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DESCRIPTION JP2008261732

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DESCRIPTION JP2008261732
An object of the present invention is to provide a high-performance ultrasonic transducer which
is not affected by moisture absorption and an ultrasonic flow velocity flowmeter using the same.
An acoustic matching body 6 has an acoustic film 7 formed on a ceramic porous body 5 having a
plurality of pores on a surface opposite to a contact surface outside a top portion of a case 2 and
on a side wall of the ceramic porous body 5. Since the sealing means 8 is provided and the pores
of the ceramic porous body 5 are sealed by the acoustic film 7, the bonding means 4 and the
sealing means 8, the surface of the ceramic porous body 5 which easily absorbs moisture in
nature is not exposed The moisture absorption of the acoustic matching body 6 can be
suppressed even if it is left under temperature change or high temperature and high humidity,
and good output sensitivity can be maintained. Further, since the ceramic porous body 5 is
protected by the acoustic film 7, the bonding means 4 and the sealing means 8, there is no
concern that a part of the ceramic porous body 5 may be chipped or dusted. [Selected figure]
Figure 1
Ultrasonic transducer and ultrasonic velocity flowmeter using it
[0001]
The present invention relates to an ultrasonic transducer and an ultrasonic flow velocity
flowmeter which measures the flow rate or flow velocity of a gas or liquid by ultrasonic waves
generated using the ultrasonic transducer.
[0002]
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1
Conventionally, in this type of ultrasonic transducer, as shown in FIG. 7 for example, it is an
acoustic matching member 50 which is provided with a piezoelectric vibrator and is incorporated
in an ultrasonic transducer which transmits or receives ultrasonic waves. A porous material 53
comprising a framework material 52 having voids 51, a low porosity layer 54 having a porosity
lower than the porosity of the porous material in at least a part of the surface to be measured, or
the porous material A binder diffusion layer is formed on at least a part of the surface and the
inside of the body.
Since the surface is closer to a flat surface as compared with a conventional porous body used as
an acoustic matching body, ultrasonic waves can be efficiently transmitted and received (see, for
example, Patent Document 1). JP 2003-111195 A
[0003]
However, in the above-mentioned conventional configuration, due to the nature of the porous
body, it is easy to absorb moisture, dew condensation occurs when it is left under high
temperature and high humidity when temperature change occurs during transport etc. The
reflection and diffusion of ultrasonic waves may occur, and the output sensitivity may decrease
due to the change in the speed of sound of the acoustic matching body. Therefore, when the
ultrasonic transducer provided with this acoustic matching body is mounted on a flow
measurement apparatus, there is a problem that the measurement accuracy of the flow velocity
and the flow rate is lowered. In addition, if the density of the porous body is reduced in order to
transmit and receive ultrasonic waves more efficiently, the strength becomes weak, and part of
the porous body may be chipped or dusted during transportation, etc. There was a concern that
other devices would be adversely affected.
[0004]
The present invention solves the above-mentioned conventional problems, and by subjecting a
ceramic porous body that is susceptible to moisture absorption to a chemical vapor deposition
process, a high-performance ultrasonic transducer that is not sensitive to moisture and is not
affected by moisture absorption It is an object of the present invention to provide an ultrasonic
flow velocity flowmeter using
[0005]
In order to solve the above problems, the ultrasonic transducer according to the present
invention includes a case having a sky shape, a piezoelectric body disposed in close contact with
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the inside of the sky portion of the case, and an outer portion of the case And an acoustic
matching body disposed in intimate contact with the bonding means, wherein the acoustic
matching body is a ceramic porous body having a plurality of pores, and an acoustic film on the
opposite side to the contact face outside the top with the case of the case. A sealing means is
provided on the side wall of the acoustic matching body formed of the ceramic porous body, and
the pores of the ceramic porous body are sealed by the acoustic film, the bonding means, and the
sealing means.
[0006]
According to the above-described configuration, the pores of the acoustic matching body formed
of the ceramic porous body are sealed by the acoustic film, the bonding means, and the sealing
means. The surface of the acoustic matching body is not exposed, and the moisture absorption of
the acoustic matching body is suppressed even if it is left under temperature change or high
temperature and high humidity, and good output sensitivity can be maintained.
In addition, since the acoustic matching body formed of the ceramic porous body is protected by
the acoustic film, the bonding means, and the sealing means, a part of the acoustic matching
body formed of the ceramic porous body is chipped or dust is generated There is no need to
worry.
[0007]
According to the present invention, it is possible to suppress the moisture absorption of the
acoustic matching body due to temperature change or being left under high temperature and
high humidity, and easily maintain the output sensitivity of the acoustic matching body, and
acoustic matching made of the ceramic porous body. The body can be protected, and if it is used
for a flow measurement device, measurement accuracy can be improved.
[0008]
In the ultrasonic transducer according to the first aspect of the present invention, the case having
a sky shape, the piezoelectric body disposed in close contact with the inside of the sky portion of
the case, and the bonding means outside the sky portion of the case And the acoustic matching
body is formed on a surface of the acoustic matching body formed of a ceramic porous body
having a plurality of pores on the surface opposite to the contact surface outside the top of the
case. An acoustic film is formed, and a sealing means is provided on a side wall of the acoustic
matching body formed of the ceramic porous body, and pores of the acoustic matching body
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formed of the ceramic porous body are the acoustic film, the joining means, and the acoustic
membrane. It is set as the structure sealed by the sealing means.
[0009]
Further, since the pores of the acoustic matching body formed of the ceramic porous body are
sealed by the acoustic film, the bonding means, and the sealing means, the acoustic matching
body formed of the ceramic porous body which easily absorbs moisture in nature The surface of
the acoustic matching body is not exposed, and the moisture absorption of the acoustic matching
body is suppressed even if it is left under temperature change or high temperature and high
humidity, and good output sensitivity can be maintained.
In addition, since the acoustic matching body formed of the ceramic porous body is protected by
the acoustic film, the bonding means, and the sealing means, a part of the acoustic matching
body formed of the ceramic porous body is chipped or dust is generated There is no need to
worry.
[0010]
Furthermore, since the sealing means is disposed around the acoustic matching body disposed so
as to be in close contact with the outside of the case with the joined portion by the joining means,
the vibration of the piezoelectric body is transmitted to the acoustic matching body through the
case. It is possible to damp the reverberation of the case that occurs during operation, and
improve the measurement accuracy.
[0011]
In the ultrasonic transducer according to the second aspect of the present invention, in
particular, the acoustic matching body formed of the ceramic porous body forming the acoustic
matching body of the first aspect is a slurry or A ceramic porous body produced by firing a
product formed by a gel casting method in which a monomer is dissolved in a slurry consisting of
an oxide-based ceramic material to which a porous material such as acrylic balls has been added
and injected into a forming mold It is configured by slicing into a shape.
[0012]
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The ceramic porous body formed by the gel casting method forms a polymer network in the
mold by radical polymerization of the monomers in the slurry, and becomes a gel wet-molded
body. Complete separation and in-situ fixing of the particles, so that non-uniformity and defects
in the ceramic porous body are unlikely to occur, and at least about 10 times stronger than
general pressure forming and cast molding Since the structure is uniform and the density
variation is small, it is possible to cope with a complicated shape, to be light and to increase the
strength.
Therefore, a part of the acoustic matching body formed of the ceramic porous body may be
chipped or dusted during assembly, etc., and the acoustic matching body formed of the ceramic
porous body is less likely to adversely affect other devices. In order to make the transmission and
reception of ultrasonic waves more efficient, the density can be reduced.
[0013]
In the ultrasonic transducer according to the third aspect of the present invention, in particular,
the sealing means according to the first or second aspect of the present invention is disposed in a
state in which the acoustic matching body is closely attached to the outside An adhesive, a paint
or the like is applied and formed between the acoustic film and the bonding means.
[0014]
Then, in a state where the acoustic matching body is disposed in close contact with the outside of
the case with the ceiling by bonding means, an adhesive, a paint, or the like is applied and
formed between the acoustic film and the bonding means. It can be sealed by a simple process
without using other parts between the acoustic matching body and the joining means.
[0015]
In the ultrasonic transducer according to the fourth invention, in particular, the acoustic film, the
bonding means and the sealing means of the invention according to any one of the first to third
inventions contain a resin binder having high affinity for each. It is as composition.
[0016]
And since the acoustic film, the bonding means and the sealing means contain resin binders
having high affinity with each other having substantially the same properties, they become easy
to bond and the strength is increased, and the acoustic film and the sealing means Alternatively,
generation of pores or the like can be suppressed in the bonding portion between the bonding
means and the sealing means, the confidentiality can be improved, and the reliability against
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temperature change or high temperature and high humidity can be further improved.
[0017]
In the ultrasonic transducer according to the fifth invention, in particular, the acoustic film, the
bonding means, and the sealing means according to any one of the first to third inventions are
heats having substantially the same curing conditions such as epoxy resin. It has a configuration
based on a curable resin.
[0018]
And since the acoustic film, the bonding means and the sealing means are based on a
thermosetting resin having substantially the same curing conditions such as epoxy resin, the
acoustic film, the bonding means and the sealing means are individually disposed. However, since
curing can be simultaneously performed in one heat curing step, simplification can be achieved
and the influence for curing can be reduced.
[0019]
In the ultrasonic transducer according to the sixth invention, in particular, the acoustic film of the
invention according to any one of the first to fifth inventions is a resin material based on a
thermosetting resin such as an epoxy resin on a release film. Is printed and then transferred onto
the surface of the acoustic matching body formed of a ceramic porous body.
[0020]
The acoustic film is formed by printing a resin material based on a thermosetting resin such as
epoxy resin on the release film, and then transferring the resin material to the surface of the
acoustic matching body formed of the ceramic porous body. Since a predetermined amount of
resin material can be applied to the surface of the acoustic matching body formed of a porous
ceramic body that has unevenness and is easy to be sucked, the thickness of the acoustic film can
be made to a predetermined thickness, so the film thickness of the acoustic film It is possible to
stabilize the acoustic performance due to the change of.
[0021]
In the ultrasonic transducer according to the seventh invention, in particular, the sealing means
of the first or second invention is formed by disposing a ring-shaped sealing member such as a
resin on the outer periphery of the acoustic matching body, The upper and lower ends are sealed
with the acoustic film by the bonding means.
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[0022]
Then, a ring-shaped sealing member such as a resin is disposed on the outer periphery of the
acoustic matching body, and the upper and lower end portions are sealed by the acoustic film
and the bonding means. The sealing means can be formed only by inserting the ring-shaped
sealing member on the outer periphery, and the time for forming the sealing means can be
shortened, and the ring-shaped sealing member such as resin is Since it is a molded article, it can
be made uniform with respect to the outer periphery of the acoustic matching body, and the
variation in the influence of the sealing member can be stabilized.
[0023]
In the ultrasonic transducer according to the eighth invention, in particular, the acoustic
matching body according to the first or second invention is oxidized by adding a porous material
such as a slurry or acrylic ball made of a bubble-introduced oxide ceramic material. The outer
shell surface of a ceramic porous body formed into a rod shape by firing a product formed by a
gel casting method in which a monomer is dissolved in a slurry made of a substance-based
ceramic material and injected into a forming mold to have a predetermined thickness An
adhesive, a paint, or the like is applied to form a sealing means, which is then sliced into a
predetermined shape, and the upper and lower ends thereof are sealed by the acoustic film and
the bonding means.
[0024]
Then, an adhesive, a paint, or the like is applied to the outer shell surface of the ceramic porous
body formed in a rod shape so as to have a predetermined thickness to form sealing means, and
then it is sliced into a predetermined shape. Therefore, the acoustic matching body and the
sealing means can be integrated, the sealing means can be formed on a plurality of acoustic
matching bodies at one time, the sealing means can be easily stabilized, and the process can be
simplified.
[0025]
Also, in order to transmit and receive ultrasonic waves more efficiently, the acoustic matching
body formed of a ceramic porous body is in the form of a ceramic porous body in which the
strength is maintained compared to before slicing, even if the density is reduced. The sealing
means formed by applying an adhesive, a paint, etc. to the outer shell surface of the body can
increase strength, prevent chipping at the time of slicing, etc., and also increase strength of the
sliced material. Handling of the matching body is facilitated.
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[0026]
In a ninth aspect of the present invention, in particular, at least one pair of the ultrasonic
transducers according to any one of the first to eighth aspects are disposed on the upstream side
and the downstream side of the flow path through which the fluid to be measured flows.
According to any one of the first to ninth inventions described above, the ultrasonic flow velocity
flowmeter is configured to measure the flow velocity and / or flow rate of the fluid to be
measured based on the ultrasonic wave propagation time between the Accordingly, it is possible
to provide an ultrasonic flow velocity flowmeter which is improved in reliability with respect to
temperature change or high temperature and high humidity with high reliability and improved
measurement accuracy.
[0027]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
The present invention is not limited by the present embodiment.
[0028]
First Embodiment FIG. 1 is a cross-sectional view of an ultrasonic transducer 1 formed of a
ceramic porous body according to a first embodiment of the present invention, and FIG. 2 is an
explanatory view of the measurement principle of an ultrasonic flow velocity flowmeter.
[0029]
The ultrasonic transducer 1 shown in FIG. 1 has a covered case 2 made of, for example, stainless
steel as a conductive material, and the piezoelectric body 3 disposed in close contact with the
inside of the covered portion of the case 2; The acoustic matching body 6 formed of the ceramic
porous body 5 disposed so as to be in close contact with the outside of the hollowed portion of
the case 2 by bonding means made of epoxy adhesive which is bonding means 4 is bonded and
fixed, The acoustic film 7 in the form of a film is formed on the surface, and the sealing means 8
is provided on the side wall where the pores of the acoustic matching body 6 formed of the
ceramic porous body 5 are exposed. The pores of the matching body 6 are sealed by the acoustic
film 7, the bonding means 4 and the sealing means 8.
[0030]
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8
As a procedure for sealing the pores of the acoustic matching body 6 formed of the ceramic
porous body 5 with the acoustic film 7, the bonding means 4 and the sealing means 8, the heat to
be the bonding means 4 on the surface of the case 2 having a sky shape After printing a resin
material based on a curable epoxy resin, the acoustic matching body 6 formed of the ceramic
porous body 5 in which a ring-shaped sheet made of an epoxy resin to be the sealing means 8 is
inserted Place.
Next, the acoustic film 7 is formed by printing an epoxy resin as a material of the acoustic film 7
on a release film, and transferring the epoxy resin to the surface of the acoustic matching body 6
formed of a ceramic porous body. Heat at temperature and time.
At this time, the acoustic film 7, the bonding means 4 and the sealing means 8 are based on a
thermosetting resin having substantially the same curing conditions of epoxy resin.
[0031]
On the other hand, the piezoelectric body 9 is made of, for example, PZT (lead zirconate titanate)
provided with silver electrodes 211 facing each other at both ends, and via the epoxy adhesive
whose upper electrode 10 is the bonding means 12 It is adhered so as to be in close contact with
the inner side of the top of the case 2
A pair of terminals 14 and 15 are attached to a conductive terminal plate 13 which closes the
lower opening of the case 2.
Furthermore, one of the terminals 14 is fixed to the terminal plate 13, and the upper electrode
10 of the piezoelectric body 9 is connected through the case 2 and the terminal plate 13.
The other terminal 15 insulates through the terminal plate 13 through the insulating portion 16
made of silicon rubber, and is connected to the lower electrode 11 of the piezoelectric body 9
with the conductive portion 17 having the nickel particle surface plated with gold interposed.
There is.
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[0032]
Here, the measurement principle of the ultrasonic flow velocity flowmeter using the ultrasonic
transducer 1 will be described in detail. As shown in FIG. It flows in the direction shown in the
figure.
A pair of ultrasonic transducers 21 and 22 are installed opposite to each other on the tube wall
20.
The ultrasonic transducers 21 and 22 are configured using a piezoelectric vibrator such as a
piezoelectric ceramic as an electrical energy / mechanical energy conversion element, and exhibit
resonance characteristics like a piezoelectric buzzer and a piezoelectric oscillator.
Here, the ultrasonic transducer 21 is used as an ultrasonic wave transmitter, and the ultrasonic
transducer 22 is used as an ultrasonic wave receiver.
[0033]
When an AC voltage of a frequency near the resonance frequency of the ultrasonic transducer 21
is applied to the piezoelectric vibrator, the ultrasonic transducer 21 operates as an ultrasonic
wave transmitter, and the operation shown in FIG. The ultrasonic wave is emitted to the
propagation path indicated by L1 in the inside, and the ultrasonic wave transmitter / receiver 22
receives the propagated ultrasonic wave and converts it into a voltage.
Subsequently, conversely, the ultrasonic transducer 22 is used as an ultrasonic wave transmitter,
and the ultrasonic transducer 21 is used as an ultrasonic wave receiver.
By applying an AC voltage of a frequency near the resonance frequency of the ultrasonic
transducer 22 to the piezoelectric vibrator, the ultrasonic transducer 22 transmits an ultrasonic
wave in the external fluid to the propagation path indicated by L2 in the same figure. The
ultrasonic transducer 21 receives the propagated ultrasonic wave and converts it into a voltage.
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Thus, since the ultrasonic transducers 21 and 22 serve as a receiver and a transmitter, they are
generally referred to as ultrasonic transducers.
[0034]
In addition, in such an ultrasonic flowmeter, when an alternating voltage is applied continuously,
ultrasonic waves are emitted continuously from the ultrasonic transducer and it becomes difficult
to measure the propagation time, so it is usually a pulse. A burst voltage signal using a signal as a
carrier is used as a drive voltage.
Hereinafter, the measurement principle will be described in more detail.
When a burst voltage signal for driving is applied to the ultrasonic transducer 21 and an
ultrasonic burst signal is emitted from the ultrasonic transducer 21, this ultrasonic burst signal
propagates the propagation path L1 with a distance of L to t After time, the ultrasonic transducer
22 is reached.
The ultrasonic transducer 22 can convert only the transmitted ultrasonic burst signal into an
electrical burst signal at a high S / N ratio.
The electrical burst signal is electrically amplified and applied again to the ultrasonic transducer
21 to emit an ultrasonic burst signal.
This device is called a sing-around device, and the time required for the ultrasonic pulse to
propagate from the ultrasonic transducer 21 and propagate in the propagation path to reach the
ultrasonic transducer 22 is called a sing-around period, The inverse is called the sing-around
frequency.
[0035]
In FIG. 2, let V be the flow velocity of the fluid flowing in the tube, C be the velocity of ultrasonic
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waves in the fluid, and θ be the angle between the flow direction of the fluid and the
propagation direction of the ultrasonic pulse.
When the ultrasonic transducer 21 is used as an ultrasonic wave transmitter and the ultrasonic
transducer 22 is used as an ultrasonic wave receiver, ultrasonic pulses emitted from the
ultrasonic transducer 21 are ultrasonic wave transducers 22. The following equation (1) is
established, assuming that the time around the time to arrive at is a time around t1 and the time
around frequency f1.
[0036]
(Equation 1) f1 = 1 / t1 = (C + V cos θ) / L (1) Conversely, the ultrasonic transducer 22 is used
as an ultrasonic wave transmitter, and the ultrasonic transducer 21 is used as an ultrasonic wave
receiver Assuming that the sing around period when used as t.sub.2 and the sing around
frequency f.sub.2, the relationship of the following equation (2) is established.
[0037]
(2) f2 = 1 / t2 = (C−V cos θ) / L (2) Therefore, the frequency difference Δf between both singaround frequencies is given by the following equation (3), and the distance of the propagation
path of the ultrasonic wave The flow velocity V of the fluid can be determined from L and the
frequency difference Δf.
[0038]
(Equation 3) Δf = f1−f2 = 2V cos θ / L (3) That is, the flow velocity V of the fluid can be
determined from the distance L of the propagation path of the ultrasonic wave and the frequency
difference Δf. Can be examined.
[0039]
Accuracy is required for such an ultrasonic flow velocity flowmeter, and in order to improve the
accuracy, an ultrasonic transducer that transmits ultrasonic waves to gas or receives ultrasonic
waves that have propagated gas is used. The acoustic impedance of the acoustic matching body
formed on the transmission / reception wavefront of the ultrasonic wave in the piezoelectric
vibrator that is being configured becomes important.
[0040]
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12
In this embodiment, the ultrasonic wave vibrated by the piezoelectric body 9 vibrates at a
specific frequency, and the vibration is transmitted to the case 2 through the epoxy adhesive as
the bonding means 12, and the epoxy bonding used as the bonding means 4. The agent is
transmitted to the acoustic matching body 6 formed of the ceramic porous body 5, and the
matched vibration is propagated through the acoustic film 5 as a sound wave to the gas which is
a medium present in the space.
At this time, the acoustic film 7 is in the form of a film, and the porosity in the vicinity of the
surface facing the fluid to be measured is lower than the porosity in the vicinity of the surface of
the acoustic matching body formed of a ceramic porous body. Because it is close to a flat surface,
the vibration of the acoustic matching member vibrated by the vibrator vibrates the fluid to be
measured (transmission), and conversely, the vibration of the fluid to be measured vibrates the
acoustic matching member (reception). It is provided to be able to do it efficiently.
[0041]
Thus, the role of the acoustic matching body 6 is to efficiently propagate the vibration of the
vibration means to the gas.
The acoustic impedance Z is defined by the velocity of sound C and the density ρ in the
substance as shown in equation (4).
[0042]
(Equation 4) Z = ρ × C (4) The acoustic impedance is largely different between the piezoelectric
body 9 which is the vibration means and the gas which is the radiation medium of the ultrasonic
wave.
For example, the acoustic impedance (Z0) of piezoceramics such as PZT (lead zirconate titanate),
which is a general piezoelectric material, is about 30 × 1000000 kg / m 2 · s.
Also, the acoustic impedance (Z3) of the gas as the radiation medium, for example air, is about
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400 kg / m 2 · s.
On such interfaces of different acoustic impedances, the propagation of the acoustic wave is
reflected, and the intensity of the transmitted acoustic wave is reduced. As a method of solving
this, with respect to each of the acoustic impedances Z0 and Z3 of the piezoelectric material
which is the vibration means and the gas which is the radiation medium of the ultrasonic wave,
the acoustic impedance having the relationship of the equation (5) between them is provided. It
is generally known how to reduce the reflection of sound and increase the transmission intensity
of the sound wave by inserting a substance.
[0043]
(5) Z = (Z0 x Z3) (1/2) (5) The optimum value when the acoustic impedance matching this
condition is matched is approximately 11 x 10000 kg / m2 · s. The substance satisfying the
acoustic impedance is required to be a solid, low in density and low in sound velocity as
understood from the equation (4).
[0044]
In the present embodiment, the acoustic matching body 6 is manufactured by firing a product
formed by a gel casting method in which a monomer is dissolved in a slurry of a bubbleintroduced oxide-based ceramic material and injected into a forming mold. The ceramic molded
body is made of a ceramic porous body sliced into a predetermined shape, and the density of the
acoustic matching body 6 is made as small as possible. Hereinafter, the method for producing a
ceramic porous body will be described in detail.
[0045]
FIG. 3 shows a manufacturing process flow of the ceramic porous body 5 used for the acoustic
matching body 6. The process comprises grinding the refractory ceramic, adding the additive to
the ceramic powder to form a slurry, introducing air bubbles, casting the slurry into a mold and
forming it, and firing. Details will be described below.
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[0046]
(Sintering-resistant ceramic pulverizing step) Pulverization of ceramic can be obtained by mixing,
pulverizing or the like with a ball mill, pot mill or the like. The average particle size of the
ceramic powder is not particularly limited, but is preferably 10 μm or less. When the ceramic
having an average particle diameter in this range is used, the powder dispersibility in the slurry
is improved, and the sinterability is also improved.
[0047]
(Slurrying Step of Ceramic Powder) 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 a suitable dispersant. As a dispersing agent, a polycarboxylic acid-based
dispersing agent (anionic dispersing agent) can be used, and specifically, ammonium
polycarboxylate and sodium polycarboxylate can be used. Preferably, a dispersant having a large
change in slurry viscosity with the added amount of 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.
[0048]
The ceramic slurry is removed before introducing the ceramic slurry bubbles, and the bubbles
are introduced while stirring the slurry. When bubbles are introduced into the ceramic slurry, a
gelling agent, and a polymerizable material comprising a monomer and a polymerization initiator
are added in order to form the desired shape. When a gelling agent is used, the slurry is gelled by
temperature control, pH control, and the like. Examples of the gelling agent include gelatin,
agarose, agar, sodium alginate and the like.
[0049]
When a polymerizable material is used, a monomer of the polymerizable material is used.
Specifically, monomers provided with one or more vinyl groups, allyl groups and the like can be
mentioned. When the slurry is composed of water or an aqueous solvent, it is preferable to use a
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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 water is prepared as a solvent in the slurry, preferably at least one
monofunctional (meth) acrylamide and at least one difunctional (meth) acrylamide are used. Use
in combination. When the slurry is prepared with an organic solvent, preferably, at least two
difunctional (meth) acrylic acids are used in combination.
[0050]
When a monofunctional monomer or a bifunctional monomer is used, ammonium persulfate,
potassium persulfide and the like are preferable. Moreover, when using the functional group
monomer which has a 2 or more functional group, Preferably, an organic peroxide, a hydrogenperoxide compound, an azo or a diazo compound is used. Specifically, it is benzoyl peroxide.
[0051]
The introduced gas is preferably retained in the slurry as bubbles by a surfactant or the like. The
surfactant is preferably added to the ceramic slurry prior to the introduction of air bubbles by
stirring or the like in the air bubble introduction step. Examples of the surfactant include anionic
surfactants such as alkyl benzene sulfonic acid and cationic surfactants such as higher alkyl
amino acids. Specifically, n-dodecylbenzene sulfonic acid, polyoxyethylene sorbitan monolaurate,
polyoxyethylene monooleate, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether,
and alkali metal salts such as sodium and potassium thereof It can be mentioned. In addition,
triethanolamine lauryl ether and the like and their halogenated salts, sulfates, acetates,
hydrochlorides and the like can be mentioned. Moreover, diethylhexyl succinic acid and its alkali
metal salt etc. can be mentioned.
[0052]
(Air Bubble Introduction Step) Air bubbles are introduced into the slurry produced as described
above. In the case of using a polymerizable material as the gelling material in this bubble
introducing step, 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 the gelation step can be adjusted by the gelation temperature and
the addition amount thereof. Usually, when a polymerization catalyst is added, gelation
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(polymerization) is rapidly started at 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. As a polymerization catalyst, N, N, N ', N'- tetramethyl
ethylene diamine etc. can be mentioned, for example.
[0053]
(Slurry Forming Step) The cell-containing ceramic slurry thus prepared is injected into a forming
die or the like and gelated to form a gel-like porous formed body. The slurry is poured into a
cylindrical mold containing a bubble-containing ceramic slurry and subjected to a polymerization
reaction or a gelation reaction to solidify. When the slurry solidifies, the bubbles present in the
slurry are also stored in the gel-like body. As a result, the solidified body becomes porous, and a
gel-like porous molded body is obtained. It is demolded, dried, degreased and fired. Drying is
carried out to evaporate the 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 component (gelling agent or polymer)
constituting the skeleton of the gel porous molded body. Usually, the temperature is 20 ° C. or
more, preferably 25 ° C. or more and 80 ° C. or less, and more preferably 25 ° C. or more and
40 ° C. or less.
[0054]
(Firing Step) Next, in order to remove the organic component from the dried product, the heating
is further performed at a high 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, Nmethylenebisacrylamide as a material for gelation, degreasing is performed at 700 ° C. for 2
days.
[0055]
After degreasing, a firing step is performed. The conditions for firing are set in consideration of
the type of ceramic material used and the like. By these steps, the ceramic porous body 11 of the
present invention can be obtained.
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[0056]
The ceramic porous body 11 is a porous body, and a plurality of voids exist. The voids are
preferably dispersed in the ceramic porous body 11. The voids may exist independently, may be
present continuously with other voids, and may be in communication with the outside. In the
acoustic matching body 10, it is preferable that the holes be continuously present.
[0057]
The ceramic porous body 11 as a whole means a porosity of 60% to 90% (here, a total porosity
including open pores and closed pores). Is preferred. More preferably, it is 80% or more and 90%
or less. The total porosity is determined by the following formula (3).
[0058]
Total porosity (%) = (1-bulk density / true density) x 100 (3) However, bulk density = weight of
sample / bulk volume of sample. True density, for example, an arbitrary amount of extremely
micronized sample is charged into a pycnometer, water is injected until a predetermined volume
is reached, and boiling is performed to eliminate voids, and from the relationship between weight
and volume, It can be asked. When the efficiency is 60% or less, the density 11 of the acoustic
matching body 1 becomes large, and when the pore diameter exceeds 90%, the mechanical
strength significantly decreases. The open porosity is more preferably 65% or more and 85% or
less. The open porosity is made as light as possible within the range allowed by the strength so
as to be close to low density and low sound velocity.
[0059]
The above materials and manufacturing conditions are optimized, and the density of the ceramic
porous body 11 of the acoustic matching body 1 in the embodiment of the present invention is
adjusted by adjusting it at 200 kg / m <3> or more and less than 400 kg / m <3>. A ceramic
porous body 11 of low strength and high strength could be realized.
[0060]
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Alternatively, for the porous ceramic body, a pore forming material is mixed with a material (for
example, alumina) forming the ceramic matrix, and the pore forming material is mixed with the
material forming the ceramic matrix and pressurized in a state of further firing treatment It may
be manufactured by the method of going, combining the said materials, and removing a pore
formation material.
The pore-forming material is formed of a material that melts upon firing, or a material that
dissolves in a specific solvent, and is, for example, an acrylic sphere (melts upon firing) or an iron
sphere (dissolves in sulfuric acid). The material forming the ceramic matrix may consist of the
main material forming the framework and the auxiliary material which is different in size from
the main material and which hardens the main material. The auxiliary material is, for example,
glass.
[0061]
As described above, in the present embodiment, the pores formed by the ceramic porous body 5
constituting the acoustic matching body 6 are sealed by the acoustic film 7, the bonding means 4
and the sealing means 8. Therefore, the skeleton of the ceramic portion of the acoustic matching
body 6 formed of the ceramic porous body 5 which is easily hygroscopic in nature is not
exposed, and the moisture absorption of the acoustic matching body is suppressed even if it is
left under temperature change or high temperature and high humidity. Therefore, good output
sensitivity can be maintained. Further, since the acoustic matching body 6 formed of the ceramic
porous body 5 is protected by the acoustic film 7, the bonding means, and the sealing means 8, a
part of the acoustic matching body formed of the ceramic porous body is missing There is no
need to worry about dusting.
[0062]
Furthermore, since the sealing means is disposed around the acoustic matching body disposed so
as to be in close contact with the outside of the case with the joined portion by the joining means,
the vibration of the piezoelectric body is transmitted to the acoustic matching body through the
case. The reverberation of the case generated during transmission can be dampened, and the
measurement accuracy can be improved.
[0063]
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Further, the ceramic porous body formed by the gel casting method, which constitutes the
acoustic matching body, forms a polymer network in the mold due to the radical polymerization
of the monomers in the slurry, and becomes a gel wet molded body. The flow process and the
solidification process are completely separated, and the particles are fixed in place, so that
nonuniformity and defects in the ceramic porous body 5 are less likely to occur, and it is about
10 for general pressure forming and cast molding. Since a double or more strength can be
obtained, a uniform structure is formed, and density variations are also small, even complex
shapes can be coped with and lightness and strength can be enhanced.
Therefore, a part of the acoustic matching body formed of the ceramic porous body may be
chipped or dusted during transportation, etc., and the acoustic matching body formed of the
ceramic porous body is less likely to adversely affect other devices. In order to make the
transmission and reception of ultrasonic waves more efficient, the density can be reduced.
[0064]
And since the acoustic film 7, the bonding means 4 and the sealing means 8 are made of resin
materials based on epoxy resin, as resin binders having high affinity to each other having
substantially the same properties, they become easy to bond and their strength As a result, the
generation of pores and the like can be suppressed in the joint portion between the acoustic film
and the sealing means or the bonding means and the sealing means, and the confidentiality is
improved, and the reliability against temperature change or high temperature and high humidity
is further improved. Can be improved.
[0065]
Further, since the acoustic film 7, the bonding means 4 and the sealing means 8 are based on
thermosetting resin having substantially the same curing conditions such as epoxy resin, the
acoustic film, the bonding means and the sealing means are individually Since it can be
simultaneously cured in one heating and curing step, it can be simplified and the number of
times of heating for curing can be reduced and its influence can be reduced. .
[0066]
Further, the acoustic film 7 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 the acoustic
matching body 6 formed of the ceramic porous body 5 Since a predetermined amount of resin
material can be applied to the surface of the acoustic matching body 6 formed of the porous
ceramic body 5 having irregularities and being easily sucked, the thickness of the acoustic film 7
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can be made to a predetermined thickness. The acoustic performance due to the change of the
film thickness of the acoustic film 7 can be stabilized.
[0067]
Second Embodiment FIG. 4 is a cross-sectional view of an ultrasonic transducer 30 according to a
second embodiment of the present invention.
In the present embodiment, the means for sealing by the acoustic film 7, the bonding means 4
and the sealing means 8 of the first embodiment is performed by another method, and the
structure of the sealing means is the same as that of the first embodiment. Only the differences
from the invention are given the same numbers, and only different configurations will be
described.
[0068]
As a procedure for sealing the pores of the acoustic matching body 6 formed of the ceramic
porous body 5 with the acoustic film 7, the bonding means 4 and the sealing means 8,
thermosetting is used as the bonding means on the surface of the case 2 having a sky shape.
After printing the resin material based on the flexible epoxy resin, the acoustic matching body 6
formed of the ceramic porous body is placed, and then the acoustic film 7 is made of a
thermosetting epoxy resin on the release film. After printing the resin material as a base, it is
rolled on the surface of the acoustic matching body 6 formed of the ceramic porous body 5 and
is fired at a predetermined temperature and time.
At this time, the acoustic film 7 and the bonding means 4 are based on a thermosetting resin
adhesive having substantially the same curing conditions of epoxy resin.
Next, an acoustic matching body formed of a ceramic porous body is formed by potting silicon,
which is the sealing means 8, onto the entire side wall of the acoustic matching body formed of
the ceramic porous body in this baked and hardened material. A sealing means is formed to seal
the pores of the
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[0069]
Since the pores of the acoustic matching body formed of the ceramic porous body are sealed in
this manner, an effect similar to that of the first embodiment can be obtained, and the acoustic
matching body formed of the ceramic porous body which is easily hygroscopic in nature. The
surface of the acoustic matching body is not exposed, and the moisture absorption of the
acoustic matching body is suppressed even if it is left under temperature change or high
temperature and high humidity, and good output sensitivity can be maintained. In addition, since
the acoustic matching body formed of the ceramic porous body is protected by the acoustic film,
the bonding means, and the sealing means, a part of the acoustic matching body formed of the
ceramic porous body is chipped or dust is generated There is no need to worry.
[0070]
Furthermore, since potting is performed around the entire side wall between the acoustic film
and the bonding means, the operation can be performed while visually checking at potting, and
the entire circumference of the side wall between the acoustic film and the bonding means can
be reliably adjusted. While you can pot.
[0071]
In addition, since the sealing means made of cold setting type silicon having flexibility is disposed
around the acoustic matching body disposed so as to be in close contact with the joining means
on the outer side of the hollowed portion of the case. Further, the reverberation of the case
generated when transmitting the vibration of the piezoelectric body to the acoustic matching
body through the case can be further suppressed, and the measurement accuracy can be
improved.
[0072]
Third Embodiment FIG. 5 is a cross-sectional view of an ultrasonic transducer 31 according to a
third embodiment of the present invention.
In the present embodiment, the means for sealing by the acoustic film 7, the bonding means 4
and the sealing means 8 of the first embodiment is performed by another method, and the
structure of the sealing means 8 is the first embodiment. The same number is assigned only to
the present invention, and only different configurations will be described.
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[0073]
The ultrasonic transducer 31 is formed by arranging a ring-shaped sealing member 8 such as
resin on the outer periphery of the acoustic matching body 6, and sealing the upper and lower
end portions thereof with the acoustic film 7 and the bonding means 4 As a configuration.
[0074]
Then, a ring-shaped sealing member 8 made of resin or the like is disposed and formed on the
outer periphery of the acoustic matching body 6, and the upper and lower ends thereof are
sealed by the acoustic film 7 and the bonding means. The sealing means can be formed only by
inserting the ring-shaped sealing member 8 on the outer periphery of the matching body 6, and
the time for forming the sealing means 8 can be shortened and the ring of resin etc. Since the
sealing member 8 in the form of a molded product is uniform on the outer periphery of the
acoustic matching body 6, the variation in the influence of the sealing member can be stabilized.
[0075]
Fourth Embodiment FIG. 6 is a cross-sectional view of an ultrasonic transducer 33 according to a
fourth embodiment of the present invention.
In the present embodiment, the means for sealing by the acoustic film, the bonding means, and
the sealing means of the first embodiment is performed by another method, and the
configuration of the sealing means is different from the invention of the first embodiment. Only,
the same number will be assigned, and only different configurations will be described.
[0076]
The ultrasonic transducer 33 dissolves a monomer in a slurry of an oxide-based ceramic material
into which bubbles are introduced or a slurry of an oxide-based ceramic material to which a
porous material such as an acrylic ball is added, and is then molded into a molding die. An
adhesive is applied to the outer shell surface of the ceramic porous body formed into a rod shape
by firing a material formed by a gel casting method to be injected to form a sealing means so as
to have a predetermined thickness, and then a predetermined shape is obtained. And the upper
and lower ends thereof are sealed by the acoustic film and the bonding means.
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[0077]
Then, an adhesive is applied to the outer shell surface of the ceramic porous body formed in a
rod shape so as to have a predetermined thickness to form a sealing means, and then it is sliced
in a predetermined shape. The matching body and the sealing means can be integrated, the
sealing means can be formed on a plurality of acoustic matching bodies at one time, the sealing
means can be easily stabilized, and the process can be simplified.
[0078]
Also, in order to transmit and receive ultrasonic waves more efficiently, the acoustic matching
body formed of a ceramic porous body is in the form of a ceramic porous body in which the
strength is maintained compared to before slicing, even if the density is reduced. The sealing
means formed by applying an adhesive, a paint, etc. to the outer shell surface of the body can
increase strength, prevent chipping at the time of slicing, etc., and also increase strength of the
sliced material. Handling of the matching body is facilitated.
[0079]
In addition, as long as it can be made and the structure of each other part is a range which
achieves the objective of this invention, the structure may be what.
[0080]
As described above, the ultrasonic transducer according to the present invention and the flow
measurement device using the same comprise an acoustic film, bonding means, and sealing
means in a conventional acoustic matching body formed of a fragile and fragile ceramic porous
body. Sealed, which improves mechanical strength and suppresses condensation of the acoustic
matching body due to temperature change or being left under high temperature and high
humidity, and makes it possible to suppress a decrease in output sensitivity due to condensation.
Therefore, it can be applied to applications such as automobile back sonar exposed to the open
air.
[0081]
Sectional view of the ultrasonic transducer according to the first embodiment of the present
invention Measurement principle of the ultrasonic flow velocity flow meter according to the first
embodiment of the present invention Illustration of ceramic porous body used for the acoustic
matching body according to the first embodiment of the present invention The figure which
shows the manufacturing process of a body The sectional view of the ultrasonic transducer in
Embodiment 2 of this invention The sectional view of the ultrasonic transducer in Embodiment 3
of this invention The ultrasonic transmission / reception in Embodiment 4 of this invention
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Cross-sectional view of a wave device An acoustic matching member partially enlarged crosssectional view for incorporation into a conventional ultrasonic transducer
Explanation of sign
[0082]
Reference Signs List 1 ultrasonic transducer 2 open case 4 bonding means 5 ceramic porous
body 6 acoustic matching body 7 acoustic film 8 sealing means 9 piezoelectric body
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