JP2008089488

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DESCRIPTION JP2008089488
A hydrophone capable of reducing noise while securing a detection frequency band by using a
small wave receiving element. A hydrophone comprising a wave receiving element for outputting
a signal based on received sound waves, wherein the wave receiving element is fixed in a housing
(101) filled with an acoustic medium (102), and the housing is A sound adjustment plate 103
that vibrates by receiving sound pressure is formed on one of the surfaces 101. [Selected figure]
Figure 1
ハイドロホン
[0001]
The present invention relates to a hydrophone.
[0002]
As a conventional hydrophone, there are some which can reduce the noise which generate ¦
occur ¦ produces when attaching to a ship and detecting the sound in water.
For example, noise generated by turbulent flow and noise generated from a large vibrating plate
(hereinafter referred to simply as noise) take advantage of the fact that the wavelength is shorter
than the sound wave that is the signal, and make the hydrophone's wave receiving surface broad.
There are some that reduce noise by averaging spatially. Also, as a technology related to an
optical fiber hydrophone, it has a structure in which an optical fiber is wound spirally and
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adhered to a diaphragm, and the optical fiber is distorted by bending vibration of the diaphragm
due to sound, and the phase of light propagated through the optical fiber There is one that
detects sound in water by modulating 変 調 (Non-Patent Document 1). This makes it possible to
configure a multiplex transmission system without using an electronic circuit in the underwater
part, so the number of cables for transmitting signals is reduced and the weight is reduced.
Although an electric hydrophone can constitute a multiplex transmission system, there is a
problem that an electronic circuit, a container for containing the electronic circuit, and a power
supply system for driving the electronic circuit become necessary and heavy. In this respect, fiber
optic hydrophones are advantageous. Also, A high pressure resistant fiber optic acoustic sensor
with pressure balance structure is obtained. With the purpose of with the cylinders 1, 2 of the
double cylindrical body connected in series via the partition plate 3 and integrally forming the
cascade type double cylindrical body with the lid 5, 5a respectively , And an optical fiber 4, 4a
wound around each inner cylinder 1a, 2a of the cascade type double cylindrical body, each lid 5
facing the inner and outer cavity portions 1L, 1H and 2H, 2L of the cylinder 1 and the cylinder 2
, 5a are respectively provided with orifices 11L, 11H and 12H, 12L for equalizing the hydrostatic
pressure of the respective inner and outer cavity portions and the outer peripheral portion of the
cascaded double cylindrical body. There is also a thing called "(patent document 1). JP, 9196749, A (abstract) Technical Research Report of the Institute of Electronics, Information and
Communication Engineers OPE95-2 "Study of optical fiber hydrophone" (Fig. 5)
[0003]
In the optical fiber hydrophone disclosed in the above-mentioned Non-Patent Document 1, noise
can be reduced by enlarging the diaphragm in the same manner as the method of spatially
averaging shown in the above-mentioned prior art. There is a problem that the resonance
frequency becomes low and the frequency band of the sound that can be detected becomes
narrow. Also in the cylindrically wound optical fiber hydrophone disclosed in Patent Document 1
described above, noise can be reduced by enlarging the cylinder in the same manner, but the
frequency of the sound that can be detected because the resonance frequency is also low. There
is a problem that the band narrows. Therefore, a hydrophone capable of reducing noise while
securing a detection frequency band by using a small receiving element has been desired.
[0004]
A hydrophone according to the present invention is a hydrophone provided with a wave
receiving element for outputting a signal based on a received sound wave, wherein the wave
receiving element is fixed in a housing filled with an acoustic medium, It is characterized in that a
first diaphragm that vibrates by receiving a sound pressure is formed on any surface of the
housing.
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[0005]
ADVANTAGE OF THE INVENTION According to the hydrophone concerning this invention, it
becomes possible to reduce noise, securing a detection frequency zone ¦ band using a small
receiving element.
[0006]
Embodiment 1
FIG. 1 illustrates the structure of a hydrophone according to Embodiment 1 of the present
invention.
The hydrophone 100 is a hydrophone according to the first embodiment, and the housing 101 is
filled with an acoustic medium 102 (a liquid such as water). A diaphragm (hereinafter referred to
as sound adjustment plate 103) that vibrates by receiving sound pressure is configured on the
front of the case 101, and the sound adjustment plate 103 vibrates so that sound is generated in
the case 101. It is supposed to be transmitted. Inside the housing 101, an optical fiber coil 106
fixed to the inner wall of the housing 101 by a support 105 is disposed. The optical fiber coil
106 is formed by winding an optical fiber in a cylindrical shape and serves as a wave receiving
element. An input / output optical fiber 107 is attached to the optical fiber coil 106 so that
signals can be input / output from / to the outside of the hydrophone 100.
[0007]
The housing 101 is formed in a rectangular parallelepiped shape, and is formed using a hard
material so that the sound outside the hydrophone 100 is not directly transmitted to the inside of
the housing 101.
[0008]
As a material of the sound adjustment plate 103, a hard material which hardly generates bending
vibration is used.
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Specifically, an aluminum alloy having both hardness and lightness is suitable. By using a
material having sufficient rigidity, the vicinity of the center of the sound adjustment plate 103 is
not bent more than other portions, so that the pressure applied to the acoustic medium 102 by
the sound adjustment plate 103 can be made uniform.
[0009]
A plurality of optical fiber coils 106 are disposed in the housing 101. The arrangement is such
that the acoustic center, which is the central position of the acoustic sensitivity, is located on the
center line of the tuning plate 103. In particular, it is desirable to arrange the optical fiber coils
106 of the same sensitivity at positions symmetrical with respect to the center line of the sound
adjustment plate 103 as an axis of symmetry. By arranging in this manner, the sensitivity of the
hydrophone can be enhanced, and the noise reduction effect by the sound adjustment plate 103
described later can be sufficiently exhibited.
[0010]
A bent portion 104 formed by reducing the thickness of the sound adjustment plate 103 is
provided at the peripheral portion of the sound adjustment plate 103. When the sound
adjustment plate 103 receives a sound pressure, the bending portion 104 bends, so that the
sound adjustment plate 103 vibrates uniformly in the out-of-plane direction. Assuming that the
sound mixing plate 103 is formed to have an equal thickness without providing the bending
portion 104, if the rigidity of the sound mixing plate 103 is not sufficient, the vicinity of the
center of the sound mixing plate 103 is larger than other portions. As a result, the pressure
applied to the acoustic medium 102 by the sound production plate 103 is biased. Therefore, the
flexible portion is formed on the peripheral edge of the sound adjustment plate 103 by providing
the bending portion 104, and the deflection is concentrated on this portion, so that the sound
adjustment plate 103 vibrates uniformly in the out-of-plane direction. It can be configured.
However, if the width in the surface direction of the bending portion 104 is formed too wide, the
uniformity of the vibration of the sound adjustment plate 103 is impaired, so it is preferable that
the surface area of the sound adjustment plate 103 be narrow.
[0011]
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In the first embodiment, the sound adjustment plate 103 corresponds to the
Also, the fiber optic sensor corresponds to the fiber optic coil 106.
first diaphragm
.
[0012]
Next, the basic operation of the hydrophone 100 will be described. (1) When sound pressure is
applied to the hydrophone 100, the sound adjustment plate 103 vibrates, pressure is transmitted
to the acoustic medium 102 in the housing 101, and the optical fiber coil 106 is distorted. (2)
Due to the distortion of the optical fiber coil 106, the path length of the light propagating in the
optical fiber changes, so that the phase propagation occurs in the light propagating in the optical
fiber. That is, distortion due to sound pressure is modulated to a phase signal and output from
the input / output optical fiber 107. The sound pressure can be detected by demodulating this
modulation phase signal by a predetermined demodulation operation process or the like. A
known technique may be used for the demodulation process.
[0013]
Next, the noise reduction effect by the sound production plate 103 will be described. In the
sound adjustment plate 103, the spatial average of the sound pressure applied to the surface
thereof vibrates as a force. Therefore, noise components having an uneven distribution are
transmitted to the inside of the housing 101 after being averaged by the sound production plate
103. As a result, the influence of noise is reduced inside the housing 101, and as a result, the
signal to noise ratio is improved. In addition, when movement to rotate the sound mixing plate
103 occurs due to noise added to the sound mixing plate 103, this is transmitted within the
housing 101, but it is canceled when it is propagated through all the optical fiber coils 106, so a
special problem is caused. Absent.
[0014]
As described above, by providing the sound adjustment plate 103 instead of increasing the size
of the optical fiber coil 106 that is the wave receiving element, the noise is canceled while using
the small size of the optical fiber coil 106 itself. It is possible to
[0015]
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As described above, according to the first embodiment, the optical fiber coil 106 is fixed in the
housing 101 filled with the acoustic medium 102, and vibration is received by sound pressure on
any surface of the housing 101. Since the sound adjusting plate 103 is configured, noise can be
averaged and canceled by the sound adjusting plate 103, and it is not necessary to increase the
size of the wave receiving element itself.
As a result, it is possible to reduce noise while securing a detection frequency band using a small
receiving element.
[0016]
Further, according to the first embodiment, the plurality of optical fiber coils 106 are provided,
and each of the optical fiber coils 106 is disposed such that the acoustic center is overlapped
with the center line of the tone adjustment plate 103. Since the hydrophone is disposed at a line
symmetrical position with the center line as the axis of symmetry, the sensitivity of the
hydrophone can be enhanced, and the noise reduction effect by the sound adjustment plate 103
can be sufficiently exhibited.
[0017]
Further, according to the first embodiment, since the bent portion 104 formed by reducing the
thickness of the peripheral portion of the sound adjustment plate 103 is provided, the deflection
is concentrated on the bend portion 104, and the sound adjustment plate 103 It can be
configured to vibrate uniformly in the out-of-plane direction.
As a result, since the sound production plate 103 vibrates uniformly according to the sound
pressure, the noise reduction effect by the sound production plate 103 is improved.
[0018]
Second Embodiment FIG. 2 illustrates the structure of a hydrophone according to Embodiment 2
of the present invention. The difference between the hydrophone 200 in FIG. 2 and the
hydrophone 100 in the first embodiment is that another pair of sound mixing plates is provided
on the surface facing the sound mixing plate 103 in FIG. In addition, since the other structure of
the hydrophone 200 is the same as that of FIG. 1, the same code ¦ symbol is attached ¦ subjected
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and description is abbreviate ¦ omitted.
[0019]
In FIG. 2, the one corresponding to the sound adjustment plate 103 in FIG. 1 is referred to as a
first sound adjustment plate 203a. Further, a second sound adjustment plate 203 b is configured
on the surface of the housing 201 facing the first sound adjustment plate 203 a. The portions
corresponding to the bending portion 104 in FIG. 1 are respectively referred to as a first bending
portion 304 a and a second bending portion 304 b. The second sound adjustment plate 203b is
adjusted in impedance balance so that the pressure of the acoustic medium 202 in the housing
does not change when it vibrates in the same direction as the first sound adjustment plate 203a.
In addition, the second sound adjustment plate 203b is disposed such that the center line
overlaps the center line of the first sound adjustment plate 203a. As in the first embodiment, the
optical fiber coil 206 is disposed at a position where the acoustic center overlaps the center line
of the first sound adjustment plate 203 a (also overlaps the center line of the second sound
adjustment plate 203 b). It is connected to the body 201.
[0020]
In the second embodiment, the "first diaphragm" corresponds to the first sound adjustment board
203a, and the "second diaphragm" corresponds to the second sound adjustment board 203b.
[0021]
Here, the impedances of the first sound adjustment plate 203a and the second sound adjustment
plate 203b refer to the combined impedance of the mechanical impedance and the radiation
impedance.
The mechanical impedance is determined by the material and shape of the sound production
plate (elasticity, resistance, parameters contributing to inertia), and the like. In addition, the
radiation impedance is the shape of the tuning plate (in particular, the area of the radiation
surface), the density of the medium (kg / m ^ 3), the speed of sound traveling through the
medium (m / s), Determined by the shape, etc. It is assumed that the balance of the impedance
determined by the first sound adjustment plate 203a and the second sound adjustment plate
203b is previously adjusted as described above.
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[0022]
The basic operation of the hydrophone 200 is the same as that of the hydrophone 100 according
to the first embodiment, but the following advantages can be obtained by including the second
sound adjustment plate 203b. When an overall acceleration is applied to the hydrophone 200
body, for example, when the hydrophone 200 body is vibrated, the first sound adjustment plate
203a and the second sound adjustment plate 203b vibrate in the same direction. The pressure
change of the acoustic medium 202 in the housing 201 is canceled. That is, the vibration of the
hydrophone 200 body is not erroneously detected, and only the vibration due to the sound wave
to be originally detected can be detected. Further, noise components having nonuniform
distribution are averaged by the first sound adjustment plate 203a and the second sound
adjustment plate 203b and transmitted to the inside of the housing 201 as in the first
embodiment, so that the housing Inside the body 201, the effects of noise are reduced, resulting
in a better signal to noise ratio.
[0023]
As described above, according to the second embodiment, the second sound adjustment plate
203 b that vibrates by receiving sound pressure is formed on the surface of the housing 201
facing the first sound adjustment plate 203 a, and Since the sound adjustment plate 203 b is
adjusted in impedance so that the pressure applied to the optical fiber coil 206 does not change
when the sound adjustment plate 203 b vibrates in the same direction as the first sound
adjustment plate 203 a, In the case of vibration, the first sound adjustment plate 203a and the
second sound adjustment plate 203b vibrate in the same direction, and the pressure change of
the acoustic medium 202 in the housing 201 is cancelled. As a result, the vibration of the
hydrophone 200 main body is not erroneously detected, and only the vibration due to the sound
wave to be originally detected can be detected. Therefore, the hydrophone 200 can be installed
in a place with a lot of vibration. , A wide range of applications of the hydrophone 200 are
secured.
[0024]
Further, according to the second embodiment, since the second sound adjustment board 203b is
arranged such that the center line overlaps with the center line of the first sound adjustment
board 203a, the acoustic center is the first sound adjustment board 203a and the second sound
adjustment board 203a. Being located on the center line of each of the second sound adjustment
plates 203b, the sensitivity of the hydrophone can be enhanced, and the noise reduction effect by
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the sound adjustment plates can be sufficiently exhibited.
[0025]
Third Embodiment
FIG. 3 illustrates the structure of a hydrophone according to Embodiment 3 of the present
invention. The difference between the hydrophone 300 in FIG. 3 and the hydrophone 200 in the
second embodiment is that a spring 308 connecting the sound adjustment plates is provided. In
addition, since the other structure of the hydrophone 300 is the same as that of FIG. 2, the same
code ¦ symbol is attached ¦ subjected and description is abbreviate ¦ omitted.
[0026]
The position, the number, and the spring constant of the spring 308 balance the spring constants
of the bent portions of the first sound adjustment plate 303a and the second sound adjustment
plate 303b, respectively, and the first sound adjustment plate 303a and the second sound
adjustment plate 303 b is set to vibrate with uniform displacement in the out-of-plane direction.
Although a coil spring, a leaf spring, a rod-shaped spring, etc. can also be used for the spring
308, a rod-shaped spring or coil spring with a small installation space is desirable.
[0027]
Compared with the configuration in which the spring 308 is provided, the deflection in the
vicinity of the center of the sound mixing plate is suppressed only by the rigidity of the first
sound collecting plate 303 a and the second sound mixing plate 303 b as in the second
embodiment. Then, each sound production board can be made thin. As a result, the hydrophone
300 can be reduced in size and weight.
[0028]
In the third embodiment, an example is shown in which the rigidity in the vicinity of the center of
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the sound adjustment plate is reinforced by connecting the first sound adjustment plate 303 a
and the second sound adjustment plate 303 b via the spring 308. It is also possible to reinforce
the rigidity by connecting the housing 301 with the vicinity of the center of each of the sound
production plates via. Also in this case, the position, number, and spring constant of the spring
are balanced with the spring constants of the bent portions of the first sound adjustment plate
303a and the second sound adjustment plate 303b, and the first sound adjustment plate 303a
and the second sound adjustment plate The sound adjustment plate 303 b is set to vibrate with
uniform displacement in the out-of-plane direction.
[0029]
In the first to third embodiments described above, an example in which a cylindrical optical fiber
coil is used as a wave receiving element has been described, but an optical fiber sensor
configured in another shape such as a spirally wound shape on a diaphragm is used. You can
also.
[0030]
In the first to third embodiments, an example in which an optical fiber coil is used as a wave
receiving element has been described. However, instead of this, another element such as a
piezoelectric material may be used.
That is, any wave receiving element can be used as long as it can effectively use the fact that the
noise in the casing is canceled and the signal-to-noise ratio in the housing is improved.
[0031]
Also, in the first to third embodiments, an example is described in which the case is filled with a
liquid to make an acoustic medium, but instead of the liquid, an elastic material that transmits
sound such as rubber is used, or a liquid and rubber A configuration in which elastic materials
are used in combination can also be used.
[0032]
In the first to third embodiments, the housing is formed in a rectangular parallelepiped shape,
but the shape is not limited to a rectangular parallelepiped, and may be, for example, a cube or a
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cylinder.
However, since it is not preferable from the viewpoint of detection accuracy that the pressure
applied to the acoustic medium becomes nonuniform, it is desirable to use a shape having
symmetry in which opposing surfaces have the same shape.
[0033]
FIG. 4 is a configuration example in the case where the casing is formed in a cylindrical shape in
the third embodiment. The reference numerals of the respective parts are the same as in FIG.
Thus, as for the shape of a housing ¦ casing, it is desirable to comprise so that the surface which
opposes may become the same shape.
[0034]
As described above, according to the third embodiment, the spring 308 having one end fixed to
the central portion of the first sound adjustment plate 303 a is provided, and the other end of the
spring 308 is the second sound adjustment Since it is configured to be fixed to the central
portion of the plate 303b, the rigidity near the center of each sound adjustment plate can be
reinforced by the spring 308, and the sound adjustment plate can be formed thin. This helps to
reduce the weight or size of the entire hydrophone. In addition, since the rigidity in the vicinity of
the center is reinforced, the vicinity of the center will be bent more than other parts, and the
pressure applied to the acoustic medium will not be biased, so the sensitivity of the hydrophone
is stabilized. It also contributes.
[0035]
Also, a spring having one end fixed to the casing is provided, and the other end of the spring is
fixed to the central part of the first sound adjustment plate 303a and / or the second sound
adjustment plate 303b. It can also be configured. By configuring in this manner, the same effect
as in the case of connecting the sound production plates with a spring can be obtained.
[0036]
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Further, according to the third embodiment, the spring 308 is configured such that the
displacement of the first sound adjustment plate 303 a or the second sound adjustment plate
303 b to which the spring 308 is fixed due to the out-of-plane vibration is uniform. Since the
constant is adjusted, the sound production plate 103 vibrates uniformly in accordance with the
sound pressure, and the sound production plate can be formed thin without impairing the noise
reduction effect of the sound production plate 103.
[0037]
The structure of the hydrophone concerning Embodiment 1 is demonstrated.
The structure of the hydrophone concerning Embodiment 2 is demonstrated. The structure of the
hydrophone concerning Embodiment 3 is demonstrated. 17 illustrates the configuration of a
hydrophone according to Embodiment 4.
Explanation of sign
[0038]
DESCRIPTION OF SYMBOLS 100 hydrophone, 101 housings, 102 acoustic media, 103 sound
adjustment board, 104 bending part, 105 support ¦ pillars, 106 optical fiber coil, 107 inputoutput optical fiber, 200 hydrophones, 201 housings, 202 acoustic media, 203a 1st Sound
adjustment board, 203b second sound adjustment board, 204a first bending portion, 204b
second bending portion, 205 post, 206 optical fiber coil, 207 input / output optical fiber, 300
hydrophone, 301 case, 302 acoustic medium, 303a 1st sound adjustment board, 303b 2nd
sound adjustment board, 304a 1st bending part, 304b 2nd bending part, 305 post, 306 optical
fiber coil, 307 input / output optical fiber, 308 spring, 400 hydrophone, 401 case, 402 sound
medium, 403 a first sound adjustment board, 403 b second sound adjustment board, 404 a first
bending portion, 404 b Bent portion 405 strut 406 optical fiber coil, 407 input and output
optical fiber, 408 spring.
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