JP2007303977A - Surface acoustic device, and liquid level detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic device having a plurality of resonance frequencies, and to provide a liquid level detector using the surface acoustic device, which detects a quantity of liquid as its liquid level. <P>SOLUTION: The liquid level detector has an IDT electrode 30 which is disposed on a piezo-electric substrate 21 and excited with a plurality of prescribed resonance frequencies, and the IDT electrode 30 is composed of a plurality of electrode finger sets 40, 41 and 42 having different prescribed resonance frequencies f1, f2 and f3. The plurality of electrode finger sets 40, 41 and 42 are arranged so as to be sifted on the piezo-electric substrate 21, and the surface acoustic device 20 is disposed in a liquid 2. A difference of insertion loss between bands of the resonance frequencies f1, f2 and f3 which is caused by such a state that the liquid 2 contacts with any of the plurality of electrode finger sets 40, 41 and 42, is detected, and then the liquid level of the liquid 2 is detected based on a change in the insertion loss. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave element and a liquid level detection device. More specifically, the present invention relates to a surface acoustic wave element having a plurality of resonance frequencies and a liquid level detection apparatus using the surface acoustic wave element.

  Conventionally, there is a surface acoustic wave element in which IDT electrodes having different resonance frequencies are formed on a piezoelectric substrate. The surface acoustic wave element includes a first surface acoustic wave resonator having a predetermined resonance frequency as a parallel arm, and a second elasticity having a resonance frequency that substantially matches the anti-resonance frequency of the first surface acoustic wave resonator. A plurality of surface wave resonators are arranged in series arms. Of the first and second surface acoustic wave resonators described above, the electrode fingers of at least one surface acoustic wave resonator are formed to have two or more different periods (for example, Patent Documents). 1).

  In addition, as a physical quantity detection sensor using a surface acoustic wave element, a slip surface acoustic wave sensor having unevenness in the vertical direction of the shear displacement on the surface of propagation of the surface acoustic wave and a flat slip surface acoustic wave sensor without unevenness are provided. A method of separating and measuring the density and viscosity of a liquid, which is installed in the same surface acoustic wave element and separates and measures the density and viscosity of the liquid by both sensors, is known (for example, see Patent Document 2).

JP-A-11-88112 (6th page, FIGS. 11 and 12) Japanese Patent Laid-Open No. 11-217055 (page 4, FIGS. 2 and 3)

  According to Patent Document 1, such a surface acoustic wave element is used as a filter, and electrode fingers are formed to have two or more different periods, and a desired frequency band outside a pass band is formed. It is configured to obtain a degree of suppression. In the case of such a configuration, the setting area width of the different period is small, and is inappropriate as a sensor for measuring a physical quantity, for example.

  The surface acoustic wave element is configured to include a plurality of series resonators or parallel resonators, but one of them is an external load, for example, when electrode fingers are immersed in a liquid or the like. Therefore, it is presumed that the frequency response is remarkably lowered or no output can be obtained.

In Patent Document 2 described above, a standard liquid and a liquid to be measured are loaded using a surface acoustic wave sensor with unevenness and a surface acoustic wave sensor without unevenness, and the surface acoustic wave generated by the mass load of the surface acoustic wave sensor is detected. The liquid density and viscosity are separated and measured by changing the speed.
However, in such a method, a very small amount of liquid is used as the liquid to be detected, and the amount of liquid stored in a container or the like cannot be measured.

  An object of the present invention is to solve the above-described problems, and a surface acoustic wave element having a plurality of resonance frequencies, and a liquid that can detect the amount of liquid as a liquid level using the surface acoustic wave element. It is to provide a position detection device.

The surface acoustic wave device of the present invention is a surface acoustic wave device including IDT electrodes that are excited at a plurality of predetermined resonance frequencies on a piezoelectric substrate, and the IDT electrodes have a plurality of electrode fingers having different predetermined resonance frequencies. A plurality of electrode finger groups arranged on the piezoelectric substrate, and when an external load is applied to any of the plurality of electrode finger groups, A change in frequency characteristics is detected.
Here, the electrode finger group means, for example, an electrode finger unit having an electrode width and a pitch for forming a predetermined resonance frequency. The external load includes, for example, a load when the electrode finger group is immersed in a liquid. Furthermore, as the frequency characteristics, insertion loss that is easy to detect is representative.

  According to the present invention, a plurality of electrode finger groups having different resonance frequencies are provided, and each of these electrode finger groups is disposed with a shifted position, so that liquid or the like is temporarily loaded on one of the electrode fingers. In this case, the insertion loss of the electrode finger group to which the liquid has adhered increases, and the insertion loss of the electrode finger group to which the liquid does not adhere does not change, so that it can be used as a sensor for detecting such a load state.

  The IDT electrode is preferably formed by connecting each of the plurality of electrode finger groups in series in a direction in which surface acoustic waves propagate.

  If the electrode finger group is configured in this manner, a surface acoustic wave element having a plurality of resonance frequencies can be realized with a simple configuration.

  The plurality of electrode finger groups form a plurality of IDT electrodes having different resonance frequencies, and each of the plurality of IDT electrodes is arranged in parallel and shifted in a direction in which the surface acoustic wave propagates. Preferably, the plurality of IDT electrodes are connected in parallel.

  By laying out a plurality of electrode finger groups in this way, a load such as the above-described liquid can be added individually and accurately to a plurality of IDT electrodes.

  The IDT electrode includes an input side electrode formed by connecting a plurality of electrode finger groups having a predetermined resonance frequency in series, and an electrode finger group having a predetermined frequency corresponding to the predetermined resonance frequency of the input side electrode. It is preferable that the output side electrode is connected and arranged in a direction in which the surface acoustic wave propagates.

  By providing the input-side electrode and the output-side electrode in this way, a surface acoustic wave element having excellent frequency characteristics is realized, and a surface acoustic wave element having a plurality of resonance frequencies by an electrode finger group having a simple configuration. Can be realized.

  The IDT electrode includes an input electrode and an output electrode arranged in a direction in which surface acoustic waves propagate, and the output electrode includes a plurality of electrode finger groups having different predetermined resonance frequencies. It is desirable that the plurality of electrode finger groups are connected in parallel and are displaced in the direction in which the surface acoustic wave propagates.

  By configuring the electrode finger group on the output electrode side in this way, it is possible to clearly separate the resonance frequencies and to detect the insertion loss stepwise.

  Further, the plurality of electrode finger groups form a plurality of IDT electrodes having different resonance frequencies, and each of the plurality of IDT electrodes is arranged in parallel to and independently of the direction in which the surface acoustic wave propagates. It is desirable that

  Since the IDT electrodes having different resonance frequencies are formed independently as described above, since the other IDT electrodes are not affected by the load in a state in which the IDT electrodes are loaded, the frequency characteristics (insertion) Loss) clearly occurs, and the detection power can be increased.

  In the present invention, each of the IDT electrodes is composed of a unidirectional electrode.

  When immersed in the liquid and then removed from the liquid contact, it is considered that the liquid is attached to the IDT electrode. In such a state, it is known that the driving of the surface acoustic wave element becomes unstable. ing. Therefore, by adopting the unidirectional electrode, it is possible to remove the liquid outside the IDT electrode formation region by moving or scattering the liquid in one direction, and to maintain stable driving.

  The liquid level detection device of the present invention includes an IDT electrode disposed in a liquid and excited on a piezoelectric substrate at a plurality of predetermined resonance frequencies, wherein the IDT electrode has a plurality of different predetermined resonance frequencies. A surface acoustic wave element comprising an electrode finger group, wherein the plurality of electrode finger groups are disposed on the piezoelectric substrate at different positions, and an excitation circuit that is disposed outside a liquid and excites the surface acoustic wave element. And a control unit having a detection circuit unit for detecting a frequency characteristic, and detecting a change in the frequency characteristic caused by a state where the liquid is in contact with any of the plurality of electrode finger groups. The liquid level of the liquid is detected.

  The frequency characteristics of the surface acoustic wave element change due to the difference in the state where the liquid contacts the surface of the IDT electrode, that is, the electrode finger group. If one of the electrode fingers having a plurality of resonance frequencies is immersed in the liquid and the other is not in contact with the liquid, the frequency characteristics of the immersed electrode fingers are different from the others. By detecting, it is possible to determine to which position of the electrode finger group the liquid is present. Therefore, the liquid level can be detected by disposing the surface acoustic wave element at an appropriate height.

  Therefore, when the liquid is stored in a container or the like, the liquid volume such as the weight of the liquid is measured from the product of the storage volume and the density of the liquid from the product of the bottom area of the container and the liquid level. Is possible.

  The surface acoustic wave element is preferably disposed so that the propagation direction of the surface acoustic wave is substantially perpendicular to the liquid surface.

  In this way, the liquid level can be detected with a simple electrode finger configuration.

  Further, each of the plurality of IDT electrodes is disposed so that the propagation direction of the surface acoustic wave is substantially horizontal with respect to the liquid surface of the liquid, and the height position with respect to the liquid surface is shifted. It is preferable.

  In this way, the IDT electrodes having different resonance frequencies are shifted in height relative to the liquid surface, and each is formed independently, so that the frequency characteristics of the IDT electrodes immersed in the liquid are The other IDT electrodes that are not immersed are not affected at all by the liquid load. Therefore, a difference in frequency characteristics (insertion loss) is clearly generated, and the detection power can be increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 5 show a liquid level detection device, a surface acoustic wave element, and a liquid level detection method according to Embodiment 1, FIG. 6 shows Embodiment 2, FIG. 7 shows Embodiment 3, FIG. FIG. 9 shows an elastic surface element according to the fifth embodiment.
(Embodiment 1)

  FIG. 1 is a perspective view showing a schematic configuration of a liquid level detection device according to Embodiment 1 of the present invention. In FIG. 1, the liquid level detection device 1 includes a surface acoustic wave element 20 as a liquid level detection sensor attached to an inner side wall 11 of a container 10 in which a liquid 2 is stored, and a control unit 80 provided outside the container 10. It is composed of

  Although the container 10 has illustrated the container of the cube in this embodiment, the shape is not restricted to a cube, It is possible to select arbitrarily. The surface acoustic wave element 20 is arranged so that the propagation direction of the surface acoustic wave (shown by an arrow) is perpendicular to the liquid surface 3.

  In the surface acoustic wave element 20, an IDT electrode 30 is formed on the main surface (sometimes referred to as a surface) of a piezoelectric substrate 21. Since the interdigital electrode fingers (see FIG. 2) constituting the IDT electrode 30 are formed perpendicular to the propagation direction W of the surface acoustic wave, the electrode fingers are parallel to the liquid surface 3.

  The controller 80 and the surface acoustic wave element 20 are connected by leads (not shown) with the inner side wall 11 of the container 10 interposed therebetween. The lead is electrically insulated and waterproofed between the container 10 and the lead. Although not shown, the control unit 80 includes an excitation circuit unit for exciting the surface acoustic wave element 20, a detection circuit unit for detecting the frequency response output of the surface acoustic wave element 20, a power source, and a detection result. The display part etc. which display are included.

Next, the configuration of the surface acoustic wave element 20 used in the present embodiment will be described.
FIG. 2 is a front view schematically showing an example of the surface acoustic wave element 20 according to this embodiment. In FIG. 2, the surface acoustic wave element 20 has an IDT electrode 30 including an input / output electrode 31 and a GND electrode 32 formed on the surface of the piezoelectric substrate 21.

  The input / output electrode 31 and the GND electrode 32 are configured by a plurality of electrode fingers as illustrated. The electrodes arranged as shown in the figure are called unidirectional electrodes, and the excited surface acoustic wave moves only in the direction of arrow W in the figure. According to such a unidirectional electrode, when a droplet is attached on the IDT electrode 30 (the input / output electrode 31 and the GND electrode 32), the droplet is moved or scattered in the arrow W direction. The droplets are removed from the upper surface of the IDT electrode 30.

  Here, the IDT electrode 30 is configured by connecting electrode finger groups 40, 41, and 42 having three different resonance frequencies continuously in series as shown in the figure. The resonance frequency of the electrode finger group 40 is f1, the resonance frequency of the electrode finger group 41 is f2, and the resonance frequency of the electrode finger group 42 is f3.

  These electrode finger groups 40 to 42 are formed by setting the width, interval, and pitch of each electrode finger corresponding to a predetermined resonance frequency. In the present embodiment, as a specific example, the center resonance frequency f2 is set to 210 MHz, the resonance frequency f1 is set to f2 + 10 MHz, and the resonance frequency f3 is set to f2-10 MHz (see FIGS. 3 to 5).

Next, the operation when the above-described surface acoustic wave element 20 is used as a liquid level detection sensor will be described with reference to the drawings. Here, three levels of liquid level detection for the surface acoustic wave element 20 attached to the container 10 will be described as an example.
FIG. 3A is an explanatory diagram showing a relationship with the IDT electrode 30 exemplifying the first level among the three levels of the liquid level. FIG. 3A shows a state in which the liquid level 3 a of the liquid 2 is at the uppermost part of the IDT electrode 30. That is, all of the electrode finger groups 40 to 42 are immersed in the liquid.

Here, an example of frequency characteristics when the IDT electrode 30 is excited will be described.
FIG. 3B is a graph showing frequency characteristics in the state shown in FIG. The horizontal axis represents the resonance frequency (unit: MHz), and the vertical axis represents the insertion loss (unit: dB). As shown in FIG. 3B, in the state where all the IDT electrodes 30 are immersed in the liquid, almost no output is generated, and a high insertion loss value is shown in each resonance frequency region described above. Yes. That is, when the resonance frequencies f1 to f3 are expressed in this way, it can be detected that the liquid level is on the liquid surface 3a (it is fully immersed).

Next, the change in frequency characteristics will be described by exemplifying the case where the liquid level is the second level.
FIG. 4A shows a position where the liquid surface 3b of the liquid 2 is not in contact with the IDT electrode 30 at all, that is, a state where there is almost no liquid 2.

Here, the frequency characteristics when the IDT electrode 30 is excited will be described.
FIG. 4B is a graph showing frequency characteristics in the liquid level state shown in FIG. The horizontal axis represents the resonance frequency (unit: MHz), and the vertical axis represents the insertion loss (unit: dB). As shown in FIG. 4B, in such a liquid level state, the frequency characteristic is not affected at all by the load of the liquid and thus exhibits a desired frequency characteristic, and the insertion loss is the resonance frequency f1, f2. , F3, the level is almost the same.

  In such a state, the level is completely different from the insertion loss in the region of the resonance frequencies f1, f2, and f3 shown in FIG. Is shown.

Next, the change in frequency characteristics will be described by exemplifying the case where the liquid level is the third level.
FIG. 5A shows the case where the liquid level 3 c of the liquid 2 is near the center of the electrode finger group 41. That is, all of the electrode finger group 40 and about half of the electrode finger group 41 are immersed in the liquid, and the electrode finger group 42 is not immersed.

Here, an example of frequency characteristics when the IDT electrode 30 is excited will be described.
FIG. 5B is a graph showing the frequency characteristics in the state shown in FIG. The horizontal axis represents the resonance frequency (unit: MHz), and the vertical axis represents the insertion loss (unit: dB). As shown in FIG. 5B, the output decreases and the insertion loss increases in the immersed electrode finger group 41 (resonance frequency f1 region).

  In the electrode finger group 42 (resonant frequency f3 region) not immersed in the liquid 2, the output level is not affected because there is no load due to the liquid 2, and the same insertion loss as the level of the resonant frequency f3 band shown in FIG. Is shown.

  In the electrode finger group 41 (resonance frequency f2 region) immersed in the liquid 2 in a range of about half, the insertion loss is lower than that of the electrode finger group 42, and the insertion loss is represented by the relationship of f3> f2> f1. Has been. Thereby, it can be detected that the liquid level is within the formation range of the electrode finger group 41.

Moreover, although illustration is abbreviate | omitted, description is added also about the case where a liquid level is other than the 3 levels mentioned above.
First, in a state where the liquid level is in the range of the electrode finger group 40, the insertion loss in the bands of the resonance frequencies f2 and f3 is at the level shown in FIG. 4B, and the insertion loss in the band of the resonance frequency f1 is shown in FIG. A value approximated to f2 shown in b) is shown. That is, the insertion loss is approximately in the relationship of f3 = f2> f1. In such a state, it can be detected that the liquid level is within the formation range of the electrode finger group 40.

  In the state where the liquid level is in the range of the electrode finger group 42, the insertion loss in the bands of the resonance frequencies f1 and f2 shows a value approximate to the resonance frequency f1 band shown in FIG. 5B, and the band of the resonance frequency f3. The insertion loss is a value approximated to the resonance frequency f2 band shown in FIG. That is, the insertion loss is approximately in the relationship of f1 = f2 <f3. When the insertion loss indicates such a state, it can be detected that the liquid level is in the region of the electrode finger group 42.

  In the first embodiment described above, the state in which there are three electrode finger groups has been described as an example. However, the number of electrode finger groups is not limited to three, and may be arbitrarily set according to the liquid level detection range and resolution requirements. can do. The configuration of the electrode fingers of each electrode finger group is also an example, and can be arbitrarily set according to the resonance frequency band and the required output level.

  Therefore, according to the first embodiment described above, the surface acoustic wave element 20 includes the electrode finger groups 40, 41, and 42 having different resonance frequencies f1, f2, and f3, and these electrode finger groups are arranged in series. Has been. Therefore, a small surface acoustic wave element 20 having a plurality of resonance frequencies can be realized with a simple configuration.

Further, when any range of the electrode finger groups 40 to 42 is immersed and loaded in the liquid 2, the insertion loss of the electrode finger group immersed in the liquid 2 becomes large, and the insertion loss of the electrode finger group not immersed is increased. Since there is no change, it is possible to determine at which position of the electrode finger group the liquid is present by detecting the difference in insertion loss in each band of the resonance frequencies f1 to f3. Is disposed at an appropriate height position, the liquid level of the liquid 2 can be detected.
(Embodiment 2)

Subsequently, Embodiment 2 of the present invention will be described with reference to the drawings. The second embodiment is characterized in that a plurality of IDT electrodes having different resonance frequencies formed in the surface acoustic wave element are arranged in parallel.
FIG. 6 is an explanatory diagram schematically illustrating an example of the configuration of the IDT electrode of the surface acoustic wave element 120 according to the second embodiment. In FIG. 6, the IDT electrode of this embodiment is configured such that IDT electrodes 130, 230, and 330 having different resonance frequencies are spaced apart in parallel to the propagation direction of the surface acoustic wave.

  The IDT electrode 130 includes an input side electrode 131 and an output side electrode 132. The input side electrode 131 is composed of an IN electrode 131a and a GND electrode 131b, and the output side electrode 132 is composed of an OUT electrode 132a and a GND electrode 132b. The input-side electrode 131 and the output-side electrode 132 are arranged in a propagation direction of the surface acoustic wave with a predetermined interval, and the electrode width of the electrode fingers, the electrode interval, the pitch, etc. so as to be the resonance frequency f3. Is set.

  The IDT electrode 230 includes an input side electrode 231 and an output side electrode 232. The input side electrode 231 includes an IN electrode 231a and a GND electrode 231b, and the output side electrode 232 includes an OUT electrode 232a and a GND electrode 232b. The input-side electrode 231 and the output-side electrode 232 are arranged in the propagation direction of the surface acoustic wave with a predetermined interval, and the electrode width of the electrode fingers, the electrode interval, the pitch, etc. so as to become the resonance frequency f2. Is set.

  The IDT electrode 330 is composed of an input side electrode 331 and an output side electrode 332. The input side electrode 331 includes an IN electrode 331a and a GND electrode 331b, and the output side electrode 332 includes an OUT electrode 332a and a GND electrode 332b. The input side electrode 331 and the output side electrode 332 are arranged in a propagation direction of the surface acoustic wave with a predetermined interval, and the electrode width of the electrode finger, the electrode interval, the pitch, etc. so as to become the resonance frequency f1. Is set.

  The resonance frequencies f1, f2, and f3 of the IDT electrodes are different from each other, and are set to the same resonance frequency band as that of the first embodiment.

Each IDT electrode is connected as shown in FIG. That is, the input side electrodes 131, 231, 331 of each IDT electrode are connected in parallel and connected to the IN terminal 70 and the GND terminal 71. Similarly, the output side electrodes 132, 232, 332 are connected in parallel and connected to the OUT terminal 73 and the GND terminal 72.
Note that the connections shown in the figure are schematically shown for easy understanding of the arrangement of the terminals.

  These IDT electrodes 130, 230, and 330 are arranged so that their positions are shifted from each other in the longitudinal direction range of the output-side electrode in the propagation direction of the surface acoustic wave.

  A method of detecting the liquid level by attaching the surface acoustic wave element 120 configured as described above to a liquid level detection device (shown in FIG. 1) will be described. As shown in FIG. 6, the case of the liquid levels A to D will be described as an example. First, since the IDT electrodes 130, 230, and 330 are not in contact with the liquid in the state of the liquid level A, the output insertion loss of the output side electrodes 132, 232, and 332 is not affected by the liquid load. Is substantially the same as the state at each of the resonance frequencies f1 to f3 shown in FIG.

  When the liquid level is B, only the output side electrode 332 is immersed in the liquid 2. The insertion loss at each resonance frequency has a relationship of f2 = f3> f1, and shows characteristics similar to the insertion loss shown in FIG. From this, it can be detected that the liquid level is at the position of the liquid surface B.

  When the liquid level is C, the output side electrodes 332 and 232 are immersed in the liquid 2. Therefore, the insertion loss at each resonance frequency has a relationship of f1 = f2 <f3, and it can be detected that the liquid level is at the position of the liquid level C.

  Furthermore, the state of the liquid level D is a state in which the output side electrodes 332, 232 and 132 are all immersed in the liquid 2. Therefore, the insertion loss at each resonance frequency shows the same characteristics as the resonance frequencies f1 to f3 shown in FIG. 3B, and it can be detected that the liquid level is at the position of the liquid level D.

  In the present embodiment, the state where there are three IDT electrodes having different resonance frequencies has been described as an example. However, the number of IDT electrodes is not limited to three, and can be arbitrarily set according to the liquid level detection range and resolution requirements. Can be set. The configuration of the electrode fingers of each IDT electrode is also an example, and can be arbitrarily set according to the resonance frequency band and the required output level.

  Therefore, according to the second embodiment described above, each IDT electrode includes the input-side electrode and the output-side electrode, thereby realizing the surface acoustic wave device 120 having excellent frequency characteristics and having different resonance frequencies. Therefore, the difference in insertion loss at each resonance frequency is more likely to appear more clearly.

Even if the IDT electrodes 130, 230, and 330 are configured independently, since the input side electrodes and the output side electrodes are connected in parallel, the connection is simplified and the number of input / output terminals and GND terminals is minimized. Can consist of numbers.
(Embodiment 3)

Subsequently, Embodiment 3 of the present invention will be described with reference to the drawings. The third embodiment is characterized in that an IDT electrode formed on a surface acoustic wave element is composed of an input electrode and an output electrode composed of electrode fingers having different resonance frequencies.
FIG. 7 is an explanatory diagram schematically showing an example of the configuration of the IDT electrode 300 of the surface acoustic wave element 220 according to the third embodiment. In FIG. 7, the IDT electrode 300 of the present embodiment includes a plurality of input-side electrodes 310 and output-side electrodes 320 having different resonance frequencies arranged in series in the propagation direction of the surface acoustic wave.

  The input-side electrode 310 is formed by interposing an interdigital IN electrode 311 and a GND electrode 312, and sequentially connecting electrode finger groups 315, 316 and 317 having three different resonance frequencies as shown in the figure. Configured. The resonance frequency of the electrode finger group 315 is f1, the resonance frequency of the electrode finger group 316 is f2, and the resonance frequency of the electrode finger group 317 is f3.

  The output side electrode 320 has the same configuration as that of the input side electrode 310, and is formed by interposing an OUT electrode 322 and a GND electrode 321. As shown in the drawing, electrode finger groups 325, 326, and 327 having three different resonance frequencies are connected in series. Are connected continuously. The resonance frequency of the electrode finger group 325 is f1, the resonance frequency of the electrode finger group 326 is f2, and the resonance frequency of the electrode finger group 327 is f3.

  In the present embodiment, the input side electrode 310 and the output side electrode 320 respectively illustrate the same configuration as the IDT electrode 30 described in the first embodiment (see FIG. 2). Therefore, the liquid level can be detected by replacing the output side electrode 320 with the IDT electrode 30 shown in FIG.

  That is, when liquid levels exist in the respective ranges of the electrode finger groups 325, 326, and 327 in the third embodiment, the appearance of insertion loss in the bands of the resonance frequencies f1, f2, and f3 is shown in FIGS. According to the insertion loss at each resonance frequency shown in (b) and FIG. 5 (b), the liquid level can be detected from this.

Therefore, in the third embodiment described above, the effects of the first and second embodiments described above are achieved. In other words, the surface acoustic wave device 220 having a plurality of resonance frequencies with a simple configuration, enabling downsizing, and the IDT electrode 300 including the input side electrode 310 and the output side electrode 320 have excellent frequency characteristics. And an accurate liquid level detection device can be provided.
(Embodiment 4)

Next, Embodiment 4 of the present invention will be described with reference to the drawings. The fourth embodiment is characterized in that an IDT electrode formed on a surface acoustic wave element is composed of an input side electrode and output side electrodes having a plurality of different resonance frequencies.
FIG. 8 is an explanatory diagram schematically illustrating an example of the configuration of the IDT electrode 300 of the surface acoustic wave element 220 according to the fourth embodiment. In FIG. 8, the IDT electrode 300 of the present embodiment includes an input side electrode 310 and an output side electrode 320 having a plurality of different resonance frequencies arranged in series in the propagation direction of the surface acoustic wave.

  The input-side electrode 310 is formed by interposing an interdigital IN electrode 311 and a GND electrode 312. The input side electrode 310 has a single resonance frequency band, and in this embodiment, the input side electrode 310 is set to the resonance frequency f2 as the center.

  The output-side electrode 320 includes an electrode finger group 325 having a resonance frequency f1, an electrode finger group 326 having a resonance frequency f2, and an electrode finger group 327 having a resonance frequency f3. Each of these electrode finger groups 325 to 327 includes an OUT electrode 322 and a GND electrode 321. Each electrode finger group 325, 326, 327 has a distance from the input-side electrode 310, each electrode width, an electrode interval, a pitch, and the like so as to have predetermined resonance frequencies f1, f2, f3.

  The electrode finger groups 325, 326, and 327 are formed with their positions shifted in the direction perpendicular to the propagation direction of the surface acoustic wave.

  The detection of the liquid level by the surface acoustic wave element 220 configured as described above can be performed in the same manner as in the third embodiment (see FIG. 7). That is, when liquid levels exist in the respective ranges of the electrode finger group 325, the electrode finger group 326, and the electrode finger group 327 in Embodiment 4, the appearance of insertion loss in the bands of the resonance frequencies f1, f2, and f3 is shown in FIG. In accordance with the insertion loss shown in (b), FIG. 4 (b), and FIG. 5 (b), the liquid level can be detected from this.

In addition, the electrode finger groups 325, 326, and 327 are formed by shifting their positions in the direction perpendicular to the propagation direction of the surface acoustic wave, so that the resonance frequencies can be clearly separated. Play.
(Embodiment 5)

Next, Embodiment 5 of the present invention will be described with reference to the drawings. The fifth embodiment is characterized in that a plurality of IDT electrodes having different resonance frequencies are provided separately from each other in the direction perpendicular to the propagation direction of the surface acoustic wave.
FIG. 9 is an explanatory diagram schematically illustrating an example of the configuration of the IDT electrode in the surface acoustic wave device according to the fifth embodiment. In FIG. 9, the surface acoustic wave element 200 of the present embodiment is configured by forming IDT electrodes 330, 340, and 350 on the surface of the piezoelectric substrate 21.

The IDT electrodes 340, 350, and 360 have the same configuration, but the IDT electrode 360 has the resonance frequency f1, the IDT electrode 350 has the resonance frequency f2, and the IDT electrode 340 has the resonance frequency f3. The width, electrode spacing, and pitch are set.
Note that the IDT electrodes described in the first to fourth embodiments may have different predetermined resonance frequencies.

  In the surface acoustic wave element 200, in the liquid level detection device (see FIG. 1), each IDT electrode has a surface acoustic wave propagation direction parallel to the liquid surface, and each surface is perpendicular to the liquid surface. It is arranged. That is, the surface acoustic wave element 200 is provided with the IDT electrode 360 downward with respect to the liquid level in the liquid level detection device.

  Therefore, for example, when the IDT electrode 360 is immersed in a liquid, there is almost no output of the IDT electrode 360, the frequency characteristics due to the IDT electrodes 350 and 340 appear, and the IDT electrode 350 has a resonance frequency f2 and the IDT electrode 340 has An insertion loss at the resonance frequency f3 is detected.

  In this way, in the present embodiment, a stepwise liquid level corresponding to the number of IDT electrodes can be detected. Further, by detecting the resonance frequency at which the frequency characteristic appears depending on the liquid level or the peak of the insertion loss appears in some cases, it is possible to provide a liquid level detecting device having a clearer resolution.

It should be noted that the present invention is not limited to the above-described embodiment, but includes modifications and improvements as long as the object of the present invention can be achieved.
For example, the configuration of the electrode finger group and the electrode finger in the first to fifth embodiments described above is an example, and the configuration thereof is not limited.

  In the second and fifth embodiments, a plurality of IDT electrodes are formed on one piezoelectric substrate. However, independent surface acoustic wave elements each having each IDT electrode are shown in FIG. 6 or FIG. As described above, the same effect can be obtained even if the liquid level detecting device is arranged and attached.

  Furthermore, based on the technical idea of the third embodiment, the structure of the IDT electrode shown in the third or fourth embodiment can be combined. In such a case, electrode finger groups having different resonance frequencies are arranged at different positions on each IDT electrode. In this way, the liquid level detection resolution can be further increased.

  Therefore, according to the first to fifth embodiments described above, a surface acoustic wave element having a plurality of resonance frequencies and a liquid level detection device that detects the amount of liquid as a liquid level using the surface acoustic wave element are provided. can do. This liquid level detection device can be employed, for example, for detecting the remaining amount of fuel or chemicals, and for measuring the remaining amount of ink in an ink cartridge used in a printer.

The perspective view which shows schematic structure of the liquid level detection apparatus which concerns on Embodiment 1 of this invention. 1 is a front view schematically showing a surface acoustic wave element according to Embodiment 1 of the present invention. (A) is explanatory drawing of the IDT electrode which illustrates the 1st level of the liquid level which concerns on Embodiment 1 of this invention, (b) is a graph which shows the frequency characteristic of the state of the liquid level shown to (a). (A) is explanatory drawing of the IDT electrode which illustrates the 2nd level of the liquid which concerns on Embodiment 1 of this invention, (b) is a graph which shows the frequency characteristic of the state of the liquid level shown to (a). (A) is explanatory drawing of the IDT electrode which illustrates the 3rd level of the liquid based on Embodiment 1 of this invention, (b) is a graph which shows the frequency characteristic of the state of the liquid level shown to (a). Explanatory drawing which shows typically the structure of the IDT electrode of the surface acoustic wave element which concerns on Embodiment 2 of this invention. Explanatory drawing which shows typically the structure of the IDT electrode of the surface acoustic wave element which concerns on Embodiment 3 of this invention. Explanatory drawing which shows typically the structure of the IDT electrode of the surface acoustic wave element which concerns on Embodiment 4 of this invention. Explanatory drawing which shows typically the structure of the IDT electrode of the surface acoustic wave element which concerns on Embodiment 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid level detection apparatus, 2 ... Liquid, 20 ... Surface acoustic wave element, 21 ... Piezoelectric substrate, 30 ... IDT electrode, 40, 41, 42 ... Electrode finger group, f1, f2, f3 ... Resonance frequency.

Claims (10)

A surface acoustic wave device including an IDT electrode excited on a piezoelectric substrate at a plurality of predetermined resonance frequencies,
The IDT electrode is composed of a plurality of electrode finger groups having different predetermined resonance frequencies, and the plurality of electrode finger groups are disposed on the piezoelectric substrate at different positions,
A surface acoustic wave device that detects a change in frequency characteristics of an electrode finger group when an external load is applied to any of the plurality of electrode finger groups. The surface acoustic wave device according to claim 1,
The surface acoustic wave device, wherein the IDT electrode is formed by connecting each of the plurality of electrode finger groups in series in a direction in which surface acoustic waves propagate. The surface acoustic wave device according to claim 1,
The plurality of electrode finger groups form a plurality of IDT electrodes having different resonance frequencies,
Each of the plurality of IDT electrodes is disposed in parallel and is displaced in a direction in which the surface acoustic wave propagates.
The surface acoustic wave device, wherein the plurality of IDT electrodes are connected in parallel. The surface acoustic wave device according to claim 1,
The IDT electrode has an input side electrode formed by connecting a plurality of electrode finger groups having a predetermined resonance frequency in series, and an electrode finger group having a predetermined frequency corresponding to the predetermined resonance frequency of the input side electrode. And a surface acoustic wave element, wherein the surface acoustic wave element is disposed in a direction in which the surface acoustic wave propagates. The surface acoustic wave device according to claim 1,
The IDT electrode is formed of an input side electrode and an output side electrode arranged in a direction in which the surface acoustic wave propagates,
The output-side electrode includes a plurality of electrode finger groups having different predetermined resonance frequencies, the plurality of electrode finger groups are connected in parallel, and are arranged with a position shifted in a direction in which surface acoustic waves propagate. A surface acoustic wave device characterized by comprising: The surface acoustic wave device according to claim 1,
The plurality of electrode finger groups form a plurality of IDT electrodes having different resonance frequencies,
The surface acoustic wave device, wherein each of the plurality of IDT electrodes is arranged in parallel and independently with a direction in which the surface acoustic wave propagates. The surface acoustic wave device according to any one of claims 1 to 6,
Each of the IDT electrodes is composed of a unidirectional electrode. An IDT electrode disposed in a liquid and excited on a piezoelectric substrate at a plurality of predetermined resonance frequencies, wherein the IDT electrode is composed of a plurality of electrode finger groups having different predetermined resonance frequencies, and the plurality of electrodes A surface acoustic wave element in which a finger group is disposed on the piezoelectric substrate at a shifted position;
A control unit having an excitation circuit unit that is disposed outside the liquid and excites the surface acoustic wave element and a detection circuit unit that detects a frequency characteristic;
A liquid level detecting device that detects a change in frequency characteristics caused by a state in which a liquid is in contact with any of the plurality of electrode finger groups, and detects a liquid level from the change in frequency characteristics. In the liquid level detection apparatus of Claim 8,
The liquid level detecting device, wherein the surface acoustic wave element is arranged so that a propagation direction of the surface acoustic wave is substantially perpendicular to a liquid surface of the liquid. In the liquid level detection apparatus of Claim 8,
Each of the plurality of IDT electrodes is disposed such that the propagation direction of the surface acoustic wave is substantially horizontal with respect to the liquid surface of the liquid, and the height position with respect to the liquid surface is shifted. A liquid level detection device.

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