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Industrial Field of the Invention The present invention relates to a sound generator, in particular
to a sound generator for underwater acoustic generation. [Description of the Related Art] In
water, low frequency is used for various marine technologies such as sonar, marine resource
exploration, fish school guidance, etc., because the transmission efficiency is high compared to
high frequency. The conventional underwater sounding body utilizes the piezoelectric
phenomenon as one of its principles. In JP-A-61-181299, an example of a piezoelectric wave
transmitter is shown. In this prior art, a lever is used to expand the displacement of the
piezoelectric body in order to avoid the limitation of the displacement of the diaphragm which is
a drawback of the piezoelectric transmitter. [Problems to be Solved by the Invention] However,
since the conventional device uses a shell structure for the sounding body, the present invention
solves the above problems by requiring a large force to displace the shell. It is an object of the
present invention to propose a sounding body capable of efficiently and largely displacing the
vibrating body. The sounding body according to the present invention comprises a coil for
generating a magnetic field, a magnetostrictive body excited by the magnetic field, a spring fixed
to the magnetostrictive body, and fixed to the other end of the spring. It is a sounding body
comprising the mass body and the vibrating plate disposed so as to face the mass body, and is a
sounding body using a piezoelectric material instead of the magnetostrictive material.
[Operation] The sound generator in the present invention generates an alternating magnetic field
by supplying an alternating current to the coil for generating a magnetic field, and vibrates the
magnetostrictive body in the magnetic field. As a result, the spring fixed to the magnetostrictive
body and the mass fixed to the other end of the spring vibrate, and repeatedly strike the
diaphragm provided so as to be held against the mass. Vibrates with a large displacement or
amplitude and transmits a strong low frequency sound to the medium. The above-mentioned
action is the same even if the magnetostrictive material is replaced with a piezoelectric material.
FIG. 1 is an explanatory view showing an embodiment of the present invention. A
magnetostrictive body 2 is disposed adjacent to the coil 1, a spring 3 is attached to the other end
of the magnetostrictive body, a mass 4 is attached to the other end of the spring, and a
diaphragm 5 is disposed adjacent to the spring. These elements are accommodated in the case 6
except the diaphragm. The diaphragm is connected to the case. By energizing the coil with an
alternating current, the magnetostrictive body in the magnetic field formed by the coil vibrates,
whereby the spring and mass receive forced vibration, and the mass strikes the diaphragm to
transmit the sound into the water . In such a vibration system, the amplitude is greatly expanded
when the forced frequency reaches the natural frequency. On the other hand, such a natural
frequency also exists for the diaphragm.
Therefore, when the natural frequency in the spring-mass system matches the natural frequency
of the diaphragm, a vibration having a maximum amplitude occurs in this sounding body. In
general, the vibration of the vibration system in water lowers the natural frequency due to the
added mass of the liquid. That is, N, = N, /(1+ε)0.5, where NW: natural frequency in water, N1:
natural frequency in air, ε: parameter showing added mass of liquid. When the vibrating body is
a disk, the natural frequency in the air is N, -λ 2/2 π R 2 (Dg / γ h n 05 where λ; a factor
determined by boundary conditions, vibration system, R; radius, D Eh ′ ′ / 12 (1−ν2), h: plate
thickness, g: gravitational acceleration, γ: weight per unit volume, E: longitudinal elastic
modulus,;: Poisson's ratio, FIG. It is a graph which shows the relationship between a frequency
and a diameter. The boundary condition is single-sided water contact, fixed in the periphery, and
the plate thickness is Loam in figure 0 calculated using the above equation. The horizontal axis
represents the diameter of the disc and the vertical axis represents the natural frequency. By
obtaining the natural frequency of the diaphragm and the natural frequency of the spring-mass
system in advance so as to match the two, a large amplitude can be obtained in the diaphragm.
Although the magnetostrictive material has been described in this embodiment, the same effect
can be obtained by replacing the magnetostrictive material with a piezoelectric material, and it is
needless to say that it is within the scope of the present invention. [Effects of the Invention] As
described above, in the present invention, the vibration of the magnetostrictive material is
expanded by matching the natural frequencies of the spring mass system and the vibrating body,
so that the sounding body can be It has the effect of significantly increasing the volume.
Brief description of the drawings
FIG. 1 is an explanatory view showing an embodiment of the present invention, and FIG. 2 is a
graph showing the relationship between the natural frequency of the disc and the diameter.
DESCRIPTION OF SYMBOLS 1 ... coil, 2 ... magnetostrictive body, 3 ... spring, 4 ... mass body, 5 ...
diaphragm, 6 ... case.
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