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(A) Industrial Application Field The present invention relates to an air ultrasonic transducer used
for measurement of distance and measurement of movement speed in the air. Mountain) Prior
Art FIG. 3 shows the structure of a conventional airborne ultrasound transducer. The figure
shows a longitudinal section, in which 2 is a vibrator composed of a piezoelectric element, 7 is a
resin plate forming an acoustic matching layer, and 8 is a case. The resin plate 7 and the vibrator
2 and the resin plate 7 and the case 8 are respectively bonded by an adhesive. Reference
numeral 3 denotes a substrate which covers the case 8 and is used for attaching lead terminals.
Two lead terminals 11 and 12 are attached. The vibrator 2 is provided with two opposing
electrodes, and is electrically connected to the lead terminal 11.12 through the lead wire. As
configured as described above, the vibrator 2 vibrates by supplying a drive signal of a
predetermined frequency between the lead terminals 11.12, and an ultrasonic wave is emitted
upward in the figure through the resin plate 7. . Also, microballoons of glass and organic
substance are dispersed in the upper resin and dispersed in a plate shape, and it is an acoustic
induction for matching the acoustic impedance CC (density × sound velocity) of the vibrator 2
and the acoustic interleaving of the air. It is set. This enhances the radiation efficiency of
ultrasonic waves into the air. (C) In the conventional airborne ultrasonic transducer of this type,
however, the number of parts is increased because a case, a vibrator, and a resin plate for
acoustic matching are used in manufacturing such a conventional airborne ultrasonic transducer.
There are problems of increased production cost and reduced reliability because many are
assembled by adhesion. An object of the present invention is to solve such conventional problems
and to provide a low cost and highly reliable airborne ultrasonic transducer. (D) Means for
Solving the Problems The air ultrasonic transducer according to the present invention is an air
ultrasonic transducer in which a transducer is accommodated in a case and an acoustic matching
layer is provided on an ultrasonic radiation surface of the transducer. In the use case, a low
density region is formed at the attachment portion of the vibrator at the time of molding of the
case, and this low density region is used as an acoustic matching layer. (E) Operation In the air
ultrasonic transducer according to the present invention, the vibrator is attached to a part of the
case, but the attachment is a low density area formed at the time of molding of the case.
Therefore, the low density region of the case has lower acoustic impedance than the other
regions, and acts as an acoustic matching layer.
(F) Embodiment FIG. 1 is a longitudinal sectional view showing the structure of an air ultrasonic
transducer according to an embodiment of the present invention. In the figure, 1 is a case, 2 is a
vibrator composed of a piezoelectric element, 3 is a substrate, and 4 is a lead. In the figure, the
upper part of the transducer 2 is an ultrasonic radiation surface, and is attached to the center of
the inner surface of the case 1. The vibrator 2 has electrodes formed on both main surfaces of a
disk-shaped piezoelectric ceramic, and in case attachment, the electrode for connection is drawn
out to the surface opposite to the surface. In the case 1, the area A to which the vibrator 2 is
attached is a low density area, and the other area B is a high density area. This concentrates the
microballoon in the area of A in the resin. Next, the method of producing the above-mentioned
air ultrasonic transducer will be described. FIGS. 2 (A) and 2 (B) show the manufacturing process
of Case 1, and 5 and 6 show a mold. First, a solution prepared by mixing microballoons of glass
or organic substance with epoxy resin is poured into a mold as shown in FIG. 2 (A). By keeping
the mold at a high temperature, the viscosity of the resin drops sharply, and the dense resin
component separates downward into two layers, the lower density microballoons. FIG. 2 (B)
shows this state. In the figure, reference numeral 10 denotes a microballoon represented
schematically, which is concentrated in the area indicated by A in FIG. By curing in this state, a
partial case including the acoustic matching layer is obtained. In this way, the process of
separately manufacturing the acoustic matching layer and the case and bonding them later can
be omitted. Also, a space for holding the vibrator is provided in the lower mold 6 shown in FIG. 2
(A), and a microballoon-like epoxy resin is poured in a state holding the vibrator, thereby causing
a vibrator for the acoustic matching layer. It is possible to simultaneously carry out the bonding
process of The thickness of the acoustic matching layer can be arbitrarily adjusted by the mixing
ratio of the resin and the microballoon. For this reason, there is no need for post-processing for
adjusting the thickness of the acoustic matching layer after molding of the case with a mold. Fg)
Effect of the Invention As described above, according to the present invention, the number of
parts decreases, Since the step of bonding the plate and the case becomes unnecessary, the
material cost and the manufacturing cost can be reduced.
Brief description of the drawings
FIG. 1 is a longitudinal sectional view showing the structure of an air ultrasonic transducer
according to an embodiment of the present invention, and FIGS. 2 (A) and 2 (B) are diagrams
showing the manufacturing process of a case constituting the transducer. It is.
FIG. 3 is a longitudinal sectional view showing the structure of a conventional air ultrasonic
transducer. 1-case, 2-oscillator, A-low density region. Applicant: Murata Manufacturing Co., Ltd.
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description, jph01190097
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