JP2009105709A - Ultrasonic transducer and ultrasonic flow measuring instrument using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high performance ultrasonic transducer which is high-sensitive, stabilizes a sound transfer path and is not affected by moisture absorption. <P>SOLUTION: Since an acoustic matching body 5 is formed by a ceramic porous body 6 having a plurality of pores, wherein a guard ring 7 is disposed so as to be in close contact with an outer circumference, and an outermost layer film 8 is formed on both top and bottom surfaces of the acoustic matching body 5, the acoustic matching body 5 has a hermetically sealed structure, wherein a porous surface of the porous body 6 that easily absorbs moisture in quality is prevented from exposing itself, moisture absorption is suppressed even though it is left under a temperature change or high temperature and high humidity, and excellent output sensitivity can be maintained. Since the porous body 6 is protected by the guard ring 7 and the outermost layer, there is no fear that a portion misses and that dust occurs. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic transducer and an ultrasonic flow measurement device that measures the flow rate and flow velocity of a gas or liquid using ultrasonic waves generated by the ultrasonic transducer.

  Conventionally, in an ultrasonic transducer equipped with a piezoelectric vibrator, for example, an acoustic matching member 50 as shown in FIG. 4 is provided. The acoustic matching member 50 includes a porous body 53 made of a skeleton material 52 having voids 51, and a low porosity layer having a porosity lower than the porosity of the porous body 53 on at least a part of the surface of the fluid to be measured. 54, or a binder diffusion layer is formed on at least a part of the surface and inside of the porous body 53.

In this case, since the surface is close to a plane as compared with a conventional porous body used as an acoustic matching layer, ultrasonic waves can be transmitted and received efficiently (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 2003-111195

  However, in the conventional configuration, when the porous body 53 forming the acoustic matching member 50 is bonded to the sealed container, the adhesive material to be used penetrates into the porous body 53 due to the nature of the porous body 53. If it varies, the way of sound transmission in the gap 51 portion of the porous body 53 and the portion where the adhesive material penetrates varies, so that the output sensitivity may be lowered by changing the sound transmission path. there were.

  Therefore, when the ultrasonic transducer including the acoustic matching member 50 is mounted on the flow measurement device, there is a problem that the measurement accuracy of the flow velocity and the flow rate is lowered.

  In particular, the porous body 53 that forms the acoustic matching member 50 changes in penetration due to capillary action depending on the state of the gap formed, and also changes depending on the viscosity of the adhesive material, the temperature at the time of bonding, etc. There is a drawback that the penetration of the adhesive material to the mass 53 is complicated.

  Further, in order to more efficiently transmit and receive ultrasonic waves, the porous body 53 is weakened when the density is reduced, and a part of the porous body 53 is missing or dust is generated during assembly. There was a concern that it would adversely affect other equipment.

  Furthermore, the porous body 53 forming the acoustic matching member 50 is easy to absorb moisture due to the porous nature, and when the temperature changes during transportation or when left in a high temperature and high humidity state. Condensation causes moisture to be reflected and causes reflection and diffusion of ultrasonic waves, and the sound speed of the acoustic matching layer is changed to reduce output sensitivity.

  Therefore, when the ultrasonic transducer having the acoustic matching layer is mounted on the flow measuring device, there is a problem that the measurement accuracy of the flow velocity and the flow rate is lowered.

  The present invention solves the above-described conventional problems, and is configured to control the penetration of the joining means into the porous body forming the acoustic matching body so as to stabilize the sound transmission path and to achieve acoustic matching. It is an object of the present invention to provide a high-performance ultrasonic transducer that is not affected by moisture absorption and an ultrasonic flow measurement device using the ultrasonic transducer that is configured to cover the entire body.

  In order to solve the above-described problems, an ultrasonic transducer according to the present invention includes a celestial case, a piezoelectric vibrator disposed so as to be in close contact with the inside of the celestial part of the case, and the outer part of the celestial part of the case. An acoustic matching body disposed so as to be in close contact with the bonding means, the acoustic matching body is formed of a porous material having a plurality of pores, and a protective ring is closely disposed on the outer periphery. The outermost layer film is formed on both upper and lower surfaces.

  With the configuration described above, the acoustic matching body has a sealed structure, and the surface of the acoustic matching layer formed of a porous material that easily absorbs moisture is not exposed. Moisture absorption of the matching layer is suppressed and good output sensitivity can be maintained.

  In addition, since the acoustic matching layer formed of a porous material is protected by the protective ring, the outermost layer film, the joining unit, and the sealing unit, there is no fear of partial chipping or dust generation.

  Furthermore, when the acoustic matching body is bonded to the case, the outermost layer film can suppress the penetration of the joining means, and the sound transmission path can be stabilized.

  According to the present invention, by adopting a sealed structure, it is possible to easily maintain the output sensitivity of the acoustic matching layer by suppressing the moisture absorption of the acoustic matching layer due to temperature change or being left under high temperature and high humidity, and at the time of assembly. The acoustic matching body formed of a ceramic porous body can be protected by suppressing chipping and dust generation, and the outermost layer film can suppress penetration of the joining means into the acoustic matching body, thereby transmitting sound. It is possible to stabilize the path and to obtain a stable output sensitivity of the acoustic matching body. If this is used in a flow measuring device, the measurement accuracy can be improved.

  An ultrasonic transducer according to a first aspect of the present invention includes a celestial case, a piezoelectric vibrator disposed so as to be in close contact with the inside of the celestial part of the case, and a bonding means on the outside of the celestial part of the case The acoustic matching body is formed of a porous material having a plurality of pores, and a protective ring is closely disposed on the outer periphery, and further on both upper and lower surfaces. Is an outermost layer film.

  With the configuration described above, the acoustic matching body has a sealed structure, and the surface of the acoustic matching layer formed of a porous material such as a ceramic porous body that easily absorbs moisture is not exposed. Even if it is left as it is, moisture absorption of the acoustic matching layer is suppressed, and good output sensitivity can be maintained.

  In addition, since the acoustic matching layer is protected by the protective ring, the outermost layer film, the joining unit, and the sealing unit, there is no fear that a part of the acoustic matching layer is lost or dust is generated.

  Furthermore, when the acoustic matching body is bonded to the case, the outermost layer film can suppress the penetration of the joining means, and the sound transmission path can be stabilized.

  In addition, since the outermost layers are formed on the top and bottom surfaces of the acoustic matching body, the acoustic matching body has no front and back surfaces. This makes it easier to handle during assembly and improves assembly reliability.

In the ultrasonic transducer according to the second invention, in particular, the acoustic matching body formed of the ceramic porous body forming the acoustic matching body of the first invention is a slurry comprising an oxide-based ceramic material into which bubbles are introduced. A ceramic porous body made by firing a gel casting method in which a monomer is dissolved in a slurry made of an oxide ceramic material to which a porous material such as an acrylic ball is added, and injected into a mold, is formed into a predetermined shape It is processed and configured.

  The ceramic porous body molded by the gel casting method forms a polymer wet network by forming a polymer network in the mold due to radical polymerization of the monomers in the slurry. By completely separating and fixing the particles in-situ, non-uniformity and defects in the ceramic porous body are unlikely to occur, and it is possible to obtain strength against general pressure molding and casting, and uniform. Since the density variation is small, even complex shapes can be handled, and it can be light and high in strength.

  Therefore, there is less concern that the acoustic matching body formed of the ceramic porous body is partially chipped or dusted during assembly or the like and adversely affects other devices, and the acoustic matching body formed of the ceramic porous body is reduced. In order to more efficiently transmit and receive ultrasonic waves, the density can be reduced.

  In the ultrasonic transducer according to the third invention, in particular, the outermost layer film of the first invention has a thermosetting property such as an epoxy resin on the release film so as to suppress penetration of the joining means to the acoustic matching body. After the resin material based on the above resin is printed, it is transferred to the surface of the acoustic matching body formed of the ceramic porous body.

  The outermost layer film is formed by printing a resin material based on a thermosetting resin such as an epoxy resin on a release film, and then transferring it to the surface of an acoustic matching body formed of a ceramic porous body. Therefore, a predetermined amount of resin material can be applied to the surface of the acoustic matching body formed of a ceramic porous body that is uneven and easy to suck in, and the thickness of the acoustic film can be set to a predetermined thickness. The acoustic performance due to the change in film thickness can be stabilized.

  In the ultrasonic transducer according to the fourth aspect of the invention, in particular, the outermost layer film of the first and third aspects of the invention is silicon carbide for increasing the viscosity to a thermosetting resin having substantially the same curing conditions such as an epoxy resin. Etc. are added.

  In addition, the suppression film and the acoustic film are ceramics that are uneven and easy to inhale because fine powders such as silicon carbide are added to the thermosetting resin having substantially the same curing conditions such as epoxy resin in order to increase the viscosity. Since the permeation of the surface of the acoustic matching body formed of a porous body can be suppressed and the thickness of the acoustic film can be made a predetermined thickness, the acoustic performance due to the change in the film thickness of the acoustic film can be stabilized. Can do.

  In the fifth invention, in particular, at least one pair of the ultrasonic transducers of any one of the first to fourth inventions is disposed on the upstream side and the downstream side of the flow path through which the fluid to be measured flows, and both ultrasonic transmission / reception units are provided. By using a flow measurement device that measures the flow velocity and / or flow rate of the fluid to be measured based on the ultrasonic propagation time between the vessels, the characteristics against temperature change or high temperature and high humidity are improved, and the reliability is improved. High measurement accuracy can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
An ultrasonic transducer 1 shown in FIG. 1 includes a piezoelectric vibrator 3 disposed so as to be in close contact with the inside of a top wall of a celestial case 2 made of a conductive material such as stainless steel, and an epoxy adhesive on the outside of the top wall. And an acoustic matching body 5 arranged in close contact with the joining means 4.

  This acoustic matching body 5 is composed of a porous body 6 made of ceramic having a plurality of pores, and a protective ring 7 made of resin is disposed so as to be in close contact with the outer periphery thereof.

  Further, on the upper and lower surfaces, an outermost layer film 8 formed of a thermosetting epoxy resin material to which fine powder such as silicon carbide is added is disposed, and one of the outermost layer films 8 is an acoustic film 9, The other is set to the suppression film 10.

  That is, the porous body 6 is sealed with the protective ring 7 and the outermost layer film 8.

  As a procedure, two thermosetting epoxy resins to which fine powders such as silicon carbide as materials for the acoustic film 9 and the suppression film 10 are added are printed on a release film. A porous body 6 having a protective ring 7 disposed on the outer circumference is placed on the outer periphery, and the film printed on the remaining release film is overlaid so as not to be displaced.

  Next, the superposed product is pre-cured in a shorter time than a predetermined time for complete curing, and the acoustic matching body 5 is created. After the bonding means 4 based on a thermosetting epoxy resin is printed on the surface of the celestial case 2, the pre-cured acoustic matching body 5 is placed, and this is placed at a predetermined temperature.・ Heat over time to cure completely.

  At this time, the thermosetting epoxy resin to which fine powders such as silicon carbide as the material of the acoustic film 9 and the suppression film 10 are added and the thermosetting epoxy resin having substantially the same curing conditions as the material of the joining means 4 are used. As a base.

  On the other hand, the piezoelectric vibrator 3 is made of, for example, PZT (lead zirconate titanate) having silver electrodes 11 and 12 at both ends, and the upper electrode 11 has an epoxy adhesive 13 as a bonding material. It is adhered so as to be in close contact with the inside of the dome portion of the case 2.

  A pair of terminals 15 and 16 are attached to the conductive terminal plate 14 that closes the lower open portion of the case 2.

  More specifically, one terminal 15 is fixed to the terminal plate 14, and the upper electrode 11 of the piezoelectric vibrator 3 is connected via the case 2 and the terminal plate 14. The other terminal 16 is connected to the lower electrode 12 of the piezoelectric vibrator 3 through an insulating portion 17 made of silicon rubber, with a conductive portion 18 having a nickel particle surface plated with gold interposed therebetween. ing.

  Here, the measurement principle of the ultrasonic flow measuring device using the ultrasonic transducer 1 will be described in detail. As shown in FIG. It flows in the direction shown in. A pair of ultrasonic transducers 1, 1 are installed on the tube wall of the flow path 19 so as to face each other.

  The operation is as follows. When an alternating voltage having a frequency near the resonance frequency of the ultrasonic transducer 1 on the upstream side is applied to the piezoelectric vibrator 3, ultrasonic waves are radiated in the propagation path indicated by L1 in the fluid, and the supersonic wave on the downstream side is radiated. It propagates to the acoustic transducer 1 and converts it to a voltage.

  Subsequently, ultrasonic waves are radiated from the downstream ultrasonic transducer 1 to the propagation path indicated by L2 in the fluid, which is received by the upstream ultrasonic transducer 1 and converted into a voltage.

  Moreover, in such an ultrasonic flow measuring device, since it is difficult to measure the propagation time because ultrasonic waves are continuously emitted from the ultrasonic transducers 1 and 1 when an alternating voltage is applied, Usually, a burst voltage signal having a pulse signal as a carrier wave is used as a drive voltage.

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

  When a driving burst voltage signal is applied to the upstream ultrasonic transducer 1 to radiate an ultrasonic burst signal, the ultrasonic burst signal propagates through the propagation path L1 having a distance of L, and is t The ultrasonic transducer 1 is reached.

  In the ultrasonic transducer 1 on the downstream side, only the transmitted ultrasonic burst signal can be converted into an electric burst signal with a high S / N ratio.

  This electrical burst signal is electrically amplified and applied again to the upstream ultrasonic transducer 11 to radiate the ultrasonic burst signal. This is called “sing around”, and the time required for an ultrasonic pulse to be radiated from the upstream ultrasonic transducer 1 and propagated through the propagation path to reach the downstream ultrasonic transducer 1 is defined as a single around period. The reciprocal is called the sing-around frequency.

  In FIG. 2, the flow velocity of the fluid flowing through the flow path 19 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 upstream ultrasonic transmitter / receiver 1 is used as an ultrasonic transmitter and the downstream ultrasonic transmitter / receiver 1 is used as an ultrasonic receiver, the ultrasonic pulses emitted from the upstream ultrasonic transmitter / receiver 1 are Assuming that the sing-around period, which is the time to reach the downstream ultrasonic transducer 1, is t1, and the sing-around frequency f1, the following equation (1) is established.

f1 = 1 / t1 = (C + Vcos θ) / L (1)
Conversely, when the downstream ultrasonic transducer 1 is used as an ultrasonic transmitter and the upstream ultrasonic transmitter / receiver 1 is used as an ultrasonic receiver, the sing-around period is t2, and the sing-around frequency f2 is used. Then, the relationship of the following formula (2) is established.

f2 = 1 / t2 = (C−Vcos 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 can be calculated from the flow velocity V.

  In FIG. 2, the measuring circuit 20 measures the flow velocity V of the fluid, and the computing means 21 computes the flow rate by multiplying this by the cross-sectional area of the flow path 19 and the correction coefficient.

  In such an ultrasonic flow velocity meter, accuracy is required, and in order to improve the accuracy, an ultrasonic transducer for transmitting an ultrasonic wave to a gas or receiving an ultrasonic wave propagating through the gas is required. The acoustic impedance of the acoustic matching body 5 formed on the ultrasonic wave transmission / reception surface of the piezoelectric vibrator is important.

In the present embodiment, the ultrasonic wave from the piezoelectric vibrator 3 vibrates at a specific frequency, and the vibration is transmitted to the case 2 via the epoxy adhesive that is the bonding means 12 and further from the epoxy adhesive that is the bonding material. The transmitted vibration is transmitted to the acoustic matching body 5 formed of the porous body 6 through the joining means 4 and the matched vibration is transmitted as a sound wave to the gas which is a medium existing in the space through the acoustic film 9. At this time, the acoustic film 9 has a film shape, and the porosity in the vicinity of the surface relative to the fluid to be measured is lower than the porosity in the vicinity of the surface of the acoustic matching body 5 formed of the porous body 6. Since it is close to a plane, the vibration of the acoustic matching body 5 vibrated by the piezoelectric vibrator 3 vibrates (transmits) the fluid to be measured, and conversely, the acoustic matching body 5 is vibrated by the vibration of the fluid to be measured. (Reception) can be performed efficiently.

  Thus, the role of the acoustic matching body 5 is to efficiently propagate the vibration of the vibration means to the gas.

  The acoustic impedance Z is defined by the sound velocity C and the density ρ in the substance as shown in Expression (4).

Z = ρ × C (4)
The acoustic impedance is greatly different between the piezoelectric vibrator 3 as a vibration means and the gas as an ultrasonic radiation medium. For example, the acoustic impedance (Z0) of a piezoceramic such as PZT (lead zirconate titanate), which is a general piezoelectric body, is about 30 × 1000000 kg / m 2 · s.

  Further, the acoustic impedance (Z3) of a gas as a radiation medium, for example, air, is about 400 kg / m 2 · s.

  On such boundary surfaces having different acoustic impedances, the propagation of the sound wave is reflected, and the intensity of the transmitted sound wave becomes weak.

  As a method for solving this, acoustic impedance Z0 and Z3 of the piezoelectric vibrator, which is the vibration means, and gas, which is the radiation medium of the ultrasonic wave, are each set to have an acoustic impedance having the relationship of Equation (5) between them. In general, a method of increasing the intensity of sound wave transmission by reducing the reflection of sound by inserting a substance is known.

Z = (Z0 × Z3) (1/2) (5)
The optimum value when the acoustic impedance satisfying this condition is matched is about 11 × 10000 kg / m 2 · s.

  A substance satisfying this acoustic impedance is required to be solid, low in density and slow in sound speed as can be seen from Equation (4).

  In the present embodiment, the acoustic matching body 5 is made by firing a gel casting method in which a monomer is dissolved in a slurry made of an oxide ceramic material into which bubbles are introduced and injected into a mold. The ceramic molded body is composed of a ceramic porous body 6 formed into a predetermined shape, and the density of the acoustic matching body 5 is made as small as possible.

  Hereinafter, the manufacturing method of the ceramic porous body 6 will be described in detail.

  FIG. 3 shows a manufacturing process flow of the ceramic porous body 6 used for the acoustic matching body 5. It comprises a step of pulverizing a non-combustible ceramic, a step of adding an additive to the ceramic powder to form a slurry, introducing bubbles, a step of casting the slurry into a mold, and a step of firing.

  This will be described in detail below.

(Hard-sintering ceramic grinding process)
The ceramic can be pulverized by mixing, pulverizing, or the like using a ball mill or pot mill. The average particle size of the ceramic powder is not particularly limited, but is preferably 10 μm or less. This is because the use of a ceramic having an average particle diameter in this range improves the powder dispersibility in the slurry and also improves the sinterability.

(Ceramic powder slurrying process)
In the ceramic slurry, water, an organic solvent, a mixed solvent thereof or the like can be used as a medium for suspending the ceramic powder. Preferably water is used.

  In order to uniformly contain the ceramic powder in the ceramic slurry, it is preferable to use an appropriate dispersant.

  As the dispersant, a polycarboxylic acid-based dispersant (anionic dispersant) can be used. Specifically, ammonium polycarboxylate or sodium polycarboxylate can be used. Preferably, a dispersant having a large change in slurry viscosity with the addition amount of the dispersant is used.

  The amount of the dispersant used is preferably 5% by weight or less, more preferably 1% by weight or less, based on the weight of the ceramic powder.

  The ceramic slurry is removed before introducing the ceramic slurry bubbles, and the bubbles are introduced while stirring the slurry.

  When air bubbles are introduced into the ceramic slurry, a gelling agent or a polymerizable material composed of a monomer and a polymerization initiator is added in order to form a desired shape.

  When a gelling agent is used, the slurry is gelled by temperature control or pH control. Examples of the gelling agent include gelatin, agarose, agar, sodium alginate and the like.

  When a polymerizable material is used, a monomer of the polymerizable material is used. Specific examples include monomers having one or more vinyl groups or allyl groups. When the slurry is composed of water or an aqueous solvent, it is preferable to use a monofunctional or bifunctional polymerizable monomer.

  Moreover, when a slurry is comprised with an organic solvent, it is preferable that it is a bifunctional polymerizable monomer. In particular, when preparing water as a solvent in the slurry, preferably, at least one monofunctional (meth) acrylic amide and at least one bifunctional (meth) acrylic amide Are used in combination.

  When the slurry is prepared with an organic solvent, preferably, at least two types of bifunctional (meth) acrylic acid are used in combination.

  When a monofunctional monomer or a bifunctional monomer is used, ammonium persulfate, potassium persulfide, or the like is preferable.

  Moreover, when using the functional monomer which has a 2 or more functional group, Preferably, an organic peroxide, a hydrogen peroxide compound, an azo, or a diazo compound is used. Specifically, it is benzoyl peroxide.

  The introduced gas is preferably held in the slurry as bubbles by a surfactant or the like.

  The surfactant is preferably added to the ceramic slurry before the introduction of bubbles by stirring or the like in the bubble introduction step.

  Examples of the surfactant include an anionic surfactant such as an alkylbenzene sulfonic acid, and a cationic surfactant such as a higher alkyl amino acid.

  Specifically, n-dodecylbenzenesulfonic acid, polyoxyethylene sorbitan monolaurate, polyoxyethylene monooleate, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, and alkali metal salts thereof such as sodium and potassium are used. Can be mentioned.

  Further, triethanolamine lauryl ether and the like and halogenated salts thereof, sulfate, acetate, hydrochloride and the like can be mentioned.

  Moreover, diethyl hexyl succinic acid and its alkali metal salt etc. can be mentioned.

(Bubble introduction process)
Bubbles are introduced into the slurry prepared as described above. In the bubble introduction step, when a polymerizable material is used as the gelling material, it is preferable to add a polymerization initiator or a polymerization initiator and a polymerization catalyst together with the polymerizable material.

  If a polymerization catalyst is added, the time of a gelation process can be adjusted with gelation temperature or its addition amount. Usually, when a polymerization catalyst is added, gelation (polymerization) starts rapidly around room temperature.

  Therefore, the use and type of the polymerization catalyst are selected in consideration of the bubble introduction method, the bubble introduction amount, and the like. Examples of the polymerization catalyst include N, N, N ′, N′-tetramethylethylenediamine and the like.

(Slurry molding process)
The cell-containing ceramic slurry thus prepared is injected into a mold or the like and gelled to form a gel-like porous molded body. The cell-containing ceramic slurry is poured into a cylindrical mold and polymerized or gelled to solidify.

  When the slurry is solidified, the air bubbles present in the slurry are also stored in the gel. As a result, the solidified body becomes porous, and a gel-like porous molded body is obtained. This is demolded, dried, degreased and fired.

  Drying is performed so as to evaporate water and solvent contained in the gel-like porous molded body. The drying conditions (temperature, humidity, time, etc.) are appropriately adjusted according to the type of solvent used for slurry preparation and the components (gelling agent or polymer) constituting the skeleton of the gel-like porous molded body.

  Usually, it is 20 ° C or higher, preferably 25 ° C or higher and 80 ° C or lower, more preferably 25 ° C or higher and 40 ° C or lower.

(Baking process)
Next, in order to remove organic components from the dried product, heating is performed at a higher temperature.

The temperature and time for degreasing are adjusted according to the amount and type of organic component used. For example, in the case of a gel-like porous molded body prepared from a slurry using methacrylamide and N, N-methylenebisacrylamide as a material for gelation, degreasing is performed at 700 ° C. for 2 days.

  After degreasing, a firing process is performed. The conditions for firing are set in consideration of the type of ceramic material used.

  Through such steps, the ceramic porous body 6 of the present embodiment can be obtained.

  The porous ceramic body 6 is porous and has a plurality of voids. The voids are preferably present dispersed in the ceramic porous body 6.

  The air gap may exist independently, may exist continuously with other air gaps, and may communicate with the outside. In the acoustic matching body 5, it is preferable that the holes exist continuously.

  It is preferable that the ceramic porous body 6 has a porosity of 60% or more and 90% or less as a whole (herein, it means a total porosity including open pores and closed pores).

  More preferably, it is 80% or more and 90% or less. The total porosity is determined by the following calculation formula (3).

Total porosity (%) = (1−bulk density / true density) × 100 (3)
However, bulk density = weight of sample / bulk volume of sample. The true density is determined by, for example, putting an arbitrary amount of a very finely divided sample into a pycnometer, injecting water until reaching a predetermined volume, boiling, etc., and removing voids, and then from the relationship between the weight and the volume. Can be sought.

  This is because when the efficiency is 60% or less, the density ρ1 of the acoustic matching body 5 increases, and when the hole diameter exceeds 90%, the mechanical strength is significantly reduced. The open porosity is more preferably 65% or more and 85% or less, and it is made lighter within the range allowed by the strength so as to be close to that having a small density and a slow sound speed.

  By optimizing the above materials and manufacturing conditions and adjusting the density of the ceramic porous body 6 of the acoustic matching body 5 in the embodiment of the present invention to 200 kg / m 3 or more and less than 400 kg / m 3, the density is low and the strength is high. A porous body 6 could be realized.

  As described above, in the present embodiment, for the purpose of obtaining a highly sensitive ultrasonic transducer, the acoustic matching body 5 is solid so as to reduce the reflection of sound and increase the intensity of sound wave transmission. A low-density ceramic porous body 6 that is fragile and fragile is used as a low-density and slow-sounding sound, and the vibration of the acoustic matching body 5 efficiently vibrates (transmits) the measured fluid. An acoustic film 9 is provided on the acoustic matching body 5 so that the acoustic matching body 5 is vibrated by the vibration of the fluid.

  Further, the acoustic matching body 5 is formed of a porous material such as a ceramic porous body 6 having a small pore diameter and a high porosity, and suppresses penetration of the joining means to the acoustic matching body 5 in advance in the acoustic matching body 5. Since the suppression film 10 is formed, the suppression film 10 can suppress the penetration of the joining means and can stabilize the sound transmission path.

Here, the brittle and fragile low-density porous body 6 used as the porous material is better in terms of transmission of sound passing through the porous body 6 and has a density in terms of transmission efficiency to the fluid to be measured. Since it is better to make it as small as possible, the condition is that the pore diameter should be as small and uniform as possible and the porosity should be high. In such a shape with a small pore size and a high porosity, that is, with a lot of pores, suction by capillary action works well, so even a thermosetting high-viscosity resin such as an epoxy resin is heated until it is thermally cured. Sometimes the viscosity drops and penetrates, and when it penetrates, if the low-density ceramic porous body 6 penetrates, the density increases accordingly, and the transmission efficiency of sound to the fluid to be measured becomes worse. In addition, since the transmission path is changed, the loss becomes large.

  Furthermore, if the permeation into the porous body 6 varies, the sound transmission path varies, which leads to variations in performance. Therefore, by suppressing the penetration of the joining means 4 by the suppression film 10, the sound transmission path is stabilized. By improving the performance, the performance can be improved and stabilized.

  In addition, the acoustic matching body 5 in which the acoustic film 9 and the suppression film 10 are formed is provided with toughness by the acoustic film 9 and the suppression film 10 on a porous material such as a porous body 6 that is hard and brittle. It can be reduced, and the influence of dust generation of the porous body during assembly can be reduced as much as possible.

  In addition, the porous body 6 formed by the gel casting method that constitutes the acoustic matching body 5 has a polymer network formed in the mold due to radical polymerization of the monomers in the slurry, resulting in a gel wet molded body. The fluid flow process and the solidification process are completely separated, and the particles are fixed in-situ, so that non-uniformity and defects in the porous body 6 hardly occur, and about 10 times compared with general pressure molding or casting. The strength can be doubled or higher, and the structure is uniform, and the density variation is small. Therefore, even complex shapes can be handled, and the strength can be increased.

  Therefore, there is less concern that a part of the acoustic matching body 5 formed of the porous body 6 is chipped or dusted during transportation or the like and adversely affects other devices, and the acoustic matching body formed of the porous body 6 is reduced. In order to make the body 5 transmit and receive ultrasonic waves more efficiently, the density can be reduced.

  Since the acoustic film 9 formed on the acoustic matching body 5 and the outermost layer film 8 serving as the suppression film 10 have the same material and shape, the acoustic matching body 5 has no front and back surfaces. There will be no mistakes in the front and back when the bonding means 4 adheres to the outside of the dome portion, handling at the time of assembly becomes easier, and the reliability of the assembly can be improved.

  The suppression film 10 and the acoustic film 9 are formed by printing a resin material based on a thermosetting resin such as an epoxy resin on the release film, and then the surface of the acoustic matching body 5 formed of the ceramic porous body 6. Therefore, a predetermined amount of resin material can be applied to the surface of the acoustic matching body 5 formed of the porous body 6 which is uneven and easy to suck in, and the thickness of the acoustic film 9 is set to a predetermined level. Since the thickness can be increased, the acoustic performance due to the change in the thickness of the acoustic film 9 can be stabilized.

  In addition, the suppression film 10 and the acoustic film 9 are uneven and sucked because fine powder such as silicon carbide is added to a thermosetting resin having substantially the same curing conditions such as epoxy resin in order to increase the viscosity. Since the penetration of the surface of the acoustic matching body 5 formed of the easy porous body 6 can be suppressed and the thickness of the acoustic film 9 can be made a predetermined thickness, the acoustic performance due to the change in the film thickness of the acoustic film 9 Can be stabilized.

In the present embodiment, for the purpose of obtaining a highly sensitive ultrasonic transducer, the acoustic matching body 5 reduces the reflection of sound and increases the intensity of sound wave transmission. A low-density ceramic porous body 6 that is brittle and fragile is used as a slow material, and a protective ring 7 made of resin is provided so as to be in close contact with the outer periphery, but this is formed on both upper and lower surfaces of the porous body. The expansion coefficient is almost the same as that of the outer layer film 8 so as to be resistant to thermal fatigue. The protective ring 7 may be made of other materials such as a dense ceramic having no pores, and other parts. The configuration may be any configuration as long as the object of the present invention is achieved.

  As described above, the ultrasonic transducer according to the present invention and the flow measuring device using the ultrasonic transducer can be applied to uses such as a metering gas meter because a highly sensitive ultrasonic transducer can be obtained. .

Sectional drawing of the ultrasonic transducer in Embodiment 1 of this invention Explanatory drawing of measurement principle of supersonic flow velocity flowmeter in Embodiment 1 of the present invention Explanatory drawing which shows the manufacturing process of the porous body used for the acoustic matching body in Embodiment 1 of this invention. Partially enlarged view of an acoustic matching body for incorporation into a conventional ultrasonic transducer

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic transmitter / receiver 2 Tensile case 3 Piezoelectric body 4 Joining means 5 Acoustic matching body 6 Porous body 7 Protective ring 8 Outermost layer film 9 Acoustic film 10 Inhibition film

Claims (5)

A celestial case, a piezoelectric vibrator disposed so as to be in close contact with the inside of the celestial portion of the case, and an acoustic matching body disposed so as to be in close contact with the outside of the celestial portion of the case by a joining means The acoustic matching body is formed of a porous material having a plurality of pores, a protective ring is closely disposed on the outer periphery, and an outermost layer film is formed on both upper and lower surfaces. . The porous material forming the acoustic matching body is formed by dissolving a monomer in a slurry made of an oxide-based ceramic material into which bubbles are introduced or a slurry made of an oxide-based ceramic material to which a porous material such as an acrylic ball is added. The ultrasonic transducer according to claim 1, wherein a ceramic porous body formed by firing a material molded by a gel casting method to be injected into a mold is processed into a predetermined shape. The outermost layer film is formed of a ceramic porous body after printing a resin material based on a thermosetting resin such as an epoxy resin on a release film so as to suppress penetration of the joining means into the acoustic matching body. The ultrasonic transducer according to claim 1, wherein the ultrasonic transducer is formed by being transferred to a surface of the acoustic matching body. The ultrasonic transducer according to claim 1 or 3, wherein the outermost layer film is obtained by adding a fine powder such as silicon carbide to a thermosetting resin having substantially the same curing conditions such as an epoxy resin in order to increase the viscosity. . At least a pair of the ultrasonic transducers according to any one of claims 1 to 4 are arranged on the upstream side and the downstream side of the flow path through which the fluid to be measured flows, and the ultrasonic propagation time between the ultrasonic transducers is set. An ultrasonic flow measuring device that measures the flow velocity and / or flow rate of the fluid to be measured.