A push-pull hydrophone and method of use, method of operation

Abstract

The application discloses a push-pull hydrophone, which comprises an inner elastic base cylinder sleeved on an optical cable, the inner wall of the inner elastic base cylinder is attached to the outer wall of the optical cable; an outer elastic base cylinder is nested on the inner elastic base cylinder, the inner elastic base cylinder and the outer elastic base cylinder are connected through a support rod, and a gap for seawater flowing through is formed between the inner elastic base cylinder and the outer elastic base cylinder; the outer wall of the inner elastic base cylinder and the outer wall of the outer elastic base cylinder are both axially wound with sensing optical fibers, the sensing optical fibers are connected with an external demodulator, the outer side of the outer elastic base cylinder is covered with a shell, and an air cavity is formed between the shell and the outer wall of the outer elastic base cylinder. The hydrophone can be matched with the existing submarine optical cable based on the existing submarine optical cable, and the hydrophone does not need to be separately connected into an array.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing system technology, specifically to a push-pull hydrophone and its usage and operation. Background Technology

[0002] Fiber optic hydrophones are important underwater transducers. Compared with piezoelectric transducers, they have advantages such as no power supply required, high sensitivity, and resistance to electromagnetic interference. They have been widely used and developed in underwater safety early warning, tsunami and earthquake monitoring, and other fields. Compared with intensity and wavelength sensing fiber optic hydrophones, phase sensing fiber optic hydrophones have higher detection sensitivity. They are usually enhanced by winding them around an elastic substrate.

[0003] The methods of winding sensing optical fibers onto an elastic matrix typically include two aspects. One is the winding of a single set of sensing optical fibers, such as the method proposed by Hao Li et al., which involves winding reinforced optical fibers onto a hollow elastic cylindrical tube for underwater acoustic monitoring [Hao Li, Qizhen Sun, Tao Liu, et al. Ultra-high sensitive quasi-distributed acoustic sensor based on coherent OTDR and cylindrical transducer[J]. Journal of Lightwave Technology, 2020, 38(4):929-938.]; and the method proposed by Lu Bin et al., which involves winding sensing optical fibers onto a solid elastic matrix to form a distributed optical fiber hydrophone [Lu Bin, Wu Bingyan, Gu Jingeng, et al. Distributed optical fiber hydrophone based on Φ-OTDR and its field test[J]. Optics Express, 2021, 29(3):3147-3162.]. Secondly, two sets of sensing optical fibers are wound around a composite elastic matrix to improve phase-sound pressure sensitivity and reduce the effect of temperature on the hydrophone, such as the air-cavity type composite elastic matrix hydrophone proposed by Rajesh R et al. [Rajesh R, Sreehari CV, Praveen KN, et al. Air backed mandrel type fiber optic hydrophone with low noise floor[C]. Proceedings of Light & Its Interactions] [with Matter, 2015.] In this composite hydrophone, one set of sensing fibers can only sense temperature to compensate for the temperature effect of the other set of sensing fibers, which serves as the underwater acoustic transducer. Yang Yue proposed a push-pull composite elastic matrix hydrophone [Yang Yue. Development of Ultra-Low Frequency Fiber Optic Hydrophone [D]. Jilin: Jilin University, 2022.]. In this composite hydrophone, the two sets of sensing fibers are wound around two thin-walled cylinders, simultaneously sensing underwater acoustic pressure, and with opposite phase changes. The phase-sound pressure sensitivity can be doubled by phase subtraction, and the common temperature change effect is also eliminated. However, the hydrophone structure is hollow in the middle, and the structure does not consider how to realize the series connection of the hydrophones, making it impossible to use with existing submarine optical cables. Summary of the Invention

[0004] This invention provides a push-pull hydrophone and its usage and operation methods to solve the technical problems of existing technologies, such as the inability to achieve series connection of composite elastic matrix hydrophones and low applicability.

[0005] This invention provides a push-pull hydrophone, comprising: an inner elastic base tube sleeved on an optical cable, the inner wall of the inner elastic base tube being fitted to the outer wall of the optical cable; an outer elastic base tube nested on the inner elastic base tube, the inner elastic base tube and the outer elastic base tube being connected by a support rod, and a gap for seawater to flow through between the inner elastic base tube and the outer elastic base tube; sensing optical fibers are wound axially on the outer walls of both the inner and outer elastic base tubes, the sensing optical fibers being connected to an external demodulator; and an outer shell covering the outer elastic base tube, forming an air cavity between the outer shell and the outer wall of the outer elastic base tube.

[0006] Furthermore, the materials of the inner elastic matrix tube and the outer elastic matrix tube are: polymer materials with low Young's modulus and high Poisson's ratio.

[0007] Furthermore, the thickness range of the inner elastic matrix tube and the outer elastic matrix tube is 0.5cm to 1.5cm.

[0008] Furthermore, the length range of the inner elastic matrix tube and the outer elastic matrix tube is 8cm to 12cm.

[0009] Furthermore, the gap width between the inner elastic matrix tube and the outer elastic matrix tube ranges from 5cm to 15cm.

[0010] Furthermore, the inner elastic matrix tube and the outer elastic matrix tube have a thickness of 1cm, a length of 10cm, and a gap width of 10cm.

[0011] The present invention also provides a method for using a push-pull hydrophone, comprising: before laying an optical cable, sequentially connecting several push-pull hydrophones at intervals required for detection onto the optical cable, wherein the sensing optical fiber in the push-pull hydrophone is connected to an external demodulator to form a hydrophone array, which is laid along with the optical cable.

[0012] The present invention also provides a method for operating a push-pull hydrophone, comprising: the acoustic pressure between the inner elastic matrix tube and the outer elastic matrix tube generates a thrust and a pressure on the inner elastic matrix tube and the outer elastic matrix tube respectively, forming a push-pull action; the inner elastic matrix tube and the outer elastic matrix tube undergo radial deformation with the acoustic pressure, changing the length and effective refractive index of the two sets of sensing optical fibers wound around the inner elastic matrix tube and the outer elastic matrix tube; the transmission phase of the laser in the two sets of sensing optical fibers undergoes opposite changes; and the acoustic pressure is calculated by the difference in the phase change in the two sets of sensing optical fibers.

[0013] The beneficial effects of this invention are:

[0014] The push-pull hydrophone of this invention is based on existing submarine optical cables and is well-matched with them, eliminating the need to separately connect hydrophones in series. It uses two sets of sensing optical fibers to detect sound pressure, generating opposite laser phase changes. This significantly improves the overall sound pressure-phase sensitivity of the hydrophone, and the subtraction of the two phase changes also cancels out the shared effect of temperature changes on the hydrophone. Furthermore, allowing seawater to flow between the two sets of sensing optical fibers enhances both sensing sensitivity and accuracy. Attached Figure Description

[0015] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings:

[0016] Figure 1 This is a cross-sectional view of a specific embodiment of the present invention;

[0017] Figure 2 This is a top sectional view of a specific embodiment of the present invention;

[0018] Figure 3 This is a schematic diagram of two hydrophones assembled and used in a specific embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] like Figure 1 , 2As shown, this embodiment of the invention provides a push-pull hydrophone, comprising: an inner elastic base cylinder 1 sleeved on an optical cable 6, the inner wall of the inner elastic base cylinder 1 being in contact with the outer wall of the optical cable 6; an outer elastic base cylinder 4 nested on the inner elastic base cylinder 1, the two ends of the inner elastic base cylinder 1 and the outer elastic base cylinder 4 being connected by eight support rods 3 arranged in a cross shape along the radial direction, and a gap for seawater to flow through between the inner elastic base cylinder 1 and the outer elastic base cylinder 4; sensing optical fibers 2 are wound axially on the outer walls of the inner elastic base cylinder 1 and the outer walls of the outer elastic base cylinder 4, the sensing optical fibers 2 being connected to an external demodulator, and an outer shell 5 covering the outer side of the outer elastic base cylinder 4, forming an air cavity between the outer shell 5 and the outer wall of the outer elastic base cylinder 4.

[0021] like Figure 2 , 3 During assembly, the inner elastic base tube 1 is first fitted onto the optical cable 6. The sensing optical fiber 2 is then wound axially around the outer wall of the inner elastic base tube 1. The outer elastic base tube 4 is then fitted onto the outside of the inner elastic base tube 1 through the support rod 3, with a gap between them for seawater to flow through. The sensing optical fiber 2 is then wound axially around the outer wall of the outer elastic base tube 4. Finally, the outer shell 5 is fitted onto the outside of the outer elastic base tube 4, forming an air cavity between the outer shell 5 and the outer wall of the outer elastic base tube 4, thus completing the assembly.

[0022] The thickness range of the inner elastic substrate tube 1 and the outer elastic substrate tube 4 is 0.5cm to 1.5cm, and the materials used are high-molecular materials with low Young's modulus and high Poisson's ratio, such as polyethylene and polyimide. The length range of the push-pull hydrophone, i.e., the length range of the two elastic substrate tubes, is 8cm to 12cm, which can reduce the impact of reduced sound pressure sensitivity caused by the constraint at both ends of the elastic substrate tubes. The width of the freely flowing seawater between the two elastic substrate tubes should be as large as possible to allow the underwater sound to propagate freely, and the width can be set in the range of 5cm to 15cm. The width of the support rod 3 should be as narrow as possible to reduce the obstruction of the fixed rod to the seawater flow, and the width of a single support rod 3 can be set at 1cm. The size of the shell is just right to cover the outer sensing optical fiber 2, and it does not need to be too large.

[0023] A specific embodiment of the present invention also provides a method for using a push-pull hydrophone, comprising: before laying the optical cable, sequentially connecting several push-pull hydrophones at intervals required for detection on the optical cable, wherein the sensing optical fiber in the push-pull hydrophone is connected to an external demodulator to form a hydrophone array, and listening to underwater acoustic signals as the optical cable is laid.

[0024] A specific embodiment of the present invention also provides a method for operating a push-pull hydrophone, comprising: the acoustic pressure between the inner elastic base tube and the outer elastic base tube generates a thrust and a pressure on the inner elastic base tube and the outer elastic base tube respectively, forming a push-pull effect; the inner elastic base tube and the outer elastic base tube undergo radial deformation with the acoustic pressure, changing the length and effective refractive index of the two sets of sensing optical fibers wound around the inner elastic base tube and the outer elastic base tube; the transmission phase of the laser in the two sets of sensing optical fibers undergoes opposite changes; and the acoustic pressure is calculated by the difference in the phase change in the two sets of sensing optical fibers.

[0025] Seawater flows freely between two elastic matrix cylinders. When an external underwater acoustic signal is applied to a push-pull hydrophone, the sound pressure in the seawater between the two elastic matrices exerts forces in two directions, acting on the two elastic matrix cylinders respectively. The change in underwater acoustic pressure is denoted as Δp. The acoustic pressure exerted on the two elastic matrix cylinders causes the two sets of sensing optical fibers to also experience acoustic pressure. Let the pressure changes on the two sets of sensing optical fibers be f1(Δp) and -f2(Δp), respectively, where f is a pressure transfer function related to the diameter, Young's modulus, and Poisson's ratio of the elastic matrix. Due to the pressure and temperature changes, the effective refractive index and length of the two sets of sensing optical fibers will change, and the phase transmission changes of the laser within them will be as follows:

[0026]

[0027]

[0028] In the formula, n effi and L i These represent the effective refractive index change and length change of the i-th sensing fiber, respectively, where i = 1 and 2; The phase change of the laser in the two sets of sensing fibers is caused by the temperature change ΔT.

[0029] Subtracting equation (2) from equation (1) yields:

[0030]

[0031] In equations (1) and (2) It can be obtained through Mach-Zehnder interferometer, Michelson interferometer, Rayleigh scattering signal, stimulated Brillouin scattering signal, or demodulation of weakly reflective fiber grating arrays. Thus, the sound pressure Δp can be inverted using equation (3). Furthermore, comparing equation (3) with equations (1) and (2), Both are greater than By appropriately optimizing the diameters, Young's modulus, and Poisson's ratio of the two sets of elastic matrices so that f1(Δp) = f2(Δp), then... Approaching twice; and in equation (3) All less than Therefore, by constructing a push-pull hydrophone, the sound pressure-phase sensitivity is increased compared to a hydrophone with a single set of sensing optical fibers wound together, and the effect of temperature is also suppressed.

[0032] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A push-pull hydrophone, characterized by, It comprises: an inner elastic matrix cylinder sleeved on the optical cable, the inner wall of which is in close contact with the outer wall of the optical cable; an outer elastic matrix cylinder nested on the inner elastic matrix cylinder, which is connected with the inner elastic matrix cylinder through a supporting rod, and has a gap for seawater flow between the inner elastic matrix cylinder and the outer elastic matrix cylinder; the outer wall of the inner elastic matrix cylinder and the outer wall of the outer elastic matrix cylinder are both wrapped with sensing optical fibers in the axial direction, which are connected with an external demodulator, and the outer side of the outer elastic matrix cylinder is covered with a shell, which forms an air cavity between the outer wall of the outer elastic matrix cylinder.

2. The push-pull hydrophone of claim 1, wherein, The materials of the inner elastic matrix cylinder and the outer elastic matrix cylinder are high-molecular materials with small Young's modulus and large Poisson's ratio.

3. The push-pull hydrophone of claim 1, wherein, The thickness of the inner elastic matrix cylinder and the outer elastic matrix cylinder ranges from 0.5 cm to 1.5 cm.

4. The push-pull hydrophone of claim 1 or 3, wherein, The length of the inner elastic matrix cylinder and the outer elastic matrix cylinder ranges from 8 cm to 12 cm.

5. The push-pull hydrophone of claim 1, wherein, The gap width between the inner elastic matrix cylinder and the outer elastic matrix cylinder ranges from 5 cm to 15 cm.

6. The push-pull hydrophone of claim 4, wherein, The thickness of the inner elastic matrix cylinder and the outer elastic matrix cylinder is 1 cm, the length is 10 cm, and the gap width between them is 10 cm.

7. A method of using a push-pull hydrophone, suitable for use in a push-pull hydrophone as claimed in any one of claims 1 to 6, characterised by, The use method of the push-pull hydrophone comprises: before laying the optical cable, a plurality of push-pull hydrophones are sleeved on the optical cable at the required interval distance, the sensing optical fibers in the push-pull hydrophones are connected with an external demodulator to form a hydrophone array, and the optical cable is laid.

8. A method of operating a push-pull hydrophone suitable for use in a push-pull hydrophone as claimed in any one of claims 1 to 6, characterised by, The working method of the push-pull hydrophone comprises: the water acoustic pressure between the inner elastic matrix cylinder and the outer elastic matrix cylinder generates a pushing force and a pressure on the inner elastic matrix cylinder and the outer elastic matrix cylinder respectively, forming a push-pull effect, the inner elastic matrix cylinder and the outer elastic matrix cylinder deform radially with the water acoustic pressure, changing the length and effective refractive index of the two groups of sensing optical fibers wrapped around the inner elastic matrix cylinder and the outer elastic matrix cylinder, the transmission phase of laser in the two groups of sensing optical fibers changes in opposite directions, and the water acoustic pressure is calculated by the difference between the phase change amounts of the two groups of sensing optical fibers.

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