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The present invention relates to a sound pressure gradient transducer for underwater acoustic
detection. A sound pressure gradient type transducer has been widely used conventionally as a
transducer having low frequency and directivity. This type of transducer has a low radiation
impedance because the radiation surface is smaller than the wavelength. Therefore, in order to
improve the sensitivity, it is necessary to lower the impedance of the transducer to increase the
efficiency of converting sound from mechanical vibration (or mechanical vibration into sound K).
However, since the transducer used in water needs to withstand hydrostatic pressure, a vibrator
with high stiffness has been used. Therefore, there is a disadvantage that the mechanical
impedance is increased and the acousto-mechanical conversion efficiency is reduced. Oh, I used
an electrodynamic type as a low stiffness vibrator, filled it with liquid, and there is one with an
internal / external pressure balance structure, but it has the drawback of low electromechanical
conversion efficiency. The present invention solves the above-mentioned drawbacks by annularly
bonding four or more diaphragms, and provides a transducer which is rigid against hydrostatic
pressure and soft against single sound pressure. A feature of the present invention is that four or
more diaphragms of the same shape are in annular contact with adjacent diaphragms in an easy
movable structure, and a sensor for detecting vibration displacement or vibration speed is
provided on four sides of this annular diaphragm. With this structure, a highly efficient sound
pressure gradient transducer with low stiffness to sound pressure is realized. Next, embodiments
of the present invention will be described with reference to the drawings. FIG. 1 shows a first
embodiment of the present invention, and is a perspective view partly in cross section. FIG. 2 is
an explanatory view of the principle according to this embodiment, showing a plane of a state in
which the upper lid is removed, 1-1.1-2.1-3.1-4, and 2-1.2- 2. As shown in 2-3.2-4, this structure
has a small thickness and is easy to be bent, and it is stretched diagonally in the vicinity of the
joint where the joint made the same angle 0 between adjacent diaphragms is the same and the
opposite joint Vibration displacement detection sensors 3 and 4, a lid 7.8 covering the upper and
lower end surfaces of the joined diaphragm, a patch 9.10 for maintaining watertightness between
the lid and the diaphragm, and the detection sensor It consists of an electric element 5.6 and a
support bar 11 supporting the upper and lower lids. The principle of operation will now be
described. First, considering the external water pressure applied when the transducer is
submerged, the four diaphragms have the same size structure and are joined at the same angle to
each other, so each diaphragm is directed toward the center Do not balance and deform each
other to receive the same force. Next, an award will be made based on the sound pressure t p (t)
of the sound coming in the Y-axis direction, and the operation of each diaphragm will be
considered in the case of receiving this.
If one of the distribution of sound pressure p (m) at a certain time t · = fllk Y axis is shown, it
becomes like FIG. The average pressure applied to the diaphragms 1-1 and 1-2 is 8 × pl (11) X 2
when the area of each diaphragm is t 7 S. Similarly, the average pressure h s xp 3 (b) × 2 applied
to the diaphragms 1-3 and 1-4 is obtained. Therefore, the difference in pressure between the two
is 8 × 2 (pm (tj-p L (Let), and each diaphragm is deformed as shown by 1-5.1-6.1-7.1-8 indicated
by a broken line). Is deformed in a shrinking direction as indicated by a broken line 3-1 to
generate a voltage. On the other hand, the sensor 4 is deformed in the extending direction as 4- 1
and generates a voltage of the opposite polarity to the former. Next, considering the point in time
when the sound wave is delayed by a half cycle, the polarity of the sound pressure distribution is
reversed, and each diaphragm is similarly deformed according to the same principle. That is,
although 0 or more from which an electrical output of double frequency is obtained comes in the
Y direction and is described as being embedded in the friend sound wave, it can be understood
by the same principle when coming from the X direction. また、X。 In the case of arriving from
other than the Y direction, the X component and Y component of the vector can be understood in
the same way. Therefore, it can be seen that the output voltages of the displacement sensors 3
and 4 show directivity as shown by 12 in FIG. Now, if a surface flexible material such as an
organic piezoelectric material is used for the displacement sensor, the junctions of the
diaphragms 2-1 ° 2-2. Since z-3 and 2-4 are movable structures, they are very flexible against
the force due to sound pressure, and a large displacement can be obtained. The above description
is given for the case where the sensors 3 and 4 have independent output terminals, however, the
polarities of the two may be reversed and connected in series for taking out, and the received
wave voltage sensitivity is increased. The position and number of sensors can be changed
according to the purpose. The number of diaphragms need not be limited to four, and may be
four or more. The structure of the bent portion is shown in FIG. 4 (A) (G) (in the form of a
concave, V or hinge on the outside as shown OK) There is no need to be air inside the diaphragm
Im, there may not be #J, and it may be filled with oil etc. In this case it is possible to thin the
packing 9, 10 so that the sound wave does not go inward. In addition, as a modification of this
embodiment, it is possible to consider a product filled with oil or a soft resin etc. except for the
lid 7.8. In this case, the diaphragm is displaced due to the sound pressure difference between the
front and back of each diaphragm, and the sensitivity is slightly reduced, but the restriction by
hydrostatic pressure is eliminated. The displacement sensors 3 and 4 may be of the
electrodynamic type or the like.
As described above, according to the present invention, it is possible to obtain a transducer
having low mechanical stiffness, high sensitivity, and directivity with respect to low frequencies
at which the radiation impedance becomes low.
Brief description of the drawings
FIG. 1 is a partially cut perspective view showing an embodiment of the present invention, FIG. 2
is an explanatory view of the principle of the present invention, FIG. 3 is a diagram showing
directivity, and FIG. It is a figure which shows the Example of a part.
1-1.1-2.1-3.1-4.1-5.1-6.1-7.1-8 ··········· Diaphragm, 2-1.2-2.2- 3.2-4 · · · · · · · · movable joints, 3, 4.
3-1.4-1 · · · · · · · · · · 5, 6 · · · · · · · · · electrical terminals, 7.8 · · · ... lid, 9.10 ...... Patsukin% 11-river ...
support rod, p (tl ······ sound pressure, pe) sound pressure of ...... time t · · P, 1 (t ·>, p! (K) Sound
pressure at Y1, Y2. 恭 l 薗 1 da