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JPH05219588

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DESCRIPTION JPH05219588
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
low frequency band high power underwater ultrasonic wave transmitter used for long distance
sonar, marine resource exploration and the like.
[0002]
2. Description of the Related Art In water, low-frequency ultrasonic waves have lower
propagation loss compared to that of high-frequency waves and can reach farther distances, so
low-frequency waves in areas such as sonars, marine resource exploration, and ocean current
surveys. The use of ultrasound has many advantages. 2. Description of the Related Art An
electrodynamic transmitter and a piezoelectric transmitter are conventionally known as
transmitters that emit high intensity ultrasonic waves in water. Although an electrodynamic
transmitter can take a large displacement, it is extremely difficult to obtain a small transducer at
low frequency due to the small generation force. Further, in the piezoelectric type wave
transmitter, a lead zirconate titanate based piezoelectric ceramic is used as an electromechanical
energy conversion material. Although the piezoelectric ceramic itself has an advantage that the
generated power is extremely large because the acoustic impedance is about 20 times or more
larger than that of water, there is a disadvantage that the acoustic radiation can not take the
displacement necessary for the medium exclusion. Considering that the acoustic radiation
impedance per unit radiation area becomes extremely small as the frequency becomes low, in
order to perform efficient acoustic radiation at low frequency, the displacement of the
piezoelectric ceramic is further expanded to perform acoustic radiation There is a need.
04-05-2019
1
[0003]
Conventionally, as a high power transmitter in a low frequency band (3 kHz or less), for example,
Journal of Acoustical Society of America (J. Acoust. Soc. Am. , Vol. 68, no. 4, pp. 1046-1052
(19800. 10)), there is known a bending and elongation transmitter using an elliptical shell shown
in FIG.
[0004]
SUMMARY OF THE INVENTION In the bending and elongation transmitter shown in FIG. 4, the
elliptical shell 21 is shown by an arrow in the figure when the active columnar body 20 made of
piezoelectric ceramic is stretched and displaced in the long axis direction. Thus, it is a transmitter
having a kind of displacement amplification mechanism that contracts at a displacement of a
multiple of the columnar body 20. (Only a quarter of the oval shell is shown by an arrow. The
resonance frequency of such a bending and elongation transmitter has a value twice or more of
the resonance frequency of the elliptic shell 21 itself because the stiffness of the active columnar
body 20 is considerably larger than that of the shell. That is, the low-frequency miniaturization of
the bending and stretching transmitter can not be achieved without considerably reducing the
resonance frequency related to the bending and stretching mode of the elliptical shell 21 itself
having a certain dimension, and the shell in the bending and stretching transmitter is A further
reduction of its resonant frequency is desired. However, for reasons to be described below, it is
extremely difficult to miniaturize the elliptical shell itself.
[0005]
In order to explain the operation of this elliptic shell, the major axis of the elliptic shell is made to
correspond to the x-axis, the minor axis to the y-axis, and the depth direction to the z-axis. . The
point at which the center of the thickness of the elliptical shell intersects the x-axis is (a, 0), and
the point at which the y-axis intersects is (0, b). That is, the major axis of the elliptical shell is a,
and the minor axis is b. Now, when the active columnar body 20 is extended and the point P is
displaced by + x in the + x direction, a displacement magnification mechanism of the elliptical
shell itself causes a displacement several times as large as -y in the -y direction at the point Q. It
will pull in the medium as a whole shell. On the other hand, when the active column shrinks, the
shell as a whole acts in the direction of removing the medium. In this case, the cross section
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2
obtained by cutting the elliptical shell along the x-axis is parallel to the x-axis, and translational
displacement is as if rolling the roller, and the rotational displacement about the z-axis is zero.
Therefore, the restriction on the movement of the shell is increased by the amount that rotation
about the z axis is not permitted, and the resonance frequency of the shell is increased. In the
bending and stretching transmitter, since the resonance frequency of the elliptical shell itself is
hard to lower for the above reasons, low frequency miniaturization is extremely difficult.
[0006]
On the other hand, when the shape of the elliptical shell is changed, the shell resonance
frequency certainly lowers as b / a is increased and the circle is approached. However, in this
case, as the b / a is increased, the displacement magnification ratio is significantly reduced
compared to the frequency decrease, and there is no merit of changing the shape and
downsizing. Also, it is recognized that the resonance frequency is lowered when the thickness of
the shell is reduced. However, in this case, not only the medium removing ability of the shell is
reduced but also the water pressure resistance is significantly deteriorated.
[0007]
It is an object of the present invention to eliminate such drawbacks of the conventional
transducers and to provide a non-directional transmitter which is compact in the low frequency
band and excellent in high power characteristics.
[0008]
The wave transmitter according to the present invention has two plate-like vibrators comprising
an active body using a piezoelectric ceramic and a disk having the active body fitted therein,
which has a Young's modulus more than that of the disk material. It is a low frequency
underwater ultrasonic wave transmitter characterized in that active bodies are bonded to each
other on the outer surface side through a low material ring.
[0009]
The transmitter according to the present invention improves the problems of the prior art by
adopting the above structure.
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The following description will be made with reference to the drawings.
[0010]
FIG. 1 shows an example of the transmitter of the present invention.
The operating principle of the transmitter of FIG. 1 will be described in detail. In FIG. 1, reference
numeral 30 denotes an active disk using a piezoelectric ceramic, in which diameter expansion
vibration is excited by inputting a voltage or a current. 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. 1, 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.
[0011]
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 expanded compared to ξ1, and ξ2> ξ1. This is repeated, and the system
integrated with the active disk and the metal disk will cause bending vibration.
[0012]
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. Further, it is
characterized in that a ring 32 made of a high strength material having a Young's modulus lower
than that of metal is sandwiched between two metal disks in order to lower the frequency. FIGS.
3A and 3B show vibration modes with and without the ring 32 (solid line) and without the ring
(dotted line). 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. Furthermore, as shown in FIG. 3, the amplitude of the vibration
mode can be large, that is, the volume velocity can be large, and a large sound pressure can be
produced.
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[0013]
The active disk used in the wave transmitter of the present invention tends to be somewhat
fragile in tensile stress, but in the wave transmitter of the present invention, as shown in FIG. 1,
the active disk is made of two metal disks. Compressive stress is applied to the active disc under
hydrostatic pressure by fitting it to the outer surface and further determining the diameter of the
active disc by about 60 to 75% of the diameter of the entire transmitter by stress analysis using
the finite element method. Can only be taken. Therefore, the low frequency underwater
ultrasonic wave transmitter based on this invention is excellent in water pressure resistance, and
can be used in depth (about 500 m of water depths). In the present invention, the outer shape of
the active body is desirably circular or rectangular, but is not limited thereto. Also, the material of
the disc is not necessarily limited to metal.
[0014]
Embodiment 1 An embodiment of the present invention will be described with reference to FIG.
In FIG. 1, 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. Therefore, 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, stainless steel SUS 304 was used for the metal disk 31,
and fiber reinforced plastic (FRP) was used for the insertion ring 32. The resonant frequency in
air of the prototyped transmitter is 3544 Hz. About the displacement of the active disk, about
19.5 times the displacement is obtained in the central portion of the integrated system of the
active disk and the metal disk.
[0015]
Next, this transmitter was placed in a water tank and driven at high power, and the sound
pressure at a point 1 m away from the acoustic radiation surface was measured. A sound
pressure of 203 dBre at 1 μmPa was obtained at 3000 Hz. The Q value in water was also as low
as 3.4. The directivity was almost omnidirectional.
04-05-2019
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[0016]
There is also a method of using an aluminum alloy instead of stainless steel as the metal disk. In
this case, since the acoustic impedance of the aluminum alloy is lower than that of stainless steel,
it is advantageous for the matching with water, and it is clear that the Q can be further reduced.
[0017]
Embodiment 2 Next, an embodiment of the present invention will be described with reference to
FIG. In FIG. 2, the disk type shown in FIG. 1 is rectangular, and an active body 40 in which
several lead zirconate titanate piezoelectric ceramics polarized in the width direction are
arranged is applied. At this time, the vibration mode of the active body is a longitudinal effect
with high conversion efficiency. In FIG. 2, the metal part is a rectangular metal shell 41, and
stainless steel SUS304 is applied to this part. Although FRP 42 is applied to a material having a
low Young's modulus inserted between two metal shells, in this case, two plates of FRP are used.
[0018]
In FIG. 2, the active body 40 has a length of 96 mm, a width of 85 mm, a thickness of 7 mm, a
metal shell 41 having a length of 96 mm, a width of 112 mm, a thick part of 14 mm, a thin part
of 7 mm, a length of FRP 42 per one The prototype was made to be 96 mm, width 14 mm, and
thickness 2 mm. The resonant frequency in air of the prototyped transmitter was 3598 Hz, and
about 11.5 times the displacement of the active body was obtained in the central part of the
integrated system of the active body and the metal shell.
[0019]
Next, this transmitter was placed in a water tank and driven at high power, and the sound
pressure at a point 1 m away from the acoustic radiation surface was measured, and a sound
pressure of 201 dBre 1 μmPa was obtained at 3000 Hz. The Q value in water was 4.5, and the
directivity was almost omnidirectional.
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[0020]
As described above, according to the present invention, it is possible to obtain a compact,
lightweight, non-directional, high-power transmitter excellent in acoustic radiation efficiency.
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