Deep sea broadband hydrophone

Abstract

The invention discloses a deep-sea broadband hydrophone which is suitable for deep-sea high-pressure, low-temperature and complex noise environments. The metal substrate (3) and the circuit board (2) are packaged in the metal shell, and the circuit board (2) is fixed on the metal substrate (3); the operational amplifier chip (1) and the bidirectional micromechanical ultrasonic transducer (5) are arranged on the circuit board (2); the sound transmission cap (4) is sealed and packaged at the opening of the metal shell and covers the bidirectional micromechanical ultrasonic transducer (5); wherein the bidirectional micromachined ultrasonic transducer (5) comprises an upper structure and a lower structure which are symmetrically arranged on the same substrate, and each of the upper structure and the lower structure comprises a PMUT unit and at least one CMUT unit; the bidirectional micromechanical ultrasonic transducer (5) is connected with the input end of the operational amplifier chip (1), and the output end of the operational amplifier chip (1) is connected with an external data acquisition system through a wire (7).

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of wideband hydrophone suitable for deep sea high pressure, low temperature and complex noise environment. BACKGROUND

[0002] Traditional hydrophone faces multiple technical bottlenecks in deep sea extreme environment. Deep sea environment (such as Mariana Trench) can reach more than 110 MPa in hydrostatic pressure, while traditional packaging materials such as epoxy resin are prone to plastic deformation or even cracking when the pressure exceeds 60 MPa, resulting in internal circuit short circuit or transducer failure. In terms of sound field noise, deep sea environment presents the characteristics of superimposed multi-source noise - low frequency band (1 Hz-1 kHz) is mainly affected by submarine earthquake and ocean current turbulence, and high frequency band (20 kHz-100 kHz) is disturbed by biological sonar (such as sperm whale) and ship propeller noise. Existing fixed bandwidth filtering technology is difficult to dynamically distinguish target signal and noise, and the signal-to-noise ratio is often less than 10 dB when detecting in wide frequency band (1 Hz-100 kHz), resulting in target signal being submerged. In addition, during the long-distance propagation of sound waves in deep sea, the signal amplitude attenuation rate reaches 0.5 dB / km due to the influence of water pressure gradient, temperature stratification and multipath effect, accompanied by significant phase distortion. The sensitivity of existing PZT piezoelectric ceramic transducer is difficult to capture weak signal, further reducing the detection accuracy. These factors jointly restrict the performance of traditional hydrophone in deep sea environment. SUMMARY

[0003] The present application proposes a deep sea wideband hydrophone to solve the problems of poor reliability, low signal-to-noise ratio and insufficient detection accuracy of traditional hydrophone in deep sea extreme high pressure, wideband complex noise and serious signal attenuation environment.

[0004] A kind of hydrophone, comprising: metal shell;Metal substrate and circuit board packaged in the interior of the metal shell, the circuit board is fixed on the metal substrate;Operational amplifier chip and bidirectional micro-mechanical ultrasonic transducer arranged on the circuit board;Sound-transparent cap sealed and packaged at the opening of the metal shell, the sound-transparent cap covers the bidirectional micro-mechanical ultrasonic transducer;Wherein, the bidirectional micro-mechanical ultrasonic transducer includes upper structure and lower structure symmetrically arranged on the same substrate, the upper structure and lower structure both include a PMUT unit and at least one CMUT unit;The bidirectional micro-mechanical ultrasonic transducer is connected with the input end of the operational amplifier chip, and the output end of the operational amplifier chip is connected with external data acquisition system through wire.

[0005] In some examples, the PMUT unit and CMUT unit of the bidirectional micro-mechanical ultrasonic transducer adopt partition design, the PMUT unit is located in the central region of the transducer, and the CMUT unit is distributed in the annular region outside the PMUT unit.

[0006] In some examples, the PMUT cell piezoelectric layer adopts a scandium-doped aluminum nitride material, and the CMUT cell electrode adopts a titanium alloy material.

[0007] In some examples, the bidirectional micro-mechanical ultrasonic transducer comprises an upper assembly and a lower assembly with a common substrate as the symmetry axis; the upper assembly comprises the upper structure and its corresponding upper vacuum cavity; the lower assembly comprises the lower structure and its corresponding lower vacuum cavity; the upper vacuum cavity and the lower vacuum cavity are independent of each other and are respectively sealed by an anodic bonding process, together forming a symmetrical double-layer vacuum cavity structure.

[0008] In some examples, the circuit board has an FPGA and an ADC, the ADC digitizes the electrical signal output by the bidirectional micro-mechanical ultrasonic transducer in real time, and the FPGA is configured to perform an FFT algorithm to extract the main frequency feature of the acoustic wave signal and automatically activate the corresponding PMUT cell or CMUT cell according to a preset frequency threshold.

[0009] In some examples, the FPGA is further configured to: when the main frequency of the acoustic wave signal is detected to be lower than 1 kHz, turn off the power supply of the CMUT cell and activate the PMUT cell; when the main frequency of the acoustic wave signal is detected to be higher than 20 kHz, turn off the power supply of the PMUT cell and activate the CMUT cell; and when the main frequency of the acoustic wave signal is detected to be between 1 kHz and 20 kHz, control the PMUT cell and the CMUT cell to work cooperatively.

[0010] In some examples, in the cooperative working mode of the PMUT cell and the CMUT cell, the FPGA performs the following steps: acquires a first electrical signal converted by the PMUT cell and a second electrical signal converted by the CMUT cell; uses a dynamic weighting fusion algorithm to fuse the first electrical signal and the second electrical signal, wherein the weight proportion of the first electrical signal decreases linearly with the increase of frequency, and the weight proportion of the second electrical signal increases linearly with the increase of frequency; and uses a digital phase-locked loop to perform phase compensation on the fused signal to eliminate the phase difference between the first electrical signal and the second electrical signal.

[0011] In some examples, the sound-transparent cap is a three-layer composite structure, comprising an inner flexible buffer layer, an intermediate rigid support layer, and an outer corrosion-resistant coating layer.

[0012] In some examples, the connection between the sound-transparent cap and the metal substrate is sealed with a deep-sea grade sealant.

[0013] In some examples, the metal substrate adopts an aviation-grade aluminum alloy or a titanium alloy material, and the surface is plated with a nickel-based alloy layer. Attached Figure Description

[0014] Figure 1 , Figure 2 This is a schematic diagram of a hydrophone according to an embodiment of the present invention.

[0015] Figure 3 This is a schematic diagram of a bidirectional micromechanical ultrasonic transducer according to an embodiment of the present invention. Detailed Implementation

[0016] like Figure 1 and Figure 2 As shown, the hydrophone includes a metal housing, an operational amplifier chip 1, a circuit board (PCB) 2, a metal substrate 3, a sound-permeable cap 4, a bidirectional micromechanical ultrasonic transducer 5, gold wires 6, a support, and wires 7. The PCB 2 and the metal substrate 3 are encapsulated inside the metal housing. The metal housing is made of high-strength aluminum alloy, providing external protection and structural integrity for the entire device.

[0017] PCB 2 is directly connected to metal substrate 3, serving as a platform for signal transmission and processing. Operational amplifier chip 1, wires, bidirectional micromechanical ultrasonic transducers, and other components are systematically arranged on it, along with integrated filtering, amplification, and bias circuit modules to synergistically enhance the overall performance of the hydrophone. The PCB uses high-frequency, high-heat-resistant FR-4 modified material with a dielectric constant between 3.5 and 4.2. Its dielectric loss tangent at 1 GHz is less than 0.02, effectively reducing signal loss and distortion during transmission.

[0018] The metal substrate 3 is made of aerospace-grade aluminum alloy or titanium alloy and undergoes a special heat treatment process to increase its tensile strength by at least 30%. Its yield strength meets the load-bearing requirements of deep-sea high-pressure environments (water pressure of 100MPa and above), ensuring that no plastic deformation occurs under extreme water pressure and maintaining the integrity of the hydrophone structure. The metal substrate 3 not only provides robust mechanical support but also serves as a low-impedance signal transmission channel. The ground terminal of the operational amplifier chip 1 is connected to the metal substrate, effectively suppressing common frequency interference.

[0019] The metal casing has an opening in the mounting area of ​​the transducer 5, which is sealed by a sound-permeable cap 4. The sound-permeable cap 4 is made of PDMS (0.5–1 mm thick), a material that matches the underwater acoustic impedance, and completely covers the bidirectional micromechanical ultrasonic transducer 5, forming a sound wave incident channel without dead angles. The sound-permeable cap 4 not only isolates the bidirectional micromechanical ultrasonic transducer 5 from the underwater environment, but also effectively transmits sound waves, improving the sound wave reception efficiency.

[0020] The transducer 5 is located at the center of the circuit PCB board 2, and its output end is connected with the input end of the operational amplifier chip 1 through the gold wire 6 to realize the transmission of the signal after the conversion of sound and electricity. The output end of the front-stage signal processing circuit integrated in the operational amplifier chip 1 is connected with the external data acquisition system through the lead wire 7 to complete the further processing and transmission of the signal.

[0021] The gold wire 6 meets the high purity (not less than 99.999%) and fine diameter control (10-20 microns), and its surface is treated by plasma to introduce functional groups and enhance the bonding strength with the chip and the PCB solder joint, thereby ensuring the long-term stability of the connection.

[0022] Figure 3 A bidirectional micromechanical ultrasonic transducer 5 is shown. The transducer includes an upper assembly and a lower assembly with a common substrate as the symmetry axis; the upper assembly includes an upper structure and its corresponding upper vacuum cavity 109a, 111a; the lower assembly includes a lower structure and its corresponding lower vacuum cavity 109b, 111b; the upper vacuum cavity and the lower vacuum cavity are independent of each other and are respectively sealed by an anodic bonding process, and together form a symmetrical double-layer vacuum cavity structure.

[0023] The upper structure and the lower structure each include a piezoelectric micromechanical ultrasonic transducer PMUT and at least one capacitive micromechanical ultrasonic transducer CMUT, the PMUT unit is located in the central region of the transducer, and the CMUT unit is distributed in the annular region outside the PMUT unit.

[0024] The PMUT unit includes, from top to bottom, a top electrode 101, a piezoelectric layer 102, a bottom electrode 103, a structure layer (elastic layer) 104, a cavity 111, and a substrate 112. The middle suspended area is called a diaphragm, and the emission of ultrasonic waves is formed by the up-and-down vibration of the diaphragm pressing the air. A direct current bias voltage is applied between the top electrode 101 and the bottom electrode 103 to form a uniform electrostatic field across the piezoelectric layer 102, which in turn produces a stretching and contracting deformation along the thickness direction, and drives the structure layer (elastic layer) 104 to deform synchronously. The material stiffness of the structure layer (elastic layer) 104 generates a reverse mechanical restoring force, and when the two are balanced, the diaphragm remains at a stable working bias point. Then, on the basis of the direct current bias, an alternating excitation signal matching the natural vibration frequency of the diaphragm is superimposed, the electric field strength across the piezoelectric layer periodically increases and decreases with the alternating signal, and during the positive half cycle, the total electric field strengthens to increase the stretching and contracting deformation amplitude of the piezoelectric layer, driving the structure layer and the diaphragm to move away from the substrate 112, and during the negative half cycle, the total electric field weakens to reduce the deformation amplitude of the piezoelectric layer, and the structure layer drives the diaphragm to rebound towards the substrate under the action of the restoring force, so that the diaphragm vibrates vertically and periodically with the bias point as the center. Finally, the up-and-down vibration of the diaphragm presses the surrounding air, forming a periodic pressure change and propagating in the form of a wave, thereby generating ultrasonic waves.

[0025] The CMUT cell includes an upper electrode 106, an insulating layer 107, a vibrating membrane 108, a cavity 109, and a substrate 105 from top to bottom. When a voltage is applied on the electrode, an electric field is generated in the cavity. An electrostatic force is generated between the vibrating membrane and the upper electrode. This electrostatic force attracts the vibrating membrane to bend and deform downward towards the cavity direction. The material stiffness of the membrane itself generates a mechanical restoring force (or elastic restoring force) in the opposite direction. As the voltage increases, the electrostatic force increases, the deformation also increases, and the restoring force also increases. Finally, at a certain specific bias voltage, the electrostatic force and the mechanical restoring force reach a balance, and the membrane remains in a stable deflection position. This bias point is the basis for the operation of the CMUT. The application of an alternating current signal will cause the membrane to vibrate near this balance point, thereby emitting or receiving ultrasonic waves. The processing technology of the bidirectional micro-mechanical ultrasonic transducer 5 uses the prior art, and the present application will not be described again.

[0026] To achieve efficient capture and accurate conversion of underwater broadband sound waves, the bidirectional micro-mechanical ultrasonic transducer of the hydrophone adopts a collaborative scheme of zoning design and function adaptation. According to the characteristic differences of sound waves of different frequencies, through the differential configuration of structural layout and material selection, each unit of the transducer can play the optimal performance in the corresponding frequency band. Specifically, the PMUT cell is located in the central region of the transducer, adopts scandium-doped aluminum nitride (Sc-AlN) piezoelectric layer, and optimizes the low-frequency sensitivity. The CMUT cell is distributed in the peripheral annular region, adopts high-voltage titanium alloy electrode, and enhances the high-frequency anti-interference ability. After the sound wave is converted into a weak electric signal, it is processed by multiple stages of amplification and filtering to improve the signal-to-noise ratio, and then transmitted to the data acquisition system, realizing high-quality conversion of underwater sound wave signals and meeting various underwater detection and monitoring requirements.

[0027] The transducer adopts a symmetrical double-layer vacuum cavity structure (each layer of independent vacuum cavity is sealed by anode bonding process), dynamically regulates the internal stress distribution through micro-electro-mechanical structure. In the deep-sea high-pressure environment, when the external pressure changes, the electric field response threshold of the CMUT / PMUT is adaptively adjusted to ensure the stability of the transduction efficiency (for example, fluctuation <5%). The upper vacuum cavity receives the incident sound wave from above. The lower vacuum cavity realizes the equivalent response of the sound wave from below. This upper and lower symmetrical design with the substrate as the symmetry axis can synergistically enhance the vibration effect through the vacuum cavity resonance effect regardless of whether the sound wave is incident from above or below, and the sensitivity is improved by 40% and the amplitude is improved by 25% compared with the traditional PZT. The mechanical coupling of the titanium alloy substrate and the vacuum cavity enables the transducer to maintain high-efficiency operation (fluctuation <5%) under a pressure of 100 MPa, far exceeding the pressure limit of conventional hydrophones (usually <60 MPa).

[0028] The hydrophone of the application is based on the design of a composite structure of CMUT and PMUT, realizes spectrum analysis and dynamic switching of working mode. The sound wave signal is digitized in real time through high-speed ADC (sampling rate >=1MHz), and the FPGA on the PCB extracts the main frequency characteristics (processing delay <1ms) using the FFT algorithm. According to the preset frequency threshold (low frequency band 1kHz, high frequency band >20kHz), the corresponding transducer unit is automatically activated: when low-frequency sound waves are detected, the central PMUT unit (using Sc-AlN piezoelectric layer, optimizing low-frequency sensitivity) is preferentially driven; when high-frequency sound waves are detected, the peripheral CMUT unit (using titanium alloy electrode, enhancing high-frequency anti-interference ability) is activated. When sound waves between the low frequency band and the high frequency band are detected, PMUT and CMUT work cooperatively. This mechanism dynamically adapts the transducer working mode through the frequency characteristics of the sound wave, significantly improving the efficiency of capturing wide-band sound waves and signal quality.

[0029] The hydrophone of the application outputs PWM signals based on the FFT processing results through FPGA, accurately controlling the power supply switch of PMUT / CMUT. When the signal main frequency is lower than 1kHz, the CMUT power supply is turned off and the PMUT electrode path is activated. The two PMUT units on the central area (each unit contains a Sc-AlN piezoelectric layer) and the double-layer vacuum cavity formed by the two PMUT units significantly improve the low-frequency vibration amplitude through resonance effect, effectively suppressing low-frequency noise interference such as ocean currents and seabed vibrations; the low dielectric loss of Sc-AlN reduces energy loss, and the symmetric structure dynamically controls the internal stress fluctuation to be lower than 5%, ensuring that the low-frequency signal phase error is lower than 3° under a high pressure environment of 100MPa, avoiding phase distortion.

[0030] When the main frequency is higher than 20kHz, switch to CMUT mode, realize nanosecond-level response speed through the capacitive conversion mechanism of the high-voltage titanium alloy electrode in the peripheral ring area, accurately capture high-frequency pulse signals, and at the same time reduce the sensitivity to turbulent high-frequency noise, significantly improve the selectivity in the 20-100kHz frequency band.

[0031] In the 1-20kHz transition frequency band, PMUT and CMUT work cooperatively, and FPGA performs the following steps: obtaining a first electric signal converted by the PMUT unit and a second electric signal converted by the CMUT unit; using a dynamic weighted fusion algorithm to fuse the first electric signal and the second electric signal, wherein the weight proportion of the first electric signal decreases linearly with the increase of frequency, and the weight proportion of the second electric signal increases linearly with the increase of frequency; using a digital phase-locked loop to compensate the phase of the fused signal, so as to eliminate the phase difference between the first electric signal and the second electric signal.

[0032] 1-10kHz dominated by PMUT, taking advantage of its high piezoelectric coefficient to improve sound pressure conversion efficiency; 10-20kHz dominated by CMUT, relying on the anti-interference ability of titanium alloy electrode to optimize high-frequency noise suppression; both through dynamic weighted fusion algorithm (PMUT contribution ratio linearly decreases with frequency, CMUT contribution ratio linearly increases with frequency) and digital phase-locked loop phase compensation to eliminate phase difference, combined with the mechanical coupling effect of double-layer vacuum cavity and titanium alloy substrate, maintaining signal stability under 100MPa pressure, improving sensitivity and signal-to-noise ratio, realizing seamless and efficient capture and high-quality conversion of underwater wide-band sound waves.

[0033] The transducer signal-to-noise ratio (SNR) is greater than or equal to 20dB, even in a multi-source noise superposition environment (such as 10kHz ship noise + 0.5Hz submarine seismic wave), the target signal can still be clearly separated. The transduction efficiency stability is significantly improved, and the efficiency fluctuation is less than 5% under 100MPa pressure (the traditional PZT material fluctuation is more than 30%).

[0034] The present application adopts a "flexible-rigid" multilayer composite packaging mechanism, which realizes high-efficiency acoustic performance and structural stability in deep-sea environment by combining metal substrate 3 and sound-transparent cap 4. The sound-transparent cap 4 adopts a three-layer modified polyurethane composite structure, with a sound-transparent rate of 95% and an acoustic impedance matching to 1.5MRayl. The sound-transparent cap 4 includes an inner flexible buffer layer, an intermediate rigid support layer and an outer corrosion-resistant coating. The flexible buffer layer absorbs external impact force and reduces dynamic pressure load. The rigid support layer provides structural stiffness and disperses stress under high pressure in deep sea. The corrosion-resistant coating uses corrosion-resistant materials (such as fluorinated polymers) to resist deep-sea salt spray and biological attachment.

[0035] The connection between the sound-transparent cap and the metal substrate adopts a deep-sea grade sealant (pressure resistance ≥100 MPa, leakage rate <0.1 mL / h), combined with IP69K standard titanium alloy waterproof joint (supporting 6000 meters deep continuous work), to build a full-sea-depth sealing protection system. The pressure limit reaches 110MPa (traditional hydrophone ≤60MPa), covering the full deep-sea area such as Mariana Trench. The structural deformation under high pressure is less than 0.05%, avoiding circuit short circuit or transducer failure caused by plastic deformation. The sealing performance is improved by more than 10 times (the leakage rate of traditional hydrophone is >1mL / h), and the device life is extended to more than 5000 hours.

[0036] The packaging glue adopts a material matched with the acoustic impedance of underwater sound, such as polyethylene, polyurethane or silicone. The external interface integrates a ceramic insulator to block the electrolytic corrosion path in the deep-sea high-pressure environment; the surface of the metal substrate is plated with a nickel-based alloy layer to effectively block the electromagnetic interference of the deep-sea detector.

[0037] The hydrophone of the application is placed in a simulated deep-sea high-pressure chamber (pressure 100 MPa, temperature 2°C) for pressure resistance, noise suppression and stability testing. The sound-transmitting cap and waterproof joint can continuously withstand 100 MPa pressure for 24 hours without leakage or deformation (see Figure 3 The output signal-to-noise ratio (SNR) of the hydrophone is ≥20 dB when the simulated 10 kHz ship noise and 0.5 Hz seabed seismic wave are superimposed. After 5000 hours of continuous operation, the gold wire bonding strength decreases by less than 3%, and the support structure maintains an insulation resistance greater than 10 12 Ω. When detecting acoustic signals in water, the periodic changes in density of the acoustic waves can cause compressive stress on the outer surface of the piezoelectric film and tensile stress on the inner surface, which in turn promotes the separation and aggregation of positive and negative charges on the film surface. The metal electrodes above and below collect the electrical signals, and the gold wire, lead wire and circuit PCB realize full-directional signal acquisition, ensuring that the hydrophone can accurately perceive acoustic signals from any direction and completely convert them into electrical signals without missing any key underwater acoustic information.

[0038] Acoustic signals in water are the target of hydrophone detection. The sound waves propagate to the inside of the hydrophone through the sound-transmitting cap. The adaptive filter module integrated in the circuit PCB analyzes the frequency characteristics of the acoustic signals in real time. When the input signal frequency is below 1 kHz, the PMUT mode (piezoelectric transducer) is enabled, which takes advantage of its high piezoelectric coefficient and high sensitivity characteristics in the low frequency band. Combined with the enhancement effect of the upper and lower vacuum cavities on low-frequency vibration (amplitude increase of 25%), it realizes efficient capture of weak low-frequency acoustic waves (such as seabed seismic waves and ocean current low-frequency disturbances), and the signal phase error is <3° under 100 MPa high pressure, ensuring the stability and accuracy of low-frequency signals.

[0039] When the frequency is higher than 20 kHz, the CMUT mode (capacitive transducer) is switched to, which takes advantage of its wide frequency response and high signal-to-noise ratio to suppress high-frequency noise. Even in a multi-source noise superimposed environment, it can still efficiently extract high-frequency target signals, achieving stable reception and conversion in the 20 kHz-100 kHz frequency band.

[0040] The hydrophone performance index of the application surpasses the traditional scheme, and provides technical support for deep sea resource exploration, environmental monitoring and military detection. Especially, the bidirectional micro-mechanical ultrasonic transducer automatically selects the CMUT or PMUT mode according to the characteristics of the sound wave, and converts the sound wave into a weak electric signal. The weak electric signal is first transmitted to the operational amplifier chip, and after multi-stage amplification, filtering and signal conditioning, the signal strength and quality are enhanced. The processed electric signal is transmitted, processed and monitored through the circuit PCB, and when necessary, further operation is carried out through the functional circuit on the PCB, such as bias adjustment or optimization of the driving signal. The metal substrate ensures the mechanical structure stability and electromagnetic shielding of the hydrophone, and at the same time assists in heat dissipation. The gold wire and the wire ensure the stable and reliable electrical connection of the entire circuit system, and finally realize the efficient conversion of the underwater sound wave signal into a high-quality electric signal, providing support for subsequent data acquisition, analysis and application.

Claims

1. A hydrophone, characterized by, The application relates to a metal shell, a metal substrate (3) and a circuit board (2) sealed in the metal shell, an operational amplifier chip (1) and a bidirectional micro-mechanical ultrasonic transducer (5) arranged on the circuit board (2), and a sound-transmitting cap (4) sealed and arranged at an opening of the metal shell and covering the bidirectional micro-mechanical ultrasonic transducer (5). The bidirectional micro-mechanical ultrasonic transducer (5) comprises an upper structure and a lower structure symmetrically arranged on a same substrate, and the upper structure and the lower structure each comprise a PMUT unit and at least one CMUT unit; the bidirectional micro-mechanical ultrasonic transducer (5) is connected with an input end of the operational amplifier chip (1), and an output end of the operational amplifier chip (1) is connected with an external data acquisition system through a wire (7). The PMUT unit and the CMUT unit of the bidirectional micro-mechanical ultrasonic transducer (5) adopt a partition design, the PMUT unit is located in a central region of the transducer, and the CMUT units are distributed in an annular region outside the PMUT unit. The piezoelectric layer of the PMUT unit adopts scandium-doped aluminum nitride material, and the electrode of the CMUT unit adopts titanium alloy material. The bidirectional micro-mechanical ultrasonic transducer (5) comprises an upper assembly and a lower assembly with a common substrate as a symmetric axis; the upper assembly comprises the upper structure and a corresponding upper vacuum cavity (109a, 111a); the lower assembly comprises the lower structure and a corresponding lower vacuum cavity (109b, 111b); the upper vacuum cavity (109a, 111a) and the lower vacuum cavity (109b, 111b) are independent of each other and are respectively sealed through an anodic bonding process, and jointly form a symmetric double-layer vacuum cavity structure. The circuit board (2) is provided with an FPGA and an ADC, the ADC digitizes an electric signal output by the bidirectional micro-mechanical ultrasonic transducer (5) in real time, and the FPGA is configured to execute an FFT algorithm to extract a main frequency feature of a sound wave signal and automatically activate a corresponding PMUT unit or CMUT unit according to a preset frequency threshold.

2. The hydrophone of claim 1, wherein, The FPGA is further configured to: when detecting that the main frequency of the sound wave signal is lower than 1 kHz, turn off the power supply of the CMUT unit and activate the PMUT unit; when detecting that the main frequency of the sound wave signal is higher than 20 kHz, turn off the power supply of the PMUT unit and activate the CMUT unit; and when detecting that the main frequency of the sound wave signal is between 1 kHz and 20 kHz, control the PMUT unit and the CMUT unit to work cooperatively.

3. The hydrophone of claim 2, wherein, In the cooperative working mode of the PMUT unit and the CMUT unit, the FPGA executes the following steps:

4. The hydrophone of claim 1 or 2 or 3, wherein, acquire a first electric signal converted by the PMUT unit and a second electric signal converted by the CMUT unit; 5. The hydrophone of claim 1, wherein, ​ 6. The hydrophone of claim 5, wherein, ​ 7. The hydrophone of claim 6, wherein, ​ ​ The first electric signal and the second electric signal are fused by using a dynamic weighted fusion algorithm, wherein the weight proportion of the first electric signal linearly decreases with the increase of frequency, and the weight proportion of the second electric signal linearly increases with the increase of frequency. The fused signal is phase compensated by using a digital phase-locked loop to eliminate the phase difference between the first electric signal and the second electric signal.

8. The hydrophone of claim 1, wherein, The sound-transparent cap (4) is a three-layer composite structure, including an inner flexible buffer layer, a middle rigid support layer and an outer corrosion-resistant coating.

9. The hydrophone of claim 1, wherein, The connection between the sound-transparent cap (4) and the metal substrate (3) is sealed by using a deep-sea sealant.

10. The hydrophone of claim 1, wherein, The metal substrate (3) is made of aviation-grade aluminum alloy or titanium alloy material, and the surface is plated with a nickel-based alloy layer.

Images