JPH0644300

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DESCRIPTION JPH0644300
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
directional acoustic transducer for underwater acoustics, and in particular, a directional
transducer that can be used in a wide measurement frequency range as a standard device for
measuring the sensitivity of the transducer. About
[0002]
2. Description of the Related Art As a method of measuring the sensitivity of underwater acoustic
transmitters and receivers, it is possible to transmit between an object to be measured and a
standard whose transmitter sensitivity or receiver sensitivity is known. There is a method of
measuring wave or wave reception and converting the wave transmission sensitivity or wave
reception sensitivity of the object to be measured from the sensitivity of the standard. This
measurement method is generally performed in the sea and lakes, but at high frequencies it is
possible to measure in a water tank. In these measurements, the reflected wave from the water
surface, the tank wall, etc. and the acoustic noise coming from the surroundings should be
negligible compared to the direct wave. Therefore, in order to avoid reflected waves and ambient
noise, it is desirable that at least the standard products have appropriate directivity.
[0003]
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FIG. 2 is a sectional view showing a conventional directional transducer, and shows an
underwater transducer used as a standard product. In the figure, reference numeral 1 denotes a
piezoelectric vibrator as an electroacoustic transducer. The piezoelectric vibrator 1 is generally a
disk-shaped piezoelectric vibrator made of piezoelectric ceramics, for example, PZT (lead titanate,
zirconate), is polarized in the thickness direction of the disk, and is positive and negative on both
sides of the disk. Electrodes are formed. A two-core waterproof cable 2 is connected to each of
the positive and negative electrodes of the piezoelectric vibrator 1, and a waterproof rubber 3
molded to prevent exposure of the conductive parts of the piezoelectric vibrator 1 and the
waterproof cable 2.
[0004]
The directional transducer according to this configuration utilizes the thickness vibration mode
of the disk of the piezoelectric vibrator 1 and has an angle φ 1/2 at which the sensitivity is
reduced to one half of the width of the main pole. Assuming that the wavelength λ and the
diameter of the disk are d, for example, when λ / d = 1.4, it becomes a directional transducer
with an angle of φ1 / 230 °.
[0005]
However, in the directional transducer of the above configuration, when the measurement
frequency range is wide, the directivity of the standard product is sharpened at high frequency,
and is made to face the object to be measured. At low frequencies, the width of the main pole of
directivity widens and is susceptible to noise.
For this reason, it was necessary to replace the standard with different directivity according to
the frequency. For example, if d is 15 mm, then the measurement frequency range is 100 KHz to
300 KHz, φ 1/2 is 45 ° to 14 °, and appropriate directivity is obtained, but if the
measurement frequency range is 50 KHz to 600 KHz, 90 ° at 50 KHz However, the sensitivity
does not decrease to 1/2, and at 600 KHz, φ1 / 2 becomes 7 degrees, and there is a problem
that it is difficult to measure a wide frequency range.
[0006]
In the present invention, when the measurement frequency range is wide, the directivity becomes
sharp, and the alignment to face the object to be measured becomes difficult, the width of the
main pole of directivity widens at low frequencies, and reflected waves and In order to eliminate
problems such as being susceptible to ambient noise, a wide range of measurement frequencies
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can be obtained by stacking a plurality of piezoelectric polymers of different dimensions as
electro-acoustic transducers with slight gaps. The purpose is to provide an excellent device that
can be measured with one standard instrument.
[0007]
SUMMARY OF THE INVENTION A directional transducer according to the present invention uses
a plurality of piezoelectric polymers of different sizes as electroacoustic transducers, and only a
few of these piezoelectric polymers are used. A gap is provided to overlap, and each piezoelectric
polymer has a structure in which an electric signal transmission means is provided, and the
piezoelectric polymer is arbitrarily selected according to the measurement frequency.
[0008]
The present invention makes it possible to eliminate the need to replace the standard for a wide
range of measurement frequencies, while suppressing the effects of noise and facilitating the
alignment.
[0009]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing
an embodiment of a directional transducer according to the present invention.
In the figure, 4a, 4b and 4c are piezoelectric polymers different in size of three sheets, for
example, formed in a circle of 30 mm, 15 mm and 7.5 mm, respectively.
The piezoelectric polymers 4a, 4b and 4c as the electroacoustic transducers have a structure in
which they are overlapped with a slight gap, for example, the center of the following electrode
surface is on the axis perpendicular to the electrode surface. It is piled up to be located.
Positive and negative electrodes (not shown) are formed on both sides of the film surfaces of the
piezoelectric polymers 4a, 4b and 4c by Al or Ni evaporation or adhesion of Cu foil. 5 is a
waterproof cable of 3 pairs of 6 cores, and 2 cores of each pair are respectively connected to
positive and negative electrodes (not shown) of the piezoelectric polymers 4a, 4b and 4c to
constitute electric signal transmission means, 3 channels Output. 6 is a molded waterproof
rubber for waterproofing.
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[0010]
As the piezoelectric polymers 4a, 4b and 4c, generally, PVDF (polyvinylidene fluoride), P (VDFTrFE) (vinylidene fluoride / trifluoroethylene copolymer), P (VDCN) -VAC) (vinylidene cyanidevinyl acetate copolymer) etc. are known.
[0011]
Next, in the case of measurement using the directional transducer according to the above
configuration, first, if the two cores of the pair of waterproof cables 5 are selected, pointing using
the piezoelectric polymer 4c having an opening of diameter 7.5 mm Configure the transmitterreceiver.
Similarly, when another pair of two cores of the waterproof cable 5 is selected, a directional
transducer using a piezoelectric polymer 4b having an opening of 15 mm in diameter is
configured. Similarly, when another pair of two cores of the waterproof cable 5 is selected, a
directional transducer using the piezoelectric polymer 4a having an opening of 30 mm in
diameter is configured. Therefore, if the directional transducers 4a, 4b and 4c of the abovementioned opening have the frequency of 50 KHz to 150 KHz, 100 KHz to 300 KHz, and 200
KHz to 600 KHz, respectively, the fluctuation of .phi. be able to.
[0012]
As described above, if the channels are switched according to the measurement frequency, the
range of 50 KHz to 600 KHz can be easily measured without changing the standard.
[0013]
The structure in which the three piezoelectric polymers 4a, 4b and 4c can be stacked means that
the acoustic impedance of the piezoelectric polymer is close to the acoustic impedance of water,
and the acoustic transparency is good. It is in utilizing the material characteristics of.
Thus, for example, reference: M. B. Moffett, J.M. M. Powers and J.A. C. McGrath, "A cc
hydrophone", J. A. S. A. 80 (2), 1986, is a particularly suitable material for this example, as the
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acoustic impedance substantially matches the acoustic impedance of water. Also, Literature:
Kokura, Satoshi, Sakano, Transducer for underwater ultrasonic wave using piezoelectric
composite material , Technical report of IEICE, US90-30 (1990) mixed particles of PZT with
rubber material described in Is also a material suitable for the present embodiment.
[0014]
Also, in the above embodiments, the case where three piezoelectric polymers are stacked to
obtain three-channel output has been described, but the present invention is not limited to this,
and N (where N ≧ 2) Of course, it is also possible to obtain an N-channel output by stacking
piezoelectric polymers. This is because the acoustic impedance of the piezoelectric polymer is
close to the acoustic impedance of water, and the material property that reflection is small is
utilized.
[0015]
Although the shape of the piezoelectric polymer has been described as being circular, it is not
limited to this, and it is also possible to change the width of the main pole of directivity in any
shape such as square or oval, etc. Of course it is possible.
[0016]
As described above in detail, according to the directional transducer according to the present
invention, a plurality of piezoelectric polymers with different dimensions are provided as a slight
gap as an electroacoustic transducer. Since the directivity width can be made constant by
switching the channel according to the measurement frequency, the influence of noise can be
suppressed and the difficulty of alignment can be eliminated. effective.
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