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JP2008193292

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DESCRIPTION JP2008193292
The present invention relates to an acoustic matching layer used in an ultrasonic transducer for
measuring the flow rate of a fluid such as a gas liquid, and in the case of bonding a porous
acoustic matching layer, the adhesive is an acoustic matching layer. The present invention is to
provide an ultrasonic transducer having stable characteristics by preventing it from being sucked
up and becoming an adhesive failure. An ultrasonic transducer according to the present
invention is configured to have a dense layer 2 on the adhesive surface of an acoustic matching
layer 1, so that the adhesive is absorbed by the acoustic matching layer 1 when adhered with an
adhesive. Can be eliminated, and an ultrasonic transducer with stable characteristics can be
obtained. [Selected figure] Figure 1
Acoustic matching layer and ultrasonic transducer and ultrasonic flow velocity / flow meter using
it
[0001]
The present invention relates to an acoustic matching layer used for an ultrasonic transducer
that measures the flow rate of a fluid such as a gas liquid, and to an ultrasonic transducer and an
ultrasonic flow velocity / flow meter using this acoustic matching layer.
[0002]
Conventionally, this type of ultrasonic transducer has a configuration as shown in FIG.
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FIG. 7 shows a cross-sectional view of the ultrasonic transducer 101, and 102 shows a cap-like
can case for housing the square columnar piezoelectric body 103. FIG. Reference numeral 104
denotes a two-layered acoustic matching layer provided on the can case 102. Reference numeral
105 denotes a ceramic porous body, and 106 denotes a dried gel of porous organic glass
contained in the ceramic porous body. A pedestal 107 is welded and joined to the can case 103,
and a conductive rubber 108 electrically connects the electrode terminal 109 and the
piezoelectric body 102. Reference numeral 110 denotes a sealing glass portion that electrically
insulates the electrode terminal 109 and the pedestal 107. Reference numeral 111 denotes a
ground terminal for electrically connecting the can case 103 and the pedestal 107 (see, for
example, Patent Document 1). Unexamined-Japanese-Patent No. 2004-45389
[0003]
In the conventional ultrasonic transducer 101 having such a configuration, the two-layer acoustic
matching layer 104 is bonded to the top surface of the can case 102 with an adhesive such as
epoxy. Since the acoustic matching layer 104 is composed of the ceramic porous body 105 and
the porous organic glass dry gel 106 contained in the ceramic porous body, the adhesive such as
epoxy is heated and cured with the temperature rise during the heat curing. The viscosity drops
sharply, the adhesive is absorbed by surface tension, and the adhesive disappears from the
interface between the acoustic matching layer 104 and the can case 102. As a result, the
adhesion becomes insufficient and the sensitivity of the ultrasonic transducer 101 is not good. It
had the problem of becoming stable.
[0004]
The present invention solves the above-mentioned conventional problems, and provides an
acoustic matching layer which does not absorb the adhesive, and an ultrasonic transducer
comprising the acoustic matching layer, and an ultrasonic vibration which can obtain stable
sensitivity. An object of the present invention is to provide an ultrasonic flowmeter with high
accuracy.
[0005]
In order to solve the above-mentioned conventional problems, the ultrasonic transducer
according to the present invention comprises a flat plate-like first porous body and a second
porous body contained in the first porous body, and the flat plate An acoustic matching layer
having a dense layer on at least one main surface of
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[0006]
According to this configuration, when bonding the acoustic matching layer, the dense layer
functions to suppress the penetration of the adhesive such as epoxy into the acoustic matching
layer, and the adhesive such as epoxy is formed between the acoustic matching layer and the can
case. The interface is not lost, stable bonding can be obtained, and an ultrasonic transducer with
stable sensitivity can be realized.
[0007]
In addition, by using this ultrasonic transducer, a highly reliable ultrasonic flow velocity / flow
meter can be configured.
[0008]
Since the ultrasonic transducer of the present invention is configured as described above, the
acoustic matching layer can be firmly joined to the can case, and it has characteristics excellent
in reliability, particularly long-term reliability.
Further, since a stable sensitivity can be obtained, it is possible to construct a highly reliable,
highly accurate ultrasonic flow velocity / flow meter by using this ultrasonic transducer.
[0009]
According to a first aspect of the present invention, the acoustic matching layer is formed of a
flat plate-like first porous body and a second porous body contained in the first porous body, and
a dense layer is formed on at least one main surface of the flat plate. Was formed.
With this configuration, when bonding the acoustic matching layer to a can case or the like, the
adhesive such as epoxy is suppressed from permeating into the dense layer of the acoustic
matching layer, so that it does not penetrate into the acoustic matching layer and strong bonding
is achieved. Thus, it is possible to realize an ultrasonic transducer in which stable sensitivity is
obtained.
Further, since a strong bond can be obtained, an ultrasonic transducer excellent in long-term
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reliability can be realized.
[0010]
In the second invention, in particular, the first porous body of the first invention is a non-oxide
ceramic having communicating holes formed by a sol-gel method.
[0011]
With this configuration, a porous ceramic having communicating holes can be easily formed, a
second porous body can be efficiently formed in the inside, and an acoustic matching layer with
excellent characteristics can be realized. it can.
In addition, the second porous body having a low strength can be protected, and the acoustic
matching layer can have a practically usable strength.
[0012]
In the third invention, in particular, the second porous body of the first invention is formed by
impregnating the first porous body with the sol-gel reaction solution.
By this configuration, the second porous body can be efficiently formed inside the first porous
body, and an acoustic matching layer with excellent characteristics can be realized.
[0013]
According to a fourth invention, in particular, the dense layer of the first invention is
impregnated with a heat-curable adhesive and formed in advance by heat-hardening. According
to this configuration, the dense layer can be easily formed. Thereby, when joining an acoustic
matching layer to a can case etc., an adhesive agent etc. will not permeate | transmit into an
acoustic matching layer, but strong joining is obtained.
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[0014]
In the fifth invention, in particular, the thickness of the dense layer of the fourth invention is set
to 1/100 or less of the wavelength of the used ultrasonic wave. According to this configuration,
an acoustic matching layer excellent in acoustic characteristics can be formed, and an ultrasonic
transducer excellent in characteristics can be realized.
[0015]
According to the sixth invention, in particular, the dense layer is provided on the side surface of
the flat acoustic matching layer of the first invention. With this configuration, practically
sufficient strength can be secured on the side surface of the acoustic matching layer without
impairing the acoustic characteristics, and an ultrasonic transducer with excellent characteristics
can be realized.
[0016]
In the seventh invention, in particular, the dense layer is provided on both main surfaces of the
flat acoustic matching layer of the first invention. With this configuration, it is possible to realize
an acoustic matching layer having a practically sufficient strength without deteriorating acoustic
characteristics, and to realize an ultrasonic transducer with excellent characteristics.
[0017]
In an eighth aspect of the invention, in particular, the acoustic matching layer according to any
one of the first to seventh aspects is joined to the top surface outside of the hollow cylindrical
case, and inside the top surface of the hollow cylindrical case. The piezoelectric members were
joined to constitute an ultrasonic transducer. Thereby, an ultrasonic transducer excellent in
acoustic characteristics can be realized.
[0018]
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According to a ninth aspect of the present invention, in particular, the ultrasonic transducer pair
according to the eighth aspect is provided so as to face the upstream side and the downstream
side of the fluid flow path with the fluid interposed therebetween. With this configuration, a
highly accurate ultrasonic flow velocity and flow meter can be realized.
[0019]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings. The present invention is not limited by the embodiments.
[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
having an outer diameter of 11 mm and a thickness of 0.75 mm, and 2 indicates a dense layer
having a thickness of 30 μm formed on the lower surface of the acoustic matching layer.
[0021]
A detailed view of the acoustic matching layer 4 is shown in FIG. In FIG. 2 (a), 3 represents a
ceramic porous body containing a large number of air bubbles, and 4 shown in FIG. 2 (b)
represents a porous organic glass made of organic glass or the like. 5 shows that a porous
organic glass is formed inside the ceramic porous body 3. FIG. 2D shows the acoustic matching
layer 1 and the dense layer formed on the lower surface of the acoustic matching layer 1.
[0022]
Hereinafter, the ceramic porous body 3 used for this kind of acoustic matching layer will be
briefly described.
[0023]
It is important that the properties required of the ceramic porous body 3 be small in density, that
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is, high in porosity, uniform in pore diameter distribution, and uniform in distribution.
In order to form such a ceramic porous body 3, a sol casting method in which a ceramic slurry
containing a large amount of bubbles is solidified and fired is suitable.
[0024]
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.
[0025]
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. At this time, air bubbles are formed as communicating holes in
the process of burning off the organic matter.
[0026]
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, this kind of ceramic porous body 3 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.
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[0027]
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. Thus, the ceramic porous body 3 having a porosity of about 85% or
more suitable for the acoustic matching layer 1 is obtained.
[0028]
Next, porous organic glass will be described. What is used for the acoustic matching layer 1 is
required to have a low sound velocity and a low density, and a porous organic glass is suitable.
The porous organic glass is prepared as follows. A glass raw material consisting of an organic
solution such as ethoxysilane or methoxysilane is diluted and dispersed in an alcohol solvent
such as methyl or ethyl in a sufficiently active state using a hydrochloric acid catalyst. The
diluted and dispersed solution is poured into the ceramic porous body 3 while adding a basic
catalyst such as aqueous ammonia. In this state, when held at 40 to 50 ° C. for 3 to 6 hours, a
porous wet gel is formed inside the ceramic.
[0029]
When this wet gel is formed again as a porous organic glass using a raw material solution such
as ethoxysilane or methoxysilane and a basic catalyst such as ammonia, it does not shrink even
when dried, that is, it hardly changes in volume. Porous organic glass is obtained. The porous
organic glass may be subjected to a hydrophobization treatment or the like depending on the
purpose of use. The hydrophobization treatment was carried out using a dimethyldiethoxysilane
solution and a basic catalyst such as ammonia. Thus, the ceramic porous body 3 including the
porous organic glass is obtained. The density of the acoustic matching layer 1 is about 0.47 [g /
cm <3>], the density of the ceramic porous body 3 is about 0.30 [g / cm <3>], and the density of
the organic glass is about 0. It was 20 [g / cm <3>].
[0030]
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An adhesive such as epoxy is formed by printing or transfer on one principal surface of the
acoustic matching layer 1 thus obtained, and heat curing is performed on a non-reactive flat
plate such as Teflon (registered trademark) to form a dense layer. 2 was formed. The dense layer
2 was made to be (1/100) or less of the ultrasonic wavelength to be used. If it is (1/100) or less
of the ultrasonic wavelength, the thickness can be acoustically ignored and the acoustic
characteristics are not impaired.
[0031]
As described above, the porous acoustic matching layer 1 composed of the first porous body and
the second porous body contained in the first porous body can be obtained. Further, since the
dense layer 2 is formed on one main surface, an adhesive such as epoxy is suppressed from
permeating the dense layer 2 of the acoustic matching layer 1 when the acoustic matching layer
1 is bonded to a can case or the like. The ultrasound matching with the acoustic matching layer 1
can be prevented, and a strong bond can be obtained, and an ultrasonic transducer with stable
sensitivity can be realized. Further, since a strong bond can be obtained, an ultrasonic transducer
excellent in long-term reliability can be realized.
[0032]
In the first embodiment, although the dense layer 2 is formed of an adhesive such as epoxy, it
may be formed of a sputtered film such as glass or metal, a vapor deposited film, a CVD film or
the like.
[0033]
Second Embodiment FIG. 3 shows a cross-sectional view of an ultrasonic transducer in a second
embodiment of the present invention.
In FIG. 3, 6 is an ultrasonic transducer, 7 is a cylindrical case with a hollow cylindrical shape, 8 is
a piezoelectric body joined to the inner surface of the can case 7, and the pedestal 9 is welded to
the can case 7 and its periphery And the piezoelectric body 8 is sealed. The conductive rubber 10
electrically connects the lower surface electrode of the piezoelectric body 8 and the terminal 10.
The terminal 11 is fixed to the pedestal 9 by an insulating material 12 such as a hermetic seal.
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The other terminal 13 is directly fixed to the pedestal 9 and connected to the upper surface
electrode of the piezoelectric body 8 through the can case 7.
[0034]
In this configuration, the acoustic matching layer 15 and the can case 7 are adhered and fixed
using an epoxy adhesive. FIG. 4 shows a cross-sectional photograph of the ultrasonic transducer
created in this manner. FIG. 4 (a) shows an acoustic matching layer 15 having a dense layer 14
and a can case 16 according to the present invention. An adhesive layer 17 made of epoxy was
clearly observed between the dense layer 14 and the can case 16. Reference numeral 18 denotes
a ceramic porous body portion, and a spherical portion 19 visible in the pores of the ceramic
porous body 18 represents porous organic glass. FIG. 4 (b) shows the acoustic matching layer 20
without the conventional dense layer 14. 21 shows a can case and 22 shows an epoxy adhesive
layer which has penetrated the acoustic matching layer 20.
[0035]
As seen in FIG. 4A, in the ultrasonic transducer comprising the acoustic matching layer 15 having
the dense layer 14 according to the present invention, the adhesive layer 17 is sufficiently
present at the interface between the acoustic matching layer 15 and the can case 16 It can be
seen that a strong bond is made. On the other hand, in the conventional ultrasonic transducer
comprising the acoustic matching layer 20 without the dense layer 14, the adhesive to be
present at the interface between the acoustic matching layer 20 and the can case 21 is absorbed
by the acoustic matching layer 20 by surface tension It can be seen that the epoxy layer 20 is
formed in the matching layer 20 and the epoxy layer to be at the interface between the acoustic
matching layer 20 and the can case 21 is eliminated. For this reason, it is difficult for the acoustic
matching layer 20 to be joined with the can case 21 with sufficient strength in the conventional
acoustic matching layer 20 without the conventional dense layer 14.
[0036]
The output characteristics of these ultrasonic transducers are shown in FIG. In FIG. 5, the
horizontal axis represents the sample number, and the vertical axis represents the output
characteristic value (relative value). In FIG. 5 (a), ● 23 shows the results of the output
characteristics of the ultrasonic transducer consisting of the acoustic matching layer 15 having
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the dense layer 14 according to the present invention and n = 9. The average value (relative
value) was 62.0 and the standard deviation was 2.9, that is, the output value (relative value) was
62.0 ± 2.9.
[0037]
In FIG. 5 (b), “□ 24” shows the result of the output characteristic of n = 9 ultrasonic
transducers made of the acoustic matching layer 20 without the conventional dense layer 14.
The average value (relative value) was 47.9 and the standard deviation was 5.8, that is, the
output value (relative value) was 47.9 ± 5.8.
[0038]
Thus, the ultrasonic transducer comprising the acoustic matching layer 15 having the dense
layer 14 according to the present invention has a larger output value than the ultrasonic
transducer comprising the acoustic matching layer 20 having no conventional dense layer 14,
The effect of reducing variation was obtained.
[0039]
These results show that in the acoustic matching layer 15 having the dense layer 14, the
adhesive such as epoxy does not penetrate into the porous acoustic matching layer 15 when
bonding, because the adhesive such as epoxy is present in the porous acoustic matching layer
15. It can be considered that there is a strong joint at the interface between the lower case and
the can case 7.
[0040]
On the other hand, in the acoustic matching layer 20 which does not have the conventional
dense layer 14, an adhesive such as epoxy is absorbed by the porous acoustic matching layer 20
and disappears from the interface between the acoustic matching layer 20 and the can case 7 It
is considered that the result was that bonding was not obtained.
That is, it is considered that adhesion failure occurs, the output value decreases, and the variation
increases.
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[0041]
The dense layer 14 may be on both the upper and lower surfaces of the acoustic matching layer
15.
In this case, it is not necessary to distinguish between the upper and lower surfaces, and the
productivity is greatly improved. Also, the acoustic performance is improved. It is considered that
this is because the thin dense layer 14 is formed on the upper surface for transmitting the
ultrasonic waves to the outside, so the transmission efficiency of the ultrasonic waves to the
outside is improved.
[0042]
Also, the dense layer 14 may be on the side of the periphery of the acoustic matching layer 15. In
this case, the strength of the porous acoustic matching layer 15 is greatly improved. That is, the
practical value is great such that destruction by assembly of the ultrasonic transducer or
handling of the element is eliminated.
[0043]
Third Embodiment FIG. 6 shows a cross-sectional view of an ultrasonic flow velocity / flow meter
according to a third embodiment of the present invention. Reference numeral 25 denotes a crosssectional view of an ultrasonic flow velocity / flow meter, 26 denotes a flow channel of fluid, 27
denotes an ultrasonic transducer according to the present invention provided on the upstream
side, and 28 denotes the present invention provided on the downstream side. Ultrasonic
transducer based. A solid arrow 29 indicates the flow direction of the fluid, and a broken arrow
30 indicates the propagation direction of the ultrasonic wave between the upstream transducer
27 and the downstream transducer 28. In the figure, θ indicates the crossing angle between the
fluid flow direction and the ultrasonic wave propagation direction.
[0044]
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In this configuration, ultrasonic waves are transmitted from the ultrasonic transducer 27 on the
upstream side, received by the ultrasonic transducer 28 on the downstream side, and ultrasonic
waves are transmitted from the ultrasonic transducer 28 on the downstream side, Transmission
and reception are alternately repeated so as to be received by the ultrasonic transducer 27. At
this time, the propagation time of the ultrasonic wave from the ultrasonic transducer 27 on the
upstream side to the ultrasonic transducer 28 on the downstream side is Tud, and the ultrasonic
wave from the ultrasonic transducer 28 on the downstream side to the ultrasonic transducer 27
on the upstream 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, then Tud = Ld / [Vs + Vf · cos (θ)] Tdu = Ld / [Vs−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 flow velocity Vf of the fluid is obtained. Furthermore, when the cross-sectional area Sr of
the flow path 26 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
26 are known in advance, the flow velocity Vf and the flow rate Qm of the fluid flowing through
the flow path 26 are measured as described above. Become.
[0046]
By using the ultrasonic transducer of the present invention, that is, in the ultrasonic transducer
having an acoustic matching layer made of a ceramic porous body and porous organic glass, the
output characteristics are output characteristics as compared with the conventional ultrasonic
transducers. Is large, it is possible to measure the flow velocity and flow rate of the fluid with
good S / N. In addition, since the acoustic matching layer and the can case are firmly joined to
each other, the mechanical strength is also large, so that a highly reliable ultrasonic flow velocity
and flow meter can be realized.
[0047]
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As described above, the ultrasonic transducer according to the present invention has a large
output characteristic, and since the acoustic matching layer and the can case are firmly joined, a
high-performance ultrasonic flow velocity excellent in reliability.・ A flow meter can also be
realized. Therefore, the present invention can be applied to household gas meters, water meters
and the like which require long-term reliability.
[0048]
Cross-sectional view of acoustic matching layer in the first embodiment of the present invention
Cross-sectional view of acoustic matching layer in the first embodiment of the present invention
Cross-sectional view of ultrasonic transducer in the first embodiment of the present invention
Fig. 6 is a photomicrograph of the cross section of the ultrasonic transducer taken at a
characteristic of the ultrasonic transducer according to the second embodiment of the present
invention. Cross section of
Explanation of sign
[0049]
1 acoustic matching layer 2 dense layer 3 ceramic porous body 4 porous organic glass 6
ultrasonic transducer 7 can case 8 piezoelectric body
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