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DESCRIPTION JP2003158796

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DESCRIPTION JP2003158796
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic generator for use in a flow rate measuring device for measuring the flow rate of an
object to be measured such as gas using ultrasonic waves, or a distance measuring device for
measuring the distance to an object. It is about
[0002]
2. Description of the Related Art FIG. 8 is a cross-sectional view showing the structure of a
conventional ultrasonic wave generator. The vibrating means 1 and the case 2 are adhered by an
epoxy adhesive 9, and both the case 2 and the aligning means 3 are adhered by the epoxy
adhesive 8. The resin 4 has the purpose of fixing the case 2 and the vibrating means 1 and the
electrodes 5 and 6 and the purpose of a sound absorbing material for preventing the vibration of
the vibrating means 1 from propagating to the opposite surface of the matching means 3 is
there.
[0003]
The vibration means 1 vibrates at about 500 kHz, and the vibration is transmitted to the case 2
through the epoxy adhesive 9 and is further transmitted to the alignment means 3 through the
epoxy adhesive 8. Then, the vibration of the alignment means 3 propagates as a sound wave to,
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for example, the gas present in the space 7.
[0004]
The role of the matching means 3 is to efficiently propagate the vibration of the vibrating means
1 to the gas, and the acoustic impedance Z defined as (Equation 1) by the sound velocity C of the
substance and the density ρ Vastly different from gas.
[0006]
The acoustic impedance Z1 of the vibration means 1 is about 30 × 10 6 (kg / m 2 s), the
acoustic impedance Z 2 of a gas such as air is 4.28 × 10 2 (kg / m 2 s), and the case 2 is made
of metal. Then, since the acoustic impedances of the vibration means 1 and the case are
substantially equal, the vibration can be transmitted without loss.
[0007]
On the interface of different acoustic impedances, reflections occur in the propagation of sound
(vibration), and as a result, the intensity of the transmitted sound is reduced.
However, it is generally known that the reflection of sound is eliminated and the loss is reduced
by inserting a substance having another acoustic impedance Z3 between substances of two
different acoustic impedances.
Z3 is defined as (Equation 2).
[0009]
The value of Z3 is 0.11 × 10 6 (kg / m 2 s) when Z 1 is 30 × 10 6 (kg / m 2 s) and Z 2 is 4. 28
× 10 2 (kg / m 2 s). A substance that satisfies this acoustic impedance is required to have a low
density and a low sound velocity.
[0010]
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Therefore, the matching means 3 reduces the density by using a micro hollow glass solidified
with an epoxy adhesive. The hollow glass needs to be sufficiently smaller than the wavelength of
the sound transmitted through the matching means 3, and therefore, a glass of 100 μm or less
in size is used. The acoustic impedance of the matching means 3 thus obtained is about 1.2 × 10
6 (kg / m 2 s).
[0011]
Furthermore, the intensity of the sound transmitted through the alignment means 3 to the gas is
also related to the thickness of the alignment means 3. FIG. 9 shows the propagation of sound in
three substances consisting of the vibration means 1, the alignment means 3 and the space 7
with gas (air), with the exception of the epoxy adhesive and the case 2 for the sake of simplicity.
The sound wave 10 from the vibration means 1 is divided into the sound wave 11 to be
transmitted and the sound wave 12 to be reflected at the interface between the matching means
3 and the gas. The reflected wave 12 is reflected at the interface between the matching means 3
and the vibrating means 1 to form a wave 13 whose phase is reversed. A portion of this wave
becomes the sound wave 14 transmitted at the interface between the matching means 3 and the
gas. Since the wave 14 and the wave 11 are synthesized, the transmittance T of the intensity of
the sound emitted to the gas is expressed by (Equation 3).
[0013]
Where Z1 is the acoustic impedance of the vibration means 1, Z2 is the acoustic impedance of
the matching means 3, Z3 is the acoustic impedance of a gas, L is the distance of the matching
means 3, and k2 is given by Eq.
[0015]
Where f is the frequency of vibration and C 2 is the speed of sound of the matching means 3.
If the distance L which becomes the transmittance | permeability maximum of (Equation 3) is
calculated | required, it will be set to L = lambda / 4. When hollow glass is used as the matching
means, the sound speed is 2000 m / s, so when the sound frequency is 500 kHz, the wavelength
λ is 4 mm. Therefore, the thickness of the alignment means 3 is 1 mm.
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[0016]
However, in the above-mentioned conventional ultrasonic wave generator, an epoxy resin is used
for bonding between the alignment means 3 and the case 2. In addition, an epoxy resin is used to
solidify the hollow glass constituting the alignment means. The gas may contain moisture or may
contain sulfur. In such a case, the moisture causes the epoxy resin contained in the adhesive for
bonding the aligning means 3 and the case 2 to swell. The sulfur may corrode the epoxy resin
contained in the adhesive bonding the aligning means 3 to the case 2. When this happens, the
acoustic impedance of the matching means changes, and efficient sound radiation, which is the
purpose of the matching means, is impeded, which may interfere with accurate measurement.
[0017]
In addition, since the thickness of the alignment means is as thick as 1 mm, sound absorption
occurs in the alignment means, and the output to the sensor receiving ultrasonic waves is
weakened, and in the alignment means using the conventional hollow glass, the precise film Since
thickness control can not be performed, there is also a problem that an output to a sensor
receiving ultrasonic waves is reduced depending on individual differences.
[0018]
The present invention solves the above-mentioned problems of the prior art, and an object
thereof is to provide an ultrasonic wave generator having high output to a sensor receiving
ultrasonic waves, which constitutes alignment means without using an epoxy adhesive. Do.
[0019]
SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems,
the present invention uses porous silica as the aligning means, and the aligning means can be
made extremely thin, so the aligning means It is difficult for the sound absorption inside to occur,
and an ultrasonic generator with a large output to the sensor can be realized.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION According to the invention described in claim
1 of the present invention, porous silica is used as the matching means, and in particular, porous
materials having a porosity of 80% or more and physical properties of 0.3 g / cm3 or less. Since
the speed of sound in silica is about 100 to 300 m / s, the matching means can be made very
thin, so that absorption of sound in the matching means is difficult to occur, and an ultrasonic
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generator with a large output to the sensor Can be realized.
[0021]
Further, in the invention according to claim 2, the binder is added to the porous silica particles
by forming the matching means as a molded body in which at least the porous silica particles are
bonded or the porous silica particles and the case are bonded by a binder. By mixing, the sound
velocity and density can be freely changed, and a material having an acoustic impedance
required as a matching means can be obtained.
Furthermore, since the porous silica particles and the case can be bonded by the binder, an
ultrasonic generator capable of accurate measurement can be realized without using an epoxy
adhesive.
[0022]
Further, the invention according to claim 3 is that in which at least a part of the surface of the
porous silica particle is covered with a binder particle, porous silica particles are made to adhere
to each other by attaching the binder particle to the porous silica particle in advance. Can
increase the strength of the bonding, so that the reliability of the alignment means can be
enhanced, and a durable ultrasonic generator can be realized.
Further, the efficiency of the invention according to claims 3 and 10 can be increased by
attaching the binder particles to the porous silica particles in advance.
[0023]
The invention according to claim 4 is that the binder particles are resin powder, so that a porous
silica molded body can be manufactured very easily, and an ultrasonic wave generator capable of
accurate measurement can be realized.
[0024]
In the invention according to claim 5, the porous silica particles or the binder particles and the
filler which is bound or entangled are used, and since the strength of bonding the porous silica
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particles can be increased, the reliability of the matching means is improved. A durable and
durable ultrasonic generator can be realized.
[0025]
In the invention according to claim 6, the filler is a fibrous substance, and the strength for
bonding the porous silica particles to each other can be further increased, so that the reliability
of the matching means is enhanced, and ultrasonic wave generation having durability is
enhanced. Can be realized.
[0026]
The invention according to claim 8 comprises the step of producing a molded body in which
porous silica particles are bound to one another by binder particles to form a molded body, and
the bonding step of bonding the molded body to the case; This method is a manufacturing
method of an ultrasonic wave generator that simultaneously performs the bonding step and the
bonding step, and since two steps can be performed simultaneously, the working efficiency can
be increased, and the porous silica particles and the case are Since the bonding can be
performed, an ultrasonic generator that can perform accurate measurement can be realized
without using an epoxy adhesive.
[0027]
In the invention according to claim 9, pressure and temperature are applied to a mixture of
porous silica particles and binder particles to soften the binder particles, thereby bonding the
porous silica particles to each other, and the binder particles are used to bind the porous silica
particles. The molded body with porous silica particles bonded to the case is used as the
matching means. By mixing the binder particles into the porous silica particles, the speed of
sound and density can be freely changed, and it is required as the matching means. An acoustic
impedance material is obtained.
Furthermore, since the porous silica particles and the case can be bonded by the binder particles,
it is possible to realize an ultrasonic generator capable of accurate measurement without using
an epoxy adhesive.
[0028]
In the invention according to claim 10, the mixture of the porous silica particles and the binder
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particles is charged with static electricity and then adhered to a case, and then the temperature is
added to soften the binder particles, thereby bonding the porous silica particles to each other.
And, the compacted body in which the porous silica particles are bonded to the case by the
binder particles is used as the matching means, and the thickness of the thin film can be
accurately controlled. Thus, it is possible to realize an ultrasonic generator that can be obtained
and can perform accurate measurement.
[0029]
In the invention according to claim 11, the mixture of the porous silica particles and the binder
particles is heated to soften the binder particles in a state where the binder particles are
softened, and the porous silica particles are bonded to each other by the binder particles. Further,
the compacted body in which the porous silica particles are bonded to the case by the binder
particles is used as the matching means, and the thickness of the thin film can be accurately
controlled. Can realize an ultrasonic generator capable of accurate measurement.
[0030]
Further, the invention according to claim 12 uses as a matching means a molded article in which
water is added to a mixture of hydrophobic porous silica particles and water-soluble organic
binder particles and the mixture is kneaded and then attached to a case to remove the water. By
mixing binder particles into porous silica particles, the speed of sound and density can be freely
changed, and a substance of acoustic impedance required as a matching means can be obtained.
Furthermore, since the porous silica particles and the case can be bonded by the binder, an
ultrasonic generator capable of accurate measurement can be realized without using an epoxy
adhesive.
[0031]
In the inventions according to claims 7 and 13, gelation is caused by adding at least one of water,
an organic solvent, or an acid or an alkali to either one of alkoxysilane or water glass to porous
silica. The xerogel prepared by the method of hydrophobization and subsequent drying is used,
and since the speed of sound in the xerogel is about 100 m / s, the matching means can be made
thinner, so that in the matching means Sound absorption is further reduced, and an ultrasonic
generator with a large output to the sensor can be realized.
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[0032]
Embodiments of the present invention will be described hereinbelow with reference to the
drawings.
[0033]
EXAMPLE 1 FIG. 1 is a cross-sectional view of an ultrasonic wave generator in Example 1 of the
present invention.
20 is an alignment means, 21 is a case main body (hereinafter referred to as a case in the present
embodiment) made of metal or the like, 22 is a lid (hereinafter referred to as a lid in the present
embodiment) of the case 21 made of the same metal or the like, 23 is a piezoelectric element And
the like, 24 is a conductive rubber, 25 and 26 are electrodes, and 27 is a gas.
A glass 29 is sealed between the electrode 25 and the lid 22 of the case to electrically insulate
the electrode 25 from the lid 22.
The vibrating means 23 is housed in a case 21, and the case 21 and the vibrating means 23 are
bonded by an adhesive 28.
An alternating voltage of about 5 V is applied between the electrodes 25 and 26.
The electrode 26 is connected to the lid 22, and the lid 22 is further welded to the case 21.
Thereby, the voltage applied to the electrode 26 is applied to the adhesive 28 through the lid 22
and the case 21.
The other electrode 25 is electrically connected to the vibration means 23 via a conductive
rubber.
Therefore, the voltage applied between the electrodes 25 and 26 will be applied to the vibrating
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means 23 and the adhesive 28. Electrically, the vibration means 23 and the adhesive 28 can be
regarded as a capacitor.
[0034]
Since the resonance frequency of the vibration means 23 is designed to be approximately 500
kHz, by applying an alternating voltage of 500 kHz to the electrodes 25 and 26, the vibration
means 23 vibrates at 500 kHz. The vibration propagates to the case 21 to vibrate it, and the
vibration of the case 21 propagates to the alignment means 20 to vibrate it. As described in the
prior art, the role of the matching means 20 is to efficiently propagate the vibration of the
vibrating means 23 to, for example, the gas 27 which is the object to be measured. The
conductive rubber 24 also serves as a shock absorbing material for the vibration to prevent the
vibration of the vibration means 23 from being transmitted to the lid 22 and to transmit the
energy of the vibration to the matching means 20 efficiently.
[0035]
Since the vibration means 23 and the conductive rubber 24 are housed in the case 21, the gas
does not enter the case 21. Therefore, the adhesive 28 does not swell with water contained in the
gas or is corroded with sulfur. By sealing the glass between the electrode 25 and the lid 22, it is
possible to reliably prevent the entry of gas into the case 21.
[0036]
Next, the alignment means 20 and the porous silica used therefor will be described with
reference to the drawings. Porous silica is prepared by gelation of water glass or alkoxysilane
such as tetramethoxysilane under certain conditions, and evaporation of the solvent inside. At
this time, the portion filled with the solvent becomes pores, but the one which has been dried
with a common hot air shrinks due to surface tension when the solvent is dried, and the pores
are crushed, and the porous body It does not become. However, those that have been subjected
to supercritical drying (referred to as airgel) or those that are obtained by hydrophobizing the gel
surface and replacing the solvent with a solvent such as toluene, acetone, or hexane and then
subjected to hot air drying have almost the surface tension working. First, as shown in FIG. 2,
primary silica particles 31 having a diameter of about 1 to 10 nm are aggregated to form an
aggregate having an interparticle distance 32 of about 40 to 100 nm. Therefore, the interparticle
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distance 32 forms a pore and becomes a porous body. In this example, a xerogel produced by
such a method was used. In addition, the same effect can be obtained by using airgel. This is
because airgel and xerogel are different only in the drying process, and the texture and physical
properties are the same as xerogel.
[0037]
Since the interparticle distance 32 is about 40 to 100 nm and about the same as the mean free
path of air molecules, the velocity of sound in the xerogel is about 100 m / s. And the aggregate
of these primary particles formed the secondary particle of about 1 micrometer-10 mm.
Although a secondary particle larger than this can be produced, since the strength is very weak,
in the present example, secondary particles of about 1 μm to 1 mm were bound by a binder and
used as a molded body. Further, the binder plays the role of adjusting the speed of sound in the
xerogel molded body, in addition to the effect of binding the xerogel particles to each other or
binding of the xerogel and the case. The mixing ratio of the binder and the xerogel is not
particularly limited, but the sound velocity in the xerogel molded body can be increased by
increasing the amount of binder particles. In addition, increasing the amount of binder also
increases the strength.
[0038]
Next, the step of preparing a xerogel compact and the bonding step will be described with
reference to the drawings. In both steps, a method using a resin binder such as phenol resin,
silicone resin, polyethylene, polypropylene, polyphenylene sulfide, thermoplastic polyimide, and
water-soluble cellulose such as methyl cellulose, hydroxypropyl cellulose, carboxymethyl
cellulose, acrylic acid, methacrylic acid There is a method of using a water-soluble acrylic such as
[0039]
First, a method of using a resin binder will be described. FIG. 3 shows a state in which the binder
particles 36 and the xerogel particles 35 are mixed. As the mixing method, the xerogel particles
and the binder particles are mixed in the same container, and mixed using a mixer or a mix rotor
so as to be as uniform as possible. Thereafter, the mixture is put into a mold and heated to melt
the binder particles, and the xerogel particles are bonded together to form a molded body
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(referred to as a mold method in this example). At this time, by placing the case 21 in the mold,
the melted binder particles bond the xerogel particles and the case, and the step of producing a
molded product and the bonding step can be performed simultaneously. Moreover, the density of
the obtained molded object can also be adjusted by adjusting the applied pressure. Other than
this method, it is possible to produce a xerogel molded product by the following two methods.
[0040]
A mixture of xerogel particles and binder particles is placed on the surface of the case 21 and
attached to the case 21 by static electricity, and then temperature is applied to melt the binder
particles and combine the xerogel particles into a molded article. At the same time, the melted
binder particles are adhered to the case 21 (in this embodiment, referred to as an electrostatic
coating method). This method has the advantage that the film thickness can be controlled to
about 5 to 10 μm.
[0041]
Further, a mixture of the xerogel particles and the binder particles is heated to bring the binder
particles into a semi-molten state and sprayed onto the surface of the case 21, whereby a
compact of xerogel particles can be produced on the surface of the case 21 (this example) Then,
it is called the thermal spraying method). This method also has an advantage that the film
thickness can be controlled to about 5 to 10 μm.
[0042]
When a part of the molded body produced by these is expanded, it will become like FIG. 4 or FIG.
By applying binder particles to the surface of the xerogel particles in advance, a molded product
as shown in FIG. 6 can be realized using a mold method, an electrostatic coating method, and a
thermal spraying method. As a result, the bonding area between the binders is increased, so that
the bonding strength is increased, and the strength can be improved, and the uniformity of the
molded product can be achieved.
[0043]
Furthermore, when performing the mold method, the electrostatic coating method, and the
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thermal spraying method, the matching means can also be stacked by attaching in advance the
matching means having different acoustic impedances depending on other materials or
compositions on the case surface. .
[0044]
Next, a method of using a water-soluble cellulose-based or acrylic-based binder will be described.
Water-soluble and solvent-based binders are excellent in adhesion and can easily solidify
powdery substances, but using these binders it is extremely possible to solidify without breaking
the pores of xerogel. Difficult to This is because pores in the xerogel are crushed when a solvent
that is easy to wet is used, and when a solvent that is difficult to wet is used, the xerogel repels
the solvent and does not mix.
[0045]
Therefore, the binder particles are dissolved in the solvent by dissolving the water-soluble binder
particles of high viscosity such as cellulose or acrylic and the xerogel particles uniformly in
advance and kneading while adding the solvent which is difficult to get wet. The binding strength
of the binder allows the xerogel to be in the form of clay, so that the form can be freely changed.
Thereafter, the solvent is removed to obtain a desired molded body. In the present example,
water was used as a solvent that is difficult to wet.
[0046]
As a mixing method, the xerogel particles and the water-soluble binder particles are mixed in the
same container, and mixed using a mixer or a mix rotor so as to be as uniform as possible.
Further, the kneading method is not particularly limited as long as the xerogel particles and the
water-soluble binder particles can be kneaded.
[0047]
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Further, the amount of water to be added is not particularly limited, but it is preferably about the
same weight as the xerogel. When the amount of water is too large, the binder becomes nonuniform, the strength at a place where the amount of binder is small is weak, air bubbles are left
when removing water, and a uniform compact can not be obtained.
[0048]
The effect of adding the filler is described. The addition of a filler is usually used to improve the
strength of the material or adjust the density of the material. The present invention can further
be used for the purpose of adjusting the speed of sound in a molded body of xerogel and a
binder.
[0049]
By adding the filler to the mixture of xerogel particles and binder particles, a state as shown in
FIG. 7 is obtained. That is, even if the secondary silica particles 41 of xerogel are not bound by
the binder particles 42, the binder particles 42 bound to the secondary silica particles 41 can be
bound by the filler 43, and as a result, the secondary silica of xerogel can be obtained. Since the
particles can be bound, the strength can be increased by adding a filler. At this time, as the filler,
a fibrous one is preferable so as to be entangled with the binder particles. Examples of fibrous
fillers include glass fibers, polyester fibers, metal fibers, kynol fibers, carbon fibers and the like.
[0050]
Further, the amount of the filler to be added is not particularly limited. The type and amount of
filler can be adjusted to obtain the desired density and sound velocity.
[0051]
From these, since the xerogel particles and the case can be bonded by the binder particles, an
ultrasonic generator capable of accurate measurement can be realized without using an epoxy
adhesive.
[0052]
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In addition, since a compact having a density of 0.4 (g / cm 3) and a sound velocity of 300 m / s
can be produced by using a xerogel, a binder and a filler, the acoustic impedance at this time is 0
according to (Equation 1) It becomes 12 × 10 6 (kg / m 2 s), and it is possible to make one
approximately equivalent to the required acoustic impedance obtained from (Equation 2).
At this time, assuming that the frequency of sound is 500 kHz, the thickness of the matching
means is about 150 μm according to (Equation 3) and (Equation 4), and this can be realized with
a xerogel molded body. And because it is very thin, it absorbs less sound in the alignment means
and does not weaken the output to the sensor. Therefore, an ultrasonic wave generator with high
sensor output can be realized.
[0053]
In the above embodiment, the object to be measured is described as a gas, but it may be a liquid
or the like. In this case, the aligning means may be coated with a water repellent agent.
[0054]
As described above, according to the inventions of claims 1 and 12, since porous silica (xerogel)
having a low sound velocity is used as the aligning means, the aligning means can be thinned,
and the aligning means can be made thin. The sound absorption in the unit is small, and an
ultrasonic generator with high sensor output can be realized.
[0055]
Further, according to the invention described in claims 2 to 4 and 7 to 13, since the xerogel
powder and the case can be joined by the binder particles, ultrasonic wave generation can be
performed accurately without using an epoxy adhesive. Can be realized.
[0056]
Further, according to the fifth and sixth aspects of the invention, the strength of the matching
means can be improved by the addition of the filler, and an ultrasonic generator with high
durability can be realized.
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