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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. (Prior Art) Since low frequency ultrasonic waves
in water have less propagation loss compared to that of high frequency waves and can reach far,
low frequency waves in the field such as sonar, marine resource exploration, ocean current
survey etc. The use of ultrasound has a number of 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
a low frequency due to the small generation force. In the piezoelectric type wave transmitter, a
lead zirconate titanate 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, the displacement of the
piezoelectric ceramic is further expanded to perform acoustic radiation in order to perform
efficient acoustic radiation at low frequencies. There is a need to do. Conventionally, for example,
Hr, S-Woollett as a high power transmitter in a low frequency band (3 KHz or less). As described
in Trend and Problem in 5 onar Transducer Design ', IEEE Trans, on Ultrasonics Engineering, I)
116-124 (1963, 11), a bending type transmission utilizing bending vibration of a disk shown in
FIG. Wave, or G, Brighamand B + Grass, "Present 5tatus in Flextens-ional Transducer 'rechnology',
J, Acoust, Soc. As described in U.S. Pat. No. 1,5, vvo 1.5 g, No. 4, pp. 1046-1052 (1980, 10), a
bending and elongation transmitter using an elliptical shell shown in FIG. 3 is known. (Problems
of the Prior Art) The bending type wave transmitter using a circular flat plate shown in FIG. 2
uses a circular bimorph oscillator as a wave transmitter as is well known. In FIG. 2, 10 is a lead
zirconate titanate piezoelectric ceramic plate, 11 is a metal plate of nickel, stainless steel or the
like, and these bodies are used as acoustic radiators.
また、12はキャビティ、13はハウジングケースである。 However, since the wave transmitter
shown in FIG. 2 can not obtain a large area piezoelectric ceramic plate as the piezoelectric
ceramic plate 10, by bonding a large number of segment ceramic plates to the metal plate 11 in a
mosaic manner. At present, bimorph oscillators have been obtained. That is, since the large-area
porcelain plate can not be used, the medium exclusion ability as a transmitter can not be said to
be sufficient, and it is unsuitable for high power transmission. Moreover, even if a large-area
piezoelectric ceramic plate is obtained, the bimorph oscillator is structurally very large in
deflection compliance, and it is not desirable to have a very large medium-removing capability.
Next, when the active columnar body 20 made of piezoelectric ceramic is stretched and displaced
in the long axis direction, the flexural shell shown in FIG. 3 is in the columnar state 20 as shown
by the arrow in the figure. It is a transmitter with a kind of displacement magnification
mechanism that contracts with several times displacement. (Only a quarter of the oval shell is
shown by an arrow. 2.) Since this transmitter uses an elliptical shell as an acoustic radiator, it has
a structurally greater rigidity than a bimorph disk, so a transmitter using the bimorph disk in FIG.
2 can be obtained. It is considered to be an excellent transmitter for high power transmission.
The resonance frequency of the bending and elongation transmitter shown in FIG. 3 is twice or
more 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, without reducing the
resonant frequency related to the bending and stretching mode of the elliptical shell 21 itself
having a certain size considerably, the low frequency miniaturization of the bending and
stretching transmitter can not be achieved. A further reduction of the shell's own common
frequency is desired. However, for reasons to be described below, it is extremely difficult to
miniaturize the elliptical shell itself. In order to explain the operation of this elliptic shell, the long
sleeve of 1 elliptic shell is made to correspond to y-axis, the minor axis to y-axis, the depth
direction to 2 axes, and a quarter part of the elliptic shell is shown in FIG. . The point at which the
center of the thickness of the elliptical shell intersects the y-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 + ξ in
the + X direction, a displacement magnification mechanism of the elliptical shell itself causes a
displacement several times as large as ξ 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 obtained by cutting the elliptical shell along
the y-axis is parallel to the y-axis, and the translational displacement is zero, just as if the roller
were transposed. Therefore, the restriction on the movement of the shell is increased by not
allowing rotation of z @ rotation, 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. On the
other hand, an attempt to reduce the frequency and reduce the frequency by changing the shape
and thickness of the elliptical shell is naturally conceivable. First of all, when the shape of the
elliptical shell is changed, the shell resonance frequency certainly decreases as the circle is made
larger and the circle becomes closer. However, in this case, the larger the value, the greater the
reduction in the displacement magnification rate compared to the decrease in the frequency, and
therefore there is no merit of reducing the size by changing the entire shape. Also, it is
recognized that the resonance frequency is lowered when the thickness of the shell is reduced.
However, in this case, there is a disadvantage that the medium removing ability of the shell is
reduced or the water pressure resistance is significantly deteriorated. SUMMARY OF THE
INVENTION It is an object of the present invention to eliminate the drawbacks of such
conventional transducers and to provide a compact, high-power bi-directional or omnidirectional
transmitter having a low frequency band. It is in. The wave transmitter according to the present
invention comprises an active columnar body using a piezoelectric ceramic or a magnetostrictive
material, non-active columnar bodies disposed on both sides of the active columnar body, the
active columnar body and the active columnar body A low frequency underwater ultrasonic wave
transmission comprising a lever connected to each end of each non-active columnar body via a
hinge and a convex shell connected to two levers via a hinge. It is a wave. (Detailed Description of
Configuration) The transmitter of the present invention solves the problems of the prior art by
adopting the above two-stage displacement enlarging mechanism. The following description will
be made with reference to the drawings. FIG. 1 shows an example of a transmitter according to
the present invention using a convex type shell. The operating principle of the transmitter of FIG.
1 will be described in detail. In FIG. 1, reference numeral 31 denotes an active columnar body
using a piezoelectric ceramic or a magnetostrictive material, and longitudinal vibration is excited
by inputting a voltage or a current. The active column 3 is hinged 32.32 'and is connected to the
lever 34 via the hinge 33.33'.
The system consisting of hinges and non-active columns is made of a material with high
mechanical strength such as high tensile steel, has a considerable rigidity for longitudinal
displacement, and works flexibly for deflection displacement. It is designed. As shown by the
arrow in FIG. 1, when the active columnar body is displaced by an amount, the lever 34 is rotated
inward by an angle θ to generate an enlarged displacement ξ at one end P% P ′ of the lever.
In this case, by using a material having a sufficiently large rigidity (for example, high tensile
strength stainless steel) for the lever, the lever exhibits almost rigid body rotation movement, and
between the hinges 32.33 (or 32 ', 33') Letting the distance of tl be the distance between the
hinge 33 and P (or 33 'and P'), the geometrically enlarged displacement ξ is l l e, l =, lξ, + (1)
Become. For example, if it is assumed that the beam displacement is 3 mm, then a 3-fold enlarged
displacement occurs at 2% 27 points with respect to the displacement ξ 1 of the active
columnar body. At this time, the non-active column acting as the fulcrum serves to transmit the
longitudinal vibration excited by the active column 31 efficiently to the lever 34, and the rigidity
of the N1 following movement is considerably large as described above. There is a need to. In
addition, when the lever 34 rotates around the fulcrum Q, Q 'by the angle θ, the hinges 32.32'
and 33.33 'in contact with the lever also undergo bending deformation by the angle θ to
generate a bending moment. . This bending will inhibit rotation, and the hinges 32, 32 ', 33' have small vertical compliance and large bending compliance, preferably hinges
(e.g. flat hinges). Furthermore, even if the lever 34 rotates by the angle θ with respect to the first
stage displacement enlarging mechanism of the present invention, the bending moment is offset
due to the structure, and the bending moment c generated in the active columnar body 31
becomes almost zero. It has smooth and excellent features. That is, since bending deformation
hardly occurs in the active columnar body, a robust first stage displacement enlarging
mechanism can be realized. With regard to the second-stage displacement magnifying
mechanism, when the longitudinal displacement is made at points P and P 'by only the wedge,
the displacement wedge further magnified by the shape effect of Conopex / El via hinges 35 and
35' is shown in FIG. It is given as indicated by the arrow. In this case, since the hinges 35 and 35
'effectively transmit the vertical position from the lever 34 to the shell, it is necessary to design
the rigidity against the longitudinal displacement to be large.
In addition, since it is necessary to reduce the common frequency of the yarn composed of the
shell 36.36 'itself and the hinges 35 and 35' for low-frequency miniaturization of the transmitter,
the hinge 35.35 'itself is against bending deformation. It is more effective to work flexibly. That
is, as the shell 36.36 'is in contact with the hinge 35', the hinge's deflection
compliance is made to be flexible against rotation as in accordance with the present invention as
compared to the case of rolling support not permitting rotation. When designed to be large, it has
become clear that the resonant frequency of the system consisting of the shell and the hinge is
experimentally lowered by approximately one half. Therefore, compared to the configuration in
which the convex shell 36. 36 'is directly bonded to the lever 34 without the hinges 35 and 35',
the transmitter according to the present invention can be further reduced in frequency and size.
As described above, since the wave transmitter of the present invention has a two-stage
displacement expanding mechanism, an extremely large displacement is given to the acoustic
radiation surface (the outer surface of the shell), and it can be said that it is compact and
excellent in acoustic radiation capability. . Furthermore, as another excellent feature of the
underwater ultrasonic low frequency wave transmitter according to the present invention,
displacement magnification of n times (n) 1 can be performed at the acoustic emission end with
respect to the displacement of the active columnar body. That is to say, the mass of the acoustic
radiation end can be reduced by a factor of 02 when converted to the active columnar side, and a
compact, lightweight, low-frequency transmitter can be obtained. Embodiment An underwater
ultrasonic wave transmitter using a convex shell as one embodiment of the present invention will
be described with reference to FIG. The wave transmitter using the convex shell shown in FIG. 1
was housed in a 10 crn thick F'RP housing case. At this time, in order to prevent the acoustic
coupling between the transmitter and the housing case and to prevent the rotational movement
of the lever 34 from being disturbed, an acoustic decoupling material mainly made of cork and
synthetic rubber is the lever 34 and the housing. It is arranged between the cases. The convex
shell which emits acoustic radiation uses a half part of an elliptical shell with a ratio of the minor
axis 2b to the major axis 2a of 0.4, and the long sleeve length of the shell is 2 a it, 50 cm, depth
aO cm 't '0, thickness is 1, Otyn ˜2. Ocm?!:した。 The lever, hinge and convex shell were
all high tensile steel. The resonant frequency in air of the manufactured transmitter is 470 H2.
About 12 times the displacement of the active columnar body is obtained in the central portion
of the convex shell.
Piezoelectric ceramic rings polarized in the thickness direction were stacked and bolted as active
columnar bodies. Next, this transmitter was placed in a water tank and driven by a noise
converter to measure the sound pressure at a point 1 m away from the acoustic radiation
surface. A sound pressure of 190 dB re 1 μPa was easily obtained. Also, the directivity is almost
omnidirectional at low frequencies, but exhibits directivity closer to bidirectionality as the
frequency becomes higher. As described above, according to the present invention, it is possible
to obtain a compact and lightweight bi-directional to non-directional high power transmitter
having excellent sound radiation efficiency.
Brief description of the drawings
FIG. 1 shows an example of a transmitter according to the present invention, FIG. 2 shows a
conventional bending transmitter, FIG. 3 shows a conventional bending transmission, and FIG.
The figure which shows the elliptical shell used for the conventional bending ¦ flexion elongation
In the figure, 10 is a piezoelectric ceramic plate, 11 is a metal plate, 12 is a cavity, 13 is a case,
20.31 is an active column, 21 is an elliptical shell, 31 'is an inactive column, 32.32', 33. The 33
'has a hinge, 36.36' Hakon Pesso Kwon. 31; Active tear-off "K threat 31 '; Non-stick PE # to * 32,
32'33.33': tZ: / S'34; Lever 35. 35 ': Hinge 36.31. '; Combera 2 Susoel / / 4' A 汲 12; Cavity 13:
Case 亭 3 Figure Zθ; Active ° Cs Ikt not zl;