The third IDT 210 generates a high-frequency signal corresponding to the SAW reflected from the fourth IDT 220. The second antenna 212 transmits radio waves corresponding to the high-frequency signal generated by the third IDT 210 to the external antenna 312 of the host device 300. The host device 300 analyzes the radio waves received by the external antenna 312 .

[0032] The measuring instrument 302 measures the difference between the time from the transmission of radio waves by the external antenna 312 to the first IDT 110 of the first piezoelectric substrate 100, through the propagation of the SAW between the first IDT 110 and the second IDT 120 of the first piezoelectric substrate 100, to the reception of the radio waves from the first IDT 110 of the first piezoelectric substrate 100 by the external antenna 312, and the time from the transmission of radio waves by the external antenna 312 to the third IDT 210 of the second piezoelectric substrate 200, through the propagation of the SAW between the third IDT 210 and the fourth IDT 220 of the second piezoelectric substrate 200, to the reception of the radio waves from the third IDT 210 of the second piezoelectric substrate 200 by the external antenna 312. Specifically, the measuring device 302 measures a delay difference between a signal generated by FMCW (frequency modulated continuous wave) from the radio wave transmitted from the external antenna 312 and the radio wave received by the external antenna 312 through SAW propagation between the first IDT 110 and the second IDT 120 of the first piezoelectric substrate 100, and a signal generated by FMCW from the radio wave transmitted from the external antenna 312 and the radio wave received by the external antenna 312 through SAW propagation between the third IDT 210 and the fourth IDT 220 of the second piezoelectric substrate 200. The strength of each signal generated by FMCW may vary depending on various factors different from the sensing target, such as the distance between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100, the distance between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100, and other external environments. In contrast, the above two time differences (delay differences) do not fluctuate due to these factors, but fluctuate according to the physical quantity measured by the first sensor 122 or the second sensor 222. Therefore, in this embodiment, it is possible to reduce the influence of factors other than the sensing target.

[0033] In this embodiment, the second IDT 120 is located on the fourth side 102d of the first piezoelectric substrate 100 relative to the first IDT 110, and the fourth IDT 220 is located on the eighth side 202d of the second piezoelectric substrate 200 relative to the third IDT 210. However, the second IDT 120 may be located on the third side 102c of the first piezoelectric substrate 100 relative to the first IDT 110, and the fourth IDT 220 may be located on the seventh side 202c of the second piezoelectric substrate 200 relative to the third IDT 210. In addition, when the second IDT 120 is located on the fourth side 102d of the first piezoelectric substrate 100 relative to the first IDT 110, the fourth IDT 220 may be located on the seventh side 202c of the second piezoelectric substrate 200 relative to the third IDT 210. Furthermore, when the second IDT 120 is located closer to the third side 102c of the first piezoelectric substrate 100 than the first IDT 110, the fourth IDT 220 may be located closer to the eighth side 202d of the second piezoelectric substrate 200 than the third IDT 210.

[0034] (Embodiment 2) 2 is a diagram showing the sensor device 10 according to embodiment 2. The sensor device 10 according to embodiment 2 is similar to the sensor device 10 according to embodiment 1 except for the following points.

[0035] The sensor device 10 further includes a fifth IDT 130 and a sixth IDT 230. The fifth IDT 130 is located on the first piezoelectric substrate 100 facing the first IDT 110 at a third distance D3. The third distance D3 is different from the first distance D1. The sixth IDT 230 is located on the second piezoelectric substrate 200 facing the third IDT 210 at a fourth distance D4. The fourth distance D4 is different from the third distance D3.

[0036] The fifth IDT 130 has a pair of comb-shaped electrodes. The fifth IDT 130 (the pair of comb-shaped electrodes) may not be electrically connected to a sensor (a sensor corresponding to the first sensor 122 electrically connected to the second IDT 120) as shown in FIG. 2, or may be electrically connected to the sensor.

[0037] In the first piezoelectric substrate 100, the fifth IDT 130 is located on the same side as the second IDT 120 with respect to the first IDT 110 (i.e., the side where the fourth side 102d of the first piezoelectric substrate 100 is located). However, the fifth IDT 130 may be located on the opposite side (i.e., the side where the third side 102c of the first piezoelectric substrate 100 is located) to the side where the second IDT 120 is located with respect to the first IDT 110 (i.e., the side where the fourth side 102d of the first piezoelectric substrate 100 is located).

[0038] 2, the fifth IDT 130 faces the first IDT 110 in the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100. Therefore, a SAW can be propagated between the first IDT 110 and the fifth IDT 130 along the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100.

[0039] The points described above regarding the fifth IDT 130 also apply to the sixth IDT 230 .

[0040] A fourth distance D4 between the third IDT 210 and the sixth IDT 230 of the second piezoelectric substrate 200 in the propagation direction of the SAW between them (in the example shown in FIG. 2, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) is longer than a third distance D3 between the first IDT 110 and the fifth IDT 130 of the first piezoelectric substrate 100 in the propagation direction of the SAW between them (in the example shown in FIG. 2, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100). However, the fourth distance D4 may be shorter than the third distance D3. In this embodiment, the third distance D3 is the distance between the center of the multiple comb-tooth portions of the first IDT110 (in the example shown in FIG. 2, six comb-tooth portions of a pair of comb-tooth electrodes of the first IDT110) in the propagation direction of the SAW between the first IDT110 and the fifth IDT130 (in the example shown in FIG. 2, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) and the center of the multiple comb-tooth portions of the fifth IDT130 (in the example shown in FIG. 2, six comb-tooth portions of a pair of comb-tooth electrodes of the fifth IDT130) in the propagation direction of the SAW between the first IDT110 and the fifth IDT130 (in the example shown in FIG. 2, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) (the distance in the propagation direction of the SAW between the first IDT110 and the fifth IDT130). The fourth distance D4 is the distance between the center of the multiple comb-tooth portions of the third IDT 210 (in the example shown in FIG. 2, the six comb-tooth portions of a pair of comb-tooth electrodes of the third IDT 210) in the propagation direction of the SAW between the third IDT 210 and the sixth IDT 230 (in the example shown in FIG. 2, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) and the center of the multiple comb-tooth portions of the 6th IDT 230 (in the example shown in FIG. 2, the six comb-tooth portions of a pair of comb-tooth electrodes of the 6th IDT 230) in the propagation direction of the SAW between the third IDT 210 and the sixth IDT 230 (in the example shown in FIG. 2, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) (the distance in the propagation direction of the SAW between the third IDT 210 and the sixth IDT 230).

[0041] In this embodiment, the first distance D1, the second distance D2, the third distance D3, and the fourth distance D4 are different from each other. Specifically, the first distance D1, the third distance D3, the second distance D2, and the fourth distance D4 are longer in this order. However, the length order of the first distance D1 to the fourth distance D4 is not limited to this.

[0042] An example of the operation of the sensor device 10 will be described with reference to FIG.

[0043] The external antenna 312 of the host device 300 transmits radio waves to the first antenna 112 of the first piezoelectric substrate 100. The first antenna 112 generates a high-frequency signal in response to the radio waves transmitted from the external antenna 312. The first IDT 110 generates a SAW in the first piezoelectric substrate 100 in response to the high-frequency signal generated by the external antenna 312. The SAW generated by the first IDT 110 propagates through the first piezoelectric substrate 100 and is reflected by the second IDT 120 and the fifth IDT 130. The reflectance of the second IDT 120 varies depending on the impedance of the first sensor 122. Therefore, the SAW reflected from the second IDT 120 corresponds to the impedance of the first sensor 122. The first IDT 110 generates a high-frequency signal in response to the SAW reflected from the second IDT 120 and the fifth IDT 130. The first antenna 112 transmits radio waves corresponding to the high frequency signal generated by the first IDT 110 to the external antenna 312 of the host device 300. The host device 300 analyzes the radio waves received by the external antenna 312.

[0044] The external antenna 312 of the host device 300 transmits radio waves to the second antenna 212 of the second piezoelectric substrate 200. The second antenna 212 generates a high-frequency signal in response to the radio waves transmitted from the external antenna 312. The third IDT 210 generates a SAW in the second piezoelectric substrate 200 in response to the high-frequency signal generated by the external antenna 312. The SAW generated by the third IDT 210 propagates through the second piezoelectric substrate 200 and is reflected by the fourth IDT 220 and the sixth IDT 230. The reflectance of the fourth IDT 220 varies depending on the impedance of the second sensor 222. Therefore, the SAW reflected from the fourth IDT 220 corresponds to the impedance of the second sensor 222. The third IDT 210 generates a high-frequency signal in response to the SAW reflected from the fourth IDT 220 and the sixth IDT 230. The second antenna 212 transmits a radio wave corresponding to the high frequency signal generated by the third IDT 210 to the external antenna 312 of the host device 300. The host device 300 analyzes the radio wave received by the external antenna 312.

[0045] The measuring device 302 measures the difference between the time from the transmission of radio waves from the external antenna 312 to the first IDT 110 of the first piezoelectric substrate 100 to the reception of radio waves from the first IDT 110 of the first piezoelectric substrate 100 by the external antenna 312, through the propagation of the SAW between the first IDT 110 and the fifth IDT 130 of the first piezoelectric substrate 100, and the time from the transmission of radio waves from the external antenna 312 to the third IDT 210 of the second piezoelectric substrate 200 to the reception of radio waves from the third IDT 210 of the second piezoelectric substrate 200 by the external antenna 312, through the propagation of the SAW between the third IDT 210 and the sixth IDT 230 of the second piezoelectric substrate 200. In this time difference (delay difference), the influence of factors other than the sensing target can be reduced, as described in the first embodiment.

[0046] As in embodiment 1, the measuring instrument 302 may measure the difference between the time from transmission to reception of radio waves from the external antenna 312, including the propagation time of the SAW between the first IDT 110 and the second IDT 120 on the first piezoelectric substrate 100, and the time from transmission to reception of radio waves from the external antenna 312, including the propagation time of the SAW between the third IDT 210 and the fourth IDT 220 on the second piezoelectric substrate 200.

[0047] The measuring device 302 may measure the difference between the time from the transmission of radio waves from the external antenna 312 to the first IDT 110 of the first piezoelectric substrate 100 to the reception of radio waves from the first IDT 110 of the first piezoelectric substrate 100 by the external antenna 312, via the propagation of the SAW between the first IDT 110 and the second IDT 120 of the first piezoelectric substrate 100, and the time from the transmission of radio waves from the external antenna 312 to the first IDT 110 of the first piezoelectric substrate 100 to the reception of radio waves from the first IDT 110 of the first piezoelectric substrate 100 by the external antenna 312, via the propagation of the SAW between the first IDT 110 and the fifth IDT 130 of the first piezoelectric substrate 100. In this time difference (delay difference), the influence of factors other than the sensing target can be reduced, as described in the first embodiment.

[0048] The measuring device 302 may measure the difference between the SAW propagating between the first IDT 110 and the second IDT 120 in the first piezoelectric substrate 100 and the SAW propagating between the first IDT 110 and the fifth IDT 130 in the first piezoelectric substrate 100. This difference can reduce noise in the first piezoelectric substrate 100 (for example, the effect that the first piezoelectric substrate 100 may have due to temperature).

[0049] For the second piezoelectric substrate 200, the same operation as that of the measuring device 302 described for the first piezoelectric substrate 100 can be performed to reduce the influence of factors other than the sensing target, and noise in the second piezoelectric substrate 200 (for example, Second Piezoelectric Substrate 200 This reduces the effect of temperature on the

[0050] (Embodiment 3) 3 is a diagram showing a sensor device 10 according to embodiment 3. The sensor device 10 according to embodiment 3 is similar to the sensor device 10 according to embodiment 1 except for the following points.

[0051] The sensor device 10 further includes a seventh IDT 140 and an eighth IDT 240. The seventh IDT 140 is located on the first piezoelectric substrate 100 facing the first IDT 110 at a fifth distance D5. The eighth IDT 240 is located on the second piezoelectric substrate 200 facing the third IDT 210 at a sixth distance D6. The sixth distance D6 is different from the fifth distance D5.

[0052] The seventh IDT 140 has a pair of comb-shaped electrodes. The seventh IDT 140 (the pair of comb-shaped electrodes) may not be electrically connected to a sensor (a sensor corresponding to the first sensor 122 electrically connected to the second IDT 120) as shown in FIG. 3, or may be electrically connected to the sensor.

[0053] In the first piezoelectric substrate 100, the seventh IDT 140 is located on the opposite side (i.e., the side where the third side 102c of the first piezoelectric substrate 100 is located) to the side where the second IDT 120 is located (i.e., the side where the fourth side 102d of the first piezoelectric substrate 100 is located) with respect to the first IDT 110. However, the seventh IDT 140 may be located on the same side as the side where the second IDT 120 is located (i.e., the side where the fourth side 102d of the first piezoelectric substrate 100 is located) with respect to the first IDT 110.

[0054] 3, the seventh IDT 140 faces the first IDT 110 in the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100. Therefore, between the first IDT 110 and the seventh IDT 140, a SAW can be propagated along the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100.

[0055] The points described above regarding the seventh IDT 140 also apply to the eighth IDT 240 .

[0056] A sixth distance D6 between the third IDT 210 and the eighth IDT 240 of the second piezoelectric substrate 200 in the propagation direction of the SAW between them (in the example shown in FIG. 3, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) is longer than a fifth distance D5 between the first IDT 110 and the seventh IDT 140 of the first piezoelectric substrate 100 in the propagation direction of the SAW between them (in the example shown in FIG. 3, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100). However, the sixth distance D6 may be shorter than the fifth distance D5. In this embodiment, the fifth distance D5 is the distance between the center of the multiple comb-tooth portions of the first IDT110 (in the example shown in FIG. 3, six comb-tooth portions of a pair of comb-tooth electrodes of the first IDT110) in the propagation direction of the SAW between the first IDT110 and the seventh IDT140 (in the example shown in FIG. 3, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) and the center of the multiple comb-tooth portions of the seventh IDT140 (in the example shown in FIG. 3, six comb-tooth portions of a pair of comb-tooth electrodes of the fifth IDT130) in the propagation direction of the SAW between the first IDT110 and the seventh IDT140 (in the example shown in FIG. 3, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) (the distance in the propagation direction of the SAW between the first IDT110 and the seventh IDT140). The sixth distance D6 is the distance between the center of the multiple comb-tooth portions of the third IDT 210 (in the example shown in FIG. 3, the six comb-tooth portions of a pair of comb-tooth electrodes of the third IDT 210) in the propagation direction of the SAW between the third IDT 210 and the eighth IDT 240 (in the example shown in FIG. 3, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) and the center of the multiple comb-tooth portions of the 8th IDT 240 (in the example shown in FIG. 3, the six comb-tooth portions of a pair of comb-tooth electrodes of the 8th IDT 240) in the propagation direction of the SAW between the third IDT 210 and the eighth IDT 240 (in the example shown in FIG. 3, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) (the distance in the propagation direction of the SAW between the third IDT 210 and the eighth IDT 240).

[0057] An example of the operation of the sensor device 10 will be described with reference to FIG.

[0058] The external antenna 312 of the host device 300 transmits radio waves to the first antenna 112 of the first piezoelectric substrate 100. The first antenna 112 generates a high-frequency signal in response to the radio waves transmitted from the external antenna 312. The first IDT 110 generates a SAW in the first piezoelectric substrate 100 in response to the high-frequency signal generated by the external antenna 312. The SAW generated by the first IDT 110 propagates through the first piezoelectric substrate 100 and is reflected by the second IDT 120, the fifth IDT 130, and the seventh IDT 140. The reflectance of the second IDT 120 varies depending on the impedance of the first sensor 122. Therefore, the SAW reflected from the second IDT 120 corresponds to the impedance of the first sensor 122. The first IDT 110 generates a high-frequency signal in response to the SAW reflected from the second IDT 120, the fifth IDT 130, and the seventh IDT 140. The first antenna 112 transmits radio waves corresponding to the high frequency signal generated by the first IDT 110 to the external antenna 312 of the host device 300. The host device 300 analyzes the radio waves received by the external antenna 312.

[0059] The external antenna 312 of the host device 300 transmits radio waves to the second antenna 212 of the second piezoelectric substrate 200. The second antenna 212 generates a high-frequency signal in response to the radio waves transmitted from the external antenna 312. The third IDT 210 generates a SAW in the second piezoelectric substrate 200 in response to the high-frequency signal generated by the external antenna 312. The SAW generated by the third IDT 210 propagates through the second piezoelectric substrate 200 and is reflected by the fourth IDT 220, the sixth IDT 230, and the eighth IDT 240. The reflectance of the fourth IDT 220 varies depending on the impedance of the second sensor 222. Therefore, the SAW reflected from the fourth IDT 220 corresponds to the impedance of the second sensor 222. The third IDT 210 generates a high-frequency signal in response to the SAW reflected from the fourth IDT 220, the sixth IDT 230, and the eighth IDT 240. The second antenna 212 transmits a radio wave corresponding to the high frequency signal generated by the third IDT 210 to the external antenna 312 of the host device 300. The host device 300 analyzes the radio wave received by the external antenna 312.

[0060] The measuring device 302 measures the difference between the time from the transmission of radio waves from the external antenna 312 to the first IDT 110 of the first piezoelectric substrate 100 to the reception of radio waves from the first IDT 110 of the first piezoelectric substrate 100 by the external antenna 312, through the propagation of the SAW between the first IDT 110 and the seventh IDT 140 of the first piezoelectric substrate 100, and the time from the transmission of radio waves from the external antenna 312 to the third IDT 210 of the second piezoelectric substrate 200 to the reception of radio waves from the third IDT 210 of the second piezoelectric substrate 200 by the external antenna 312, through the propagation of the SAW between the third IDT 210 and the eighth IDT 240 of the second piezoelectric substrate 200. In this time difference (delay difference), the influence of factors other than the sensing target can be reduced, as described in the first embodiment.

[0061] As in the first embodiment, the measuring device 302 may measure a difference between a time from transmission to reception of radio waves of the external antenna 312, including a propagation time of the SAW between the first IDT 110 and the second IDT 120 on the first piezoelectric substrate 100, and a time from transmission to reception of radio waves of the external antenna 312, including a propagation time of the SAW between the third IDT 210 and the fourth IDT 220 on the second piezoelectric substrate 200. As in the second embodiment, the measuring device 302 may measure a difference between a time from transmission to reception of radio waves of the external antenna 312, including a propagation time of the SAW between the first IDT 110 and the fifth IDT 130 on the first piezoelectric substrate 100, and a time from transmission to reception of radio waves of the external antenna 312, including a propagation time of the SAW between the third IDT 210 and the sixth IDT 230 on the second piezoelectric substrate 200.

[0062] As in the second embodiment, the measuring device 302 may measure the difference between the time from transmission to reception of the radio wave of the external antenna 312, including the propagation time of the SAW between the first IDT 110 and the second IDT 120 in the first piezoelectric substrate 100, and the time from transmission to reception of the radio wave of the external antenna 312, including the propagation time of the SAW between the first IDT 110 and the fifth IDT 130 in the first piezoelectric substrate 100. Furthermore, the measuring device 302 may measure the difference between the time from transmission to reception of the radio wave of the external antenna 312, including the propagation time of the SAW between the first IDT 110 and the second IDT 120 in the first piezoelectric substrate 100, and the time from transmission to reception of the radio wave of the external antenna 312, including the propagation time of the SAW between the first IDT 110 and the seventh IDT 140 in the first piezoelectric substrate 100. In these differences, the influence of factors different from the sensing target can be reduced as described in the first or second embodiment.

[0063] As in the second embodiment, the measuring device 302 may measure a difference between a SAW propagating between the first IDT 110 and the second IDT 120 in the first piezoelectric substrate 100 and a SAW propagating between the first IDT 110 and the fifth IDT 130 in the first piezoelectric substrate 100. Furthermore, the measuring device 302 may measure a difference between a SAW propagating between the first IDT 110 and the second IDT 120 in the first piezoelectric substrate 100 and a SAW propagating between the first IDT 110 and the seventh IDT 140 in the first piezoelectric substrate 100. In terms of these differences, noise in the first piezoelectric substrate 100 (for example, an effect that the first piezoelectric substrate 100 may be subjected to due to temperature) can be reduced.

[0064] For the second piezoelectric substrate 200, the effects of factors other than the sensing target can be reduced by performing operations similar to those described above for the first piezoelectric substrate 100 of the measuring device 302, and noise in the second piezoelectric substrate 200 (for example, effects that the second piezoelectric substrate 200 may experience due to temperature) can be reduced.

[0065] FIG. 4 is a graph showing signals generated by FMCW (frequency modulated continuous wave) from radio waves transmitted from the external antenna 312 and radio waves received by the external antenna 312 in the sensor device 10 shown in FIG.

[0066] In the graph shown in FIG. 4, the vertical axis indicates the strength of the signal measured by measuring instrument 302, and the horizontal axis indicates the delay time of the signal measured by measuring instrument 302.

[0067] The signal S1 is a signal that has undergone SAW propagation between the first IDT 110 and the second IDT 120 on the first piezoelectric substrate 100. The signal S2 is a signal that has undergone SAW propagation between the third IDT 210 and the fourth IDT 220 on the second piezoelectric substrate 200. The signal S3 is a signal that has undergone SAW propagation between the first IDT 110 and the fifth IDT 130 on the first piezoelectric substrate 100. The signal S4 is a signal that has undergone SAW propagation between the third IDT 210 and the sixth IDT 230 on the second piezoelectric substrate 200. The signal S5 is a signal that has undergone SAW propagation between the first IDT 110 and the seventh IDT 140 on the first piezoelectric substrate 100. The signal S6 is a signal that has passed through the propagation of a SAW between the third IDT 210 and the eighth IDT 240 on the second piezoelectric substrate 200.

[0068] The signal S1, the signal S3, the signal S2, the signal S4, the signal S3, and the signal S6 are generated in this order. Specifically, the first distance D1, the third distance D3, the second distance D2, the fourth distance D4, the fifth distance D5, and the sixth distance D6 are longer in this order. That is, the first distance D1, the second distance D2, the third distance D3, the fourth distance D4, the fifth distance D5, and the sixth distance D6 are different from each other. Also, the propagation speed of the SAW in each of the first distance D1 to the sixth distance D6 is substantially equal. Therefore, the generation order of the signal S1 to the signal S6 coincides with the length order of the first distance D1 to the sixth distance D6. In this way, it is possible to prevent the signal S1 to the signal S6 from overlapping (not being generated at the same timing).

[0069] The strength of each of the signals S1 to S6 may vary due to various factors different from the sensing target, such as the distance between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100, the distance between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100, other external environments, etc. In contrast, the time difference (delay difference) between two of the signals S1 to S6 (for example, the time difference between the signals S1 and S4) does not vary due to these factors, but varies according to the physical quantity measured by the first sensor 122 or the second sensor 222. Therefore, the influence of factors different from the sensing target can be reduced.

[0070] In this embodiment, the number of reflectors on each piezoelectric substrate is 3. In this case, as described in Non-Patent Document 1, when measuring temperature based on delay time difference and phase difference, a wide temperature range can be measured with high accuracy.

[0071] (Embodiment 4) 5 is a diagram showing the sensor device 10 according to the embodiment 4. The sensor device 10 according to the embodiment 4 is similar to the sensor device 10 according to the embodiment 3 except for the following points.

[0072] The sensor device 10 further includes a ninth IDT 150 and a tenth IDT 250. The ninth IDT 150 is located on the first piezoelectric substrate 100 facing the first IDT 110 at a seventh distance D7. The tenth IDT 250 is located on the second piezoelectric substrate 200 facing the third IDT 210 at an eighth distance D8. The eighth distance D8 is different from the seventh distance D7.

[0073] The ninth IDT 150 has a pair of comb-shaped electrodes. The ninth IDT 150 (the pair of comb-shaped electrodes) may not be electrically connected to a sensor (a sensor corresponding to the first sensor 122 electrically connected to the second IDT 120) as shown in FIG. 5, or may be electrically connected to the sensor.

[0074] In the first piezoelectric substrate 100, the ninth IDT 150 is located on the opposite side (i.e., the side where the third side 102c of the first piezoelectric substrate 100 is located) to the side where the second IDT 120 is located (i.e., the side where the fourth side 102d of the first piezoelectric substrate 100 is located) with respect to the first IDT 110. However, the ninth IDT 150 may be located on the same side as the side where the second IDT 120 is located (i.e., the side where the fourth side 102d of the first piezoelectric substrate 100 is located) with respect to the first IDT 110.

[0075] 5, the ninth IDT 150 faces the first IDT 110 in the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100. Therefore, between the first IDT 110 and the ninth IDT 150, a SAW can be propagated along the extension direction of the first side 102a and the second side 102b of the first piezoelectric substrate 100.

[0076] The points described above regarding the ninth IDT 150 also apply to the tenth IDT 250 .

[0077] An eighth distance D8 between the third IDT 210 and the tenth IDT 250 of the second piezoelectric substrate 200 in the propagation direction of the SAW between them (in the example shown in FIG. 5, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) is longer than a seventh distance D7 between the first IDT 110 and the ninth IDT 150 of the first piezoelectric substrate 100 in the propagation direction of the SAW between them (in the example shown in FIG. 5, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100). However, the eighth distance D8 may be shorter than the seventh distance D7. In this embodiment, the seventh distance D7 is the distance between the center of the multiple comb-tooth portions of the first IDT110 (in the example shown in FIG. 5, six comb-tooth portions of a pair of comb-tooth electrodes of the first IDT110) in the propagation direction of the SAW between the first IDT110 and the 9th IDT150 (in the example shown in FIG. 5, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) and the center of the multiple comb-tooth portions of the 9th IDT150 (in the example shown in FIG. 5, six comb-tooth portions of a pair of comb-tooth electrodes of the 9th IDT150) in the propagation direction of the SAW between the first IDT110 and the 9th IDT150 (in the example shown in FIG. 5, the extension direction of the first side 102a or the second side 102b of the first piezoelectric substrate 100) (the distance in the propagation direction of the SAW between the first IDT110 and the 9th IDT150). The eighth distance D8 is the distance between the center of the multiple comb-tooth portions of the third IDT 210 (in the example shown in FIG. 5, the six comb-tooth portions of a pair of comb-tooth electrodes of the third IDT 210) in the propagation direction of the SAW between the third IDT 210 and the tenth IDT 250 (in the example shown in FIG. 5, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) and the center of the multiple comb-tooth portions of the tenth IDT 250 (in the example shown in FIG. 5, the six comb-tooth portions of a pair of comb-tooth electrodes of the tenth IDT 250) in the propagation direction of the SAW between the third IDT 210 and the tenth IDT 250 (in the example shown in FIG. 5, the extension direction of the fifth side 202a or the sixth side 202b of the second piezoelectric substrate 200) (the distance in the propagation direction of the SAW between the third IDT 210 and the tenth IDT 250).

[0078] An example of the operation of the sensor device 10 will be described with reference to FIG.

[0079] The external antenna 312 of the host device 300 transmits radio waves to the first antenna 112 of the first piezoelectric substrate 100. The first antenna 112 generates a high-frequency signal in response to the radio waves transmitted from the external antenna 312. The first IDT 110 generates a SAW in the first piezoelectric substrate 100 in response to the high-frequency signal generated by the external antenna 312. The SAW generated by the first IDT 110 propagates through the first piezoelectric substrate 100 and is reflected by the second IDT 120, the fifth IDT 130, the seventh IDT 140, and the ninth IDT 150. The reflectance of the second IDT 120 varies depending on the impedance of the first sensor 122. Therefore, the SAW reflected from the second IDT 120 corresponds to the impedance of the first sensor 122. The first IDT 110 generates a high-frequency signal corresponding to the SAW reflected from the second IDT 120, the fifth IDT 130, the seventh IDT 140, and the ninth IDT 150. The first antenna 112 transmits a radio wave corresponding to the high-frequency signal generated by the first IDT 110 to an external antenna 312 of the host device 300. The host device 300 analyzes the radio wave received by the external antenna 312.

[0080] The external antenna 312 of the host device 300 transmits radio waves to the second antenna 212 of the second piezoelectric substrate 200. The second antenna 212 generates a high-frequency signal in response to the radio waves transmitted from the external antenna 312. The third IDT 210 generates a SAW in the second piezoelectric substrate 200 in response to the high-frequency signal generated by the external antenna 312. The SAW generated by the third IDT 210 propagates through the second piezoelectric substrate 200 and is reflected by the fourth IDT 220, the sixth IDT 230, the eighth IDT 240, and the tenth IDT 250. The reflectance of the fourth IDT 220 varies depending on the impedance of the second sensor 222. Therefore, the SAW reflected from the fourth IDT 220 corresponds to the impedance of the second sensor 222. The third IDT 210 generates a high frequency signal corresponding to the SAW reflected from the fourth IDT 220, the sixth IDT 230, the eighth IDT 240, and the tenth IDT 250. The second antenna 212 transmits a radio wave corresponding to the high frequency signal generated by the third IDT 210 to an external antenna 312 of the host device 300. The host device 300 analyzes the radio wave received by the external antenna 312.

[0081] The measuring device 302 measures the difference between the time from the transmission of radio waves from the external antenna 312 to the first IDT 110 of the first piezoelectric substrate 100 to the reception of radio waves from the first IDT 110 of the first piezoelectric substrate 100 by the external antenna 312, through the propagation of the SAW between the first IDT 110 and the ninth IDT 150 of the first piezoelectric substrate 100, and the time from the transmission of radio waves from the external antenna 312 to the third IDT 210 of the second piezoelectric substrate 200 to the reception of radio waves from the third IDT 210 of the second piezoelectric substrate 200 by the external antenna 312, through the propagation of the SAW between the third IDT 210 and the tenth IDT 250 of the second piezoelectric substrate 200. In this time difference (delay difference), the influence of factors other than the sensing target can be reduced, as described in the first embodiment.

[0082] As in embodiment 3, the measuring instrument 302 may measure the difference between the time from transmission to reception of radio waves from the external antenna 312, including the propagation time of the SAW between the first IDT 110 on the first piezoelectric substrate 100 and an IDT other than the first IDT 110, and the time from transmission to reception of radio waves from the external antenna 312, including the propagation time of the SAW between the third IDT 210 on the second piezoelectric substrate 200 and an IDT other than the third IDT 210.

[0083] As in the third embodiment, the measuring device 302 may measure the difference between the time from transmission to reception of radio waves from the external antenna 312, including the propagation time of the SAW between the first IDT 110 and the second IDT 120 on the first piezoelectric substrate 100, and the time from transmission to reception of radio waves from the external antenna 312, including the propagation time of the SAW between the first IDT 110 and an IDT other than the first IDT 110 and the second IDT 120 on the first piezoelectric substrate 100. As described in the first to third embodiments, the influence of factors other than the sensing target on this difference can be reduced.

[0084] As in the third embodiment, the measuring device 302 may measure a difference between a SAW propagating between the first IDT 110 and the second IDT 120 in the first piezoelectric substrate 100 and a SAW propagating between the first IDT 110 and an IDT other than the first IDT 110 and the second IDT 120 in the first piezoelectric substrate 100. This difference can reduce noise in the first piezoelectric substrate 100 (for example, an effect that the first piezoelectric substrate 100 may have due to temperature).

[0085] For the second piezoelectric substrate 200, the effects of factors other than the sensing target can be reduced by performing operations similar to those described above for the first piezoelectric substrate 100 of the measuring device 302, and noise in the second piezoelectric substrate 200 (for example, effects that the second piezoelectric substrate 200 may experience due to temperature) can be reduced.

[0086] FIG. 6 is a graph showing signals generated by FMCW (frequency modulated continuous wave) from radio waves transmitted from external antenna 312 and radio waves received by external antenna 312 in sensor device 10 shown in FIG.

[0087] In the graph shown in FIG. 6, the vertical axis indicates the strength of the signal measured by measuring instrument 302, and the horizontal axis indicates the delay time of the signal measured by measuring instrument 302.

[0088] The signal S1 is a signal that has undergone SAW propagation between the first IDT 110 and the second IDT 120 on the first piezoelectric substrate 100. The signal S2 is a signal that has undergone SAW propagation between the third IDT 210 and the fourth IDT 220 on the second piezoelectric substrate 200. The signal S3 is a signal that has undergone SAW propagation between the first IDT 110 and the fifth IDT 130 on the first piezoelectric substrate 100. The signal S4 is a signal that has undergone SAW propagation between the third IDT 210 and the sixth IDT 230 on the second piezoelectric substrate 200. The signal S5 is a signal that has undergone SAW propagation between the first IDT 110 and the seventh IDT 140 on the first piezoelectric substrate 100. The signal S6 is a signal that has undergone SAW propagation between the third IDT 210 and the eighth IDT 240 on the second piezoelectric substrate 200. The signal S7 is a signal that has undergone SAW propagation between the first IDT 110 and the ninth IDT 150 on the first piezoelectric substrate 100. The signal S8 is a signal that has undergone SAW propagation between the third IDT 210 and the tenth IDT 250 on the second piezoelectric substrate 200.

[0089] The signal S1, the signal S3, the signal S2, the signal S4, the signal S5, the signal S6, the signal S7, and the signal S8 are generated in this order. Specifically, the first distance D1, the third distance D3, the second distance D2, the fourth distance D4, the fifth distance D5, the sixth distance D6, the seventh distance D7, and the eighth distance D8 are longer in this order. That is, the first distance D1, the second distance D2, the third distance D3, the fourth distance D4, the fifth distance D5, the sixth distance D6, the seventh distance D7, and the eighth distance D8 are different from each other. Also, the propagation speed of the SAW in each of the first distance D1 to the eighth distance D8 is substantially equal. Therefore, the generation order of the signal S1 to the signal S8 is consistent with the length order of the first distance D1 to the eighth distance D8. In this way, it is possible to prevent the signal S1 to the signal S8 from overlapping (not being generated at the same timing).

[0090] The strength of each of the signals S1 to S8 may vary due to various factors different from the sensing target, such as the distance between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100, the distance between the external antenna 312 of the host device 300 and the first antenna 112 of the first piezoelectric substrate 100, other external environments, etc. In contrast, the time difference (delay difference) between two signals among the signals S1 to S8 does not vary due to these factors, but varies according to the physical quantity measured by the first sensor 122 or the second sensor 222. Therefore, it is possible to reduce the influence of factors different from the sensing target.

[0091] (Embodiment 4) 7 is a diagram showing the sensor device 10 according to the embodiment 5. The sensor device 10 according to the embodiment 5 is similar to the sensor device 10 according to the embodiment 4 except for the following points.

[0092] The sensor device 10 includes a first impedance section 124. The first impedance section 124 is, for example, a fixed impedance section that is fixed to a specific impedance. Alternatively, the first impedance section 124 may be a variable impedance section that is adjustable to a specific impedance. The first impedance section 124 is located on the first piezoelectric substrate 100. The first impedance section 124 is, for example, configured by a conductive pattern such as a metal pattern provided on the first piezoelectric substrate 100. The first impedance section 124 may be provided outside the first piezoelectric substrate 100.

[0093] The first impedance section 124 is electrically connected to the second IDT 120 and the first sensor 122. Specifically, the first sensor 122 and the first impedance section 124 are connected in series between a pair of comb-tooth electrodes of the second IDT 120. In this case, the impedance connected to the second IDT 120 is a composite impedance of the first sensor 122 and the first impedance section 124 connected in series. Therefore, the impedance connected to the second IDT 120 can be made higher than when the first impedance section 124 is not connected to the second IDT 120 and the first sensor 122 is connected to the second IDT 120. Alternatively, the first sensor 122 and the first impedance section 124 may be connected in parallel between a pair of comb-tooth electrodes of the second IDT 120. In this case, the impedance connected to the second IDT 120 is a composite impedance of the first sensor 122 and the first impedance section 124 connected in parallel. Therefore, the impedance connected to the second IDT 120 can be made lower than when the first impedance section 124 is not connected to the second IDT 120 and the first sensor 122 is connected to the second IDT 120.

[0094] The sensor device 10 includes a second impedance section 224. The second impedance section 224 is electrically connected to the fourth IDT 220 and the second sensor 222 in the same manner as the first impedance section 124.

[0095] Fig. 8 is a graph showing an example of a schematic relationship between the impedance connected to the second IDT 120 and the level of a signal generated by the second IDT 120. In Fig. 8, the horizontal axis of the graph represents the impedance connected to the second IDT 120. Furthermore, the vertical axis of the graph represents the level of the signal generated by the second IDT 120.

[0096] 8, the level of the signal generated by the second IDT 120 varies linearly with different slopes in three sections A, B, and C on the horizontal axis with respect to the impedance connected to the second IDT 120. The impedance connected to the second IDT 120 increases in the order of section A, section B, and section C. The lengths of section A, section B, and section C decrease in the order of section B, section C, and section A.

[0097] The first sensor 122 is used in a section where the level of the signal generated by the second IDT 120 varies linearly with respect to the impedance connected to the second IDT 120. In this case, it is desirable that the length of the section where the level of the signal generated by the second IDT 120 varies linearly with respect to the impedance connected to the second IDT 120 is long. Therefore, in the graph shown in FIG. 8, it is desirable that the first sensor 122 operates in section B rather than section A or section C. However, when the first impedance section 124 is not connected to the second IDT 120 and the first sensor 122 is connected to the second IDT 120, the first sensor 122 may operate in section A or section C.

[0098] In the case where the first sensor 122 is connected to the second IDT 120 without the first impedance section 124 being connected to the second IDT 120, when the first sensor 122 operates in section A, the first sensor 122 and the first impedance section 124 can be connected in series between a pair of comb-tooth electrodes of the second IDT 120. In this case, the first sensor 122 can be operated in section B instead of section A by setting the impedance of the first impedance section 124 to an appropriate impedance.

[0099] In the case where the first sensor 122 is connected to the second IDT 120 without the first impedance section 124 being connected to the second IDT 120, when the first sensor 122 operates in section C, the first sensor 122 and the first impedance section 124 can be connected in parallel between a pair of comb-tooth electrodes of the second IDT 120. In this case, by setting the impedance of the first impedance section 124 to an appropriate impedance, the first sensor 122 can be operated in section B instead of section C.

[0100] The matters explained regarding the first sensor 122 and the first impedance section 124 using FIG. 8 also apply to the second sensor 222 and the second impedance section 224.

[0101] In the fourth embodiment, the sensor device 10 includes both the first impedance section 124 and the second impedance section 224. However, the sensor device 10 may include only one of the first impedance section 124 and the second impedance section 224. Furthermore, the matters described for the sensor device 10 of the fourth embodiment also apply to the sensor devices 10 according to each of the first to third embodiments.

[0102] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

[0103] For example, in the above embodiment, the sensor device 10 includes two piezoelectric substrates (the first piezoelectric substrate 100 and the second piezoelectric substrate 200). However, the sensor device 10 may include three or more piezoelectric substrates. Even when the sensor device 10 includes three or more piezoelectric substrates, the sensor device 10 can operate in the same manner as the above embodiment.

[0104] In addition, in the first embodiment shown in Fig. 1, each piezoelectric substrate has one IDT in addition to the IDT electrically connected to the antenna, in the second embodiment shown in Fig. 2, each piezoelectric substrate has two IDTs in addition to the IDT electrically connected to the antenna, in the third embodiment shown in Fig. 3, each piezoelectric substrate has three IDTs in addition to the IDT electrically connected to the antenna, and in the fourth embodiment shown in Fig. 5 and the fifth embodiment shown in Fig. 7, each piezoelectric substrate has four IDTs in addition to the IDT electrically connected to the antenna. As is clear from these embodiments, each piezoelectric substrate may have five or more IDTs in addition to the IDT connected to the antenna. [Explanation of symbols]

[0105] 10 Sensor device 100 first piezoelectric substrate 102a Side 1 102b Side 2 102c Third Side 102d Side 4 110 1st IDT 112 First Antenna 120 2nd IDT 122 First Sensor 124 First impedance section 130 5th IDT 140 7th IDT 150 9th IDT 200 second piezoelectric substrate 202a Side 5 202b Side 6 202c Side 7 202d Side 8 210 3rd IDT 212 Second Antenna 220 4th IDT 222 Second Sensor 224 Second impedance section 230 6th IDT 240 8th IDT 250 10th IDT 300 Host device 302 Measuring instruments 312 External Antenna D1 First distance D2 2nd distance D3 Third distance D4 4th distance D5 5th distance D6 6th distance D7 7th distance D8 8th distance

Claims

1. A first piezoelectric substrate; a first IDT located on the first piezoelectric substrate and electrically connected to a first antenna for transmitting and receiving radio waves to and from an external antenna; a second IDT electrically connected to a first sensor having an impedance that changes in response to an external physical quantity, the second IDT being positioned on the first piezoelectric substrate and facing the first IDT at a first distance; A second piezoelectric substrate; a third IDT located on the second piezoelectric substrate and electrically connected to a second antenna for transmitting and receiving radio waves to and from the external antenna; a fourth IDT electrically connected to a second sensor having an impedance that changes in response to an external physical quantity, the fourth IDT being positioned on the second piezoelectric substrate and facing the third IDT at a second distance; a fifth IDT that is not electrically connected to a sensor having an impedance that changes in response to an external physical quantity, and that is positioned on the first piezoelectric substrate to face the first IDT at a third distance; a sixth IDT that is not electrically connected to a sensor having an impedance that changes in response to an external physical quantity, the sixth IDT being positioned on the second piezoelectric substrate to face the third IDT at a fourth distance; Including, The sensor device, wherein the first distance, the second distance, the third distance, and the fourth distance are different from each other.

2. 2. The sensor device according to claim 1, a seventh IDT located on the first piezoelectric substrate and facing the first IDT at a fifth distance; an eighth IDT located on the second piezoelectric substrate and facing the third IDT at a sixth distance; Further comprising: The sensor device, wherein the first distance, the second distance, the third distance, the fourth distance, the fifth distance, and the sixth distance are different from each other.

3. The sensor device according to claim 2, a ninth IDT located on the first piezoelectric substrate and facing the first IDT at a seventh distance; a tenth IDT located on the second piezoelectric substrate and facing the third IDT at an eighth distance; Further comprising: The sensor device, wherein the first distance, the second distance, the third distance, the fourth distance, the fifth distance, the sixth distance, the seventh distance, and the eighth distance are different from each other.

4. The sensor device according to any one of claims 1 to 3, The sensor device further includes a measuring device that measures the difference between a time from the transmission of radio waves by the external antenna to the first IDT of the first piezoelectric substrate, through the propagation of surface acoustic waves between the first IDT and the second IDT of the first piezoelectric substrate, to the reception of radio waves from the first IDT of the first piezoelectric substrate by the external antenna, and a time from the transmission of radio waves by the external antenna to the third IDT of the second piezoelectric substrate, through the propagation of surface acoustic waves between the third IDT and the fourth IDT of the second piezoelectric substrate, to the reception of radio waves from the third IDT of the second piezoelectric substrate by the external antenna.

5. The sensor device according to any one of claims 1 to 3, The sensor device further includes a measuring device that measures the difference between the time from the transmission of radio waves by the external antenna to the first IDT of the first piezoelectric substrate, through the propagation of surface acoustic waves between the first IDT and the fifth IDT of the first piezoelectric substrate, to the reception of radio waves from the first IDT of the first piezoelectric substrate by the external antenna, and the time from the transmission of radio waves by the external antenna to the third IDT of the second piezoelectric substrate, through the propagation of surface acoustic waves between the third IDT and the sixth IDT of the second piezoelectric substrate, to the reception of radio waves from the third IDT of the second piezoelectric substrate by the external antenna.

6. The sensor device according to claim 2 or 3, The sensor device further includes a measuring device that measures the difference between the time from the transmission of radio waves by the external antenna to the first IDT of the first piezoelectric substrate, through the propagation of surface acoustic waves between the first IDT and the seventh IDT of the first piezoelectric substrate, to the reception of radio waves from the first IDT of the first piezoelectric substrate by the external antenna, and the time from the transmission of radio waves by the external antenna to the third IDT of the second piezoelectric substrate, through the propagation of surface acoustic waves between the third IDT and the eighth IDT of the second piezoelectric substrate, to the reception of radio waves from the third IDT of the second piezoelectric substrate by the external antenna.

7. The sensor device according to claim 3, The sensor device further includes a measuring device that measures the difference between the time from the transmission of radio waves by the external antenna to the first IDT of the first piezoelectric substrate, through the propagation of surface acoustic waves between the first IDT and the ninth IDT of the first piezoelectric substrate, to the reception of radio waves from the first IDT of the first piezoelectric substrate by the external antenna, and the time from the transmission of radio waves by the external antenna to the third IDT of the second piezoelectric substrate, through the propagation of surface acoustic waves between the third IDT and the tenth IDT of the second piezoelectric substrate, to the reception of radio waves from the third IDT of the second piezoelectric substrate by the external antenna.

8. The sensor device according to any one of claims 1 to 7, The sensor device further includes a first impedance section electrically connected to the second IDT and the first sensor.

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