JP2018061209A - Laminate, ultrasonic transducer and ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate including an acoustic matching layer having high mechanical strength and suitable acoustic characteristics, an ultrasonic transducer and an ultrasonic flow meter.SOLUTION: The laminate includes: a piezoelectric body; a first acoustic matching layer which is disposed in direct contact with the piezoelectric body or via another layer. The density of the first acoustic matching layer is 10 kg/m-100 kg/m.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a laminate including a piezoelectric body and an acoustic matching layer, an ultrasonic transducer, and an ultrasonic flowmeter.

  In recent years, an ultrasonic flowmeter that measures the flow time of ultrasonic waves and measures the flow rate by measuring the moving speed of a fluid is being used for a gas meter or the like. An ultrasonic flowmeter generally includes a piezoelectric vibrator and detects ultrasonic waves using the piezoelectric vibrator. When the fluid is a gas, since the difference in acoustic impedance between the gas and the piezoelectric vibrator is large, the ultrasonic wave propagating through the gas is easily reflected at the interface with the piezoelectric vibrator. For this reason, an acoustic matching layer may be provided at the interface between the piezoelectric vibrator and the gas in order to efficiently cause the ultrasonic wave to enter the piezoelectric vibrator.

  Patent Document 1 discloses a material that can be used as an acoustic matching layer. Patent Document 2 discloses an ultrasonic transducer having two acoustic matching layers.

Japanese Patent No. 2559144 Japanese Patent No. 3552054

  In conventional ultrasonic transducers, high sensitivity cannot be obtained because the acoustic impedance matching between the acoustic matching layer and the ultrasonic radiation medium is not sufficient. The present disclosure provides a laminate, an ultrasonic transducer, and an ultrasonic flow meter that include an acoustic matching layer with appropriate acoustic characteristics.

The laminated body of the present disclosure is a first acoustic matching layer disposed in contact with a piezoelectric body, the piezoelectric body, directly or via another layer, and a plastic closed-cell foam including a plurality of closed pores A first acoustic matching layer including a body and having an average pore diameter of the closed pore of 1 μm to 100 μm and a density of 10 kg / m ^{3 to} 100 kg / m ³ .

  According to the laminated body, the ultrasonic transducer and the ultrasonic flowmeter of the present disclosure, since the acoustic matching layer having appropriate acoustic characteristics is included, a highly sensitive ultrasonic transducer and ultrasonic flowmeter can be realized.

FIG. 1 is a block diagram illustrating an ultrasonic flowmeter of the present disclosure. FIG. 2 is a schematic end view showing the first embodiment of the laminate and the ultrasonic transducer according to the present disclosure. FIG. 3A is a process cross-sectional view illustrating the method for manufacturing the ultrasonic transducer according to the first embodiment. FIG. 3B is a process cross-sectional view illustrating the method of manufacturing the ultrasonic transducer according to the first embodiment. FIG. 4 is a schematic end view showing a second embodiment of the laminated body and ultrasonic wave transmission / reception of the present disclosure. FIG. 5 is an electron micrograph of the surface of the plastic closed cell foam. The left side of FIG. 6 is an electron micrograph of the surface of the plastic closed cell foam, and the right side is a part of the written soybean.

  The outline | summary of the laminated body of this indication, an ultrasonic transducer, and an ultrasonic flowmeter is as follows.

[Item 1]
A piezoelectric body;
A first acoustic matching layer disposed in contact with the piezoelectric body directly or via another layer,
Including plastic closed cell foam with multiple closed pores,
An average pore diameter of the closed pore is 1 μm or more and 100 μm or less;
A first acoustic matching layer having a density of 10 kg / m ³ or more and 100 kg / m ³ or less,
Laminated body.

[Item 2]
Item 2. The laminate according to item 1, wherein an acoustic impedance of the first acoustic matching layer is in a range of 5 × 10 ³ kg / s · m ^{2 to} 350 × 10 ³ kg / s · m ² .

[Item 3]
Item 3. The laminate according to Item 1 or 2, wherein an average distance between adjacent pores of the closed pore is 50 nm or more and 1 µm or less.

[Item 4]
The laminated body of any one of the items 1 to 3 whose sound speed of a said 1st acoustic matching layer is 500 m / s or more.

[Item 5]
The laminate according to any one of items 1 to 4, wherein the plastic closed-cell foam is a polymethacrylimide foam.

[Item 6]
6. The laminate according to any one of items 1 to 5, wherein the thickness of the first acoustic matching layer is approximately ¼ of a wavelength λ of a sound wave propagating through the first acoustic matching layer.

[Item 7]
A second acoustic matching layer positioned between the piezoelectric body and the first acoustic matching layer;
The second acoustic matching layer, 50 kg / m ³ or more 1500 kg / m ³ or less, and has a density greater than the first acoustic matching layer, the laminate as described in any one of 1 to 6.

[Item 8]
Item 8. The laminate according to Item 7, wherein the relationship between the acoustic impedance Za of the first acoustic matching layer and the acoustic impedance Zb of the second acoustic matching layer is Za <Zb.

[Item 9]
The laminate according to item 7 or 8, wherein the thickness of the second acoustic matching layer is approximately ¼ of the wavelength λ of a sound wave propagating through the second acoustic matching layer.

[Item 10]
The laminate according to any one of items 1 to 6, wherein the first acoustic matching layer is directly bonded to the piezoelectric body.

[Item 11]
The laminate according to item 7, wherein the second acoustic matching layer is disposed in direct contact with the first acoustic matching layer and the piezoelectric body.

[Item 12]
Item 8. The laminate according to Item 7, further comprising a structural support layer having a density of 1000 kg / m ³ or more between the first acoustic matching layer and the second acoustic matching layer.

[Item 13]
Item 13. The laminate according to item 12, wherein the thickness of the structural support layer is less than 1/8 of a wavelength λ of a sound wave propagating through the structural support layer.

[Item 14]
An ultrasonic transducer comprising the laminate according to any one of items 1 to 13.

[Item 15]
The laminate according to any one of items 1 to 6,
A main body having a convex shape having a top plate, and a case having a cover plate covering the convex opening,
The piezoelectric body is located within the convex shape and is fixed to the inner surface of the top plate,
The first acoustic matching layer is an ultrasonic transducer that is fixed to an outer surface of the top plate.

[Item 16]
The laminate according to any one of items 7 to 9,
A main body having a convex shape having a top plate, and a case having a cover plate covering the convex opening,
The piezoelectric body is located within the convex shape and is fixed to the inner surface of the top plate,
The second acoustic matching layer is fixed to the outer surface of the top plate,
The ultrasonic transducer according to claim 1, wherein the first acoustic matching layer is in contact with the second acoustic matching layer.

[Item 17]
The ultrasonic transducer according to item 15 or 16, wherein the case is made of a metal material.

[Item 18]
A flow path through which the fluid to be measured flows;
A pair of ultrasonic transducers arranged in the flow path for transmitting and receiving ultrasonic signals, the ultrasonic transducer according to any one of items 14 to 16,
A time measuring unit for measuring an ultrasonic propagation time between the pair of ultrasonic transducers;
A calculation unit that calculates a flow rate of the flow path based on a signal from the time measurement unit;
Ultrasonic flow meter equipped with.

  Hereinafter, embodiments of the laminate, the ultrasonic transducer, and the ultrasonic flowmeter of the present disclosure will be described in detail with reference to the drawings.

(First embodiment)
Hereinafter, an example of the ultrasonic transducer and the ultrasonic flowmeter of the present embodiment will be described in detail.

[Configuration of ultrasonic flowmeter]
FIG. 1 shows a schematic configuration of an ultrasonic flowmeter of the present disclosure. As shown in FIG. 1, the ultrasonic flowmeter includes a flow path through which a fluid to be measured flows, a pair of ultrasonic transducers 11 and 12 disposed in the flow path, a time measurement unit 31, and a calculation unit 32. . In the flow path defined by the tube wall 13, the fluid flows at the flow velocity V in the direction shown in the figure. The flow rate of the fluid flowing through this flow path is measured. On the tube wall 13, a pair of ultrasonic transducers (first and second ultrasonic transducers) 11, 12 are installed facing each other. The ultrasonic transducers 11 and 12 include a piezoelectric vibrator such as a piezoelectric ceramic which is an electric energy / mechanical energy conversion element, and exhibit resonance characteristics like a piezoelectric buzzer or a piezoelectric oscillator. First, the ultrasonic transmitter / receiver 11 is used as an ultrasonic transmitter and the ultrasonic transmitter / receiver 12 is used as an ultrasonic receiver. When the time measuring unit 31 applies an AC voltage having a frequency near the resonance frequency to the piezoelectric vibrator of the ultrasonic transducer 11, the ultrasonic transducer 11 passes along the propagation path indicated by L1 in the fluid in the tube. Ultrasound is radiated along. The ultrasonic transducer 12 receives the ultrasonic wave propagating in the fluid and converts it into a voltage. Subsequently, on the contrary, the ultrasonic transducer 12 is used as an ultrasonic transmitter, and the ultrasonic transducer 11 is used as an ultrasonic receiver. When the time measuring unit 31 applies an alternating voltage having a frequency near the resonance frequency of the ultrasonic transducer 12 to the piezoelectric vibrator, the ultrasonic transducer 12 propagates in the fluid in the tube as indicated by L2 in the figure. Ultrasonic waves are radiated along the path, and the ultrasonic transducer 11 receives the propagated ultrasonic waves and converts them into voltages. As described above, the ultrasonic transducers 11 and 12 serve as a receiver and a transmitter.

In such an ultrasonic flow meter, when an AC voltage is continuously applied, it is difficult to measure the propagation time because the ultrasonic wave is continuously emitted from the ultrasonic transducer. A burst voltage signal is used as a drive voltage. When the time measurement unit 31 applies a driving burst voltage signal to the ultrasonic transducer 11 and radiates the ultrasonic burst signal from the ultrasonic transducer 11, the ultrasonic burst signal is transmitted through a propagation path L1 having a distance L. And reaches the ultrasonic transducer 12 after time t. The ultrasonic transducer 12 can convert only the transmitted ultrasonic burst signal into an electric burst signal with a high S / N ratio. The time measuring unit 31 electrically amplifies the electric burst signal, applies it to the ultrasonic transducer 11 again, and radiates the ultrasonic burst signal. This device is called a single-around device, and the time required for an ultrasonic pulse to radiate from the ultrasonic transducer 11 and propagate through the propagation path to reach the ultrasonic transducer 12 is called a single-around period. The reciprocal is called the sing-around frequency. In FIG. 1, the flow velocity of the fluid flowing in the pipe is V, the velocity of the ultrasonic wave in the fluid is C, and the angle between the direction of flow of the fluid and the propagation direction of the ultrasonic pulse is θ. When the ultrasonic transmitter / receiver 11 is used as a transmitter and the ultrasonic transmitter / receiver 12 is used as a receiver, the ultrasonic pulse emitted from the ultrasonic transmitter / receiver 11 reaches the ultrasonic transmitter / receiver 12. When the sing-around period, which is the sound wave propagation time, is t1, and the sing-around frequency is f1, the following equation (1) is established.
f1 = 1 / t1 = (C + V cos θ) / L (1)

Conversely, when the ultrasonic transducer 12 is used as a transmitter and the ultrasonic transmitter / receiver 11 is used as a receiver, a sing-around period that is an ultrasonic propagation time is t2, and a sing-around frequency is f2. Then, the relationship of the following formula (2) is established.
f2 = 1 / t2 = (C−V cos θ) / L (2)

Therefore, the frequency difference Δf between the two sing-around frequencies is expressed by the following equation (3), and the fluid flow velocity V can be obtained from the ultrasonic propagation path distance L and the frequency difference Δf.
Δf = f1-f2 = 2V cos θ / L (3)

  That is, the flow velocity V of the fluid can be obtained from the distance L of the ultrasonic propagation path and the frequency difference Δf, and the flow rate can be examined from the flow velocity V.

  The ultrasonic flowmeter includes a time measurement unit 31 and a calculation unit 32. The time measuring unit 31 includes a drive circuit that generates a burst voltage signal that drives the ultrasonic transducers 11 and 12 and a reception circuit that electrically amplifies the electrical burst signal converted by the ultrasonic transducers 11 and 12. In addition, the single-around periods t1 and t2 which are ultrasonic propagation times are obtained by the above-described procedure. The computing unit 32 calculates the flow velocity and flow rate of the fluid from the relationship between the obtained sing-around periods t1 and t2 and Equation (3). The time measurement unit 31 and the calculation unit 32 are configured by, for example, a microcomputer, a memory, and a program that defines a procedure for performing the above-described calculation. A part of the time measurement unit 31 and the calculation unit 32 may be configured by an electronic circuit or the like.

[Ultrasonic transducer]
FIG. 2 is a cross-sectional view illustrating an example of the ultrasonic transducer 11 used in the ultrasonic flowmeter of the present disclosure. The ultrasonic transducer 12 also has the same structure as the ultrasonic transducer 11. The ultrasonic transducer 11 includes a laminated body 28 and a case 29.

  The stacked body 28 includes the piezoelectric body 21 and the first acoustic matching layer 26. The first acoustic matching layer 26 is in contact with the piezoelectric body 21 directly or through another layer. The piezoelectric body 21 is made of piezoelectric ceramics or a single crystal and is polarized in the thickness direction. The piezoelectric body 21 has electrodes on the upper and lower surfaces in the thickness direction, and generates ultrasonic vibrations by applying a voltage to the electrodes.

  The case 29 includes a main body 22 having a convex shape having a top plate 22 u and a lid plate 23. The main body 22 and the lid plate 23 are made of a conductive material, for example, a metal that can ensure reliability against an external fluid. The piezoelectric body 21 is positioned within the convex shape of the main body 22 and is attached to the inner surface 22a of the top plate 22u. The opening located at the bottom of the convex shape of the main body 22 is covered with a cover plate 23 and the inner space of the main body 22 is sealed. For this reason, the case 29 has gas shielding properties, and even if the ultrasonic transducer 11 is exposed to various fluids, the internal piezoelectric body 21 is not deteriorated and has high reliability. Drive terminals 24 a and 24 b are attached to the lid plate 23. Of the two drive terminals 24 a and 24 b, one drive terminal 24 a is electrically connected to the upper surface electrode of the piezoelectric body 21 through the cover plate 23 and the main body 22. The other drive terminal 24 b is electrically insulated from the cover plate 23 by an insulating material 25 and is electrically connected to the lower surface electrode of the piezoelectric body 21 in the main body 22.

  The first acoustic matching layer 26 transmits ultrasonic waves to the fluid or receives ultrasonic waves that have propagated through the fluid. The first acoustic matching layer 26 efficiently outputs the mechanical vibration of the piezoelectric body 21 excited by the drive AC voltage as an ultrasonic wave to an external medium, and efficiently reaches the ultrasonic wave to the piezoelectric body 21 as the reached ultrasonic wave. Tell. Thereby, a voltage is efficiently converted into an ultrasonic wave, and an ultrasonic wave is efficiently converted into a voltage. The first acoustic matching layer 26 is attached to the outer surface 22 b of the top plate 22 u of the main body 22.

When the acoustic impedances of the piezoelectric body 21 and the fluid are Z1 and Z2, respectively, and the ideal acoustic impedance required for the first acoustic matching layer 26 is Z3, the acoustic impedance Z3 is obtained by Z3 = √ (Z1 · Z2). It is done. The acoustic impedance of the piezoelectric body 21 is about 30 × 10 ⁶ kg / m ² · s, and the acoustic impedance of hydrogen is about 110 kg / m ² · s. Substituting the numerical values described above into this equation yields Z3 = 57 × 10 ³ (kg / m ² · s). The acoustic impedance is defined by the following equation (4).
Acoustic impedance = (density) x (sound speed) (4)

In the present embodiment, the first acoustic matching layer 26 has a density of 10 kg / m ³ or more and 100 kg / m ³ or less. The speed of sound propagating through the first acoustic matching layer 26 is 500 m / s or more, and preferably 500 m / s or more and 3500 m / s or less. By appropriately selecting the density and sound velocity in this range, the acoustic impedance of the first acoustic matching layer 26 is in the range of 5 × 10 ³ kg / s · m ^{2 to} 350 × 10 ³ kg / s · m ^2. Can take a value.

Examples of a material suitable for the first acoustic matching layer 26 having such physical properties include a hard microporous body. For example, the first acoustic matching layer 26 is a hard plastic closed cell foam. Examples of rigid plastic closed cell foams include polymethacrylimide foams. The polymethacrylimide foam is, for example, sold by Roehm Gmbh & Co KG under the trade name ROHACEELL (R), and can be purchased from Daicel Evonik Co., Ltd. in Japan. The density of ROHACELL is published in the catalog as being in the range of 10 kg / m ³ or more and 100 kg / m ³ or less.

  5 and 6 show examples of SEM (scanning electron microscope) photographs of the surface of the plastic closed-cell foam. In this photograph, the pores, that is, closed cells (closed pores) appear relatively white, and the partition (plastic) appears relatively black between the closed cells. is there. Therefore, the distance between adjacent pores corresponds to the thinnest part of the partition wall.

  The average pore diameter of the closed pore in the polymethacrylimide foam is preferably 1 μm or more and 100 μm or less. Here, the pore diameter is defined by the diameter of each inscribed circle of the closed pore in the observation field by the electron microscope (see FIG. 5). The average pore diameter is defined as the average value of the pore diameters of the closed pores in the observation field of view by an electron microscope including at least 100 closed pores.

  In addition, the average distance between adjacent pores is determined by measuring the distance between adjacent regions in an observation field by an electron microscope including at least 10 closed pores (see FIG. 6). It is desirable that the distance between adjacent pores is uniformly distributed within a range of 50 nm to 1 μm.

  According to the simulation by calculation and the experimental results described below, the average pore diameter of the closed pores and the distance between adjacent pores affect the acoustic propagation characteristics. In order to realize good acoustic propagation characteristics, it is desirable that these values be in the above-mentioned range. The distance between adjacent closed pores corresponds to the average thickness of the closed-cell partition walls.

  In addition, since the polymethacrylimide foam has a rigid and strong molecular structure, it has excellent mechanical strength and workability compared to other hard foams.

  The first acoustic matching layer 26 preferably has a thickness that is approximately ¼ of the wavelength λ of the sound wave propagating through the first acoustic matching layer 26. As a result, the sound wave reflected between the two principal surfaces of the first acoustic matching layer 26 and incident on the piezoelectric body 21 is weakened by a phase shift of 1/2. Therefore, the intensity of the sound wave incident on the piezoelectric body 21 with a delay due to unnecessary reflection can be reduced and the influence of the reflected wave can be suppressed.

In the present embodiment, the top plate 22 u of the case 29 functions as a structure support layer that supports the stacked body 28. The top plate 22u desirably has a density of 1000 kg / m ³ or more. Moreover, the thickness of the top plate 22u has a thickness of 1/8 or less of the wavelength λ of the sound wave propagating through the top plate 22u. When the top plate 22u satisfies this condition, reflection of sound waves on the top plate 22u is suppressed.

  The ultrasonic transducer of this embodiment can be manufactured, for example, according to the following procedure. First, as shown in FIG. 3A, a case 29, a piezoelectric body 21, and a first acoustic matching layer 26 are prepared. The first acoustic matching layer 26 is processed in advance so as to have a desired thickness. The piezoelectric body 21 is attached to the inner surface 22a of the top plate 22u in the main body 22 of the case 29 with an adhesive or the like. The first acoustic matching layer 26 is attached to the outer surface 22b of the top plate 22u. Thereafter, as shown in FIG. 3B, the piezoelectric body 21 and the drive terminal 24b are connected. Finally, the opening of the main body 22 is closed with the lid plate 23 using an adhesive or the like, thereby completing the ultrasonic transducer.

According to the laminated body of the present embodiment, the first acoustic matching layer 26 has a density of 10 kg / m ³ or more and 100 kg / m ³ or less, so that an acoustic impedance difference between the piezoelectric body that emits ultrasonic waves and the gas. It is possible to suppress the reflection of the ultrasonic wave due to, so that the ultrasonic wave can be efficiently incident on the piezoelectric body. Therefore, a highly sensitive ultrasonic transducer and ultrasonic flowmeter can be realized. In particular, the first acoustic matching layer 26 is composed of a structure having closed cells, the average pore diameter of the closed pores is 1 μm to 100 μm, and the distance between adjacent pores is within the range of 50 nm to 1 μm. Thus, excellent acoustic characteristics can be realized. Therefore, an ultrasonic transducer and ultrasonic flowmeter with higher sensitivity can be realized. The structure having closed cells of the first acoustic matching layer 26 includes a polymethacrylimide foam. Since the polymethacrylimide foam has the characteristics of being highly elastic while being low in density, it has resistance to impact during the production process and is excellent in mechanical strength and workability. Therefore, it is possible to manufacture a laminated body and an ultrasonic transducer with a high yield. Therefore, since the acoustic matching layer is relatively easy to handle, it is possible to obtain a laminated body that is excellent in productivity, has a small variation in characteristics, and can efficiently make sound waves incident on the piezoelectric body from the fluid. . Further, by using such a laminate, an ultrasonic transducer and an ultrasonic flowmeter capable of detecting a fluid with high sensitivity can be realized.

(Second Embodiment)
FIG. 4 schematically shows the structure of an ultrasonic transducer used in the ultrasonic flowmeter of this embodiment. In FIG. 4, the same or similar components as those in the first embodiment shown in FIG. The description of the same or similar configuration as the first embodiment may be omitted. The ultrasonic transducer shown in FIG. 4 is different from that of the first embodiment in that a laminated body 28 ′ including a piezoelectric body 21, a first acoustic matching layer 26 and a second acoustic matching layer 27 is provided.

The second acoustic matching layer 27 is located between the piezoelectric body 21 and the first acoustic matching layer 26. In the present embodiment, the second acoustic matching layer 27 is attached to the outer surface 22 b of the top plate 22 u, and the first acoustic matching layer 26 is in contact with the second acoustic matching layer 27. The second acoustic matching layer 27 has a density of 50 kg / m ³ or more and 1500 kg / m ³ or less. Further, the density of the second acoustic matching layer 27 is larger than the density of the first acoustic matching layer. When the acoustic impedance of the first acoustic matching layer 26 is Za and the acoustic impedance of the second acoustic matching layer 27 is Zb, the relationship Za <Zb is satisfied. Zb is smaller than the acoustic impedance of the piezoelectric body 21. When the stacked body 28 ′ further includes the second acoustic matching layer 27 having such acoustic characteristics, the sound wave incident on the first acoustic matching layer 26 can be incident on the piezoelectric body 21 more efficiently. Become.

  The second acoustic matching layer 27 is a material having a closed pore. For example, the second acoustic matching layer 27 is made of a foamed resin such as polymethacrylimide or a composite material. The composite material may be, for example, a material obtained by solidifying a glass balloon (hollow minute glass sphere) or a plastic balloon with a resin material. Moreover, these foamed resins and composite materials may have a structure in which the surface is covered with a gas barrier film. The thickness of the second acoustic matching layer 27 is desirably ¼ of the sound wave propagating through the second acoustic matching layer 27 for the same reason as in the first embodiment.

In the present embodiment, the first acoustic matching layer 26 and the second acoustic matching layer 27 are in direct contact with each other. The second acoustic matching layer 27 is in contact with the outer surface 22 b of the top plate 22 u of the case 29. The top plate 22u of the case 29 functions as a structure support layer that supports the stacked body 28 '. The top plate 22u desirably has a density of 1000 kg / m ³ or more. Moreover, the thickness of the top plate 22u has a thickness of 1/8 or less of the wavelength λ of the sound wave propagating through the top plate 22u. When the top plate 22u satisfies this condition, reflection of sound waves on the top plate 22u is suppressed.

  According to the laminated body of the present embodiment, since the laminated body 28 ′ includes the second acoustic matching layer 27, sound waves propagating in the fluid can be incident on the piezoelectric body with higher efficiency. Therefore, in addition to the features described in the first embodiment, an ultrasonic transducer and an ultrasonic flowmeter that can detect a fluid with higher sensitivity can be realized.

(Example)
Hereinafter, the ultrasonic transducers and ultrasonic flowmeters of the first and second embodiments will be described, and the results of examining the characteristics will be described.

1. Sample Preparation [Reference Example (A)]
(A) Production of second acoustic matching layer (silica porous body) A spherical acrylic resin having a diameter of several tens of μm and a sintered silica powder having a diameter of 1 μm or less were mixed, followed by pressure molding. The molded body was dried and then fired at 900 ° C. to form a porous silica body. Thereafter, the thickness of the porous silica material was adjusted to ¼ of the ultrasonic oscillation wavelength to obtain a second acoustic matching layer. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the second acoustic matching layer was 1500 m / s. The density was 570 kg / m ³ and the thickness was 750 μm.

(B) Lamination of second acoustic matching layer and first acoustic matching layer A gel raw material solution prepared by mixing tetramethoxysilane, ethanol, and an aqueous ammonia solution (0.1 N) in a molar ratio of 1: 3: 4. Then, it was applied in a thickness of 90 μm on the second acoustic matching layer that had been cleaned in advance so that the hydroxyl group was exposed on the surface by plasma cleaning. Thereafter, the applied gel raw material liquid was solidified to obtain a silica wet gel layer. The second acoustic matching layer on which the silica wet gel layer was formed was hydrophobized in a 5% by weight hexane solution of trimethylethoxysilane, and then supercritical drying with carbon dioxide (12 MPa, 50 ° C.) to obtain silica. An acoustic matching layer in which the dried gel and the second acoustic matching layer were laminated was obtained. Since the hydroxyl group on the second acoustic matching layer and the alkoxy group of tetramethoxysilane reacted to form a chemical bond, a first acoustic matching layer with good adhesion was obtained. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer was 180 m / s, and the density was 200 kg / m ³ .

(C) Joining of acoustic matching layer to case and piezoelectric layer After temporarily bonding an epoxy adhesive sheet on both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the second acoustic matching layer 27 The top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(D) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the cover plate 23, the drive terminals 24a, 24b, etc. to the main body 22.

[Example (B)]
(A) Processing of first acoustic matching layer As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 30 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 60 μm, an average wall thickness of 80 nm, and a diameter of 10.8 mm. The speed of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 1200 m / s. The thickness of the first acoustic matching layer 26 was adjusted to 600 μm.

(B) Bonding of acoustic matching layer to case and piezoelectric layer After temporarily bonding an epoxy adhesive sheet on both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the first acoustic matching layer 26 The top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Example (C)]
(A) Processing of first acoustic matching layer As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 50 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 40 μm, an average wall thickness of 200 nm, and a diameter of 10.8 mm. The speed of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 2000 m / s. The thickness of the first acoustic matching layer 26 was adjusted to 1000 μm.

(B) Bonding of acoustic matching layer to case and piezoelectric layer After temporarily bonding an epoxy adhesive sheet on both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the first acoustic matching layer 26 The top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Example (D)]
(A) Processing of first acoustic matching layer As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 70 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 25 μm, an average wall thickness of 400 nm, and a diameter of 10.8 mm. The speed of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 3000 m / s. The thickness of the first acoustic matching layer 26 was adjusted to 1500 μm.

(B) Bonding of acoustic matching layer to case and piezoelectric layer After temporarily bonding an epoxy adhesive sheet on both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the first acoustic matching layer 26 The top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Reference Example (E)]
(A) Processing of first acoustic matching layer As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 70 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 200 μm, an average wall thickness of 2000 nm, and a diameter of 10.8 mm. The speed of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 400 m / s. The thickness of the first acoustic matching layer 26 was adjusted to 200 μm.

(B) Bonding of acoustic matching layer to case and piezoelectric layer After temporarily bonding an epoxy adhesive sheet on both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the first acoustic matching layer 26 The top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Reference Example (F)]
(A) Processing of first acoustic matching layer As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 70 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 300 μm, an average wall thickness of 3250 nm, and a diameter of 10.8 mm. The speed of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 460 m / s. The thickness of the first acoustic matching layer 26 was adjusted to 230 μm.

(B) Bonding of acoustic matching layer to case and piezoelectric layer After temporarily bonding an epoxy adhesive sheet on both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the first acoustic matching layer 26 The top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Example (G)]
(A) Manufacture of second acoustic matching layer (glass epoxy) 27 Organic polymer, inorganic material fiber body, foam body, sintered porous body, glass balloon or plastic balloon solidified with resin material, glass balloon heated A compressed material or the like can be used. Here, the jig was filled with a glass balloon, then impregnated with an epoxy solution, and thermally cured at 120 ° C. The thickness of the cured molded body was cut so as to be ¼ of the ultrasonic oscillation wavelength, whereby the second acoustic matching layer 27 was obtained. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the second acoustic matching layer 27 was 2500 m / s. The density was 520 kg / m ³ and the thickness was 1250 μm.

(B) Joining the second acoustic matching layer to the case and the piezoelectric layer After temporarily bonding an epoxy adhesive sheet to both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the second acoustic matching layer 27, the top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Lamination of Second Acoustic Matching Layer 27 and First Acoustic Matching Layer 26 As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 30 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 60 μm, an average wall thickness of 80 nm, and a diameter of 10.8 mm. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 1200 m / s, and the thickness was 600 μm. An epoxy resin was applied to the surface of the second acoustic matching layer 27 with a thickness of about 50 μm, and the first acoustic matching layer 26 was placed thereon and bonded by thermal pressing.

(D) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Example (H)]
(A) Manufacture of second acoustic matching layer (glass epoxy) 27 Organic polymer, inorganic material fiber body, foam body, sintered porous body, glass balloon or plastic balloon solidified with resin material, glass balloon heated A compressed material or the like can be used. Here, the jig was filled with a glass balloon, then impregnated with an epoxy solution, and thermally cured at 120 ° C. The thickness of the cured molded body was cut so as to be ¼ of the ultrasonic oscillation wavelength, whereby the second acoustic matching layer 27 was obtained. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the second acoustic matching layer 27 was 2500 m / s. The density was 520 kg / m ³ and the thickness was 1250 μm.

(B) Joining the second acoustic matching layer to the case and the piezoelectric layer After temporarily bonding an epoxy adhesive sheet to both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the second acoustic matching layer 27, the top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Lamination of Second Acoustic Matching Layer 27 and First Acoustic Matching Layer 26 As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 30 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 60 μm, an average wall thickness of 80 nm, and a diameter of 10.8 mm. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 1200 m / s, and the thickness was 600 μm. An epoxy resin was applied to the surface of the second acoustic matching layer 27 with a thickness of about 150 μm, and the first acoustic matching layer 26 was placed thereon and bonded by thermal pressing.

(D) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Example (I)]
(A) Manufacture of second acoustic matching layer (glass epoxy) 27 Organic polymer, inorganic material fiber body, foam body, sintered porous body, glass balloon or plastic balloon solidified with resin material, glass balloon heated A compressed material or the like can be used. Here, the jig was filled with a glass balloon, then impregnated with an epoxy solution, and thermally cured at 120 ° C. The thickness of the cured molded body was cut so as to be ¼ of the ultrasonic oscillation wavelength, whereby the second acoustic matching layer 27 was obtained. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the second acoustic matching layer 27 was 2500 m / s. The density was 520 kg / m ³ and the thickness was 1250 μm.

(B) Joining the second acoustic matching layer to the case and the piezoelectric layer After temporarily bonding an epoxy adhesive sheet to both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the second acoustic matching layer 27, the top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Lamination of Second Acoustic Matching Layer 27 and First Acoustic Matching Layer 26 As the first acoustic matching layer 26, polymethacrylimide hard plastic foam ROHACELL (R) (density 50 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 40 μm, an average wall thickness of 200 nm, and a diameter of 10.8 mm. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 2000 m / s, and the thickness was 100 μm. An epoxy resin was applied to the surface of the second acoustic matching layer 27 with a thickness of about 50 μm, and the first acoustic matching layer 26 was placed thereon and bonded by thermal pressing.

(D) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Example (J)]
(A) Manufacture of second acoustic matching layer (glass epoxy) 27 Organic polymer, inorganic material fiber body, foam body, sintered porous body, glass balloon or plastic balloon solidified with resin material, glass balloon heated A compressed material or the like can be used. Here, the jig was filled with a glass balloon, then impregnated with an epoxy solution, and thermally cured at 120 ° C. The thickness of the cured molded body was cut so as to be ¼ of the ultrasonic oscillation wavelength, whereby the second acoustic matching layer 27 was obtained. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the second acoustic matching layer 27 was 2500 m / s. The density was 520 kg / m ³ and the thickness was 1250 μm.

(B) Joining the second acoustic matching layer to the case and the piezoelectric layer After temporarily bonding an epoxy adhesive sheet to both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the second acoustic matching layer 27, the top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Lamination of Second Acoustic Matching Layer 27 and First Acoustic Matching Layer 26 As the first acoustic matching layer 26, polymethacrylimide rigid plastic foam ROHACELL (R) (density 70 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 25 μm, an average wall thickness of 400 nm, and a diameter of 10.8 mm. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 3000 m / s, and the thickness was 1500 μm. An epoxy resin was applied to the surface of the second acoustic matching layer 27 with a thickness of about 50 μm, and the first acoustic matching layer 26 was placed thereon and bonded by thermal pressing.

(D) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Reference Example (K)]
(A) Manufacture of second acoustic matching layer (glass epoxy) 27 Organic polymer, inorganic material fiber body, foam body, sintered porous body, glass balloon or plastic balloon solidified with resin material, glass balloon heated A compressed material or the like can be used. Here, the jig was filled with a glass balloon, then impregnated with an epoxy solution, and thermally cured at 120 ° C. The thickness of the cured molded body was cut so as to be ¼ of the ultrasonic oscillation wavelength, whereby the second acoustic matching layer 27 was obtained. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the second acoustic matching layer 27 was 2500 m / s. The density was 520 kg / m ³ and the thickness was 1250 μm.

(B) Joining the second acoustic matching layer to the case and the piezoelectric layer After temporarily bonding an epoxy adhesive sheet to both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the second acoustic matching layer 27, the top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Lamination of Second Acoustic Matching Layer 27 and First Acoustic Matching Layer 26 As the first acoustic matching layer 26, polymethacrylimide rigid plastic foam ROHACELL (R) (density 70 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 200 μm, an average wall thickness of 2000 nm, and a diameter of 10.8 mm. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 400 m / s, and the thickness was 200 μm. An epoxy resin was applied to the surface of the second acoustic matching layer 27 with a thickness of about 50 μm, and the first acoustic matching layer 26 was placed thereon and bonded by thermal pressing.

(D) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

[Reference Example (L)]
(A) Manufacture of second acoustic matching layer (glass epoxy) 27 Organic polymer, inorganic material fiber body, foam body, sintered porous body, glass balloon or plastic balloon solidified with resin material, glass balloon heated A compressed material or the like can be used. Here, the jig was filled with a glass balloon, then impregnated with an epoxy solution, and thermally cured at 120 ° C. The thickness of the cured molded body was cut so as to be ¼ of the ultrasonic oscillation wavelength, whereby the second acoustic matching layer 27 was obtained. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the second acoustic matching layer 27 was 2500 m / s. The density was 520 kg / m ³ and the thickness was 1250 μm.

(B) Joining the second acoustic matching layer to the case and the piezoelectric layer After temporarily bonding an epoxy adhesive sheet to both sides of the top plate 22u of the main body 22 of the case 29, the piezoelectric body 21 and the second acoustic matching layer 27, the top plate 22u was sandwiched and heated while being pressed to be cured and bonded.

(C) Lamination of Second Acoustic Matching Layer 27 and First Acoustic Matching Layer 26 As the first acoustic matching layer 26, polymethacrylimide rigid plastic foam ROHACELL (R) (density 70 kg / m ³ ) was used. This material was processed into a cylindrical shape having an average pore size of 300 μm, an average wall thickness of 3250 nm, and a diameter of 10.8 mm. The sound velocity of the ultrasonic wave of about 500 kHz propagating through the first acoustic matching layer 26 was 460 m / s, and the thickness was 230 μm. An epoxy resin was applied to the surface of the second acoustic matching layer 27 with a thickness of about 50 μm, and the first acoustic matching layer 26 was placed thereon and bonded by thermal pressing.

(D) Formation of Ultrasonic Transceiver An ultrasonic transducer was obtained by assembling the main body 22 with the cover plate 23, the drive terminals 24a and 24b, and the like.

2. Evaluation of characteristics The sensitivity of the fabricated ultrasonic transducer was measured. The pair of produced ultrasonic transducers were made to face each other, and one was used as a transmitter and the other was used as a receiver to transmit / receive ultrasonic waves. A value normalized based on the measurement result of Reference Example (A) was obtained. Further, the brittleness / workability of the first acoustic matching layer was evaluated by the bulk modulus. Specifically, a value obtained by normalizing the bulk modulus shown in the catalog of the material used for the first acoustic matching layer with the bulk modulus of the material of Reference Example (A) was obtained. Table 1 summarizes these values and the characteristics of the first acoustic matching layer 26 and the second acoustic matching layer 27.

The symbols “x”, “Δ”, “◯” and “◎” in the column of performance evaluation in Table 1 were classified according to the following ranges.
(sensitivity)
×: Less than 1 △: 1 or more and less than 1.5 ○: 1.5 or more and less than 2 ◎: 2 or more (brittleness / workability)
×: 1 or less △: 2 or more and less than 5 ○: 5 or more and less than 30 ◎: 30 or more

3. Consideration of a result As shown in Table 1, it turns out that the polymethacrylimide foam is excellent in brittleness and workability compared with a silica porous body. Further, from the relationship between the average bubble diameter and sensitivity of Examples B to F, it can be seen that the sensitivity is better when the average bubble diameter is 100 μm or less and the average thickness of the partition walls is 1 μm or less. According to the results of detailed experiments by the inventors of the present application, the sensitivity of the ultrasonic transducer is improved when the average bubble diameter is 1 μm or more and 100 μm or less and the average thickness of the partition walls is 50 nm or more and 1 μm or less. It can also be seen that higher sensitivity is obtained when the sound velocity of the first acoustic matching layer is greater than 500 m / s.

  From the comparison between Examples G to L and Examples B to F, when the stacked body further includes the second acoustic matching layer 27, the sensitivity is further improved as compared with the case where only the first acoustic matching layer 26 is provided. I understand.

  The laminate and the ultrasonic transducer of the present disclosure are preferably used for flow meters for measuring various fluids. Further, the present invention is suitably used for various devices having sonar performance, such as a detection device that detects a target object and a distance measuring device that measures a distance to the target object.

DESCRIPTION OF SYMBOLS 11, 12 Ultrasonic transducer 22 Main body 22u Top plate 22a Inner surface 22b Outer surface 23 Cover plate 24a, 24b Drive terminal 25 Insulation material 26 1st acoustic matching layer 27 2nd acoustic matching layer 28, 28 'Laminated body 29 Case 31 hours Measurement unit 32 Calculation unit

Claims (18)

A piezoelectric body;
A first acoustic matching layer disposed in contact with the piezoelectric body directly or via another layer,
Including plastic closed cell foam with multiple closed pores,
An average pore diameter of the closed pore is 1 μm or more and 100 μm or less;
A first acoustic matching layer having a density of 10 kg / m ³ or more and 100 kg / m ³ or less,
Laminated body. The laminate according to claim 1, wherein an acoustic impedance of the first acoustic matching layer is in a range of 5 × 10 ³ kg / s · m ^{2 to} 350 × 10 ³ kg / s · m ² .   The layered product according to claim 1 or 2 whose average distance between adjacent pores of said closed pore is 50 nm or more and 1 micrometer or less.   The laminated body in any one of Claim 1 to 3 whose sound speed of a said 1st acoustic matching layer is 500 m / s or more.   The laminate according to any one of claims 1 to 4, wherein the plastic closed-cell foam is a polymethacrylimide foam.   The laminate according to any one of claims 1 to 5, wherein the thickness of the first acoustic matching layer is approximately ¼ of a wavelength λ of a sound wave propagating through the first acoustic matching layer. A second acoustic matching layer positioned between the piezoelectric body and the first acoustic matching layer;
The second acoustic matching layer, 50 kg / m ³ or more 1500 kg / m ³ or less, and having a density greater than the first acoustic matching layer, the laminated body according to any one of claims 1 to 6.   The laminate according to claim 7, wherein a relationship between an acoustic impedance Za of the first acoustic matching layer and an acoustic impedance Zb of the second acoustic matching layer is Za <Zb.   The laminate according to claim 7 or 8, wherein a thickness of the second acoustic matching layer is approximately ¼ of a wavelength λ of a sound wave propagating through the second acoustic matching layer.   The laminated body according to claim 1, wherein the first acoustic matching layer is directly bonded to the piezoelectric body.   The laminate according to claim 7, wherein the second acoustic matching layer is disposed in direct contact with the first acoustic matching layer and the piezoelectric body. The laminate according to claim 7, further comprising a structural support layer having a density of 1000 kg / m ³ or more between the first acoustic matching layer and the second acoustic matching layer.   The laminate according to claim 12, wherein the thickness of the structural support layer is less than 1/8 of a wavelength λ of a sound wave propagating in the structural support layer.   An ultrasonic transducer comprising the laminate according to any one of claims 1 to 13. A laminate according to any one of claims 1 to 6;
A main body having a convex shape having a top plate, and a case having a cover plate covering the convex opening,
The piezoelectric body is located within the convex shape and is fixed to the inner surface of the top plate,
The first acoustic matching layer is an ultrasonic transducer that is fixed to an outer surface of the top plate. The laminate according to any one of claims 7 to 9,
A main body having a convex shape having a top plate, and a case having a cover plate covering the convex opening,
The piezoelectric body is located within the convex shape and is fixed to the inner surface of the top plate,
The second acoustic matching layer is fixed to the outer surface of the top plate,
The ultrasonic transducer according to claim 1, wherein the first acoustic matching layer is in contact with the second acoustic matching layer.   The ultrasonic transducer according to claim 15 or 16, wherein the case is made of a metal material. A flow path through which the fluid to be measured flows;
A pair of ultrasonic transducers arranged in the flow path for transmitting and receiving ultrasonic signals, the ultrasonic transducer according to any one of claims 14 to 16,
A time measuring unit for measuring an ultrasonic propagation time between the pair of ultrasonic transducers;
A calculation unit that calculates a flow rate of the flow path based on a signal from the time measurement unit;
Ultrasonic flow meter equipped with.

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