JP2009246572A - Surface acoustic wave sensor element and surface acoustic wave sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a SAW sensor with high sensitivity and high resolution which is reduced in manufacturing cost by decreasing the number of components. <P>SOLUTION: A SAW sensor element 1 includes a piezoelectric substrate 2 having a thin plate portion 3a and a thick plate portion 3b in a length direction, a SAW resonator 5 for detection and a first SAW filter 6 formed on the thin plate portion, and a reference SAW resonator 7 and a second SAW filter 8 formed on the thick plate portion. A first oscillation circuit 22 is connected between the SAW resonator for detection and first SAW filter to oscillate at an oscillation frequency for detection, and a second oscillation circuit 23 is connected between the reference SAW resonator and second SAW filter to oscillate at a reference oscillation frequency; and waves thereof are passed through the first and second SAW filters to remove unnecessary signal components, and input to a frequency mixer 24 to detect the difference between and the sum of them. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention uses a surface acoustic wave (SAW) excited by an IDT (interdigital transducer) formed on a piezoelectric substrate to detect and measure acceleration, external force, displacement, etc., and a SAW for use in the SAW sensor. The present invention relates to a sensor element.

  Conventionally, various sensors that measure acceleration, external force, or displacement using SAW have been proposed (Patent Documents 1 to 3). For example, an external force sensor described in Patent Document 1 supports a long plate-like beam made of a piezoelectric material in a cantilever manner, and includes an oscillator composed of a transmission electrode, a reception electrode, and an amplifier for exciting SAW on both the front and back surfaces of the beam. The configuration is provided. When the beam is bent by the action of an external force, the SAW propagation speed changes due to the distortion generated on the surface of the beam, and the oscillation frequency of both oscillators changes. Measure the thickness. Furthermore, the inclination sensor described in Patent Document 2 is different from the difference in temperature characteristics between the SAW resonators by making the electrode patterns of the transmitting electrode and the receiving electrode of the SAW resonator formed on both surfaces of the cantilever similar to each other. Measurement accuracy is improved by suppressing frequency drift of frequency.

  Further, in the external force sensor described in Patent Document 3, SAW resonators each having a transmitting unit and a receiving unit made of comb-shaped electrodes are arranged on the surface of a cantilever supported in a cantilever manner. In the embodiment in which the transmitting unit and the receiving unit are arranged in the length direction of the cantilever, the length direction of the lever, that is, the vertical displacement can be detected, and the embodiment is arranged in the length direction of the lever, that is, in the width direction. Then, twist, that is, displacement in the width direction can be detected. Further, in the embodiment in which two parallel receiving units and a common transmitting unit are provided on the surface of the cantilever, the displacement in the length direction and the torsional displacement are simultaneously detected from the sum and difference of the signals of each receiving unit. can do.

  Furthermore, a pressure sensor device that measures pressure using SAW is known (see, for example, Patent Document 4). In this pressure sensor device, a pressure detecting SAW element is provided in a thin part where the thickness of the piezoelectric substrate is reduced, and a reference SAW element is provided in the other thick part, and a difference between resonance frequencies of both SAW elements is obtained. The pressure is detected by the change.

JP-A-2-228530 JP-A-5-141969 Japanese Patent Laid-Open No. 9-133691 Special reprint WO2005 / 052533

  In general, a sensor using SAW detects a change in the frequency output from the SAW resonator, and therefore, even a slight change in the measurement object is highly sensitive compared to a sensor that detects a change in the output voltage. It has features that can be detected. In order to ensure high sensor sensitivity, it is necessary to increase the purity of the output signal, and a band-pass filter is used for this purpose. However, in the conventional sensor using the SAW described above, a bandpass filter separate from the cantilever-shaped piezoelectric substrate on which the SAW resonator is formed is connected to the subsequent stage of the mixer that mixes two detected frequencies. . As a result, there arises a problem that the number of parts increases, the manufacturing cost increases, and the configuration of the entire sensor becomes complicated.

  In order to realize a high-sensitivity and high-resolution sensor, it is necessary to match the SAW resonator of the piezoelectric substrate and / or the oscillator composed thereof with the subsequent band-pass filter in a balanced manner. However, when the piezoelectric substrate and the band-pass filter are configured separately as in the prior art, for example, the individual difference between the two tends to increase in the temperature characteristics and the like, and there is a possibility of causing inconveniences such as variations in the performance of the entire sensor and a decrease in performance. There is.

  Therefore, the present invention has been made in view of the above-described conventional problems, and the object thereof is to reduce the number of parts to suppress an increase in manufacturing cost, to reduce performance variation, and to have high sensitivity and high resolution. It is to realize a SAW sensor.

  Another object of the present invention is to provide a SAW sensor element suitable for realizing such a SAW sensor.

  According to the present invention, in order to achieve the above object, a piezoelectric substrate having a thin plate portion and a thick plate portion along the length direction, and a detection substrate for exciting SAW formed on the thin plate portion of the piezoelectric substrate. IDT, a reference IDT formed on the thick plate portion of the piezoelectric substrate for exciting SAW, a first SAW filter formed on the piezoelectric substrate and connected to the output of the detection IDT, and formed on the piezoelectric substrate A SAW sensor element having a second SAW filter connected to the output of the reference IDT, a first oscillation circuit connecting the detection IDT of the SAW sensor element and the first SAW filter, a reference IDT of the SAW sensor element, and the first IDT A second oscillation circuit for connecting between the two SAW filters, a frequency mixer connected to each output of the first SAW filter and the second SAW filter of the SAW sensor element, and a frequency mixer SAW sensor and a connected frequency detector is provided.

  The detection IDT and the reference IDT for exciting the SAW are, for example, a two-port SAW resonator or SAW having two input and output IDTs each composed of a pair of crossed finger electrodes and reflectors arranged on both sides thereof. As a filter or as a 1-port SAW resonator having an IDT composed of a pair of crossed finger electrodes and reflectors arranged on both sides thereof, or 2 for input and output each composed of a pair of crossed finger electrodes It can be configured as a transversal SAW filter having two IDTs.

  When a load such as an external force acts on the SAW sensor element, the propagation speed of the SAW changes due to the distortion of the surface of the thin plate portion, and the oscillation frequency on the detection side and the oscillation frequency on the reference side taken out from the frequency mixer Since the difference and the sum of fluctuate from the frequency value in the no-load state, the applied external force or the like can be measured by detecting either one of them with a frequency detector. At that time, the oscillation frequencies output from the first and second oscillation circuits are cut off by the first and second SAW filters, respectively, and extra frequency components that may become noise are cut, and only the frequency components in the desired range are the subsequent frequency mixers. Therefore, the applied external force or the like can be detected with high sensitivity and high resolution.

  Furthermore, since the first and second SAW filters are formed on the same piezoelectric substrate as the detection IDT and the reference IDT, the configuration of the entire SAW sensor can be simplified and the number of parts can be reduced. In addition, since the detection IDT, the reference IDT, and the first and second SAW filters can be simultaneously formed on the piezoelectric substrate using the conventional manufacturing process as they are, the manufacturing cost can be reduced and the performance due to individual differences between them can be reduced. The variation of the can be reduced.

  At this time, if the first SAW filter is provided in the thin plate portion of the piezoelectric substrate together with the detection IDT, the frequency characteristic is shifted in the same manner as the detection IDT due to the influence of temperature change, distortion generated in the thin plate portion, and the like. Convenient. Particularly, when the IDT for detection and the first SAW filter are arranged in parallel with each other in the length direction of the piezoelectric substrate, the distortion caused by the bending of the thin plate portion acts substantially equally along the length direction of the piezoelectric substrate. .

  In addition, if only the detection IDT is provided in the thin plate portion of the piezoelectric substrate and the first SAW filter is provided in the region of the other piezoelectric substrate, the area of the thin plate portion can be reduced, so that an external force acting on the SAW sensor element can be reduced. Even if it is the same size, the stress received per unit area of the thin plate portion is increased. As a result, the fluctuation amount of the oscillation frequency on the detection side becomes larger, so that the SAW sensor can be made more sensitive.

  In some embodiments, all or some of the components of the first and second oscillator circuits are formed on the piezoelectric substrate of the SAW sensor element. As a result, the number of parts constituting the SAW sensor can be reduced, the entire configuration can be simplified, and the manufacturing cost can be further reduced.

  In another embodiment, the SAW sensor element is supported in a cantilever manner, with the end on the thick plate portion side being a free end and the end on the thin plate portion side being rigidly fixed along the length direction of the piezoelectric substrate. To do. As a result, when an external force or acceleration is applied to the SAW sensor element, the end on the thick plate portion side is displaced corresponding to the size and direction, the thin plate portion is bent, and the SAW propagation speed on the surface of the thin plate portion changes. Therefore, it is possible to configure a sensor for measuring acceleration, external force, or displacement from the difference or sum of the detection-side oscillation frequency and the reference-side oscillation frequency.

  In yet another embodiment, a bandpass filter connected between the frequency mixer and the frequency detector is further provided. As a result, the difference or sum of the oscillation frequencies output from the frequency mixer can be selectively extracted.

  According to another aspect of the present invention, a piezoelectric substrate having a thin plate portion and a thick plate portion along the length direction, a detection IDT formed on the thin plate portion of the piezoelectric substrate for exciting the SAW, A reference IDT formed on the thick plate portion of the piezoelectric substrate for exciting the SAW, a first SAW filter formed on the piezoelectric substrate and connected to the output of the detection IDT, and formed on the piezoelectric substrate and the reference A SAW sensor element comprising a second SAW filter connected to the output of the industrial IDT is provided.

  In this SAW sensor element, the first and second SAW filters cut the unnecessary frequency components that can become noise from the oscillation frequency oscillated based on the resonance frequencies of the detection IDT and the reference IDT, respectively, and the frequency components of the desired band Therefore, a high-sensitivity and high-resolution SAW sensor can be realized. Since the detection IDT, the reference IDT, and the first and second SAW filters are formed on one piezoelectric substrate, when the SAW sensor is configured using the IDT, the configuration of the entire sensor is simplified and the number of parts is increased. Can be reduced.

  In one embodiment, the SAW sensor element connects between all or part of the components of the first oscillation circuit that connects between the detection IDT and the first SAW filter, and between the reference IDT and the second SAW filter. All or some of the components of the second oscillation circuit are provided on the piezoelectric substrate. The SAW sensor configured using this can reduce the number of parts and reduce the manufacturing cost. Moreover, since the components and wiring on the piezoelectric substrate including the components of the first oscillation circuit and the second oscillation circuit can be formed using the conventional manufacturing process as they are, it is more convenient.

  In another embodiment, some of the components of the bandpass filter connected to the outputs of the first SAW filter and the second SAW filter are provided on the piezoelectric substrate. The SAW sensor configured using this can further reduce the number of parts and further reduce the manufacturing cost.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each drawing, the same or similar components are denoted by the same or similar reference numerals.

  1A and 1B schematically show the configuration of a first embodiment of a SAW sensor element according to the present invention. The SAW sensor element 1 of the present embodiment has a piezoelectric substrate 2 made of a rectangular crystal having a predetermined length and width. The piezoelectric substrate 2 includes a thin plate portion 3a having a recess formed on the lower surface thereof by etching or the like near the lengthwise end portion 2a on the left side in the drawing along the length direction, and a thickness extending to the right lengthwise end portion 2b. And a plate portion 3b. The piezoelectric substrate 2 can be formed of a known piezoelectric material other than quartz such as lithium tantalate and lithium niobate. When the SAW sensor using the SAW sensor element 1 is a sensor that measures acceleration, external force, or displacement, the piezoelectric substrate 2 is rigidly fixed to the support portion 4 with one lengthwise end portion 2a as a fixed end, and The other end 2b in the length direction is supported as a free end.

  On the upper surface of the piezoelectric substrate 2, the detection SAW resonator 5 and the first SAW filter 6 are formed in the region of the thin plate portion 3a, and the reference SAW resonator 7 and the second SAW filter 8 are formed in the region of the thick plate portion 3b. Is formed. The detection SAW resonator 5 is a two-port type, and is disposed on both sides of the input side IDT 9 and the output side IDT 10 each consisting of a pair of cross-finger electrodes 9a, 9b, 10a, 10b along the SAW propagation direction. And one reflector 11, 11. The first SAW filter 6 is in the vertical double mode, and is arranged on both sides of the input side IDT 12 and the output side IDT 13 each consisting of a pair of crossed finger electrodes 12a, 12b, 13a, 13b along the SAW propagation direction. Each has one reflector 14,14. The detection SAW resonator 5 and the first SAW filter 6 of the present embodiment are arranged in parallel with each other so that the SAW propagation direction is parallel to the length direction of the piezoelectric substrate 2.

  The pass band of the first SAW filter 6 is set so that the resonance frequency of the detection SAW resonator 5 is surely included. In an embodiment, the center frequency of the first SAW filter 6 can be matched with the resonance frequency of the detection SAW resonator 5. This is realized, for example, by making the electrode pitch of the input side and output side IDTs 9 and 10 of the reference SAW resonator 7 and the electrode pitch of the input side and output side IDTs 12 and 13 of the first SAW filter 6 the same.

  Similarly, the reference SAW resonator 7 is a two-port type, and includes an input-side IDT 15 and an output-side IDT 16 each consisting of a pair of cross finger electrodes 15a, 15b, 16a, 16b along the SAW propagation direction, and both sides thereof. Each having one reflector 17, 17. The second SAW filter 8 is in the vertical double mode, and is arranged on both sides of the input IDT 18 and the output IDT 19 each consisting of a pair of crossed finger electrodes 18a, 18b, 19a, 19b along the SAW propagation direction. Each has one reflector 20,20. The reference SAW resonator 7 and the second SAW filter 8 of the present embodiment are arranged in parallel with each other so that the SAW propagation direction is parallel to the length direction of the piezoelectric substrate 2.

  The pass band of the second SAW filter 8 is set so that the resonance frequency of the reference SAW resonator 7 is surely included. In an embodiment, the center frequency of the second SAW filter 8 can be matched with the resonance frequency of the reference SAW resonator 7. This is similarly realized by making the electrode pitches of the input side and output side IDTs 15 and 16 of the reference SAW resonator 7 and the electrode pitches of the input side and output side IDTs 18 and 19 of the second SAW filter 8 the same. .

  FIG. 2 shows a configuration of a SAW sensor 21 using the SAW sensor element 1 of FIG. In addition to the SAW sensor element 1, the SAW sensor 21 includes a first oscillation circuit 22 connected between the detection SAW resonator 5 and the first SAW filter 6, a reference SAW resonator 7 and a second SAW filter 8. And a second oscillation circuit 23 connected between the two. The output terminals 6 a and 8 a of the first and second SAW filters are connected to the frequency mixer 24, and the output thereof is connected to the frequency detector 25. The frequency detector 25 is composed of, for example, a frequency counter.

  The first oscillation circuit 22 includes, for example, an amplifier connected to the output IDT 10 of the detection SAW resonator, a phase shifter, and a DC cut capacitor, and the output of the phase shifter is an IDT 9 for input of the detection SAW resonator. It is composed of a feedback circuit that feeds back to. The first oscillation circuit 22 oscillates and outputs a predetermined detection frequency fs based on the resonance frequency of the detection SAW resonator 5.

  Similarly, the second oscillation circuit 23 includes, for example, an amplifier connected to the output IDT 16 of the reference SAW resonator, a phase shifter, and a DC cut capacitor, and the output of the phase shifter is the output of the detection SAW resonator. It is composed of a feedback circuit that feeds back to the input IDT 15. The second oscillation circuit 23 oscillates and outputs a predetermined reference frequency fr based on the resonance frequency of the reference SAW resonator 7.

  The oscillation frequency fs output from the first oscillation circuit 22 cuts an extra frequency component that may become noise by the first SAW filter 6, passes the frequency component in a desired range, and outputs it to the frequency mixer 24. Similarly, the oscillation frequency fr output from the second oscillation circuit 23 cuts an extra frequency component that may become noise by the second SAW filter 8, passes the frequency component in a desired range, and outputs it to the frequency mixer. The frequency mixer 24 extracts the difference (Δf = fs−fr) and the sum (fs + fr) between the two input oscillation frequencies fs and fr and outputs them to the frequency detector 25. The difference and sum of the oscillation frequencies can be selectively extracted by inserting a low-pass filter or a high-pass filter between the frequency mixer 24 and the frequency detector 25.

  The SAW sensor 21 operates as follows when the SAW sensor element 1 is rigidly fixed to the support portion 4 at one end 2a in the longitudinal direction and supported in a cantilever manner as described above. When acceleration or external force is applied to the SAW sensor element 1, the longitudinal end 2b of the free end of the piezoelectric substrate 2 as shown by an arrow 26 in FIG. Displaces perpendicularly to the surface.

  In a no-load state in which no acceleration or external force acts on the SAW sensor element 1 and the lengthwise end 2b is not displaced, the oscillation frequency fs on the detection side and the oscillation frequency fr on the reference side are set to be the same. Can do. In this case, the difference Δf between the oscillation frequencies fs and fr is zero. In another embodiment, the oscillation frequencies fs and fr can be set to different values.

  When acceleration or an external force acts on the SAW sensor element 1 and the longitudinal end 2b is displaced, the thin plate portion 3a of the piezoelectric substrate 2 bends, and tensile strain or compression strain is generated on the upper surface depending on the direction of the bend. As a result, the SAW propagation speed on the upper surface of the thin plate portion 3a changes, and the oscillation frequency from the first oscillation circuit 22 on the detection side increases or decreases. On the other hand, since the thick plate portion 3b does not bend even if the lengthwise end portion 2b is displaced, the oscillation frequency fr from the second oscillation circuit 23 on the reference side does not fluctuate. Therefore, the magnitude of the acceleration or external force acting on the SAW sensor element can be detected with high sensitivity as the difference or sum of the oscillation frequencies fs and fr.

  In this embodiment, the first and second SAW filters 6 and 8 are formed on one piezoelectric substrate 2 on which the detection SAW resonator 5 and the reference SAW resonator 7 are formed, so that the number of components constituting the SAW sensor is increased. And can be formed using the conventional manufacturing process as it is, and the manufacturing cost can be reduced.

  Furthermore, in the present embodiment, the first SAW filter 6 is provided in the same thin plate portion 3a as the detection SAW resonator 5, so that the frequency range thereof is the same as that of the detection SAW resonator 5 in accordance with the temperature change and distortion of the thin plate portion. It changes as well. Therefore, the variation in performance can be reduced as compared with the case where they are provided separately, and even if the first SAW filter 6 is set to a relatively narrow band, the oscillation frequency fs on the detection side is surely in that frequency range. Therefore, a SAW sensor with higher performance and higher sensitivity can be obtained.

  FIG. 3 shows the frequency characteristics of the SAW sensor 21 of this embodiment. In the figure, the solid line represents the signal output from the frequency detector 25 in this embodiment after converting it into a voltage. Furthermore, in the same figure, as a comparative example, an output signal when the first and second SAW filters 6 and 8 are omitted from the SAW sensor element 1 of the present embodiment is indicated by a broken line. From this figure, it can be seen that in this embodiment, noise components included in a frequency region other than a narrow range near the center frequency can be effectively removed.

  In another embodiment, each of the detection SAW resonator 5 and the reference SAW resonator 7 can be composed of SAW filters. In this case, these detection and reference SAW filters are used as phase shifters, and the first and second oscillation circuits 22 and 23 are configured so as to be able to oscillate predetermined oscillation frequencies fs and fr, respectively.

  4A and 4B schematically show the configuration of a modification of the first embodiment. This embodiment is different from the configuration of FIG. 1 in that DC cut capacitors 27 and 28 constituting a part of the first and second oscillation circuits 22 and 23 are formed on the piezoelectric substrate 1. Thereby, the number of parts which comprise a SAW sensor can be decreased, and manufacturing cost can be suppressed lower. Further, the SAW sensor element 1 is more convenient because each component and wiring can be simultaneously formed on the piezoelectric substrate by using a conventional manufacturing process as it is.

  In still another embodiment, not only the DC cut capacitors 27 and 28 but also all other components constituting the first and second oscillation circuits 22 and 23 can be formed on the piezoelectric substrate 2. Thereby, the number of parts can be further reduced and the manufacturing cost can be reduced.

  FIGS. 5A and 5B schematically show the configuration of another modification of the first embodiment. In this embodiment, in the SAW sensor 21 of FIG. 2, a capacitor 29 constituting a part of a low-pass filter for removing the sum of the oscillation frequency from the output of the frequency mixer 25 is formed on the piezoelectric substrate 1. Different from the configuration of FIG. In this embodiment, a component 30 such as an inductor constituting the low-pass filter other than the capacitor 29 is connected between the capacitor 29 and the frequency mixer 24 as a separate component from the SAW sensor element 1 and its output. 30 a is connected to the frequency detector 25. As a result, the number of parts constituting the SAW sensor can be reduced, and the manufacturing cost can be further reduced.

  FIGS. 6A and 6B schematically show the configuration of a second embodiment of the SAW sensor element according to the present invention. In the SAW sensor element 31 of the second embodiment, the piezoelectric substrate 32 is formed to be longer than the piezoelectric substrate 2 of the first embodiment, and only the detection SAW resonator 5 is formed on the upper surface thereof in the region of the thin plate portion 33a. This is different from the first embodiment in that the first SAW filter 6 is formed in the thick plate portion between the fixed end and the lengthwise end portion 32a on the left side in the drawing. The detection SAW resonator 5 and the first SAW filter 6 are arranged along the length direction of the piezoelectric substrate 32 and the SAW propagation direction is parallel to the length direction of the piezoelectric substrate 32.

  Furthermore, in this embodiment, the reference SAW resonator 7 and the second SAW filter 8 are disposed on the piezoelectric substrate 32 in the region of the thick plate portion 33b between the free end and the lengthwise end portion 32b on the right side in the drawing. It differs from the first embodiment in that it is formed along the length direction. Similarly, the reference SAW resonator 7 and the second SAW filter 8 are arranged such that the SAW propagation direction is parallel to the length direction of the piezoelectric substrate 2.

  In the present embodiment, since only the detection SAW resonator 5 is provided on the thin plate portion 33, the area thereof can be reduced. Thereby, even if the external force acting on the SAW sensor element 31 has the same magnitude, the stress applied to the thin plate portion 32a per unit area is increased, so that the frequency fluctuation amount is further increased. As a result, a more sensitive SAW sensor can be obtained.

  In the present invention, a SAW element of a different type from the above embodiments can be used in place of the detection SAW resonator 5 and the reference SAW resonator 7 of the first embodiment.

  FIGS. 7A and 7B schematically show the structure of a third embodiment of the SAW sensor element according to the present invention. The SAW sensor element 41 of the third embodiment has the same piezoelectric substrate 2 as that of the first embodiment, but the detection SAW resonator 5 of the thin plate portion 3a and the reference SAW resonator 7 of the thick plate portion 3b are respectively transformers. The second embodiment is different from the first embodiment in that it is composed of Versal type SAW filters 42 and 43. The detection SAW filter 42 includes an input-side IDT 44 and an output-side IDT 45 each including a pair of crossed finger electrodes along the SAW propagation direction, and a shielding electrode 46 disposed therebetween. The reference SAW filter 43 includes an input-side IDT 47 and an output-side IDT 48 each including a pair of cross-finger electrodes along the SAW propagation direction, and a shielding electrode 49 disposed therebetween.

  FIGS. 8A and 8B schematically show the structure of a fourth embodiment of the SAW sensor element according to the present invention. The SAW sensor element 51 of the fourth embodiment has the same piezoelectric substrate 2 as that of the first embodiment, but the detection SAW resonator 5 of the thin plate portion 3a and the reference SAW resonator 7 of the thick plate portion 3b are each 1 The second embodiment is different from the first embodiment in that the port SAW resonators 52 and 53 are configured. The detection SAW resonator 52 includes an IDT 54 composed of a pair of cross-finger electrodes along the SAW propagation direction, and reflectors 55 and 55 disposed on both sides thereof. The reference SAW resonator 53 includes an IDT 56 composed of a pair of cross finger electrodes along the SAW propagation direction, and reflectors 57 and 57 disposed on both sides thereof.

  The present invention is not limited to the above embodiments, and can be implemented with various modifications or changes within the technical scope thereof. For example, the present invention can be similarly applied to a pressure sensor as described in Patent Document 4.

(A) is a schematic plan view of a first embodiment of a SAW sensor element according to the present invention, and (B) is a side view thereof. The block diagram of the SAW sensor by this invention using the SAW sensor element of 1st Example. The diagram which shows the frequency characteristic of the SAW sensor of FIG. (A) is a schematic plan view showing a modification of the first embodiment, and (B) is a side view thereof. (A) is a schematic plan view showing another modification of the first embodiment, and (B) is a side view thereof. (A) is a schematic plan view of a second embodiment of a SAW sensor element according to the present invention, and (B) is a side view thereof. (A) is a schematic plan view of a third embodiment of a SAW sensor element according to the present invention, and (B) is a side view thereof. (A) is a schematic plan view of a fourth embodiment of a SAW sensor element according to the present invention, and (B) is a side view thereof.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 31, 41, 51 ... SAW sensor element, 2, 32 ... Piezoelectric substrate, 2a, 2b, 32a, 32b ... End in length direction, 3a, 33a ... Thin plate portion, 3b, 33b ... Thick plate portion, 4 ... Support part, 5 ... detecting SAW resonator, 6 ... first SAW filter, 7 ... reference SAW resonator, 8 ... second SAW filter, 9, 12, 15, 18, 44, 47 ... input side IDT, 9a, 9b , 10a, 10b, 12a, 12b, 13a, 13b, 15a, 15b, 16a, 16b, 18a, 18b, 19a, 19b ... crossing finger electrodes, 10, 13, 16, 19, 45, 48 ... output side IDT, 11 , 14, 17, 20, 55, 57 ... reflector, 21 ... SAW sensor, 22 ... first oscillation circuit, 23 ... second oscillation circuit, 24 ... frequency mixer, 25 ... frequency detector, 26 ... arrow, 27 , 28, 29 ... Sita, 30 ... parts, 30a ... output, 42, 43 ... transversal SAW filter, 46, 49 ... shield electrode, 52, 53 ... one-port SAW resonator, 54, 56 ... IDT.

Claims (7)

A piezoelectric substrate having a thin plate portion and a thick plate portion along the length direction, a detection IDT formed on the thin plate portion of the piezoelectric substrate for exciting a surface acoustic wave, and the thickness of the piezoelectric substrate A reference IDT formed on the plate portion for exciting the surface acoustic wave, a first surface acoustic wave filter formed on the piezoelectric substrate and connected to the output of the detection IDT, and on the piezoelectric substrate A surface acoustic wave sensor element comprising a second surface acoustic wave filter formed and connected to the output of the reference IDT;
A first oscillation circuit that connects between the IDT for detection of the surface acoustic wave sensor element and the first surface acoustic wave filter;
A second oscillation circuit that connects between the reference IDT of the surface acoustic wave sensor element and the second surface acoustic wave filter;
A frequency mixer connected to each output of the first surface acoustic wave filter and the second surface acoustic wave filter of the surface acoustic wave sensor element;
A surface acoustic wave sensor comprising: a frequency detector connected to the frequency mixer.   2. The surface acoustic wave sensor according to claim 1, wherein all or part of components of the first oscillation circuit and the second oscillation circuit are formed on the piezoelectric substrate of the surface acoustic wave sensor element. .   The surface of the piezoelectric substrate is supported in a cantilever manner, with the end on the thick plate portion side being a free end and the end on the thin plate portion side being rigidly fixed along the length direction of the piezoelectric substrate. The surface acoustic wave sensor according to claim 1, wherein the surface acoustic wave sensor is provided.   4. The surface acoustic wave sensor according to claim 1, further comprising a band pass filter connected between the frequency mixer and the frequency detector.   A piezoelectric substrate having a thin plate portion and a thick plate portion along the length direction, a detection IDT formed on the thin plate portion of the piezoelectric substrate for exciting a surface acoustic wave, and the thickness of the piezoelectric substrate A reference IDT formed on the plate portion for exciting the surface acoustic wave, a first surface acoustic wave filter formed on the piezoelectric substrate and connected to the output of the detection IDT, and on the piezoelectric substrate A surface acoustic wave sensor element comprising: a second surface acoustic wave filter formed and connected to the output of the reference IDT.   All or a part of the components of the first oscillation circuit that connects between the detection IDT and the first surface acoustic wave filter, and between the reference IDT and the second surface acoustic wave filter are connected. 6. The surface acoustic wave sensor element according to claim 5, wherein all or part of the components of the second oscillation circuit are provided on the piezoelectric substrate.   The elastic part according to claim 5 or 6, wherein a part of components of a band-pass filter connected to outputs of the first surface acoustic wave filter and the second surface acoustic wave filter is provided on the piezoelectric substrate. Surface wave sensor.

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