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JPH06225380

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DESCRIPTION JPH06225380
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
compact, lightweight, low-frequency, high-power, flexible disk type underwater wave transmitter
used for long distance sonar, marine resource exploration, etc. is there.
[0002]
2. Description of the Related Art When a transmitter is placed in water, the outer wall is
subjected to a large pressure due to hydrostatic pressure. The pressure gets stronger as the
water depth gets deeper, and reaches 50 atmospheres at 500 m depth. Therefore, in a deep use
transmitter, the pressure due to hydrostatic pressure is canceled, and a pressure compensation
mechanism is required for the inside of the vibrating surface.
[0003]
Conventional pressure compensation mechanisms in low frequency transmitters generally use
compressed gas. The pressure compensation is performed by filling the inside of the transmitter
with a gas of the same pressure so that the surrounding water is in equilibrium with the pressure
by the hydrostatic pressure. There is also a method in which the inside of the transmitter is filled
with a liquid such as oil instead of the compressed gas to perform pressure compensation.
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[0004]
As an example of the prior art, a ring shell wave transmitter provided with a pressure
compensation mechanism in IEE processing (IEEE PROC., Vol. 131, Part F, No. 3, pp 275-279,
JUNE 1984) is shown It is done. The half section sectional view is shown in FIG. In the wave
transmitter shown in FIG. 3, when submerged in water, water can enter the boot 21 inside the
shell 20 via the glass fiber tube 22 to provide pressure compensation.
[0005]
The pressure compensation mechanism using compressed gas has a problem that the storage
room for storing high pressure gas becomes large because a general low frequency wave
transmitter has a large internal air gap structure. In addition, in order to set the gas pressure to
be balanced at the depth of use, changing the depth of use requires a complicated system that
can change the gas pressure of the compressed gas, which results in the miniaturization of the
transmitter. Was a factor to prevent
[0006]
The pressure compensation mechanism with oil or other liquid can eliminate the effect of depth
of use, but since the liquid such as oil has an acoustic impedance approximately two orders of
magnitude higher than high-pressure gas, the amplitude of the vibrating surface is suppressed,
and high-pressure gas A larger driving force is required to obtain the same sound pressure as in
use.
[0007]
Therefore, the conventional pressure compensation mechanism tends to be large in shape, and is
not suitable for reducing the size and weight of the transmitter.
[0008]
In the pressure compensation mechanism shown in FIG. 3, the inflow of water causes the air
pressure inside the shell 20 to rise, and the volume of the air chamber 23 to decrease.
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At 50 atm, the volume of the air chamber 23 becomes 1/50 of the original volume.
Due to this double adverse effect, there is a disadvantage that an increase in resonance frequency
and a decrease in transmission level occur.
[0009]
An object of the present invention is to provide a bent disk type underwater wave transmitter
having a pressure compensation mechanism which can cope with fluctuations in depth of use
without inhibiting small size and light weight and does not cause deterioration of efficiency.
[0010]
SUMMARY OF THE INVENTION In the present invention, two plate-like vibrators comprising an
active body using a piezoelectric ceramic and a disc having the active body inserted therein are
made of a material having a Young's modulus lower than that of the disc material. In a radial
bending disk type wave transmitter with active bodies bonded to each other on the outer surface
side, a pressure compensation mechanism in which the outer surface of the wave transmitter is
covered with an air bag connected to a narrow air gap inside the It is a bending disc type
underwater wave transmitter which has.
[0011]
FIG. 2 shows an example of the transmitter of the present invention.
The operating principle of the transmitter of FIG. 2 will be described in detail.
In FIG. 2, reference numeral 30 denotes an active disc body using a piezoelectric ceramic, in
which diameter expansion vibration is excited by inputting a voltage. The active disc is bonded by
means of a strong adhesive to the inside of a recess of a metal disc 31 made of a material of high
mechanical strength such as high tensile steel. In FIG. 2, two metal disks having such an active
disk inserted therein are prepared, and an adhesive and bolting 35 are made via a ring 32 made
of a material having a lower Young's modulus than metal and a high strength. It is joined.
Further, the outer periphery is molded with a urethane resin 34 or the like through a protective
plate 33.
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[0012]
When the active disk is displaced by ξ 1, the joint portion of the two metal disks serves as the
support end, and the system of the active disk and the metal disk is displaced by ξ 2. At this
time, ξ2 is larger than ξ1 and ξ2> ξ1. This is repeated, and the system integrated with the
active disk and the metal disk will cause bending vibration.
[0013]
In the wave transmitter of the present invention, since the active disk and the metal disk are
integrally vibrated, it is possible to easily reduce the thickness and weight. Furthermore, it is
characterized in that a ring 32 made of a material having a lower Young's modulus than a metal
and a high strength material is sandwiched between two metal disks in order to lower the
frequency. By inserting the ring 32, the bending vibration of the integrated system of the active
disk and the metal disk is performed as if the support portion is close to the pin end support, and
the frequency can be reduced.
[0014]
Furthermore, the principle of the pressure compensation mechanism of the present invention will
be described with reference to FIG.
[0015]
The pressure compensation mechanism of the present invention is comprised of an air bag 11
mounted on the outer surface of a bending disk type wave transmitter 10.
The air bag 11 is filled with air, and communicates with the air gap 13 in the central portion of
the transmitter through the tube 12 through a hole made in the side of the transmitter. When the
transmitter is disposed in water, the water pressure is applied to the outer wall of the transmitter
and at the same time the water pressure is also applied to the air bag 11, and the pressure causes
the air in the air bag to flow into the air gap 13 in the central part of the transmitter. . This
balances the surrounding water pressure and the pressure inside the transmitter. The connecting
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tube 12 passes through the portion between the two plate-like vibrating conductors in FIG.
[0016]
According to the pressure compensation mechanism of the present invention, even if the depth of
use changes, the outflow amount of air in the air bag can be automatically adjusted to achieve
pressure balance.
[0017]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG.
FIG. 2 shows the configuration of the bending disk type wave transmitter. In FIG. 2, the diameter
of the active disk 30 is 104 mm, the thickness is 7 mm, the diameter of the metal disk 31 is 160
mm, the thickness is 14 mm at the thick portion, 7 mm at the thin portion, the inner diameter of
the insertion ring 32 is 150 mm, the outer diameter 160 mm, the thickness It was designed with
2 mm. Accordingly, the thickness of the void portion is 4 mm, and its volume is extremely small.
In addition, the dimensions of the entire transmitter become 160 mmφ × 32 mm at the stage
before molding. Next, lead zirconate titanate piezoelectric ceramic was used for the active disk
30, aluminum alloy A 7075-T6 was used for the metal disk 31, and fiber reinforced plastic (FRP)
was used for the insertion ring 32.
[0018]
An embodiment in which a pressure compensation mechanism is mounted on the transmitter
shown in FIG. 2 is shown in FIG. The air bag 11 made of high strength resin is attached to the
outer surface of the bending disk type wave transmitter 10, and the air bag 11 and the air gap
13 in the central portion of the wave transmitter are made from the holes opened on the side of
the wave transmitter. It is connected via a tube 12. The size of the air bag 11 is designed
according to the depth of use. Assuming that the outer wall of the wave transmitter and the air
bag 11 are subjected to water pressure of 50 atm, the size of the air bag 11 is about 50 times the
volume of the air gap 13 in the center of the wave transmitter. Just do it. Here, the object of
application of the pressure compensation mechanism of the present invention is a bent disk type
transmitter shown in FIG. 2, and in this transmitter, the volume of the air gap in the central part
is as small as 70.7 cm 3 (cc) . Therefore, the volume of the air bag 11 is not so large as 3500 cc
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(3.5 liters), and not only the weight reduction but also the miniaturization in water can be
achieved.
[0019]
The resonant frequency in air of the prototyped transmitter is 2430 Hz.
[0020]
Next, this transmitter was put in water and driven at high power under 50 atm, and the sound
pressure at a point 1 m away from the acoustic radiation surface was measured, and a sound
pressure of 198 dBre 1 μPa was obtained at 1872 Hz.
The Q factor in water was also 5.8, and the directivity was almost omnidirectional, and almost no
deterioration in performance due to the pressure compensation mechanism was observed.
[0021]
As described above, according to the present invention, it is possible to cope with a change in
depth of use without impairing the feature of small size and light weight with respect to the
bending disk type wave transmitter, and the efficiency deterioration and the acoustic impedance.
It is possible to provide a pressure compensation mechanism that does not introduce a change in
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