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DESCRIPTION JP2008193293

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DESCRIPTION JP2008193293
The present invention relates to a method of manufacturing an acoustic matching layer used for
an ultrasonic transducer, and in particular to provide an acoustic matching layer having stable
characteristics. SOLUTION: A predetermined amount of ceramic slurry 4 is charged into a mixing
vessel 3 consisting of a fixed volume, and the U-shaped rotor 6 is used to stabilize all the gas in
the mixing vessel of the fixed volume by being contained in the slurry. Produce a density acoustic
matching layer. [Selected figure] Figure 2
Manufacturing method of acoustic matching layer and ultrasonic transducer and ultrasonic flow
velocity and flow meter using it
[0001]
The present invention relates to an acoustic matching layer used for an ultrasonic transducer,
and more particularly to an acoustic matching layer made of a ceramic porous body which is an
inorganic material and a method of manufacturing the same.
[0002]
Conventionally, an acoustic matching layer made of this kind of inorganic material introduces
and mixes gas into the ceramic slurry containing the surfactant from the outside, and forms a
ceramic compact with a large amount of gas, that is, a large porosity, that is, a low density. It was
dried, fired and manufactured.
[0003]
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The acoustic matching layer thus produced is shown in FIG.
FIG. 12 shows a cross-sectional view of the acoustic matching layer 101, and 102 shows pores
constituted by communicating holes.
The acoustic matching layer 101 used for the ultrasonic transducer generally has a porosity of
80% or more and a density of 0.4 g / cm <3> or less in many cases (for example, Patent
Document 1) reference). Japanese Patent Application Publication No. 2001-261463
[0004]
In the conventional acoustic matching layer 101 having such a configuration, the density is not
stable because many pores consisting of communicating holes are introduced. Alternatively,
there is a problem that the characteristics of the ultrasonic transducer are not stable because the
pore diameter is largely dispersed.
[0005]
The present invention solves the above-mentioned conventional problems, and realizes an
acoustic matching layer having a stable density even if it includes many pores consisting of
communicating holes, a dense pore diameter, and an ultrasonic wave of stable characteristics. It
aims at providing a vibrator.
[0006]
In order to solve the conventional problems, the acoustic matching layer according to the present
invention injects a predetermined amount of ceramic slurry into a fixed volume mixer, and the
gas in the fixed volume mixer in the predetermined amount of ceramic slurry. Were mixed to
obtain a cell-containing ceramic slurry, to obtain a gel-like porous molded body, dried, degreased,
and fired to form a ceramic porous body.
In addition, a U-shaped rotor was used to mix the ceramic slurry and the gas.
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[0007]
Since the predetermined amount of ceramic slurry is introduced into the constant volume mixer
and all the gas in the constant volume mixer is contained in the ceramic slurry, the density of the
ceramic slurry containing gas is equal to the internal volume of the constant volume mixer and
Since it is determined by the amount of the ceramic slurry of a predetermined amount, it
becomes a ceramic slurry containing a large amount of gas of a stable density reproducibly. In
addition, since the gas is mixed with the ceramic slurry by the U-shaped rotor, dense pores are
formed, and a ceramic slurry having a large pore-free pore distribution can be obtained. The
ceramic slurry is dried and fired to form an acoustic matching layer. If an ultrasonic transducer is
configured with this acoustic matching layer, an ultrasonic transducer with excellent
characteristics and stable characteristics can be realized.
[0008]
The acoustic matching layer according to the present invention is excellent in acoustic
characteristics since the density is low, there are no large pores, and the pore distribution is
uniform, so an ultrasonic transducer with excellent characteristics and stable characteristics. Can
be realized.
[0009]
In the first invention, a predetermined amount of ceramic slurry is injected into a fixed volume
mixer, and all the gas in the fixed volume mixer is mixed into the predetermined volume ceramic
slurry, and the ceramic slurry contains bubbles. The gel-like porous molded body is dried,
degreased and fired to form an acoustic matching layer made of a ceramic porous body.
This makes it possible to obtain a ceramic slurry containing a large number of air bubbles with a
reproducible and stable density, and to realize an acoustic matching layer with stable
characteristics.
[0010]
In the second invention, in particular, when mixing the gas of the first invention into the ceramic
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slurry, the U-shaped rotor is used. As a result, it is possible to obtain a ceramic slurry in which
many fine bubbles are introduced, no large bubbles, and uniform pore diameter distribution, and
an acoustic matching layer with stable characteristics can be realized.
[0011]
In the third invention, in particular, the rotor of the second invention has a plurality of blades. By
this configuration, the introduction efficiency of the gas into the ceramic slurry is significantly
improved, and the miniaturization of the bubbles is promoted. As a result, an acoustic matching
layer with stable characteristics can be realized, and the result is an increase in productivity.
[0012]
In the fourth invention, in particular, the rotary blade central axis of the second invention is
inclined. With this configuration, upper and lower convection can be realized in the mixing of the
ceramic slurry, and the mixing efficiency can be greatly improved, and the ceramic slurry can be
made to flow to every corner in the constant volume mixer. The result is a significant
improvement in As a result, an acoustic matching layer with a uniform pore distribution can be
realized, and an acoustic matching layer with stable characteristics can be realized.
[0013]
According to a fifth aspect of the invention, in particular, the rotary blade central axis of the
second aspect of the invention is eccentric to the center of the constant volume mixer. By this
configuration, the flow of the ceramic slurry in the mixer becomes asymmetric, the mixing
efficiency of the slurry is improved, and the productivity is improved.
[0014]
In the sixth invention, in particular, the distance between the rotor of the second invention and
the side wall of the constant volume mixer is equal to or less than a predetermined distance. With
this configuration, when the ceramic slurry passes between the rotor and the side wall of the
mixer, the bubbles are further refined, and a dense ceramic slurry having a pore diameter can be
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obtained. For this reason, an acoustic matching layer excellent in acoustic characteristics can be
realized.
[0015]
In the seventh invention, in particular, an ultrasonic transducer is configured using the acoustic
matching layer manufactured by the manufacturing method according to any one of the first to
sixth inventions. According to this configuration, an ultrasonic transducer excellent in acoustic
characteristics and excellent in reproducibility can be realized.
[0016]
In the eighth invention, in particular, the acoustic matching layer of the seventh invention is
configured to be hydrophobic. According to this configuration, an ultrasonic transducer excellent
in reliability, particularly water resistance can be realized.
[0017]
In the ninth invention, in particular, a dense layer is provided on at least one main surface of the
acoustic matching layer of the eighth invention. With this configuration, it is possible to realize
an excellent ultrasonic transducer with further improved acoustic characteristics.
[0018]
In the tenth invention, in particular, the ultrasonic transducers according to the seventh to ninth
inventions are used as a pair and arranged so as to face the upstream side and the downstream
side of the flow path of the fluid through the fluid. It was decided to constitute a flow meter. With
this configuration, a highly accurate ultrasonic flow velocity and flow meter can be realized.
[0019]
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Hereinafter, embodiments of the present invention will be described with reference to the
drawings. The present invention is not limited by the embodiment.
[0020]
First Embodiment FIG. 1 shows a cross-sectional view of an acoustic matching layer according to
a first embodiment of the present invention. In FIG. 1, 1 indicates an acoustic matching layer. The
characteristics required for the acoustic matching layer 1 are generally required to have a low
acoustic impedance. Therefore, a material having a low density and a low sound velocity is
required. Therefore, it is comprised by the porous inorganic ceramic body containing many pores
2 which consist of communicating holes.
[0021]
Below, the manufacturing method of this kind of porous inorganic ceramic is demonstrated
easily. It is important that the properties required of the porous ceramic body be high in porosity,
uniform in pore size distribution, and uniform in distribution. In order to form such a porous
ceramic body, a sol casting method in which a ceramic slurry containing a large amount of
bubbles is solidified and fired is suitable. The steps of the sol casting method will be briefly
described. First, the ceramic powder material and the gelling material containing the crosslinking
agent, the catalyst, the surfactant and the like are sufficiently mixed. At this time, it is preferable
to use water or an organic solvent as a mixed medium. Thus, a ceramic slurry is formed. At this
time, a dispersant, a lubricant, a thickener, a sizing agent and the like may be added.
[0022]
Next, a foaming agent is added to the ceramic slurry, stirred and mixed, and a predetermined
amount of air bubbles are introduced into the slurry. In addition, if the ceramic slurry is
sufficiently degassed in advance before introducing air bubbles, the introduction amount of air
bubbles is stabilized. In this way, the ceramic slurry in which the bubbles are introduced is placed
in a mold so as to have a predetermined shape, and then molded. After drying, the resultant is
demolded, and an organic substance such as a surfactant is burned off to form a ceramic molded
body containing many bubbles.
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[0023]
Thereafter, the ceramic molded body is fired at a predetermined temperature and time. At this
time, when an oxide based material such as alumina based, mullite based or zirconia based is
used as the ceramic powder material, such a ceramic porous body can be formed relatively easily
by sol casting method. In addition, even if non-oxide ceramic materials such as silicon carbide,
silicon nitride, aluminum nitride, boron nitride and graphite are used, it is relatively easy to carry
out this kind of ceramic porous body by sol casting method. It can be formed.
[0024]
When a non-oxide ceramic material is used, the dimensional change before and after firing is
small, so the formability is good. In the case of ordinary oxide ceramic materials, the dimensions
before and after firing often shrink by about 10 to 50%, but in the case of non-oxide materials,
they slightly oxidize during firing and increase in volume. Since the dimensional change before
and after firing often falls below about 10 [%] in many cases, it is very suitable as a ceramic
porous body of this type.
[0025]
In the above-described steps, the most important step for stable production is the step of
introducing a predetermined amount of air bubbles into the slurry.
[0026]
The slurry mixer in Embodiment 1 of this invention is shown in FIG.
In FIG. 2, 3 shows the mixer of fixed volume. Reference numeral 4 denotes a ceramic slurry
which is deaerated and then introduced into the constant volume mixer 3. Reference numeral 5
denotes a lid for sealing the mixer 3, 6 denotes a U-shaped rotor, and an arrow 7 denotes the
rotation direction of the rotation shaft 8 of the rotor 6. When the U-shaped rotor 6 is rotated at
about 500 to 3000 rpm, in about 5 to 6 minutes, the ceramic slurry 4 becomes a bubblecontaining slurry containing residual gas in the mixer 3 and expands. The entire inside of the
mixer 3 will be filled. By mixing the slurry 4 in the constant volume mixer 3 in this manner, it is
possible to obtain a foam-containing ceramic slurry having a stable density, and realize the
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acoustic matching layer 1 made of a porous ceramic body having a stable density. be able to. For
example, assuming that the internal volume of the constant-volume mixer 3 is 500 [mL] and the
solid content equivalent after firing of the ceramic slurry 4 is 150 [g], the density of the porous
ceramic after firing is about 0.30 [V]. g / cm <3>]. At this time, the density of the porous ceramic
can be controlled by 0.30. ± .0.01 [g / cm <3>] by controlling the amount of slurry to be
charged to. ± .5.0 g. If the measurement accuracy is normal, ie ± 1.0 [g], a more stable porous
ceramic is obtained, and its density is controlled to 0.300 ± 0.002 [g / cm <3>]. It will be
[0027]
Next, FIG. 3 shows a conventional mixer. 9 indicates an open type mixer, 10 indicates an input
ceramic slurry, 11 indicates a bowl-shaped rotary blade, and an arrow 12 indicates the rotational
direction of the rotary shaft 13 of the bowl-shaped rotor. Conventionally, the bowl-shaped rotary
blade 11 is rotated at about 500 to 3000 rpm, and the height at which the ceramic slurry 10
contains gas and expands is adjusted by visual observation or the like to adjust the density of the
bubble-containing slurry. As a result, the density of the bubble-containing slurry becomes
unstable, and the characteristics of the acoustic matching layer made of porous ceramic also
become unstable.
[0028]
Also, conventionally, since a bowl-shaped rotor was used, a gas is trapped at the top portion 14
of the bowl-shaped rotor, and the gas is united at this portion, and the viscosity of the ceramic
slurry 10 and the rotational speed of the rotor etc. As a result, large bubbles are determined
depending on the balance with the above, and are released into the expanded bubble-containing
slurry in the mixing container 9. For this reason, in the conventional bubble-containing slurry, it
has become very difficult to remove large bubbles, which has been a factor to deteriorate the
characteristics as an acoustic matching layer.
[0029]
The external appearance photograph of the porous ceramic rod manufactured in this way is
shown by FIG. 4, FIG. FIG. 4 shows a porous ceramic rod 15 manufactured using the U-shaped
rotor according to Embodiment 1 of the present invention. The ceramic rod 15 has an outer
diameter of about 15 mm and a length of about 100 mm, and when used as an acoustic matching
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layer, it is cut into a disc shape. It shows a smooth surface.
[0030]
On the other hand, in the case of the porous ceramic rod 16 manufactured using the
conventional paddle-type rotary wing shown in FIG. 5, large bubbles of about 1 to 2 mm in outer
diameter are scattered at the tip of the arrow 17. Thus, when the slurry is mixed by the U-shaped
rotor according to the present invention, it can be seen that the porous ceramic has a smooth
surface and is composed of fine cells.
[0031]
FIG. 6 shows the distribution of pore sizes of these porous ceramic rods. In the figure, the
abscissa represents the pore diameter, and the ordinate represents the cumulative percentage
[%]. The solid line 18 shows the pore size distribution in the cross section of the ceramic rod
made of the ceramic slurry mixed with the U-shaped rotor according to the present invention, the
pore size rising from about 10 [μm] and about 100 to 150 [μm] The distribution showed a
cumulative percentage exceeding 80 [%]. On the other hand, the pore size distribution shown by
the dotted line 19 depends on the cross section of the ceramic rod manufactured from the
ceramic slurry mixed by the conventional paddle rotor. In this case, the pore diameter gradually
rises from about 10 [μm] and is about 500 [μm] and the cumulative percentage finally exceeds
80 [%].
[0032]
The densities of these porous ceramic rods were both about 0.30 [g / cm <3>].
[0033]
Second Embodiment FIG. 7 shows a mixer according to a second embodiment.
A difference from the first embodiment is that a plurality of U-shaped rotors are used. The two Ushaped rotary wings 20 and 21 are rotated in opposite directions with respect to the rotation
axes 22 and 23 as shown by arrows 24 and 25 respectively. By this configuration, the mixing
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efficiency was significantly improved, and the ceramic slurry 4 was able to expand and fill the
entire inside of the mixing container in several minutes at about 500 to 3000 rpm.
[0034]
Further, since the U-shaped rotors 20 and 21 are plural in number, the pore diameter contained
in the ceramic slurry is further refined, and the pore diameter distribution is as shown by the
dashed dotted line 26 in FIG. It was refined to a cumulative percentage exceeding 90 [%] at a
pore diameter of about 100 [μm]. This is considered to be the result of the relative velocity of
the rotors becoming very large and the air bubbles contained in the slurry being torn off because
the U-shaped rotors 20 and 21 rotate in reverse.
[0035]
Third Embodiment FIG. 8 shows a mixing container according to a third embodiment of the
present invention. The difference from the second embodiment is that the U-shaped rotor is
inclined. The two U-shaped rotors 27 and 28 rotate in reverse while inclining with respect to
each other. This configuration further improves the mixing efficiency of the slurry 4. That is, by
inclining the U-shaped rotors 27 and 28, it becomes possible to convectively mix the expanded
and filled bubble-containing slurry containing the gas up and down. As a result, the difference in
density which tends to occur up and down is also eliminated, and a more uniform bubblecontaining slurry can be obtained, and a stable acoustic matching layer can be manufactured.
[0036]
Fourth Embodiment FIG. 9 shows a mixing container 30 according to a fourth embodiment of the
present invention. In FIG. 9, the rotation center of the U-shaped rotor 29 is eccentrically fixed
from the center of the mixing container 30. By this configuration, the rotational flow of the slurry
4 becomes an asymmetric flow in the mixing vessel 30, and the mixing efficiency is improved.
Further, because of the asymmetry, the bubble-containing slurry is between the U-shaped rotor
29 and the mixing container 30 side wall in a portion close to the side wall of the mixing
container 30 of the U-shaped rotor 29 (right side in FIG. 9). Since the gas-containing air bubbles
are crushed, the air bubbles become finer and finer.
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[0037]
That is, the flow is rapid on the right side of FIG. 9 and is a slow flow on the left side. As a result
of adding strength and weakness to the asymmetric flow generated by the U-shaped rotor 29 as
described above, it can be considered that miniaturization is further advanced. This tendency was
particularly observed when the distance between the U-shaped rotor 29 and the side wall of the
mixing vessel 30 was several mm or less.
[0038]
Fifth Embodiment FIG. 10 shows a cross-sectional view of an ultrasonic transducer in a fifth
embodiment of the present invention. From the ceramic rod described in the above embodiment,
a disc having an outer diameter of 10 to 11 mm and a thickness of 0.75 to 1.00 mm was cut out
to form an acoustic matching layer. The density of the acoustic matching layer 32 was about
0.30 [g / cm <3>], and the speed of sound was about 1500 [m / s].
[0039]
In FIG. 10, reference numeral 31 denotes an ultrasonic transducer, and reference numeral 32
denotes an acoustic matching layer, which are adhered and fixed to the upper surface of the caplike can case 33. A piezoelectric body 34 is adhesively fixed to the inside of the can case 33.
Electrodes made of baked silver or the like are provided on the upper and lower surfaces of the
piezoelectric body 34. Further, the lower periphery of the can case 33 was fixed by welding to
the pedestal portion 35. The conductive rubber 36 electrically connects the lower surface
electrode of the piezoelectric body 34 and the terminal 37. The terminal 37 is fixed to the
pedestal 35 by an insulating material 38 such as a hermetic seal. The other terminal 39 is
directly fixed to the pedestal 35 and is connected to the upper surface electrode of the
piezoelectric body 34 through the can case 33.
[0040]
In this configuration, when a high frequency voltage is applied between the terminals 37 and 39,
the piezoelectric body 34 vibrates, and the vibration is emitted as an ultrasonic wave from the
surface through the acoustic matching layer 32. The ultrasonic transducer composed of the
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acoustic matching layer 32 having such stable characteristics has a very uniform output
characteristic. That is, in the ultrasonic transducer based on the present invention, the output
variation, which was conventionally about 100 ± 5 [%], is less than 100 ± 2 [%] in the zero
output variation.
[0041]
Further, by subjecting the acoustic matching layer 32 made of porous ceramic to a
hydrophobization treatment, it is possible to obtain a highly reliable ultrasonic transducer that
exhibits particularly excellent characteristics of moisture resistance. That is, the deterioration of
the output was not recognized even in the high temperature and high humidity test. It is
considered that this is because the acoustic matching layer 32 made of porous ceramic has been
subjected to a hydrophobization treatment, so that condensation and the like no longer occur
inside.
[0042]
The output can be further improved by providing a dense layer, for example, a thin epoxy sheet,
a thin glass print layer, or a deposited layer of glass, metal or the like on the surface of the
acoustic matching layer 32. It is believed that this makes the surface smoother and the
ultrasound output is larger. That is, since the unevenness of the porous ceramic surface is
eliminated and the surface is smooth, it is considered that the energy of the ultrasonic vibration
is transmitted to the outside more efficiently.
[0043]
Sixth Embodiment FIG. 11 shows a cross-sectional view of an ultrasonic flow velocity / flow
meter according to a sixth embodiment of the present invention. 40 is a cross-sectional view of
an ultrasonic flow velocity / flow meter, 41 is a flow channel of fluid, 42 is an ultrasonic
transducer according to the present invention provided on the upstream side, 43 is an invention
provided on the downstream side. Ultrasonic transducer based. A solid arrow 44 indicates the
flow direction of the fluid, and a broken arrow 45 indicates the propagation direction of the
ultrasonic wave between the transducer 42 on the upstream side and the transducer 43 on the
downstream side. In the figure, θ indicates the crossing angle between the fluid flow direction
and the ultrasonic wave propagation direction.
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[0044]
In this configuration, ultrasonic waves are transmitted from the ultrasonic transducer 42 on the
upstream side, received by the ultrasonic transducer 43 on the downstream side, and ultrasonic
waves transmitted from the ultrasonic transducer 43 on the downstream side, It is alternately
repeated to be received by the ultrasonic transducer 42. At this time, the propagation time of the
ultrasonic wave from the upstream ultrasonic transducer 42 to the downstream ultrasonic
transducer 43 is Tud, and the ultrasonic wave from the downstream ultrasonic transducer 43 to
the upstream ultrasonic transducer 42 is Assuming that the propagation time of the sound wave
is Tdu, the propagation speed at which the ultrasonic wave propagates in the fluid is Vs, and the
flow velocity of the fluid is Vf, It becomes cos (θ)]. Ld indicates the distance between the
ultrasonic transducers. From these, Vs + Vf · cos (θ) = Ld / Tud Vs−Vf · cos (θ) = Ld / Tdu, and
by subtracting these two sides, 2 * Vf · cos (θ) = (Ld / Tud) − ( Ld / Tdu) = Ld * [(1 / Tud)-(1 /
Tdu)] Accordingly, Vf = {Ld / [2 · cos (θ)]} * [(1 / Tud) − (1 / Tdu)], and the fluid flow velocity Vf
is obtained. Furthermore, when the cross-sectional area Sr of the flow path 41 is multiplied, it
becomes the flow rate Qm.
[0045]
That is, Qm = Sr * Vf becomes the measured flow rate value. As described above, since the
distance Lp between the ultrasonic transducers and the cross-sectional area Sr of the flow path
41 are known in advance, the flow velocity Vf and the flow rate Qm of the fluid flowing in the
flow passage 41 are measured as described above. Become.
[0046]
By using the ultrasonic transducer according to the present invention, that is, in the ultrasonic
flow velocity / flow meter comprising an ultrasonic transducer having an acoustic matching layer
made of a porous ceramic body, the ultrasonic output characteristics are stable. Therefore, it can
be manufactured with high yield. In addition, since the reliability of the ultrasonic transducer is
high, a highly reliable ultrasonic flow velocity and flowmeter can be realized.
[0047]
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As described above, since the ultrasonic transducer according to the present invention has a
stable ultrasonic output, it is possible to realize a highly reliable, high-performance ultrasonic
flow velocity / flow meter having excellent reproducibility.
[0048]
Therefore, it is applicable to applications such as household gas meters and water meters that
require high performance and long-term reliability.
[0049]
Sectional view of the acoustic matching layer in Embodiment 1 of the present invention Sectional
view of the mixing container in Embodiment 1 of the present invention Sectional view of the
conventional mixing container The external appearance photograph of the porous ceramic rod in
Embodiment 1 of the present invention The figure which shows the figure which shows the
external appearance photograph of the conventional porous ceramic rod The pore distribution
figure in Embodiment 1 of this invention The sectional view of the mixing container in
Embodiment 2 of this invention The cross section of the mixing container in Embodiment 3 of
this invention Cross-sectional view of the mixing container in the fourth embodiment of the
present invention Cross-sectional view of the ultrasonic transducer in the fifth embodiment of the
present invention Cross-sectional view of the ultrasonic flow velocity and flow meter in the sixth
embodiment of the present invention Cross section of layer
Explanation of sign
[0050]
1 acoustic matching layer 2 pore 3 constant volume mixer 4 ceramic slurry 6 U-shaped rotor
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