JP2004184423A - Ultrasonic transducer and ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic transmitting transducer high in a manufacturing yield, and reliability, while providing a acoustic matching layer formed with a material of low mechanical strength and low speed of the sound. <P>SOLUTION: The ultrasonic transducer is provided with: a piezoelectric body 4; an acoustic matching layer 3 provided on the piezoelectric body 4; and a protector part 2 being in contact with at least a part of a side of the acoustic matching layer 3 and provided on a fixed position to the piezoelectric body 4. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an ultrasonic transceiver having an acoustic matching layer, a method for manufacturing the same, and an ultrasonic flowmeter provided with the ultrasonic transceiver.

    In recent years, an ultrasonic flowmeter that measures the time that an ultrasonic wave travels a predetermined distance in a pipe through which a fluid flows and measures the moving speed of the fluid to determine the flow rate based on the moving speed has been used in gas meters and the like. It is getting.

  FIG. 35 shows a sectional configuration of a main part of such an ultrasonic flowmeter. The ultrasonic flowmeter is arranged so that a fluid to be measured whose flow rate is to be measured flows through the pipe. On the tube wall 102, a pair of ultrasonic transceivers 101a and 101b are installed facing each other. The ultrasonic transceivers 101a and 101b are configured using a piezoelectric vibrator such as a piezoelectric ceramic as an electric energy / mechanical energy conversion element, and exhibit resonance characteristics like a piezoelectric buzzer and a piezoelectric oscillator.

  In the state shown in FIG. 35, the ultrasonic transceiver 101a is used as an ultrasonic transmitter, and the ultrasonic transceiver 101b is used as an ultrasonic receiver.

  When an AC voltage having a frequency near the resonance frequency of the ultrasonic transceiver 101a is applied to a piezoelectric body (piezoelectric vibrator) in the ultrasonic transceiver 101a, the ultrasonic transceiver 101a functions as an ultrasonic transmitter, Emit ultrasonic waves into the fluid. The emitted ultrasonic wave propagates along the path L1 and reaches the ultrasonic transceiver 101b. At this time, the ultrasonic transceiver 101b functions as a wave receiver, receives the ultrasonic wave, and converts it into a voltage.

  Next, this time, the ultrasonic transceiver 101b functions as an ultrasonic transmitter, and the ultrasonic transceiver 101a functions as an ultrasonic receiver. That is, by applying an AC voltage having a frequency near the resonance frequency of the ultrasonic transceiver 101b to the piezoelectric body in the ultrasonic transceiver 101b, the ultrasonic transceiver 101b emits ultrasonic waves into the fluid. The emitted ultrasonic wave propagates along the path L2 and reaches the ultrasonic transceiver 101a. The ultrasonic transceiver 101a receives the transmitted ultrasonic wave and converts it into a voltage.

  As described above, since the ultrasonic transceivers 101a and 101b alternately perform the function as a transmitter and the function as a receiver, they are generally referred to as an ultrasonic transceiver (or an ultrasonic transceiver). .

  In the ultrasonic flow meter shown in FIG. 35, if an AC voltage is continuously applied, ultrasonic waves are continuously emitted from the ultrasonic transceiver, and it becomes difficult to measure the propagation time. Is used as a drive voltage.

  Hereinafter, the measurement principle of the ultrasonic flowmeter will be described in more detail.

  When an ultrasonic burst signal is emitted from the ultrasonic transceiver 101a by applying a driving burst voltage signal to the ultrasonic transceiver 101a, the ultrasonic burst signal propagates along the path L1 and after the time t, the ultrasonic transceiver 101a It reaches 101b. It is assumed that the distance of the route L1 is L, similarly to the distance of the route L2.

  The ultrasonic transceiver 101b can convert only the transmitted ultrasonic burst signal into an electric burst signal with a high S / N ratio. The electric burst signal is electrically amplified and applied again to the ultrasonic transceiver 101a to emit an ultrasonic burst signal. A device that performs such an operation is called a “sing-around device”. Further, the time from when the ultrasonic pulse is emitted from the ultrasonic transceiver 101a to when it reaches the ultrasonic transceiver 102b is referred to as a “sing-around period”. The reciprocal of the "sing-around period" is called the "sing-around frequency."

  In FIG. 35, V is the flow velocity of the fluid flowing through the pipe, C is the velocity of the ultrasonic wave in the fluid, and θ is the angle between the flowing direction of the fluid and the propagation direction of the ultrasonic pulse. When the ultrasonic transmitter / receiver 101a is used as an ultrasonic transmitter and the ultrasonic transmitter / receiver 101b is used as an ultrasonic receiver, the time when an ultrasonic pulse emitted from the ultrasonic transmitter / receiver 101a reaches the ultrasonic transmitter / receiver 101b. If the sing-around period is t1 and the sing-around frequency f1 is, the following equation (1) is established.

  f1 = 1 / t1 = (C + Vcos θ) / L (1)

  Conversely, when the ultrasonic transceiver 101b is used as an ultrasonic transmitter and the ultrasonic transceiver 101a is used as an ultrasonic receiver, the sing-around period is t2 and the sing-around frequency f2 is as follows. The relationship of (2) is established.

  f2 = 1 / t2 = (C-Vcos θ) / L (2)

  The frequency difference Δf between both sing-around frequencies is expressed by the following equation (3).

  Δf = f1−f2 = 2Vcosθ / L (3)

  According to Equation (3), the flow velocity V of the fluid can be obtained from the distance L of the ultrasonic wave propagation path and the frequency difference Δf. Then, the flow rate can be determined from the flow velocity V.

  In such an ultrasonic flowmeter, high accuracy is required. In order to improve the accuracy, the acoustic impedance of the acoustic matching layer formed on the ultrasonic transmitting / receiving surface of the piezoelectric body in the ultrasonic transmitting / receiving device is important. The acoustic matching layer plays an important role particularly when the ultrasonic transceiver radiates (transmits) ultrasonic waves to the gas and receives ultrasonic waves transmitted through the gas.

  Hereinafter, the role of the acoustic matching layer will be described with reference to FIG. FIG. 36 shows a cross-sectional configuration of a conventional ultrasonic transceiver 103.

  The illustrated ultrasonic transceiver 103 includes a piezoelectric body 106 fixed inside a sensor case 105 and an acoustic matching layer 104 fixed outside the sensor case 105. The acoustic matching layer 104 is bonded to the sensor case 105 with an epoxy-based adhesive or the like. Similarly, the piezoelectric body 106 is also adhered to the sensor case 105.

  The ultrasonic vibration of the piezoelectric body 106 is transmitted to the sensor case 106 via the adhesive layer, and further transmitted to the acoustic matching layer 104 via another adhesive layer. Thereafter, the ultrasonic vibration is radiated as a sound wave to a gas (ultrasonic propagation medium) in contact with the acoustic matching layer 104.

  The role of the acoustic matching layer 104 is to efficiently propagate the vibration of the piezoelectric body to the gas. Hereinafter, this point will be described in more detail.

  The acoustic impedance Z of a substance is defined by the following equation (4) using the sound velocity C and the density ρ of the substance.

  Z = ρ × C (4)

The acoustic impedance of a gas to be radiated by ultrasonic waves is significantly different from the acoustic impedance of a piezoelectric body. The acoustic impedance Z1 of piezoceramics such as PZT (lead zirconate titanate), which is a general piezoelectric material, is about 30 × 10 ⁶ kg / m ² / s. On the other hand, the acoustic impedance Z3 of the air is about 400 kg / m ² / s.

  At the interface between substances having different acoustic impedances, sound waves are easily reflected, and the intensity of sound waves passing through the interface decreases. For this reason, a substance having an acoustic impedance Z2 represented by Expression (5) is inserted between the piezoelectric body and the gas.

Z2 = (Z1 × Z3) ^1/2 (5)

  When a substance having such an acoustic impedance Z2 is inserted, reflection at the boundary surface is suppressed, and the transmittance of sound waves is improved.

When the acoustic impedance Z1 is 30 × 10 ⁶ kg / m ² / s and the acoustic impedance Z3 is 400 kg / m ² / s, the acoustic impedance Z2 satisfying the expression (5) is 11 × 10 ⁴ kg / m ² / s. About. Naturally, a substance having a value of 11 × 10 ⁴ kg / m ² / s must satisfy Expression (4), that is, Z2 = ρ × C. It is extremely difficult to find such substances from solid materials. The reason is that, while being solid, it is required that the density ρ be sufficiently small and the sound velocity C be low.

  At present, as a material of the acoustic matching layer, a material obtained by solidifying a glass balloon or a plastic balloon with a resin material is widely used. As a method for producing a material suitable for such an acoustic matching layer, a method of thermally compressing a hollow glass sphere, a method of foaming a molten material, and the like are disclosed in, for example, Patent Document 1.

However, the acoustic impedance of these materials is a value larger than 50 × 10 ⁴ kg / m ² / s, and it cannot be said that the equation (5) is satisfied. In order to obtain a highly sensitive ultrasonic transceiver, it is necessary to form the acoustic matching layer with a material whose acoustic impedance is further reduced.

  In order to meet such a demand, the present applicant has invented an acoustic matching material that sufficiently satisfies the expression (5) and disclosed it in Japanese Patent Application No. 2001-056051. This material is manufactured using a dry gel having durability, and has a low density ρ and a low sound velocity C.

An ultrasonic transceiver having an acoustic matching layer formed of a material such as a dried gel having an extremely low acoustic impedance can transmit and receive ultrasonic waves efficiently and with high sensitivity to and from a gas. As a result, an apparatus capable of measuring the gas flow rate with high accuracy is realized.
Patent No. 2559144

  However, very low acoustic impedance materials, such as dried gels, generally have low mechanical strength. In particular, the dried gel is relatively strong in the stress in the compression direction, but extremely weak in the stress in the tension and bending directions, and easily broken by a weak impact.

  In addition, since such a material has a very low sound velocity, the thickness of the appropriate acoustic matching layer (about １ ／ of the transmission / reception wavelength) for obtaining the maximum transmission / reception sensitivity is extremely thin. For example, if the sound velocity of the material is 60 to 400 m / s, the preferred thickness of the acoustic matching layer is about 30 to 200 μm when transmitting and receiving ultrasonic waves of about 500 kHz. With such a thickness, it is extremely difficult to treat the acoustic matching layer as a single member, and it is almost impossible to fabricate an ultrasonic transceiver by bonding the acoustic matching layer to a sensor case or a piezoelectric body. However, even if possible, practical application is difficult from the viewpoint of manufacturing yield and cost.

  In addition, due to the low mechanical strength of the acoustic matching layer, there is a possibility that the ultrasonic vibration itself may cause peeling of the acoustic matching layer during use as an ultrasonic transmitter / receiver, so that the reliability may be reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a high yield while providing an acoustic matching layer formed of a material having a low mechanical strength such as a dried gel and a low sound speed. Another object of the present invention is to provide an ultrasonic transceiver having high reliability and a method of manufacturing the same.

  Another object of the present invention is to provide an ultrasonic flowmeter provided with the above-mentioned ultrasonic transceiver.

  An ultrasonic transceiver according to an aspect of the invention includes a piezoelectric body, an acoustic matching layer provided on the piezoelectric body, and a position that is in contact with at least a part of a side surface of the acoustic matching layer and is fixed to the piezoelectric body. And a protection unit provided in the control unit.

  In a preferred embodiment, the protection portion protrudes in the ultrasonic wave emitting direction from a plane at the same level as the main surface of the piezoelectric body, and the height of the protection portion with respect to the main surface of the piezoelectric body is equal to the acoustic height. It defines the thickness of the matching layer.

  In a preferred embodiment, the height of the protection portion is not less than 5 μm and not more than 2500 μm.

  In a preferred embodiment, the thickness of the acoustic matching layer is substantially equal to the height of the protection portion.

  In a preferred embodiment, the thickness of the acoustic matching layer is about １ ／ of the wavelength of the ultrasonic wave transmitted and / or received by the piezoelectric body.

In a preferred embodiment, the acoustic matching layer has a density of 50 kg / m ³ or more and 1000 k.
g / m ³ or less.

In a preferred embodiment, the acoustic matching layer has an acoustic impedance of 2.5 × 10 ^3.
It is formed from a material of not less than kg / m ² / s and not more than 1.0 × 10 ⁶ kg / m ² / s.

  In a preferred embodiment, the acoustic matching layer is formed from an inorganic material.

  In a preferred embodiment, the inorganic material is a dried gel of an inorganic oxide.

  In a preferred embodiment, the inorganic oxide has a water-repellent solid skeleton.

  In a preferred embodiment, the acoustic matching layer is solidified from a fluid state on the piezoelectric body provided with the protection portion.

  In a preferred embodiment, the piezoelectric device further includes a lower acoustic matching layer provided between the main surface of the piezoelectric body and the acoustic matching layer, and the protection unit protrudes from the main surface of the lower acoustic matching layer. The height of the protection portion with respect to the main surface of the acoustic matching layer defines the thickness of the acoustic matching layer positioned at the uppermost layer.

  In a preferred embodiment, the protection section is constituted by a part of the lower acoustic matching layer, and is integrated with the lower acoustic matching layer.

  In a preferred embodiment, the height of the protection portion is not less than 5 μm and not more than 2500 μm.

  In a preferred embodiment, the height of the protection section is substantially equal to the thickness of the acoustic matching layer located on the uppermost layer.

  In a preferred embodiment, each of the acoustic matching layer and the lower acoustic matching layer has a thickness of about ４ of a wavelength of an ultrasonic wave transmitted and received by the piezoelectric body.

In a preferred embodiment, the density of the first acoustic matching layer is not less than 50 kg / m ^{3 and not} more than 1000 k.
g / m ³ or less.

In a preferred embodiment, the acoustic impedance of the lower acoustic matching layer is larger than the acoustic impedance of the acoustic matching layer, and is not less than 2.5 × 10 ³ kg / m ² / s and 3.0 × 10 ⁷ kg / m ² / s. s or less.

  In a preferred embodiment, the protection portion exists on the outer periphery of the acoustic matching layer located on the uppermost layer.

  In a preferred embodiment, the protection portion covers the entire outer peripheral side surface of the acoustic matching layer located on the uppermost layer.

  In a preferred embodiment, the protection portion is disposed outside a main surface of the piezoelectric body.

  In a preferred embodiment, the protection section is provided on a main surface of the piezoelectric body.

  In a preferred embodiment, the protection section is provided on the lower acoustic matching layer.

  In a preferred embodiment, the protection section is constituted by a part of the lower acoustic matching layer, and is integrated with the lower acoustic matching layer.

  In a preferred embodiment, the apparatus further comprises a structural support for supporting the piezoelectric body.

  In a preferred embodiment, the apparatus further comprises a structural support for supporting the piezoelectric body, and the protection portion is provided on the structural support.

  In a preferred embodiment, the structural support is formed from a press-formed metal, and the protection portion is configured by a portion of the structural support that is bent by press forming.

  In a preferred embodiment, the height of the protection portion is not less than 5 μm and not more than 2500 μm.

  In a preferred embodiment, the thickness of the acoustic matching layer is substantially equal to the height of the protection portion.

  In a preferred embodiment, the thickness of the acoustic matching layer is about １ ／ of the wavelength of the ultrasonic wave transmitted and received by the piezoelectric body.

In a preferred embodiment, the density of the acoustic matching layer is 50 kg / m ³ or more and 1000 k.
g / m ³ or less.

The acoustic impedance of the acoustic matching layer is from 2.5 × 10 ³ kg / m ² / s to 1.0 × 10 ⁶ kg / m ² / s.

  In a preferred embodiment, the piezoelectric device further includes a back load member disposed on a back surface of the piezoelectric body, and the protection member is provided on the back load member.

  In a preferred embodiment, the protection portion is constituted by a part of the back load member, and is integrated with the back load member.

  In a preferred embodiment, at least a part of a surface of the acoustic matching layer in contact with the holding portion has been subjected to a surface treatment for imparting a hydroxyl group.

  In a preferred embodiment, at least a part of a surface where the acoustic matching layer contacts the holding portion has been subjected to a surface roughening treatment.

  In a preferred embodiment, at least a part of a surface where the acoustic matching layer contacts the holding portion is porous.

  In a preferred embodiment, a part of the acoustic matching layer of the ultrasonic transceiver that is in contact with the acoustic matching layer penetrates and is integrated.

Another ultrasonic transceiver according to the present invention includes a piezoelectric body that performs ultrasonic vibration, a density of 50 kg / m ³ or more and 1000 kg / m ³ or less, and an acoustic impedance of 2.5 × 10 ³ kg / m ² /. s
An upper acoustic matching layer formed of a material of 1.0 × 10 ⁶ kg / m ² / s or less; a lower acoustic matching layer provided between the piezoelectric body and the upper acoustic matching layer; An acoustic matching layer and a structural support that supports the piezoelectric body and shields the piezoelectric body from an ultrasonic wave propagating fluid, wherein the ultrasonic transceiver contacts at least a part of a side surface of the upper acoustic matching layer. It has a protection unit.

  The protection part is formed by a part of the lower acoustic matching layer, and is integrated with the lower acoustic matching layer.

  In a preferred embodiment, the elastic modulus of the protection part is substantially equal to the elastic modulus of the acoustic matching layer.

  An ultrasonic flow meter according to the present invention is configured such that a flow measurement unit through which a fluid to be measured flows, a pair of ultrasonic transceivers provided in the flow measurement unit, for transmitting and receiving ultrasonic signals, and a pair of the ultrasonic transceivers. A measuring means for measuring the time that the ultrasonic wave propagates, and an ultrasonic flow meter comprising a flow rate calculating means for calculating a flow rate based on a signal from the measuring means, wherein the pair of ultrasonic transceivers Each is any one of the ultrasonic transceivers described above.

  In a preferred embodiment, the piezoelectric body of the ultrasonic transceiver is shielded from the fluid to be measured.

  An apparatus according to the present invention includes any one of the above-described ultrasonic transceivers.

  According to a method of manufacturing an ultrasonic transceiver according to the present invention, there is provided a step (a) of preparing a piezoelectric body having a main surface and a convex portion received on the main surface, and acoustic matching on the main surface of the piezoelectric body. Forming a layer and contacting at least a part of the side surface of the acoustic matching layer with the side surface of the projection.

  In a preferred embodiment, the step (b) includes a step of supplying a gel raw material on the main surface of the piezoelectric element, and a step of forming the acoustic matching layer by drying and solidifying the gel raw material. Contains.

  In a preferred embodiment, the step (a) includes a step of processing the surface of the piezoelectric body to form the main surface and the projection.

In a preferred embodiment, the step (a) includes a step of fixing the projection on the surface of the piezoelectric body.

  In a preferred embodiment, the step (a) includes a step of fixing the piezoelectric body to the structural support.

  The method of manufacturing an ultrasonic transceiver according to the present invention includes an ultrasonic transceiver including an upper acoustic matching layer, a piezoelectric body, and a lower acoustic matching layer provided between the upper acoustic matching layer and the piezoelectric body. A method of preparing a member having a recess and functioning as the lower acoustic matching layer (a); and supplying a gel material to the recess of the member (b). (C) forming the upper acoustic matching layer by drying and solidifying the gel raw material.

  In a preferred embodiment, the step (b) includes a step of permeating the gel material into the member.

  In a preferred embodiment, the gel raw material is permeated throughout the member.

  In a preferred embodiment, the step (b) is performed after the positional relationship between the member and the piezoelectric body is fixed. The step (b) may be performed before fixing the arrangement relationship between the member and the piezoelectric body.

  An ultrasonic transmitter / receiver according to the present invention includes a piezoelectric body, an acoustic matching layer provided on the piezoelectric body, and a protection unit arranged to be in contact with an outer peripheral surface of the acoustic matching layer.

  The ultrasonic transceiver of the present invention is arranged so as to be in contact with a structural support, a piezoelectric body and an acoustic matching layer provided at positions opposed to each other with the structural support interposed therebetween, and an outer peripheral surface of the acoustic matching layer. And a protection unit.

  Still another ultrasonic transducer of the present invention includes a piezoelectric body having a main surface for transmitting and / or receiving ultrasonic waves, and an acoustic matching member provided on the main surface of the piezoelectric body. Wherein the acoustic matching member has a first acoustic matching portion and a second acoustic matching portion having an average density lower than the average density of the first acoustic matching portion. The first acoustic matching portion is in contact with a side surface of the second acoustic matching portion.

  In a preferred embodiment, the first acoustic matching section is thicker than the second acoustic matching section, and is radiated from a main surface of the piezoelectric body, passes through the second acoustic matching section, and has an upper surface of the first acoustic matching section. And the phase of the ultrasonic wave arriving at the same level as that of the ultrasonic wave radiated from the main surface and transmitted through the first acoustic matching portion and reaching the upper surface of the first acoustic matching portion substantially coincides with each other. ing.

  In a preferred embodiment, when the wavelength of the ultrasonic wave in the first acoustic matching portion is λ1, the thickness of the first acoustic matching portion is k1 · λ1 (k1 is ８ or more and ３ or less). And is different from the thickness of the 21st acoustic matching portion.

  In a preferred embodiment, the second acoustic matching portion is composed of N acoustic matching layers (N is an integer of 1 or more), and each of the N acoustic matching layers includes the supersonic wave in each acoustic matching layer. It has a size of k2 times the wavelength of the sound wave (k2 is 1/8 or more and 1/3 or less).

  In a preferred embodiment, the thickness of the acoustic matching layer located on the outermost layer of the second acoustic matching portion is about １ ／ of the wavelength of the ultrasonic wave in the acoustic matching layer located on the outermost layer of the second acoustic matching portion. It is.

  In a preferred embodiment, of the second acoustic matching portion, an acoustic matching layer formed at a position closest to a main surface of the piezoelectric body is made of the same material as the material of the first acoustic matching portion. .

  In a preferred embodiment, of the second acoustic matching portion, an acoustic matching layer formed at a position closest to a main surface of the piezoelectric body is formed integrally with the first acoustic matching portion.

  In a preferred embodiment, at least one acoustic matching layer included in the second acoustic matching portion is formed from a dry gel.

  In a preferred embodiment, the dried gel is made of an inorganic material.

  In a preferred embodiment, the dry gel has a water-repellent solid skeleton.

  In a preferred embodiment, at least a part of a surface of the member constituting the sound wave transducer that contacts the acoustic matching portion is a rough surface or a porous surface.

  In a preferred embodiment, of the members constituting the ultrasonic transducer, at least a part of a surface in contact with the second acoustic matching portion, a part of the second acoustic matching portion is penetrated and integrated with the member. .

  In a preferred embodiment, at least a part of the second acoustic matching portion is formed of a dry gel, and the first acoustic matching portion is formed of a material having higher mechanical strength than the dry gel.

  In a preferred embodiment, at least a part of the first acoustic matching portion is formed of a porous ceramic.

  In a preferred embodiment, a thickness of the first acoustic matching portion changes according to a position on a main surface of the piezoelectric body.

  In a preferred embodiment, a thickness of the second acoustic matching portion changes according to a position on the main surface of the piezoelectric body.

  An ultrasonic flowmeter according to the present invention includes a flow measurement unit through which a fluid to be measured flows, a pair of ultrasonic transducers provided in the flow measurement unit, for transmitting and receiving an ultrasonic signal, and the pair of ultrasonic transmission and reception. A measuring unit that measures the time that the ultrasonic wave propagates between the vessels, and an ultrasonic flow meter that includes a flow rate calculating unit that calculates a flow rate based on a signal from the measuring unit, wherein the pair of ultrasonic waves Each of the transducers is any one of the ultrasonic transducers described above.

  In a preferred embodiment, a piezoelectric body of the ultrasonic transducer is shielded from the fluid to be measured.

  In a preferred embodiment, the fluid to be measured is a gas.

  The device of the present invention includes any one of the above-described ultrasonic transducers.

  The method of manufacturing an ultrasonic transducer according to the present invention includes: (a) a first surface and a second surface opposite to the first surface, wherein electrodes are provided on the first and second surfaces. Providing a formed piezoelectric body; (b) forming a second acoustic matching portion on at least one of the first and second surfaces of the piezoelectric body; and (c) forming the piezoelectric body. A step of supplying a gel raw material into a space formed by the second acoustic matching portion; (d) a step of gelling the gel raw material liquid to obtain a wet gel; Drying.

  In a preferred embodiment, the step (c) includes: (c1) a step of supplying a first gel raw material into the space; and (c2) a step of gelling the first gel raw material liquid to form a first wet gel. Forming a layer, (c3) supplying a second gel material on the first wet gel layer, and (c4) gelling the second gel material liquid to form a second wet material. Forming a gel layer, wherein the step (e) comprises drying the first and second wet gel layers to form first and second sound gels from the first and second wet gel layers, respectively. Forming a matching layer and a second acoustic matching layer.

  In a preferred embodiment, in the step (c4), the first wet gel layer is modified so as to change an acoustic impedance of the first acoustic matching layer.

  An ultrasonic wave transmitter / receiver according to the present invention includes an ultrasonic wave including: a piezoelectric body having a main surface for transmitting and / or receiving ultrasonic waves; and an acoustic matching member provided on the main surface of the piezoelectric body. A transducer, wherein the acoustic matching member has a first acoustic matching portion and a second acoustic matching portion having a mechanical strength lower than a mechanical strength of the first acoustic matching portion; The one acoustic matching part is in contact with the side surface of the second acoustic matching part.

  According to the present invention, a high-performance ultrasonic transceiver using a thin acoustic matching layer formed of a material having extremely low acoustic impedance and low mechanical strength can be put to practical use. Reliability in use is also improved. According to the first aspect of the present invention, since the protection portion that protects the acoustic matching layer and can be used to regulate the thickness of the acoustic matching layer is provided, the mechanical strength is low and the acoustic matching layer is thin. Can be formed with high accuracy and high reproducibility. As a result, a highly reliable ultrasonic transducer capable of transmitting and receiving a wideband ultrasonic wave with high sensitivity is provided. Further, in the second aspect of the present invention, a protective portion (protective portion and acoustic matching layer = protective matching layer) that also functions as an acoustic matching layer can be provided at an arbitrary position on the main surface of the piezoelectric body. By adjusting the sound speed and the thickness of the two types of acoustic matching layers, the phases of the ultrasonic waves radiated from the two types of acoustic matching layers having different thicknesses can be aligned, and the transmission / reception sensitivity of the ultrasonic waves can be increased. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a cross section of an ultrasonic transceiver (ultrasonic transducer) according to the first embodiment of the present invention. The illustrated ultrasonic transceiver 1 includes a piezoelectric body 4, an acoustic matching layer 3 provided on the piezoelectric body 4, and a protection unit 2 fixed to the piezoelectric body 4.

  The piezoelectric body 4 is formed of a material having piezoelectricity and is polarized in the thickness direction. Unillustrated electrodes are formed on the upper and lower surfaces of the piezoelectric body 4, and emit ultrasonic waves based on signals applied to the electrodes. When receiving an ultrasonic wave, a voltage signal is generated between the electrodes. In the present invention, the material of the piezoelectric body 4 is arbitrary, and a known material can be used.

  The height H of the protection portion 2 with respect to the main surface (ultrasonic wave transmitting / receiving surface) S1 of the piezoelectric body 4 defines the thickness of the acoustic matching layer 3. In a preferred embodiment, the height of the protection portion 2 is acoustic. It is substantially equal to the thickness of the matching phase layer 3.

  FIG. 2 shows an upper surface of the ultrasonic transceiver 1 of FIG. As can be seen from FIG. 2, in the ultrasonic transceiver 1 of the present embodiment, the ring-shaped protection unit 2 surrounds the acoustic matching layer 3, and the entire outer peripheral surface (side surface) of the acoustic matching layer 3 is inside the protection unit 2. It is in contact with the peripheral surface. By providing such a protection portion 2 on the upper surface of the piezoelectric body 4, the acoustic matching layer 3 is less likely to be separated from the piezoelectric body 4, and the acoustic matching layer 3 can be prevented from being damaged. As a result, the reliability of the ultrasonic transceiver 1 in the manufacturing stage and the use stage is significantly improved.

  According to the manufacturing method described later, the thickness of the acoustic matching layer 3 can be controlled with high precision by adjusting the height H of the protection portion 2. Therefore, since the acoustic matching layer 3 can be formed stably with high accuracy, it is possible to manufacture an ultrasonic transceiver having excellent quality with high yield. If the thickness of the acoustic matching layer 3 varies from element to element, the characteristics (such as sensitivity) of the ultrasonic transceiver fluctuate. Therefore, it is important to form the acoustic matching layer 3 having a predetermined thickness with good reproducibility. . As described above, the appropriate thickness of the acoustic matching layer for obtaining the maximum transmission / reception sensitivity is about １ ／ of the wavelength of the transmitted / received ultrasonic wave. Therefore, when transmitting and receiving ultrasonic waves of about 500 kHz using a dry gel having a sound speed of about 280 m / s as the acoustic matching layer, it is necessary to set the preferable thickness of the acoustic matching layer of the dry gel to about 140 μm. . If the thickness differs by about 10%, the transmission / reception sensitivity may vary by about 20%. As described above, even if the thickness of the acoustic matching layer 3 slightly changes, the transmission / reception sensitivity greatly changes. However, according to the present embodiment, the acoustic matching layer 3 having a desired thickness is formed with good reproducibility. I have.

  The ultrasonic transceiver 1 of the present embodiment is manufactured, for example, as follows.

  First, a piezoelectric body 4 is prepared according to the wavelength of the ultrasonic wave to be transmitted and received. As the piezoelectric body 4, a material having high piezoelectricity such as piezoelectric ceramics or piezoelectric single crystal is preferable. As the piezoelectric ceramic, lead zirconate titanate, barium titanate, lead titanate, lead niobate, or the like can be used. As the piezoelectric single crystal, a lead zirconate titanate single crystal, lithium niobate, quartz, or the like can be used.

  In the present embodiment, the piezoelectric body 4 is made of lead zirconate titanate piezoelectric ceramics, and the frequency of the transmitted and received ultrasonic waves is set to 500 kHz. In order to allow the piezoelectric body 4 to efficiently transmit and receive such ultrasonic waves, the resonance frequency of the element is designed to be 500 kHz. For this reason, in the present embodiment, the piezoelectric body 4 formed of a piezoelectric ceramic having a cylindrical shape with a diameter of 12 mm and a thickness of about 3 mm is used.

  The ring-shaped protective portion 2 having an outer diameter of 12 mm, an inner diameter of 11 mm, and a thickness of 140 μm is joined to such a piezoelectric body 4. In the present embodiment, a metal ring made of stainless steel is used as the protection unit 2. The bonding between the stainless protection part 2 and the piezoelectric body 4 can be performed by bonding with an adhesive. For example, an epoxy resin may be used as an adhesive and cured by leaving it in a thermostat at 150 ° C. for 2 hours while applying a pressure of 0.2 MPa.

  In the present embodiment, the acoustic matching layer 3 is formed from a dried gel. Since the acoustic velocity of the acoustic matching layer 3 formed from the dried gel is about 280 m / s, the wavelength of the ultrasonic wave in the acoustic matching layer 3 is about 640 μm. For this reason, the thickness of the acoustic matching layer 3 is set to 140 μm so as to be equal to about の of the ultrasonic wavelength in the acoustic matching layer 3. In order to form the acoustic matching layer 3 having this thickness, in the present embodiment, the thickness of the protection section 2 is set to 140 μm.

  First, the role of the protection unit 2 is to protect the acoustic matching layer 3 from external mechanical shock or thermal shock during the manufacturing and use stages of the ultrasonic transceiver 1. Second, during operation (use) as the ultrasonic transceiver 1, protecting the ultrasonic transceiver 1 from vibration of transmitted / received ultrasonic waves also plays an important role.

  In order for the acoustic matching layer 3 to play its role, it is extremely important that the piezoelectric body 4 and the acoustic matching layer 3 are in close contact with each other. If any separation occurs between the piezoelectric body 4 and the acoustic matching layer 3, it cannot function as the acoustic matching layer 3.

  In order to maintain the adhesion between the piezoelectric body 4 and the acoustic matching layer 3, the inventor of the present application has a very effective structure in which the protective portion 2 is provided on the outer peripheral portion of the acoustic matching layer 3 as shown in FIG. I found something. If the protection unit 2 is not provided, there is a possibility that the characteristics of the ultrasonic transmitter / receiver 1 are significantly deteriorated at the time of manufacture or use, and the ultrasonic transmitter / receiver 1 with high performance cannot be put to practical use.

  The acoustic matching layer 3 of the present embodiment is formed from a material having an extremely small acoustic impedance defined by the product (ρ × C) of the density ρ and the sound velocity C. For this reason, the transmission / reception efficiency of ultrasonic waves with respect to a gas such as air can be extremely increased. In this embodiment, as described above, a dry gel is used as a material having an extremely small acoustic impedance.

  By forming the acoustic matching layer 3 from a dried gel, the acoustic matching between the gas and the piezoelectric body is improved as compared with the case where the acoustic matching layer is formed from a conventional material obtained by solidifying a glass balloon or a plastic balloon with a resin material. Since it is extremely improved, the ultrasonic transmission / reception efficiency can be remarkably improved.

  The `` dry gel '' in this specification is a porous body formed by a sol-gel reaction, and a solid skeleton solidified by a reaction of a gel raw material liquid passes through a wet gel configured to include a solvent, It is formed by drying and removing the solvent. This dried gel is a nanoporous body in which continuous pores having an average pore diameter of about several nm to several μm are formed by a solid skeleton of nanometer size.

  Because of the porous body having such a fine structure, the sound velocity propagating in the solid part is extremely low, and the sound velocity propagating in the gas part in the porous body by the pores is also extremely low. . Therefore, a very low value of about 500 m / s or less is exhibited as the sound velocity, and a low acoustic impedance completely different from the conventional acoustic matching layer can be obtained. Further, the nanometer-sized pore portion has a feature that a sound pressure can be radiated at a high sound pressure when used as an acoustic matching layer because the gas has a large pressure loss.

  Various materials such as an inorganic material and an organic polymer material can be used as the material of such a dried gel. As the solid skeleton of the inorganic material, silicon oxide (silica), aluminum oxide (alumina), titanium oxide, or the like can be used. As the solid skeleton of the organic material, a general thermosetting resin or a thermoplastic resin can be used. For example, polyurethane, polyurea, a phenol cured resin, polyacrylamide, polymethyl methacrylate, or the like can be used. .

  In the present embodiment, the acoustic matching layer 3 is formed from the above-mentioned dried gel inside the concave space P1 (see FIG. 1) formed in advance by the piezoelectric body 4 and the protection portion 2. That is, after the liquid gel raw material liquid is poured into the concave space P1 formed by the piezoelectric body 4 and the protection portion 2, the gelation, the hydrophobization, and the drying are performed, so that the acoustic matching layer 3 is dried. Form a gel. In this embodiment, a dry gel having a solid skeleton of silicon oxide is used as the acoustic matching layer 3.

  Specifically, the acoustic matching layer 3 can be formed by sequentially performing the following steps 1 to 4.

  1. A gel raw material liquid (sol) prepared by mixing tetraethoxysilane, ethanol, and an aqueous ammonia solution (0.1 N) at a molar ratio of 1: 3: 4 is prepared.

  2. This gel raw material liquid is dropped with a dropper into a concave space formed by the piezoelectric body and the protective part. At this time, an excess amount of the gel raw material liquid is dropped from the volume of the concave space P1. Next, a cutting operation using a Teflon (registered trademark) flat plate (not shown) was performed so that the height of the gel raw material liquid stored in the concave space P1 was the same as the height H of the protective portion. Then, cover with a Teflon plate.

  3. Leave at room temperature for about one day, and after the raw material liquid has gelled (formation of wet gel), remove the Teflon plate. Thereafter, a hydrophobic treatment is performed in a 5% by weight hexane solution of trimethylethoxysilane.

  4. Introduce into a supercritical drying tank, and perform supercritical drying at 12 MPa and 50 ° C. under a carbon dioxide atmosphere. Thus, a dried gel is formed.

Through the steps 1 to 4, for example, the acoustic matching layer 4 having a density ρ of 0.3 × 10 ³ kg / m ³ , a sound velocity C of 280 m / s, and a thickness of 140 μm can be formed.

According to the present invention, the density is 50 kg / m ³ or more and 1000 kg / m ³ or less, and the acoustic impedance is 2.5 × 10 ³ kg / m ² / s or more and 1.0 × 10 ⁶ kg / m ² / s or less. A remarkable effect is exhibited when the acoustic matching layer is formed from a material. According to the above-described method, such an acoustic matching layer can be suitably manufactured.

  According to the above method, the thickness of the acoustic matching layer 3 can be made substantially equal to the height H of the protection portion 2, so that the thickness of the acoustic matching layer 3 can be controlled with high accuracy by the protection portion 2. It can be said that the protection part 2 functions as a guide for the gel raw material liquid at a certain stage in the manufacturing process.

  According to the above method, since the acoustic matching layer 3 with small thickness variation can be formed with high yield, it is possible to suppress the characteristic variation of the ultrasonic transceiver. In the present invention, it is not essential that the height of the protection portion 2 is equal to the thickness of the acoustic matching layer 3. When the height of the protection part 2 is larger than the thickness of the acoustic matching layer 3, the function of suppressing the contraction of the acoustic matching layer 3 and protecting it from mechanical shock is sufficiently exhibited. Conversely, even when the height of the protection portion 2 is smaller than the thickness of the acoustic matching layer 3, if the protection portion 2 is not provided, the shrinkage of the acoustic matching layer 3 is suppressed, and the mechanical shock is suppressed. The protective function is exerted to a high degree.

The transmission / reception waveform of the ultrasonic transceiver including the acoustic matching layer 3 manufactured by the above method was measured. FIG. 3A shows a waveform diagram obtained by the measurement. For comparison, FIG. 3B shows transmission / reception waveforms when a material obtained by solidifying a glass balloon with epoxy is used for the acoustic matching layer. The acoustic matching layer of the glass balloon used here has a density of 0.52 g / cm ³ and a sound velocity of 2500.
m / s and thickness is 1.25 mm.

Note that, as described in the related art, it is desirable that the acoustic impedance of the acoustic matching layer indicates a value defined by Expression (5). In the present embodiment, the piezoelectric body 4 is made of lead zirconate titanate piezoelectric ceramics, and air is set as a propagation medium for transmitting ultrasonic waves. Therefore, since the density of the piezoelectric body 4 is 7.7 × 10 ³ kg / m ³ and the sound speed is 3800 m / s, the acoustic impedance is about 29 × 10 ⁶ kg / m ² / s. On the other hand, the density of the air is 0.00118 kg / m ³ and the sound velocity is 340 m / s, so that the acoustic impedance is about 0.0004 × 10 ⁶ kg / m ² / s. Therefore, from equation (5), the preferred acoustic impedance of the acoustic matching layer is theoretically about 0.1 × 10 ⁶ kg / m ² / s.

The acoustic impedance of the acoustic matching layer 3 in the ultrasonic transceiver 1 of the present embodiment is about 0.084 × 10 ⁶ kg because the density is 0.3 × 10 ³ kg / m ³ and the sound speed is 280 m / s.
/ M ² / s, which is very close to the theoretical ideal value.

  As can be seen from FIG. 3, according to the present embodiment, it is possible to obtain three times or more the transmission / reception sensitivity as compared with the conventional sensor. Further, in the present embodiment, since the protection unit 2 is provided, even an ultrasonic transceiver having an acoustic matching layer formed of a fragile dry gel having low mechanical strength is manufactured with a high yield, and even in use. Thus, reliable operation can be continued for a long time. External vibration test, thermal shock test, continuous vibration test, etc. were performed to evaluate whether the acoustic matching layer 3 was separated from the piezoelectric body 4 under severe conditions. However, the performance of the ultrasonic transceiver deteriorated. There was no, and extremely stable operation could be confirmed.

  In the present embodiment, when the wet gel is dried in step 4 to obtain a dry gel, a supercritical drying method is used, but drying in a normal atmosphere may be performed. In this case, shrinkage occurs in the process of changing from a wet gel to a dry gel, and a volume change of about 10 to 20% occurs. When such volume shrinkage occurs, in the conventional configuration, the acoustic matching layer 3 is separated from the piezoelectric body 4. However, in the case of the present embodiment, the shrinkage of the dried gel mainly occurs only in the thickness direction due to the presence of the protection portion 2 as shown in FIG. That is, almost no in-plane stress is generated at the interface between the piezoelectric body 4 and the acoustic matching layer 3, and peeling of the acoustic matching layer 3 is effectively prevented. Therefore, even if an air drying method that is simpler than the supercritical drying method is adopted, the ultrasonic transceiver 1 with high sensitivity and high reliability can be manufactured, and the manufacturing cost can be reduced.

  Preferably, the height of the protection portion 2 is set so that the final thickness of the acoustic matching layer 3 has an optimum size in consideration of the shrinkage ratio of the dried gel. If the thickness of the thinnest portion of the acoustic matching layer 3 is reduced to 90% or less of the average thickness because the degree of shrinkage becomes too large, the characteristics of the acoustic matching layer 3 are undesirably deteriorated. According to the supercritical drying method, the thickness of the thinnest portion of the acoustic matching layer 3 can be maintained at 98% or more of the average thickness.

  The upper surface of the piezoelectric body 4 that is in contact with the lower surface of the acoustic matching layer 3 and the inner surface of the protection portion 2 that is in contact with the side surface of the acoustic matching layer 3 must be subjected to surface treatment such as plasma cleaning or acid treatment in advance. Is preferred. When a hydroxyl group is formed on the contact surface by such a treatment, the chemical bond between the dried gel and the piezoelectric body 4 and the protection portion 2 can be further strengthened.

  In order to realize strong coupling between the acoustic matching layer 3 and the piezoelectric body 4 and the protection unit 2, a region of the surfaces of the piezoelectric body 4 and the protection unit 2 which is in contact with the acoustic matching layer 3 may be roughened. . As a method of surface roughening, ordinary sanding, blasting, physical or chemical etching, or the like can be effectively used.

  In order to improve the adhesion between the acoustic matching layer 3 and the protection portion 2, it is also effective to use a porous material as the material of the protection portion 2. By forming the protection part 2 from the porous body, a part of the acoustic matching layer 3 penetrates into the protection part 2 and is integrated, so that a stronger adhesion state can be obtained.

  Examples of the porous body that can be used for the protection unit 2 include metals, ceramics, resins, and the like manufactured by a foaming method or the like. Various materials such as stainless steel, nickel and copper can be used as the porous metal, alumina and barium titanate can be used as the ceramic, and various materials such as epoxy and urethane can be used as the resin.

  In this specification, “protecting the acoustic matching layer” means not only protecting the acoustic matching layer from mechanical vibration and impact, but also a process of manufacturing the acoustic matching layer from a material that contracts during formation. This also includes suppression of separation of the matching layer. By adopting a member that protects the acoustic matching layer in this manner, even if the acoustic matching layer is formed from a material having low mechanical strength and contractility, the function of the acoustic matching layer (piezoelectricity due to acoustic matching). The function of efficiently transmitting and receiving ultrasonic waves between the body and the propagation medium of ultrasonic waves) can be maintained at a practical level.

(Embodiment 2)
A second embodiment of the present invention will be described with reference to FIG.

  In the present embodiment, the protection unit and the piezoelectric body are integrated. More specifically, a concave portion 5a is formed in the center of the main surface of the piezoelectric body 5, and a part 5b of the piezoelectric body 5 is used as a protection portion. In other words, a part 5b of the piezoelectric body 5 functions as a protection unit, and the protection unit and the piezoelectric body are integrally formed.

  The ultrasonic transceiver in FIG. 5 is manufactured as follows.

  First, after preparing the piezoelectric body 5 which has been subjected to the polarization processing, one surface (main surface) of the piezoelectric body 5 is processed to form the concave portion 5a. Processing for forming the concave portion 5a can be performed by an end mill or sand blast. The depth of the recess 5a corresponds to the height of the protection part (5b). Thereafter, an electrode is formed on the surface on which the concave portion 5a is formed, and an electrode is also formed on the surface of the piezoelectric body opposite to the concave portion. The electrode is formed by forming a metal film of gold, nickel, or the like by, for example, plating or sputtering.

  According to the present embodiment, since the piezoelectric body 5 is processed and the peripheral portion of the main surface thereof functions as a protection section, a step of bonding a separately manufactured protection section to the piezoelectric body becomes unnecessary. When bonding is used for bonding the protection unit, it is necessary to consider a change in the height of the protection unit due to the presence of the adhesive layer. However, according to the present embodiment, the protection unit whose height is defined with high accuracy is required. Since the thickness of the acoustic matching layer 3 can be adjusted with high precision, a stable and high-performance ultrasonic transceiver can be provided.

  Also in the present embodiment, it is preferable to perform a process of forming a hydroxyl group on a portion of the surface of the piezoelectric body 5 that contacts the acoustic matching layer 3. Further, when forming the concave portion 5 a in the piezoelectric body 5, if the piezoelectric body 5 is roughened, the adhesion between the acoustic matching layer 3 and the piezoelectric body 5 can be further improved.

  In the first and second embodiments, the portion functioning as the protection unit is formed in a ring shape having a side surface perpendicular to the main surface of the piezoelectric body 5. However, the side surface of the protection section may have a taper as shown in FIG. Further, as shown in FIG. 7, it is not necessary to make contact with the entire outer peripheral side surface of the acoustic matching layer 3, and the acoustic matching layer 3 has a structure divided into a plurality of portions or a structure in which a cutout is formed in a part. May be.

  According to the configuration of the first or second embodiment, even when a material having a low density such as a dry gel and a low sound speed is used for the acoustic matching layer, the protection portion strengthens the coupling between the acoustic matching layer and the piezoelectric body. As a result, it is possible to exhibit high transmission / reception sensitivity, facilitate the handling of the ultrasonic transmission oscillator in the manufacturing process, and provide a high-performance ultrasonic transmission oscillator at a high yield. In addition, a device which is hardly deteriorated in characteristics due to a mechanical shock at the stage of using the ultrasonic transmitting transducer and a vibration accompanying transmission / reception of ultrasonic waves, and which is excellent in reliability is realized.

(Embodiment 3)
A third embodiment of the present invention will be described with reference to FIG.

  The feature of the present embodiment lies in that the structural support 6 is provided. The structural support 6 shown in FIG. 8 includes a disk-shaped support portion 6a to which the acoustic matching layer 3 is fixed, and a cylindrical portion 6b extending continuously in the axial direction from the disk-shaped support portion. The end of the cylindrical portion has an L-shaped cross section and is easily fixed to a plate 60 for shielding, another device, or the like.

  The acoustic matching layer 3 and the protection unit 2 are arranged on the surface of the support 6a of the structural support 6, and the piezoelectric body 4 is arranged on the back of the support 6a. That is, the piezoelectric body 4 and the acoustic matching 3 are provided at positions facing each other with the structural support 6 interposed therebetween. The use of such a structural support 6 makes it extremely easy to handle an ultrasonic transceiver (ultrasonic transducer).

  The structural support 6 can be composed of a sealable container (sensor case). In this case, if the open end of the cylindrical portion 6b of the structural support 6 is closed with a shielding plate 60 or the like and the inside of the structural support 6 is filled with an inert gas, the piezoelectric material 4 is removed from the fluid to be measured for the flow velocity. Can be shut off. Since a voltage is applied to the piezoelectric body 4, there is a risk that the combustible gas may catch fire if the piezoelectric body 4 is surrounded by a combustible gas. However, since the structural support 6 is constituted by a closed type container and the inside is shielded from the outside, such ignition can be prevented, so that ultrasonic waves can be safely emitted even to combustible gas. . Further, even when the external gas is not flammable, the piezoelectric material 4 is shielded from the external gas even when the ultrasonic wave is radiated to a gas that may react with the piezoelectric material 4 and degrade the characteristics of the piezoelectric material 4. By doing so, it is possible to suppress the deterioration of the piezoelectric body 4 and realize highly reliable operation for a long period of time.

  In the example of FIG. 8, the protection unit 2 is disposed on the outer peripheral portion of the ultrasonic transmission / reception surface of the piezoelectric body 4. Generally, since the protection unit 2 does not play the role of the acoustic matching layer 3, when the protection unit 2 is arranged on the main surface of the piezoelectric body 4, the portion becomes a portion that does not contribute to transmission and reception of ultrasonic waves, and transmission / reception sensitivity is reduced. I will.

  In order to prevent the structural support 6 from becoming an acoustically obstructive factor, it is desirable that the thickness of the disc-shaped support 6a with which the piezoelectric body 4 comes into contact is set to １ ／ or less of the wavelength of the transmitted and received ultrasonic waves. . By setting the thickness to about １ ／ or less of the wavelength, the structural support 6 does not inhibit the propagation of the ultrasonic wave.

  In this embodiment, stainless steel is used as the material of the structural support 6, and the thickness of the structural support 6 is set to 0.2 mm. Since the speed of sound in stainless steel is about 5500 m / s, 0.2 mm corresponds to about 1/55 of the wavelength of an ultrasonic wave having a frequency of 500 kHz. Since the structural support 6 is formed of such a thin stainless steel, even if the structural support 6 is interposed in the propagation path of the ultrasonic wave, there is almost no acoustic obstacle.

  The material of the structural support 6 is not limited to a metal material, and may be selected from ceramics, glass, and resins according to the purpose. In the present embodiment, an external fluid and the piezoelectric body are reliably separated from each other, and even if a mechanical shock is applied to the structural support 6, a strength that can prevent contact between the piezoelectric body and the external fluid is provided. Therefore, the structural support 6 is made of a metal material. Accordingly, high safety can be ensured even when ultrasonic waves are transmitted and received, for example, for flammable or explosive gas.

  When transmitting / receiving ultrasonic waves to / from a safe gas, the structural support 6 may be formed from a material such as resin for the purpose of cost reduction.

  In order to enhance the adhesion between the structural support 6 and the acoustic matching layer 3, a portion of the surface of the structural support 6 that contacts the acoustic matching layer 3 is subjected to a plasma treatment or an acid treatment for adding a hydroxyl group in advance. Is preferred. This part may be roughened by sanding, sandblasting, chemical and / or physical etching, or the like.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described with reference to FIG.

  In the ultrasonic transceiver of the present embodiment, a part 7a of the structural support 7 functions as a protection unit, and the structural support 7 and the protection unit are integrated. For example, when fabricating the structural support 7 by press-molding a metal material such as stainless steel, a concave portion 7b is formed in the disk-shaped support portion, and the periphery of the concave portion 7b (bent by press-molding the structural support 7). Portion 7a) can be used as a protection.

  By adopting such a configuration, it is possible to omit the step of joining the protective portion to the structural support. Further, similarly to the first embodiment, since the height of the protection portion does not vary due to the adhesive layer, a high-sensitivity ultrasonic transceiver can be manufactured with high yield.

  Although FIG. 9 does not show a plate for sealing the structural support 7, such a plate may be fixed to or integrated with the structural support 7 as necessary. The same applies to other embodiments described below.

(Embodiment 5)
A fifth embodiment of the present invention will be described with reference to FIGS.

  The ultrasonic transceiver according to the present embodiment includes another acoustic matching layer (lower acoustic matching layer) 8 disposed between the acoustic matching layer 3 and the piezoelectric body 4. Except for the insertion of the lower acoustic matching layer 8, the configuration of the present embodiment is the same as the configuration of the second embodiment.

  The acoustic matching layer plays a role in suppressing internal reflection of sound waves due to acoustic impedance mismatch and efficiently radiating ultrasonic waves from a piezoelectric body to a medium (ultrasonic propagation medium). Such an acoustic matching layer is sufficient when transmitting or receiving ultrasonic waves having a single frequency (continuous ultrasonic waves).

  In contrast, an ordinary ultrasonic transceiver transmits and receives pulsed or burst-like ultrasonic waves. The pulsed or burst-like ultrasonic waves contain not a single frequency component but a broadband frequency component. In order to transmit and receive such ultrasonic waves with high sensitivity, it is preferable to gradually change the acoustic impedance of the acoustic matching layer between the piezoelectric body and the ultrasonic wave propagation medium. To gradually change the acoustic impedance in this way, the acoustic matching layer may be multi-layered, and the acoustic impedance of the constituent layers may be gradually shifted.

In the present embodiment, as shown in FIG. 10, the acoustic matching layer has two layers. Specifically, a porous sintered body made of ceramics is used as the lower acoustic matching layer 8. The acoustic matching layer 8 has an apparent density of about 0.64 × 10 ³ kg / m ³ , a sound speed of 2000 m / s, and an acoustic impedance of about 1.28 × 10 ⁶ kg / m ² / s. As the ceramic, a barium titanate-based material is used.

  The “apparent density” is a density including a space portion included in the porous body. About 80% of the volume of the porous ceramics is a space (hole), and the substantial part of the ceramics is about 20% by volume of the whole. Such a porous ceramic is formed by mixing and pressure-molding a resin ball and a ceramic powder, and then heating, burning and removing the resin ball in the process of sintering the ceramic. If heating is performed abruptly during sintering, the resin ball expands or rapidly gasifies and breaks the ceramic structure, so it is preferable to perform gentle heating.

  In the present embodiment, after the lower acoustic matching layer 8 is fixed to the piezoelectric body 4 (directly the structural support 6), the opposite side of the acoustic matching layer 8 from the piezoelectric body 4 is fixed. The protective part 2 is bonded to the surface. As the protective part 2, one made of a stainless steel ring can be used similarly to the protective part 2 used in the first embodiment. All joining can be performed with an epoxy-based adhesive.

  In this manner, a dried gel layer to be the acoustic matching layer 3 was formed in the recess formed by the lower acoustic matching layer 8 and the protection portion 2 in the same manner as in the first embodiment.

In the present embodiment, in Step 1 similar to Step 1 in Embodiment 1, the density of the dried gel is adjusted by changing the concentration of ammonia serving as a gelling catalyst, and the density of the acoustic matching layer is adjusted to 0.2 × A dry gel layer is formed at 10 ³ kg / m ³ , a sound speed of 160 m / s, and an acoustic impedance of about 0.032 × 10 ⁶ kg / m ² / s. Since the sound speed of the acoustic matching layer is 160 m / s, the height of the protection part 2 is set to 80 μm so as to be １ ／ of the ultrasonic wavelength in the acoustic matching layer. It is preferable to perform a treatment for imparting a hydroxyl group by plasma etching on the inner surface of the protection unit 2.

FIG. 11A shows a transmission / reception waveform of the ultrasonic transceiver in the present embodiment. In the graph of FIG. 11, the vertical axis represents signal amplitude, and the horizontal axis represents time. The numerical value on the axis is an index notation, for example, “2.0E-04” means 2.0 × 10 ⁻⁴ . The same applies to other graphs.

  In the ultrasonic transmitter / receiver used for the measurement, the thickness of the porous ceramics serving as the lower acoustic matching layer 8 was set to 1 mm, and the thickness of the protective portion 2 and the first acoustic matching layer (dry gel layer) 3 was set to 80 μm. did.

  For comparison, in the ultrasonic transmitter / receiver of FIG. 10, instead of the two acoustic matching layers 3 and 8, an ultrasonic transmitter / receiver using a conventional acoustic matching layer obtained by fixing a glass balloon with epoxy was manufactured. Transmission and reception waveforms were measured. FIG. 11B shows the measurement results.

  By using two acoustic matching layers, a sensitivity approximately 20 times higher than that of a conventional ultrasonic sensor could be obtained. Also, as compared with the ultrasonic sensor according to the first embodiment, it can be seen that the sensitivity is increased and the band is broadened (shortened pulse). As described above, by forming the acoustic matching layer into two layers, it becomes possible to provide an ultrasonic transceiver that is extremely suitable for transmitting and receiving pulses and burst waves.

(Embodiment 6)
A sixth embodiment of the present invention will be described with reference to FIG.

  In the present embodiment, a part of the lower acoustic matching layer 9 functions as a protection unit, and the acoustic matching layer 9 and the protection unit are integrated. In this example, the acoustic matching layer 9 is processed to form a concave portion on the main surface. The dry gel layer that becomes the upper acoustic matching layer 3 is formed in the recess of the lower acoustic matching layer 9.

  By adopting such a configuration, the step of joining the protection section to the acoustic matching layer 9 can be omitted. In addition, the problem that the height of the protective portion varies due to the adhesive layer can be solved, and an ultrasonic transceiver that operates with high sensitivity over a wide band can be manufactured with high yield.

  In the present embodiment, the lower acoustic matching layer 9 is formed of a porous body. Therefore, the coupling with the upper acoustic matching layer 3 is strong, and high sensitivity and high stability can be secured. In order to further enhance the adhesiveness, it is preferable that the contact surface between the upper acoustic matching layer 3 and the lower acoustic matching layer 9 be subjected to a plasma treatment for imparting a hydroxyl group or an acid treatment in advance.

  In this embodiment and the above-described fifth embodiment, the acoustic matching layer has a two-layer structure. However, the ultrasonic vibrator of the present invention is not limited to such a structure, and has a multilayer structure of three or more layers. You may have. By making the acoustic matching layer multilayer, the sensitivity can be further increased and the band can be widened. However, in order to increase the sensitivity by increasing the number of layers, it is necessary to form the outermost acoustic matching layer from a material having an extremely low acoustic impedance. Therefore, in practice, it is practical to adopt a two-layer structure.

(Embodiment 7)
A seventh embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 13, in the ultrasonic transceiver according to the present embodiment, a back load member 10 is joined to the back side of the piezoelectric body 4, and the protection unit 2 is formed on the back load member 10. In other respects, it has the same configuration as the third embodiment.

  The back load member 10 has a function of attenuating ultrasonic waves radiated from the piezoelectric body 4 to the back side, and is made of any material that can exhibit such a function. Is also good.

  The protection portion 2 is formed of a tubular metal, and is adhered to the main surface of the back load member 10. The thickness of the protection portion 2 is equal to the total thickness of the piezoelectric body 4, the lower acoustic matching layer 8, and the upper acoustic matching layer 3. In the present embodiment, since the thickness of the piezoelectric body 4 is set to 3 mm, the thickness of the acoustic matching layer 8 is set to 1 mm, and the thickness of the acoustic matching layer 3 is set to 0.08 mm, the thickness of the protection portion 2 is 4 mm. 0.08 mm.

  The back load member 10 of the present embodiment is formed from ferrite rubber. Ferrite rubber is a material in which iron powder is dispersed in rubber, and has a high sound wave attenuation rate. By bonding such a back load member 10 to the back surface of the piezoelectric body 4, the ultrasonic wave radiated from the back side of the piezoelectric body 4 is attenuated, so that a wide band (short pulse width) ultrasonic wave can be transmitted and received. It becomes possible.

  FIG. 14 shows transmission / reception waveforms measured for the ultrasonic transceiver having the configuration of FIG. Although the transmission / reception sensitivity of the present embodiment is lower than that of the ultrasonic transmitter / receiver of the third embodiment, an operation in a wider band is realized, and an ultrasonic transmitter / receiver suitable for transmitting / receiving short-width pulses is configured. can do.

  Instead of the back load member 10 shown in FIG. 13, a back load member 11 shown in FIG. 15 may be used. A part of the back load member 11 shown in FIG. 15 functions as a protection unit, and the protection unit and the back load member are integrated. The back load member 11 has a configuration in which a concave portion is formed in a region other than the peripheral portion of the main surface. The piezoelectric body 4 is inserted into the concave portion, and is bonded to the inner surface of the concave portion of the back load member 11. The depth of the concave portion provided in the back load member 11 is set to be larger than the height of the piezoelectric body 4. If a dry gel layer serving as an acoustic matching layer is formed on the upper surface of the piezoelectric body 4 after insertion, the figure can be obtained. 15 configurations are obtained. By employing the back load member 11, the same broadband as that of the ultrasonic transceiver shown in FIG. 13 is achieved.

(Embodiment 8)
An embodiment of the method for manufacturing the ultrasonic transceiver shown in FIG. 12 will be described with reference to FIG.

  First, as shown in FIG. 16A, the piezoelectric body 4 and the lower acoustic matching layer 9 are joined to the structural support 6. An adhesive can be used for joining. As described above, the piezoelectric body 4 is formed from piezoelectric ceramics, and the structural support 6 is formed from stainless steel. The lower acoustic matching layer 9 is formed of a porous ceramic having a concave portion on the upper surface. This concave portion is formed by processing the upper surface of a flat porous ceramic using a lathe or the like.

  Next, as shown in FIG. 16B, a dried gel to be an upper acoustic matching layer is formed in the concave portion of the acoustic matching layer 9 adhered to the structural support 6. The formation of the dried gel can be performed by the method described in the first embodiment.

  In order to sufficiently infiltrate the gel material into the acoustic matching layer 9 formed of porous ceramics, it is preferable that the gel material is poured and then placed in a vacuum or reduced pressure atmosphere. In this manner, in the present embodiment, the gel raw material permeates not only the portion functioning as the protective portion of the acoustic matching layer 9 but also the entire inside of the acoustic matching layer 9. This allows the dried gel to be firmly bonded to the lower acoustic matching layer 9 and makes the characteristics of the acoustic matching layer 9 uniform (FIG. 16C). Hereinafter, this point will be described with reference to FIG.

  FIG. 17A shows a state in which the gel raw material has sufficiently penetrated into the lower acoustic matching layer 9. For this reason, the lower acoustic matching layer 9 acoustically functions as a single layer, and the acoustic impedance is stepped from a relatively high value of the acoustic matching layer 9 to a relatively low value of the upper acoustic matching layer. Decrease in shape.

  On the other hand, when the penetration of the gel raw material is insufficient, an acoustic matching layer having a substantially three-layer structure is formed as shown in FIG. In this case, the acoustic impedance of the lowermost layer (first layer) where the penetration of the gel raw material is insufficient is smaller than the set value, so that the acoustic impedance of the middle layer (second layer) is the largest. When the distribution of the acoustic impedance becomes as shown in FIG. 17B, the acoustic impedance does not decrease stepwise from the piezoelectric body (not shown) disposed below in the figure toward the gas serving as the ultrasonic wave propagation medium. Since the characteristics of the ultrasonic transducer deteriorate, it is preferable to sufficiently permeate the gel raw material.

  In the above embodiment, as shown in FIG. 16, after the step of fixing the lower acoustic matching layer 9 to the structural support 6, the step of forming the first acoustic matching layer 3 is performed. May be reversed. Another manufacturing method will be described with reference to FIGS.

  First, as shown in FIG. 18A, an acoustic matching layer 9 having a portion functioning as a protection unit is prepared. Next, as shown in FIG. 18B, the gel raw material is dropped into the concave portion of the acoustic matching layer 9, and the gel raw material in the concave portion is cut so as to match the height of the protective portion. It permeates the entire acoustic matching layer 9. After hardening and hydrophobizing the gel material, the gel raw material is dried by a supercritical drying method, and an acoustic matching layer 3 made of a dried gel is formed on the lower acoustic matching layer 9 as shown in FIG. .

  After that, as shown in FIG. 18D, the acoustic matching layer is bonded to the structural support 6 to which the piezoelectric body 4 is fixed. The acoustic matching layer shown in FIG. 18C may be directly bonded to the piezoelectric body 4 without using the structural support 6.

  In addition, it is preferable to select optimal pressing conditions so that the dried gel is not destroyed by pressing during bonding. Since the strength of the dried gel with respect to the stress in the compression direction is relatively high, the production yield hardly decreases in the bonding step.

  It is preferable that the material of the acoustic matching layer 3 and the material of the acoustic matching layer 9 be selected such that the elastic modulus of the upper acoustic matching layer 3 and the elastic modulus of the lower acoustic matching layer 9 show values close to each other. When the two elastic moduli are close to each other, a uniform pressure can be applied to the entire bonding surface, and it becomes easy to manufacture a highly sensitive ultrasonic transceiver with a high yield.

  In the method shown in FIGS. 18A to 18D, in the step of forming a dry gel on the acoustic matching layer 9, it is not necessary to handle a piezoelectric body or a structural support, so that equipment such as a drying apparatus is small. It is possible to manufacture an ultrasonic transducer at low cost.

  In the step of forming the dried gel, a chemical load may be applied to an organic substance such as an adhesive layer. However, performing the bonding step after the formation of the dried gel does not deteriorate the bonded portion.

(Embodiment 9)
Another embodiment of the present invention will be described with reference to FIG.

  A feature of the present embodiment is that the protection portion 2 is formed not only in the outer peripheral portion of the region where the acoustic matching layer 3 is formed, but also in the region.

  When a dry gel layer is formed from a gel raw material via a wet gel, irregularities may be formed on the upper surface of the dry gel layer. In addition, when the wet gel is dried by a normal drying method without using supercritical drying, the dried gel shrinks, and concavities as shown in FIG. 4 are easily formed in the dried gel.

  When the ultrasonic wave transmitting and receiving surface is wide, the above irregularities are likely to be large, and even if the thickness of the acoustic matching layer is set to the optimal value, the thickness of the acoustic matching layer may actually be larger than the optimal value depending on the place. It will shift.

  Since the speed of sound in the dried gel layer is extremely slow, it must be formed extremely thin in order to function properly as an acoustic matching layer, and the allowable error range of the thickness is small.

  By forming a protective portion having a layout as shown in FIG. 19A or 19B, an error in the thickness of the acoustic matching layer can be suppressed to about ± 5% from the target value.

  As shown in FIG. 19 (a) or FIG. 19 (b), when the protection part 2 is also provided inside the ultrasonic wave emitting surface of the ultrasonic transmitter / receiver, the fluctuation of the thickness of the acoustic matching layer 3 can be minimized. However, the protection part 2 provided inside the ultrasonic wave emitting surface may be a hindrance to transmission and reception of ultrasonic waves. In order to prevent the acoustic characteristics from deteriorating due to the protection unit 2, it is preferable that the size of the protection unit 2 be as small as possible within a range that functions as the protection unit 2.

  In the configuration example of FIG. 19A, the protection portions 2 having a circular cross section are randomly arranged. However, the cross section shape of the protection portion 2 is not limited to a circle, and may be a rectangle or a polygon. Also, the arrangement is not limited to random arrangement.

  In the configuration example of FIG. 19B, a concentric protection section 2 is provided. In this configuration example, the protection unit 2 is also present inside the ultrasonic wave emitting surface of the ultrasonic transceiver, but deterioration of the characteristics of the ultrasonic transceiver is prevented. The configuration of FIG. 19B is effective when transmitting an ultrasonic wave to a position separated from the ultrasonic wave emitting surface by a short distance L on the center axis of the ultrasonic transmitter / receiver.

  Assuming that the distance between the protection unit 2 and the center of the ultrasonic wave emitting surface is r, the distance r preferably satisfies the following expression (6).

  Here, λ is the wavelength in the gas through which the ultrasonic wave propagates, and L is the distance from the ultrasonic radiation surface of the ultrasonic transceiver. For example, when the frequency is 500 kHz, the ultrasonic wave propagation medium is air (sound speed 340 m / s), and the measurement distance L is 10 mm, the radius r from the center is 2.6 to 3.7 mm and 4.6 from Equation (6). It can be seen that it is preferable to provide the protection part 2 at positions of about 5.4 mm, 6.1 to 6.7 mm. Providing the protection unit 2 at such a position is effective in preventing disturbance of the sound field due to sound interference and preventing deterioration of the sensitivity of ultrasonic waves at a short distance.

  When each point on the sound wave emitting surface of the ultrasonic transmitter / receiver is regarded as a point sound source, an ultrasonic wave to be transmitted is obtained by synthesizing a spherical wave radiated from each point sound source. When the distance from the ultrasonic wave emitting surface is short, ultrasonic waves having different phases cancel each other, and there are positions where high-power ultrasonic waves cannot be transmitted. In order to radiate only ultrasonic waves having the same phase from the ultrasonic radiation surface, it is effective to provide the protection unit 2 in a region where ultrasonic waves having different phases are radiated. When the protection unit 2 is provided in such a region, the emission of ultrasonic waves having different phases can be suppressed, so that disturbance of the sound field at a short distance can be prevented and high-power ultrasonic transmission can be performed.

(Embodiment 10)
FIG. 20 is a sectional view showing a tenth embodiment of the ultrasonic transducer according to the present invention. The ultrasonic transducer 21 of the present embodiment includes a piezoelectric body 22, electrodes 23 a and 23 b provided on both surfaces of the piezoelectric body 22, and a protective matching layer (first layer) provided on the piezoelectric body 22 via the electrode 23 a. (A first acoustic matching unit) 24 and an acoustic matching layer (second acoustic matching unit) 25 provided on the piezoelectric body 22 via an electrode 23a.

  FIG. 21 is a top view of the ultrasonic transducer 21 shown in FIG. As can be seen from FIG. 21, the ultrasonic transducer according to the present embodiment has a structure in which protective matching layers 24 and acoustic matching layers 25 having different thicknesses (heights) are alternately and concentrically arranged. I have.

  The piezoelectric body 22 in the present embodiment is formed from a material having piezoelectricity and is polarized in the thickness direction. When a voltage is applied to the electrodes 23 a and 23 b provided on the upper and lower surfaces of the piezoelectric body 22, ultrasonic waves are generated in the piezoelectric body 22 based on the voltage signal, and the ultrasonic waves are transmitted through the protective matching layer 24 and the acoustic matching layer 25. The light is radiated to a sound wave propagation medium (such as a gas) 26. Further, the ultrasonic wave propagating through the ultrasonic wave propagation medium 26 propagates to the piezoelectric body 22 via the protective matching layer 24 and the acoustic matching layer 25. The incident ultrasonic waves deform the piezoelectric body 22, and a voltage signal is generated between the electrodes 23a and 23b.

  The material of the piezoelectric body 22 is arbitrary, and those formed from various known materials can be used. A known electrostrictive body may be used instead of the piezoelectric body 22. The electrodes 23a and 23b are preferably formed of metal, but may be formed of a conductive material other than metal.

  The protection matching layer 24 and the acoustic matching layer 25 efficiently propagate the ultrasonic vibration generated by the piezoelectric body 22 to the propagation medium 26, and efficiently transmit the ultrasonic wave propagated through the ultrasonic propagation medium 26 to the piezoelectric body 22. It has a function to communicate.

  The acoustic matching layer 25 of the present embodiment is preferably formed from a dried gel. The dried gel is a porous body formed by a sol-gel reaction, and is a material capable of extremely reducing the acoustic impedance defined by the product of the density ρ and the sound velocity C (ρ × C). For this reason, by using the acoustic matching layer 25 formed of the dried gel, the transmission and reception efficiency of the ultrasonic wave with respect to the gas such as the air can be extremely increased.

  A dry gel is obtained by forming a wet gel and then drying the wet gel. For the wet gel, first, a gel raw material liquid is prepared, and a wet gel can be prepared by the reaction of the gel raw material liquid. The wet gel has a solid skeleton solidified by the reaction of the gel raw material liquid, and the solid skeleton contains a solvent.

  The dried gel obtained by drying the wet gel is a porous body, and has continuous pores in the gap of the solid skeleton of about several nm to several μm. The average size of the pores is extremely small, about 1 nm to several μm.

  As the production conditions are adjusted to reduce the density of the dried gel, the sound speed in the solid portion of the dried gel becomes extremely low, and the sound speed in the gas portion in the pores becomes extremely low. Therefore, the sound velocity of the dried gel shows a low value of 500 m / sec or less in a low density state, and shows an extremely low acoustic impedance. In particular, the solid skeleton and the dried gel having a small pore size of about several nm show an extremely low sound velocity. Further, since the gas has a large pressure loss in the nanometer-sized pores, when the acoustic matching layer is formed from the dried gel, sound waves can be emitted at a high sound pressure.

  According to the production method described below, the acoustic impedance of the dried gel can be arbitrarily controlled within a wide range by adjusting the production process conditions even with the same raw material. In addition, by changing the manufacturing process conditions, it is possible to produce an acoustic matching layer in which only the sound speed is changed while the density is substantially the same.

  Dried gels have these advantageous characteristics, but low mechanical strength. For this reason, it was difficult to increase the production yield, and the reliability during use was low. As described in the first to ninth embodiments, the provision of the member for protecting the dried gel having low mechanical strength improves the production yield and the reliability.

  The protective portions in the first to ninth embodiments are extremely effective in improving the manufacturing yield of the ultrasonic transducer or the reliability in use, and can control the thickness of the acoustic matching layer with high accuracy. This is effective for stabilizing the performance of the ultrasonic transducer. However, as described above, when a protection portion is provided on a surface (principal surface) on which the piezoelectric body emits or receives ultrasonic waves, the protection portion may be an acoustic obstacle. This is because, in the first to ninth embodiments, the thickness of the protective portion formed of a material different from the material of the acoustic matching layer is set to be substantially equal to the thickness of the acoustic matching layer. This is because the sound speed differs between the protective portion and the acoustic matching layer, and the protective portion having substantially the same thickness as the acoustic matching layer does not function as the acoustic matching layer. For this reason, since the protection part of Embodiments 1-9 may become a factor which obstructs transmission / reception of an ultrasonic wave, it is preferable to arrange | position outside the main surface of a piezoelectric body.

  However, depending on securing reliability against more severe environmental conditions, or limiting the outer diameter of the ultrasonic transducer, there may be a case where a protection section must be provided above the piezoelectric body.

  In the present embodiment, a protection portion (made of a material having a relatively high density and a higher mechanical strength than the acoustic matching layer 25) that functions to protect the acoustic matching layer 25 is provided on the main surface of the piezoelectric body. A configuration that does not impair the performance of the ultrasonic transducer while having it is adopted.

  In the present embodiment, the thickness of the protection portion provided on the main surface of the piezoelectric body 22 is set to about １ ／ of the wavelength of the transmitted and received ultrasonic waves. Thereby, the protection part having relatively high mechanical strength also functions as an acoustic matching layer. For this reason, in the present specification, such a protection portion may be referred to as a “protection matching layer”. By adopting such a configuration, the protection section that protects the acoustic matching layer also plays a role as the acoustic matching layer, so that a highly sensitive ultrasonic transducer can be realized.

  The thickness at which the function as the acoustic matching layer is best exhibited is １ ／ of the wavelength of the ultrasonic wave. On the other hand, the sound speed in the protective matching layer 24 and the sound speed in the acoustic matching layer 25 are different. Therefore, as shown in FIG. 20, the thickness L3 of the protective matching layer 24 and the thickness L1 of the acoustic matching layer 25 have different sizes (L3> L1).

  If the thickness of each of the protective matching layer 24 and the acoustic matching layer 25 is set to about １ ／ of the speed of sound, the thickness of the protective matching layer 24 is different from the thickness of the acoustic matching layer 25. Ultrasonic waves emitted from the upper surface may interfere with ultrasonic waves emitted from the upper surface of the protective matching layer 24. In order to realize a high-sensitivity ultrasonic transducer, the phase relationship between the ultrasonic waves radiated from each transducer is extremely important.

  FIG. 22A shows the waveform of the ultrasonic wave on the upper surface of the protective matching layer 24, and FIG. 22B shows the waveform of the ultrasonic wave at the same level as the upper surface of the protective matching layer 24 above the acoustic matching layer 25. Is shown. In addition, the code | symbol "ta" in FIG.22 (b) has shown the time which an ultrasonic wave propagates in the ultrasonic wave propagation medium 26. FIG. One scale on the horizontal axis in each graph is about 3 μsec when the frequency of the ultrasonic wave is 500 kHz.

  The ultrasonic waves emitted from the upper surface of the acoustic matching layer 25 reach the same level as the upper surface of the protective matching layer 24 through the ultrasonic wave propagation medium 26 such as gas. Therefore, depending on the speed of sound in the propagation medium 26 and the size L2 of the propagation medium 26, the phase relationship of the ultrasonic waveform at the same level as the upper surface of the protective matching layer 24 above the acoustic matching layer 25 changes.

  The signal waveforms in FIGS. 22A and 22B are obtained on the assumption that the wavelengths and amplitudes of the ultrasonic waves radiated from the protective matching layer 24 and the acoustic matching layer 25 are equal.

  When the thickness L3 of the protective matching layer 24 and the thickness L1 of the acoustic matching layer 25 are each 1/4 of the ultrasonic wavelength of each layer, the ultrasonic wave propagates between the lower surface and the upper surface of the protective matching layer 24. This time is equal to the time required for the ultrasonic wave to propagate between the lower surface and the upper surface of the acoustic matching layer 25. Therefore, the phase of the ultrasonic wave radiated from the upper surface of the acoustic matching layer 25 reaches the same level as that of the upper surface of the protective matching layer 24, and propagates through the protective matching layer 24 to be applied to the upper surface of the protective matching layer 24. It is behind the phase of the reached ultrasonic wave. This phase delay corresponds to the time during which the ultrasonic wave emitted from the upper surface of the acoustic matching layer 25 propagates through the propagation medium 26 by the distance L2.

Assuming that the frequency of the ultrasonic wave to be transmitted and received is f [sec- ¹ ], the time required for the ultrasonic wave to travel a distance equal to one wavelength of the ultrasonic wave is 1 / f [sec]. The time t3 required for the ultrasonic wave to pass through the protective matching layer 24 of the present embodiment is ｆf [sec]. On the other hand, the time t2 required for the ultrasonic wave to pass through the acoustic matching layer 25 of the present embodiment is also ４f [sec]. Here, assuming that the time required for the ultrasonic wave to propagate through the propagation medium 26 by the distance of L2 is t2 (= ta), the ultrasonic wave radiated from the upper surface of the protective matching layer 24 depends on the time t2. Interference occurs between the sound wave and the ultrasonic wave emitted from the upper surface of the acoustic matching layer 25. The interference changes the waveform and sensitivity of the ultrasonic wave.

  FIG. 22C shows an ultrasonic waveform observed when the time t2 is 1 / 2f [second], and FIG. 22D shows a case where the time t2 is 1 / f [second]. 2 shows an ultrasonic waveform observed. As can be seen from FIGS. 22 (c) and (d), the sensitivity of the observed ultrasonic wave greatly differs depending on the value of the time t2. When the time t2 is equal to 1 / 2f [second], the phase shift becomes a half wavelength of the ultrasonic wave, and the sensitivity of the observed ultrasonic wave is reduced. On the other hand, when the time t2 is 1 / f [second], the phase shift is an integral multiple of the wavelength of the ultrasonic vibrator, and thus the sensitivity of the observed ultrasonic wave is high. When the time t2 is in the range of 1 / 2f to 1 / f [second], the transmission / reception sensitivity of the ultrasonic wave increases as the time t2 approaches 1 / 2f [second] to 1 / f [second].

  When the ultrasonic wave radiated from the acoustic matching layer 25 propagates through the propagation medium 26 and reaches the same level as the upper surface of the protective matching layer 24, the phase of the ultrasonic wave becomes the phase of the ultrasonic wave propagating through the protective matching layer 24. By adjusting the thicknesses of the acoustic matching layer 25 and the protective matching layer 24 so as to substantially match the above, a highly sensitive ultrasonic transducer can be provided. It should be noted that, in the present specification, when "the phases substantially match", it means that the difference between the phases of the ultrasonic waves is 1/4 or less of the wavelength of the ultrasonic waves, and the smaller the phase difference is, the more preferable.

  FIG. 23 is a cross-sectional view schematically showing the phase of the ultrasonic wave when the time t2 is 1 / f [second]. In this figure, the phase of the ultrasonic wave on the upper surface of the protective matching layer 24 matches the phase of the ultrasonic wave above the acoustic matching layer 25 and at the same level as the upper surface of the protective matching layer. When such a phase coincidence occurs, the transmission and reception sensitivity of the ultrasonic wave is maximized. Note that, even when such perfect phase matching does not occur, if the phase shift is set to be small, the transmission / reception sensitivity of the ultrasonic wave is sufficiently improved as compared with the related art. The phase shift is preferably adjusted to １ ／ or less, more preferably に お け る or less, of the ultrasonic wavelength in the ultrasonic propagation medium.

  By simply controlling the thickness L1 of the acoustic matching layer 25 and the thickness L3 of the protective matching layer 24 to about １ ／ of the ultrasonic wavelength in the acoustic matching layer 25 and the protective matching layer 24, respectively, the size of L2 becomes Since (L3-L1) is uniquely determined, t2 cannot be set arbitrarily. Therefore, in order to set the time t2 to a desired value, not only the thickness of the acoustic matching layer 25 and the protective matching layer 24 but also the speed of sound in the acoustic matching layer 25 and the protective matching layer 24 are appropriately controlled. There is a need. In a preferred embodiment of the present invention, the acoustic matching layer 25 is formed from a dry gel that allows easy control of the speed of sound.

Next, an embodiment of a method of manufacturing the ultrasonic transducer 21 of the present embodiment will be described with reference to FIGS. In the present embodiment, air (density: 1.18 kg / m ³ , sound velocity: about 340 m / s, acoustic impedance: about 4.0 × 10 ² kg / m ² / s) is considered as the ultrasonic wave propagation medium 26.

  First, as shown in FIG. 24A, a piezoelectric body 22 is prepared according to the wavelength of the ultrasonic wave to be transmitted and received. At this stage, the piezoelectric body 22 is not provided with the protective matching layer 24 shown in FIG. As the piezoelectric body 22, a material having high piezoelectricity such as a piezoelectric ceramic or a piezoelectric single crystal is preferable. As the piezoelectric ceramic, lead zirconate titanate, barium titanate, lead titanate, lead niobate, or the like can be used. As the piezoelectric single crystal, a lead zirconate titanate single crystal, lithium niobate, quartz, or the like can be used.

  In the present embodiment, the piezoelectric body 22 is made of lead zirconate titanate ceramics, and the wavelength of the transmitted and received ultrasonic waves is set to 500 kHz. To enable the piezoelectric body 22 to efficiently transmit and receive such ultrasonic waves, the resonance frequency of the piezoelectric body 22 is designed to be 500 kHz. For this reason, in the present embodiment, the piezoelectric body 22 formed of a piezoelectric ceramic having a cylindrical shape with a diameter of 12 mm and a thickness of about 3.8 mm is used. Electrodes 23a and 23b are formed on both surfaces of the piezoelectric body 22 by baking silver, and a polarization process is performed in this direction.

  Next, three ring-shaped members functioning as the protective matching layer 24 are prepared, and are joined to the main surface of the piezoelectric body 22 as shown in FIG. At this time, each center of the ring-shaped member is aligned with the center of the piezoelectric body 22, as shown in FIG. The three ring-shaped members functioning as the protective matching layer 24 include a first ring-shaped member having an outer diameter of 12 mm, an inner diameter of 11 mm, and a thickness of 1.0 mm, and a first ring-shaped member having an outer diameter of 8 mm, an inner diameter of 7 mm, and a thickness of 1.0 mm. A second ring-shaped member and a third ring-shaped member having an outer diameter of 4 mm, an inner diameter of 3 mm, and a thickness of 1.0 mm.

The protective matching layer 24 in the present embodiment is required not only to have a function of protecting the acoustic matching layer with high mechanical strength but also to have a relatively low acoustic impedance in order to fulfill the function of the acoustic matching layer. Can be In this embodiment, a porous ceramic is used as such a material. This porous ceramic has an apparent density of 0.64 × 10 ³ kg.
/ M ³ , the sound speed is 2000 m / s, and the acoustic impedance is about 1.28 × 10 ⁶ kg / m ³ . As the ceramic, a barium titanate-based material is used. The “apparent density” is a density including a space portion included in the porous body. About 80% of the volume of the porous ceramic is a space portion, and the substantial portion of the ceramic is about 20% by volume.

  As described above, since the sound speed of the protective matching layer 24 is about 2000 m / s, the thickness of a quarter of the wavelength at 500 kHz corresponds to 1.0 mm. For this reason, in the present embodiment, the thickness of the ring-shaped member functioning as the protective matching layer 24 is set to 1.0 mm.

  The porous ceramic used in the present embodiment can be manufactured as follows.

  First, fine resin balls and ceramic powder are mixed and pressed. Thereafter, the ceramic is sintered. During this sintering process, the resin balls are heated, burned and removed. If heating is performed rapidly during sintering, the resin balls may expand or suddenly gasify, and the ceramic structure may be destroyed. For this reason, sintering is preferably performed by gentle heating.

  In the present embodiment, the protection matching layer 24 made of such porous ceramics and the piezoelectric body 22 are joined by bonding with an adhesive. For example, when an epoxy resin is used as an adhesive and left for about 2 hours in a thermostat at 150 ° C. while applying a pressure of about 0.1 MPa, the adhesive hardens, and the protective matching layer 24 and the piezoelectric body 22 Join.

  Next, as shown in FIG. 24B, an acoustic matching layer 25 is provided on the composite formed of the piezoelectric body 22 and the protective matching layer 24 thus formed. In the present embodiment, the acoustic matching layer 25 is formed from a dried gel.

  In the present embodiment, first, after the acoustic matching layer 25 having the thickness shown in FIG. 24B is formed, the acoustic matching layer 25 is thinned as shown in FIG. At this time, the thickness L3 of the protective matching layer 24 and the thickness L1 of the acoustic matching layer are set so that the distance L2 (= L3−L1) shown in FIG. 20 is equal to one wavelength of the ultrasonic wave in the air. Specifically, since the frequency of the transmitted and received ultrasonic waves is 500 kHz, one wavelength of the ultrasonic waves in the air is 0.62 mm. On the other hand, since the thickness L3 of the protective matching layer 24 is 1.0 mm, the thickness L1 of the acoustic matching layer 25 is 0.32 mm (= 1.0 mm-0.62 mm). In order for the acoustic matching layer 25 to function properly as an acoustic matching layer, the thickness L1 (= 0.32 mm) is most preferably １ ／ of the wavelength of the ultrasonic wave propagating through the acoustic matching layer 25. desirable. Therefore, it is necessary to have a material characteristic having a sound speed such that 0.32 mm is １ ／ of the wavelength of the transmitted and received ultrasonic waves. According to the calculation, the acoustic matching layer 25 having a thickness of 0.32 mm may be formed from a dried gel having a sound speed of 640 m / s.

  The thickness of the protective matching layer 24 is preferably １ ／ of the ultrasonic wavelength in the protective matching layer 24, but is not limited to this size. The range may be 1/8 to 1/3 of the ultrasonic wavelength, and more preferably 1/6 to 1/4 of the ultrasonic wavelength. When the wavelength of the ultrasonic wave has a distribution, it is preferable to determine the thickness based on the peak wavelength. In the present specification, when there is a distribution in the wavelength, “１ ／ of the wavelength” means “１ ／ of the peak wavelength”.

  When the acoustic matching layer 25 is a single layer, the thickness of the acoustic matching layer 25 is also preferably １ ／ of the ultrasonic wavelength in the acoustic matching layer 25, but is not limited to this size. The range may be 1/8 to 1/3 of the ultrasonic wavelength, and more preferably 1/6 to 1/4 of the ultrasonic wavelength. When the acoustic matching layer has a multilayer structure, each constituent layer preferably has the above thickness. An ultrasonic transducer in which the acoustic matching layer has a multilayer structure will be described later as a second embodiment.

  Various materials such as an inorganic material and an organic polymer material can be used as the material of the dried gel forming the acoustic matching layer 25. As the solid skeleton of the inorganic material, silicon oxide (silica), aluminum oxide (alumina), titanium oxide, or the like can be used. As the solid skeleton of the organic material, general thermosetting resins and thermoplastic resins can be used, and for example, polyurethane, polyurea, phenol resin, polyacrylamide, polymethyl methacrylate, and the like can be used.

  In this embodiment, silicon oxide (silica) is used as the solid skeleton as the material of the acoustic matching layer 25 from the viewpoints of cost, environmental stability, ease of manufacture, and stable temperature characteristics of the ultrasonic transducer. Use a dry gel.

  The sound speed of 640 m / s is a relatively high value as the sound speed of the dried gel. For this reason, in the present embodiment, when a dry gel layer is formed as the acoustic matching layer 25, a conventional manufacturing method in which a drying step is performed subsequent to a gelling step (hereinafter, referred to as a “first gelling step”). Instead, a method of performing the second gelation step after the first gelation step is employed.

  When only the first gelation step is performed without performing the second gelation step, it is difficult to obtain a dried gel having a relatively high sound speed. Since the density of the dried gel increases substantially in proportion to the speed of sound, “high sound speed” means “high density”. When the concentration of the gel raw material in the gel raw material liquid is increased for the purpose of increasing the sound speed of the gel, the gelling reaction does not proceed uniformly, and a wet gel having a random sound speed distribution is formed. The dried gel obtained by drying this wet gel also has a random density distribution. Therefore, if the concentration of the gel raw material in the gel raw material liquid is increased, it is extremely difficult to make the sound speed uniform.

  In the present embodiment, in order to avoid non-uniformity of the gel, the speed of sound of the dried gel formed in the first gelation step is adjusted to about 200 m / s or less, and the density is further increased by the second gelation step, so that the uniformity is obtained. Increase the speed of sound. In the second gelling step, the wet gel obtained in the first gelling step is again immersed in the gel raw material liquid (second gelling raw material liquid). In the second gelling step, the concentration of ammonia serving as a catalyst in the second gelling raw material liquid is adjusted to be low. Therefore, gelation does not occur outside the wet gel obtained in the first gelation step. However, inside the wet gel obtained in the first gelling step, the second gelling raw material liquid grows so as to adhere to the skeleton formed in the first gelling step. Therefore, the reaction proceeds even under conditions where the gel raw material liquid itself does not gel. In this way, the sound speed and density of the gel can be changed.

  Specifically, by performing the following steps, the acoustic matching layer 25 made of dry gel is formed.

Step 1: Preparation of first gelled gel raw material liquid Tetraethoxysilane / ethanol / water / hydrogen chloride were mixed at a molar ratio of 1/2/1 / 0.000078 in a 65 ° C. constant temperature bath for 3 hours. Promotes the hydrolysis of tetraethoxysilane. Further, a gel raw material liquid is prepared by adding water / NH ₃ at a ratio of 2.5 / 0.0057 (molar ratio to tetraethoxysilane) and mixing.

Step 2: First gelling step The gel raw material liquid (first gelling raw liquid) adjusted as described above is dropped into a space formed by the piezoelectric body 22 and the protective matching layer 24. At this time, a Teflon sheet is wound around the outer periphery of the outermost protective matching layer 24 to form a frame so that the gel raw material liquid does not spill.

  The sample to which the gel raw material liquid has been dropped is left at 50 ° C. for about 1 day while keeping the sample horizontal in a thermostat. Thus, the gel raw material liquid supplied into the space formed by the piezoelectric body 22 and the protective matching layer 24 gels, forming a wet gel.

Step 3: Second gelation step (adjustment of sound speed and density)
When the acoustic matching layer obtained in the first gelation step is directly subjected to the drying step, the density is about 2.0 × 10 ² kg / m ³ and the sound speed is about 200 m / s. In the present embodiment, the second gelation step is performed for the purpose of further increasing the speed of sound and the density.

  First, the wet gel obtained in the first gelling step is washed with ethanol to prepare a second gelling raw material liquid. As the second gelling raw material liquid, a mixture of tetraethoxysilane / ethanol / 0.1N aqueous ammonia mixed at a volume ratio of 60/35/5 is used.

  The composite comprising the piezoelectric body 22 / wet gel / protective matching layer 24 obtained in the first gelling step is immersed in the second gelling raw material liquid in a closed container and left in a constant temperature bath at 70 ° C. for about 48 hours. I do. In the second gelation step, the gel skeleton obtained in the first gelation step grows, and the density and the speed of sound increase.

Step 4: Hydrophobizing Step The hydrophobizing step is not always necessary, but is preferably performed because performance may be degraded due to moisture absorption. In the hydrophobizing step, after the second gelling step, the second gelling raw material liquid remaining in the wet gel is replaced and washed with ethanol, and then dimethyldimethoxysilane / ethanol / 10% by weight ammonia water is added. The hydrophobizing step is carried out by immersing in a hydrophobizing liquid obtained by mixing at a weight ratio of 45/45/10 at 40 ° C. for about 1 day.

Step 5: Drying Step In order to obtain a dry gel from the wet gel obtained in the above steps, a drying step is performed. In this embodiment, a supercritical drying method is used as the drying method. As described above, dry gel is a very small porous material with a nanometer size. Depending on the thickness of the skeleton, the strength of the bond, and the size of the pores, the solvent is dried from the wet gel to the dry gel. In such a case, it may be destroyed by the surface tension of the solvent.

  For this reason, the supercritical drying method in which surface tension does not work can be used effectively. Specifically, after replacing the above-mentioned hydrophobizing liquid with ethanol, the composite of the piezoelectric body 22 / wet gel / protective unit acoustic matching layer 25 obtained in the above steps is put into a pressure-resistant container, and the wet gel The ethanol inside is replaced with liquefied carbon dioxide.

  Further, by pumping liquefied carbon dioxide into the container, the pressure in the container is increased to 10 MPa. Thereafter, the inside of the container was brought into a supercritical state by raising the temperature to 50 ° C. Next, while maintaining the temperature at 50 ° C., the pressure is slowly released to complete the drying.

Step 6: Thickness Adjusting Step The dry gel layer thus formed was ground by a lathe so that only the acoustic matching layer 25 had a thickness of 0.32 mm.

The density of the dried gel forming the acoustic matching layer 25 thus obtained is about 0.6 × 10 ³ kg / m ³ , and the speed of sound is about 640 m / s. In addition, although the dry gel which becomes the acoustic matching layer 25 has penetrated into a part of the protective matching layer 24, it does not affect the sound speed of the protective matching layer 24.

  Before the step of forming the acoustic matching layer from the dried gel, it is preferable to treat the surface of the electrode 23b so that the adhesion between the electrode 23b and the acoustic matching layer 25 is improved. When the adhesion between the electrode 23b and the acoustic matching layer 25 is increased by the surface treatment, the reliability is further improved. As such a surface treatment, a plasma treatment or the like in which a hydroxyl group is imparted to an electrode on the surface of the piezoelectric body that easily forms a chemical bond with the dried gel can be employed. Alternatively, it is also effective to provide an anchor effect by forming physical irregularities on the surface of the electrode 23b. Specifically, a chemical and / or physical etching process can be suitably employed.

  In the present embodiment, after forming the gel to be the acoustic matching layer 25, grinding with a lathe is performed to adjust the thickness of the dried gel. The adjustment of the thickness may be performed by adjusting the amount (height) of the first gelling raw material liquid dropped in the first gelling step. In this case, 33.9 μL of the gel raw material liquid is accurately measured with a micropipette and dropped on the piezoelectric body 22 so that the thickness of the acoustic matching layer to be formed is finally about 0.32 mm. . Since the protective matching layer 24 is a porous body having 80% voids, it is necessary to calculate the amount of dripping by converting the volume absorbed by the porous body.

FIG. 25 shows transmission / reception waveforms of the ultrasonic transducer thus manufactured. In FIG. 25, the ultrasonic transmission / reception waveform of the present embodiment is indicated by a solid line, and the ultrasonic transmission / reception waveform of the ultrasonic transmitter / receiver (comparative example) in which the protection unit and the acoustic matching layer 25 have the same thickness is indicated by a dotted line. Have been. As can be seen from FIG. 25, according to the present embodiment, the amplitude of the signal increases.
High sensitivity can be achieved by using the structure of the present invention.

  In the present embodiment, in order to align the phases of the ultrasonic waves at the same level as the upper surface of the protective matching layer 24, the ultrasonic waves propagating through the acoustic matching layer 25 and the propagation medium 26 transmit the ultrasonic waves propagating through the protective matching layer 24. Compared with the sound wave, the phase is delayed by exactly the wavelength. In the case where the protective matching layer 24 is formed from a material having a higher sound velocity, or when the thickness L3 of the protective matching layer 24 is set to be large, the phase lag due to the propagation medium 26 is set to two or more ultrasonic wavelengths. May be.

(Embodiment 11)
Next, an eleventh embodiment of the ultrasonic transducer according to the present invention will be described with reference to FIG. The main feature of this embodiment is that the acoustic matching layer has a laminated structure including a lower first acoustic matching layer 25a and an upper second acoustic matching layer 25b.

  Even when the acoustic matching layer 25 has a two-layer structure, it is preferable that the thickness of each of the acoustic matching layers 25a and 25b is set to about １ ／ of the ultrasonic wavelength in each acoustic matching layer.

  Also in the present embodiment, as in the tenth embodiment, in order to align the phases of the ultrasonic waves at the same level as the upper surface of the protective matching layer 24, the ultrasonic waves propagating through the acoustic matching layer 25 and the propagation medium 26 are Compared to the ultrasonic wave propagating through the protective matching layer 24, a phase delay of approximately an integral multiple of the ultrasonic wave wavelength is generated.

  In the configuration shown in FIG. 26, when the ultrasonic wave propagates through the protective matching layer 24 and reaches the upper surface of the protective matching layer 24, the ultrasonic wave having the same phase as the ultrasonic wave is transmitted to the first acoustic matching layer and the second acoustic matching layer. The boundary surface of 25b has been reached. This is because the sound speed of the first acoustic matching layer 25a is lower than the sound speed of the protective matching layer 24. It takes an additional 1 / 4f [second] for the ultrasonic wave to reach the upper surface of the second acoustic matching layer 25b from the upper surface of the first acoustic matching layer 25a. Therefore, if it is set so that the time from when the propagation medium 26 propagates from the upper surface of the acoustic matching layer 25b to reach the same level as the upper surface of the protective matching layer 24 becomes ／ f [sec], the upper surface of the protective matching layer 24 becomes The phases are aligned at the level. With such a configuration, there is a shift of one wavelength between the ultrasonic wave radiated through the acoustic matching layers 25a and 25b and the ultrasonic wave radiated through the protective matching layer 24. Since the two ultrasonic waves interfere with each other and strengthen each other, the amplitude of the ultrasonic waves increases.

  A method for manufacturing the acoustic matching layers 25a and 25b in the present embodiment will be described.

  First, the protective matching layer 24 is manufactured in the same manner as in the method of manufacturing the acoustic matching layer 25 according to the tenth embodiment. Porous ceramic is used as the material of the protective matching layer 24, and its thickness (L7) is set to 1.0 mm.

  In the present embodiment, the distance (L6) from the upper surface of the second acoustic matching layer 25b to the upper surface level of the protective matching layer 24 is set so that the time for propagating through the propagation medium 26 such as air is ４f [sec]. Set to 0.51 mm. As a result, the total thickness (L4 + L5) of the first acoustic matching layer 25a and the second acoustic matching layer 25b becomes equal to 0.49 mm.

  In this embodiment, when the sound speed of the second acoustic matching layer 25b is set to 200 m / s, the thickness (L5) of the second acoustic matching layer 25b is preferably set to 0.10 mm. If L5 = 0.10 mm, the thickness (L4) of the first acoustic matching layer 25a is 0.39 mm (= 0.49 mm-0.10 mm). In order for the thickness of the first acoustic matching layer 25a to correspond to １ ／ wavelength of the ultrasonic wave in the first acoustic matching layer 25a, the sound speed of the first acoustic matching layer 25a needs to be 780 m / s. .

  Next, a method of manufacturing the two acoustic matching layers 25a and 25b as described above will be described. The feature of this method is that the second gelation step performed in the tenth embodiment is performed twice. That is, in this embodiment, after performing the second gelation step (2-1 gelation step) in which gelation is not performed outside the wet gel formed in the first gelation step, the gel is also formed outside the wet gel. A second gelation step (2-2nd gelation step) in which gelation occurs is performed.

  In the present embodiment, first, the first acoustic matching layer 25a is formed by performing the same steps as the steps 1 to 6 performed in the tenth embodiment. However, the second gelation step at this time is a 2-1 gelation step.

It is anticipated that the acoustic impedance will increase in the 2-2 gelation step performed thereafter, and in the 2-1 gelation step, the density of the first acoustic matching layer 25a is about 0.5 × 10 ³ kg / m ³ , and the sound speed is 500 m / m3. The processing time is adjusted to about s. In the present embodiment, the processing time is shorter than the processing time of the second gelling step in the tenth embodiment, and is set to about 36 hours.

  Next, by performing a 2-2 gelling step, the acoustic impedance of the first acoustic matching layer 25a is increased, and the second acoustic matching layer 25b is formed on the first acoustic matching layer 25a. This 2-2 gelation step was specifically performed as follows.

2-2 gelation step:
First, a liquid obtained by mixing tetraethoxysilane / ethanol / 0.05N aqueous ammonia at a molar ratio of 1/4/3 is prepared as a 2-2 gelling raw material liquid. The 2-2 gelling raw material liquid is filled in a space formed by the first acoustic matching layer 25a and the protective matching layer 24. Next, the gelation is completed by being left at room temperature for about 24 hours. Thus, while adjusting the acoustic impedance of the first acoustic matching layer 25a, a wet gel to be the second acoustic matching layer 25b is formed.

  Thereafter, the acoustic matching layers 25a and 25b are completed by performing a hydrophobicizing step, a drying step, and a thickness adjusting step in the same manner as in the tenth embodiment. The acoustic matching layers 25a and 25b in the present embodiment are characterized as follows.

First acoustic matching layer 25a
Density: 0.7 × 10 ³ kg / m ³ , speed of sound: 780 m / s
Acoustic impedance: 5.46 × 10 ⁵ kg / m ² / s
Thickness: 0.39mm
Second acoustic matching layer 25b
Density: 0.2 × 10 ³ kg / m ³ , Speed of sound: 200 m / s
Acoustic impedance: 4.0 × 10 ⁴ kg / m ² / s
Thickness: 0.10mm

  FIG. 27 shows transmission / reception waveforms of the ultrasonic transceiver of the present embodiment. In FIG. 27, the ultrasonic transmission / reception waveform of the ultrasonic transmission / reception device of the present embodiment is shown by a solid line, and the transmission / reception waveform shape of the ultrasonic transmission / reception device (comparative example) in which the acoustic matching layer and the protective matching layer have the same thickness. Is indicated by a dotted line. As can be seen from FIG. 27, according to the ultrasonic transducer of the present embodiment, high sensitivity can be realized.

  In this embodiment, the acoustic matching layer 25 has two layers. However, even when three or more layers are used, the same effect can be obtained by designing the upper surface of the protective matching layer 24 so that the phases of the ultrasonic waves are aligned. can get.

(Embodiment 12)
A twelfth embodiment of the ultrasonic transducer according to the present invention will be described with reference to FIG. A feature of the present embodiment is that the first acoustic matching layer 25a and the protective matching layer 24 are integrally formed of the same material. Above the first acoustic matching layer 25a, a second acoustic matching layer 25b made of dry gel is formed.

  In the present embodiment, the sound speed and the wavelength of the ultrasonic waves in the first acoustic matching layer 25a and the protective matching layer 24 are equal, and the thickness L11 of the protective matching layer 24 is set to 波長 wavelength of the ultrasonic waves. Therefore, the thickness L8 of the first acoustic matching layer 25a is smaller than a quarter wavelength of the ultrasonic wave. The thickness L8 of the first acoustic matching layer 25a is determined by the thickness L9 of the second acoustic matching layer 25b and the distance L10 from the upper surface of the second acoustic matching layer 25b to the upper surface level of the protective matching layer 24.

  Also in this embodiment, the phase lag between the ultrasonic wave radiated through the acoustic matching layers 25a and 5b and the ultrasonic wave radiated through the protective matching layer 24 is an integral multiple of the ultrasonic wavelength. Is adopted. Therefore, the phases of the ultrasonic waves propagating through the acoustic matching layers 25a and 25b and the propagation medium 26 are aligned at the upper surface level of the protective matching layer 24.

  The thickness of the second acoustic matching layer 25b is more important than the thickness of the first acoustic matching layer 25a in order to increase the sensitivity of the ultrasonic waves transmitted through the acoustic matching layers 25a and 25b. In the present embodiment, the thickness of the second acoustic matching layer 25b is set to about の of the wavelength of the transmitted / received ultrasonic wave. The thickness of the first acoustic matching layer 25a also affects the sensitivity, but most of the influence extends to the frequency bandwidth.

  For this reason, in the present embodiment, first, the characteristics of the dried gel layer that can constitute the second acoustic matching layer 25b are determined in terms of the mechanical strength of the material and the like. Next, the thickness L8 of the first acoustic matching layer 25a formed of the same material as the protective matching layer 24 and the thickness L10 of the sound wave propagation medium are set.

In this embodiment, a porous ceramic is used as the material of the protective matching layer 24 as in the above-described embodiment, and the thickness (L11) is set to １ ／ of the ultrasonic wavelength. That is, L11 is set to 1.0 mm. In this case, the sound speed of the first acoustic matching layer 25a formed of the porous ceramic is 200 m / s, and the density is 0.2 × 10 ³ kg / m ³ . L9 is set to 0.10 mm in order to set the thickness of the second acoustic matching layer 25b formed of the dried gel to １ ／ of the ultrasonic wavelength.

  At this time, the following equation 7 is established.

  L8 + L10 = 0.9 [mm] (7)

  Equation 7 is derived from setting L11 to 1.0 mm and L9 to 0.1 mm.

  In order to exhibit excellent characteristics, it is preferable that the following expression is satisfied.

  L8 / 1 + L10 / (17/25) = 1 [wavelength] (8)

  In this embodiment, since an ultrasonic wave having a frequency of 500 kHz is transmitted and received, one wavelength of the ultrasonic wave in the acoustic matching layer 25a is 1.0 mm, and one wavelength of the ultrasonic wave in the sound wave propagation medium 26 is 17/25 mm. Equation 8 is the sum of the ratio of the thickness L8 of the first acoustic matching layer 25a to one wavelength of the ultrasonic wave and the ratio of the thickness L10 of the propagation medium 26 to one wavelength of the ultrasonic wave. Satisfying Expression 8 means that the ultrasonic wave advances by one wavelength when transmitting through the first acoustic matching layer 25a and the sound wave propagation medium 26. In other words, it means that the effective thickness of the first acoustic matching layer 25a and the sound wave propagation medium 26 felt by the ultrasonic wave is one wavelength.

  When L8 and L10 satisfying Expressions 7 and 8 are calculated, L8 = about 0.69 mm and L10 = 0.21 mm.

  Next, a method for manufacturing the ultrasonic transducer according to the present embodiment will be described with reference to FIGS.

  First, as shown in FIG. 29A, a 1.0 mm-thick pellet made of porous ceramics is prepared, and this pellet is processed as shown in FIG. 29B. In the present embodiment, a groove is formed on the upper surface of the pellet, and the thickness of the groove bottom is adjusted to 0.69 mm. The bottom of the groove is a portion that functions as the first acoustic matching layer 25a. The groove is formed in a ring shape as shown in FIG.

  Next, as shown in FIG. 29C, a second acoustic matching layer 25b is formed inside the groove. The thickness of the acoustic matching layer 25b is set to 0.1 mm. The composite of the protection matching layer 24 / acoustic matching layers 25a and 25b is joined to the piezoelectric body 22 to form the ultrasonic transducer 21 as shown in FIG.

  The first acoustic matching layer 25b is made of a first gel in the same manner as in the first embodiment using a liquid obtained by mixing tetramethoxysilane / ethanol / 0.05N aqueous ammonia at a molar ratio of 1/7/4. It is formed by performing a conversion step.

  The composite including the protective matching layer 24 and the acoustic matching layers 25a and 25b can be bonded to the piezoelectric body using an epoxy-based adhesive, as in the first embodiment.

  According to the present embodiment, since the protective matching layer 24 and the acoustic matching layer 25a can be formed collectively, the manufacturing process can be simplified and the manufacturing cost can be reduced.

(Embodiment 13)
A thirteenth embodiment of the ultrasonic transducer according to the present invention will be described with reference to FIG. A feature of the present embodiment is that it has a structural support.

  The ultrasonic transducer according to the first embodiment has the structural support 27 between the piezoelectric body 22 and the first acoustic matching layer 25 or the protective matching layer 24 except for the ultrasonic transducer according to the first embodiment. It has the same configuration as the configuration of the transmission / reception recording medium.

  The structural support 27 includes a disk-shaped support portion to which the acoustic matching layer 25 and the like are fixed, and a cylindrical portion continuously extending in the axial direction from the disk-shaped support portion. The end face of the cylindrical portion is bent in an L-shaped cross section, and is easily fixed to a plate (not shown) for shielding the piezoelectric body 22 or another device.

  The acoustic matching layer 25 and the protective matching layer 24 are arranged on the surface of the structural support 27, and the piezoelectric body 22 is arranged on the back surface of the support. By using such a structural support 27, handling of the ultrasonic transducer is extremely easy.

  The structural support can be composed of a sealable container (sensor case). In this case, if the open end of the cylindrical portion of the structural support 27 is closed with a shielding plate or the like and the inside of the structural support 27 is filled with an inert gas, the piezoelectric body 22 is cut off from the fluid to be subjected to the flow rate measurement. be able to.

  Since a voltage is applied to the piezoelectric body 22, there is a risk that the combustible gas may be ignited when the piezoelectric body comes into contact with a combustible gas or the like. However, the structural support 27 is formed of a hermetically sealed container, and by blocking the inside of the piezoelectric body 22 from an external fluid or the like, such a flammability can be prevented, and a super-flammable gas can be safely protected. Sound waves can be transmitted and received.

  Further, even if the piezoelectric body 22 is not a combustible gas and transmits / receives ultrasonic waves to / from a gas which reacts with the piezoelectric body 22 and may deteriorate the characteristics of the piezoelectric body 22, the piezoelectric body 22 is shielded from external gas. Is preferred. By doing so, the deterioration of the piezoelectric body 22 can be prevented, and a highly reliable operation can be realized for a long period of time.

  The portion of the structural support 27 located between the piezoelectric body 22 and the acoustic matching layer 25 or the protective matching layer 24 does not function as an acoustic matching layer. Therefore, in order to prevent the structural support 27 from acting as an acoustic obstacle, the thickness of the portion of the structural support 27 located between the piezoelectric body 22 and the acoustic matching layer 25 or the protective matching layer 24 Is desirably about １ ／ or less of the wavelength of the transmitted and received ultrasonic waves.

  In the present embodiment, the structural support 27 is made of stainless steel, and the thickness of the above-mentioned portion is set to 0.2 mm.

  The sound speed of stainless steel is about 5500 m / sec, and the wavelength of the ultrasonic wave at 500 kHz is about 11 mm. Since the thickness of 0.2 mm corresponds to about 1/55 of the wavelength, the presence of the structural support 27 hardly causes acoustic inhibition.

  The material of the structural support 27 is not limited to a metal material such as stainless steel, and a material according to the purpose is selected from ceramic, glass, resin, and the like. In the present embodiment, the metal material is used to reliably separate the external fluid and the piezoelectric body, and to provide a strength capable of preventing the piezoelectric body from being in contact with the external fluid even if any mechanical shock is applied to the structural support. To produce the structural support 27. Accordingly, high safety can be ensured even when ultrasonic waves are transmitted and received, for example, for a combustible or explosive gas.

  When transmitting and receiving ultrasonic waves to and from a safe gas, a structural support made of a material such as a resin may be used for the purpose of cost reduction.

(Embodiment 14)
A fourteenth embodiment of the ultrasonic transducer according to the present invention will be described with reference to FIGS. 31 (a) and 31 (b). FIGS. 31A and 31B are top views of the present embodiment.

  In the example shown in FIG. 21, a ring made of porous ceramics (three ring-shaped members having the same width and different diameters) functioning as the protective matching layer 24 is used and arranged on the main surface of the piezoelectric body so that their centers coincide with each other. However, as shown in FIG. 31A, the protection matching layer 24 may be formed using rings having different widths. Further, as shown in FIG. 31B, the island-shaped protective matching layers 24 may be randomly arranged.

  When the protective matching layer 24 and the acoustic matching layer 25 are regularly arranged on the main surface of the ultrasonic transducer, the phase of the ultrasonic wave is shifted at a certain angle with respect to the main surface. Align, the amplitude increases. This is called “side lobe” and is a hindrance in performing ultrasonic measurement. However, as shown in FIG. 31, by employing a configuration in which the arrangement of the protective matching layers 24 does not have periodicity, side lobes can be suppressed, and highly accurate and reliable ultrasonic measurement can be performed. .

(Embodiment 15)
A fifteenth embodiment of the ultrasonic transducer according to the present invention will be described with reference to FIG.

  The ultrasonic transducer of the present embodiment has a first feature in that the thickness of the protective matching layer 24 has an in-plane distribution. In each of the above embodiments, the thickness of the protective matching layer 24 is set uniformly in the plane, but in the present embodiment, an in-plane distribution is intentionally given. A second feature of the present embodiment is that the protective matching layer 24 provided on the piezoelectric body 22 is formed of two different materials.

  According to the configuration of the present embodiment, by adopting different materials and / or providing in-plane distributions of different thicknesses, it is possible to suppress side lobes or change the frequency of ultrasonic waves to be transmitted / received to broaden the band. Can be.

  The thickness of each protective matching layer 24 is preferably included in the range of 1/8 to 1/3 of the ultrasonic wavelength, and in the range of 1/6 to 1/4 of the ultrasonic wavelength. More preferably, it is contained within. However, the thickness of a part of the protective matching layer 24 having a different thickness may be out of the above range. Since the protective matching layer 24 having a thickness outside the above range does not function as an acoustic matching layer, the sensitivity of ultrasonic transmission and reception is reduced. However, by disposing a protective layer that does not function as an acoustic matching layer (which can no longer be called a “protective matching layer”) at an appropriate position on the piezoelectric body, it is possible to prevent the disturbance of the ultrasonic field at a short distance and obtain a good ultrasonic wave. Sound wave measurement can be enabled.

(Embodiment 16)
An embodiment of the ultrasonic flowmeter according to the present invention will be described with reference to FIG.

  The ultrasonic flow meter according to the present embodiment is installed so that the fluid to be measured flows at a speed V in the pipe functioning as the flow rate measuring unit 51. Ultrasonic transmission / reception devices 1a and 1b formed from the ultrasonic transmission / reception device of the present invention are disposed opposite to the tube wall 52 of the flow rate measurement unit 51.

  At some point, the ultrasound transceiver 1a functions as an ultrasound transmitter and the ultrasound transceiver 1b functions as an ultrasound receiver, but at other times, the ultrasound transceiver 1a And the ultrasonic transceiver 1b functions as an ultrasonic transmitter. This switching is performed by the switching circuit 53.

  The ultrasonic transceivers 1a and 1b are connected via a switching circuit 53 to a drive circuit 54 that drives the ultrasonic transceivers 1a and 1b and a reception detection circuit 55 that detects ultrasonic pulses. The output of the reception detection circuit 55 is sent to a timer 56 that measures the propagation time of the ultrasonic pulse. The output of the timer 56 is sent to a calculation unit 57 that calculates the flow rate. The calculation unit 57 calculates the velocity V of the fluid flowing in the flow measurement unit 51 based on the measured propagation time of the ultrasonic pulse, and obtains the flow rate. The drive circuit 54 and the timer 56 are connected to the control unit 58, and are controlled by a control signal output from the control unit 58.

  Hereinafter, the operation of the ultrasonic flowmeter will be described in more detail.

  It is assumed that the LP gas flows through the flow rate measuring unit 51 as the fluid to be measured. The driving frequency of the ultrasonic transmission / reception devices 1a and 1b is set to about 500 kHz. The control unit 58 outputs a transmission start signal to the drive circuit 54 and, at the same time, causes the timer 56 to start time measurement. When receiving the transmission start signal, the drive circuit 54 drives the ultrasonic transmission receiver 1a and transmits an ultrasonic pulse. The transmitted ultrasonic pulse propagates through the flow measuring unit 51 and is received by the ultrasonic transmission receiver 1b. The received ultrasonic pulse is converted into an electric signal by the ultrasonic transmission receiver 1 b and output to the reception detection circuit 55.

  The reception detection circuit 55 determines the reception timing of the reception signal, and stops the timer 56. The calculation unit 57 calculates the propagation time t1.

  Next, the switching circuit 53 switches the ultrasonic transmission / receivers 1a and 1b connected to the drive circuit 54 and the reception detection circuit 55. Then, again, the control unit 59 outputs a transmission start signal to the drive circuit 54 and, at the same time, causes the timer 56 to start time measurement. Contrary to the measurement of the propagation time t1, an ultrasonic pulse is transmitted by the ultrasonic transmission receiver 1b, received by the ultrasonic transmission receiver 1a, and the arithmetic unit 57 calculates the propagation time t2.

  Here, the distance connecting the centers of the ultrasonic transmission receiver 1a and the ultrasonic transmission receiver 1b is L, the sound velocity of the LP gas in a windless state is C, the flow velocity in the flow rate measuring unit 51 is V, and The angle between the direction of the flow of the measurement fluid and the line connecting the centers of the ultrasonic transmission / reception receivers 1a and 1b is defined as θ.

  The propagation times t1 and t2 are each obtained by measurement. Since the distance L is known, if the times t1 and t2 are measured, the flow velocity V is obtained, and the flow rate can be determined from the flow velocity V.

  In such an ultrasonic flowmeter, the propagation times t1 and t2 are measured by a method called a zero-cross method. In this method, an appropriate threshold level is set for a reception waveform as shown in FIG. 34A, and the time when the amplitude exceeds the threshold level and the amplitude next becomes 0 is measured. If the S / N of the received signal is poor, the point where the amplitude becomes 0 fluctuates with time depending on the noise level, so that t1 and t2 cannot be measured accurately, and it is difficult to measure an accurate flow rate. In some cases.

  When the ultrasonic transceiver of the present invention is used as an ultrasonic transducer of such an ultrasonic flowmeter, the S / N of a received signal is improved, and t1 and t2 can be measured with high accuracy. .

  As shown in FIG. 34B, when the rising of the received signal is slower (narrow band) than in the case of FIG. 34A, t1 and t2 are measured with respect to the set value of the threshold level. The position of the peak of the received signal may fluctuate, resulting in a measurement error. However, since the ultrasonic transceiver according to the present invention operates properly in a wide band, the rising of the received signal is good, and accurate flow measurement can be performed stably. In addition, it is preferable to use the average value of the values obtained by several other measurements as the values of t1 and t2.

  Being able to transmit and receive broadband ultrasonic waves means that the signal falls quickly. Therefore, even when the measurement is repeated quickly, there is no influence of the previous transmission / reception signal. As a result, even if the measurement repetition frequency is increased, instantaneous measurement can be performed, and gas leakage and the like can be detected instantaneously.

  In each of the above embodiments, the upper surface of the uppermost acoustic matching layer (first acoustic matching layer) is exposed, but this surface may be covered with a protective film having a thickness of 10 μm or less. Such a protective film avoids direct contact between the atmosphere and the acoustic matching layer, and contributes to maintaining the characteristics of the acoustic matching layer for a long time. The protective film is made of, for example, a film (not limited to a single layer) made of a material such as aluminum, silicon oxide, low-melting glass, or a polymer. The protective film is deposited by a sputtering method, a CVD method, or the like.

  According to the present invention, a high-performance ultrasonic transceiver using a thin acoustic matching layer formed of a material having extremely low acoustic impedance and low mechanical strength can be put to practical use. Reliability in use is also improved.

It is sectional drawing which shows the ultrasonic transceiver in Embodiment 1 of this invention. It is a top view of the ultrasonic transceiver in Embodiment 1 of this invention. (A) is a graph showing a transmission / reception waveform of the ultrasonic transducer in Embodiment 1 of the present invention, and (b) is a graph showing a transmission / reception waveform of the conventional ultrasonic transducer. FIG. 4 is a cross-sectional view schematically illustrating a case where the acoustic matching layer contracts in the first embodiment of the present invention. It is sectional drawing of the ultrasonic transceiver in Embodiment 2 of this invention. It is sectional drawing which shows other structures of the protection part in Embodiment 2 of this invention. It is a top view which shows other structures of the protection part in Embodiment 2 of this invention. It is sectional drawing of the ultrasonic transceiver in Embodiment 3 of this invention. It is sectional drawing of the ultrasonic transceiver in Embodiment 4 of this invention. It is sectional drawing of the ultrasonic transceiver in Embodiment 5 of this invention. (A) is a graph which shows the transmission / reception waveform of the ultrasonic transducer in Embodiment 5 of this invention, (b) is a graph which shows the transmission / reception waveform of the conventional ultrasonic transducer. It is sectional drawing which shows the other structure of the lower acoustic matching layer in Embodiment 6 of this invention. It is sectional drawing of the ultrasonic transceiver in Embodiment 7 of this invention. It is a graph which shows the transmission-and-reception waveform of the ultrasonic transducer in Embodiment 7 of this invention. It is sectional drawing of the ultrasonic transceiver of another structure in Embodiment 7 of this invention. 13A to 13C are process cross-sectional views illustrating a method of manufacturing the ultrasonic transducer illustrated in FIG. FIG. 17A is a cross-sectional view showing an acoustic matching layer in a case where gel penetration is sufficient in the manufacturing process shown in FIG. 16, and FIG. 17B is a sectional view showing an acoustic matching layer in a case where gel penetration is insufficient. It is sectional drawing. 13A to 13D are process cross-sectional views illustrating another method of manufacturing the ultrasonic transducer illustrated in FIG. (A) And (b) is a top view which shows each other structural example of a protection part, respectively. It is sectional drawing of the 10th embodiment of the ultrasonic transducer by this invention. It is a top view of the 10th embodiment of the ultrasonic transducer by the present invention. It is a schematic diagram which shows the interference of the ultrasonic wave in 10th Embodiment of the ultrasonic transducer by this invention. It is sectional drawing which shows typically the phase of the ultrasonic wave which propagated through the protective matching layer and the acoustic matching layer. (A) to (c) are process cross-sectional views showing a method of manufacturing an ultrasonic transducer according to a tenth embodiment of the present invention. It is a transmission / reception waveform diagram of the 10th embodiment of the ultrasonic transducer according to the present invention. It is a sectional view of an eleventh embodiment of the ultrasonic transducer according to the present invention. It is a transmission / reception waveform diagram of the eleventh embodiment of the ultrasonic transducer according to the present invention. It is a sectional view of a 12th embodiment of an ultrasonic transducer by the present invention. (A) to (d) are process cross-sectional views showing a method for manufacturing a twelfth embodiment of the ultrasonic transducer according to the present invention. It is a sectional view of a 13th embodiment of an ultrasonic transducer by the present invention. (A) and (b) are top views, respectively, of a fourteenth embodiment of an ultrasonic transducer according to the present invention. It is sectional drawing of the 15th embodiment of the ultrasonic transducer by this invention. It is a block diagram showing an ultrasonic flowmeter in Embodiment 16 of the present invention. (A) And (b) is a graph which shows the waveform measured by the ultrasonic flowmeter of this invention. It is sectional drawing which shows the conventional ultrasonic flowmeter. It is sectional drawing of the conventional ultrasonic transceiver.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Ultrasonic transceiver 2 Protector 3 Acoustic matching layer (first acoustic matching layer)
4 Piezoelectric body 5 Piezoelectric body provided with a portion functioning as protection part 6 Structural support (piezoelectric container or case)
Reference Signs List 7 Structural support provided with part functioning as protection part 8 Second acoustic matching layer 9 First acoustic matching layer provided with part functioning as protection part 10 Back load material 11 Back load provided with part functioning as protection part Material 51 Flow rate measurement unit 52 Tube wall 53 Switching circuit 54 Drive circuit 55 Reception detection circuit 56 Timer 57 Operation unit 58 Control unit 101 Ultrasonic transceiver 102 Tube wall 103 Ultrasonic transceiver 104 Acoustic matching layer 105 Sensor case 106 Piezoelectric body

Claims (56)

A piezoelectric body,
An acoustic matching layer provided on the piezoelectric body,
A protection portion that is in contact with at least a part of the side surface of the acoustic matching layer and is provided at a position fixed with respect to the piezoelectric body;
Ultrasound transceiver equipped with.   The protection unit protrudes in the ultrasonic wave emitting direction from a plane at the same level as the main surface of the piezoelectric body, and the height of the protection unit with respect to the main surface of the piezoelectric body is the thickness of the acoustic matching layer. The ultrasonic transceiver according to claim 1, wherein   The ultrasonic transceiver according to claim 1, wherein the height of the protection unit is not less than 5 μm and not more than 2500 μm.   The ultrasonic transceiver according to claim 3, wherein the thickness of the acoustic matching layer is substantially equal to the height of the protection unit.   The ultrasonic transceiver according to any one of claims 1 to 4, wherein a thickness of the acoustic matching layer is about 1/4 of a wavelength of an ultrasonic wave transmitted and / or received by the piezoelectric body. The ultrasonic transceiver according to claim 1, wherein the acoustic matching layer is formed of a material having a density of 50 kg / m ³ or more and 1000 kg / m ³ or less. 7. The acoustic matching layer according to claim 1, wherein the acoustic impedance is formed from a material having an acoustic impedance of 2.5 × 10 ³ kg / m ² / s to 1.0 × 10 ⁶ kg / m ² / s. 2. The ultrasonic transceiver according to claim 1.   The ultrasonic transceiver according to claim 6, wherein the acoustic matching layer is formed of an inorganic material.   The ultrasonic transceiver according to claim 8, wherein the inorganic material is a dried gel of an inorganic oxide.   The ultrasonic transceiver according to claim 9, wherein the inorganic oxide has a water-repellent solid skeleton.   The ultrasonic transceiver according to any one of claims 1 to 10, wherein the acoustic matching layer is solidified from a fluid state on the piezoelectric body provided with the protection unit. It has a lower acoustic matching layer provided between the main surface of the piezoelectric body and the acoustic matching layer,
The protection unit protrudes from the main surface of the lower acoustic matching layer, and the height of the protection unit with respect to the main surface of the acoustic matching layer defines the thickness of the acoustic matching layer positioned at the uppermost layer. The ultrasonic transceiver according to claim 1, wherein   The ultrasonic transceiver according to claim 12, wherein the protection unit is configured by a part of the lower acoustic matching layer, and is integrated with the lower acoustic matching layer.   14. The ultrasonic transceiver according to claim 12, wherein the height of the protection unit is 5 μm or more and 2500 μm or less.   The ultrasonic transceiver according to claim 14, wherein the height of the protection unit is substantially equal to a thickness of the acoustic matching layer located on an uppermost layer.   The supersonic wave according to any one of claims 12 to 15, wherein the acoustic matching layer and the lower acoustic matching layer each have a thickness of about 1/4 of a wavelength of an ultrasonic wave transmitted and received by the piezoelectric body. Sound wave transceiver. The density of the acoustic matching layer, the ultrasonic transducer according to any of claims 12 16 or less 50 kg / m ³ or more 1000 kg / m ^3. The acoustic impedance of the lower acoustic matching layer is larger than the acoustic impedance of the first acoustic matching layer, and is not less than 2.5 × 10 ³ kg / m ² / s and not more than 3.0 × 10 ⁷ kg / m ² / s. The ultrasonic transceiver according to any one of claims 12 to 17, wherein   The ultrasonic transceiver according to any one of claims 1 to 18, wherein the protection unit is provided on an outer periphery of the acoustic matching layer located on an uppermost layer.   20. The ultrasonic transceiver according to claim 19, wherein the protection unit covers the entire outer peripheral side surface of the acoustic matching layer located on the uppermost layer.   21. The ultrasonic transceiver according to claim 19, wherein the protection unit is disposed outside a main surface of the piezoelectric body.   The ultrasonic transceiver according to claim 1, wherein the protection unit is provided on a main surface of the piezoelectric body.   19. The ultrasonic transceiver according to claim 12, wherein the protection unit is provided on the lower acoustic matching layer.   The ultrasonic transceiver according to any one of claims 1 to 11, wherein the protection unit includes a part of the piezoelectric body and is integrated with the piezoelectric body.   25. The ultrasonic transceiver according to claim 1, further comprising a structural support for supporting the piezoelectric body. Further comprising a structural support for supporting the piezoelectric body,
The ultrasonic transceiver according to claim 1, wherein the protection unit is provided on the structural support. The structural support is formed from a pressed metal,
27. The ultrasonic transceiver according to claim 26, wherein the protection unit is configured by a portion of the structural support that is bent by press molding.   28. The ultrasonic transceiver according to claim 26, wherein the height of the protection unit is not less than 5 μm and not more than 2500 μm.   The ultrasonic transceiver according to claim 28, wherein a thickness of the acoustic matching layer is substantially equal to the height of the protection unit.   30. The ultrasonic transceiver according to claim 28, wherein a thickness of the acoustic matching layer is about 1/4 of a wavelength of an ultrasonic wave transmitted and received by the piezoelectric body. 31. The ultrasonic transceiver according to claim 26, wherein the density of the acoustic matching layer is 50 kg / m ³ or more and 1000 kg / m ³ or less. 31. The ultrasonic wave according to claim 25, wherein the acoustic impedance of the acoustic matching layer is 2.5 × 10 ³ kg / m ² / s or more and 1.0 × 10 ⁶ kg / m ² / s or less. Transceiver. It further comprises a back load member arranged on the back surface of the piezoelectric body and attenuating ultrasonic waves radiated in the back direction from the piezoelectric body,
The ultrasonic transceiver according to claim 1, wherein the protection member is provided on the back load member.   The ultrasonic transceiver according to claim 33, wherein the protection unit is configured by a part of the back load member, and is integrated with the back load member.   The ultrasonic transceiver according to any one of claims 1 to 34, wherein at least a part of a surface of the acoustic matching layer in contact with the holding unit has been subjected to a surface treatment for imparting a hydroxyl group.   The ultrasonic transceiver according to any one of claims 1 to 34, wherein at least a part of a surface of the acoustic matching layer in contact with the holding unit has been subjected to a surface roughening process.   The ultrasonic transceiver according to any one of claims 1 to 34, wherein at least a part of a surface of the acoustic matching layer in contact with the holding unit is porous.   The ultrasonic transceiver according to any one of claims 1 to 34, wherein a part of the acoustic matching layer penetrates and is integrated with a part of the ultrasonic transceiver that is in contact with the acoustic matching layer. A piezoelectric body that performs ultrasonic vibration,
A material having a claim density of 50 kg / m ³ or more and 1000 kg / m ³ or less and an acoustic impedance of 2.5 × 10 ³ kg / m ² / s or more and 1.0 × 10 ⁶ kg / m ² / s or less An upper acoustic matching layer formed,
A lower acoustic matching layer provided between the piezoelectric body and the upper acoustic matching layer,
A structural support that supports the lower acoustic matching layer and the piezoelectric body, and shields the piezoelectric body from an ultrasonic wave propagating fluid,
An ultrasonic transceiver having:
An ultrasonic transmitter / receiver, comprising: a protection portion that contacts at least a part of a side surface of the upper acoustic matching layer.   40. The ultrasonic transceiver according to claim 39, wherein the protection unit is formed by a part of the lower acoustic matching layer, and is integrated with the lower acoustic matching layer.   The ultrasonic transceiver according to any one of claims 1 to 40, wherein an elastic modulus of the protection unit is substantially equal to an elastic modulus of the acoustic matching layer. A flow measurement unit through which the fluid to be measured flows;
A pair of ultrasonic transceivers that are provided in the flow measurement unit and transmit and receive ultrasonic signals,
Measuring means for measuring the time that ultrasonic waves propagate between the pair of ultrasonic transceivers,
An ultrasonic flowmeter comprising a flow rate calculating means for calculating a flow rate based on a signal from the measuring means,
An ultrasonic flowmeter, wherein each of the pair of ultrasonic transceivers is the ultrasonic transceiver according to any one of claims 1 to 41.   The ultrasonic flowmeter according to claim 42, wherein the piezoelectric body of the ultrasonic transceiver is shielded from the fluid to be measured.   An apparatus comprising the ultrasonic transceiver according to any one of claims 1 to 41. (A) preparing a piezoelectric body having a main surface and a convex portion received on the main surface;
(B) forming an acoustic matching layer on the main surface of the piezoelectric body and bringing at least a part of the side surface of the acoustic matching layer into contact with the side surface of the projection;
A method for manufacturing an ultrasonic transceiver having: The step (b) is a step of supplying a gel raw material onto a main surface of the piezoelectric element;
Forming the acoustic matching layer by drying and solidifying the gel raw material;
The production method according to claim 45, comprising:   The manufacturing method according to claim 45, wherein the step (a) includes a step of processing the surface of the piezoelectric body to form the main surface and the projection.   The manufacturing method according to claim 45, wherein the step (a) includes a step of fixing the projection on the surface of the piezoelectric body.   The manufacturing method according to claim 45, wherein the step (a) includes a step of fixing the piezoelectric body to the structural support. An upper acoustic matching layer, a piezoelectric body, and a method of manufacturing an ultrasonic transceiver including a lower acoustic matching layer provided between the upper acoustic matching layer and the piezoelectric body,
(A) preparing a member having a concave portion and functioning as the lower acoustic matching layer;
(B) supplying a gel raw material to the concave portion of the member;
(C) forming the upper acoustic matching layer by drying and solidifying the gel raw material;
The method that includes.   The method according to claim 50, wherein the step (b) includes a step of infiltrating the gel material into the member.   The manufacturing method according to claim 51, wherein the gel raw material is permeated throughout the member.   The manufacturing method according to claim 50, wherein the step (b) is performed after fixing an arrangement relationship between the member and the piezoelectric body.   The manufacturing method according to claim 50, wherein the step (b) is performed before fixing an arrangement relationship between the member and the piezoelectric body. A piezoelectric body,
An acoustic matching layer provided on the piezoelectric body,
A protection portion disposed so as to be in contact with the outer peripheral surface of the acoustic matching layer;
Ultrasound transceiver equipped with. A structural support;
A piezoelectric body and an acoustic matching layer provided at positions facing each other with the structural support therebetween,
A protection portion disposed so as to be in contact with the outer peripheral surface of the acoustic matching layer;
Ultrasound transceiver equipped with.

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