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DESCRIPTION JPS61169099

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DESCRIPTION JPS61169099
[0001]
FIELD OF THE INVENTION The present invention relates to an ultrasonic transducer for
transmitting and receiving ultrasonic waves in air. 2. Related Art Recently, ultrasonic transducers
have been actively used in the field of distance measurement or position measurement sensors,
surface shape inspection sensors, and the like. This ultrasonic transducer is, for example, a ULTR
5 ONIC 5 (VOL, 16. S]CPTKMBKR,197B。 P19γ) and the present applicant as
described in the specification of Japanese Patent Application No. 58-44947, using a polymer
resin such as a silicone resin or an epoxy resin as a base material, in which glass, carbon or
plastic is spherical shell A configuration is known in which a thin layer made of a composite
material in which the hollow hollow spheres are mixed is used as an acoustic matching layer. The
conventional ultrasonic transducer will be described below with reference to FIG. In FIG. 4, 1 is a
piezoelectric vibrator for finely moving the thickness, 2 is a polymer resin matrix 6 such as
silicone resin or epoxy resin, and gas is contained as a filler using glass, carbon or plastic as a
spherical shell material. The composite material is a composite material in which fine hollow
spheres 3 having a flat particle diameter of about 10 μm are mixed, and is bonded to the
ultrasonic wave emitting surface 4 of the piezoelectric vibrator 1. A backing material 6 is
adhered to the second surface of the piezoelectric vibrator 1. Next, the operation of the above
configuration will be described. When the ultrasonic transducer is used in air to transmit and
receive ultrasonic waves, the composite material 2 is acoustically matched in order to obtain an
acoustic impedance match between the piezoelectric vibrator 1 and air acting as an acoustic load.
The transmission / reception sensitivity can be improved as compared with the case of acting as
a layer and using the piezoelectric vibrator alone. Problems to be solved by the invention
However, in the above configuration, firstly, as the polymer resin matrix 6 which is the matrix of
the composite material 2 forming the acoustic matching layer, silicone resin frfI or 27 m5 density
of 1000 to 1300 is obtained. Since the epoxy resin or the like is used and the density of the base
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material 5 itself is relatively large, the density of the composite material 2 can not be reduced.
Further, the density of the micro hollow spheres 3 mixed with the base material 6 as a filler is a
value of about 100 to eooKy / m 'for relatively small particle size conventionally used, and the
density of air at ordinary temperature of 1.2 KP Since it is very large compared with / m5, it was
difficult to reduce the density of the composite material 2 which used these as a filler.
Furthermore, when mixing the above-mentioned micro hollow spheres 3t to the base material 5,
the mixing volume ratio can not be made sufficiently large because the average particle diameter
has a size of several tens of μm, and therefore the density of the composite material 2 can be
reduced It was difficult.
As described above, it is difficult to reduce the density of the composite material 2 used as the
acoustic matching layer because of the density of the base material 6, the density of the micro
hollow spheres 3, and the size of the particle diameter. Second, the ultrasonic waves are scattered
by the hollow hollow spheres 3 because the diameter of the hollow hollow spheres 30 is not
sufficiently smaller than the wavelength of the ultrasonic wave propagating in the thickness
direction of the acoustic matching layer made of the composite material 2. The ultrasonic
attenuation in the acoustic matching layer is high. As described above, since the density and
ultrasonic attenuation of the composite material 2 used as the acoustic matching layer can not be
reduced, the transmission and reception sensitivity of the ultrasonic transducer is low. As a
specific example of the prior art, a composite material 2 in which thermally expandable
microballoons 3 having a density of 15 oKy / m "and a mean particle size of 5oμm are mixed
with a silicone resin having a density of 1000Kp / m 'at a weight ratio of 0.1. Density was about
640, 7 mB, and the speed of sound was 4801a / 11 p ultrasonic attenuation was about 10 dB / ff
at 1 M field. The present invention solves the above problems of the prior art, and aims to
improve the transmission and reception sensitivity of an airborne ultrasonic transducer by
realizing an acoustic matching layer material with small density and ultrasonic attenuation. It is
Means for Solving the Problems The present invention achieves the above object by bonding a
polymer film containing pores to an ultrasonic radiation surface of a piezoelectric vibrator to
form an acoustic matching layer. The present invention efficiently realizes acoustic impedance
matching between the piezoelectric vibrator and air acting as an acoustic load by realizing an
acoustic matching layer having a low density and a small ultrasonic attenuation by the agate
structure, in the air. The transmission / reception sensitivity of the ultrasonic transducer to be
used is improved. Embodiment Hereinafter, a first embodiment of the present invention will be
described with reference to the drawings. FIG. 1 is a cross-sectional view of an ultrasonic wave
according to a first embodiment of the present invention. 10 is a disk-type piezoelectric vibrator
that vibrates in thickness, 12 is a porous polymer film bonded to the ultrasonic wave emitting
surface 11 to act as an acoustic matching layer, 13 is pores included in the porous polymer film
12, and 14 is piezoelectric It is a backing material adhered to the second surface of the vibrator
1Q. The porous polymer film 12 is formed by forming an olefin-based hydrocarbon such as
polyethylene or polypropylene having a small density among polymer resins in a porous state by
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the phase separation method, and the film thickness is in the direction of thickness of the
polymer porous film 12 It is about the wavelength of the propagating ultrasound. The porous
polymer membrane 12 used in the present example is Asahi Kasei l polyolefin porous membrane
“HighBore 2000J, and the measured values of this density P and sound velocity are respectively
approximately ρ = 300 KP / m ′?
== 6001178 or so, so the acoustic impedance Za b-* 1.8 x 105 N, S / m! ′となる。 "The
porosity of the pores contained in HighBore 2000J is 70%, the average pore diameter of the
pores is 0.16 μm, the porosity is high, and the diameter of the pores is extremely small. When
the porous polymer film 12 is used in IMH, the diameter of the pore 13 is sufficiently smaller
than 9 with respect to the wavelength λ-0, 6ff of the ultrasonic wave propagating in the film,
and hence the ultrasonic wave is scattered by the pore 13 The resulting ultrasonic attenuation is
small. The measured value is about 3 dB / m at 1 MHz. The porous polymer film 12 is an
acoustic impedance between the piezoelectric vibrator 10 as an acoustic matching layer and air
serving as an acoustic load of the ultrasonic transducer. To improve the transmission and
reception sensitivity of the ultrasonic transducer. Here, the acoustic impedance p-: yxZ of the
piezoelectric vibrator 1 o is about 3 × 10 'N, S / ms. The acoustic impedance 7xZ of air is about
40 ON, S / m '. Accordingly, the acoustic impedance ZIIO of the acoustic matching layer for
obtaining the acoustic impedance matching between the piezoelectric vibrator 1o and air is Z! II
(+ = J 酊) q = 1.1 × 10 5 N, 57 m 5 or so [+7] size is desirable, but the acoustic impedance of the
porous polymer film 12 in the present embodiment 2. The measured value of is about 1.8 × 105
N, S / m ′, and has a value close to 2 m0 Nikanari. Moreover, it is also possible to use "Cel Bore"
manufactured by Mizu Chemical Industries, Ltd. as a polyolefin porous film having the same
performance as the above-mentioned polyolefin porous film "High bore 2000J." As is clear from
the above examples, according to this example, the density is extremely high using a low density
polyolefin resin as the polymer material and using the porous polymer membrane made porous
by the phase separation method or the elution method. In order to obtain an acoustic matching
layer which is small and hence has low acoustic impedance and low ultrasonic attenuation.
Therefore, by bonding the acoustic matching layer of the present embodiment to the ultrasonic
radiation surface of the piezoelectric vibrator, a highly sensitive ultrasonic transducer can be
realized. When the acoustic matching layer in the present embodiment is used in FIG. 2 or when
the acoustic matching layer made of a composite material in which micro hollow spheres are
mixed using the polymer material of the conventional example as a base material is used to make
a single matching structure. The results of calculation of transmission / reception sensitivity are
shown. The curve 20.21 shows the case where the acoustic matching layer in the present
embodiment is used, and the acoustic matching layer made of the conventional composite
material is used.
As can be seen from these results, it is understood that the peak value of the transmission /
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reception sensitivity is improved by about 6 (within iB) as compared with the conventional
example. FIG. 3 is a cross-sectional view of an ultrasonic transducer according to a second
embodiment of the present invention. The reference numeral 16 denotes a concave-type
piezoelectric member that vibrates in thickness, and the vibrators 11 to 14 are the same as in the
first embodiment. When the ultrasonic wave emitting surface 11 is a curved surface as in the
concave type piezoelectric vibrator in the present embodiment, it is difficult to form an acoustic
matching layer having a multilayer structure of two or more layers on the ultrasonic wave
emitting surface However, as shown in the present embodiment, it is easy to form the porous
polymer film 12 on the ultrasonic radiation surface 11 as a single layer of acoustic matching
layer. In the case of a more matched structure, in general, the pulse response characteristics of
the ultrasonic transducer are insufficient as compared with a multilayer matched structure of two
or more layers, but the simple matched layer structure is required when good pulse response
characteristics are not required. It is characterized by the fact that it is easier to manufacture by
using an ultrasonic transducer with more matching structure. The first one. When the porous
polymer film 12 is bonded to the ultrasonic wave emitting surface 11 of the piezoelectric
vibrator 10 or 16 in the second embodiment, the porous polymer film 12 generally has good
hydrophilicity because it is an open cell, and hence the bonding Agent penetrates into the porous
polymer membrane 12 and the density of the porous polymer membrane 12 is increased, and as
a result, the acoustic impedance may be increased and the transmission / reception sensitivity
may be reduced. By using the treated non-hydrophilic polymeric porous membrane, it is possible
to prevent the penetration of the adhesive. Also, the reliability can be enhanced with respect to
use conditions such as humidity. In the above example, it is obvious that the porous polymer
membrane 12 can have a smaller density than the conventional composite material because the
pores 13 do not have spherical shells of glass, carbon, plastic or the like as in the prior art. In the
above invention, a porous polymer membrane made porous by phase separation method or
elution method using an olefin hydrocarbon as a raw material is used, but an acoustic matching
layer is made of a polymer foam made of a polymeric material such as polystyrene and
polyurethane. It may be It is also apparent that the piezoelectric vibrator may use other vibration
modes other than thickness vibration. Furthermore, even when the acoustic matching layer has a
multilayer structure of two or more layers, the porous polymer membrane of the present
invention can be used as one of the acoustic matching layers. The effect of the invention In
summary, the present invention incorporates pores having a size sufficiently smaller than the
wavelength by bonding a polymer film with a thickness of the wavelength as an acoustic
matching layer to the ultrasonic radiation surface of the piezoelectric vibrator. An ultrasonic
transducer having high sensitivity can be realized as compared with an ultrasonic transducer
using a composite material in which conventional micro hollow spheres are mixed with a
polymer material as an acoustic matching layer, and the effect is large.
[0002]
Brief description of the drawings
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[0003]
FIG. 1 is a cross-sectional view of an ultrasonic transducer according to a first embodiment of the
present invention, and FIG. 2 is a comparison diagram of transmission / reception sensitivity to
the frequency of the ultrasonic transducer according to the embodiment of the present invention
and the prior art. FIG. 3 is a cross-sectional view of an ultrasonic transducer according to a
second embodiment of the present invention, and FIG. 4 is a cross-sectional view of an ultrasonic
transducer according to the prior art.
10.15 · · · · · · Piezoelectric vibrator, · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
· · · · · · · · · · · · · · · .... puff king material. Name of agent Attorney Nakao Toshio One other person
Fig. 13-Paper hole f 4--J White Kin τ 杆 f. + I-fit 放 third rI! J tp--MP + uu K T j-single pore 14-to
1 kin γ 1 IJ-JE (* Th) 1, <
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