System and method for equivalent reproduction of seabed acoustic boundary based on acoustic metasurface

Abstract

The present application relates to a kind of seabed acoustic boundary equivalent reproduction system and method based on acoustic super surface, belong to underwater acoustic environment simulation technical field.System includes underwater acoustic test space, target boundary parameter processing module, programmable acoustic super surface array, configuration generation module, acoustic excitation module, acoustic measurement module, signal processing and sound field reconstruction module and calibration module.Target boundary parameter processing module converts target acoustic parameter into target acoustic response, configuration generation module generates space configuration scheme, programmable acoustic super surface array is set in test space according to scheme.Acoustic excitation module emits test sound wave, acoustic measurement module receives sound wave, signal processing and sound field reconstruction module obtains measured acoustic response, calibration module updates configuration scheme according to the deviation of measured response and target response to meet the preset error condition.The present application can equivalently reproduce different seabed boundary acoustic response, and provide controllable and repeatable boundary condition for underwater acoustic test.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic environment simulation technology, specifically relating to a system and method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces. Background Technology

[0002] Acoustic metasurfaces consist of multiple subwavelength acoustic modulation units, enabling the manipulation of sound wave reflection amplitude, phase, and propagation direction, providing a technical means for artificially constructing underwater boundaries with predetermined acoustic responses. Current metasurface research and applications primarily focus on sound absorption, focusing, beam deflection, and wavefront manipulation.

[0003] For example, Chinese invention patent CN113593009B proposes a metasurface-based reflective acoustic holographic imaging method. This method generates reflected sound waves by designing metasurface unit structures and reconstructs the target image on the imaging surface. However, this approach is geared towards holographic imaging scenarios, and its control objective is to eliminate acoustic interference to accurately reconstruct the image, rather than to reproduce the spatially varying multi-parameter acoustic response, including reflection, absorption, and scattering. Furthermore, this type of approach is an open-loop design, lacking a mechanism for closed-loop correction based on the deviation between the measured acoustic response and the target response, thus failing to guarantee reproduction accuracy.

[0004] To address this, the present invention provides a system and method for equivalent reproduction of seabed acoustic boundaries based on programmable acoustic metasurfaces, in order to solve the technical problem that existing metasurface technology cannot be applied to simulated seabed acoustic environments and form a metasurface spatial configuration based on the acoustic response of the target seabed boundary to achieve reconfigurable equivalent reproduction. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a system and method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces. Using acoustic response as the equivalent object, it eliminates the need for laying real seabed material. By spatially discretizing and independently configuring each region, it reproduces various complex seabed boundaries. Closed-loop calibration automatically compensates for errors, providing controllable and repeatable boundary conditions for underwater acoustic experiments.

[0006] This invention provides a system for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces, comprising: An underwater acoustic testing space is used to contain water and provide an acoustic testing environment. The target boundary parameter processing module is used to acquire the geometric information, spatial partitioning information and acoustic parameters of the target seabed boundary, and convert the acoustic parameters into the target acoustic response of the boundary to be reproduced. The target acoustic response includes at least one of reflection amplitude, reflection phase, absorption coefficient, scattering intensity and scattering direction distribution, and is expressed as a function of frequency, incident angle and boundary spatial position. A programmable acoustic metasurface array is set at a predetermined boundary position in an underwater acoustic test space. It includes multiple acoustic control units, each of which corresponds to one or more acoustic control regions on the target seabed boundary and is configured to generate predetermined reflection amplitude, reflection phase, absorption characteristics or scattering characteristics for incident sound waves. The configuration generation module is used to divide the target seabed boundary to be reproduced into multiple acoustic control regions. Based on the target acoustic response corresponding to each acoustic control region, the unit type, unit state, structural parameters, control parameters or spatial coding method of each corresponding region in the programmable acoustic metasurface array are determined, and a metasurface array configuration scheme is generated. The acoustic excitation module, located in the underwater acoustic test space, is used to emit test acoustic waves to the programmable acoustic metasurface array; The acoustic measurement module, set up in the underwater acoustic test space, is used to receive reflected or scattered sound waves formed by a programmable acoustic metasurface array to obtain the raw sound pressure signal. The signal processing and sound field reconstruction module is connected to the acoustic measurement module. It is used to process the original sound pressure signal, reconstruct the sound field formed by the programmable acoustic metasurface array, and obtain the measured acoustic response. The calibration module is connected to the signal processing and sound field reconstruction module and the configuration generation module, respectively. It is used to receive the measured acoustic response and the target acoustic response, generate configuration update information based on the deviation between the measured acoustic response and the target acoustic response, and output it to the configuration generation module. The configuration generation module updates the configuration scheme of the programmable acoustic metasurface array according to the configuration update information until the acoustic response of the reproduced boundary meets the preset error conditions.

[0007] This technical solution uses acoustic response as the equivalent object, eliminating the need for laying real seabed materials and reducing material dependence and laying and maintenance costs. By discretizing the target seabed boundary space into multiple independently configured regions, the unit type and state of each region can be determined separately, thereby achieving equivalent reproduction of various complex boundaries such as uniform seabed, seabed partitions, seabed boundaries, and undulating seabeds. Different scenarios can be switched by changing the unit state or spatial configuration without removing and re-laying the boundary. Through the acoustic measurement module, signal processing and sound field reconstruction module, and calibration module forming a closed loop, the configuration scheme can be automatically updated according to the measured deviation, compensating for the impact of manufacturing errors, installation errors, and environmental changes on the reproduction accuracy. This solution can provide controllable and repeatable seabed acoustic boundary conditions in a pool or tank, providing platform support for underwater acoustic equipment testing and acoustic experiments.

[0008] In some embodiments, the acoustic excitation module includes an arbitrary waveform generator, a power amplifier, and an underwater sound source. The output of the arbitrary waveform generator is connected to the input of the power amplifier, and the output of the power amplifier is connected to the input of the underwater sound source. The arbitrary waveform generator is used to generate continuous waves, pulse signals, linear frequency modulated signals, or coded signals. The power amplifier is used to amplify the signal, and the underwater sound source is used to convert the amplified electrical signal into underwater sound waves.

[0009] This technical solution can generate various preset test signals such as continuous waves, pulse signals, linear frequency modulation signals or coded signals according to the test requirements. After power amplification, the signals are converted into underwater sound waves by the underwater sound source, enabling the system to have multi-waveform and multi-frequency acoustic excitation capabilities, and meeting the differentiated test signal requirements of different underwater acoustic tests.

[0010] In some embodiments, the acoustic measurement module includes one or more hydrophones, and the multiple hydrophones are arranged in a linear array, area array, or spatial array.

[0011] This technical solution acquires sound pressure signals from different spatial locations simultaneously through the spatial deployment of multiple hydrophones, providing multi-channel raw sound pressure data for subsequent sound field reconstruction, thereby improving the spatial coverage and data acquisition efficiency of sound field measurement.

[0012] In some embodiments, the acoustic measurement module further includes a three-dimensional displacement platform on which the hydrophone is fixedly mounted. The three-dimensional displacement platform is used to change the spatial position of the hydrophone relative to the programmable acoustic metasurface array, so that the acoustic measurement module can obtain sound pressure information at different spatial positions.

[0013] This technical solution changes the spatial position of the hydrophone relative to the programmable acoustic metasurface array through a three-dimensional displacement platform, enabling the system to obtain sound pressure information at multiple different spatial positions within a preset area. This provides a data basis for the spatial reconstruction of two-dimensional or three-dimensional sound fields and avoids measurement blind spots caused by the fixed position of the hydrophone.

[0014] Based on the aforementioned equivalent reproduction system of seabed acoustic boundaries based on acoustic metasurfaces, this invention also provides a method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces, applied to the aforementioned equivalent reproduction system of seabed acoustic boundaries. The method for equivalent reproduction of seabed acoustic boundaries includes the following steps: S1, acquire the geometric information, spatial partitioning information and acoustic parameters of the target seabed boundary, and establish an acoustic response description of the target seabed boundary; S2, perform experimental scale equivalent transformation on the acoustic parameters of the target seabed boundary to obtain the target acoustic response to be reproduced; S3, divide the target seabed boundary into multiple acoustic control regions and determine the target acoustic response corresponding to each acoustic control region; S4. Based on the target acoustic response of each acoustic control region, match the corresponding acoustic control unit or determine the corresponding acoustic control unit configuration parameters to generate a spatial configuration scheme for the programmable acoustic metasurface array. S5, set up a programmable acoustic metasurface array according to the spatial configuration scheme, and place it at the preset boundary position of the underwater acoustic test space to form an equivalent seabed acoustic boundary; S6 emits test acoustic waves into the programmable acoustic metasurface array to obtain the original sound pressure signal of the equivalent seabed acoustic boundary; S7 processes the original sound pressure signal to reconstruct the sound field and obtain the actual acoustic response of the equivalent seabed acoustic boundary. S8. Compare the actual acoustic response with the target acoustic response. If the deviation between the two does not meet the preset error condition, adjust the type, state, parameters or spatial arrangement of the acoustic control unit, and repeat steps S6 to S8 until the preset error condition is met.

[0015] This technical solution integrates target acquisition, scaling conversion, spatial discretization, configuration generation, acoustic wave emission, signal acquisition, sound field reconstruction, and deviation comparison into a cohesive whole through a complete closed-loop process from S1 to S8. In S8, a deviation judgment and iterative adjustment mechanism is introduced. When a deviation exists between the measured acoustic response and the target acoustic response, the unit configuration is automatically adjusted and measurements are repeated until the preset error conditions are met. This closed-loop feedback mechanism enables the reproduction process to have self-correcting capabilities, ensuring that the acoustic response generated by the artificial boundary is sufficiently close to the target seabed boundary. This solves the problem of unreliable reproduction accuracy in open-loop schemes, achieving true "equivalent reproduction."

[0016] In some embodiments, in step S4, the acoustic control unit or unit state with the smallest deviation from the target acoustic response of each acoustic control region is selected from the metasurface response database.

[0017] This technical solution automatically selects the unit with the smallest deviation from the database, thus providing objective criteria for configuration selection.

[0018] In some embodiments, in step S4, for the first For each acoustic control region, the configuration generation module selects the optimal configuration from the metasurface response database using the objective function in equation (1):

[0019] In equation (1), , , and These represent the total number of acoustic control regions in the two coordinate directions, respectively. Indicates the spatial location index of the acoustic control region; Indicates the first The optimal configuration parameters obtained by matching each acoustic control region. Indicates candidate configuration parameters. This represents a metasurface response database. This indicates the reflection amplitude corresponding to the candidate configuration parameter. This indicates the reflection phase corresponding to the candidate configuration parameter. This represents the absorption coefficient corresponding to the candidate configuration parameter. The weighting coefficient represents the reflection amplitude. The weighting coefficients representing the reflection phase. The weighting coefficient represents the absorption coefficient. This represents the phase difference function that takes into account phase periodicity. Indicates the first The target reflection amplitude corresponding to each acoustic control region Indicates the first The target reflection phase corresponding to each acoustic control region Indicates the first The target absorption coefficient corresponding to each acoustic control region.

[0020] This technical solution uses the minimum weighted sum of squares of amplitude, phase, and absorption coefficient as the objective function to provide a quantitative criterion for optimal configuration, making the matching result mathematically certain and reasonable.

[0021] In some embodiments, in step S4, the configuration parameters of each acoustic control region in the programmable acoustic metasurface array are determined by reverse design based on the three-dimensional target acoustic field corresponding to the target seabed boundary.

[0022] This technical solution uses the three-dimensional target sound field as the design basis to solve the configuration parameters in reverse. It does not require the prior establishment of a database and is suitable for scenarios where the target sound field is complex or lacks a unit library.

[0023] In some embodiments, the metasurface configuration parameters are set as follows: , No. The calculated sound field on each target plane is: The target sound field is Then the objective function of reverse design can be expressed as: (2); In equation (2), Indicates the number of target planes. Represents the weights of different target planes. This represents a regular expression used to constrain configuration parameters. This represents the weight coefficient of the regularization term.

[0024] This technical solution aims to minimize the weighted error of the sound field across multiple target planes and introduces regularization terms to constrain the rationality of the configuration, ensuring overall matching of the three-dimensional sound field and that the configuration is feasible.

[0025] In some embodiments, in step S6, the hydrophone is moved within a preset area by a three-dimensional displacement platform to obtain the original sound pressure signals at multiple spatial locations.

[0026] This technical solution acquires the original sound pressure signals from multiple spatial locations using a three-dimensional displacement platform, providing sufficient input data for sound field reconstruction and avoiding sound field reconstruction distortion caused by insufficient sampling points.

[0027] Based on the above scheme, the equivalent reproduction system of seabed acoustic boundaries based on acoustic metasurfaces in this embodiment of the invention uses the acoustic response of the seabed boundary as the equivalent reproduction object. The target seabed acoustic parameters are converted into target acoustic responses through the target boundary parameter processing module. It does not require the actual laying of mud, sand, gravel or multi-layer sedimentary materials in the underwater acoustic test space, reducing the dependence on real seabed materials and their preparation, laying and maintenance processes. The configuration generation module discretizes the target seabed boundary space into multiple acoustic control regions, and determines the unit type, state or parameters of each region according to the target acoustic response of each region. This enables the same underwater acoustic test platform to reproduce various boundary forms such as uniform seabed, different seabed partitions, seabed boundaries and undulating seabeds, overcoming the shortcomings of traditional methods that are difficult to independently configure the acoustic responses of different locations. By changing the unit state or spatial configuration of the programmable acoustic metasurface array, different seabed acoustic scenarios can be switched without completely dismantling the test boundary. This solves the problem that existing artificial boundaries such as rigid reflectors and sound-absorbing materials have limited adjustable parameters and reconfigurability, and require reprocessing or replacement of boundary components. Simultaneously, the acoustic excitation module emits test sound waves, the acoustic measurement module receives reflected or scattered sound waves, the signal processing and sound field reconstruction module obtains the measured acoustic response, and the calibration module generates configuration update information based on the deviation between the measured response and the target response and outputs it to the configuration generation module, forming a complete closed loop of "target setting → configuration generation → measurement → comparison → correction". This can correct the configuration based on the actual acoustic response and automatically compensate for the impact of manufacturing errors, installation errors and environmental changes on the reproduction accuracy. It solves the problem of unreliable reproduction accuracy in open-loop schemes and provides controllable and repeatable seabed boundary conditions for underwater acoustic experiments.

[0028] The equivalent reproduction method of seabed acoustic boundaries based on acoustic metasurfaces in this invention involves: S1 obtaining the acoustic parameters of the target seabed boundary and establishing an acoustic response description, providing a unified data foundation for subsequent steps; S2 performing an experimental scale equivalent transformation on the target acoustic parameters, ensuring that scaled-down experiments have a standard physical basis and guaranteeing the comparability of experimental results under different scale coefficients; S3 discretizing the target boundary space; S4 generating a configuration scheme based on the target acoustic response of each region; S5 setting up a metasurface array according to the scheme to form an equivalent boundary; S6 emitting test sound waves; S7 processing the original sound pressure signal and reconstructing the sound field to obtain the actual acoustic response; and S8 comparing the actual response with the target response. If the deviation does not meet the preset conditions, the unit configuration is adjusted and S6 to S8 are repeated until the error requirements are met, forming a complete closed-loop iterative process. This process enables the reproduction process to have self-correcting capabilities, ensuring that the acoustic response generated by the final artificial boundary is sufficiently close to the target seabed boundary, solving the problem that existing methods cannot verify and guarantee reproduction accuracy. Furthermore, the standardized method steps ensure comparability and repeatability between different experiments. This invention can provide controllable seabed acoustic boundary conditions for experiments such as underwater sound propagation, sonar detection, target echo, reverberation, sonar imaging, and underwater communication, and provides a basis for testing and comparing different underwater acoustic devices under unified and repeatable test conditions. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the structure of the equivalent reproduction system in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the modular combination of the acoustic control unit and the configuration of the underwater acoustic boundary space in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the rotating cover type acoustic control unit in Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the structure of the fluid-modulated side-branch resonant cavity acoustic control unit in Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the slider-adjustable reflective acoustic control unit in Embodiment 2 of the present invention.

[0030] In the picture: 1. Underwater acoustic test space; 2. Programmable acoustic metasurface array; 3. Target boundary parameter processing module; 4. Configuration generation module; 5. Acoustic excitation module; 6. Acoustic measurement module; 7. Calibration module; 8. Multi-channel synchronous acquisition module; 9. Signal processing and sound field reconstruction module; 10. Control and data processing module; 21. Rotating cover type acoustic control unit; 211. Fixed substrate; 212. Preset resonant cavity; 213. Rotatable top cover; 214. Rotating shaft; 215. Micro motor; 22. Fluid-adjustable side-branch resonant cavity acoustic control unit; 221. Main channel; 222. Side-branch resonant cavity; 223. Fluid adjustment end; 23. Slider-adjustable reflective acoustic control unit; 231. Entrance opening; 232. Cavity; 233. Slider; 51. Arbitrary waveform generator; 52. Power amplifier; 53. Underwater sound source. Detailed Implementation

[0031] The technical solutions in 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 a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be understood that the terms "center", "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] Example 1 like Figure 1As shown, in one embodiment of the seabed acoustic boundary equivalent reproduction system and method based on acoustic metasurface of the present invention, the seabed acoustic boundary equivalent reproduction system based on acoustic metasurface includes an underwater acoustic test space 1, a programmable acoustic metasurface array 2, a target boundary parameter processing module 3, a configuration generation module 4, an acoustic excitation module 5, an acoustic measurement module 6, a signal processing and sound field reconstruction module 9, a calibration module 7, a multi-channel synchronous acquisition device, a three-dimensional displacement platform, and a control and data processing device.

[0036] In some embodiments, such as Figure 1 As shown, the underwater acoustic test space 1 is a pool or tank used to contain the water medium and provide an acoustic testing environment. The programmable acoustic metasurface array 2 is set at the bottom of the underwater acoustic test space 1 at a preset boundary position to form an artificial seabed acoustic boundary to be reproduced.

[0037] In some embodiments, such as Figure 1 As shown, the programmable acoustic metasurface array 2 is disposed at the bottom or other predetermined boundary position of the underwater acoustic test space 1, and includes multiple acoustic control units arranged along a one-dimensional direction or a two-dimensional plane. Each acoustic control unit corresponds to one or more acoustic control regions of the target seabed boundary and is configured to generate predetermined reflection amplitude, reflection phase, absorption characteristics, or scattering characteristics for the incident sound wave. The programmable acoustic metasurface array 2 is disposed on a planar support substrate, a partitioned support substrate, or a support substrate with a predetermined undulating shape to reproduce uniform seabed boundaries, boundaries of different seabed substrates, seabed boundary transitions, spatially gradient boundaries, or undulating seabed boundaries.

[0038] As an illustrative embodiment, a programmable acoustic metasurface array can be disposed on a planar support substrate, a partitioned support substrate, or a support substrate with a predetermined undulating shape to reproduce uniform seabed boundaries, boundaries of different seabed substrates, boundaries between seabed substrates, spatially gradient boundaries, or undulating seabed boundaries. Figure 2 Several exemplary combinations of different acoustic response modules are shown. Figure 2 Different modules are distinguished by different filling patterns, representing acoustic control modules with different reflection amplitudes, reflection phases, or absorption coefficients, without limiting their specific internal structures. The differences in filling patterns are only used to distinguish the acoustic response types of the modules; the same filling pattern indicates modules with the same or similar acoustic responses, while different filling patterns indicate differences in acoustic responses. Figure 2 Taking (a) as an example, it can be used to simulate the material interface verification scenario of the seabed transitioning from the first medium to the second medium through the horizontal combination of module A and module C. The sound waves are reflected, transmitted and scattered at the interface of the two types of seabed. Its sound propagation characteristics are significantly different from those of a single uniform seabed. This combination can be used to verify the accuracy of the boundary acoustic response reproduction of the system under the condition of sudden change in seabed. Figure 2(b) uses a combination of module A as the background region and module B as the embedded region. The outer module A occupies most of the region, and the central position is formed by module B to form a local heterogeneous region. This combination can be used to simulate the abnormal scenario of different substrates in a homogeneous substrate (such as a small sandy protrusion in a silty substrate). This combination is suitable for experimental research on target detection or the scattering characteristics of local anomalies. Figure 2 (c) consists entirely of modules C, each positioned at a different height, forming an undulating terrain. This can be used to simulate scenarios with raised or hilly seabed topography, and is suitable for studying sound propagation and reverberation characteristics under undulating seabed boundary conditions. It should be noted that the above combination method is only an illustrative example, and the arrangement, number, and spatial distribution of the modules can be adjusted according to the acoustic response requirements of the actual target seabed boundary.

[0039] It should be noted that, in this invention, "programmable" means that the programmable acoustic metasurface array 2 can change the type, operating state, structural parameters, control parameters, or spatial arrangement of each acoustic control unit according to the acoustic response of different target seabed boundaries. The changing methods include at least one of the following: module selection, module replacement, module rearrangement, mechanical adjustment, electric drive adjustment, hydraulic adjustment, pneumatic adjustment, and other adjustment methods capable of changing the acoustic response of the unit. For programmable acoustic metasurfaces using a modular assembly method, programmability manifests as the selection, replacement, and rearrangement of acoustic control units or acoustic control modules. For programmable acoustic metasurfaces using a dynamic adjustment method, programmability manifests as changing the operating state or control parameters of the acoustic control units through mechanical adjustment, electric drive adjustment, fluid adjustment, or other driving methods. The above different implementation methods can be used individually or in combination.

[0040] In some embodiments, such as Figure 1 As shown, the target boundary parameter processing module 3 is used to acquire the geometric information, spatial zoning information, and acoustic parameters of the target seabed boundary, and convert the acoustic parameters into the target acoustic response of the boundary to be reproduced. The geometric information of the target seabed boundary includes at least one of the following: boundary profile, spatial coordinates, topographic height, slope, roughness, seabed zoning range, and sediment layer thickness. The acoustic parameters of the target seabed boundary include at least one of the following: density, P-wave velocity, S-wave velocity, attenuation coefficient, acoustic impedance, reflection coefficient, absorption coefficient, scattering intensity, and scattering direction distribution. The above information can be obtained through at least one of the following methods: on-site measurement, seabed acoustic parameter database query, theoretical model calculation, or numerical simulation.

[0041] The target acoustic response includes at least one of reflection amplitude, reflection phase, absorption coefficient, scattering intensity, and scattering direction distribution, and is expressed as a function of frequency, incident angle, and boundary spatial position. In one embodiment, the target seabed boundary is located in spatial position... ,frequency and angle of incidence The complex reflection coefficient is expressed as: (3); In equation (3), Indicates the spatial location of the target's seabed boundary. ,frequency and angle of incidence Complex reflection coefficient under the following conditions The amplitude of the target reflection. For the target reflection phase, It represents the imaginary unit.

[0042] In some embodiments, for seabed boundaries with azimuth dependence, the acoustic azimuth angle can also be used as the independent variable of the target acoustic response. When the obtained original seabed parameters are density, sound velocity, attenuation coefficient, sediment layer thickness, and interface roughness, the original parameters are converted into complex reflection coefficient, absorption coefficient, or scattering parameters at the target frequency and target incident angle using a layered medium reflection model, seabed acoustic model, or numerical calculation method.

[0043] When the system is used for scaled-down underwater acoustic experiments, the target boundary parameter processing module 3 also performs equivalent transformations on the geometric scale, operating frequency, spatial location, and acoustic response parameters of the actual seabed boundary based on the preset scaled-down relationship between the actual seabed environment and the underwater acoustic test space 1, thus obtaining the acoustic response of the target boundary at the experimental scale. Let the characteristic length of the actual seabed scene be... The corresponding feature length at the experimental scale is Then the geometric scaling factor is: (4); In equation (4), To ensure that the dimensionless wavenumbers in the actual scenario and the experimental scenario are consistent, they can satisfy the following: (5); This leads to the experimental frequency: (6); In equation (6), This represents the frequency of sound waves at the experimental scale. This represents the speed of sound in water in a real-world scenario. This represents the speed of sound in the water medium during the experimental scenario. This indicates the frequency of sound waves in a real-world scenario.

[0044] When the actual and experimental scenarios use water media with similar sound speeds, the experimental frequency can be approximately converted using the reciprocal of the geometric scaling factor. The spatial coordinates of the target seabed boundary are converted according to equation (7): (7); In equation (7), Represents the spatial coordinates of the actual seabed boundary. Represents the spatial coordinates of the target's seabed boundary.

[0045] In some embodiments, the acoustic equivalence condition is that the experimental-scale artificial boundary and the actual seabed boundary have the same or similar complex reflection coefficients at the corresponding dimensionless frequency and incident angle, i.e.: (8); In equation (8), The complex reflection coefficient represents the artificial boundary at the experimental scale. The negative reflection coefficient, denoted by ", represents the actual seabed boundary. "" indicates that the deviation between the two meets the preset conditions.

[0046] In some embodiments, different equivalent priorities are set for different acoustic parameters according to the experimental purpose. When the experimental focus is on seabed reflection and target echo, priority is given to ensuring the equivalence of reflection amplitude and reflection phase; when the experimental focus is on propagation loss or reverberation, the absorption and scattering parameters are further configured equivalently.

[0047] In some embodiments, such as Figure 1 As shown, the configuration generation module 4 is used to divide the target seabed boundary to be reproduced into multiple acoustic control regions. Based on the target acoustic response corresponding to each acoustic control region, it determines the unit type, unit state, structural parameters, control parameters, or spatial encoding method of each corresponding region in the programmable acoustic metasurface array 2, and generates a metasurface array configuration scheme. The spatial division method includes at least one of the following: equal-size grid division, adaptive grid division, division according to seabed type, division according to topographic changes, and division according to the gradient of target acoustic parameters.

[0048] The configuration generation module 4 includes or can access a metasurface response database. This database stores the acoustic responses of different metasurface elements or element states under preset frequencies and incident angles. Each entry in the database includes at least a configuration identifier and a corresponding acoustic response. The configuration identifier includes at least one of the following: module number, element number, element state, spatial location number, structural parameters, arrangement direction, and control parameters. The corresponding acoustic response includes at least one of the following parameters under preset frequencies, incident angles, and underwater medium conditions: reflection amplitude, reflection phase, absorption coefficient, scattering intensity, and scattering direction. The metasurface response database is established through theoretical calculations, numerical simulations, pre-calibration experiments, or existing module parameters.

[0049] The configuration generation module 4 selects the corresponding unit or unit state from the metasurface response database based on the target acoustic response of each acoustic control region, or determines the corresponding configuration parameters using a parameter inversion method. For programmable acoustic metasurfaces using a modular assembly method, the configuration scheme guides the selection, replacement, and spatial arrangement of different acoustic control modules. For programmable acoustic metasurfaces implemented using a dynamic adjustment method, the configuration generation module 4 converts the configuration scheme into corresponding drive control commands.

[0050] In some embodiments, such as Figure 1 As shown, the acoustic excitation module 5 is located within the underwater acoustic test space 1 and is used to emit test acoustic waves into the programmable acoustic metasurface array 2. The acoustic excitation module 5 includes an arbitrary waveform generator 51, a power amplifier 52, and an underwater sound source 53. The output of the arbitrary waveform generator 51 is connected to the input of the power amplifier 52, and the output of the power amplifier 52 is connected to the input of the underwater sound source 53. The arbitrary waveform generator 51 is used to generate continuous waves, pulse signals, linear frequency modulated signals, coded signals, or other preset test signals. The power amplifier 52 is used to amplify the power of the test signals. The underwater sound source 53 is used to convert the amplified electrical signals into underwater acoustic waves and irradiate the programmable acoustic metasurface array 2 according to a preset frequency, waveform, and incident direction.

[0051] In some embodiments, such as Figure 1 As shown, the acoustic measurement module 6 is located within the underwater acoustic test space 1 and is used to receive reflected or scattered sound waves generated by the programmable acoustic metasurface array 2 to obtain the raw sound pressure signal. The acoustic measurement module 6 includes one or more hydrophones, which can be arranged in a linear array, area array, or spatial array. The hydrophones are fixed at preset measurement positions or mounted on a three-dimensional displacement platform. The three-dimensional displacement platform is used to change the position of the hydrophone array relative to the programmable acoustic metasurface array 2 to complete the scanning measurement of the reflected sound field, scattered sound field, or local acoustic response.

[0052] In some embodiments, such as Figure 1 As shown, the multi-channel synchronous acquisition module 8 is used to synchronously acquire the sound pressure signals output by each hydrophone and transmit the acquired measurement signals to the control and data processing module 10. The multi-channel synchronous acquisition module 8 includes at least one of a multi-channel data acquisition card, a synchronous clock unit, a signal conditioning unit, and a data transmission unit.

[0053] In some embodiments, such as Figure 1 As shown, the signal processing and sound field reconstruction module 9 is connected to the acoustic measurement module 6. It is used to process the original sound pressure signal, reconstruct the sound field formed by the programmable acoustic metasurface array 2, and obtain the measured acoustic response. The signal processing includes at least one of filtering, noise reduction, time window truncation, spectrum analysis, and phase correction.

[0054] In some embodiments, such as Figure 1 As shown, the calibration module 7 is connected to the signal processing and sound field reconstruction module 9 and the configuration generation module 4 respectively. It is used to receive the measured acoustic response and the target acoustic response, generate configuration update information based on the deviation between the measured acoustic response and the target acoustic response, and output it to the configuration generation module 4. This allows the configuration generation module 4 to update the configuration scheme of the programmable acoustic metasurface array 2 based on the configuration update information until the acoustic response of the reproduced boundary meets the preset error condition.

[0055] The preset error conditions are determined based on the test target, operating frequency band, incident angle range, and type of acoustic parameters to be reproduced. The preset error conditions include at least one of the following: reflection amplitude error meets a preset amplitude threshold, reflection phase error meets a preset phase threshold, absorption coefficient error meets a preset absorption threshold, scattering intensity error meets a preset scattering threshold, and overall sound field error meets a preset sound field error threshold.

[0056] When the reproduction error meets the preset conditions, the control and data processing device saves the current metasurface array configuration and uses it as a callable configuration for the corresponding seabed acoustic boundary. When the reproduction error does not meet the preset conditions, the calibration module 7 generates configuration update information based on the deviation of each acoustic control region. The configuration generation module 4 adjusts the module type, unit state, control parameters, or spatial arrangement of the corresponding region based on the configuration update information, and re-performs acoustic excitation and measurement. Configuration updates are performed on a single acoustic control region, multiple adjacent regions, or the entire programmable acoustic metasurface array 2. For local parameter deviations, the corresponding region is adjusted first; for deviations caused by unit coupling or overall acoustic field interference, multiple regions are jointly optimized. Closed-loop calibration is not the only necessary method for implementing this invention. When the established metasurface response database can meet the preset reproduction requirements, a configuration scheme can also be directly generated based on the target acoustic response and open-loop reproduction can be performed.

[0057] In some embodiments, such as Figure 1 As shown, the control and data processing module 10 includes a computer, a controller, a memory, and a corresponding data processing program. When the data processing program is executed by the computer, it implements the functions of the target boundary parameter processing module 3, the configuration generation module 4, the signal processing and sound field reconstruction module 9, and the calibration module 7.

[0058] Example 2 This embodiment illustrates the structural design of the acoustic control unit in Embodiment 1.

[0059] In some embodiments, such as Figure 3 As shown, the acoustic control unit is a rotating cover type acoustic control unit 21, including a fixed base 211, multiple preset resonant cavities 212 disposed within the fixed base 211, a rotatable top cover 213 disposed above the fixed base 211, a rotating shaft 214 connected to the rotatable top cover 213, and a micro motor 215 for driving the rotating shaft 214 to rotate. The rotatable top cover 213 has an opening area, and the multiple preset resonant cavities 212 within the fixed base 211 each have different geometric parameters or acoustic responses. When the micro motor 215 drives the rotatable top cover 213 to rotate, the opening area can communicate with different preset resonant cavities 212, allowing incident sound waves to enter the corresponding resonant cavity, thereby switching the reflection phase, reflection amplitude, or transmission phase state of the acoustic control unit. The control parameters include at least one of the following: top cover rotation angle, resonant cavity number, encoding state, micro motor 215 driving steps, and rotating shaft 214 position.

[0060] In some embodiments, such as Figure 4 As shown, the acoustic control unit is a fluid-adjustable side-branch resonant cavity acoustic control unit 22, including a main channel 221, multiple side-branch resonant cavities 222 connected to the main channel 221, and a fluid adjustment end 223 connected to the side-branch resonant cavities 222. Incident sound waves propagate along the main channel 221, and the multiple side-branch resonant cavities 222 are coupled to the main channel 221 through neck openings. By injecting or extracting fluid into the side-branch resonant cavities 222 through the fluid adjustment end 223, the liquid level, effective cavity volume 232, or equivalent acoustic mass within the side-branch resonant cavities 222 can be changed, thereby adjusting the amplitude and phase response of the acoustic control unit. Control parameters include at least one of the following: fluid volume, liquid level, effective cavity depth of the side-branch resonant cavity 222, neck opening size, main channel 221 height, and fluid adjustment amount.

[0061] In some embodiments, such as Figure 5As shown, the acoustic control unit is a slider-adjustable reflective acoustic control unit 23, including an incident opening 231, a cavity 232, a slider 233 disposed within the cavity 232, and an adjustment mechanism for driving the slider 233. The slider 233 can move along the axial direction of the cavity 232 to change the effective height, effective volume, or equivalent sound path of the cavity 232. When the position of the slider 233 changes, the reflection phase, reflection amplitude, or equivalent impedance generated by the acoustic control unit for the incident sound wave changes accordingly. The control parameters include at least one of the following: slider 233 displacement, effective height of the cavity 232, effective volume of the cavity 232, slider 233 diameter, number of driving steps, and reflection phase state.

[0062] Furthermore, the acoustic control unit can also be a cavity-type unit, a Helmholtz resonant unit, a labyrinth channel-type unit, a diaphragm resonant unit, a gradient impedance unit, a composite unit containing lossy materials, or a combination of the above structures. As long as the acoustic control unit can provide selectable or adjustable reflection amplitude, reflection phase, absorption characteristics, or scattering characteristics according to the acoustic response of the target boundary, it can be used as a component unit of the programmable acoustic metasurface array 2 of this invention.

[0063] Example 3 This embodiment illustrates the method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces provided by the present invention.

[0064] S1: Obtain the geometric information, spatial partitioning information, and acoustic parameters of the target seabed boundary, and establish an acoustic response description of the target seabed boundary.

[0065] The geometric information of the target seabed boundary includes boundary contour, spatial coordinates, topographic height, slope, roughness, seabed zoning range, and sediment layer thickness. The acoustic parameters of the target seabed boundary include density, P-wave velocity, S-wave velocity, attenuation coefficient, acoustic impedance, reflection coefficient, absorption coefficient, scattering intensity, and scattering direction distribution. This information is obtained through at least one of the following methods: field measurement, querying a seabed acoustic parameter database, theoretical model calculation, or numerical simulation.

[0066] S2, perform experimental scale equivalent transformation on the acoustic parameters of the target seabed boundary to obtain the target acoustic response to be reproduced.

[0067] The experimental scale equivalent transformation is based on the sound propagation similarity criterion, and the experimental frequency, boundary spatial location, and corresponding acoustic parameters are determined according to the geometric scaling relationship. Let the characteristic length of the actual seabed scene be... The corresponding feature length at the experimental scale is Then the geometric scaling factor is: (4); In equation (4), .

[0068] The experimental frequency satisfies: (6); In equation (6), This represents the frequency of sound waves at the experimental scale. This represents the speed of sound in water in a real-world scenario. This represents the speed of sound in the water medium during the experimental scenario. This indicates the frequency of sound waves in a real-world scenario.

[0069] The spatial coordinates of the target seabed boundary are transformed according to the relationship in equation (7): (7); In equation (7), Represents the spatial coordinates of the actual seabed boundary. Represents the spatial coordinates of the target's seabed boundary.

[0070] S3 divides the target seabed boundary into multiple acoustic control regions and determines the target acoustic response corresponding to each acoustic control region.

[0071] Spatial partitioning methods include at least one of the following: uniform-size grid partitioning, adaptive grid partitioning, partitioning according to substrate type, partitioning according to terrain changes, and partitioning according to the gradient of target acoustic parameters. After partitioning, each acoustic control region has a corresponding target acoustic response.

[0072] S4. Based on the target acoustic response of each acoustic control region, determine the unit type, unit state, structural parameters, control parameters or spatial coding method of each corresponding region in the programmable acoustic metasurface array 2, and generate a metasurface array configuration scheme.

[0073] This step can be implemented using either a response database matching method or a reverse design method based on the target sound field. The specific operation of these two methods is explained in detail in Examples 4 and 5.

[0074] S5. Set up the programmable acoustic metasurface array 2 according to the spatial configuration scheme, and place it at the preset boundary position of the underwater acoustic test space 1 to form an equivalent seabed acoustic boundary.

[0075] According to the spatial configuration scheme generated in step S4, different acoustic control modules are installed at the corresponding positions on the supporting frame, or the corresponding control parameters are input into the dynamically adjustable acoustic control unit to form a programmable acoustic metasurface array 2.

[0076] S6 transmits test acoustic waves to the programmable acoustic metasurface array 2 to obtain the original sound pressure signal of the equivalent seabed acoustic boundary.

[0077] The acoustic excitation module 5 emits test sound waves into the programmable acoustic metasurface array 2 according to a preset frequency, waveform, and incident angle. The acoustic measurement module 6 receives the reflected or scattered sound waves formed by the programmable acoustic metasurface array 2 to obtain the raw sound pressure signal. In one embodiment, a three-dimensional displacement platform moves the hydrophone within a preset area to obtain the raw sound pressure signals at multiple spatial locations.

[0078] S7: Perform signal processing on the original sound pressure signal to reconstruct the sound field and obtain the actual acoustic response of the equivalent seabed acoustic boundary.

[0079] Signal processing includes at least one of filtering, denoising, time-windowing, spectral analysis, and phase correction. In one implementation, the incident sound pressure and reflected sound pressure are separated by reference measurement, time-windowing, sound field decomposition, or other methods, and the actual complex reflection coefficient of the artificial boundary is calculated. (9); In equation (9), This represents the actual complex reflection coefficient of the artificial boundary. The complex spectrum representing the reflected sound pressure. The complex spectrum represents the incident sound pressure.

[0080] For spatially non-uniform seabed boundaries, sound pressure information (raw sound pressure signals) at multiple spatial locations is obtained through a three-dimensional displacement platform, and the two-dimensional or three-dimensional sound field formed by the artificial boundary is reconstructed accordingly.

[0081] S8. Compare the actual acoustic response with the target acoustic response. If the deviation between the two does not meet the preset error condition, adjust the type, state, parameters or spatial arrangement of the acoustic control unit, and repeat steps S6 to S8 until the preset error condition is met.

[0082] In one implementation, the reproduction error is expressed as: (10); In equation (10), Indicates the reproduction error. This represents the actual measured reflection amplitude. This represents the actual measured reflection phase. This indicates the target reflection amplitude in the corresponding area. This indicates the target reflection phase in the corresponding region. and This represents the error weight.

[0083] Deviation evaluation is performed individually for each acoustic control region, or based on the overall acoustic field response of multiple acoustic control regions. Configuration adjustments are made for individual acoustic control units, local array regions, or the entire programmable acoustic metasurface array 2. When the reproduction error meets preset conditions, the current metasurface array configuration is saved and used as a callable configuration for the corresponding seabed acoustic boundary.

[0084] Example 4 This embodiment provides a specific implementation of step S4. Its core concept is to pre-establish an acoustic response database of candidate acoustic control units or modules at different frequencies and incident angles, and then select the configuration with the smallest deviation from the target acoustic response for each acoustic control region from the database.

[0085] A programmable acoustic metasurface response database is pre-established. This database records the acoustic responses of different acoustic control modules, unit states, or control parameters under preset frequencies and incident angles. Each data entry in the database includes at least a configuration identifier and a corresponding acoustic response. The configuration identifier includes at least one of the following: module number, unit number, unit state, spatial location number, structural parameters, arrangement direction, and control parameters. The corresponding acoustic response includes at least one of the following parameters under preset frequencies, incident angles, and underwater medium conditions: reflection amplitude, reflection phase, absorption coefficient, scattering intensity, and scattering direction. The structural parameters include at least one of the following: aperture of the acoustic control unit, cavity depth, channel length, channel height, aperture ratio, equivalent impedance layer thickness, filling material parameters, and unit arrangement within the module. For the programmable acoustic metasurface array 2 using a modular assembly method, the control parameters include at least one of the following: module number, module installation position, module arrangement direction, module combination method, and unit status number; for the acoustic control unit using an adjustable structure, the control parameters may also include at least one of the following: adjustable aperture, adjustable channel height, adjustable cavity depth, mechanical displacement, driving voltage, driving current, hydraulic adjustment amount, or pneumatic adjustment amount.

[0086] The metasurface response database is established through theoretical calculations, numerical simulations, pre-calibration experiments, or existing module parameters. When using theoretical calculations, the reflection amplitude, reflection phase, or absorption response of the acoustic control unit at a preset frequency and incident angle is calculated based on its geometric parameters, material parameters, and boundary conditions. When using numerical simulations, the acoustic response under different unit states is obtained through finite element method, transfer matrix method, or equivalent impedance model. When using pre-calibration, the acoustic control unit or module is placed in an underwater acoustic testing environment, and its measured reflected sound pressure, incident sound pressure, or scattered sound field is obtained using acoustic excitation and measurement devices, from which the corresponding acoustic response parameters are calculated.

[0087] In this embodiment, a piece of data in the metasurface response database can be represented as: ,in, Indicates the first The number of each acoustic control unit or acoustic control module. This indicates the working or configuration status of the unit or module. This indicates the corresponding structural or control parameters. Indicates the test frequency. Indicates the angle of incidence of the sound wave. Indicates the reflection amplitude. Indicates the reflection phase, Indicates the absorption coefficient. This represents the scattering intensity or scattering direction parameter.

[0088] To determine the spatial location of each acoustic control region and establish the correspondence between the target acoustic response and the programmable acoustic metasurface array, a local two-dimensional coordinate system is established in the plane containing the programmable acoustic metasurface array. Two independent directions within the array plane are defined as the first coordinate direction and the second coordinate direction, respectively. The acoustic control regions are sequentially numbered along the first coordinate direction. The acoustic control regions are numbered sequentially along the second coordinate direction. Spatial index pairs The location of a single acoustic control region is uniquely determined. The acoustic control region is located in the first... The first coordinate direction partition and the first The acoustic control region is located at the intersection of the second coordinate direction partitions. The target acoustic response and configuration parameters of each subsequent acoustic control region are based on this spatial index. Associate location identifiers.

[0089] For the For each acoustic control region, the configuration generation module 4 selects the optimal configuration from the metasurface response database using the objective function in equation (1):

[0090] In equation (1), Indicates the first The optimal configuration parameters obtained by matching each acoustic control region. Indicates candidate configuration parameters. This represents a metasurface response database. This indicates the reflection amplitude corresponding to the candidate configuration parameter. This indicates the reflection phase corresponding to the candidate configuration parameter. This represents the absorption coefficient corresponding to the candidate configuration parameter. The weighting coefficient represents the reflection amplitude. The weighting coefficients representing the reflection phase. The weighting coefficient represents the absorption coefficient. This represents the phase difference function that takes into account phase periodicity. Indicates the first The target reflection amplitude corresponding to each acoustic control region Indicates the first The target reflection phase corresponding to each acoustic control region Indicates the first The target absorption coefficient corresponding to each acoustic control region.

[0091] The above matching process is performed on each acoustic control region separately, and the optimal configuration parameters of all regions are arranged according to their spatial positions to obtain the metasurface array spatial configuration matrix: (11); In equation (11), each element in the matrix represents the module type, unit state, or control parameter of the corresponding acoustic control region. This configuration matrix serves as the basis for setting the programmable acoustic metasurface array 2 in step S5.

[0092] Example 5 This embodiment provides another specific implementation of S4. Its core concept is: instead of relying on a pre-established response database, the three-dimensional spatial sound field distribution corresponding to the target seabed boundary is used as the design target, and the optimal configuration parameters of each region of the metasurface are solved in reverse through an optimization algorithm.

[0093] First, based on the reflection, absorption, and scattering characteristics of the target seabed boundary, the target sound pressure distribution on one or more target planes is determined. The target planes are set at different heights above the metasurface array to constrain the three-dimensional sound field formed by the artificial boundary.

[0094] Then, the propagation relationship between the metasurface array plane and each target plane is established based on the sound wave propagation model. The sound field corresponding to the metasurface array is calculated using the angular spectrum propagation method, Huygens-Fresnel principle, boundary element method, finite element method, or other sound field propagation models.

[0095] Let the metasurface configuration parameters be as follows: , No. The calculated sound field on each target plane is: The target sound field is Then the objective function of reverse design can be expressed as: (2); In equation (2), Indicates the number of target planes. Represents the weights of different target planes. This represents a regular expression used to constrain configuration parameters. This represents the weighting coefficient of the regularization term. The regularization term is used to constrain the differences in configuration parameters between adjacent acoustic control regions or to ensure that the configuration parameters meet the preset value range, thus avoiding unrealizable configurations in the optimization results.

[0096] Configuration generation module 4 uses gradient optimization, adjoint variable method, genetic algorithm, particle swarm optimization, Bayesian optimization, or other optimization methods to solve the above objective function, obtaining the metasurface configuration parameters that satisfy the target acoustic field constraints. After the solution is completed, the obtained configuration parameters are used as the basis for setting the programmable acoustic metasurface array 2 in S5.

[0097] Example 6 This embodiment illustrates the specific application of the equivalent reproduction method of seabed acoustic boundaries based on acoustic metasurfaces in different seabed boundary scenarios.

[0098] For a uniform seabed boundary, the configuration generation module 4 selects an acoustic control module that is the same or similar to the target seabed based on the reflection amplitude, reflection phase or absorption coefficient, and configures it in all or most of the acoustic control area to form a spatially approximately uniform artificial seabed acoustic boundary.

[0099] For different substrate zones and substrate boundaries, the metasurface array is divided into multiple configuration zones based on the spatial range of different substrate regions. Each configuration zone adopts a module or unit state corresponding to the acoustic response of the target substrate. The substrate boundary position can be configured directly according to the target boundary contour, or one or more transition regions can be set to make the acoustic parameters between adjacent zones change gradually.

[0100] For undulating seabed boundaries, geometric reproduction, acoustic equivalent reproduction, or a combination of both can be used.

[0101] When using the geometric reproduction method, the programmable acoustic metasurface array 2 is mounted on a support substrate with a predetermined undulating profile, so that the geometry of the array corresponds to the scaled-down target seabed topography.

[0102] When using the acoustic equivalent reproduction method, the programmable acoustic metasurface array 2 maintains a plane or approximately a plane, and compensates for the differences in propagation paths caused by the undulating seabed by setting the spatially varying reflection phase and reflection amplitude.

[0103] For a local height of The target undulating boundary, in the plane wave at the incident angle Initial reflection phase compensation amount corresponding to the local height at incidence It can be represented as: (12); In equation (12), This represents the wavenumber of the sound wave in the experimental water medium. The generation module 4 combines this phase compensation amount with the reflection phase of the target substrate itself to obtain the target phase for the corresponding acoustic control region.

[0104] It should be noted that closed-loop calibration is not the only necessary method for implementing this invention. When the accuracy of the metasurface response database meets the reproduction error requirements, a metasurface array configuration scheme can also be directly generated based on the target acoustic response and the deployment can be completed in one go, without the need for experimental feedback and iterative correction. Both of the above methods fall within the protection scope of this invention.

[0105] The seabed acoustic boundary equivalent reproduction system provided by this invention can also be used in combination with underwater targets, sonar transmitting and receiving equipment, synthetic aperture sonar, underwater vehicles or underwater communication equipment to study the impact of seabed boundary changes on sound propagation, multipath effects, reverberation, target echoes, sonar imaging results or underwater communication channels.

[0106] Through the description of several embodiments of the seabed acoustic boundary equivalent reproduction system and method based on acoustic metasurface of the present invention, it can be seen that the embodiments of the seabed acoustic boundary equivalent reproduction system and method based on acoustic metasurface of the present invention have at least one or more of the following advantages: 1. The acoustic metasurface-based seabed acoustic boundary equivalent reproduction system provided by this invention uses acoustic response as the equivalent object and does not require laying real seabed material. By discretizing the target boundary into multiple independent regions and configuring the unit type or state of each region, it can reproduce various boundary forms such as uniform seabed, seabed partition, seabed boundary and undulating seabed. Moreover, when switching scenes, there is no need to remove and re-lay the boundary, which improves the adaptability and reconfigurability of the test platform.

[0107] 2. The equivalent reproduction system of seabed acoustic boundary based on acoustic metasurface provided by the present invention forms a closed-loop feedback link through acoustic measurement module 6, signal processing and sound field reconstruction module 9 and calibration module 7. It can automatically update the configuration scheme according to the deviation between the measured acoustic response and the target acoustic response until the preset error condition is met, thereby compensating for the impact of manufacturing error, installation error and environmental changes on the reproduction accuracy, and solving the problem that the reproduction accuracy cannot be guaranteed in the open-loop scheme.

[0108] 3. The present invention provides an equivalent reproduction method for the acoustic boundary of the seabed based on acoustic metasurfaces. The present invention enables scaled-down experiments to have a unified physical basis through the equivalent conversion of the S2 experimental scale, ensuring the comparability of experimental results under different scaled-down coefficients. It solves the problem that the experimental results are difficult to reproduce and verify due to the inconsistent scale conversion methods in existing scaled-down experiments, and improves the consistency and reliability of scaled-down experimental results.

[0109] 4. The present invention provides a method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces. The present invention forms a closed-loop iterative process through S6 to S8, and uses the deviation between the measured response and the target response as the adjustment basis to automatically iterate until the preset error conditions are met, so that the reproduction process has self-correction capability, ensuring that the acoustic response generated by the artificial boundary is close enough to the target seabed boundary, and truly realizing "equivalent reproduction".

[0110] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A system for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces, characterized in that, include: An underwater acoustic testing space is used to contain water and provide an acoustic testing environment. The target boundary parameter processing module is used to acquire the geometric information, spatial partitioning information and acoustic parameters of the target seabed boundary, and convert the acoustic parameters into the target acoustic response of the boundary to be reproduced. The target acoustic response includes at least one of reflection amplitude, reflection phase, absorption coefficient, scattering intensity and scattering direction distribution, and is expressed as a function of frequency, incident angle and boundary spatial position. A programmable acoustic metasurface array is set at a predetermined boundary position in an underwater acoustic test space. It includes multiple acoustic control units, each of which corresponds to one or more acoustic control regions on the target seabed boundary and is configured to generate predetermined reflection amplitude, reflection phase, absorption characteristics or scattering characteristics for incident sound waves. The configuration generation module is used to divide the target seabed boundary to be reproduced into multiple acoustic control regions. Based on the target acoustic response corresponding to each acoustic control region, the unit type, unit state, structural parameters, control parameters or spatial coding method of each corresponding region in the programmable acoustic metasurface array are determined, and a metasurface array configuration scheme is generated. The acoustic excitation module, located in the underwater acoustic test space, is used to emit test acoustic waves to the programmable acoustic metasurface array; The acoustic measurement module, set up in the underwater acoustic test space, is used to receive reflected or scattered sound waves formed by a programmable acoustic metasurface array to obtain the raw sound pressure signal. The signal processing and sound field reconstruction module is connected to the acoustic measurement module. It is used to process the original sound pressure signal, reconstruct the sound field formed by the programmable acoustic metasurface array, and obtain the measured acoustic response. The calibration module is connected to the signal processing and sound field reconstruction module and the configuration generation module, respectively. It is used to receive the measured acoustic response and the target acoustic response, generate configuration update information based on the deviation between the measured acoustic response and the target acoustic response, and output it to the configuration generation module. The configuration generation module updates the configuration scheme of the programmable acoustic metasurface array according to the configuration update information until the acoustic response of the reproduced boundary meets the preset error conditions.

2. The system for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 1, characterized in that, The acoustic excitation module includes an arbitrary waveform generator, a power amplifier, and an underwater sound source. The output of the arbitrary waveform generator is connected to the input of the power amplifier, and the output of the power amplifier is connected to the input of the underwater sound source. The arbitrary waveform generator is used to generate continuous waves, pulse signals, linear frequency modulated signals, or coded signals. The power amplifier is used to amplify the signals. The underwater sound source is used to convert the amplified electrical signals into underwater sound waves.

3. The system for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 1, characterized in that, The acoustic measurement module includes one or more hydrophones, and multiple hydrophones can be arranged in a linear array, area array, or spatial array.

4. The system for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 3, characterized in that, The acoustic measurement module also includes a three-dimensional displacement platform, on which the hydrophone is fixedly mounted. The three-dimensional displacement platform is used to change the spatial position of the hydrophone relative to the programmable acoustic metasurface array, so that the acoustic measurement module can obtain sound pressure information at different spatial positions.

5. A method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces, characterized in that, Applied to the seabed acoustic boundary equivalent reproduction system as described in any one of claims 1-4, the seabed acoustic boundary equivalent reproduction method includes the following steps: S1, acquire the geometric information, spatial partitioning information and acoustic parameters of the target seabed boundary, and establish an acoustic response description of the target seabed boundary; S2, perform experimental scale equivalent transformation on the acoustic parameters of the target seabed boundary to obtain the target acoustic response to be reproduced; S3, divide the target seabed boundary into multiple acoustic control regions and determine the target acoustic response corresponding to each acoustic control region; S4. Based on the target acoustic response of each acoustic control region, match the corresponding acoustic control unit or determine the corresponding acoustic control unit configuration parameters to generate a spatial configuration scheme for the programmable acoustic metasurface array. S5, set up a programmable acoustic metasurface array according to the spatial configuration scheme, and place it at the preset boundary position of the underwater acoustic test space to form an equivalent seabed acoustic boundary; S6 emits test acoustic waves into the programmable acoustic metasurface array to obtain the original sound pressure signal of the equivalent seabed acoustic boundary; S7 processes the original sound pressure signal to reconstruct the sound field and obtain the actual acoustic response of the equivalent seabed acoustic boundary. S8. Compare the actual acoustic response with the target acoustic response. If the deviation between the two does not meet the preset error condition, adjust the type, state, parameters or spatial arrangement of the acoustic control unit, and repeat steps S6 to S8 until the preset error condition is met.

6. The method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 5, characterized in that, In step S4, the acoustic control unit or unit state with the smallest deviation from the target acoustic response of each acoustic control region is selected from the metasurface response database.

7. The method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 6, characterized in that, In step S4, for the first For each acoustic control region, the configuration generation module selects the optimal configuration from the metasurface response database using the objective function in equation (1): In equation (1), , , and These represent the total number of acoustic control regions in the two coordinate directions, respectively. Indicates the spatial location index of the acoustic control region; Indicates the first The optimal configuration parameters obtained by matching each acoustic control region. Indicates candidate configuration parameters. This represents a metasurface response database. This indicates the reflection amplitude corresponding to the candidate configuration parameter. This indicates the reflection phase corresponding to the candidate configuration parameter. This represents the absorption coefficient corresponding to the candidate configuration parameter. The weighting coefficient represents the reflection amplitude. The weighting coefficients representing the reflection phase. The weighting coefficient represents the absorption coefficient. This represents the phase difference function that takes into account phase periodicity. Indicates the first The target reflection amplitude corresponding to each acoustic control region Indicates the first The target reflection phase corresponding to each acoustic control region Indicates the first The target absorption coefficient corresponding to each acoustic control region.

8. The method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 5, characterized in that, In step S4, based on the three-dimensional target acoustic field corresponding to the target seabed boundary, the configuration parameters of each acoustic control region in the programmable acoustic metasurface array are determined by reverse design.

9. The method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 8, characterized in that, Let the metasurface configuration parameters be as follows: , No. The calculated sound field on each target plane is: The target sound field is Then the objective function of reverse design can be expressed as: （2）； In equation (2), Indicates the number of target planes. Represents the weights of different target planes. This represents a regular expression used to constrain configuration parameters. This represents the weight coefficient of the regularization term.

10. The method for equivalent reproduction of seabed acoustic boundaries based on acoustic metasurfaces according to claim 5, characterized in that, In step S6, the hydrophone is moved within a preset area by a three-dimensional displacement platform to obtain the original sound pressure signals at multiple spatial locations.

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