Acoustic detection sensor, acoustic detection device

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]

[0001] The present invention relates to an acoustic detection sensor capable of detecting sound in water and an acoustic detection device using the same. [Background technology]

[0002] Conventionally, acoustic sensors using optical fiber coils have been proposed as underwater acoustic sensors. For example, a high-water-pressure-resistant optical fiber hydrophone has been proposed, in which a cylindrical hollow elastic body is placed inside an optical fiber coil with an air layer between them, the opening of the hollow elastic body is closed with a lid, and an orifice is formed in the lid (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-68087 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional acoustic sensors using optical fiber coils are point sensors that detect sound in a specific area, and it is difficult to perform distributed measurement over a wide area. For example, by arranging multiple acoustic sensors such as those described in Patent Document 1, it is possible to approach distributed measurement, but if you want to improve the distance resolution in particular, you will need to install a large number of sensors, which will increase costs.

[0005] Meanwhile, the Distributed Acoustic Sensor (DAS) has been proposed as a distributed acoustic sensor for distributed measurement. DAS is a method of continuously injecting short pulse waves of coherent light into an optical fiber and observing extremely small levels of backscattered light. However, connecting a conventional optical cable to a DAS does not provide sufficient detection sensitivity, and there is a demand for acoustic sensors with higher sensitivity.

[0006] The present invention has been made in view of the above problems, and has an object to provide a sound detection sensor or the like that is capable of detecting sound with high sensitivity. [Means for solving the problem]

[0007] In order to achieve the above-mentioned 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 membrane material arranged so as to cover the main body and the low acoustic impedance material from the outer periphery, and an optical fiber in close contact with the inner surface of the membrane material, and 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 low acoustic impedance material has an acoustic impedance of 1.5×10 6 kg / m 2 s or less or Shore E hardness 20 degrees or less The acoustic detection sensor is characterized by the above.

[0009] The main body may be an elongated body, with a linear or spiral groove formed in the longitudinal direction of the main body, the low acoustic impedance material filled in the groove, and a portion of the optical fiber positioned so as to be in contact with the low acoustic impedance material.

[0010] The main body may be an elongated body, and a linear groove may be formed in the longitudinal direction of the main body, the low acoustic impedance material may be filled in the groove, and the optical fiber may be arranged along the groove.

[0011] The main body may be an elongated body, and a spiral groove may be formed in the longitudinal direction of the main body, the low acoustic impedance material may be filled in the groove, and the optical fiber may be arranged along the groove.

[0012] The main body may be an elongated body, and the low acoustic impedance material may be disposed so as to cover the entire outer circumferential surface of the main body.

[0013] The optical fiber may be arranged spirally relative to the longitudinal direction of the main body.

[0014] According to the first aspect of the present invention, by arranging the optical fiber on the inner surface of the film material and covering the optical fiber with a low acoustic impedance material on the inner surface of the film material, even slight acoustic vibrations can be efficiently transmitted to the optical fiber, allowing vibrations to be detected with high sensitivity by the optical fiber.

[0015] In particular, the acoustic impedance of low acoustic impedance materials is 1.5 × 10 6 kg / m 2 If the Shore E hardness of the low acoustic impedance material is 20 degrees or less, vibration can be detected more reliably and sensitively by the optical fiber.

[0016] Furthermore, by arranging the optical fiber linearly or spirally outside the elongated body so that at least a portion of the optical fiber is in contact with the low acoustic impedance material, it is possible to measure the acoustic distribution over a wide range.

[0017] Furthermore, by arranging the optical fiber linearly outside the elongated body, it is possible to measure the acoustic distribution over a wide range. In this case, if the optical fiber is arranged linearly, there is no need to make the total length of the optical fiber excessively long.

[0018] The optical fiber may also be arranged spirally around the outer periphery of the elongated body, thereby making it possible to arrange the optical fiber around the entire periphery of the elongated body.

[0019] Furthermore, by forming grooves in the main body and filling the grooves with a low acoustic impedance material, the rigidity of the main body can be ensured in areas other than the grooves. Also, the reflection of acoustic vibrations in the grooves can be utilized.

[0020] Furthermore, if a low acoustic impedance material is arranged so as to cover the entire outer periphery of the main body, manufacturing is easy. Even in this case, the optical fiber can be arranged either linearly or spirally. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a sound detection sensor or the like that is capable of detecting sound with high sensitivity. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2A is a diagram showing an acoustic detection sensor 1, and FIG. 2B is a cross-sectional view taken along line AA in FIG. [Figure 2] FIG. 1(a) is a diagram showing an acoustic detection device 20, and FIG. 1(b) is a diagram showing an acoustic detection device 20a. [Figure 3] FIG. 1A is a diagram showing an acoustic detection sensor 1a, and FIG. 1B is a cross-sectional view taken along line BB in FIG. [Figure 4] FIG. 1A is a diagram showing an acoustic detection sensor 1b, and FIG. 1B is a cross-sectional view taken along line CC in FIG. [Figure 5] FIG. 1A is a diagram showing an acoustic detection sensor 1c, and FIG. 1B is a cross-sectional view taken along line DD in FIG. [Figure 6] FIG. 1A is a diagram showing an acoustic detection sensor 1d, and FIG. 1B is a cross-sectional view taken along line HH in FIG. [Figure 7] FIG. [Figure 8] FIG. 1(a) is a diagram showing the state of use of the cable 30, and FIG. 1(b) is a diagram showing how to use the towing cable 30a. [Figure 9] A diagram showing the test method. [Figure 10] FIG. 1( a ) is a diagram showing the test results of Example 1, and FIG. 1( b ) is a diagram showing the test results of Example 2. [Figure 11] FIG. 10 is a diagram showing test results of a comparative example. [Figure 12] A diagram showing the relationship between the minimum detectable sound pressure and Shore E hardness. [Figure 13] Rubber hardness comparison chart. DETAILED DESCRIPTION OF THE INVENTION

[0023] (First embodiment) An acoustic detection sensor according to an embodiment of the present invention will be described below. Fig. 1(a) is a partial perspective view showing the acoustic detection sensor 1, and Fig. 1(b) is a cross-sectional view taken along line AA in 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 membrane material 9, etc.

[0024] In this embodiment, the sound detection sensor 1 is an elongated body. That is, the main body 3 is an elongated body and bears the tension and the like of the sound detection sensor 1. The material and structure of the main body 3 are not particularly limited. For example, a member having a certain degree of rigidity or a member having flexibility can be applied. Furthermore, as will be described later, an existing cable or structure can also be applied as the main body 3.

[0025] Grooves 11 are formed on the outer periphery of the main body 3. In this embodiment, the grooves 11 are formed in two locations facing each other. The number and positions of the grooves 11 are not limited to the example shown in the figure. The grooves 11 are formed in a substantially straight line in the longitudinal direction of the main body 3.

[0026] The grooves 11 are filled with a low acoustic impedance material 5. That is, the low acoustic impedance material is provided on at least a part of the outer periphery of the main body 3. In the present invention, the low acoustic impedance material 5 has an acoustic impedance lower than that of water (1.5×10 6 kg / m 2 s) and below, but 5 × 10 3 kg / m 2 It is more desirable that the acoustic impedance is equal to or less than 1 / 2 s. For example, a foam such as expanded polystyrene is suitable as such a low acoustic impedance material 5. The acoustic impedance can be measured according to JISA1405-1:2007.

[0027] The membrane material 9 is arranged so as to cover the outer periphery of the main body 3 and the low acoustic impedance material 5. That is, a portion of the membrane material 9 is in close contact with the low acoustic impedance material 5. The membrane material 9 can be made of a thin metal film, rubber, or the like, but it is preferable that the material has a certain degree of elasticity and excellent water resistance. For example, neoprene rubber is suitable. Furthermore, the membrane material 9 preferably has a thickness of, for example, 1 mm or less, and more preferably 0.5 mm or less. If the membrane material 9 is too thick, its deformation resistance to acoustic vibrations will increase.

[0028] To protect the membrane material 9, a protective layer may be provided on the outer periphery of the membrane material 9. In this case, if the membrane material 9 is completely covered, vibrations are less likely to be transmitted to the membrane material 9. Therefore, the protective layer may be made of, for example, metal wires or fibers woven in a mesh with gaps so that the membrane material 9 is partially exposed.

[0029] The optical fiber 7 is in close contact with the inner surface of the film material 9. The optical fiber 7 is arranged along the groove 11. That is, the optical fiber 7 is arranged between the film material 9 and the low acoustic impedance material 5, and on the inner surface side of the film material 9, the optical fiber 7 is arranged on the outer surface of the low acoustic impedance material 5. As described above, the grooves 11 are formed in 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 fiber 7 is also formed in two locations facing each other and is formed in a substantially straight line in the longitudinal direction of the main body 3.

[0030] The optical fiber 7 may be a glass fiber or a resin fiber. The optical fiber 7 may be a single-mode fiber, a multi-core fiber, or a fiber having a diffraction grating (Fiber Bragg Gratings: FBG).

[0031] Next, we will explain an acoustic detection device using the acoustic detection sensor 1. Fig. 2(a) is a diagram showing an acoustic detection device 20. In the acoustic detection device 20, an optical fiber 7 and a light-emitting unit 13 are connected at one end of the acoustic detection sensor 1, and an optical fiber 7 and a light-receiving unit 15 are connected at the other end of the acoustic detection sensor 1.

[0032] The acoustic detection device 20 causes light to enter the optical fiber 7 from one end of the light-emitting unit 13, and receives the light emitted from the other end with the light-receiving unit 15. At this time, if any part of the acoustic detection sensor 1 receives acoustic vibrations, the optical fiber 7 is subjected to slight stress due to the vibrations, which causes changes in the phase and intensity of the light propagating through the optical fiber 7. By detecting this change in the light-receiving unit 15, it is possible to detect an external change (acoustic vibration) at any part of the acoustic detection sensor 1.

[0033] In this way, in the method of detecting sound using light that transmits from one end of the optical fiber 7 to the other, the light receiving unit 15 detects light with the same intensity as the light incident from the light emitting unit 13, so the S / N ratio can be increased and sensitivity is good. However, with this method, it is not possible to know at which part of the sound detection sensor 1 the sound was detected. In other words, distribution measurement is not possible.

[0034] Therefore, when performing distribution measurement, an acoustic detection device 20a shown in Fig. 2(b) can be used. In the acoustic detection device 20a, a light emitting unit 13 and a light receiving unit 15 are connected to an optical fiber 7 at one end of the acoustic detection sensor 1. The optical fiber 7 is connected to the light emitting unit 13 and the light receiving unit 15 via a branching filter. In addition, an anti-reflection treatment is applied to the other end of the optical fiber 7 to prevent light reflected at the end face from returning.

[0035] The acoustic detection device 20a continuously emits pulsed light from the light emitter 13 into the optical fiber 7, and receives the backscattered light from the optical fiber 7 with the light receiver 15. At this time, it is possible to determine the position of the acoustic detection unit from the time from incidence to reception of the backscattered light. In other words, when a certain part of the acoustic detection sensor 1 is subjected to acoustic vibration, a slight change in stress occurs in the optical fiber 7 at that part, which causes a change in the backscattered light. This makes it possible to determine whether or not acoustic vibration is present.

[0036] Furthermore, since the positional information of the external change can be obtained from the time when the backscattered light reaches the light receiving section 15, it is possible to know at which part of the sound detection sensor 1 the acoustic vibration has been detected.

[0037] Note that by using a multicore fiber in which multiple cores are arranged as the optical fiber 7, irradiating each core with the same pulsed light, and collecting the backscattered light from each core, it is possible to obtain the same effect as extending the length of the optical fiber that can be used as a sensor, and the S / N ratio is improved. Similarly, by using an optical fiber with an FGB, the intensity of the backscattered light can be increased, thereby improving the S / N ratio in distributed measurement. In this way, by using a multicore fiber or an FBG fiber as the optical fiber 7, it is possible to improve the detection sensitivity.

[0038] It is believed that the reason why this embodiment is able to detect sound with high sensitivity is due to the following principle: As described above, when an optical fiber is used for sound detection, it is important to efficiently transmit acoustic vibrations to the optical fiber and detect changes in backscattered light, etc.

[0039] In this embodiment, the membrane material 9 ensures water resistance, and the membrane 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. In this case, if the optical fiber 7 is placed on the outer surface of a material with a high acoustic impedance (for example, water or a material with a high acoustic impedance relative to the membrane material 9), the vibration of the optical fiber 7 (membrane material 9) is reduced by this material. As a result, the acoustic vibration cannot be transmitted to the optical fiber 7 efficiently.

[0040] In contrast to this, by arranging the low acoustic impedance material 5 on the inner surface (optical fiber 7 side) of the film material 9, the vibration transmitted to the film material 9 can be efficiently transmitted to the optical fiber 7. In other words, the vibration of the film material 9 is not impeded, and the acoustic vibration can be efficiently transmitted to the optical fiber 7.

[0041] Since the acoustic impedance of air is extremely low, one method is to use a completely air layer as the low acoustic impedance material 5. However, if it is a completely air layer, it is not possible to suppress the bending of the film material 9 during use, and the optical fiber is constantly significantly distorted, making accurate measurements impossible. Therefore, in order to support the film material 9 from the inner side with a slight reaction force to maintain its shape while allowing the film material 9 to vibrate, it is desirable to fill it with an elastic body (solid) with low acoustic impedance, such as foam.

[0042] As described above, according to this embodiment, by arranging the film material 9 on the outer surface side of the sound detection sensor 1, the film material 9 can reliably receive acoustic vibrations. The film material 9 also ensures water resistance. Furthermore, by arranging the low acoustic impedance material 5 on the inner surface side of the film material 9, sound can be detected efficiently without interfering with the vibrations of the film material 9 and the optical fiber 7.

[0043] Furthermore, sound distribution measurement is possible by using the sound detection sensor 1 as a DAS. In this case, the low acoustic impedance material 5 is placed in the groove 11 on the outer circumferential surface of the main body 3, and the optical fiber 7 is placed along the groove 11. Therefore, the structure is simple, and even if the length of the sound detection sensor 1 is increased, manufacturability is good.

[0044] (Second embodiment) Next, a second embodiment will be described. Fig. 3(a) is a partial 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 in Fig. 3(a). In the following description, components that have the same functions as the acoustic detection sensor 1 etc. are denoted by the same reference numerals as in Figs. 1 and 2, and redundant description will be omitted.

[0045] The sound detection sensor 1a has a configuration similar to that of the sound detection sensor 1, but differs in the form of the optical fiber 7. In the sound detection sensor 1a, a groove 11 is formed spirally in the longitudinal direction of the main body 3 on the outer circumferential surface of the main body 3. In the illustrated example, one groove 11 is formed, but multiple grooves 11 may be provided.

[0046] The groove 11 is filled with a low acoustic impedance material 5. The optical fiber 7 is arranged along the groove 11. That is, the optical fiber 7 is arranged spirally in the longitudinal direction of the main body 3.

[0047] According to the second embodiment, it is possible to obtain the same effects as those of the first embodiment. Furthermore, since the optical fiber 7 is arranged around the entire circumference of the sound detection sensor 1, it is possible to detect sounds from all directions.

[0048] (Third embodiment) Next, a third embodiment will be described. Fig. 4(a) is a partial 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 in Fig. 4(a). The acoustic detection sensor 1b has almost the same configuration as the acoustic detection sensor 1, but differs in the form of the low acoustic impedance material 5, etc.

[0049] In 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 periphery of the main body 3. In other words, the film material 9 is arranged so as to cover the entire outer periphery of the low acoustic impedance material 5.

[0050] The optical fibers 7 are arranged in a substantially straight line in the longitudinal direction of the sound detection sensor 1b. In the illustrated example, two optical fibers 7 are formed at two locations facing each other, but the number of optical fibers 7 may be one, or three or more.

[0051] According to the third embodiment, it is possible to obtain the same effects as those of the first embodiment. In addition, since the groove 11 is not required in the main body 3, the manufacturability is good and the third embodiment can be applied to a main body 3 in which the groove 11 cannot be formed.

[0052] (Fourth embodiment) Next, a fourth embodiment will be described. Fig. 5(a) is a partial 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 in Fig. 5(a). The acoustic detection sensor 1c has almost the same configuration as the acoustic detection sensor 1b, but differs in the form of the optical fiber 7, etc.

[0053] In the sound detection sensor 1c, similar to the sound 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 periphery of the main body 3. In other words, the film material 9 is arranged so as to cover the entire outer periphery of the low acoustic impedance material 5.

[0054] The optical fiber 7 is arranged in a spiral shape in the longitudinal direction of the sound detection sensor 1c. Although the illustrated example shows an example in which one optical fiber 7 is arranged, there may be multiple optical fibers 7. In this way, even when no groove is formed, the optical fiber 7 may be arranged in a spiral shape.

[0055] According to the fourth embodiment, it is possible to obtain the same effects as those of the third embodiment. Furthermore, 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 manufacturability is good.

[0056] (Fifth embodiment) Next, a fifth embodiment will be described. Fig. 6(a) is a partial perspective view showing an acoustic detection sensor 1d according to the fifth embodiment, and Fig. 6(b) is a cross-sectional view taken along line HH in Fig. 6(a). The acoustic detection sensor 1d has a configuration similar to that of the acoustic detection sensor 1c, but differs in the form of the groove 11, etc.

[0057] In the acoustic detection sensor 1d, like the acoustic detection sensor 1c, the optical fiber 7 is arranged in a spiral shape, but the low acoustic impedance material 5 is not formed around the entire outer periphery of the main body 3, but is arranged at predetermined intervals in the circumferential direction on the outer periphery. The low acoustic impedance material 5 is arranged in the groove 11. In this case, the groove 11 and the low acoustic impedance material 5 are not formed in a spiral shape in the axial direction of the main body 3, but are arranged linearly in the axial direction. In other words, the optical fiber 7 and the low acoustic impedance material 5 are not formed in the same direction in the axial direction.

[0058] In this case, the optical fiber 7 is not arranged so as to be in contact with the low acoustic impedance material 5 over its 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 is in contact with the main body 3 at other locations. In other words, only a portion of the optical fiber 7 is arranged so as to be in contact with the low acoustic impedance material 5.

[0059] Even in this case, the film material 9 is arranged so as to entirely cover the main body 3, the low acoustic impedance material 5, and the optical fiber 7. Although the illustrated example shows an example in which one optical fiber 7 is arranged, a plurality of optical fibers 7 may be arranged. Furthermore, instead of arranging the groove 11 and the low acoustic impedance material 5 linearly, they may be arranged spirally in the axial direction of the main body 3, and the optical fiber 7 may be arranged linearly. In other words, the groove 11 and the low acoustic impedance material 5 may be arranged linearly or spirally in the main body 3, and the optical fiber 7 may be arranged at a different angle to the groove 11 and the low acoustic impedance material 5 with respect to the axial direction.

[0060] According to the fifth embodiment, it is possible to obtain the same effects as those of the third embodiment, etc. In this way, even if the groove 11 is not formed along the optical fiber 7, as long as at least a part of the optical fiber 7 is in contact with the low acoustic impedance material 5, it is possible to obtain substantially the same effects. (acoustic detection cable) Next, an example of using an acoustic detection device using an acoustic detection sensor will be described. Fig. 7 is a cross-sectional view showing a cable 30. In the following description, an example using the acoustic detection sensor 1c will be described, but other acoustic detection sensors can also be used as appropriate.

[0061] 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 a low acoustic impedance material 5, an optical fiber 7, and a film material 9 are arranged around the power transmission cable 31. In this way, the main body 3 can be an existing long body such as a communication cable, a power transmission cable, or a pipe.

[0062] The braided tube 33 is disposed on the outermost layer of the cable 30. As described above, the braided tube 33 is a protective member that is woven with gaps to expose a portion of the inner layer membrane material 9. By using the braided tube 33, it is possible to suppress wear and damage to the membrane material 9 caused by contact or rubbing against other components.

[0063] 8(a) is a schematic diagram showing the 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 over only a part of the entire length of the cable 30. For example, when used as a submarine cable, the acoustic detection sensor 1c may be arranged only in a portion located on the seabed.

[0064] Furthermore, as shown in FIG. 8(b), the acoustic detection sensor 1c may be used in a tow cable 30a. In this way, the acoustic detection sensor according to the present invention can be used in any location, particularly underwater, by utilizing an existing long body as the main body. The main body 3 is not limited to long bodies such as cables. For example, floating facilities, ship hulls, tetrapods, and other undersea structures can also be used as the main body. In this case, a portion of the outer surface of the structure is used as the main body 3, a low acoustic impedance material 5 is disposed on that portion of the structure, and a membrane material 9 with an optical fiber 7 tightly attached to its inner surface is disposed so as to cover the portion of the structure near that portion and the low acoustic impedance material 5 from the outside. [Example]

[0065] Next, various acoustic detection sensors were used to evaluate their sensitivity. Figure 9 is a schematic diagram showing the test method. A prototype acoustic detection sensor 47 was placed underwater in a 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 anti-reflection treatment.

[0066] The acoustic detection sensor 47 used in the test was as follows: Example 1: an acoustic impedance of 3.3×10 3 kg / m 2 In Example 2, an optical fiber was spirally arranged on a rod-shaped member (made of polystyrene foam) with an acoustic impedance of 3.2 × 10 6 kg / m 2 A spiral groove is formed on the outer periphery of a rod-shaped material (made of acrylic resin) of s, and an acoustic impedance of 3.3 × 10 3 kg / m 2The optical fiber was spirally arranged along the groove. 6 kg / m 2 Similarly, an optical fiber was arranged spirally around the outer periphery of the rod-shaped member s.

[0067] An underwater speaker 43 was placed near the bottom of the water tank 41. Underwater speaker 43 generated sound waves with a frequency of 40 Hz to 200 Hz and a sound pressure of 80 dB to 160 dB toward the sound detection sensor 47. The distance between underwater speaker 43 and sound detection sensor 47 was 12 cm.

[0068] A hydrophone 45 was installed directly above the underwater speaker 43 and near the sound detection sensor 47. The hydrophone 45 measured the sound pressure from the underwater speaker 43. At the same time, the DAS 49 measured the magnitude of vibration of the optical fiber 7. The results are shown in Figures 10(a), 10(b), and 11.

[0069] 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 the comparative example. In each figure, the black circle (E in the figure) shows the results at 200 Hz, the black square (G in the figure) shows the results at 100 Hz, and the black triangle (F in the figure) shows the results at 40 Hz.

[0070] For all samples, vibration increased with respect to sound pressure, making it possible to detect sound. However, as shown in Figures 10(a) and 10(b), Examples 1 and 2, in which the optical fiber was wound around the outer periphery of the low acoustic impedance material, had larger vibrations with respect to sound pressure than the comparative example. In other words, it was confirmed that Examples 1 and 2 could detect sound with good sensitivity.

[0071] In the above explanation, the characteristics of the low acoustic impedance material 5 are defined as a material 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 with respect to the hardness of the material, illustrating the relationship between the minimum detectable sound pressure and Shore E hardness.

[0072] In the figure, I is a styrene foam rod, J is a silicone foam rod, K is a silicone rod (3D molded product), L is a rubber rod, M is a vinyl chloride rod, and N is a metal pipe. As shown in the figure, there is a correlation between the minimum detectable sound pressure and 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 with a Shore E hardness of 20 degrees or less is suitable as a low acoustic impedance material.

[0073] Additionally, Figure 13 is a comparison table of spring-type, durometer, and ASKER rubber hardness (original source: PackingLand website https: / / www.packing.ko.jp / SIRYOU / gomukoudo1.htm), and the area enclosed in the added box shows the relationship between Shore E hardness and ASKER C hardness. Shore E hardness and ASKER C hardness can be said to be roughly the same standard. Therefore, ASKER C hardness of 20 degrees or less is suitable as a low acoustic impedance material.

[0074] 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 limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0075] 1, 1a, 1b, 1c, 1d.... Acoustic detection sensors 3...Main body 5. Low acoustic impedance material 7...Optical fiber 9……Membrane material 11……groove 13....Light emitting part 15……Light receiving section 20, 20a....Sound detection device 30...Cable 30a………Towing cable 31...Power transmission cable 33...Braided tube 41...Aquarium 43...Underwater speaker 45...Hydrophone 47...Sound detection sensor 49………DAS

Claims

1. 1. An acoustic detection sensor for use underwater, comprising: a main body; a low acoustic impedance material provided on at least a portion of the outer periphery of the main body; a film material disposed so as to cover the outer periphery of the main body portion and the low acoustic impedance material; an optical fiber that is in close contact with the inner surface of the film material; Equipped with the optical fiber is disposed on the outer surface of the low acoustic impedance material on the inner surface side of the film material, The acoustic detection sensor is characterized in that the low acoustic impedance material 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.

2. The main body is an elongated body, A linear or spiral groove is formed in the longitudinal direction of the main body portion, The groove is filled with the low acoustic impedance material, 2. The acoustic detection sensor according to claim 1, wherein a portion of the optical fiber is disposed so as to be in contact with the low acoustic impedance material.

3. The main body is an elongated body, A linear groove is formed in the longitudinal direction of the main body portion, The groove is filled with the low acoustic impedance material, The acoustic detection sensor according to claim 1 , wherein the optical fiber is arranged along the groove.

4. The main body is an elongated body, A spiral groove is formed in the longitudinal direction of the main body portion, The groove is filled with the low acoustic impedance material. The acoustic detection sensor according to claim 1 , wherein the optical fiber is arranged along the groove.

5. The main body is an elongated body, The acoustic detection sensor according to claim 1 , wherein the low acoustic impedance material is disposed so as to cover the entire outer peripheral surface of the main body.

6. 6. The sound detection sensor according to claim 5, wherein the optical fiber is arranged in a spiral shape relative to the longitudinal direction of the main body.

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