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DESCRIPTION JPH05344582

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DESCRIPTION JPH05344582
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
low frequency band high power underwater 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 force is extremely large because the acoustic impedance is about 20 times or more
larger than that of water, there is a drawback that the displacement necessary for the medium
exclusion can not be taken in the acoustic radiation. 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.
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[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)), a bending and elongation transmitter using an elliptical shell shown in FIG. 5 is
known.
[0004]
SUMMARY OF THE INVENTION In the bending and elongation transmitter shown in FIG. 5, the
elliptical shell 21 is shown by an arrow in the drawing when the active columnar body 20 made
of piezoelectric ceramic is extended 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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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 elongation transmitter, the low frequency miniaturization is extremely difficult
because the resonance frequency of the elliptical shell itself is difficult to lower for the reasons as
described above.
[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]
Therefore, it is easy to think of a structure as shown in FIG. 2 as a compact transmitter that
overcomes the disadvantages of such conventional transducers. In the wave transmitter shown in
FIG. 2, two disc-shaped vibrators in which the active disc body 40 made of piezoelectric ceramic
is inserted into the metal disc 41 having the main surface depressed are prepared, and these are
prepared as the active disc body 40. Are bonded together with bolts 42 so that they are on the
outer surface side. As a driving principle of this transmitter, a disk-like vibration consisting of an
active disk 40 and a metal disk 41 in which the active disk 40 is fitted using a radial expansion
vibration in which the active disk 40 is displaced in the radial direction. The system is designed
to expand the displacement by converting it into bending vibration of the body. This transmitter
structure has the advantage that it can be easily made thinner and lighter without deteriorating
the water pressure resistance characteristics. However, since the periphery of the metal disk is
fixed, low frequency and high power are limited, and further low frequency and high power
require improvement.
[0008]
An object of the present invention is to provide an omnidirectional low-frequency transmitter
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which is compact and lightweight and has high power characteristics.
[0009]
[Means for Solving the Problems] The wave transmitter according to the present invention
comprises two disk-like vibrators comprising an active disk using a circular piezoelectric ceramic
and a disk having the active disk inserted therein. It is a low frequency underwater wave
transmitter characterized in that the active disks are connected to each other on the outer
surface side through a ring made of a high strength material.
[0010]
The transmitter according to the present invention improves the problems of the prior art by
adopting the above structure.
The following description will be made with reference to the drawings.
[0011]
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 circular piezoelectric ceramic. The active disk body 30
is polarized in the thickness direction, and by inputting a voltage along the polarization direction,
diameter spread vibration is excited. Furthermore, the active disc is bonded by means of a strong
adhesive to the inside of the recess of the metal disc 31 made of a material of high mechanical
strength such as high tensile steel. In FIG. 1, two such metal disks in which such an active disk is
fitted are prepared, and they are joined by a spring band 35 on the end face through an O-ring
32 made of a high strength material. Further, the outer periphery is molded with a urethane resin
34 or the like through a protective plate 33.
[0012]
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When the active disk is displaced radially by ξ1, the joint portion of the two metal disks, ie, the
O-ring portion becomes a support end, and the system of the active disk and the metal disk is
displaced by 中心 2 in the central axis direction Do. 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 takes bending vibration.
[0013]
In the wave transmitter of the present invention, the angular displacement of the metal disk
peripheral portion is made close to free (pin end support) by sandwiching the O-ring 32 made of
a high strength material between two metal disks. Since the active disk and the metal disk are
integrally vibrated, it is possible to easily make the device thinner, lighter, lower in frequency and
higher in power. FIGS. 3A and 3B show vibration modes with and without the O-ring 32
(axisymmetric, shown by a half model). In each of FIGS. 3A and 3B, a solid line indicates a
structural displacement diagram by modal analysis, a broken line indicates a structural prototype
diagram, and θa and θb indicate angular displacement in each case. By inserting the O-ring 32,
the bending vibration of the system in which the active disk and the metal disk are integrated is
performed in a state in which the support portion is close to the pin end support, and a low
frequency can be achieved. Furthermore, as shown in FIG. 3, the amplitude of the vibration mode
can be large as θa> θb, that is, the amount of medium to be excluded is also large, so that a
large sound pressure can be produced.
[0014]
The active disc used in the wave transmitter of the present invention tends to be somewhat
fragile in tensile stress, but in the present invention, as shown in FIG. 1, the active disc 30 is
formed on the outer surfaces of two metal discs. Further, compressive stress is applied to the
active disc 30 under hydrostatic pressure by determining the diameter of the active disc 30 to
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 wave transmitter
based on the present invention is excellent in water pressure resistance, and can be used at depth
(about 500 m in depth). In the present invention, the outer shape of the active body is preferably
a disk in terms of excellent simplicity, but is not limited thereto. For example, in order to actively
use the longitudinal effect longitudinal vibration of the piezoelectric ceramic, a structure in which
a large number of piezoelectric ceramic segments are arranged radially from the center as shown
in FIGS. 4A and 4B is also effective.
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[0015]
The invention of claim 3 will be described in detail with reference to FIGS. 4 (a) and 4 (b). In FIGS.
4A and 4B, reference numeral 50 denotes a piezoelectric ceramic segment group as an active
body. Each segment is polarized in the radial direction of the transmitter, and the polarization
directions of the adjacent segments are reversed. Longitudinal effect longitudinal vibration (33
modes) is excited by inputting a voltage along the polarization direction. This active segment
group is bonded by means of a strong adhesive to the inside of the recess of a metal disk 51
made of a material of high mechanical strength such as high tensile steel. In FIGS. 4A and 4B, two
metal disks in which such active segment groups are fitted are prepared, and are joined by a
spring band 55 via an O-ring 52 made of a high strength material. Further, the outer periphery is
molded with a urethane resin 54 or the like through a protective plate 53.
[0016]
The transmitter according to the present invention is characterized by actively utilizing the
longitudinal effect longitudinal vibration (33 mode) with high conversion efficiency. Therefore,
an active body portion made of piezoelectric ceramic is formed by radially bonding segments
polarized in the radial direction from the center, and a voltage is input in the radial direction for
each segment. At this time, the input voltage can be adjusted by appropriately setting the interelectrode distance of each segment, in consideration of the power consumption and the electric
field strength of the piezoelectric ceramic. It is also characterized in that pressure compensation
is applied by bolting 57 of the central portion of the transmitter via a tapered spacer 58 so that
compressive stress is always applied to each segment.
[0017]
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 7 mm, the diameter of the
metal disk 31 160 mm, the thickness 14 mm, the thin 7 mm, the inner diameter of the inserted
O-ring 32 140 mm, the thickness 8 mm 2, 2 The gap of each vibrating body was designed to be 4
mm. Therefore, the dimensions of the entire transmitter become 160 mmφ × 32 mm at the
stage before molding. A lead zirconate titanate piezoelectric ceramic is used for the active disk
30, an aluminum alloy A7075-T6 is used for the metal disk 31, and a maraging steel is used for
the inserted O-ring 32. The resonant frequency in air of this transmitter is 3125 Hz. For the
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radial displacement of the active disk, a displacement of about 17.1 times is obtained on the
central portion of the integrated system of the active disk and the metal disk, ie, on the central
axis of the transmitter.
[0018]
Next, according to the characteristics of the transmitter in the water tank, the sound pressure at a
point 1 m away from the acoustic radiation surface is 202 dBre and 1 μPa at 2500 Hz. In
addition, the Q value in water can also be obtained at a considerably low value of about 5.1. The
directivity is almost omnidirectional.
[0019]
Embodiment 2 Next, an embodiment of the present invention will be described with reference to
FIGS. 4 (a) and 4 (b). In FIG. 4, the active segment group 50 has a diagonal length of 180 mm, a
thickness of 7 mm, a diameter of the metal disk 51 of 200 mm, a thickness of 14 mm, a thin
portion of 7 mm, the insertion ring 52 has an inner diameter of 180 mm, a thickness of 8 mm,
The two vibrator gaps were designed to be 4 mm. Accordingly, the overall size of the transmitter
is approximately 200 mmφ × 32 mm. Although the outer shape of the active segment group 50
is configured as an octagon in FIG. 1, the outer shape is not necessarily limited to the octagon
and may be a regular polygon. A lead zirconate titanate piezoelectric ceramic is used for the
active segment group 50, an aluminum alloy A7075-T6 is used for the metal disk 51, and a
maraging steel is used for the insertion ring 52. The resonant frequency in air of this transmitter
is 2579 Hz.
[0020]
Next, regarding the characteristics of this transmitter at the water tank, the sound pressure at a
point 1 m away from the acoustic radiation surface is a sound pressure of 205 dBre 1 μPa at
2000 Hz. The Q value in water is also about 5.6, and the directivity is almost omnidirectional.
[0021]
As described above, according to the present invention, it is possible to obtain a non-directional
high-power low-frequency transmitter of small size, light weight and excellent in acoustic
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radiation efficiency.
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