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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer used in an apparatus or the like for measuring the distance between an
object existing in the air and the shape of an object by transmitting and receiving ultrasonic
signals. When configuring the ultrasonic wave 2g for air having an operating frequency of
several hundred KHz or more using the configuration of the conventional example and its
problems with the piezoelectric vibrator? As shown in FIG. 1, an acoustic matching layer Back load material 5 is bonded to the super .gamma.f wave radiation surface 2 and the
back surface 3 of the piezoelectric vibrator 1, respectively. -Polymers such as ricone resin (2
ingredients) were used in place of the material of η4. The acoustic innoyance of silicone resin,
which is often used, is about 1 x 106 NS / nf, and in order to achieve acoustic matching between
the piezoelectric vibrator 1 and air, a g9 matching layer material with a smaller acoustic
impedance is desired. It was For this purpose, the present inventor has proposed in the whole
past (a composite material made by mixing microspheres having a very small specific gravity
with a polymer material such as lycon resin as a filler material) as the acoustic matching layer
material. The above-mentioned conventional example or the proposal of the present inventor (A
polymer material such as silicone resin used as a matching layer material in / 'C or a composite
material thereof easily adsorbs dust and the like in the air to its surface Since the target strength
is also small, it has the disadvantage that the surface and the peripheral part are easily exfoliated
by receiving an external force. Further, as shown in FIG. 2, in order to protect the surface of the
acoustic matching layer 4 provided on the surface of the piezoelectric vibrator 1, a protective
member 6 made of a mesh such as a metal fine wire or a porous plate such as metal or plastic is
used. In the case of airborne ultrasonic waves of several hundred KHz or more, the wavelength is
as short as about 1 mm or less, so that the size of the protective member 6 is sufficiently smaller
than the wavelength of the ultrasonic waves. It is difficult for the ultrasonic wave to be scattered
by the protective member 6 and has a disadvantage that the ultrasonic wave attenuation is
increased. SUMMARY OF THE INVENTION The present invention provides an ultrasonic
transducer that eliminates the drawbacks of the conventional acoustic matching layer airborne
ultrasonic transducer, has very low ultrasonic attenuation, and can protect the acoustic matching
layer from dirt and mechanical damage. Purpose. The present invention was made in order to
achieve the above object, and by affixing a protective film in close contact with the surface of the
acoustic matching layer and stretching it, ultrasonic attenuation does not cause any trouble in
practical use of the ultrasonic transducer. It is an object of the present invention to provide an
ultrasonic transducer having a relatively small matching layer protective film. Description of the
Embodiments Embodiments of the present invention will be described below with reference to
the drawings.
FIG. 3 shows a cross-sectional view of an ultrasonic transducer according to an embodiment of
the present invention. In FIG. 3, 7 is a piezoelectric vibrator such as a piezoelectric ceramic
vibrator, 8 is an acoustic matching layer, and 9 is an optional one. It is a back load material to be
provided, and the acoustic matching layer 8 includes a multilayer structure such as a two-layer
or three-layer structure in addition to the single-layer matching structure. 10 is closely attached
to the surface of the acoustic matching layer 8 It is a plastic protective film. It is necessary that
the surface of the acoustic matching layer 8 and the plastic protective film 10 be completely in
close contact with each other so as not to interpose an air layer therebetween. Fig. 4 and Fig. 4
show the measurement results of the transmission / reception sensitivity peak value to the
transmission / reception sensitivity-frequency characteristics and the film thickness when the
film thickness is used as a parameter when a polyethylene terephthalate (polyester) thin film is
used as the plastic protective film 10. 5 is shown. The ultrasonic transducer used in this
measurement is an acoustic matching layer consisting of a composite material in which a silicone
resin is used as the base material and a very low specific gravity cari cloth is mixed on one side
of a piezoelectric ceramic transducer with a diameter of 30 mm and a thickness of 2.2 mm.
Furthermore, a plastic protective film is provided thereon, and a back load material is provided
on the other side. As can be seen from FIG. 4, as the film thickness of the plastic protective film
becomes thicker, the center frequency shifts to a lower frequency side, and in the case of a film
thickness of 9 μm, the central frequency decreases by about 10% compared to the case where
the plastic protective film is not provided. doing. In order to make the center frequency of the
ultrasonic transducer having a plastic protective film equal to the central frequency without the
protective film in anticipation of this reduction in central frequency, the center of the ultrasonic
transducer before the protective film is provided It is necessary to set the frequency high, which
makes it difficult to manufacture the acoustic matching layer 10 because it needs to be made
thinner. In addition, if the frequency becomes high, the ultrasonic attenuation in the acoustic
matching layer becomes large, and the transmission / reception sensitivity of the ultrasonic
transmitter-receiver is lowered. Further, from FIG. 5, the plastic protective film thickness at which
the transmission / reception sensitivity is reduced by 6 dB is about 8 μm, and this film thickness
corresponds to about 0.003 times the wavelength of the ultrasonic wave propagating through
the plastic. If the plastic protective film is thicker than 8 μm, the transmission sensitivity will be
reduced by 6 dB or more, or if the plastic protective film is not used, the ultrasonic wave is
applied to obtain the same level of receiving power. It is necessary to increase the transmission
voltage to two times or more. Therefore, it becomes difficult to design a power supply circuit of
the transmission circuit, and it is necessary to use a circuit element used for the transmission
circuit as a high breakdown voltage element, which causes a cost increase of the transmission
Therefore, it is desirable that the reduction of the center frequency by the plastic protective film
be 10% or less, but for this purpose, the thickness of the plastic protective film is made about
0.003 times or less of the wavelength of ultrasonic waves propagating in the plastic. There is a
need. As described in the embodiments of the invention, it is preferable to use a cocoon and
plastic 2.). Protective film 101 '; I so that there is no air layer between them (in a close contact
and stretched). (/)) C is cheap and 17% of air is interposed between the matching layer 8 and the
protective film 1o: 7 is transmitted / received by the protective film when 7 intervenes. IJ: It is
experimentally determined that the decrease is more than 20 dB (It). Furthermore, according to
the present invention In addition to polyethylene terephthalate, polypropylene (polypropylene),
simmer, etc. may be used. Effect of the invention 1 '), as described above (the ultrasonic
transducer of the present invention: the plastic thin film of about 0.003 times or less of one
wavelength as the protective film of the acoustic matching layer In this way, it is possible to
protect the matching layer from contamination and mechanical damage without greatly reducing
the sensitivity and the frequency of the ultrasonic transducer and the frequency of the ultrasonic
Brief description of the drawings
1 and 2 are sectional views of a conventional ultrasonic transducer, and FIG. 3 is a sectional view
of an ultrasonic transducer according to an embodiment of the present invention. FIG. 7 is a
diagram showing a small number of misfires 71, 7 2 2 1 '8 degrees peak values against the 7fold plastic protective film J of the present invention when 17 is a parameter.
7. Photoelectric film moving member, 8... Acoustic matching layer, 9... Back load material, 1 o ..
plastic 'protective film. The name of the representative 升 中 ト To? Toshio and one other person,
Fig. 1 J ・ '5 竿 2 Fig. Nose 1.15 3rd. , (CLB)
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description, jps60208199
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