JP2022111084A - Acoustic detection sensor and acoustic detection device - Google Patents

Abstract

To provide an acoustic detection sensor, etc., with which it is possible to detect acoustics with high sensitivity.SOLUTION: An acoustic detection sensor 1 is used underwater and comprises primarily a body unit 3, a low acoustic impedance material 5, an optical fiber 7, a film material 9, etc. The body unit 3 is a long body bearing the tension, etc., of the acoustic detection sensor 1. A groove 11 is formed on the outer circumference of the body unit 3. Inside of the groove 11 is filled with the low acoustic impedance material 5. This means that the low acoustic impedance material is provided in at least a portion of the outer circumference of the body unit 3. The film material 9 is arranged so as to cover the body unit 3 and the low acoustic impedance material 5 from the outer circumference. The optical fiber 7 is closely attached to the inner surface of the film material 9. The optical fiber 7 is arranged along the groove 11. This means that the optical fiber 7 is arranged between the film material 9 and the low acoustic impedance material 5, and the optical fiber 7 is covered with the low acoustic impedance material 5 on the inner surface side of the film material 9.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an acoustic detection sensor capable of detecting sound in water and an acoustic detection device using the same.

Conventionally, an acoustic sensor using an optical fiber coil has been proposed as an underwater acoustic sensor. For example, a high water pressure resistant optical fiber hydrophone is produced by placing a cylindrical hollow elastic body inside an optical fiber coil with an air layer interposed therebetween, closing the opening of the hollow elastic body with a lid, and forming an orifice in the lid. It has been proposed (Patent Document 1).

JP 2012-68087 A

However, the conventional acoustic sensor using an optical fiber coil is a point sensor for detecting sound in a certain part, and it is difficult to perform distribution measurement over a wide range. For example, by arranging a plurality of acoustic sensors of Patent Document 1, it is possible to approach the distribution measurement, but especially when trying to increase the distance resolution, it is necessary to install a large number of sensors, resulting in an increase in cost.

On the other hand, a DAS (Distributed Acoustic Sensor) has been proposed as a distributed acoustic sensor that performs distribution measurement. DAS is a method of continuously launching short pulses of coherent light into an optical fiber and observing very small levels of backscattered light. However, connecting a conventional optical cable to a DAS does not provide sufficient detection sensitivity, and an acoustic sensor with higher sensitivity is desired.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an acoustic detection sensor and the like capable of detecting acoustic sounds with high sensitivity.

In order to achieve the above object, a first invention is an acoustic detection sensor for use underwater, comprising a main body, a low acoustic impedance material provided on at least a part of the outer periphery of the main body, A film material arranged so as to cover the main body and the low acoustic impedance material from the outer periphery; An acoustic detection sensor characterized by being positioned on an outer surface of a low acoustic impedance material.

The low acoustic impedance material preferably has an acoustic impedance of 1.5×10 ⁶ kg/m ² s or less or a Shore E hardness of 20 degrees or less.

The main body is an elongated body, and a linear or spiral groove is formed in the longitudinal direction of the main body, the groove is filled with the low acoustic impedance material, and a part of the optical fiber is It may be placed in contact with the low acoustic impedance material.

The main body is an elongated body, and a linear groove is formed in the longitudinal direction of the main body, the low acoustic impedance material is filled in the groove, and the optical fiber is arranged along the groove. may

The main body is an elongated body, and a spiral groove is formed in the longitudinal direction of the main body, and the optical fiber is arranged along the groove filled with the low acoustic impedance material in the groove. may be

The main body may be an elongated body, and the low acoustic impedance material may be arranged so as to cover the entire outer peripheral surface of the main body.

The optical fiber may be helically arranged in the longitudinal direction of the main body.

According to the first invention, by arranging the optical fiber on the inner surface of the membrane material and covering the optical fiber with the low acoustic impedance material on the inner surface side of the membrane material, even a slight acoustic vibration Vibration can be efficiently transmitted to the optical fiber. Therefore, the vibration can be detected with high sensitivity by the optical fiber.

In particular, if the acoustic impedance of the low acoustic impedance material is 1.5×10 ⁶ kg/m ² s or less, or if the Shore E hardness of the low acoustic impedance material is 20 degrees or less, vibration can be more reliably and sensitively caused by the optical fiber. can be detected.

Also, by arranging an optical fiber linearly or spirally on the outside of the elongated body and arranging it so that at least a part of the optical fiber is in contact with the low acoustic impedance material, it is possible to measure the distribution of sound over a wide range. can be done.

In addition, by arranging the optical fiber linearly outside the elongated body, it is possible to measure the distribution of sound over a wide range. At this time, if the optical fibers are arranged in a straight line, there is no need to excessively lengthen the total length of the optical fibers.

Also, the optical fiber may be spirally arranged around the outer circumference of the elongated body. By doing so, the optical fibers can be arranged over the entire circumference of the elongated body.

Further, by forming grooves in the main body and filling the grooves with a low acoustic impedance material, it is possible to ensure the rigidity of the main body in areas other than the grooves. It is also possible to use the reflection of acoustic vibrations within the grooves.

Further, if the low acoustic impedance material is arranged so as to cover the entire outer peripheral surface of the main body, manufacturing is facilitated. Even in this case, the optical fibers can be arranged in a straight line or in a spiral.

ADVANTAGE OF THE INVENTION According to this invention, the acoustic detection sensor etc. which can detect a sound with high sensitivity can be provided.

(a) is a diagram showing the acoustic detection sensor 1, and (b) is a sectional view taken along the line AA of (a). (a) is a diagram showing an acoustic detection device 20, and (b) is a diagram showing an acoustic detection device 20a. (a) is a diagram showing an acoustic detection sensor 1a, and (b) is a sectional view taken along line BB of (a). (a) is a diagram showing an acoustic detection sensor 1b, and (b) is a sectional view taken along line CC of (a). (a) is a diagram showing an acoustic detection sensor 1c, and (b) is a sectional view taken along line DD of (a). (a) is a diagram showing an acoustic detection sensor 1d, and (b) is a sectional view taken along the line HH of (a). FIG. 3 is a cross-sectional view showing a cable 30; (a) is a figure which shows the usage condition of the cable 30, (b) is a figure which shows the usage method of the towing cable 30a. The figure which shows a test method. (a) is a diagram showing the test results of Example 1, and (b) is a diagram showing the test results of Example 2. FIG. The figure which shows the test result of a comparative example. The figure which showed the relationship between the detection minimum sound pressure and Shore E hardness. Rubber hardness comparison chart.

(First embodiment)
An acoustic detection sensor according to an embodiment of the present invention will be described below. FIG. 1(a) is a partially perspective view showing the acoustic detection sensor 1, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). The acoustic detection sensor 1 is used underwater, and is mainly composed of a main body 3, a low acoustic impedance material 5, an optical fiber 7, a film material 9, and the like.

In this embodiment, the acoustic detection sensor 1 is elongated. That is, the body portion 3 is an elongated body and takes charge of the tension of the sound detection sensor 1 and the like. In addition, the material and structure of the main body part 3 are not particularly limited. For example, a member having a certain degree of rigidity or a member having flexibility can be applied. Also, as will be described later, as the body portion 3, an existing cable or structure can be applied.

A groove 11 is formed in the outer peripheral portion of the body portion 3 . In this embodiment, the grooves 11 are formed at two locations facing each other. Note that the number of grooves 11 arranged and the positions where the grooves 11 are arranged are not limited to the illustrated example. The groove 11 is formed in a straight line substantially straight in the longitudinal direction of the body portion 3 .

The groove 11 is filled with a low acoustic impedance material 5 . That is, the low acoustic impedance material is provided on at least part of the outer peripheral portion of the main body portion 3 . In the present invention, the low acoustic impedance material 5 is, for example, a member having an acoustic impedance equal to or lower than the acoustic impedance of water (1.5× ^{10 6} kg/m ² s). It is more desirable to be ² s or less. As such a low acoustic impedance material 5, a foam such as styrene foam is suitable. Acoustic impedance can be measured according to JISA1405-1:2007.

A film material 9 is arranged so as to cover the main body part 3 and the low acoustic impedance material 5 from the outer periphery. That is, part of the film material 9 is in close contact with the low acoustic impedance material 5 . A metal thin film, rubber, or the like can be applied to the film material 9, but it is desirable that the material has a certain degree of stretchability and excellent water resistance. For example, neoprene rubber is suitable. Moreover, the film material 9 preferably has a thickness of, for example, 1 mm or less, and more preferably 0.5 mm or less. If the film material 9 becomes too thick, the deformation resistance against acoustic vibration increases.

In order to protect the film material 9 , a protective layer may be provided on the outer peripheral portion of the film material 9 . In this case, if the film material 9 is completely covered, vibrations are less likely to be transmitted to the film material 9. Therefore, the protective layer is woven in a net shape with gaps, for example, so that the film material 9 is partially exposed. It can be composed of embedded metal wires, fibers, or the like.

The optical fiber 7 is in close contact with the inner surface of the film material 9 . An optical fiber 7 is arranged along the groove 11 . That is, the optical fiber 7 is arranged between the membrane material 9 and the low acoustic impedance material 5 , and the optical fiber 7 is arranged on the outer surface of the low acoustic impedance material 5 on the inner surface side of the membrane material 9 . In addition, as described above, the grooves 11 are formed at two locations facing each other, and are formed in a substantially straight line in the longitudinal direction of the main body 3 . Accordingly, the optical fibers 7 are similarly formed at two locations facing each other, and are formed in a substantially straight line in the longitudinal direction of the main body 3 .

The optical fiber 7 may be glass fiber or resin fiber. Also, the optical fiber 7 may be a single mode fiber, or may be a multi-core fiber or a fiber having a diffraction grating (Fiber Bragg Gratings: FBG).

Next, an acoustic detection device using the acoustic detection sensor 1 will be described. FIG. 2A is a diagram showing the acoustic detection device 20. FIG. In the acoustic detection device 20, the optical fiber 7 and the light emitting section 13 are connected at one end of the acoustic detection sensor 1, and the optical fiber 7 and the light receiving section 15 are connected at the other end of the acoustic detection sensor 1. be done.

The acoustic detection device 20 causes light to enter the optical fiber 7 from one light emitting portion 13 side, and receives light emitted from the other end portion by the light receiving portion 15 . At this time, if any part of the acoustic detection sensor 1 receives acoustic vibration, the optical fiber 7 is slightly stressed by this vibration, and the phase and intensity of the light propagating through the optical fiber 7 change accordingly. occur. By detecting this change in the light receiving section 15, an external change (acoustic vibration) at any part of the sound detecting sensor 1 can be detected.

In this way, in the method of detecting sound using light transmitted from one end of the optical fiber 7 to the other end, in the light receiving section 15, light having an intensity similar to that of light incident from the light emitting section 13 is detected. is detected, the S/N ratio can be increased and the sensitivity is good. On the other hand, with this method, it is not possible to know which part of the sound detection sensor 1 detected the sound. That is, no distribution measurement is possible.

Therefore, when performing distribution measurement, an acoustic detection device 20a shown in FIG. 2(b) can be used. In the acoustic detection device 20 a , the light emitting section 13 and the light receiving section 15 are connected to the optical fiber 7 at one end of the acoustic detection sensor 1 . The optical fiber 7 is connected to the light emitting section 13 and the light receiving section 15 via a branching filter. Further, the other end of the optical fiber 7 is subjected to antireflection treatment so that the reflected light from the end face is not returned.

The acoustic detection device 20 a continuously causes pulsed light to enter the optical fiber 7 from the light emitting section 13 and receives backscattered light from the optical fiber 7 at the light receiving section 15 . At this time, it is possible to grasp the position of the acoustic detection unit from the time from incidence to reception of the backscattered light. That is, when a certain portion of the acoustic detection sensor 1 receives acoustic vibration, a slight change in stress occurs in the optical fiber 7 at that portion, thereby changing the backscattered light. Therefore, it is possible to grasp the presence or absence of acoustic vibration.

Further, since the positional information of the external change can be obtained from the time at which the backscattered light reaches the light receiving section 15, it is possible to know at which part of the acoustic detection sensor 1 the acoustic vibration was detected.

As the optical fiber 7, a multi-core fiber in which a plurality of cores are arranged is used, the same pulsed light is incident on each core, and the backscattered light from each core is collected, so that it can be practically used as a sensor. An effect similar to that obtained by extending the length of an optical fiber can be obtained, and the S/N ratio is improved. Similarly, the use of an optical fiber with an FGB can increase the intensity of the backscattered light, thus improving the signal-to-noise ratio in distributed measurements. By using a multi-core fiber or an FBG fiber as the optical fiber 7 in this way, the detection sensitivity can be improved.

In this embodiment, it is considered that the reason why sound detection is possible with high sensitivity is based on the following principle. As described above, when an optical fiber is used for acoustic detection, it is important to efficiently transmit acoustic vibrations to the optical fiber to detect changes such as backscattered light.

In this embodiment, the film material 9 ensures water resistance, and the film material 9 itself is used as a vibrating body. That is, the acoustic vibration is first transmitted to the membrane material 9 , and the vibration of the membrane material 9 transmits the vibration to the optical fiber 7 . At this time, if the optical fiber 7 is placed on the outer surface of a high acoustic impedance material (such as water or a member having a high acoustic impedance with respect to the membrane material 9), this member causes the optical fiber 7 (membrane material 9) to vibrate. Reduce. Therefore, acoustic vibration cannot be efficiently transmitted to the optical fiber 7 .

On the other hand, by arranging the low acoustic impedance material 5 on the inner surface of the film material 9 (on the optical fiber 7 side), the vibration transmitted to the film material 9 can be efficiently transmitted to the optical fiber 7 side. That is, the vibration of the film material 9 is not hindered, and acoustic vibration can be efficiently transmitted to the optical fiber 7 .

Since the acoustic impedance of air is extremely low, the low acoustic impedance material 5 may be a complete air layer. However, if the air layer is completely formed, the bending of the film material 9 cannot be suppressed during use, and the optical fiber is constantly greatly distorted, making accurate measurement impossible. Therefore, in order to allow vibration of the membrane material 9 while supporting the membrane material 9 with some reaction force from the inner surface side and allowing the membrane material 9 to vibrate, an elastic body (solid body) such as a foam having a low acoustic impedance is required. ) should be filled.

As described above, according to the present embodiment, by arranging the film member 9 on the outer surface side of the sound detection sensor 1, the film member 9 can reliably receive acoustic vibrations. Also, the film material 9 can ensure water resistance. In addition, by arranging the low acoustic impedance material 5 on the inner surface side of the film material 9 , the sound can be detected efficiently without disturbing the vibration of the film material 9 and the optical fiber 7 .

Moreover, by using the acoustic detection sensor 1 as a DAS, it is possible to measure the acoustic distribution. At this time, since the structure is such that the low acoustic impedance material 5 is arranged in the groove 11 on the outer peripheral surface of the main body 3 and the optical fiber 7 is arranged along the groove 11, the structure is simple, and the acoustic detection sensor 1 can be used. Even if the length is increased, the manufacturability is good.

(Second embodiment)
Next, a second embodiment will be described. FIG. 3(a) is a partially perspective view showing an acoustic detection sensor 1a according to the second embodiment, and FIG. 3(b) is a cross-sectional view taken along line BB of FIG. 3(a). In the following description, the same reference numerals as in FIGS. 1 and 2 are given to the components having the same functions as those of the sound detection sensor 1 and the like, and overlapping descriptions are omitted.

The acoustic detection sensor 1a has substantially the same configuration as the acoustic detection sensor 1, but the optical fiber 7 and the like are different. In the acoustic detection sensor 1 a , a groove 11 is spirally formed in the outer peripheral surface of the main body 3 in the longitudinal direction of the main body 3 . Although the illustrated example shows an example in which one groove 11 is formed, a plurality of grooves 11 may be provided.

The interior of the groove 11 is filled with a low acoustic impedance material 5 . Also, the optical fiber 7 is arranged along the groove 11 . That is, the optical fiber 7 is spirally arranged in the longitudinal direction of the body portion 3 .

According to the second embodiment, effects similar to those of the first embodiment can be obtained. Moreover, since the optical fiber 7 is arranged over the entire circumference of the sound detection sensor 1, sound from all directions can be detected.

(Third embodiment)
Next, a third embodiment will be described. FIG. 4(a) is a partially perspective view showing an acoustic detection sensor 1b according to the third embodiment, and FIG. 4(b) is a cross-sectional view taken along line CC of FIG. 4(a). The acoustic detection sensor 1b has substantially the same configuration as the acoustic detection sensor 1, but differs in the mode of the low acoustic impedance material 5 and the like.

In the acoustic detection sensor 1b, a groove is not formed on the outer periphery of the main body 3, and the low acoustic impedance material 5 is arranged so as to cover the entire outer peripheral surface of the main body 3. As shown in FIG. That is, the film material 9 is arranged so as to cover the entire outer peripheral surface of the low acoustic impedance material 5 .

The optical fiber 7 is arranged substantially linearly with respect to the longitudinal direction of the acoustic detection sensor 1b. Although the illustrated example shows an example in which two optical fibers 7 are formed at two locations facing each other, the number of optical fibers 7 may be one, or three or more. .

According to the third embodiment, effects similar to those of the first embodiment can be obtained. Moreover, since the groove 11 is not required in the main body 3, the manufacturability is good, and the present invention can be applied to the main body 3 in which the groove 11 cannot be formed.

(Fourth embodiment)
Next, a fourth embodiment will be described. FIG. 5(a) is a partially perspective view showing an acoustic detection sensor 1c according to the fourth embodiment, and FIG. 5(b) is a cross-sectional view taken along line DD of FIG. 5(a). The acoustic detection sensor 1c has substantially the same configuration as the acoustic detection sensor 1b, but the optical fiber 7 and the like are different.

In the acoustic detection sensor 1c, similarly to the acoustic detection sensor 1b, no groove is formed on the outer periphery of the main body 3, and the low acoustic impedance material 5 is arranged so as to cover the entire outer peripheral surface of the main body 3. FIG. That is, the film material 9 is arranged so as to cover the entire outer peripheral surface of the low acoustic impedance material 5 .

The optical fiber 7 is spirally arranged in the longitudinal direction of the acoustic detection sensor 1c. In addition, although the illustrated example shows an example in which one optical fiber 7 is arranged, the number of optical fibers 7 may be plural. In this manner, the optical fibers 7 may be arranged in a spiral even if no groove is formed.

According to the fourth embodiment, effects similar to those of the third embodiment can be obtained. In addition, since it is not necessary to arrange the optical fiber 7 along the groove, even if the optical fiber is arranged in a spiral shape, there is no risk of misalignment, and the productivity is excellent.

(Fifth embodiment)
Next, a fifth embodiment will be described. FIG. 6(a) is a partially perspective view showing an acoustic detection sensor 1d according to the fifth embodiment, and FIG. 6(b) is a sectional view taken along the line HH of FIG. 6(a). The acoustic detection sensor 1d has substantially the same configuration as the acoustic detection sensor 1c, but differs in the form of the grooves 11 and the like.

In the acoustic detection sensor 1d, the optical fiber 7 is spirally arranged in the same manner as the acoustic detection sensor 1c. They are arranged at predetermined intervals in the circumferential direction on the outer peripheral surface. A low acoustic impedance material 5 is placed in the groove 11 . At this time, the grooves 11 and the low acoustic impedance material 5 are not spirally formed in the axial direction of the main body 3, but arranged linearly in the axial direction. That is, the optical fiber 7 and the low acoustic impedance material 5 are not formed facing in the same direction with respect to the axial direction.

In this case, the optical fiber 7 is not placed in contact with the low acoustic impedance material 5 over the entire length, but is in contact with the low acoustic impedance material 5 at predetermined intervals in the longitudinal direction of the optical fiber 7. , and contact with the body portion 3 at other portions. That is, only a portion of optical fiber 7 is placed in contact with low acoustic impedance material 5 .

Even in this case, the film material 9 is arranged so as to cover the main body part 3 , the low acoustic impedance material 5 and the optical fiber 7 as a whole. In addition, although the illustrated example shows an example in which one optical fiber 7 is arranged, the number of optical fibers 7 may be plural. Further, instead of arranging the grooves 11 and the low acoustic impedance material 5 linearly, they may be helically arranged with respect to the axial direction of the main body 3 and the optical fibers 7 may be arranged linearly. That is, the groove 11 and the low acoustic impedance material 5 are arranged linearly or spirally in the main body 3, and the optical fiber 7 is arranged at an angle different from that of the groove 11 and the low acoustic impedance material 5 with respect to the axial direction. may

According to the fifth embodiment, effects similar to those of the third embodiment and the like can be obtained. Thus, even if the groove 11 is not formed along the optical fiber 7, if at least a part of the optical fiber 7 is in contact with the low acoustic impedance material 5, substantially the same effect can be obtained.
(acoustic detection cable)
Next, a usage example of an acoustic detection device using an acoustic detection sensor will be described. FIG. 7 is a cross-sectional view showing the cable 30. As shown in FIG. In the following description, an example using the acoustic detection sensor 1c will be described, but other acoustic detection sensors can also be applied as appropriate.

The cable 30 has a power transmission cable 31 inside. That is, the main body 3 described above is the power transmission cable 31 , and the low acoustic impedance material 5 , the optical fiber 7 , and the film material 9 are arranged around the power transmission cable 31 . Thus, as the body part 3, an existing long body such as a communication cable, a power transmission cable, or a pipe can be used.

A braided tube 33 is arranged on the outermost layer of the cable 30 . As described above, the braided tube 33 is a protective member that is woven with a gap so that a part of the inner layer film material 9 is exposed. By using the braided tube 33, it is possible to suppress wear and damage to the film material 9 due to the film material 9 coming into contact with or rubbing against other members.

FIG. 8(a) is a schematic diagram showing a state in which the cable 30 is used as a submarine cable. The acoustic detection sensor 1c may be arranged over the entire length of the cable 30, or may be arranged only along part of the entire length of the cable 30. FIG. For example, when used as a submarine cable, the acoustic detection sensor 1c may be arranged only at a portion located on the seabed.

Also, as shown in FIG. 8(b), the acoustic detection sensor 1c may be used for the towing cable 30a. In this way, the acoustic detection sensor according to the present invention can use an existing elongated body as the main body, and can be used especially in any part of the water. Note that the main body 3 is not limited to a long body such as a cable. For example, floating facilities, ship bodies, submarine structures such as tetrapods, etc. are also applicable as the main body. In this case, a part of the outer surface of the structure is used as the main body part 3, a low acoustic impedance material 5 is arranged in a part of the structure, and a part of the structure near the part and the low acoustic impedance material 5 The film material 9 with the optical fiber 7 in close contact with the inner surface may be arranged so as to cover the outer periphery of the optical fiber 7 .

Next, various acoustic detection sensors were used and their sensitivities were evaluated. FIG. 9 is a schematic diagram showing the test method. A prototype acoustic detection sensor 47 was installed in the water tank 41 . A single-mode optical fiber was used as the optical fiber. A DAS 49 was connected to one end of the optical fiber of the acoustic detection sensor 47 . The other end of the optical fiber was subjected to antireflection treatment.

The acoustic detection sensor 47 to be tested was as follows. In Example 1, an optical fiber was helically arranged on a rod-shaped member (made of expanded polystyrene) having an acoustic impedance of 3.3×10 ³ kg/m ² s. In Example 2, a spiral groove was formed in the outer circumference of a rod-shaped member (made of acrylic resin) having an acoustic impedance of 3.2×10 ⁶ kg/m ² s, and an acoustic impedance of 3.3×10 was formed in the groove. A material of ³ kg/m ² s was filled, and an optical fiber was arranged spirally along the groove. As a comparative example, an optical fiber was similarly arranged spirally around the outer periphery of a rod-shaped member having an acoustic impedance of 1.8×10 ⁶ kg/m ² s.

An underwater speaker 43 is arranged near the bottom of the water tank 41 . A sound wave having a frequency of 40 Hz to 200 Hz and a sound pressure of 80 dB to 160 dB was generated toward the sound detection sensor 47 by the underwater speaker 43 . The distance between the underwater speaker 43 and the sound detection sensor 47 was set to 12 cm.

A hydrophone 45 was installed just above the underwater speaker 43 and in the vicinity of the sound detection sensor 47 . The sound pressure from the underwater speaker 43 was measured by the hydrophone 45 . At the same time, the DAS 49 measured the magnitude of vibration of the optical fiber 7 . The results are shown in FIGS. 10(a), 10(b) and 11. FIG.

10(a) shows the results of Example 1, FIG. 10(b) shows the results of Example 2, and FIG. 11 shows the results of Comparative Example. In each figure, black circles (E in the figure) are the results at 200 Hz, black squares (G in the figure) are the results at 100 Hz, and black triangles (F in the figure) are the results at 40 Hz.

For all the samples, the vibration increased with respect to the sound pressure, and the sound could be detected. However, as shown in FIGS. 10(a) and 10(b), Examples 1 and 2, in which the optical fiber was wound around the low acoustic impedance material, exhibited greater vibration with respect to sound pressure than the comparative example. That is, it was confirmed that Examples 1 and 2 can detect sound with high sensitivity.

In the above description, the characteristics of the low acoustic impedance material 5 are defined as materials with low acoustic impedance, but they can also be defined by ASKER C hardness or Shore E hardness. FIG. 12 is a graph showing the results of evaluating the detection sensitivity to the hardness of the material, and showing the relationship between the lowest detected sound pressure and the Shore E hardness.

In the figure, I is a styrene foam rod, J is a silicon foam rod, K is a silicon rod (3D molded product), L is a rubber rod, M is a vinyl chloride rod, and N is a metal tube. be. As shown in the figure, there is a correlation between the minimum detected sound pressure and the Shore E hardness, and the characteristics of the low acoustic impedance material 5 can also be defined by hardness such as Shore E hardness. For example, a material having a Shore E hardness of 20 degrees or less is suitable as a low acoustic impedance material.

In addition, FIG. 13 is a rubber hardness comparison table of spring type, durometer, and ASKER (original figure source: PackingLand HP https://www.packing.ko.jp/SIRYOU/gomukoudo1.htm), enclosed in the added frame The only part is the relationship between Shore E hardness and ASKER C hardness. It can be said that Shore E hardness and ASKER C hardness are almost the same standard. Therefore, a material having an ASKER C hardness of 20 degrees or less is suitable as a low acoustic impedance material.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not influenced by the above-described embodiments. It is obvious that a person skilled in the art can conceive various modifications or modifications within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. be understood to belong to

1, 1a, 1b, 1c, 1d ...... Acoustic detection sensor 3 ...... Body portion 5 ...... Low acoustic impedance material 7 ...... Optical fiber 9 ...... Film material 11 ...... Groove 13 ...... Light emitting unit 15 Light receiving units 20, 20a Acoustic detector 30 Cable 30a Towing cable 31 Power transmission cable 33 Braided tube 41 Water tank 43 Underwater Speaker 45 Hydrophone 47 Sound detection sensor 49 DAS

Claims (7)

An acoustic detection sensor for use in water, comprising:
a main body;
a low acoustic impedance material provided on at least part of the outer peripheral portion of the main body;
a film material arranged to cover the main body and the low acoustic impedance material from the outer periphery;
an optical fiber in close contact with the inner surface of the film material;
and
The acoustic detection sensor, wherein the optical fiber is arranged on the outer surface of the low acoustic impedance material on the inner surface side of the membrane material. The acoustic detection sensor according to claim 1, wherein the low acoustic impedance material has an acoustic impedance of 1.5 x ¹⁰⁶ kg/ ^m2s or less or a Shore E hardness of 20 degrees or less. The main body is an elongated body,
A linear or spiral groove is formed in the longitudinal direction of the main body,
The groove is filled with the low acoustic impedance material,
3. The acoustic detection sensor of claim 1 or claim 2, wherein a portion of the optical fiber is placed in contact with the low acoustic impedance material. The main body is an elongated body,
A linear groove is formed in the longitudinal direction of the main body,
The groove is filled with the low acoustic impedance material,
3. The acoustic detection sensor according to claim 1, wherein the optical fiber is arranged along the groove. The main body is an elongated body,
A spiral groove is formed in the longitudinal direction of the main body,
The groove is filled with the low acoustic impedance material,
3. The acoustic detection sensor according to claim 1, wherein the optical fiber is arranged along the groove. The main body is an elongated body,
3. The acoustic detection sensor according to claim 1, wherein the low acoustic impedance material is arranged so as to cover the entire outer peripheral surface of the main body. 7. The acoustic detection sensor according to claim 6, wherein the optical fiber is spirally arranged in the longitudinal direction of the main body.

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