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JPS6313498

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DESCRIPTION JPS6313498
[0001]
FIELD OF THE INVENTION The present invention relates to a high power underwater ultrasonic
transducer with broad band and omnidirectionality. (Prior Art) Conventionally, cylindrical
piezoelectric ceramic transducers operating in a radial mode as shown in FIG. 3 as is well known
are widely used as transducers having nondirectionality. The transducer shown in FIG. 3 has
silver or gold baked electrodes 31.32 formed on the inner and outer surfaces, and a DC high
electric field is applied between the electrodes 31.32 and polarization processing is radially
performed in the thickness direction as shown by arrows. It has been subjected. This transducer
expands and contracts in diameter uniformly by applying an AC voltage from the electrical
terminals 33. 34, so-called radial expansion with respect to the central axis O-θ 'in radial
oscillation mode (radial extensional mode). Omnidirectional acoustic radiation is provided from
the outer surface of the cylinder as indicated by the double arrows. [Problems to be Solved by the
Invention] The conventional cylindrical piezoelectric ceramic transducer can emit
omnidirectional acoustic radiation to the central axis, but has the following problems. As is
apparent from FIG. 3, all conventional transducers are made of piezoelectric ceramics.
Piezoelectric ceramics have a density of about 8. Since the sound velocity related to scratching is
3000 to 3500 m / sec at OX 10 "kg / m", the specific acoustic impedance (defined by the product
of density and sound velocity) is 24 x 10 'to 28 x 10' M K S It is nearly 20 times larger than the
intrinsic acoustic impedance of rayls and medium water, which is extremely large. This results in
mismatching of the acoustic impedance between the water and the transducer, resulting in
bandwidths limited to 15 percent to at most 30 percent. Therefore, for example, when a
conventional transducer is used in a sonar system, there is a drawback that the tailing of the
pulse becomes long and the distance resolution is degraded due to the narrow band
characteristic. In general, to obtain a compact pulse response characteristic with small pulse
tailing, a broad band transducer is necessary and indispensable. In order to obtain a wide band in
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cylindrical piezoelectric ceramic transducers, in order to improve the impedance matching with
water, it is necessary to reduce the mechanical impedance of the transducer (this corresponds to
the acoustic emission area. In the prior art, it has been necessary to reduce the wall thickness,
which corresponds to reducing the mass of the transducer.
However, if the thickness of the transducer is reduced, processing of the piezoelectric ceramic
becomes difficult, and the mechanical strength significantly deteriorates, and high power
acoustic radiation becomes impossible. An object of the present invention is to realize an
omnidirectional transducer having a wide band, high efficiency acoustic radiation characteristics,
and capable of high power transmission. SUMMARY OF THE INVENTION The basic construction
of the transducer according to the invention consists of a piezoceramic cylindrical oscillator
operating in the scratching vibration mode and a fiber reinforced composite material in which
the fibers are arranged in one direction only. The sheet made of the fiber-reinforced composite
material is one coated in the circumferential direction of the piezoelectric ceramic cylindrical
vibrator so that the fiber direction coincides with the central axis of the cylinder. Also, if
necessary, carbon fibers, glass fibers or aramid fibers may be strongly wound on the fiber
reinforced composite material sheet. That is, in the transducer according to the present
invention, a sheet made of a piezoelectric ceramic cylindrical vibrator and a thick fiber-reinforced
composite material having rigidity with respect to the central axis direction wound in multiple
layers integrally forms a uniform scratch. It is an omnidirectional underwater ultrasonic
transducer that operates in a series vibration mode. Operation A representative example of the
omnidirectional high power underwater ultrasonic transducer according to the present invention
is shown in FIG. In the perspective view of the transducer shown in FIG. 1, 11.11 'is a cylindrical
piezoelectric ceramic vibrator, 21 is a sheet made of a fiber reinforced composite material in
which fibers are arranged in the direction of the central axis of the cylinder. The outer surfaces of
the pieces 11 and 11 'are multiply wound with an organic adhesive. In the vibrator 11.11 ',
similar to the conventional cylindrical piezoelectric ceramic transducer shown in FIG. 3,
scratching is performed, and 11 and 11' are driven in phase. In order to achieve efficient acoustic
radiation, it is imperative that the cylinder 12 made of a fiber-reinforced composite sheet be
integrated with the vibrators 11 and 11 'and that the scratching be taken in the vibration mode.
It is desirable that the cylinder 12 be extremely rigid in the direction of the central axis O-O 'in
order for the transducer to vibrate uniformly. As shown in FIG. 2, the sheet 21 made of fiber
reinforced composite material used in the present transducer is arranged so that the direction of
the fibers (indicated by the arrow) coincides with the central axis of the cylinder (biaxially in FIG.
2) It must be. Further, in order to be easily wound around the cylindrical piezoelectric ceramic
vibrator 11.11 ', it is easier to manufacture the transducer if it is flexible in the X-axis direction of
FIG.
As such a material, glass fiber reinforced composite material (G-FRP). Carbon fiber reinforced
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composite materials (0-FRP) are preferred. Since the sheet 21 made of such a composite material
as shown in FIG. 2 contains no fibers in the circumferential direction, it has the speed of sound of
plastics which is a matrix in the radial vibration mode. This is smaller than the sound velocity of
piezoelectric ceramics. Therefore, with regard to the cylinder vibration mode, the transducer in
which the cylinder 12 is G-FRP or 0-FRP according to the present invention can be realized with
a smaller size than the conventional piezoelectric ceramic cylinder alone, which results in
miniaturization It is advantageous in terms of Furthermore, the transducer according to the
present invention has a significantly improved acoustic impedance match with water since the
effective mass per unit acoustic emission area is substantially reduced compared to conventional
transducers, and a broadband transducer can be obtained. Can be realized. As is well known,
piezoelectric ceramics are brittle against tension and strong against compressive force, and
therefore, it is more advantageous to use K under compressive bias stress in order to realize a
high power transducer. In the transducer according to the present invention, the composite
material sheet is wound with a certain degree of tension on the outside of the cylindrical
piezoelectric ceramic vibrators 11 and 11 ', in which case a certain optimum bias stress is
applied to the vibrator 11.11'. It is difficult to give stable in mass production. As a
countermeasure for this, it is extremely effective to supply a compressive stress to the
piezoelectric vibrators 11 and 11 'by winding glass fibers, carbon fibers or aramid fibers around
the surface of the cylinder 12 as necessary. An embodiment of a transducer according to the
present invention is also shown in FIG. In FIG. 1, 11 and 11 'are cylindrical piezoelectric ceramic
vibrators, and silver baked electrodes are formed on the inner and outer surfaces. Polarization is
performed by applying a direct current high electric field (4 KV / mm) in oil at 100 ° C. using
this electrode, and as is well known, the mobile elements 11 and 11 'have an anti-slip vibration in
the transverse effect 31 mode. In this case, the transducers 11, 11 'are driven in phase. 12 is a 0FTLP cylinder in which carbon fibers are arranged in the central axis 0-0 direction. A 0.5 mm
thick 0-FRP sheet is wound in five layers. In this case, an epoxy-based adhesive is applied to the
inside of the 0-FRP sheet so that compressive stress is applied to the piezoelectric vibrators 11
and 11 ', and the sheet is firmly wound while applying tension.
Therefore, the cylinder 12 exhibits high rigidity against bending deformation in the direction of
the central axis 0-0 ', and the scraping of the cylindrical piezoelectric ceramic vibrator is
indicated by a double arrow as a whole of the transducer in response to the vibration mode. As
such, uniform scraping can be vibrated in an oscillating mode. Furthermore, in the present
embodiment, the outer surface of the cylinder 12 is tightly wound with glass fiber for the
purpose of applying uniform compressive bias stress to increase the mechanical strength at the
time of operation. . The cylindrical vibrators 11 and 11 'in the present embodiment have exactly
the same shape, the wall thickness is 5 mm, and the height is triple M. The height of this
transducer is 12 and the outer diameter is 10 ffi. As is well known, the transducer of this
embodiment can maintain watertightness by molding the whole with neoprene / rubber by
making the upper and lower surfaces of the transducer side by side with a PRP disk, and in this
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state, the center frequency 9 is obtained. Operating at 5 KHz, both transmit and receive
sensitivities can achieve fractional bandwidths exceeding 40%. In addition, the present
transducer has a bias stress application mechanism with respect to the transducer 11.11 'and the
improved acoustic matching with water, so that the conventional cylindrical piezoelectric at the
acoustic radiation power per transducer unit mass. It is possible to greatly exceed ceramic
transducers. As described in detail above, according to the present invention, it is possible to
provide an underwater ultrasonic transducer excellent in wide band and high power
characteristics.
[0002]
Brief description of the drawings
[0003]
FIG. 1 shows an example of an omnidirectional cylindrical transducer according to the present
invention.
FIG. 2 is a view showing a fiber reinforced composite material used for the transducer of the
present invention. FIG. 3 is a view showing a conventional nondirectional cylindrical piezoelectric
ceramic transducer. In the figure, 11.11 'is a cylindrical piezoelectric ceramic vibrator, 12 is a
cylinder formed by winding multiple sheets made of a fiber-reinforced composite material, o-o' is
a central axis of the cylinder, and 21 is a composite material. A sheet 31.32 is an electrode, and
33.34 is an electric terminal. Figure 1 Figure 2 Figure 3
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