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WO2015053253A1 - Capteur ultrasonore, et dispositif capteur - Google Patents

Capteur ultrasonore, et dispositif capteur Download PDF

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Publication number
WO2015053253A1
WO2015053253A1 PCT/JP2014/076770 JP2014076770W WO2015053253A1 WO 2015053253 A1 WO2015053253 A1 WO 2015053253A1 JP 2014076770 W JP2014076770 W JP 2014076770W WO 2015053253 A1 WO2015053253 A1 WO 2015053253A1
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Prior art keywords
layer
piezoelectric layer
piezoelectric
thickness
ultrasonic sensor
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PCT/JP2014/076770
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English (en)
Japanese (ja)
Inventor
秀嗣 三神
恒介 渡辺
純 多保田
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株式会社村田製作所
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Publication of WO2015053253A1 publication Critical patent/WO2015053253A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R17/00—Piezoelectric transducers; Electrostrictive transducers

Definitions

  • the present invention relates to an ultrasonic sensor having a piezoelectric element, and a sensor device including such an ultrasonic sensor.
  • a general ultrasonic sensor forms a unimorph structure by bonding a piezoelectric element to the inner bottom surface of a metal case, and transmits and receives ultrasonic waves by bending vibration of the bottom of the metal case.
  • Patent Documents 1 and 2 disclose an ultrasonic sensor including a stacked piezoelectric element.
  • a stacked piezoelectric element is configured by stacking a plurality of piezoelectric layers and connecting the plurality of piezoelectric layers in parallel.
  • the technology using the laminated piezoelectric element is disclosed in Patent Document 3 below, although the technical field is different from that of the ultrasonic sensor.
  • JP 2002-204497 A Japanese Patent Laid-Open No. 01-245799 JP 2003-337140 A
  • the present invention relates to an ultrasonic sensor capable of increasing the sound pressure when ultrasonic waves are transmitted using a laminated piezoelectric element as compared with the prior art, and a sensor device including such an ultrasonic sensor.
  • the purpose is to provide.
  • An ultrasonic sensor includes a bottomed cylindrical case and a piezoelectric element that is provided on an inner surface of a bottom portion of the case and that bends and vibrates together with the bottom portion of the case. Includes a plurality of piezoelectric layers that are sequentially stacked in the direction away from the bottom with electrodes interposed therebetween and electrically connected in parallel, and the plurality of piezoelectric layers are provided farthest from the case side. The thickness of the piezoelectric layer is the smallest.
  • An ultrasonic sensor includes a bottomed cylindrical case and a piezoelectric element that is provided on an inner surface of a bottom portion of the case and that bends and vibrates together with the bottom portion of the case. Includes a first piezoelectric layer and a second piezoelectric layer, which are sequentially stacked in a direction away from the bottom portion with electrodes interposed therebetween and electrically connected in parallel, and the first piezoelectric layer has a thickness greater than the thickness of the first piezoelectric layer. 2 The thickness of the piezoelectric layer is smaller.
  • the ratio of the thickness of the first piezoelectric layer to the total thickness of the first piezoelectric layer and the second piezoelectric layer is from 58% to 80%.
  • An ultrasonic sensor includes: a bottomed cylindrical case; and a piezoelectric element that is provided on an inner surface of a bottom portion of the case and that bends and vibrates together with the bottom portion of the case. Includes a first piezoelectric layer, a second piezoelectric layer, and a third piezoelectric layer, which are sequentially stacked in a direction away from the bottom portion with an electrode interposed therebetween and electrically connected in parallel. The thicknesses of the second piezoelectric layer and the third piezoelectric layer become smaller in this order.
  • the ratio of the thickness of the first piezoelectric layer to the total thickness of the first piezoelectric layer, the second piezoelectric layer, and the third piezoelectric layer is 40% or more and 72% or less,
  • the ratio of the total thickness of the first piezoelectric layer and the second piezoelectric layer is 76% or more and 90% or less.
  • An ultrasonic sensor includes: a bottomed cylindrical case; and a piezoelectric element that is provided on an inner surface of the bottom of the case and that bends and vibrates with the bottom of the case. Includes a first piezoelectric layer, a second piezoelectric layer, a third piezoelectric layer, and a fourth piezoelectric layer, which are sequentially stacked in a direction away from the bottom portion with electrodes interposed therebetween and electrically connected in parallel, The thicknesses of the first piezoelectric layer, the second piezoelectric layer, the third piezoelectric layer, and the fourth piezoelectric layer are reduced in this order.
  • the ratio of the thickness of the first piezoelectric layer to the total thickness of the first piezoelectric layer, the second piezoelectric layer, the third piezoelectric layer, and the fourth piezoelectric layer is 40% or more. 60% or less, and the ratio of the total thickness of the first piezoelectric layer and the second piezoelectric layer is 64% or more and 83% or less, and the first piezoelectric layer, the second piezoelectric layer, and the second piezoelectric layer.
  • the ratio of the total thickness of the three piezoelectric layers is 84% or more and 95% or less.
  • An ultrasonic sensor includes a bottomed cylindrical case, and a piezoelectric element that is provided on an inner surface of the bottom of the case and bends and vibrates together with the bottom of the case. Includes a piezoelectric layer composed of n layers (n is an integer of 2 or more) stacked in a direction away from the bottom portion with an electrode interposed therebetween, and wherein the piezoelectric layer is composed of the n layers.
  • the thickness T1 of the piezoelectric layer positioned first from the bottom side is a value satisfying the following formula (1):
  • the thickness Tk of the piezoelectric layer located kth (k is an integer of 2 or more) from the bottom side is a value that satisfies the following formula (2).
  • the electrode provided in the piezoelectric element is formed so as to be electrically connected to the external electrode, and is formed so as not to be electrically connected to the internal electrode connecting the piezoelectric layers in parallel.
  • a floating electrode is provided at a position symmetrical to the internal electrode with respect to a plane passing through the center in the stacking direction of the piezoelectric elements.
  • a sensor device includes the ultrasonic sensor according to the present invention and a signal generation circuit that outputs a signal for driving the ultrasonic sensor, and the ultrasonic sensor includes the signal generation circuit.
  • the signal output from the circuit is input without being amplified.
  • an ultrasonic sensor capable of increasing the sound pressure when transmitting ultrasonic waves using a multilayer piezoelectric element as compared with the conventional one, and such an ultrasonic sensor.
  • a sensor device can be provided.
  • FIG. 2 is a diagram illustrating an outline of a circuit configuration of a sensor device according to Embodiment 1.
  • FIG. 3 is a diagram showing functional blocks of the sensor device in Embodiment 1.
  • FIG. 1 is a cross-sectional view illustrating an ultrasonic sensor according to Embodiment 1.
  • FIG. (A) is a top view which shows a part of ultrasonic sensor in Embodiment 1
  • (B) is sectional drawing which shows a part of ultrasonic sensor in Embodiment 1.
  • FIG. FIG. 3 is a cross-sectional view showing a state when a part of the ultrasonic sensor according to Embodiment 1 is bending-vibrated.
  • FIG. 3 is an enlarged cross-sectional view showing a metal case and a piezoelectric element of the ultrasonic sensor according to Embodiment 1.
  • FIG. 3 is a diagram illustrating a circuit configuration of a first piezoelectric layer and a second piezoelectric layer that constitute a piezoelectric element of the ultrasonic sensor according to Embodiment 1.
  • FIG. It is a figure for demonstrating the relationship between the thickness of a general piezoelectric element (piezoelectric body layer), and electric field strength. It is a figure for demonstrating the relationship between the piezoelectric material layer which has half thickness of the piezoelectric element shown in FIG. 8, and electric field strength.
  • FIG. 6 is an enlarged cross-sectional view showing a piezoelectric element in a second embodiment.
  • FIG. 6 is a diagram illustrating a circuit configuration of each piezoelectric layer constituting a piezoelectric element of an ultrasonic sensor according to Embodiment 2.
  • FIG. 6 In the configuration of the second embodiment, the voltage sensitivity, the charge sensitivity, and the generated electric energy are numerically calculated by changing the thickness ratio of each piezoelectric layer.
  • FIG. 6 is an enlarged cross-sectional view illustrating a piezoelectric element in a third embodiment.
  • FIG. 6 is a diagram showing a circuit configuration of each piezoelectric layer constituting a piezoelectric element of an ultrasonic sensor in a third embodiment.
  • the voltage sensitivity, the charge sensitivity, and the generated electric energy are numerically calculated by changing the thickness ratio of each piezoelectric layer.
  • FIG. 10 is an enlarged cross-sectional view illustrating a piezoelectric element according to a fifth embodiment.
  • FIG. 9 is an equivalent circuit corresponding to the circuit configuration of Embodiments 1 to 5 in Embodiment 6.
  • FIG. It is a figure which expands and shows the connection part of the amplifier circuit (transformer) and capacity
  • FIG. 10 is a diagram showing an outline of a circuit configuration of a sensor device in a sixth embodiment.
  • FIG. 10 is a diagram illustrating functional blocks of a sensor device according to a sixth embodiment.
  • FIG. 25 is a diagram showing functional blocks of a sensor device in a modification of the sixth embodiment.
  • FIG. 1 is a diagram illustrating an outline of a circuit configuration of the sensor device 1000.
  • the sensor device 1000 includes an ultrasonic sensor 100, a power source 200, a signal generation circuit 300, an amplification circuit 400, and a detection circuit 500.
  • the power source 200 outputs a DC voltage of 12 V, for example, and the DC voltage is input to the signal generation circuit 300 and converted into an AC voltage having a predetermined frequency.
  • the AC voltage is supplied to the ultrasonic sensor 100 while being boosted by the amplifier circuit 400.
  • the ultrasonic sensor 100 is driven, and ultrasonic waves are transmitted (transmitted) from the ultrasonic sensor 100 toward the air.
  • the sensor device 1000 will be described in more detail.
  • FIG. 2 is a diagram illustrating functional blocks of the sensor device 1000.
  • the sensor device 1000 includes an IC, and the IC includes a microcomputer 600 and a memory 610.
  • the microcomputer 600 reads data stored in the memory 610 and outputs a control signal suitable for driving the ultrasonic sensor 100.
  • the signal generation circuit 300 generates an AC voltage from the DC voltage based on the control signal output from the microcomputer 600, and outputs the AC voltage to the amplification circuit 400 (transformer).
  • the AC voltage boosted by the amplifier circuit 400 is supplied to the ultrasonic sensor 100. The higher the voltage input to the ultrasonic sensor 100 is, the stronger the ultrasonic sensor 100 is driven, the stronger the sound pressure generated, and the longer the detectable distance.
  • the ultrasonic sensor 100 has a resistor 110 and a capacitor 120 connected in parallel.
  • the received signal generated by the ultrasonic sensor 100 is sent to the reception amplifier 510 and input to the microcomputer 600 through the detection circuit 500.
  • the microcomputer 600 makes it possible to grasp the presence / absence of the target and information related to movement.
  • FIG. 3 is a cross-sectional view showing the ultrasonic sensor 100.
  • 4A is a plan view showing only the metal case 10 and the piezoelectric element 20 in the ultrasonic sensor 100
  • FIG. 4B is a plan view showing the metal case 10 and the piezoelectric element 20 in the ultrasonic sensor 100.
  • the ultrasonic sensor 100 includes a metal case 10, a piezoelectric element 20, a sound absorbing material 40, silicone 41 to 44, a relay substrate 51, lead wires 52, 53, Pin terminals 54 and 55, a connector 56, and a filling resin 60 are provided.
  • the metal case 10 includes a disk-shaped bottom part 11 and a cylindrical side wall part 14 provided along the periphery of the bottom part 11 and has a bottomed cylindrical shape as a whole.
  • the bottom portion 11 has an inner surface 12 and an outer surface 13, and the piezoelectric element 20 is disposed on the inner surface 12 of the bottom portion 11, and is joined to the inner surface 12 using an adhesive or the like (not shown).
  • the metal case 10 is made of aluminum having high elasticity and light weight, for example.
  • the metal case 10 is manufactured by forging or cutting such aluminum, for example.
  • the metal case 10 is an example of the “case” in the present invention.
  • the material of the case is not necessarily limited to metal, and may be made of resin, for example.
  • the silicones 41 and 42 have an annular shape, and are arranged so as to fix the piezoelectric element 20 to the inner surface 12 while surrounding the piezoelectric element 20.
  • the sound absorbing material 40 (also referred to as a damper) is made of a molded body having high elasticity, and faces the piezoelectric element 20 with a space therebetween.
  • the silicone 43 is provided so as to block the space on the side where the piezoelectric element 20 and the sound absorbing material 40 are arranged in the internal space of the metal case 10.
  • the silicone 44 holds the relay substrate 51.
  • the piezoelectric element 20 is provided with electrodes (not shown) on the front and back surfaces.
  • the electrode located on the inner surface 12 side of the bottom 11 when viewed from the piezoelectric element 20 is electrically connected to the outside (GND) through the metal case 10, the lead wire 52, the relay substrate 51, the pin terminal 54, and the connector 56.
  • the electrode located on the side opposite to the bottom 11 when viewed from the piezoelectric element 20 is electrically connected to the outside through the lead wire 53, the relay substrate 51, the pin terminal 55, and the connector 56.
  • FIG. 5 is a cross-sectional view showing a state where the bottom 11 of the metal case 10 and the piezoelectric element 20 are bending-vibrated.
  • a unimorph structure is formed by the bottom 11 of the metal case 10 and the piezoelectric element 20, and a stress neutral surface is formed during bending vibration.
  • the stress neutral surface is a surface serving as a boundary between the portion where the tensile stress is generated and the portion where the compressive stress is generated, and is located at the position of the joint surface between the bottom portion 11 of the metal case 10 and the piezoelectric element 20. It is formed.
  • the amount of expansion / contraction on the stress neutral surface is almost zero, the amount of expansion / contraction is small near the stress neutral surface, and the amount of expansion / contraction increases as the distance from the stress neutral surface increases.
  • each piezoelectric layer has a configuration in which the piezoelectric layer farthest from the bottom 11 of the metal case 10 is thinner than the piezoelectric layer closest to the bottom 11 of the metal case 10. According to this configuration, the sound pressure at the time of transmitting an ultrasonic wave increases, and the maximum detection distance by the ultrasonic sensor increases. In addition, by setting the thickness of each piezoelectric layer to be within an optimal range, it is possible to efficiently extract energy at the time of reception. This will be specifically described below.
  • FIG. 6 is an enlarged cross-sectional view showing the bottom 11 of the metal case 10 and the piezoelectric element 20.
  • the piezoelectric element 20 has a two-layer structure including a first piezoelectric layer 21 (hereinafter referred to as a first layer 21) and a second piezoelectric layer 22 (hereinafter referred to as a second layer 22).
  • the first layer 21 and the second layer 22 are produced by laminating a common electrode 32 between two piezoelectric layers made of thin piezoelectric ceramic having a strip shape, and firing them together. Is done.
  • the first layer 21 and the second layer 22 are laminated in this order in a direction away from the bottom 11, and an electrode 31 is provided on the opposite side of the electrode 32 of the first layer 21.
  • An electrode 33 is provided on the opposite side.
  • Two unit cells are constituted by the first layer 21 and the second layer 22 sandwiched between the electrodes 31 to 33 (internal electrodes). As shown in FIG. 7, these two unit cells are arranged on the side surface of the piezoelectric element. They are connected in parallel by provided external electrodes (electrode patterns or wiring members) (not shown).
  • the white arrow in FIG. 6 shows the polarization direction of each piezoelectric material layer.
  • the piezoelectric element will be described as having a laminated structure.
  • the white arrows in FIGS. 8 to 10 indicate the polarization direction of each piezoelectric layer.
  • the driving force per unit thickness of the piezoelectric element is proportional to the electric field strength E applied to the piezoelectric element.
  • E Vdd / t is established between the thickness t of the piezoelectric element having a single layer (one layer) structure and the electric field intensity E formed by the voltage Vdd applied to the piezoelectric element.
  • the electric field strength E is proportional to the force F. That is, the force F increases as the thickness decreases.
  • the power supply outputs a DC voltage of about 12V, for example, the AC voltage that can be generated by the signal generation circuit is 12V or less in principle. In order to realize a detection range on the order of several meters, 12 V or less is insufficient, and a mechanism for increasing the voltage is required.
  • a transformer (amplifying circuit 400) using magnetic coupling is simple and inexpensive.
  • the piezoelectric element shown in FIG. 10 has a structure in which two piezoelectric elements (piezoelectric layers) shown in FIG. 9 are laminated. With this structure, even with a piezoelectric element having a thickness t, the electric field strength can be doubled. In other words, the same force as before lamination can be realized with half the voltage before lamination.
  • the required voltage can be reduced accordingly.
  • the ultrasonic sensor can be driven without using a boosting means such as a transformer.
  • a two-layer structure including the first layer 21 and the second layer 22 is employed.
  • the thickness T2 of the second layer 22 is smaller than the thickness T1 of the first layer 21. That is, the second layer 22 farthest from the bottom 11 of the metal case 10 has a feature that it is thinner than the first layer 21 closest to the bottom 11 of the metal case 10. More specifically, the ratio of the thickness T1 of the first layer 21 to the total thickness (T1 + T2) of the thickness T1 of the first layer 21 and the thickness T2 of the second layer 22 is 58% or more and 80% or less. . That is, a relationship of 0.58 ⁇ T1 / (T1 + T2) ⁇ 0.80 is established between T1 and T2.
  • T1 is, for example, 350 ⁇ m
  • T2 is, for example, 150 ⁇ m.
  • the first layer 21 and the second layer 22 are polarized in the thickness direction as indicated by white arrows in FIG.
  • the first layer 21 and the second layer 22 are polarized in opposite directions with the electrode 32 as a boundary.
  • the work amount (F ⁇ m) is small in the portion near the stress neutral plane formed by the bending vibration. The further away from the elevation, the greater the work load.
  • the sound pressure of the transmitted ultrasonic wave is larger in the portion far from the stress neutral surface than in the portion near the stress neutral surface.
  • the sound pressure when transmitting ultrasonic waves can be calculated by adding the sound pressure of each piezoelectric layer.
  • the influence of the work amount of the piezoelectric layer (the second layer 22 in the present embodiment) farthest from the bottom 11 of the metal case 10 is dominant. That is, compared with the case where the thickness of the 1st layer 21 and the 2nd layer 22 is the same, or the case where the 2nd layer 22 is thicker than the 1st layer 21, in the case of this Embodiment, the 2nd layer 22 is By being thinner than the first layer 21, it is possible to increase the sound pressure when transmitting ultrasonic waves.
  • the sensitivity when receiving the reflected wave by the above configuration is improved.
  • there are two types of sensitivity when receiving reflected waves voltage sensitivity and charge sensitivity, and the generated electrical energy expressed as 1 ⁇ 2 of the product of charge sensitivity and voltage sensitivity is large. It can be said that the sensor has a high S / N, that is, a high sensitivity during reception.
  • the deformation stress generated in the piezoelectric layer due to bending vibration is reversed between positive and negative with respect to the stress neutral plane, and its magnitude increases in proportion to the distance from the stress neutral plane.
  • the electric field generated in the piezoelectric layer is proportional to the deformation stress generated in the piezoelectric layer, the electric field generated in the piezoelectric layer increases in proportion to the distance from the stress neutral plane.
  • the stress neutral surface is a joint surface between the metal case 10 and the piezoelectric element 20.
  • the voltage inside the piezoelectric layer increases in a quadratic function with respect to the thickness direction. Therefore, in the case of a laminated structure composed of a plurality of piezoelectric layers having the same thickness as in Patent Document 1 described at the beginning, a portion near the stress neutral plane, that is, a layer near the bottom of the metal case 10 is generated. An unbalanced state is formed in which the voltage is low and the generated voltage is high as the distance from the bottom of the metal case 10 increases.
  • Patent Document 2 has a demerit that requires a complicated circuit operation in which all layers are connected at the time of transmission and other than the outermost layer is disconnected at the time of reception.
  • the ratio of the thickness T1 of the first layer 21 to the total thickness (T1 + T2) of the thickness T1 of the first layer 21 and the thickness T2 of the second layer 22 is 58%. More than 80%.
  • the generated voltage of the first layer 21 and the second layer 22 is substantially the same, reducing the loss, and more Much of the generated electrical energy can be extracted. That is, the generated electrical energy can be greatly increased, and a highly sensitive ultrasonic sensor can be realized.
  • FIG. 11 shows the result of numerical calculation of the voltage sensitivity and the charge sensitivity when receiving a reflected wave having a certain intensity by changing the thickness ratio of the first layer in the configuration of the first embodiment by the finite element method. is there.
  • FIG. 12 is based on the voltage sensitivity and the charge sensitivity shown in FIG. 11, and is a diagram showing the relationship between the thickness ratio of the first layer and the generated electric energy.
  • the metal case 10 is made of aluminum with a Young's modulus of 70 GPa, and the bottom 11 has a disk shape with a thickness of 650 ⁇ m and a radius of 7 mm.
  • the piezoelectric element is made of, for example, lead zirconate titanate having a Young's modulus of 75 GPa, has a total thickness of 500 ⁇ m, and is a rectangular parallelepiped having a surface direction of 6.5 mm ⁇ 3.9 mm.
  • the piezoelectric element is composed of two piezoelectric layers, and has a structure in which the polarization direction is reversed with a common electrode provided therein as a boundary.
  • the electrode provided on the adhesion surface with the metal case and the electrode on the opposite side are short-circuited, and are fixed to 0V.
  • a common electrode provided inside the piezoelectric element is taken out as an electrode that doubles as drive and detection.
  • the charge sensitivity, voltage sensitivity, and generated electrical energy when the thickness ratio of the first layer was changed from 0% to 100% were determined. As shown in FIG. 11, the charge sensitivity increases the thickness ratio of the first layer. It increased monotonously. On the other hand, the voltage sensitivity was maximized when the thickness ratio of the first layer was approximately 62%, and thereafter decreased as the thickness ratio of the first layer increased.
  • the generated electric energy becomes maximum when the thickness ratio of the first layer is about 70%, and the generated electric energy is about 20% compared to the case where the thickness ratio of the first layer is 50%. Increased.
  • the generated electric energy is maximized when the thickness ratio of the first layer is approximately 70%, but a sufficient effect is exhibited even in the range of 58% to 80%.
  • FIG. 13 is an enlarged cross-sectional view of the piezoelectric element 20A according to the second embodiment.
  • the piezoelectric element 20A includes a first piezoelectric layer 21 (first layer 21), a second piezoelectric layer 22 (second layer 22), and a third piezoelectric layer 23 (hereinafter referred to as a third layer 23). It has a layer structure.
  • the first layer 21, the second layer 22, and the third layer 23 are stacked in this order in the direction away from the bottom 11.
  • An electrode 31 is provided between the first layer 21 and the bottom 11 of the metal case 10
  • an electrode 32 is provided between the first layer 21 and the second layer 22, and the second layer 22 and the third layer are provided.
  • 23 is provided with an electrode 33, and an electrode 34 is provided on the surface of the third layer 23.
  • Three unit cells are constituted by the first layer 21, the second layer 22, and the third layer 23 sandwiched between the electrodes 31 to 34 (internal electrodes). As shown in FIG. They are connected in parallel by an external electrode (electrode pattern or wiring member) (not shown) provided on the side surface of the piezoelectric element.
  • the ratio of the thickness T1 of the first layer 21 to the total thickness (T1 + T2 + T3) of the thickness T1 of the first layer 21, the thickness T2 of the second layer 22, and the thickness T3 of the third layer 23 is 40% or more and 72. % Or less.
  • the ratio of the total thickness of the first layer 21 and the second layer 22 to the total thickness (T1 + T2 + T3) is 76% or more and 90% or less.
  • the piezoelectric layer farthest from the bottom 11 of the metal case 10 is thinner than the piezoelectric layer closest to the bottom 11 of the metal case 10. It has a configuration.
  • the first layer, the second layer, and the third layer may be configured such that each thickness decreases in this order.
  • the first layer 21, the second layer 22, and the third layer 23 are polarized in the thickness direction as indicated by white arrows in FIG.
  • the first layer 21 and the second layer 22 are polarized in a direction away from each other with the electrode 32 therebetween.
  • the second layer 22 and the third layer 23 are polarized in a direction approaching each other with the electrode 33 therebetween.
  • the third layer 23 is thinner than the first layer 21, the sound pressure at the time of transmitting ultrasonic waves can be increased. Furthermore, since the voltage generated in the piezoelectric layer is a quadratic function, according to this configuration, the generated voltages of the first layer 21, the second layer 22, and the third layer 23 are substantially the same, reducing the loss. Therefore, it becomes possible to extract more generated electric energy. That is, the generated electrical energy can be greatly increased, and a highly sensitive ultrasonic sensor can be realized.
  • FIG. 15 shows the result of calculating the generated electric energy based on the numerical calculation of the voltage sensitivity and the charge sensitivity by the finite element method by changing the thickness ratio of each layer in the configuration of the second embodiment.
  • the generated electric energy becomes maximum when the thickness ratio of the first layer is about 58% and the total ratio of the first layer and the second layer is 82%.
  • the generated electrical energy increased by about 25%.
  • the thickness ratio of the first layer is 40% or more and 72% or less and the ratio of the total thickness of the first layer and the second layer is 76% or more and 90% or less. (See Examples A2 to A4).
  • FIG. 16 is an enlarged cross-sectional view of the piezoelectric element 20B according to the third embodiment.
  • the piezoelectric element 20B includes a first piezoelectric layer 21 (first layer 21), a second piezoelectric layer 22 (second layer 22), a third layer 23 (third layer 23), and a fourth piezoelectric layer (first layer). It has a four-layer structure consisting of four layers 24).
  • the first layer 21, the second layer 22, the third layer 23, and the fourth layer 24 are stacked in this order in a direction away from the bottom 11.
  • An electrode 31 is provided between the first layer 21 and the bottom 11 of the metal case 10
  • an electrode 32 is provided between the first layer 21 and the second layer 22, and the second layer 22 and the third layer are provided.
  • An electrode 33 is provided between the third layer 23 and the fourth layer 24, and an electrode 35 is provided on the surface of the fourth layer 24.
  • Each unit cell is constituted by the first layer 21, the second layer 22, the third layer 23, and the fourth layer 24 sandwiched between the electrodes 31 to 35 (internal electrodes). As shown in FIG.
  • the two unit cells are connected in parallel by an external electrode (an electrode pattern or a wiring member) (not shown) provided on the side surface of the piezoelectric element.
  • the ratio of the thickness T1 of the first layer 21 to the total thickness (T1 + T2 + T3 + T4) of the thickness T1 of the first layer 21, the thickness T2 of the second layer 22, and the thickness T3 of the third layer 23 is 40% or more 60 % Or less.
  • the ratio of the total thickness of the first layer 21 and the second layer 22 to the total thickness (T1 + T2 + T3 + T4) is 64% or more and 83% or less.
  • the ratio of the total thickness of the first layer 21, the second layer 22, and the third layer 23 to the total thickness (T1 + T2 + T3 + T4) is 84% or more and 95% or less.
  • each piezoelectric layer has a piezoelectric layer farthest from the bottom 11 of the metal case 10 than a piezoelectric layer closest to the bottom 11 of the metal case 10.
  • the structure is thin.
  • the first layer, the second layer, the third layer, and the fourth layer may be configured such that the thicknesses thereof are reduced in this order.
  • the first layer 21, the second layer 22, the third layer 23, and the fourth layer 24 are polarized in the thickness direction as indicated by white arrows in FIG.
  • the first layer 21 and the second layer 22 are polarized in a direction away from each other with the electrode 32 therebetween.
  • the second layer 22 and the third layer 23 are polarized in a direction approaching each other with the electrode 33 therebetween.
  • the third layer 23 and the fourth layer 24 are polarized in a direction away from each other with the electrode 34 therebetween.
  • the fourth layer 24 is thinner than the first layer 21, it is possible to increase the sound pressure when transmitting ultrasonic waves. Furthermore, since the voltage generated in the piezoelectric layer is a quadratic function, according to the configuration, the generated voltages of the first layer 21, the second layer 22, the third layer 23, and the fourth layer 24 are substantially the same. Thus, loss can be reduced and more generated electric energy can be extracted. That is, the generated electrical energy can be greatly increased, and a highly sensitive ultrasonic sensor can be realized.
  • FIG. 18 shows the results of calculating the generated electrical energy based on the numerical calculation of the voltage sensitivity and the charge sensitivity by the finite element method with the thickness ratio of each layer changed in the configuration of the third embodiment.
  • the generated electric energy is such that the thickness ratio of the first layer is 50%, the total ratio of the first layer and the second layer is 69%, and the first layer and the second layer When the total ratio of the third layer and the third layer is 87%, the maximum is obtained, and the generated electric energy is increased by about 25% as compared with the case of Comparative Example B.
  • the ratio of the thickness of the first layer is 40% or more and 60% or less, and the ratio of the total thickness of the first layer and the second layer is 64% or more and 83% or less, and When the ratio of the total thickness of the first layer, the second layer, and the third layer was 84% or more and 95% or less, a sufficient effect was exhibited (see Examples B2 to B5).
  • the voltage generated in the piezoelectric layer is a quadratic function.
  • the piezoelectric element has a piezoelectric layer composed of n layers (n is an integer of 2 or more).
  • the total thickness of the piezoelectric layer composed of n layers is T.
  • the k-th coordinate (k is an integer between 1 and n) in the t-axis direction that divides the voltage V (t) at the coordinate t farthest from the bottom 11 of the metal case 10 into n equal parts.
  • the voltage is ideally k * V (t) / n.
  • the voltage V (t) at the coordinate t farthest from the bottom 11 of the metal case 10 among the piezoelectric elements. Is divided into n equal parts. If the value obtained at this time is the target voltage value, the generated voltage at each coordinate (t1, t2, t3...) When the coordinate t (thickness t) is divided into n is substantially the same as the target voltage value (for example, , ⁇ 10%). Therefore, the thickness T1 of the piezoelectric layer located first from the bottom 11 side of the metal case 10 is a value that satisfies the following equation (1).
  • the thickness Tk of the piezoelectric layer located kth (k is an integer of 2 or more) from the bottom 11 side of the metal case 10 is a value that satisfies the following equation (2).
  • the generated voltage in each piezoelectric layer is substantially the same as the target voltage value ( ⁇ 10%), reducing loss and extracting more generated electric energy. Can do.
  • FIG. 19 is an enlarged cross-sectional view of the piezoelectric element 20C according to the fifth embodiment.
  • the piezoelectric element 20C includes a first piezoelectric layer 21 (first layer 21), a second piezoelectric layer 22 (second layer 22), a third layer 23 (third layer 23), and a fourth piezoelectric layer (first layer). It has a four-layer structure consisting of four layers 24).
  • the first layer 21, the second layer 22, the third layer 23, and the fourth layer 24 are stacked in this order in a direction away from the bottom 11.
  • An electrode 31 is provided between the first layer 21 and the bottom 11 of the metal case 10
  • an electrode 32 is provided between the first layer 21 and the second layer 22, and the second layer 22 and the third layer are provided.
  • An electrode 33 is provided between the third layer 23 and the fourth layer 24, and an electrode 35 is provided on the surface of the fourth layer 24.
  • a first external electrode 38 is provided on the first side surface of the piezoelectric element 20C.
  • a second external electrode 39 is provided on the second side surface facing the first side surface.
  • the electrode 31, the electrode 33, and the electrode 35 are electrically connected to the first external electrode 38, and the electrode 32 and the electrode 34 are electrically connected to the second external electrode 39.
  • unit cells are constituted by the first layer 21, the second layer 22, the third layer 23, and the fourth layer 24 sandwiched between the electrodes 31 to 35 (internal electrodes), and these four unit cells are piezoelectric elements. These are connected in parallel by external electrodes 38 and 39 provided on the side surfaces of them and wiring members (not shown).
  • the floating electrode is provided so as to be plane-symmetric with the internal electrode with respect to the plane X.
  • the first floating electrodes 36a and 36b are provided so as to be plane-symmetric with the electrode 33 with respect to the plane X. Although the first floating electrodes 36a and 36b are separated from each other, they may be integrally formed. In the stacking direction of the piezoelectric elements 20C, the dimension Ta from the position of the surface X to the position where the electrode 33 is formed is the dimension Ta from the position of the surface X to the position where the first floating electrodes 36a and 36b are formed. Is equal to
  • second floating electrodes 37a and 37b are provided so as to be plane-symmetric with the electrode 34 with respect to the plane X. Although the second floating electrodes 37a and 37b are separated from each other, they may be integrally formed. In the stacking direction of the piezoelectric elements 20C, the dimension Tb from the position of the surface X to the position where the electrode 34 is formed is the dimension Tb from the position of the surface X to the position where the second floating electrodes 37a and 37b are formed. Is equal to
  • an electrode 35 is further provided so as to be plane-symmetric with the electrode 31 with respect to the plane X.
  • the dimension Tc from the position of the surface X to the position where the electrode 31 is formed is equal to the dimension Tc from the position of the surface X to the position where the electrode 35 is formed.
  • the floating electrodes 36a, 36b, 37a, and 37b are electrodes that are not electrically connected to any of the internal electrodes (electrodes 31 to 35) and the external electrodes 38 and 39.
  • the floating electrodes 36a, 36b, 37a, 37b are preferably made of the same material as the internal electrodes (electrodes 31 to 35), but may be made of another electrode material.
  • the fourth layer 24 is thinner than the first layer 21, it is possible to increase the sound pressure when transmitting ultrasonic waves. Further, by providing the floating electrode, it is possible to prevent a warp that may occur due to a difference in shrinkage rate between the internal electrode and the ceramic during firing of the piezoelectric ceramic.
  • the idea of providing a floating electrode to prevent warping can also be applied when the piezoelectric element is composed of a piezoelectric layer having a two-layer structure (Embodiment 1), and the piezoelectric element is a piezoelectric layer having a three-layer structure
  • the present invention can be applied to the case where the piezoelectric element is composed of piezoelectric layers having a plurality of layer structures other than 2 to 4 (Embodiment 2). Also with the configuration of the present embodiment, the generated electrical energy can be significantly increased, and a highly sensitive ultrasonic sensor can be realized.
  • an amplifier circuit 400 is used in the sensor device of each of the embodiments described above. In the fifth embodiment, the amplifier circuit 400 is not used. This configuration can be applied to any of Embodiments 1 to 5 described above. Hereinafter, the operation and effect when the amplifier circuit 400 is not used and the signal output from the signal generation circuit 300 is input to the ultrasonic sensor 100 without being amplified will be described.
  • FIG. 20 is an equivalent circuit corresponding to the circuit configuration of the first to fifth embodiments, and shows an equivalent circuit including the amplifier circuit 400 (transformer) and the ultrasonic sensor 100 (piezoelectric element).
  • the ultrasonic sensor 100 In addition to the function of transmitting ultrasonic waves, the ultrasonic sensor 100 also has a detection function of receiving ultrasonic waves, and the charge accumulated in the capacitor C2 is detected at the time of detection.
  • FIG. 21 is an enlarged view showing a connection portion between the amplifier circuit 400 (transformer) and the capacitor C2.
  • the circuit including L2 and C2 constitutes an LC resonance circuit.
  • this LC resonance circuit has a very large amplification factor at the resonance frequency, a component close to the resonance frequency in the electromagnetic wave (external noise) is greatly amplified. Therefore, it can be said that the configuration having a transformer is more susceptible to external noise than the configuration having no transformer.
  • the piezoelectric element may have a thickness of 340 ⁇ m and a stacked configuration including six piezoelectric layers.
  • the step-up ratio of the transformer can be reduced. That is, since the size of the transformer can be reduced, an effect that the entire detection function can be made smaller than before can be obtained.
  • a sensor device 1002 shown in FIG. 25 is obtained by adding a booster circuit 210 to the configuration of FIG.
  • the point that the transformer is not used is common to the case of FIG. 24, and the voltage can be raised from the power supply (12 V) to, for example, 40 V by the booster circuit 210. That is, the sound pressure of the ultrasonic sensor can be increased, the sensitivity of the ultrasonic sensor can be increased, and the detection distance can be increased.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Transducers For Ultrasonic Waves (AREA)

Abstract

Un capteur ultrasonore comprend un boîtier (10) et un élément piézoélectrique (20) placé sur la face interne (12) de la section inférieure (11) du boîtier et qui est soumis à des vibrations de déformation angulaire conjointement avec la section inférieure (11). L'élément piézoélectrique (20) comprend une première couche piézoélectrique (21) et une seconde couche piézoélectrique (22) qui sont empilées en partant de la section inférieure (11), sont séparées par une électrode et connectées électriquement en parallèle. L'épaisseur de la seconde couche piézoélectrique (22) est inférieur à l'épaisseur de la première couche piézoélectrique (21). La présente invention permet d'augmenter la pression acoustique lorsqu'une onde ultrasonore est transmise.
PCT/JP2014/076770 2013-10-11 2014-10-07 Capteur ultrasonore, et dispositif capteur WO2015053253A1 (fr)

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JP2013213962 2013-10-11
JP2013-213962 2013-10-11

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WO2015053253A1 true WO2015053253A1 (fr) 2015-04-16

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WO (1) WO2015053253A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110324769A (zh) * 2018-03-28 2019-10-11 精工爱普生株式会社 超声波传感器以及超声波装置
CN114092976A (zh) * 2020-07-30 2022-02-25 京东方科技集团股份有限公司 指纹识别单元及其制备方法、指纹识别模组和显示装置

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH01261879A (ja) * 1988-04-13 1989-10-18 Jgc Corp 積層型変位素子
JP2000156988A (ja) * 1998-09-18 2000-06-06 Seiko Instruments Inc 圧電アクチュエ―タおよび圧電アクチュエ―タ付電子機器
JP2002204497A (ja) * 2000-12-28 2002-07-19 Ngk Spark Plug Co Ltd 超音波センサ
JP2010069618A (ja) * 2008-09-16 2010-04-02 Brother Ind Ltd 液体吐出ヘッド及び圧電アクチュエータ

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH01261879A (ja) * 1988-04-13 1989-10-18 Jgc Corp 積層型変位素子
JP2000156988A (ja) * 1998-09-18 2000-06-06 Seiko Instruments Inc 圧電アクチュエ―タおよび圧電アクチュエ―タ付電子機器
JP2002204497A (ja) * 2000-12-28 2002-07-19 Ngk Spark Plug Co Ltd 超音波センサ
JP2010069618A (ja) * 2008-09-16 2010-04-02 Brother Ind Ltd 液体吐出ヘッド及び圧電アクチュエータ

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110324769A (zh) * 2018-03-28 2019-10-11 精工爱普生株式会社 超声波传感器以及超声波装置
CN110324769B (zh) * 2018-03-28 2022-04-08 精工爱普生株式会社 超声波传感器以及超声波装置
CN114092976A (zh) * 2020-07-30 2022-02-25 京东方科技集团股份有限公司 指纹识别单元及其制备方法、指纹识别模组和显示装置

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