JP5194418B2 - Hydrophone - Google Patents

Description

  The present invention relates to a hydrophone.

As a conventional hydrophone, there is one that can reduce noise generated when it is attached to a ship and detects sound in water. For example, noise generated by turbulent flow and noise generated from a large vibrating plate (hereinafter simply referred to as noise) is used to make the receiving surface of the hydrophone wider by utilizing the fact that the wavelength is shorter than the sound wave that becomes the signal. Some have reduced noise by spatial averaging.
As a technology related to optical fiber hydrophones, the optical fiber is wound in a spiral shape and bonded to the diaphragm. The optical fiber is distorted by the bending vibration of the diaphragm due to sound, and the phase of the light propagated through the optical fiber. There is a technique for detecting underwater sound in such a manner that is modulated (Non-Patent Document 1). In this case, since a multiplex transmission system can be configured without using an electronic circuit in the underwater portion, the number of cables for transmitting signals is reduced and the weight is reduced. A multiplex transmission system can be configured even with an electric hydrophone, but there is a problem that an electronic circuit, a container for storing the electronic circuit, and a power supply system for driving the electronic circuit are necessary and heavy. In this respect, the optical fiber hydrophone has an advantage.
In addition, “a high water pressure resistant optical fiber type acoustic sensor with a pressure balance structure is obtained. ”With the lids 5 and 5 a at both ends of the cascaded double cylinder formed integrally by connecting the cylinders 1 and 2 of the double cylinder in series via the partition plate 3. Each of the lids 5 is formed by winding the optical fibers 4 and 4a around the inner cylinders 1a and 2a of the cascaded double cylindrical body and facing the inner and outer cavities 1L and 1H and 2H and 2L of the cylinder 1 and the cylinder 2, respectively. , 5a are provided with orifices 11L, 11H and 12H, 12L, respectively, for equalizing the hydrostatic pressure between the inner and outer cavities and the outer periphery of the cascaded double cylindrical body. Is also known (Patent Document 1).
JP-A-9-196749 (summary) IEICE technical report OPE95-2 "Research on optical fiber hydrophones" (Figure 5)

In the optical fiber hydrophone disclosed in Non-Patent Document 1, noise can be reduced by enlarging the diaphragm in the same manner as the spatial averaging method described in the prior art. There is a problem that the resonance frequency is lowered and the frequency band of the detectable sound is narrowed.
In addition, in the optical fiber hydrophone wound in a cylindrical shape shown in Patent Document 1 as well, noise can be reduced by increasing the size of the cylinder in the same manner. There is a problem that the band becomes narrow.
Therefore, a hydrophone capable of reducing noise while ensuring a detection frequency band using a small receiving element has been desired.

The hydrophone according to the present invention is a hydrophone provided with a wave receiving element that outputs a signal based on a received sound wave, and the wave receiving element is placed in a casing filled with a fluid acoustic medium. A first diaphragm that is fixed and configured to vibrate by receiving sound pressure is formed on any surface of the housing, and a second diaphragm that vibrates by receiving sound pressure on a surface facing the first diaphragm And the second diaphragm is adjusted in impedance so that the pressure applied to the receiving element by the acoustic medium does not change when the second diaphragm vibrates in the same direction as the first diaphragm. It is what.

  According to the hydrophone according to the present invention, it is possible to reduce noise while securing a detection frequency band using a small wave receiving element.

Embodiment 1 FIG.
FIG. 1 illustrates the configuration 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 (liquid such as water).
A vibration plate (hereinafter referred to as a sound adjustment plate 103) that vibrates in response to sound pressure is configured on the front surface of the housing 101. When the sound adjustment plate 103 vibrates, sound is generated in the housing 101. It comes to be transmitted.
An optical fiber coil 106 fixed to the inner wall of the casing 101 with a support column 105 is disposed inside the casing 101.
The optical fiber coil 106 is formed by winding an optical fiber in a cylindrical shape, and plays a role 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.

  The casing 101 is formed in a rectangular parallelepiped shape, and is formed using a hard material so that sound outside the hydrophone 100 is not directly transmitted to the inside of the casing 101.

As the material of the sound control plate 103, a hard material that hardly causes flexural vibration is used. Specifically, an aluminum alloy having both hardness and lightness is suitable.
By using a material with sufficient rigidity, the vicinity of the center of the sound adjusting plate 103 does not bend more greatly than other portions, so that the pressure applied to the acoustic medium 102 by the sound adjusting plate 103 can be made uniform.

A plurality of optical fiber coils 106 are arranged in the housing 101. The arrangement is such that the acoustic center, which is the central position of the acoustic sensitivity, is positioned on the center line of the sound control plate 103.
In particular, it is desirable that the optical fiber coils 106 having the same sensitivity be arranged at a line-symmetric position with the center line of the sound adjusting plate 103 as the axis of symmetry.
By arranging in this way, the sensitivity of the hydrophone can be increased, and the noise reduction effect by the sound adjusting plate 103 described later can be sufficiently exhibited.

A bent portion 104 formed by reducing the thickness of the sound adjusting plate 103 is provided at the peripheral portion of the sound adjusting plate 103. When the sound adjusting plate 103 receives sound pressure, the bent portion 104 is bent, so that the sound adjusting plate 103 vibrates uniformly in the out-of-plane direction.
If the sound adjusting plate 103 is formed with an equal thickness without providing the bent portion 104, if the sound adjusting plate 103 has insufficient rigidity, the vicinity of the center of the sound adjusting plate 103 is larger than the other portions. As a result, the pressure applied to the acoustic medium 102 by the sound adjusting plate 103 is biased.
Therefore, by providing the bent portion 104, a flexible portion is formed on the periphery of the sound adjusting plate 103, and the bending is concentrated on this portion, so that the sound adjusting plate 103 vibrates uniformly in the out-of-plane direction. Can be configured.
However, if the width of the bent portion 104 in the surface direction is too wide, the uniformity of vibration of the sound regulating plate 103 is impaired.

  In the first embodiment, the sound adjusting plate 103 corresponds to the “first diaphragm”. The “optical fiber sensor” corresponds to the optical fiber coil 106.

Next, the basic operation of the hydrophone 100 will be described.
(1)
When sound pressure is applied to the hydrophone 100, the sound adjusting plate 103 vibrates and 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 through the optical fiber changes, so that phase displacement occurs in the light propagating through the optical fiber. That is, distortion due to sound pressure is modulated into a phase signal and output from the input / output optical fiber 107.
The sound pressure can be detected by demodulating the modulation phase signal by a predetermined demodulation calculation process or the like. A known technique may be used for the demodulation process.

Next, the noise reduction effect by the sound control plate 103 will be described.
The sound control plate 103 vibrates with the spatial average of the sound pressure applied to the surface as a force. Therefore, a noise component having a non-uniform distribution is averaged by the sound adjusting plate 103 and then transmitted to the housing 101.
Thereby, the influence of noise is reduced inside the housing 101, and as a result, the signal-to-noise ratio is improved.
In addition, if the movement which the sound-tuning board 103 rotates with the noise added to the sound-handling board 103 arises, this will be propagated in the housing | casing 101, but since it will be canceled after propagating all the optical fiber coils 106, a special problem is Absent.

  In this way, by providing the sound adjusting plate 103 instead of making the optical fiber coil 106 itself, which is a wave receiving element, large, the noise can be canceled while using a small optical fiber coil 106 itself. Can do it.

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,
Since the sound control plate 103 that vibrates in response to sound pressure is configured on any surface of the housing 101,
Noise can be averaged and canceled by the sound adjusting plate 103, and the receiving element itself does not need to be enlarged. As a result, it is possible to reduce noise while securing a detection frequency band using a small wave receiving element.

Further, according to the first embodiment,
A plurality of optical fiber coils 106;
Since each optical fiber coil 106 is arranged so that the acoustic center overlaps the center line of the sound shaping plate 103, and further arranged at a line-symmetrical position with the center line of the sound shaping plate 103 as the symmetry axis,
The sensitivity of the hydrophone can be increased and the noise reduction effect by the sound control plate 103 can be sufficiently exhibited.

Further, according to the first embodiment,
Since the bent portion 104 formed by reducing the thickness of the peripheral portion of the sound adjusting plate 103 is provided,
The bend can be concentrated on the bent portion 104 so that the sound adjusting plate 103 can be vibrated uniformly in the out-of-plane direction. As a result, the sound control plate 103 vibrates uniformly according to the sound pressure, so that the noise reduction effect by the sound control plate 103 is improved.

Embodiment 2. FIG.
FIG. 2 explains the configuration of the 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 control plates is provided on the surface facing the sound control plate 103 in FIG.
Since other configurations of the hydrophone 200 are the same as those in FIG. 1, the same reference numerals are given and description thereof is omitted.

In FIG. 2, what corresponds to the sound control plate 103 of FIG. 1 is referred to as a first sound control plate 203a.
Further, a second sound adjusting plate 203b is formed on the surface of the housing 201 facing the first sound adjusting plate 203a. The parts corresponding to the bent part 104 in FIG. 1 are referred to as a first bent part 304a and a second bent part 304b, respectively.
The impedance balance of the second sound adjusting plate 203b is adjusted 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 adjusting plate 203a.
Further, the second sound adjusting plate 203b is disposed so that the center line overlaps the center line of the first sound adjusting plate 203a.
As in the first embodiment, the optical fiber coil 206 is arranged at a position where the acoustic center overlaps the center line of the first sound shaping plate 203a (also overlaps the center line of the second sound shaping plate 203b). Connected to the body 201.

  In the second embodiment, the “first diaphragm” corresponds to the first sound adjusting plate 203a, and the “second diaphragm” corresponds to the second sound adjusting plate 203b.

Here, the impedance of the first sound adjusting plate 203a and the second sound adjusting plate 203b refers to the combined impedance of mechanical impedance and radiation impedance.
The mechanical impedance is determined by the material and shape of the sound adjusting plate (parameters contributing to elasticity, resistance, and inertia).
In addition, the radiation impedance is the shape of the sound-tuning plate (particularly the area of the radiation surface), the density of the medium (kg / m ^ 3), the speed of sound transmitted through the medium (m / s), Determined by shape, etc.
It is assumed that the impedance balance determined by the first sound adjusting plate 203a and the second sound adjusting plate 203b is adjusted in advance as described above.

The basic operation of the hydrophone 200 is the same as that of the hydrophone 100 in the first embodiment, but the following effects are achieved by providing the second sound control plate 203b.
When overall acceleration is applied to the hydrophone 200 main body, for example, when the hydrophone 200 main body is vibrated, the first sound adjusting plate 203a and the second sound adjusting plate 203b vibrate in the same direction. The pressure change of the acoustic medium 202 in the housing 201 is cancelled.
That is, the vibration of the hydrophone 200 main body is not erroneously detected, and only the vibration due to the sound wave that should be detected can be detected.
In addition, since noise components having a non-uniform distribution are averaged by the first sound-adjusting plate 203a and the second sound-adjusting plate 203b as in the first embodiment, the noise components are transmitted to the case 201. Inside the body 201, the influence of noise is reduced, resulting in a better signal to noise ratio.

As described above, according to the second embodiment,
On the surface of the housing 201 facing the first sound control plate 203a,
Constituting a second sound control plate 203b that vibrates in response to sound pressure;
The second sound control plate 203b is
Since the impedance is adjusted so that the pressure applied to the optical fiber coil 206 by the acoustic medium 202 does not change when vibrating in the same direction as the first sound regulating plate 203a,
When the main body of the hydrophone 200 is vibrated, the first sound adjusting plate 203a and the second sound adjusting plate 203b vibrate in the same direction, and the pressure change of the acoustic medium 202 in the housing 201 is cancelled. .
Accordingly, it is possible to detect only the vibration due to the sound wave that should be detected without erroneously detecting the vibration of the main body of the hydrophone 200, so that the hydrophone 200 can be installed in a place with a lot of vibration. Wide application of the hydrophone 200 is ensured.

Further, according to the second embodiment,
The second sound control plate 203b is
Since the center line is arranged so as to overlap the center line of the first sound control plate 203a,
The acoustic center is located on the center line of each of the first sound adjusting plate 203a and the second sound adjusting plate 203b, so that the sensitivity of the hydrophone can be increased and the noise reduction effect by the sound adjusting plate can be sufficiently exhibited. Can do.

Embodiment 3 FIG.
FIG. 3 illustrates a configuration 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 is provided to connect the sound control plates.
Since other configurations of the hydrophone 300 are the same as those in FIG. 2, the same reference numerals are given and description thereof is omitted.

The position, number, and spring constant of the spring 308 are balanced with the spring constants of the bent portions of the first sound adjusting plate 303a and the second sound adjusting plate 303b, and the first sound adjusting plate 303a and the second sound adjusting plate. 303b is set to vibrate with a uniform displacement in the out-of-plane direction.
The spring 308 can be a coil spring, a leaf spring, a rod spring, or the like, but is preferably a rod spring or a coil spring with a small installation space.

Compared with the configuration in which the spring 308 is provided, so that the bending of the vicinity of the center of the sound adjusting plate is suppressed only by the rigidity of the first sound adjusting plate 303a and the second sound adjusting plate 303b as in the second embodiment. Then, each sound control board can be made thin.
Thereby, size reduction or weight reduction of the hydrophone 300 can be achieved.

In the third embodiment, an example in which the rigidity near the center of the sound adjusting plate is reinforced by connecting the first sound adjusting plate 303a and the second sound adjusting plate 303b via the spring 308 is shown. It is also possible to reinforce the rigidity by connecting the vicinity of the center of each sound regulating plate and the housing 301 via the.
Also in this case, the position, number, and spring constant of the spring balance the spring constants of the bent portions of the first sound adjusting plate 303a and the second sound adjusting plate 303b, and the first sound adjusting plate 303a and the second sound adjusting plate 303a. The sound control plate 303b is set to vibrate with a uniform displacement in the out-of-plane direction.

  In Embodiments 1 to 3 described above, the example in which the cylindrical optical fiber coil is used as the wave receiving element has been described. However, an optical fiber sensor configured in another shape such as a spiral shape wound around the diaphragm is used. You can also.

In the first to third embodiments, the example in which the optical fiber coil is used as the wave receiving element has been described. However, instead of this, another element such as a piezoelectric material may be used.
In other words, any wave receiving element can be used as long as it can effectively use the noise canceling plate to improve the signal-to-noise ratio in the housing.

  In the first to third embodiments, the example in which the housing is filled with the liquid and used as the acoustic medium has been described. Instead of the liquid, an elastic material that transmits sound such as rubber is used, or the liquid and rubber are used. A configuration using an elastic material in combination can also be used.

In the first to third embodiments, the casing is formed in a rectangular parallelepiped shape, but the shape is not limited to a rectangular parallelepiped, and may be a cube or a cylinder, for example.
However, since it is not preferable from the viewpoint of detection accuracy that the pressure applied to the acoustic medium is not uniform, it is desirable to use a symmetrical shape in which the opposing surfaces have the same shape.

FIG. 4 is a configuration example when the casing is formed in a cylindrical shape in the third embodiment. The reference numerals of the respective parts are the same as those in FIG.
As described above, it is desirable to configure the casing so that the opposing surfaces have the same shape.

As described above, according to the third embodiment,
A spring 308 having one end fixed to the center of the first sound control plate 303a is provided,
Since the other end of the spring 308 is fixed to the center of the second sound control plate 303b,
The rigidity in the vicinity of the center of each sound-tuning plate can be reinforced by the spring 308, and the sound-tuning plate can be formed thin. This contributes to the weight reduction or size reduction of the entire hydrophone.
In addition, since the rigidity near the center is reinforced, the vicinity of the center will bend more than other parts, and the pressure applied to the acoustic medium will not be biased. Also contributes.

In addition, a spring having one end fixed to the housing is provided,
The other end of the spring may be fixed to the central part of the first sound adjusting plate 303a, the second sound adjusting plate 303b, or both.
By comprising in this way, there exists an effect similar to the case where the sound control boards are connected with a spring.

Moreover, according to the third embodiment,
Spring 308 is
Since the spring constant is adjusted so that the displacement due to the vibration in the out-of-plane direction of the first sound adjusting plate 303a or the second sound adjusting plate 303b to which the spring 308 is fixed is uniform.
The sound control plate 103 vibrates uniformly according to the sound pressure, and the sound control plate can be formed thin without impairing the noise reduction effect of the sound control plate 103.

A configuration of the hydrophone according to Embodiment 1 will be described. The configuration of the hydrophone according to Embodiment 2 will be described. A configuration of a hydrophone according to Embodiment 3 will be described. A configuration of the hydrophone according to Embodiment 4 will be described.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Hydrophone, 101 Case, 102 Acoustic medium, 103 Sound-tuning plate, 104 Bending part, 105 Support | pillar, 106 Optical fiber coil, 107 Input / output optical fiber, 200 Hydrophone, 201 Case, 202 Acoustic medium, 203a 1st Sound adjusting plate, 203b second sound adjusting plate, 204a first bent portion, 204b second bent portion, 205 strut, 206 optical fiber coil, 207 input / output optical fiber, 300 hydrophone, 301 housing, 302 acoustic medium, 303a First tuned plate, 303b Second tuned plate, 304a First bent portion, 304b Second bent portion, 305 Post, 306 Optical fiber coil, 307 Input / output optical fiber, 308 Spring, 400 Hydrophone, 401 Housing, 402 acoustic medium, 403a first sound adjusting plate, 403b second sound adjusting plate, 404a First bent portion, 404b Second bent portion, 405 column, 406 optical fiber coil, 407 input / output optical fiber, 408 spring.

Claims (13)

A hydrophone including a wave receiving element that outputs a signal based on a received sound wave,
Fixing the receiving element in a housing filled with a fluid acoustic medium,
A first diaphragm that vibrates in response to sound pressure is formed on any surface of the housing ,
On the surface facing the first diaphragm, a second diaphragm that vibrates by receiving sound pressure is configured,
The second diaphragm is
Impedance is adjusted so that the pressure applied to the receiving element by the acoustic medium does not change when it vibrates in the same direction as the first diaphragm.
Hydrophone which is characterized a call.   The hydrophone according to claim 1, wherein the wave receiving element is disposed such that an acoustic center thereof overlaps a center line of the first diaphragm. A plurality of the receiving elements,
The hydrophone according to claim 2, wherein the wave receiving element is disposed at a line-symmetrical position with a center line of the first diaphragm as a symmetry axis. The second diaphragm is
The hydrophone according to claim 1 , wherein a center line is arranged so as to overlap a center line of the first diaphragm. Provide a spring with one end secured to the housing,
The hydrophone according to any one of claims 1 to 4 , wherein the other end of the spring is fixed to a central portion of the first diaphragm. Provide a spring with one end secured to the housing,
Hydrophone according to any one of claims 1 to 4, characterized in that the other end of the spring, fixed to the central portion of the second diaphragm. A spring having one end fixed to the vicinity of the center of the first diaphragm;
Hydrophone according to any one of claims 1 to 4, characterized in that the other end of the spring, fixed to the central portion of the second diaphragm. The spring is
As the displacement due to vibration of the plane direction of said fixed the spring first diaphragm and the second diaphragm is uniform, claims 5 to, characterized in that formed by adjusting the spring constant 8. The hydrophone according to any one of 7 . The hydrophone according to any one of claims 1 to 8 , further comprising a bent portion formed by reducing a thickness of a peripheral portion of the first diaphragm. Hydrophone according to any one of claims 1 to 8, characterized in that a bent portion formed by reducing the thickness of the peripheral portion of the second diaphragm. The hydrophone according to any one of claims 1 to 10 , wherein the first diaphragm is made of an aluminum alloy. It said second diaphragm hydrophone according to any one of claims 1 to 10, characterized in that it is formed of an aluminum alloy. The hydrophone according to any one of claims 1 to 12 , wherein an optical fiber sensor is used as the wave receiving element.

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