JPH0771356B2 - Optical fiber hydrophone - Google Patents

Description

The present invention relates to an optical fiber hydrophone, and more particularly to an optical fiber hydrophone that can be used under high water pressure.

[Conventional technology]

An example of a conventional optical fiber hydrophone will be described with reference to the drawings. FIG. 6 (a) is an external view showing an example of a conventional structure, and FIG. 6 (b) is a sectional view showing the structure taken along line XY in FIG. 6 (a).

A diaphragm 42 is formed on both flat surfaces of a flat support frame 41 by bonding or attachment. Further, there are two curved side surface portions 45 for smoothly connecting the surfaces of the diaphragms 42 mounted on both sides. Further, the thickness of the wall of the support frame 41 is sufficiently thicker than the thickness of the diaphragm 42 and there is a space inside, and the optical fiber 43 (particularly the polarization-maintaining optical fiber) is further included in the side surface of the support frame. The part 45 and the vibration plate 42 are wound in close contact with each other while being in contact with each other, and the part in contact with the vibration plate 42 is fixed with an adhesive (for example, epoxy-based synthetic resin).

When the hydrophone receives a sound wave and the size of the hydrophone is sufficiently smaller than the wavelength of the sound wave, the hydrophone becomes pressure-sensitive and the two diaphragms are simultaneously pulled inside or outside the support framework. . Therefore, as shown in FIG. 4 (a), the diaphragm 2A attached to the supporting frame 1A bulges outward of the supporting frame 1A, and the optical fiber 31A fixed to the diaphragm 2A is pulled outward, Stress acts in the diametrical direction parallel to the diaphragm of that cross section. As shown in Fig. 4 (b), the diaphragm attached to the support framework 1B.
2B is recessed inward of the support framework 1B, the optical fiber 31B fixed to the vibration 2A is compressed inward, and a compressive stress acts in the diametrical direction parallel to the diaphragm of the cross section.

On the other hand, a normal optical fiber has a core at its center, and has a structure having a concentric cross section around the core surrounded by a clad having a refractive index smaller than that of the core.
However, in order to preserve the polarization plane of the optical fiber, it is necessary to consider the arrangement of the core and the clad. That is, as shown in FIG. 5A, a so-called elliptical clad type in which an optical fiber has an elliptical clad whose cross section is arranged around a core 40, and the periphery is filled with a support 42 so that the outer shape is circular, or only the core is formed. An elliptic core type having an elliptical shape or a so-called panda having two stress applying portions 46A and 46B of the same size on both sides of the core 45 as shown in FIG. 5 (b). There is a mold.

Further, rotation of the polarization plane has been observed when an external force is applied to the optical fiber having such a structure, or bending or stress is applied. As a result, the polarization plane rotates due to a change in the external force applied to the optical fiber, and the amount of rotation is detected through an analyzer or the like, whereby the pressure acting on the diaphragm, that is, the sound pressure can be measured.

However, since there is a space inside the support framework 41 and a part of the space is configured to come into contact with the outer surface with a thin diaphragm, it cannot withstand a large external pressure, and therefore, in shallow water with a shallow water depth. Can only be used.

[Problems to be solved by the invention]

As described above, the problem of the conventional technique to be solved by the present invention is that it can withstand a large external pressure due to the presence of the internal space surrounded by the supporting frame and the diaphragm that constitute the optical fiber hydrophone. It cannot be used in the deep sea (approx. 100 kg of pressure is generated per cm ² at a water depth of 1000 m) and cannot be used.

Therefore, an object of the present invention is to provide an optical fiber hydrophone which can solve the above-mentioned drawbacks and can be used under high water pressure in deep sea.

[Means for solving problems]

The optical fiber hydrophone of the present invention has vibrating plates formed on both flat surfaces of a flat supporting frame, and has at least two side surface portions that connect the surfaces of the vibrating plates on both surfaces with smooth curved surfaces. In an optical fiber hydrophone in which an optical fiber is closely wound through a curved surface and fixed to the diaphragm, an elastic body in which air bubbles are scattered between the diaphragms is woven in a mesh space between the fibers. Insert a sound insulation body made of onion skin paper on both sides of which has a resin coating, and fill the sound insulation body and the liquid in the space surrounded by the support framework and the vibration plate, and It is configured with an acoustic tube penetrating the support framework.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings illustrating an embodiment. FIG. 1 is an external view showing the structure of an embodiment of the present invention, FIG. 2 (a) is a sectional view showing the structure of FIG. 1 taken along the line XY, and FIG. 2 (b) is a sound insulator. FIG. 3 is an explanatory diagram showing an example of the structure, and FIG. 3 is a block diagram showing the configuration of a measurement system using the present invention.

First, the outline of the present invention will be described.

In order to construct the optical fiber hydrophone for high water pressure which is the object of the present invention, it is necessary to provide the internal space formed by the support framework of the optical fiber hydrophone and the diaphragm with high water pressure resistance. For example, the internal space may be filled with a liquid such as oil to form an internal / external pressure equilibrium type, and the volume variation due to the compressibility of the liquid may be partitioned by a movable thin rubber film or the like.

Further, when viewed from the diaphragm, the same pressure is applied from the diaphragms on both sides, so that there is liquid between the diaphragms and the movement of the diaphragms is restricted. Therefore, according to this method, the high water pressure resistance of the optical fiber hydrophone itself is obtained, but the sensitivity is extremely lowered.

Therefore, it is conceivable to place an air layer inside the support framework. However, in the case where glass beads containing air bubbles are hardened with an epoxy resin, the walls of the glass beads do not elastically deform when an alternating pressure such as a sound wave is applied, and thus do not serve as air bubbles. Therefore, it is necessary to make the boundary between the bubble and another object in contact with the elastic body flexible. The onion skin paper rich in elongated fibrous cells containing gas was laminated as needed and coated with a rubber sheet or epoxy resin, etc., which fulfills this purpose and contains gas against external pressure. The part is hard to collapse.

Therefore, it is possible to maintain the effect of not becoming a load that hinders the vibration of the diaphragm under high pressure, that is, the sound insulation effect.

Here, the configuration and operation of one embodiment of the present invention will be described. With reference to FIG. 1, this embodiment comprises a support frame 1, a diaphragm 2, an optical fiber 3, an acoustic tube 4, and a sound insulator 6.

The vibration plate 2 is formed on both flat surfaces of the flat support frame 1 by adhesion or attachment. Further, the support frame 1 is provided with curved side surface portions 5 at two positions which are smoothly connected to the surfaces of the diaphragms 2 attached to both surfaces. Further, the thickness of the wall of the support frame 1 is configured to be sufficiently thicker than the thickness of the diaphragm 2, and the acoustic tube 4 which penetrates the support frame 1 and has a used frequency in an attenuation range is provided. A thin film that prevents the passage of internal and external liquids such as rubber is placed on the outside of the acoustic tube 4, and it also attenuates high-frequency sounds due to the noise of living organisms in the sea. . Support framework 1
In addition, the polarization-maintaining optical fiber 3 is wound closely while being in contact with the side surface portion 5 and the diaphragm 2 described above, and at least the portion in contact with the diaphragm 2 is made of an epoxy synthetic resin adhesive. It is stuck. The internal structure of the support framework 1 and the overall operation and measurement system will be described below.

Next, the sound insulation 6 inside the support framework 1 which is the center of the present invention, and the configuration and operation related thereto will be described.

As shown in FIGS. 2 (a) and 2 (b), in the inner space surrounded by the support framework 1 and the diaphragm 2, gas-containing elongated fibrous cells (like a vascular bundle was crushed in some places) Depending on the situation) onion skin paper 8 is stacked and pressed, and it has a sound insulation 6 which is coated and laminated with a rubber sheet or a coating material 10 such as epoxy resin, and is fixed to the support framework 1. Therefore, the protrusion 1A is provided and fixed. The remaining portion of these internal spaces is filled with 15 liquids such as oil (for example, transformer oil) having a large difference from the acoustic impedance of water (seawater). It is also possible to make two sound insulators and press them against the diaphragm 2.

Further, as shown in FIG. 2C, as another example of the sound insulation body 6,
It is possible to use a synthetic rubber or a synthetic resin as the coating material and disperse the bubbles 9 therein (without using a glass ball).

Although the sound insulators 6 of the above two examples each have a small bubble diameter due to the pressure even under high water pressure, since they can contain bubbles sufficient for sound insulation, they must maintain good sound insulation characteristics under high water pressure. Is possible.

Next, a measurement system using the optical fiber hydrophone 21 of the present invention will be described.

As shown in FIG. 3, coherent monochromatic light (so-called laser light) having a controlled wavelength is generated from the light source 11. The laser light is emitted as parallel rays by the lens 13A, is polarized by the polarizer 12 in a predetermined direction (an angle of 45 degrees between the X axis and the Y axis of the optical fiber), and is focused again by the lens 13B. Fiber optic hydrophone 21 through fiber 14A
To enter. When a sound wave is present around the optical fiber hydrophone 21, the polarization state at the exit end of the optical fiber changes due to the pressure of the sound wave. However, the optical fiber hydrophone 21 has a predetermined direction (generally the same as the polarization angle of the polarizer). The optical signal is output from the output signal 22 corresponding to the intensity of the sound wave applied to the optical fiber hydrophone 21 by focusing with the lens 18B and detecting it with the photodiode 19. Output as.

The sound pressure measurement in the deep sea using the optical fiber hydrophone of the present invention can be performed by the above method.

〔The invention's effect〕

As described in detail above, the optical fiber hydrophone of the present invention is an elastic body in which air bubbles are scattered inside the diaphragm of the optical fiber hydrophone, for example, a laminated onion skin paper is coated with a rubber sheet or an epoxy resin. Since it is possible to provide a sound insulation body, or a sound insulation body in which air bubbles are dispersed in synthetic rubber / compound resin, it is possible to use it in the deep sea where a large external pressure is applied.

[Brief description of drawings]

FIG. 1 is an external view showing the structure of one embodiment of the present invention, FIG. 2 (a) is a sectional view showing the structure taken along line XY in FIG. 1, and FIG.
(B) and (c) are explanatory views showing an example of the structure of the sound insulation body,
FIG. 3 is a block diagram showing the configuration of a measurement system using the present invention, FIGS. 4 (a) and 4 (b) are explanatory views showing the state of the optical fiber when the diaphragm vibrates, and FIG. 5 (a). And (b)
Is a cross-sectional view showing an example of the structure of a polarization-maintaining optical fiber, FIG. 6 (a) is an external view showing an example of the structure according to the prior art, and FIG. 6 (b) is cut at XY in FIG. 6 (a). A sectional view showing the structure. 1 ... Support frame, 2 ... Vibration plate, 3 ... Optical fiber, 4
…… Sound tube, 5 …… Side part, 6 …… Sound insulation.

Claims (1)

[Claims] 1. A vibration plate is formed on both flat surfaces of a flat support frame and has at least two side surface portions that connect the surfaces of the vibration plates on both sides with smooth curved surfaces, and the optical fiber is passed through the curved surfaces. In an optical fiber hydrophone that is closely wound around and fixed to the diaphragm, an elastic body in which air bubbles are scattered between the diaphragms has a space between the fibers and is woven in a net shape. Insert a sound insulation body made of onion skin paper with resin coating on both sides of the fibrous body, fill the sound insulation body and the liquid in the space surrounded by the support framework and the diaphragm, and An optical fiber hydrophone having an acoustic tube penetrating therethrough.