An underwater microphone

Abstract

This invention provides an underwater microphone, comprising a pickup core and an encapsulation system. The pickup core comprises a hollow, open-ended active material tube, sealed at both ends by end caps. The pickup core is fixed inside the encapsulation system, with a certain gap maintained between them. The encapsulation system is a hollow, sealed structure, with part of its outer shell made of deformable material. The interior of the pickup core and the gap between the pickup core and the encapsulation system are filled with an insulating fluid. The pressure of the insulating fluid inside the pickup core is set as P1, and the pressure of the insulating fluid in the gap between the pickup core and the encapsulation system is set as P2. A pressure control valve is provided on the end caps, which is closed by default. When P1 and P2 are different, the pressure control valve opens to allow the insulating fluid to flow, making P1 equal to P2. The advantage of this invention is that it avoids Helmoholtz resonance, resulting in a flat low-frequency sensitivity of the microphone.

Description

Technical Field

[0001] This invention belongs to the field of sound information perception in a sound field, and specifically relates to an underwater sound pickup. Background Technology

[0002] Underwater microphones (hydrophones) are primarily used to pick up acoustic information in a sound field and are a core component of acoustic systems. In recent years, with the rapid development of technologies such as "deep-sea" and "deep-earth," the hydrostatic pressure resistance of these in-situ sensing components has become a key concern for instrument developers. For example, in marine seismic exploration, piezoelectric detectors used in OBN, OBS, and OBC technologies require pressure resistance exceeding 35 MPa; in mid-ocean ridge sulfide exploration, microphones are expected to withstand pressures of 45 MPa; in deep-sea manned submersibles such as the "Jiaolong" and "Deep Sea Warrior," microphones are expected to withstand pressures of 70 to 100 MPa; and in deep-earth exploration, microphones are required to withstand pressures exceeding 200 MPa.

[0003] A microphone that can withstand hydrostatic pressure exceeding 1000m can be called a deep-water microphone. Deep-water microphones have been extensively researched internationally: B&K's 8105 and 8106 can withstand pressures up to 1000m; Teledyne's Benthos series of microphones can withstand pressures up to 1700m; Geospace's deepender series can withstand pressures up to 35MPa; and the most well-known product is High-Tech's HTI series, which can withstand pressures ranging from 30MPa to 70MPa. In recent years, driven by demand, many excellent design solutions have emerged, such as: Reference [1] the invention patent "A Deep-Water Broadband Spherical Transducer" with application publication number CN102097093A uses multi-rigid matching layer technology to release hydrostatic pressure; Reference [2] the invention patent "A Hydrophone and Its Manufacturing Method" with application publication number CN109474871A uses oil filling to balance hydrostatic pressure; Reference [3] the invention patent "A Spherical Hydrophone with Ultra-High Hydrostatic Pressure Resistance" with application publication number CN109239695A uses overflow method to balance hydrostatic pressure; Reference [4] The invention patent with publication number CN104486705A, "A pressure-compensated deep-sea hydrophone", uses piston compensation to balance the hydrostatic pressure; the invention patent with publication number CN105323685A, "A full-depth low-frequency broadband high-sensitivity piezoelectric hydrophone", the utility model patent with publication number CN204389015U, "Miniaturized deep-sea hydrophone", and the utility model patent with publication number CN205138629U, "Deep-sea high-sensitivity circular tube hydrophone", utilize the pressure-resistant characteristics of the piezoelectric circular tube to release the hydrostatic pressure.

[0004] In summary, existing deep-water microphones can be structurally categorized into two types: pressure-release and pressure-balanced. Pressure-release microphones utilize the pressure-resistant properties of their structure to release hydrostatic pressure, and this is currently the most commonly used design. Examples include the HTI series, the invention patent CN105323685A ("A Full-Depth Low-Frequency Broadband High-Sensitivity Piezoelectric Hydrophone"), the utility model patent CN204389015U ("Miniaturized Deep-Water Hydrophone"), and the utility model patent CN205138629U ("Deep-Water High-Sensitivity Circular Tube Hydrophone"). This design can improve the microphone's pressure resistance by adjusting the ceramic tube thickness. However, it should be noted that as the ceramic tube thickness increases, its free capacitance decreases, thus reducing the microphone's acoustic performance (microphone performance is typically evaluated using a quality factor, Q=M). 2 *C f Where M is the sensitivity of the microphone, and C f (For the free capacitance of the pickup), this approach presents difficulties in designing pickups with pressure resistance requirements exceeding 6000m due to size constraints. Pressure balancing refers to using overflow or oil filling methods to balance the hydrostatic pressure inside and outside the active material. This approach can withstand extremely high hydrostatic pressure and is widely used in deep-sea applications, such as the invention patents CN109474871A "A Hydrophone and Its Manufacturing Method" and CN109239695A "A Spherical Hydrophone with Ultra-High Hydrostatic Pressure Resistance". However, this structural design usually requires a fluid channel to balance the hydrostatic pressure inside and outside the piezoelectric cavity. However, this fluid channel and the piezoelectric cavity will form a Helmholtz resonant cavity, resulting in uneven low-frequency sensitivity of the pickup. The simplest way to solve Helmoholtz resonance interference is to directly cut off the fluid channel. After cutting off the fluid channel, the microphone sensitivity is very flat. However, the problem with this method is that without a fluid channel, the internal and external pressures cannot be balanced. When the internal and external hydrostatic pressure difference exceeds the stress limit of the ceramic, the microphone will also break, and the result is roughly similar to the pressure release method.

[0005] A comprehensive analysis of the advantages and disadvantages of the two design schemes reveals that retaining the fluid channel can easily achieve pressure balance of the piezoelectric structure, greatly improving the pressure resistance of the pickup. However, the Helmoholtz resonance caused by the channel will lead to fluctuations in the pickup's sensitivity, especially a significant decrease in low-frequency sensitivity. Cutting off the fluid channel can flatten the sensitivity, but it will hinder pressure balance and reduce the pickup's pressure resistance. Summary of the Invention

[0006] The purpose of this invention is to overcome the defect of existing microphones where the Helmoholtz resonance caused by the retention of the fluid channel leads to fluctuations in microphone sensitivity.

[0007] To achieve the above objectives, the present invention proposes an underwater sound pickup, which includes a vibration pickup core and an encapsulation system;

[0008] The vibration pickup core includes a hollow, open-ended active material tube.

[0009] The two ends of the active material circular tube are sealed by end caps;

[0010] The vibration pickup core is fixed inside the packaging system, and a certain gap is maintained between it and the packaging system.

[0011] The encapsulation system is a hollow sealed structure, and part of its outer shell is made of deformable material;

[0012] The interior of the vibration pickup core and the gap between the vibration pickup core and the packaging system are filled with insulating fluid.

[0013] The pressure of the insulating fluid inside the vibration pickup core is set as P1, and the pressure of the insulating fluid in the gap between the vibration pickup core and the packaging system is set as P2.

[0014] The end cap is equipped with a pressure control valve, which is initially closed. When P1 and P2 are different, the pressure control valve opens to allow the insulating fluid to flow. When P1 and P2 are the same, the valve closes.

[0015] As an improvement to the aforementioned microphone, the pressure control valve is a two-way valve: a first one-way valve and a second one-way valve;

[0016] The first check valve and the second check valve open in opposite directions, that is, one opens into the active material tube and the other opens into the active material tube.

[0017] As an improvement to the aforementioned microphone, the end cap includes a first end cap and a second end cap, which respectively seal the active material tube from both ends.

[0018] A first check valve is installed on the first end cap; a second check valve is installed on the second end cap.

[0019] As an improvement to the aforementioned microphone, the end cap is a cup-shaped structure with the cup opening facing the outside of the active material tube, and a one-way valve is installed in the cup.

[0020] The one-way valve consists of: a disc spring, a slider, a ball valve, and a limit screw;

[0021] The position of the limiting screw is fixed after it is connected to the end cap;

[0022] When the one-way valve is opening inward, its components are arranged in the following order from the bottom of the cup to the opening: disc spring, slider, ball valve, and limit screw; the limit screw is used to limit the circumferential movement range of the ball valve.

[0023] When the one-way valve is opening outwards, its components are arranged in the following order from the bottom of the cup to the opening: ball valve, slider, disc spring, and limit screw; the slider is used to limit the circumferential movement range of the ball valve.

[0024] When the disc spring is deformed by force, it drives the slider to move, causing the ball valve to open or close.

[0025] The bottom of the end cap, the limiting screw, the disc spring, and the middle of the slider all have openings, allowing fluid to pass through the ball valve when it is open.

[0026] As an improvement to the aforementioned pickup, the opening pressure of the first one-way valve and the second one-way valve is greater than the maximum sound pressure of the detected sound field, but less than the confining pressure resistance of the active material circular tube.

[0027] As an improvement to the aforementioned pickup, the active material tube adopts radial segmented polarization, that is, an electrode is set inside the active material tube, and the external electrode is divided into two segments with opposite polarization directions.

[0028] As an improvement to the aforementioned microphone, the encapsulation system includes a hollow bladder with openings at both ends, the bladder being made of a deformable material;

[0029] Both ends of the bladder are sealed by a lower bladder connector and an upper bladder connector; the outer sides of both ends of the bladder are tightly bound by a first bladder clamp and a second bladder clamp;

[0030] The lower connector of the bladder has an opening in the middle, which is sealed with a first sealing element;

[0031] The connector on the bladder has a central opening; the shielded cable passes through the central opening of the connector on the bladder; and a second seal is used to seal the central opening of the connector on the bladder.

[0032] As an improvement to the aforementioned microphone, the first sealing element is an oil plug; an O-ring is provided between the oil plug and the opening in the middle of the lower connector of the bladder;

[0033] The second sealing element includes a wire plug and a watertight head, which seal the opening in the middle of the upper connector of the bladder from the inside and the outside of the upper connector, respectively;

[0034] The inner ends of the bladder are respectively provided with a first rubber pad and a second rubber pad to fix the vibration pickup core.

[0035] As an improvement to the aforementioned microphone, the active material tube is a piezoelectric ceramic tube.

[0036] As an improvement to the aforementioned microphone, the insulating fluid is castor oil or transformer oil.

[0037] Compared with the prior art, the advantages of the present invention are:

[0038] Except for occasional switching moments, the first and second end caps at both ends of the active material cylindrical tube remain closed. This closure of the fluid channel prevents Helmoholtz resonance, resulting in a flat low-frequency sensitivity for the pickup. A two-ended open-ended pickup exhibits a sensitivity peak at low frequencies, corresponding to the Helmoholtz resonance. Below this resonance, the sensitivity drops rapidly, affecting low-frequency signal reception, and the fluctuations in sensitivity also impact the quality of the received signal. In contrast, the pickup of this invention can extend to extremely low frequencies with a very flat sensitivity and higher signal quality. Furthermore, the ceramic tube used in this invention can be less than 0.5 mm thick, resulting in higher free capacitance. Attached Figure Description

[0039] Figure 1 The diagram shown is a schematic of the microphone structure.

[0040] Figure 2 The diagram shown is a schematic of an active material circular tube structure.

[0041] Figure 3 The diagram shows a core image of a pickup unit with open ends.

[0042] Figure 4 The diagram shown is a schematic diagram of the pickup core of the sound pickup device in this application;

[0043] Figure 5 The diagram shown is a comparison of the sensitivity of the pickup with both ends open and the pickup of this application.

[0044] Figure 6 The diagram shown is a schematic of the pickup structure in Example 1;

[0045] Figure 7 The diagram shown is a schematic diagram of the first check valve structure in Embodiment 1;

[0046] Figure 8 The diagram shown is a schematic diagram of the second check valve structure in Example 1.

[0047] Figure label:

[0048] 1. Active material round tube 2. First end cap

[0049] 3. Second end cap; 4. First rubber gasket

[0050] 5. Second rubber pad 6. Skin bag

[0051] 7. First leather strap tightening 8. Second leather strap tightening

[0052] 9. Subcutaneous connector 10. Superior connector

[0053] 11. Oil plug 12. O-ring

[0054] 13. Wire plug 14. Watertight connector

[0055] 15. Shielded cable; 21. First check valve

[0056] 31. Second one-way valve 201. Positive electrode

[0057] 202. Electrode isolation; 203. Negative electrode

[0058] 204, internal electrode 302, first opening

[0059] 303, Second opening 601, First ball valve

[0060] 602. First limit screw; 603. First disc spring

[0061] 604, First slider; 701, Second ball valve

[0062] 702, Second slider; 703, Second disc spring

[0063] 704, Second Limit Screw Detailed Implementation

[0064] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0065] This invention addresses the shortcomings of both preserving and severing the fluid channel, and combines the advantages of both to provide a microphone with high and flat sensitivity and large free capacitance, capable of operating in both hydrostatic (high pressure) and dynamic (low pressure) environments. The aim is to provide a microphone for sensing information in acoustic applications such as those in the deep sea and deep earth.

[0066] For deep application environments, the technical solution adopted in this invention is as follows: Figure 1 As shown:

[0067] The microphone consists of two parts: a pickup core and an encapsulation system. The pickup core comprises an active material cylindrical tube 1, a first end cap 2, a second end cap 3, a first one-way valve 21, and a second one-way valve 31, with the first and second one-way valves 21 installed in opposite directions. The encapsulation system comprises a bladder 6, a first bladder clamp 7, a second bladder clamp 8, a lower bladder connector 9, an upper bladder connector 10, an oil plug 11, an O-ring 12, a wire plug 13, a watertight connector 14, and a shielded cable 15. The pickup core is supported within the encapsulation system by a first rubber pad 4 and a second rubber pad 5. The entire microphone, including the active material cylindrical tube 1 and the rubber bladder 6, is filled with an insulating fluid, such as silicone oil, castor oil, or transformer oil. The insulating fluid is injected into the microphone through the oil plug 11. During injection, a special tool is used to open either the first one-way valve 21 or the second one-way valve 31 to ensure sufficient oil filling inside the pickup core. The opening pressure of the first one-way valve 21 and the second one-way valve 31 is greater than the maximum sound pressure of the sound field being detected, but less than the confining pressure resistance of the active material circular tube 1.

[0068] The first one-way valve 21 and the second one-way valve 31 can be installed on the first end cover 2 and the second end cover 3 respectively, or they can be installed on one of the end covers at the same time.

[0069] As the microphone's working depth increases, P_out (ambient pressure) > P_mid (pressure in the bladder). At this point, the internal volume of the bladder 6 will be compressed, and real-time dynamic adjustment will make P_out = P_mid. Then, P_mid > P_in (internal pressure of the sensing core component). When P_mid - P_in ≥ P_open (opening pressure of the first one-way valve 21 and the second one-way valve 31), the inward-opening valve in either the first one-way valve 21 or the second one-way valve 31 will open, while the outward-opening valve will close. The internal insulating fluid flows through the open valve into the active material circular tube 1. When P_mid - P_in ≤ P_open, both the first one-way valve 21 and the second one-way valve 31 will close.

[0070] When the microphone's working depth decreases, P_out (ambient pressure) < P_mid (pressure in the bladder). At this time, the internal volume of the bladder 6 will expand, and real-time dynamic adjustment will make P_out = P_mid. At this time, P_mid < P_in (internal pressure of the sensing core component). When P_in - P_out ≥ P_open (opening pressure of the first one-way valve 21 and the second one-way valve 31), the inward-opening valve in the first one-way valve 21 or the second one-way valve 31 will close, while the outward-opening valve will open. The insulating fluid inside the active material circular tube 1 flows into the bladder through the opened valve. When P_in - P_out ≤ P_open, both the first one-way valve 21 and the second one-way valve 31 will close.

[0071] In summary, when the working environment pressure changes, the maximum pressure difference between the inside and outside of the active material tube 1 inside the microphone is only P_open. The switching pressure of a typical small-sized check valve is only a few Newtons to tens of Newtons. Therefore, the active material tube 1 can be designed to be very thin without damage. This solution has a larger free capacitance, and the microphone has a larger quality factor.

[0072] The specific details of the active material circular tube 1 in this invention are as follows: Figure 2 As shown, radial segmented polarization is employed, meaning the internal electrodes of the ceramic tube are integrated, but the external electrodes are divided into two segments with opposite polarization directions. Specifically, if the upper segment is radially inwardly polarized, the lower segment is radially outwardly polarized. The positive and negative electrodes of the sound pickup device are led from the external electrodes of the two segments of the active material circular tube, respectively. The specific mechanism is as follows: the inner electrode 204 is attached to the inner wall of the active material circular tube 1, and the positive electrode 201 and negative electrode 203 are attached to the outer wall of the active material circular tube 1. The positive electrode 201 and negative electrode 203 are separated by an electrode separator 202. The left and right halves of the active material circular tube 1 have opposite polarization directions.

[0073] The main difference between this invention and common open-ended deep-sea microphones is that this invention differs from such microphones at both ends. Figure 3 and Figure 4 As shown, the main difference between these two types of microphones lies in their vibration pickup cores. See also... Figure 3 It can be seen that the open-ended deep-sea microphone has a first opening 302 and a second opening 303 on the first end cap 2 and the second end cap 3, which are used to balance the pressure inside and outside the active material circular tube 1. Of course, in extreme cases, the first end cap 2 and the second end cap 3 may not even exist. The present invention, as described... Figure 4 As shown, a first check valve 21 or a second check valve 31 is used instead of the first opening 302 and the second opening 303.

[0074] The beneficial effects of the present invention are as follows: As can be seen from the above working principle introduction, except for occasional switching moments, the first end cap 2 and the second end cap 3 at both ends of the active material circular tube 1 are always in a closed state. The closure of the fluid channel avoids the generation of Helmoholtz resonance, making the low-frequency sensitivity of the pickup flat. Figure 5 This comparison of the sensitivity of the pickup of this invention with that of a deep-sea pickup with open ends shows that the open-end pickup exhibits a sensitivity peak at low frequencies, corresponding to the Helmoholtz resonance of the pickup. Below this resonance, the sensitivity drops rapidly, affecting low-frequency signal reception, and the fluctuations in sensitivity also impact the quality of the received signal. In contrast, the pickup of this invention can extend its sensitivity to extremely low frequencies and is very flat, resulting in higher signal quality. The active material tube used in this invention can be a piezoelectric ceramic tube; when using ceramic material, the thickness can be less than 0.5 mm, resulting in higher free capacitance.

[0075] The first check valve 21 or the second check valve 31 in this invention can be a readily available and mature check valve, such as an axial flow check valve, a side outlet check valve, a low flow resistance check valve, a Hi-Q check valve, a high-pressure check valve, or a check valve with a pilot valve. Alternatively, the check valve described in Embodiment 1 below can be used.

[0076] Example 1:

[0077] like Figure 6 , Figure 7 and Figure 8 As shown, a high hydrostatic pressure resistant sound pickup device comprises two parts: a pickup core and an encapsulation system. The pickup core consists of an active material cylindrical tube 1, a first end cap 2, a second end cap 3, a first one-way valve 21, and a second one-way valve 31, etc., wherein the first one-way valve 21 and the second one-way valve 31 are installed with opposite opening directions. The encapsulation system consists of a bladder 6, a first bladder clamp 7, a second bladder clamp 8, a lower bladder connector 9, an upper bladder connector 10, an oil plug 11, an O-ring 12, a wire plug 13, a watertight connector 14, a shielded cable 15, etc. The pickup core is supported and placed within the encapsulation system by a first rubber pad 4 and a second rubber pad 5. The entire pickup, including the active material cylindrical tube 1 and the bladder 6, is filled with an insulating fluid, which can be silicone oil, castor oil, transformer oil, etc. Insulating fluid is injected into the microphone through oil plug 11. During injection, a special tool is needed to open either the first one-way valve 21 or the second one-way valve 31 to ensure sufficient oil filling inside the vibration core. In this embodiment, the first one-way valve 21 is integrated into the instrument with the first end cap 2. It is an inward-opening one-way valve. The specific structure of the first one-way valve 21 is as follows... Figure 7 As shown, the instrument includes: a first ball valve 601, a first limiting screw 602, a first disc spring 603, and a first slider 604. The first end cap 2, the first limiting screw 602, the first disc spring 603, and the first slider 604 all have a central hole structure to ensure smooth fluid flow when the first ball valve 601 is open. The first limiting screw 602 is tightened onto the first end cap 2 to limit the circumferential movement range of the first ball valve 601. The first disc spring 603 controls the opening pressure of the first one-way valve 21. Similar to the first one-way valve 21, a second one-way valve 31 is integrated into the instrument on the second end cap 3. This is an outward-opening one-way valve, and the specific structure of the second one-way valve 31 is as follows... Figure 8 As shown, the system includes: a second ball valve 701, a second slider 702, a second disc spring 703, and a second limiting screw 704. The second end cap 3, the second slider 702, the second disc spring 703, and the second limiting screw 704 all have a central hole structure to ensure smooth fluid flow when the second ball valve 701 is open. The second limiting screw 704 is tightened onto the second end cap 3. The second slider 702 limits the circumferential movement range of the second ball valve 701, and the second disc spring 703 controls the opening pressure of the second check valve 31.

[0078] In this embodiment, the microphone is filled with castor oil. Before filling, the castor oil needs to be fully evacuated to reduce the gas content inside. Before filling, a special tool is needed to open the first one-way valve 21 to keep the inside filled with liquid.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An underwater microphone, characterized in that, The pickup includes a pickup core and a packaging system; The vibration pickup core includes a hollow, open-ended active material tube. The two ends of the active material circular tube are sealed by end caps; The vibration pickup core is fixed inside the packaging system, and a certain gap is maintained between it and the packaging system. The encapsulation system is a hollow sealed structure, and part of its outer shell is made of deformable material; The interior of the vibration pickup core and the gap between the vibration pickup core and the packaging system are filled with insulating fluid. The pressure of the insulating fluid inside the vibration pickup core is set as P1, and the pressure of the insulating fluid in the gap between the vibration pickup core and the packaging system is set as P2. The end cap is equipped with a pressure control valve, which is initially closed. When P1 and P2 are different, the pressure control valve opens to allow the insulating fluid to flow. When P1 and P2 are the same, the valve closes. The pressure control valve consists of two check valves: a first check valve and a second check valve. The first check valve and the second check valve open in opposite directions, that is, one opens into the active material tube and the other opens into the active material tube. The opening pressure of the first one-way valve and the second one-way valve is greater than the maximum sound pressure of the sound field being detected, but less than the confining pressure resistance of the active material circular tube.

2. The underwater microphone according to claim 1, characterized in that: The end cap includes a first end cap and a second end cap, which respectively seal the active material tube from both ends; A first check valve is installed on the first end cap; a second check valve is installed on the second end cap.

3. The underwater microphone according to claim 1, characterized in that: The end cap has a cup-shaped structure with the cup opening facing the outside of the active material tube, and a one-way valve is installed in the cup. The one-way valve consists of: a disc spring, a slider, a ball valve, and a limit screw; The position of the limiting screw is fixed after it is connected to the end cap; When the one-way valve is opening inward, its components are arranged in the following order from the bottom of the cup to the opening: disc spring, slider, ball valve, and limit screw; the limit screw is used to limit the circumferential movement range of the ball valve. When the one-way valve is opening outwards, its components are arranged in the following order from the bottom of the cup to the opening: ball valve, slider, disc spring, and limit screw; the slider is used to limit the circumferential movement range of the ball valve. When the disc spring is deformed by force, it drives the slider to move, causing the ball valve to open or close. The bottom of the end cap, the limiting screw, the disc spring, and the middle of the slider all have openings, allowing fluid to pass through the ball valve when it is open.

4. The underwater microphone according to claim 1, characterized in that: The active material tube adopts radial segmented polarization, that is, an electrode is set inside the active material tube, and the external electrode is divided into two segments with opposite polarization directions.

5. The underwater microphone according to claim 1, characterized in that: The encapsulation system includes a hollow bladder with openings at both ends, the bladder being made of a deformable material; Both ends of the bladder are sealed by a lower bladder connector and an upper bladder connector; the outer sides of both ends of the bladder are tightly bound by a first bladder clamp and a second bladder clamp; The lower connector of the bladder has an opening in the middle, which is sealed with a first sealing element; The connector on the bladder has a central opening; the shielded cable passes through the central opening of the connector on the bladder; and a second seal is used to seal the central opening of the connector on the bladder.

6. The underwater microphone according to claim 5, characterized in that: The first sealing element is an oil plug; an O-ring is provided between the oil plug and the opening in the middle of the lower connector of the bladder; The second sealing element includes a wire plug and a watertight head, which seal the opening in the middle of the upper connector of the bladder from the inside and the outside of the upper connector, respectively; The inner ends of the bladder are respectively provided with a first rubber pad and a second rubber pad to fix the vibration pickup core.

7. The underwater microphone according to claim 1, characterized in that, The active material tube is a piezoelectric ceramic tube.

8. The underwater microphone according to claim 1, characterized in that, The insulating fluid is castor oil or transformer oil.

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