JP2009005383A - Ultrasonic wave transmitting/receiving apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic wave transmitting/receiving apparatus capable of being proper to mass-production despite of provision of an acoustic matching layer using dry gel. <P>SOLUTION: The ultrasonic wave transmitting/receiving apparatus is provided with: a piezoelectric material 2; and the acoustic matching member 5 including the dry gel, and also with a matching member case 4 for containing therein the acoustic matching member 5. The matching member case 4 includes: a bottom side part fixed to an ultrasonic transmitting/receiving wave front of the piezoelectric material 2; and a side face part projected from the bottom side part in the direction of emission of an ultrasonic wave and covering the whole of the side faces of the acoustic matching member 5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic transducer having an acoustic matching member and a method for manufacturing the same. In particular, the present invention relates to an ultrasonic transducer using a dry gel as an acoustic matching member and a method for manufacturing the ultrasonic transducer in order to transmit and receive ultrasonic waves with high sensitivity to a gas.

  2. Description of the Related Art In recent years, ultrasonic flowmeters that measure the time during which ultrasonic waves propagate through a propagation path, measure the moving speed of a fluid, and measure the flow rate are being used in gas meters and the like. FIG. 17 shows a cross-sectional configuration of the main part of this type of ultrasonic flowmeter.

  In the ultrasonic flow meter shown in FIG. 17, the fluid to be measured whose flow rate is to be measured is arranged to flow in the pipe. On the tube wall 102, a pair of ultrasonic transducers 101a and 101b are installed facing each other. The ultrasonic transducers 101a and 101b are configured by using ultrasonic transducers (piezoelectric bodies) such as piezoelectric ceramics as electromechanical transducers, and exhibit resonance characteristics similar to piezoelectric buzzers and piezoelectric oscillators.

  In the example of FIG. 17, at the first stage, the ultrasonic transducer 101a is used as an ultrasonic transmitter, and the ultrasonic transducer 101b is used as an ultrasonic receiver. In this stage, an alternating voltage having a frequency near the resonance frequency of the ultrasonic transducer 101a is applied to the piezoelectric body in the ultrasonic transducer 101a. Then, the ultrasonic transducer 101a functions as an ultrasonic transducer and radiates ultrasonic waves into a fluid (for example, natural gas or hydrogen gas). The emitted ultrasonic wave propagates to the path L1 and reaches the ultrasonic wave receiver 101b. At this time, the ultrasonic transmitter / receiver 101b functions as a receiver, and receives the ultrasonic wave and converts it into a voltage.

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

  As described above, the ultrasonic transducers 101a and 101b are generally collectively referred to as “ultrasonic transducers” in order to alternately perform a function as a transmitter and a function as a receiver.

  In the ultrasonic flow meter shown in FIG. 17, when an alternating voltage is continuously applied, it is difficult to measure the propagation time because ultrasonic waves are continuously emitted from the ultrasonic transducer, so that a pulse signal is usually used. A burst voltage signal having a carrier wave as a carrier voltage is used as a drive voltage.

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

  First, an ultrasonic burst signal is radiated from the ultrasonic transducer 101a by applying a driving burst voltage signal to the ultrasonic transducer 101a. As a result, the ultrasonic burst signal propagates through the path L1 and reaches the ultrasonic transducer 101b after time t. The distance of the path L1 is equal to the distance of the path L2, and is L.

  The ultrasonic transducer 101b can convert only the transmitted ultrasonic burst signal into an electric burst signal with a high S / N ratio. This electric burst signal is electrically amplified and applied again to the ultrasonic transducer 101a to radiate the ultrasonic burst signal. An apparatus that operates in this manner is called a “sing-around type apparatus”.

  In addition, the time from when an ultrasonic pulse is radiated from the ultrasonic transducer 101a until it reaches the ultrasonic transducer 102b is referred to as a “sing-around period”. The reciprocal of the “sing around period” is called the “sing around frequency”.

  In FIG. 17, 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 transducer 101a is used as an ultrasonic transmitter and the ultrasonic transducer 101b is used as an ultrasonic receiver, an ultrasonic pulse emitted from the ultrasonic transmitter / receiver 101a is converted into an ultrasonic transducer 101b. If the sing-around period, which is the time to reach, is t1, and the sing-around frequency f1, the following equation (1) is established.

  f1 = 1 / t1 = (C + Vcos θ) / L (1)

  Conversely, if the ultrasonic transducer 101b is used as an ultrasonic transmitter and the ultrasonic transmitter / receiver 101 is used as an ultrasonic receiver, the sing-around period is t2, and the sing-around frequency is f2, The relationship of the following formula (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 = 2V cos θ / L (3)

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

  Such an ultrasonic flowmeter is required to have high accuracy. In order to improve accuracy, the acoustic impedance of the acoustic matching member formed on the ultrasonic transmission / reception surface of the piezoelectric body in the ultrasonic transducer is important. The acoustic matching member plays an important role particularly when the ultrasonic transducer radiates (transmits) ultrasonic waves to the gas and receives ultrasonic waves that have propagated through the gas.

  Hereinafter, the role of the acoustic matching member will be described with reference to FIG. FIG. 18 shows a cross-sectional configuration of a conventional ultrasonic transducer 103.

  The illustrated ultrasonic transducer 103 includes a piezoelectric body 104 and an acoustic matching member 105 bonded to one surface of the piezoelectric body 103. The acoustic matching member 105 is bonded to one surface of the piezoelectric body 105 with an epoxy adhesive.

  The ultrasonic vibration of the piezoelectric body 104 is transmitted to the acoustic matching member 105 through the adhesive layer. Thereafter, the ultrasonic vibration is radiated as a sound wave to the gas (ultrasonic propagation medium) in contact with the acoustic matching member 105.

  The role of the acoustic matching member 105 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 speed of sound C in the substance and the density ρ of the substance.

  Z = ρ × C (4)

The acoustic impedance of the gas to be radiated by ultrasonic waves is significantly different from the acoustic impedance of the piezoelectric body. The acoustic impedance Z1 of a piezoceramic such as PZT (lead zirconate titanate), which is a general piezoelectric body, is about 2.9 × 10 ⁷ kg / m ² / sec. On the other hand, the acoustic impedance Z3 of air is about 4.0 × 10 ² kg / m ² / sec.

  At the boundary surfaces with different acoustic impedances, the sound waves are easily reflected, and the intensity of the sound waves transmitted through the boundary surfaces is reduced. 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)

  It is known that when a substance having such an acoustic impedance Z2 is inserted, reflection at the boundary surface is suppressed and sound wave transmittance is improved.

An acoustic impedance ^{Z1 2.9 × 10 7 kg / m} 2 / sec, when the acoustic impedance ^{Z3 4.0 × 10 2 kg / m} 2 / sec, the acoustic impedance Z2 satisfying the equation (5) is 1. It becomes about 1 × 10 ⁵ kg / m ² / sec. A substance with a value of 1.1 × 10 ⁵ kg / m ² / sec must of course satisfy the formula (4), ie Z2 = ρ × C. It is extremely difficult to find such substances from solid materials. The reason is that it is required to have a sufficiently low density ρ and a low sound velocity C while being solid.

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

However, the acoustic impedance of these materials is larger than 5.0 × 10 ⁵ kg / m ² / sec, and it is difficult to say that the expression (5) is satisfied. In order to obtain a highly sensitive ultrasonic transducer, it is necessary to form an acoustic matching member with a material having a further reduced acoustic impedance.

  In order to solve such a problem, the present applicant has invented an acoustic matching material that sufficiently satisfies the formula (5), and disclosed it in the specification of Japanese Patent Application No. 2001-056051. This material is produced using a dry gel imparted with durability, has a low density ρ, and a low sound velocity C. An ultrasonic transducer equipped with an acoustic matching member made of a material with extremely low acoustic impedance, such as dry gel, can transmit and receive ultrasonic waves efficiently and with high sensitivity to gas. The gas flow rate can be measured with high accuracy.

  In addition, the present applicant has found that it is effective to provide a protective part to improve the reliability of an ultrasonic sensor using a dry gel as an acoustic matching member, and in the specification of Japanese Patent Application No. 2002-194203. Disclosure.

  Furthermore, the present applicant discloses in the specification of Japanese Patent Application No. 2002-370421 an ultrasonic transducer including a single-layer or multi-layer acoustic matching member made of a dry gel having an arbitrary acoustic impedance and a manufacturing method thereof. ing.

Japanese Patent No. 2559144 (JP-A-2-177799)

  According to the technique disclosed in Japanese Patent Application No. 2002-194203, in order to protect the acoustic matching layer made of a dry gel having low mechanical strength, the acoustic matching layer is surrounded by the protective portion, so that the reliability is improved. However, there are problems in handling the gel raw material solution and adhesion to the piezoelectric body, and it is not necessarily suitable for mass production.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an ultrasonic wave transmission / reception suitable for mass production while having a protective structure for protecting an acoustic matching layer having a relatively low mechanical strength. And an ultrasonic flowmeter provided with the ultrasonic transducer.

  An ultrasonic transducer according to the present invention is an ultrasonic transducer including an electromechanical transducer and an acoustic matching member including a dry gel, and further includes a matching member case that holds the acoustic matching member inside. The alignment member case includes a bottom surface portion fixed to the ultrasonic wave transmitting / receiving surface of the electromechanical transducer, and a side surface portion protruding in the ultrasonic radiation direction from the bottom surface portion and covering the entire side surface of the acoustic matching member. And have.

  In a preferred embodiment, a bottom surface portion of the matching member case is joined to an ultrasonic wave transmitting / receiving surface of the electromechanical transducer.

  In a preferred embodiment, the thickness of the bottom surface portion of the alignment member case is 1/20 or less of the wavelength of ultrasonic waves to be transmitted and received.

  In a preferred embodiment, the alignment member case has a shape capable of holding the gel raw material liquid therein.

  In a preferred embodiment, the depth of the matching member case is equal to or greater than the thickness of the acoustic matching member.

  In a preferred embodiment, the upper end of the alignment member case is bent.

  In a preferred embodiment, the inner surface of the alignment member case is treated to add a hydroxyl group.

  In a preferred embodiment, the inner surface of the alignment member case is roughened.

  In a preferred embodiment, the alignment member case is a metal press-molded body.

  Another ultrasonic transducer according to the present invention is an ultrasonic transducer including an electromechanical transducer and an acoustic matching member including a dry gel, and further includes a case for holding the acoustic matching member therein. The case further includes a cover that covers the ultrasonic transmission / reception surface of the electromechanical transducer, and the front surface of the cover has an angle θ (0 ° with respect to the normal of the ultrasonic transmission / reception surface of the electromechanical transducer. It is inclined by <θ <90 °).

  In a preferred embodiment, the acoustic matching member includes a dry gel and a plurality of particles that can settle in the gel raw material liquid.

  In a preferred embodiment, the acoustic matching member has a multilayer structure, and the acoustic matching member includes a composite layer of a plurality of particles and a dry gel, and / or a dry gel single layer.

  In a preferred embodiment, the plurality of particles are not chemically bonded to each other.

  In a preferred embodiment, each of the plurality of particles is a glass bead.

  In a preferred embodiment, irregularities are formed on the bottom surface portion of the alignment member case, and an adhesive layer exists between the bottom surface portion and the electromechanical transducer.

  In preferable embodiment, the unevenness | corrugation formed in the bottom face part of the said alignment member case has a concentric pattern.

  In a preferred embodiment, a container for storing the electromechanical conversion element is further provided.

  In a preferred embodiment, the container shields the electromechanical conversion element from the outside.

  The ultrasonic flowmeter of the present invention includes a flow rate measurement unit through which a fluid to be measured flows, a pair of ultrasonic transducers that are provided in the flow rate measurement unit and transmit / receive ultrasonic signals, and the pair of ultrasonic transmission / reception units. An ultrasonic flowmeter comprising a measurement circuit for measuring a time during which an ultrasonic wave propagates between devices, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit, wherein the pair of ultrasonic waves Each of the transducers is one of the above-described ultrasonic transducers.

  In a preferred embodiment, the measurement fluid is a gas.

  In a preferred embodiment, an electromechanical transducer element in the ultrasonic transducer is shielded from the fluid to be measured.

  The device of the present invention is a device comprising any one of the above ultrasonic transducers.

  A 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, and electrodes on the first and second surfaces. A step of preparing the formed electromechanical transducer, and (b) forming an acoustic matching member made of dry gel inside the matching member case having a bottom surface portion and a side surface portion. Forming a composite, and (c) joining the alignment member case side of the composite to at least one of the first and second surfaces of the electromechanical transducer.

  Another ultrasonic transducer manufacturing method according to the present invention includes: (a) a first surface and a second surface opposite to the first surface, the first and second surfaces being A step of preparing an electromechanical conversion element on which an electrode is formed; and (b) preparing an alignment member case having a bottom surface portion and a side surface portion; and at least one of the first and second surfaces of the electromechanical conversion element Joining the bottom surface portion of the matching member case to the side, and (c) forming an acoustic matching member made of dry gel inside the matching member case.

  In a preferred embodiment, the step (b) includes a step of placing a gel raw material liquid that forms the dried gel and a plurality of particles that can settle in the gel raw material liquid inside the alignment member case. .

  According to the present invention, an ultrasonic transducer suitable for mass production, a manufacturing method thereof, and an ultrasonic wave including the ultrasonic transducer, including a protective structure for an acoustic matching layer having a relatively low mechanical strength. A flow meter can be provided.

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

(Embodiment 1)
FIG. 1 shows a cross section of a first embodiment of an ultrasonic transducer according to the present invention. The illustrated ultrasonic transducer 1 includes a piezoelectric body (electromechanical transducer) 2, a pair of electrodes 3 a and 3 b provided on both surfaces of the piezoelectric body 2, and the main body of the piezoelectric body 2 via the electrodes 3 a. A matching member case 4 joined to a surface (ultrasonic wave transmitting / receiving surface) and an acoustic matching member 5 formed inside the matching member case 4 are provided.

  The piezoelectric body 2 is made of a piezoelectric material and is polarized in the thickness direction (vertical direction in FIG. 1). When a voltage signal is applied between the electrode 3 a provided on the upper surface side of the piezoelectric body 2 and the electrode 3 b provided on the lower surface side, the piezoelectric body 2 expands and contracts based on the voltage signal and Ultrasonic waves are emitted from the acoustic wave transmitting / receiving surface. The ultrasonic waves are radiated to an ultrasonic propagation medium (for example, gas) 6 through the bottom surface portion of the alignment member case 4 and the acoustic matching member 5 formed in the alignment member case 4. On the other hand, the ultrasonic wave that has propagated through the propagation medium 6 reaches the piezoelectric body 2 via the acoustic matching member 5 and the bottom surface portion of the matching member case 4, and generates a voltage signal between the electrodes 3a and 3b. In this way, one piezoelectric body 2 can perform both transmission and reception of ultrasonic waves.

  The material of the piezoelectric body 2 used in this embodiment is arbitrary, and a known piezoelectric material can be used. Further, instead of the piezoelectric body 2, an electrostrictive body may be used. Also when using an electrostrictive body, the material is arbitrary and a well-known material can be used. The electrodes 3a and 3b are also formed from a known conductive material.

  The acoustic matching member 5 plays a role of efficiently propagating the ultrasonic wave generated by the piezoelectric body 2 to the propagation medium 6 and also plays a role of efficiently transmitting the ultrasonic wave propagated through the propagation medium 6 to the piezoelectric body 2. The acoustic matching member 5 of this embodiment is formed from a single layer of dry gel. Dry gel is a material that can make the acoustic impedance defined by the product of density ρ and speed of sound C (ρ × C) extremely small. Therefore, the efficiency of transmitting and receiving ultrasonic waves to a gas such as air is improved. Can be very high.

  A dry gel is a porous body formed by a sol-gel reaction. More specifically, it has a solid skeleton that is solidified by the reaction of the gel raw material liquid. First, a wet gel in which the solid skeleton part contains a solvent is formed, and then the solvent is removed by drying to obtain a final dry gel. This dry gel is a porous body having a solid skeleton part of several nm to several μm, and continuous pores having an average pore diameter in the range of about 1 nm to several μm formed between the solid skeleton parts. is there.

  The dry gel has such a property that, in a low density state, the speed of sound propagating through the solid portion becomes extremely small, and the speed of sound propagating through the gas portion in the porous body by the pores becomes extremely small. Therefore, in a low density state, the sound speed shows a very slow value of 500 m / sec or less, and an extremely low acoustic impedance. In particular, when the solid skeleton and the pore diameter are as small as several nanometers, a porous body having an extremely slow sound speed can be obtained. In addition, the nanometer-sized pores have a feature that sound waves can be emitted with a high sound pressure when used as an acoustic matching member because the pressure loss of the gas is large.

  Although it is a dry gel having such advantageous performance, it has a problem that it is difficult to handle due to its low strength. For this reason, it may be damaged by processing into a desired shape, impact during handling, or pressurization during joining with other components. Even if there is no breakage, even if microcracks occur and the initial performance does not change, cracks increase due to long-term use or repeated thermal shock, and the ultrasonic transducer Performance may be degraded. Furthermore, a dried gel that has been subjected to a hydrophobic treatment for stabilization is difficult or almost impossible to adhere due to its water repellency.

  For this reason, in order to improve the manufacturing yield and improve the reliability of the ultrasonic transducer, the processed dry gel is not processed and the dried gel is handled or the ultrasonic transducer is used. It is desirable to prevent stress from being applied to the dried gel when the vessel is incorporated.

  In the present embodiment, the matching member case 4 having the configuration shown in FIG. 1 is employed in order to realize a highly reliable ultrasonic transducer using such a dry gel having low mechanical strength. Then, the gel raw material liquid is filled inside the alignment member case 4 and solidified and dried inside the case 4 to form a dry gel layer. Thus, after producing the composite body in which the matching member case 4 and the acoustic matching member 5 are integrated, the composite body is joined to the piezoelectric body 2, so that it is not necessary to process the dried gel. Even when the acoustic matching member 5 is handled, the dry gel is not directly touched. Further, even in the process of fixing the acoustic matching member 5 to the piezoelectric body 2, stress is hardly applied to the dry gel, so that initial microcracks are not formed in the dry gel.

  Thus, according to the configuration of the present embodiment, the acoustic matching member 5 is prevented from being damaged even when the ultrasonic transducer is used for a long period of time or in an environment where thermal shock is repeatedly applied. Long-term reliability can be ensured.

  Hereinafter, the manufacturing method of the ultrasonic transducer of this embodiment will be described.

  First, a piezoelectric body 2 is prepared in accordance with the wavelength of ultrasonic waves to be transmitted and / or received. The piezoelectric body 2 is preferably a material having high piezoelectricity such as piezoelectric ceramics or a piezoelectric single crystal. As the piezoelectric ceramic, lead zirconate titanate, barium titanate, lead titanate, lead niobate, or the like can be used. As the piezoelectric single crystal, lead zirconate titanate single crystal, lithium niobate, quartz, or the like can be used.

  In the present embodiment, lead zirconate titanate ceramics are used as the piezoelectric body 2, and the frequency of ultrasonic waves to be transmitted and received is set to 500 kHz. In order for the piezoelectric body 2 to efficiently transmit and receive such ultrasonic waves, the resonance frequency of the piezoelectric element is designed to be about 500 kHz.

  The sound speed of lead zirconate titanate-based ceramics is about 3800 m / sec, and it is known that the piezoelectric body strongly resonates when its thickness is ½ the wavelength. The transmission / reception efficiency is improved.

  For this reason, in this embodiment, the piezoelectric body 2 made of piezoelectric ceramics suitable for transmitting and receiving ultrasonic waves of 500 kHz is used by forming a cylindrical shape having a diameter of 12 mm and a thickness of about 3.8 mm. Silver electrodes 3a and 3b by baking are provided on the upper and lower surfaces of the piezoelectric body 2, and the piezoelectric body 2 is polarized in this direction.

  A stainless steel matching member case 4 having an acoustic matching layer 5 manufactured by a method described in detail later is bonded to one main surface of the piezoelectric body 2.

  The alignment member case 4 requires the following characteristics.

1. The gel raw material liquid can be held in the inner part. 2. It is chemically stable with respect to the gel raw material liquid. 3. It can be bonded to the piezoelectric body. 4. It is difficult to cause acoustic interference.

  Stainless steel satisfies the above conditions 1 to 3. Then, in consideration of the sound speed of the material constituting the bottom surface portion of the alignment member case 4, if the thickness of the material is appropriately set, it is possible to prevent acoustic interference, so the fourth condition Can also be satisfied.

  The thickness of the bottom surface portion of the alignment member case 4 is preferably set to 1/20 or less of the wavelength of ultrasonic waves to be transmitted and received. This is because if the thickness of this portion is larger than 1/20 of the wavelength of the ultrasonic wave to be transmitted / received, the sensitivity is lowered and the waveform is greatly affected. The speed of sound of stainless steel is about 5500 m / second, and one wavelength of ultrasonic waves at 500 kHz is about 11 mm. Therefore, by setting the thickness of the matching member case 4 to 0.55 mm or less, the influence of the matching member case 4 on the performance of the ultrasonic transceiver is reduced.

  More preferably, the thickness of the bottom surface portion of the alignment member case 4 is not more than 1/40 of the wavelength of the ultrasonic wave to be transmitted and received. Since the alignment member case 4 of the present embodiment is set to a thickness of 0.2 mm so that it can be easily produced by metal press molding, it suppresses acoustic obstruction and is suitable for mass production. The thickness of 0.2 mm is about 1/55 of the wavelength of ultrasonic waves to be transmitted and received, and has very little influence on the performance of the ultrasonic transceiver.

  In this embodiment, the alignment member case 4 is formed from stainless steel that is press-molded. However, the material is not limited to stainless steel as long as it satisfies the above conditions 1 to 4, and formed from other materials. Can do. Other materials (ceramics and other metals) may be selected as appropriate in consideration of the cost and usage environment.

  As a material of the dry gel constituting the acoustic matching member 5, an inorganic material, an organic polymer material, or the like can be used. As the solid skeleton portion of the inorganic material, silicon oxide (silica), aluminum oxide (alumina), titanium oxide, or the like can be used. In addition, as the solid skeleton portion of the organic material, a general thermosetting resin or thermoplastic resin can be used. For example, polyurethane, polyurea, phenol curable resin, polyacrylamide, polymethyl methacrylate, or the like can be used. .

  In the present embodiment, a dry gel having silicon oxide as a solid skeleton is employed because of cost, environmental stability, and ease of manufacture. An acoustic matching member made of such a dry gel is formed inside the matching member case. It is preferable that the characteristics of the dry gel serving as the acoustic matching member be as shown in the above (Equation 5) because the transmission / reception sensitivity becomes high.

In the present embodiment, the piezoelectric body 2 is made of lead zirconate titanate having a density of 7.7 × 10 ³ kg / m ³ and a sound velocity of 3800 m / sec. Therefore, its acoustic impedance is 2.9 × 10 ⁷ kg / m. / Sec. On the other hand, air is used as the propagation medium 6. Since air has a density of about 1.18 kg / m ³ and a sound velocity of 340 m / second, its acoustic impedance is about 4.0 × 10 ² kg / m ² / second.

By substituting the above numerical values into the equation (5) and calculating the acoustic impedance suitable for the one-layer acoustic matching member, 1.1 × 10 ⁵ kg / m ² / sec is obtained. As the dry gel having such characteristics, it is preferable to use a dry gel having a density of 0.28 × 10 ³ kg / m ³ and a sound velocity of 400 m / sec. Further, when the thickness of the dry gel layer functioning as the acoustic matching member 5 is set to about ¼ of the wavelength of ultrasonic waves to be transmitted / received, it is particularly preferable because the transmission / reception efficiency becomes high. In the present embodiment, the speed of ultrasonic waves to be used is 400 m / sec and the frequency is 500 kHz, so the thickness of the dried gel is set to 0.20 mm.

  Next, a method of forming the acoustic matching member 5 inside the matching member case 4 will be described with reference to FIGS.

  First, an alignment member case 4 shown in FIG. The size of the bottom surface of the alignment member case 4 is set to be substantially equal to the size (diameter 12 mm) of the main surface of the piezoelectric body. The case depth of the alignment member case 4 is made larger than the thickness of the dry gel so that the gel raw material liquid does not overflow from the inside of the case and the formed acoustic alignment member 5 is not touched by the hand. Has been. In this embodiment, since the thickness of the dry gel is 0.2 mm, the depth of the case is set to 0.4 mm.

  In order to improve the adhesion between the inside of the alignment member case 4 and the dried gel, the alignment member case 4 is ultrasonically cleaned with acetone, and then plasma treatment is performed on the inside of the alignment member case 4 to add a hydroxyl group. preferable. By applying a hydroxyl group to the inner surface of the case, the dried gel and the case 4 are chemically bonded.

  Next, as shown in FIG. 2 (b), the gel raw material liquid 5 a is injected into the alignment member case 4 by a quantitative dropping device. The volume of the gel raw material liquid 5a is reduced to about 90% after drying because of shrinkage due to gel and drying. For this reason, the dripping amount of the gel raw material liquid 5a is set to 25 μl, for example, so that the thickness of the dry gel finally formed is 0.2 mm. The mixing ratio of the gel raw material liquid can be tetramethoxysilane / ethanol / ammonia water = 1/4 (molar ratio). The amount of the gel raw material liquid 5a is appropriately optimized based on the size of the piezoelectric body 2 and the acoustic matching member 5 to be used and the frequency of the ultrasonic waves.

  The alignment material case 4 in which the gel material solution 5a is dropped is left on a horizontal table in a thermostat set at 50 ° C. for about 1 day, so that the gel material solution is placed inside the alignment member case 4. Is gelled to form a wet gel. At this time, it is efficient to perform batch processing by arranging a large number of alignment member cases 4 (not shown) on one tray. The following processing is the same.

  The wet gel thus formed is further hydrophobized. In the hydrophobization treatment, after forming a wet gel, dimethyldimethoxysilane / ethanol / 10 wt% ammonia water was mixed at a ratio of 45/45/10 by weight with a hydrophobization solution obtained at 40 ° C. For about 1 day.

  Finally, the wet gel is dried in the air to obtain a dry gel layer (acoustic matching member 5) formed inside the matching member case 4 (FIG. 2 (c)). In addition, although the hydrophobization process is not essential, it is preferable to perform for stabilization of a dry gel.

  When the acoustic matching member 5 made of the dried gel is formed by drying the solvent of the wet gel, an important parameter in which the temperature during the heat treatment affects the characteristics of the acoustic matching member 5 in each step of gelation, density adjustment and drying. It becomes. On the other hand, the acoustic matching member 5 is required to have a uniform density and sound speed. This is because if the density and sound speed of the acoustic matching member 5 are not uniform, the role of the acoustic matching member cannot be sufficiently achieved. In order to form the acoustic matching member 5 having a uniform density and sound speed, it is important that the temperature in each step of gelation, density adjustment, and drying is sufficiently controlled.

  The matching member case 4 shown in FIG. 3A has a relatively smaller heat capacity than a container (piezoelectric case 40 shown in FIG. 3B) for shielding the piezoelectric body from the outside. For this reason, the temperature of the alignment member case 4 can be made to follow smoothly with respect to the change of preset temperature. As a result, it is possible to form the acoustic matching member 5 made of a dried gel having a sufficiently uniform density and sound speed. In the piezoelectric case 40 having the structure as shown in FIG. 3B, when the temperature control is not sufficiently performed at the time of manufacture, a nonuniform portion is generated in the density and sound speed of the acoustic matching layer (dry gel).

  As shown in FIGS. 4 (a) and 4 (b), a case is considered in which the bottom surfaces of cases 4 and 40 storing wet gel are heated by heater 41 to control the temperature of the wet gel. In this case, the temperature of the outer peripheral portion tends to be lower than the center of the bottom surface portion of the cases 4 and 40. FIG. 4C shows the distribution of temperature within the case bottom. A curve a shows the temperature distribution in the matching member case 4 of FIG. 4A, and a curve b shows the temperature distribution in the piezoelectric body case 40 of FIG. As can be seen from FIG. 4C, the use of the matching member case 4 in this embodiment is effective in forming the uniform acoustic matching member 5 because a uniform temperature distribution is easily obtained.

Next, the matching member case / acoustic matching member composite produced by the above-described method is joined to the piezoelectric body 2 as shown in FIG. Joining is performed by adhesion of an epoxy adhesive. At the time of joining, an adhesive film is formed on the piezoelectric body 2 by printing so that a large force is not applied to the dry gel as the acoustic matching member 5, and a composite of the matching member case / acoustic matching member is formed thereon. Install. After this, the upper end is bent consistent member casing 4, pressurized with 0.1 kg / cm ^3, and cured for 2 hours in 120 ° C.. The thickness of the adhesive layer formed between the piezoelectric body 2 and the alignment member case 4 is, for example, about 30 μm.

  The ultrasonic transducer formed in this way can transmit and receive ultrasonic waves about seven times higher than an ultrasonic transducer having an acoustic matching member in which a conventional glass balloon is hardened with an epoxy resin.

  In this way, by using the bottomed matching member case 4 having a shallow bottom for an ultrasonic transducer, the acoustic matching member 5 made of a dry gel is used, which is high for long-term use and in severe environments. Reliability can be demonstrated.

  In this embodiment, after the acoustic matching member made of dry gel is formed inside the matching member case 4, the composite made of the matching member case / acoustic matching member is joined to the piezoelectric body, and the ultrasonic transducer is used. Although manufactured, the acoustic matching member 5 made of dried gel may be formed after the matching member case is joined to the piezoelectric body 2. In this case, since the matching member case / piezoelectric composite is handled, there is a problem in mass production such as an increase in parts handled when forming the gel layer. Therefore, it is suitable when using a dry gel with lower strength.

  In this embodiment, the alignment member case 4 having a flat bottom surface is used. However, the alignment member case 4 may be provided with irregularities on the bottom surface. FIG. 5A shows a cross section of a combination of the alignment member case 4 and the piezoelectric body 2 having irregularities on the bottom surface, and FIG. 5B is a top view thereof.

  When the unevenness as shown in FIGS. 5A and 5B is provided on the bottom surface of the case 4, a gap is formed between the bottom surface of the case 4 and the piezoelectric body 2. When the case 4 and the piezoelectric body 2 are joined by filling the space in the gap with the adhesive, there is an advantage that the adhesive force is increased. If the unevenness on the bottom surface is sufficiently smaller than the wavelength of the ultrasonic wave, it does not become an acoustic hindrance factor.

  On the other hand, when the size of the irregularities formed on the bottom surface of the case 4 is increased and the maximum thickness of the adhesive layer is set to a size that cannot be ignored compared to the wavelength of the ultrasonic wave, the radiated acoustic power of the ultrasonic wave at that portion descend. By forming concentric concavities and convexities as shown in FIG. 5B on the bottom surface of the alignment member case 4, there is an advantage that it is possible to prevent disturbance of the sound field due to ultrasonic interference at a short distance. .

  The shape of the matching member case 4 suitably used in the present embodiment is that the acoustic matching member is held inside and can be fixed to the ultrasonic wave transmitting / receiving surface of the piezoelectric body, and protrudes in the ultrasonic radiation direction from the bottom surface portion. The side surface portion covers the entire side surface of the acoustic matching member. As long as it has such a configuration, the case 4 shown in FIG. 1 can be modified with a high degree of freedom.

  In addition, the side part of the container shown in FIG.3 (b) has the part 40a bend | folded to an opposite side by an upper end. Such a portion 40a is not preferable because it easily breaks. In contrast, the alignment member case 4 shown in FIG. 3A does not have a sharply bent portion and is suitable for mass production. In addition, the alignment member case 4 of FIG. 3A does not need to surround the piezoelectric body 2, and accordingly, the matching member case 4 is easily reduced in size and handled easily. In addition, even when wet gels are placed in a large number of cases 4 and heat-treated at the same time, there is no need to increase the size of equipment such as a thermostatic bath.

  The cross-sectional shape of the alignment member case 4 is not limited to that in the above embodiment, and the alignment member case suitably used in the present invention has various cross-sectional shapes shown in FIGS. 6 (a) to 6 (d). Well.

(Embodiment 2)
Next, a second embodiment of the ultrasonic transducer according to the present invention will be described with reference to FIG.

  In the ultrasonic transducer of this embodiment, the acoustic matching member is composed of two dry gel layers having different acoustic impedances. Except for this point, the ultrasonic transducer of this embodiment has the same configuration as that of the ultrasonic transducer in the first embodiment.

  In general, the acoustic matching member plays a role of efficiently radiating ultrasonic waves from the piezoelectric body 2 to the ultrasonic propagation medium 5 while suppressing internal reflection of sound waves due to mismatch of acoustic impedance. When transmitting and receiving ultrasonic waves having a single frequency (that is, continuous wave ultrasonic waves), it is sufficient to provide one layer of an acoustic matching member having a uniform acoustic impedance with a thickness corresponding to the frequency. .

  However, in an ordinary ultrasonic transducer, it is common to transmit and receive pulsed or burst ultrasonic waves. Pulsed or burst ultrasonic waves include a wide range of frequency components rather than a single frequency component. In order to perform such ultrasonic wave transmission / reception with high sensitivity, it is preferable to gradually change the acoustic impedance of the acoustic matching member between the piezoelectric body and the ultrasonic propagation medium. In order to gradually change the acoustic impedance, the acoustic matching member may be multilayered and the acoustic impedance of the constituent layers may be gradually changed.

  The acoustic impedance of the acoustic matching member greatly affects the performance of the ultrasonic transducer. In general, the acoustic impedance of the single-layer acoustic matching member is set so as to satisfy the relationship shown in the equation (5). It is known that one of them is determined so as to satisfy the relationships of equations (6) to (7).

Z1 = (Z0 ⁴ × Z3 ³ ) ^1/7 (6)
Z2 = (Z0 × Z3 ⁶ ) ^1/7 (7)

  In equations (6) to (7), Z0 is the acoustic impedance of the piezoelectric body, Z1 is the acoustic impedance of the first acoustic matching layer, Z2 is the acoustic impedance of the second acoustic matching layer, and Z3 is the acoustic impedance of the propagation medium.

As described above, when Z1 and Z2 are calculated considering air as the propagation medium 5, Z1 is about 2.40 × 10 ⁵ kg / m ² / sec, and Z2 is 1.98 × 10 ³ kg / m ^2. / Sec.

However, the acoustic impedance of 2.40 × 10 ⁵ kg / m ² / sec is extremely low as a solid material and extremely low in strength, and is not suitable for practical use. For this reason, as a dry gel having strength that can be practically used and having an acoustic impedance close to Z1, in this embodiment, the density is 0.15 kg / m ³ , the sound velocity is about 100 m / second, and the acoustic impedance is 1.5 × 10 6. ⁴ using the dry gel layers is kg / m ² / sec to form an acoustic matching layer 5b.

As the first acoustic matching layer 5a, a dry gel layer having a density of 0.8 kg / m ³ , a sound velocity of 1000 m / second, and an acoustic impedance of 8.0 kg / m ² / second is used. The acoustic impedance value suitable for the first acoustic matching layer 5a is set to a value with high transmission / reception sensitivity by a one-dimensional computer simulation.

  Further, as described above, the thickness of the first acoustic matching layer is set to 500 μm so that the thickness of each acoustic matching layer is about ¼ of the wavelength of ultrasonic waves to be transmitted and received, and the thickness of the second acoustic matching layer is set. Set the thickness to 50 μm.

  The acoustic matching layers 5a and 5b made of dried gels having different acoustic impedances are formed through a first gelation process and a second gelation process in which the gelation process is divided into two stages. The present applicant discloses in Japanese Patent Application No. 2002-370421 a method for forming a multilayer dry gel layer having different acoustic impedances using the first and second gelation steps. A dry gel layer was formed.

  When the acoustic characteristics of an ultrasonic transducer having a two-layer acoustic matching member made of a dried gel obtained by the above-described process were evaluated, an ultrasonic transducer using a conventional glass balloon as the acoustic matching member was evaluated. It was found that a transmission / reception sensitivity of about 40 times can be obtained.

  In this embodiment, since the two acoustic matching members are made of the same silica oxide, defects such as peeling are unlikely to occur, and the acoustic matching member is manufactured with high yield. In addition, it is possible to continue operation with long-term reliability even during use. Although the acoustic matching member of this embodiment has a two-layer structure, the acoustic matching member may have a multilayer structure of three or more layers.

(Embodiment 3)
Next, a third embodiment of the ultrasonic transducer according to the present invention will be described with reference to FIG.

  The acoustic matching member of this embodiment is formed from a composite of a porous body and a dry gel. Except for this point, the ultrasonic transducer of this embodiment has the same configuration as the ultrasonic transducer of the first embodiment.

  In the ultrasonic transducer shown in FIG. 8, after a separately prepared porous body is disposed on the bottom surface of the alignment member case, a dry gel layer is formed thereon. With such a configuration, it is possible to precisely control the thickness of the first matching layer portion, and it becomes easy to manufacture an ultrasonic transducer with uniform performance.

  The porous body was manufactured as follows. That is, silica powder and glass are mixed with acrylic beads and press-molded. Thereafter, the acrylic is removed by combustion, and the silica and glass are sintered. Since the silica / glass composite thus formed has a density of about 0.6 and a sound velocity of about 2000 m / sec, a thickness suitable as an acoustic matching member is about 1.0 mm at 500 kHz. In this embodiment, both sides of the silica / glass composite are polished and the thickness is set to 1.0 mm.

  After placing the porous body produced by the above method inside the alignment member case 4, the gel raw material liquid was poured into the case 4. Then, by performing gelation and drying, a first matching layer made of a porous body and a dried gel and a second matching layer made of a dry gel alone were laminated inside the matching member case 4.

In this embodiment, a dry gel having characteristics of a density of 0.15 × 10 ³ kg / m ³ , a sound speed of 100 m / sec, and an acoustic impedance of 1.5 × 10 ⁴ kg / m ² / sec was produced. The injection amount of the gel raw material liquid was adjusted so that the thickness of the second acoustic matching layer made of the dry gel alone was about ¼ (about 50 μm) of the wavelength of ultrasonic waves to be transmitted and received.

The density of the first acoustic matching layer formed from the composite of the silica / glass porous body and the dry gel is about 0.72 × 10 ³ kg / m ³ , and the sound velocity is the same as the silica / glass porous body. is there.

  The ultrasonic transducer formed in this way can obtain a transmission / reception sensitivity 30 times or more that of a conventional ultrasonic transducer.

  As shown in FIG. 9, it is good also considering the dry gel layer formed in the upper part of a porous body as many layers. By doing so, an ultrasonic transducer capable of transmitting and receiving broadband ultrasonic waves can be realized.

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

  In the present embodiment, the acoustic matching member is formed using a composite made of dried gel and small-diameter particles. Except for this point, the ultrasonic transducer of this embodiment has the same configuration as the ultrasonic transducer of the first embodiment.

  Hereinafter, the manufacturing method of the ultrasonic transducer according to this embodiment will be described.

  First, small-diameter particles having a density that settles in the gel raw material liquid are quantitatively placed in the matching member case and set so as to be close to the closest packing. At this time, it is effective to apply ultrasonic vibration so as to stably and closely pack. This time, glass beads having a particle diameter of about 50 μm were used as small-diameter particles. When the glass bead diameter is large, it becomes an obstacle to the transmission and reception of ultrasonic waves.

  The amount of glass beads placed in the alignment member case depends on the thickness of the glass bead / dry gel composite corresponding to the first alignment layer. Since the sound speed of the glass bead / dry gel composite is about 2000 m / sec, the thickness of the first matching layer is about 1.0 mm so that it is about 1/4 of the wavelength of the ultrasonic wave to be transmitted and received.

  When filling a sphere with a certain space, the filling rate is the state in which the face-centered cubic lattice structure is packed most closely, and in this case, about 74% of the volume of the filled portion is filled with glass beads. Actually, however, it is almost impossible to fill up to this point. When glass beads are filled in a certain container, the filling rate of glass beads is usually about 60% experimentally.

The gel raw material liquid is gently injected into the glass bead layer in the alignment member case thus formed. At this time, since the glass beads are not bonded to each other, it is necessary to prevent the structure from collapsing as much as possible. The gel raw material liquid was prepared so that the formed dry gel had a density of 0.25 × 10 3 kg / m ³ and a sound velocity of 300 m / s.

  The gel raw material liquid is injected in such a way that the glass beads are completely immersed in the gel raw material liquid and further a thickness corresponding to a layer of a single gel serving as the second matching layer is formed. In this case, since a dry gel having a sound velocity of 300 m / s is used as the second matching layer, the second matching layer was injected in consideration of a thickness of 150 μm, which is about ¼ of the wavelength of ultrasonic waves to be transmitted and received. After filling the gel raw material liquid, ultrasonic vibration was applied to remove bubbles and refill the glass beads.

  Thereafter, the gel raw material liquid is gelled (solidified) to fix the relative positional relationship of the glass beads, and the first matching layer made of small-diameter particles and the dried gel and the second matching layer made of the dried gel are simultaneously formed. .

  In this way, the gelling process is only required once compared to the case where the acoustic matching member 5 is made into two layers in the second embodiment, and in comparison with the third embodiment, the porous material constituting the first matching layer is used. Since the body part does not need to be molded, an advantageous effect that the process can be shortened and the cost can be reduced can be obtained.

The first acoustic matching layer thus formed is a composite of glass beads and dry gel. This density is about 1.4 × 10 ³ kg / m ³ because the true density of the glass beads is about 2.2 × 10 ³ kg / m ³ and the filling rate is 60%.

  According to the ultrasonic transducer of this embodiment, it is possible to obtain a transmission / reception sensitivity about 10 times that of a conventional ultrasonic transducer.

  The glass beads are only in contact with each other, and the particles are essentially not joined together. For this reason, the sound speed is relatively slow, and it can be suitably used as an acoustic matching layer of an aerial ultrasonic transducer.

  As shown in FIG. 11, an acoustic matching member having a multilayer structure of three or more layers may be formed using two or more dry gel layers. By multilayering the acoustic matching member and changing the acoustic impedance in each layer stepwise, it is possible to transmit and receive broadband ultrasonic waves with high efficiency.

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

  As shown in FIG. 12, the ultrasonic transducer of the present embodiment has 77 attached to a bent portion in the upper part of the alignment member case 4. Except for this point, the ultrasonic transducer of this embodiment has the same configuration as the ultrasonic transducer of the first embodiment.

  The sensor cover 7 includes a mesh-shaped front protective part 7 a and an attachment part 7 b that fixes the front protective part 7 a to the alignment member case 4. The mesh size of the mesh structure of the front protective part 7a is set to a size of about 20 to 1000 μm, for example, so as not to disturb the flow of the fluid and to prevent the propagation of ultrasonic waves. In this embodiment, the sensor cover 7 is made of stainless steel, and the joining between the alignment member case 4 and the attachment portion 7b and the joining between the front surface protection portion 7a and the attachment portion 7b are both performed by welding. Yes.

  As shown in FIG. 12, when the surface of the acoustic matching member 5 is protected by the sensor cover 7, the acoustic matching member 5 is not touched when the ultrasonic transducer is handled. Therefore, subsequent work can be performed without giving a failure factor to the ultrasonic transducer. Moreover, since the strength of the alignment member case 4 is increased by attaching the sensor cover 7, the case deformation is suppressed even if a large force is applied to the alignment member case 4. For this reason, peeling of the acoustic matching member 5 from the matching member case 4 can be prevented, and reliability can be improved.

  The shape of the sensor cover 7 is not limited to that shown in FIG. For example, as shown in FIG. 13A, the front protective part 7 a may be inclined by an angle θ (0 ° <θ <90 °) with respect to the normal line standing on the surface of the acoustic matching member 5. When such an inclination is given to the front protective part 7a, a particularly preferable effect can be obtained when it is used for an ultrasonic flowmeter described later with reference to FIG. That is, by setting the angle formed by the line connecting the surfaces where the two ultrasonic transducers face each other and the direction in which the fluid flows and the inclination angle θ of the front surface protection portion 7a to be equal, It is possible to accurately measure the flow rate without disturbing the flow.

  The sensor cover 7 is not limited to the case where the sensor cover 7 is used by being attached to the alignment member case 4, and may be used by being attached to a member constituting the ultrasonic transducer other than the alignment member case 4 as shown in FIG. 13B. good. In the example shown in FIG. 13B, a cylindrical attachment portion 7 b made of, for example, SUS (stainless steel) is bonded to the side surface of the piezoelectric body 2 using an adhesive portion 9.

  Even when an ultrasonic transducer having such a configuration is used in an ultrasonic flowmeter, it is possible to measure the flow rate without disturbing the flow of fluid in the measurement unit. Further, when handling the sensor, for example, when attached to the flow path, the acoustic matching layer that is easily damaged is not touched. For this reason, a stable flowmeter with a good yield can be provided at low cost.

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

  The ultrasonic transceiver according to the present embodiment further includes a structural support 8 that shields the piezoelectric body 2 from the outside. Except for this point, the ultrasonic transmission / reception transducer according to the present embodiment has the same configuration as the ultrasonic transducer according to the first embodiment.

  The structural support 8 includes a container 8a that houses the piezoelectric body 2 and a bottom plate 8b that seals the container 8a. The bottom plate 8 b is provided with a lead portion 8 c for connecting a circuit (not shown) and the piezoelectric body 2. The piezoelectric body is bonded to the flat portion of the container 8 a, and the side surface of the container 8 a surrounds the piezoelectric body 2. The end of the side surface of the container 8a is bent outward and joined to the bottom plate 8b. Such a structural support 8 is preferably made of stainless steel, for example.

  By using the structural support body 8 that shields the piezoelectric body 2 from the outside, handling of the ultrasonic transducer is further facilitated. Further, if the inside of the structural support 13 is filled with an inert gas, the piezoelectric body 2 can be cut off from the fluid whose flow is to be measured, so that the safety can be improved when measuring the flow rate of the combustible gas. Is possible. Since voltage is applied to the electrodes 3a and 3b of the piezoelectric body 2 during operation, there is a risk that the combustible gas may be ignited when the piezoelectric body 2 comes into contact with the combustible gas. However, the structural support 8 is composed of a hermetic container, and the internal space in which the piezoelectric body 2 is provided is cut off from an external fluid or the like to prevent such ignition and prevent combustible gas. Even ultrasonic waves can be transmitted and received safely.

  In addition, there is a medium that may react with the piezoelectric body 2 even if it is a fluid other than the flammable gas and may deteriorate the characteristics of the piezoelectric body 2. Even when ultrasonic waves are transmitted to and received from such a medium, according to the present embodiment, it is possible to prevent deterioration of the piezoelectric body 2 and realize a highly reliable operation over a long period of time. It becomes.

  The material of the structural support 8 is not limited to a metal material such as stainless steel, and a material corresponding to the purpose is selected from ceramic, glass, resin, and the like. In the present embodiment, the external fluid and the piezoelectric body 2 are reliably separated, and even if any mechanical impact is applied to the structural support 8, the strength is such that contact between the piezoelectric body 2 and the external fluid is prevented. In order to give, the structural support 13 is made from a metal material.

  When ultrasonic waves are transmitted / received to / from a safe gas, the structural support 8 made of a material such as resin may be used for the purpose of cost reduction.

  The structural support 8 and the alignment member case 4 are preferably joined after the acoustic matching member 5 is formed in the alignment member case 4. As described with reference to FIGS. 3A and 3B, in the step of forming the acoustic matching member 5 made of dry gel, it is preferable to reduce the heat capacity of the case and make the temperature distribution uniform. For this reason, when a dry gel is formed after joining the alignment member case 4 and the structural support 8, the alignment member case 4 and the structural support 8 have a large heat capacity as a whole. There is a possibility that a portion having a nonuniform sound speed may be formed. For this reason, it is preferable to complete the dry gel in the case 4 before attaching the alignment member case 4 to the structural support 8.

(Embodiment 7)
An embodiment of an ultrasonic flowmeter according to the present invention will be described with reference to FIG.

  The ultrasonic flowmeter of the present embodiment is installed so that the fluid to be measured flows at a velocity V in a pipe that functions as the flow rate measuring unit 51. Ultrasonic transducers 1a and 1b formed from the ultrasonic transducer of the present invention are disposed on the tube wall 52 of the flow rate measuring unit 51 so as to face each other.

  At some point, the ultrasonic transducer 1a functions as an ultrasonic transmitter and the ultrasonic transducer 1b functions as an ultrasonic receiver. At other points, the ultrasonic transducer 1a is supersonic. During the sound wave, it functions as a wave receiver, and the ultrasonic wave transmitter / receiver 1b functions as an ultrasonic wave transmitter. This switching is performed by the switching circuit 53.

  The ultrasonic transducers 1 a and 1 b are connected via a switching circuit 53 to a drive circuit 54 that drives the ultrasonic transducers 1 a and 1 b and a reception detection circuit 55 that detects ultrasonic pulses. . The output of the received wave 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 computing unit 57 calculates the velocity V of the fluid flowing in the flow rate measuring 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 controlled by a control signal output from the control unit 58.

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

  Consider a case in which LP gas flows through the flow rate measuring unit 51 as a fluid to be measured, for example. The drive frequency of the ultrasonic transducers 1a and 1b is about 500 kHz. The control unit 58 starts the time measurement of the timer 56 at the same time as outputting the transmission start signal to the drive circuit 54.

  When the drive circuit 54 receives the transmission start signal, the drive circuit 54 drives the ultrasonic transducer 1a to transmit an ultrasonic pulse. The transmitted ultrasonic pulse propagates through the flow rate measuring unit 51 and is received by the ultrasonic transducer 1b. The received ultrasonic pulse is converted into an electrical signal by the ultrasonic transmitter / receiver 1 b and output to the received wave detection circuit 55.

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

  Next, the ultrasonic transducers 1 a and 1 b connected to the drive circuit 54 and the received wave detection circuit 55 are switched by the switching circuit 53. Then, again, the control unit 59 outputs a transmission start signal to the drive circuit 54 and simultaneously starts time measurement of the timer 56.

  Contrary to the measurement of the propagation time t1, an ultrasonic pulse is transmitted by the ultrasonic transducer 1b, received by the ultrasonic transducer 1a, and the propagation time t2 is calculated by the calculation unit 57.

  Here, L is the distance connecting the centers of the ultrasonic transducer 1a and the ultrasonic transducer 1b, C is the velocity of sound in the absence of LP gas, V is the flow velocity in the flow measurement unit 51, and the non-measurement fluid Is the angle between the direction of the flow and the line connecting the centers of the ultrasonic transducers 1a and 1b.

  The propagation times t1 and t2 are each obtained by measurement. Since the distance L is known, the flow velocity V can be obtained by measuring the times t1 and t2, 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 received waveform as shown in FIG. 9A, and the time at which the amplitude becomes 0 after the threshold level is measured is measured.

  When the S / N of the received signal is poor, the point at which the amplitude becomes 0 fluctuates with time depending on the noise level. Therefore, t1 and t2 cannot be measured accurately, and an accurate flow rate can be measured. It can be difficult.

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

  Further, in this embodiment, the ultrasonic flowmeter in which the ultrasonic transducer is arranged as a so-called Z-path type as shown in FIG. 15 has been described, but the arrangement form of the ultrasonic transceiver is The present invention is not limited, and as shown in FIGS. 16A to 16C, the same effect can be obtained even with arrangement forms such as a V path, a W path, and an I path.

  In each of the above embodiments, the upper surface of the uppermost acoustic matching layer (first acoustic matching layer) is such that the dry gel layer is in direct contact with the propagation medium 6, and this surface is a protective film having a thickness of about 10 μm or less. It may be covered with.

  Such a protective film avoids direct contact between the atmosphere and the acoustic matching member, and contributes to maintaining the performance of the acoustic matching member over a long period of time.

  The protective film is configured by a film (not limited to a single layer) made of a material such as aluminum, silicon oxide, low-melting glass, or polymer. The protective film is deposited by sputtering or CVD method.

  According to the present invention, an ultrasonic transducer suitable for mass production, a manufacturing method thereof, and an ultrasonic wave including the ultrasonic transducer, including a protective structure for an acoustic matching layer having a relatively low mechanical strength. A flow meter can be provided.

It is a figure which shows one cross section of the ultrasonic transducer in Embodiment 1 of this invention. (A) to (c) are process cross-sectional views illustrating a method for manufacturing the ultrasonic transducer according to the first embodiment. (A) is sectional drawing which shows the structure of the case used suitably by this invention, (b) is sectional drawing which shows the container which has the space surrounding a piezoelectric material. (A) And (b) is sectional drawing which shows the heating method of the case / container shown to FIG. 3 (a) and (b), respectively, (c) is a figure which shows temperature distribution. (A) is sectional drawing of the case where the unevenness | corrugation is formed in the bottom face, (b) is a top view. (A)-(d) is sectional drawing which shows the example of a modification of an alignment member case, respectively. It is sectional drawing which shows the ultrasonic transducer in Embodiment 2 of this invention. It is sectional drawing which shows the ultrasonic transducer in Embodiment 3 of this invention. It is sectional drawing which shows the modification of the ultrasonic transducer in Embodiment 3 of this invention. It is sectional drawing which shows the ultrasonic transducer in Embodiment 4 of this invention. It is sectional drawing which shows the modification of the ultrasonic transducer in Embodiment 4 of this invention. It is sectional drawing which shows the ultrasonic transducer in Embodiment 5 of this invention. It is sectional drawing which shows the modification of the ultrasonic transducer in Embodiment 5 of this invention. It is sectional drawing which shows the other modification of the ultrasonic transducer in Embodiment 5 of this invention. It is sectional drawing which shows the ultrasonic transducer in Embodiment 6 of this invention. It is a figure which shows embodiment of the ultrasonic flowmeter of this invention. (A)-(c) is a figure which shows the example of improvement of the ultrasonic flowmeter shown in FIG. 15, respectively. It is a figure which shows one cross section of the conventional ultrasonic flowmeter. It is a figure which shows one cross section of the conventional ultrasonic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic transmitter / receiver 2 Piezoelectric body 3 Electrode 4 Matching member case 5 Acoustic matching member 6 Propagation medium 7 Sensor cover 8 Structure support body 51 Flow measurement part 52 Tube wall 53 Switching circuit 54 Drive circuit 55 Received wave detection circuit 56 Timer 57 Calculation unit 58 Control unit 101 Ultrasonic transducer 102 Tube wall 103 Ultrasonic transducer 104 Piezoelectric body 105 Acoustic matching member

Claims (7)

An ultrasonic transducer including an electromechanical transducer and an acoustic matching member including a dry gel,
An alignment member case for holding the acoustic alignment member therein;
The alignment member case is
A bottom surface portion fixed to the ultrasonic wave transmitting / receiving surface of the electromechanical transducer;
A side surface portion protruding in the ultrasonic radiation direction from the bottom surface portion and covering the entire side surface of the acoustic matching member;
Have
The acoustic matching member is an ultrasonic transducer including a dry gel and a plurality of particles that can settle in the gel raw material liquid. The acoustic matching member has a multilayer structure,
The ultrasonic transducer according to claim 1, wherein the acoustic matching member includes a composite layer of a plurality of particles and a dry gel and / or a dry gel single layer.   The ultrasonic transducer according to claim 1, wherein the plurality of particles are not chemically bonded to each other.   The ultrasonic transducer according to claim 1, wherein each of the plurality of particles is a glass bead.   2. The ultrasonic transducer according to claim 1, wherein unevenness is formed on a bottom surface portion of the alignment member case, and an adhesive layer is present between the bottom surface portion and the electromechanical transducer.   6. The ultrasonic transducer according to claim 1, wherein the unevenness formed on the bottom surface portion of the alignment member case has a periodic pattern. (A) preparing an electromechanical transducer having a first surface and a second surface opposite to the first surface, and having electrodes formed on the first and second surfaces;
(B) preparing an alignment member case having a bottom surface portion and a side surface portion, and joining the bottom surface portion of the alignment member case to at least one side of the first and second surfaces of the electromechanical transducer;
(C) forming an acoustic matching member formed from a dry gel inside the matching member case;
A method of manufacturing an ultrasonic transmitter / receiver including:

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