A sonar invisibility device based on topological acoustic materials and a control method thereof

Abstract

The application discloses a sonar invisibility device based on topological acoustic materials and a control method thereof. The device comprises a topological acoustic material invisibility layer (composed of two-dimensional phononic crystal units with a honeycomb lattice arrangement, thickness λ / 10~λ / 5, non-zero topological Chern number C≠0), a projection angle control system (resolution ≤0.001 rad, response time ≤100 ns), an acoustic sensor array, an adaptive invisibility controller (reflection coefficient ≤0.1, control period ≤1 μs), an active noise cancellation unit and an acoustic characteristic management interface. The topological acoustic material has the characteristic of one-way transmission of acoustic phonons, and can be switched (switching time ≤1 μs) between the invisibility mode and the reflection mode through the projection angle control. The passive topological invisibility and the active noise cancellation are cooperated to realize the invisibility effect ≥30 dB. The application can realize low-frequency broadband adaptive acoustic invisibility, and form an integrated underwater system of detection-invisibility-countermeasure.

Description

Technical Field

[0001] This invention relates to the fields of underwater acoustic stealth and underwater acoustic countermeasures, specifically to a sonar stealth device and its control method based on topological acoustic materials. This invention can be applied to submarine acoustic stealth systems, underwater unmanned platform stealth, surface ship acoustic characteristic control, torpedo acoustic stealth, and other fields, and is particularly suitable for acoustic stealth scenarios that counter low-frequency sonar detection and multi-static sonar detection. Acoustic stealth technology is one of the key technologies for improving the survivability and penetration capability of underwater equipment. With sonar technology gradually achieving low-frequency detection capabilities, the development of acoustic stealth technology faces significant challenges. Background Technology

[0002] Sonar stealth (acoustic stealth) is crucial for the survivability of underwater platforms. Submarines, unmanned underwater vehicles, and other platforms evade enemy sonar detection by reducing their radiated noise and echo intensity. Traditional acoustic stealth technologies mainly include anechoic tiles, vibration-damping rafts, and shape stealth. However, with the development of sonar technology towards low-frequency, multi-site, and omnidirectional capabilities, traditional acoustic stealth technologies face severe challenges. Acoustic metamaterials are a class of artificial composite materials with extraordinary physical properties, enabling the suppression of high-wavelength (low-frequency) sound wave propagation through small-sized structures. Existing acoustic stealth technologies mainly include the following schemes: (a) Sound-absorbing tile covering layer Covering the surface of the submarine hull with sound-absorbing rubber or polyurethane material can absorb incident sound waves from enemy active sonar. This method has the following problems: (1) poor absorption effect on low-frequency sound waves (< 5 kHz); (2) narrow sound absorption bandwidth, making it difficult to deal with broadband sonar; (3) ineffective against passive sonar detection (radiated noise); (4) large thickness, affecting the platform's maneuverability. (ii) Vibration-isolated raft The vibration of the power equipment is isolated from the shell by elastic support. This method has the following problems: (1) it has limited isolation effect on low frequency vibration; (2) it occupies a lot of cabin space; and (3) it increases the weight of the platform. (III) Stealth Design The method reduces acoustic wave reflection echoes by optimizing the hull shape. However, this method has the following problems: (1) it has a significant impact on hydrodynamic performance; (2) it cannot cope with multi-base sonar detection; and (3) it has limited effectiveness against low-frequency sonar. (iv) Active noise reduction technology The method cancels out radiated noise by emitting anti-phase sound waves. However, this method has the following problems: (1) it requires real-time measurement and precise control; (2) it consumes a lot of power; and (3) the system is complex and has low reliability. The emergence of acoustic metamaterials has provided a new solution to the problem of low-frequency noise control in acoustic engineering. In recent years, topological acoustic materials, as a new type of acoustic metamaterial, have opened up a completely new avenue for acoustic stealth technology due to their properties such as unidirectional sound wave transmission and topologically protected boundary states. The common limitation of existing technologies is that: It has poor stealth capabilities against low-frequency sound waves; Its narrow sound absorption bandwidth makes it difficult to cope with broadband sonar. Passive stealth and active stealth are separate and lack unified control; Unable to cope with multi-base sonar detection; It lacks adjustable stealth capabilities. To address the above problems, this invention provides a sonar stealth device based on topological acoustic materials and its control method. Summary of the Invention

[0003] (a) Purpose of the invention This invention aims to solve the technical problems of existing acoustic stealth technology, such as poor low-frequency sound wave performance, narrow sound absorption bandwidth, separation of passive and active stealth, and inability to cope with multi-static sonar detection. It provides a sonar stealth device based on topological acoustic materials and its control method. (II) Technical Solution This invention provides a sonar stealth device based on topological acoustic materials, characterized in that it comprises: A topological acoustic material cloaking layer is applied to the surface of the target platform shell and is composed of phononic crystals or acoustic metamaterial unit arrays with non-zero topological Chern numbers C ≠ 0. A projection angle control system is connected to the topological acoustic material cloaking layer and is used to control the projection angle θ of the topological acoustic material through an external field. The projection angle is defined as θ = arctan(β_s / β_r), satisfying β_r² + β_s² = 1. A sound wave absorption enhancement layer is disposed inside the topological acoustic material cloaking layer to absorb residual sound waves that penetrate the topological layer; An acoustic sensor array, embedded in the topological acoustic material camouflage layer, is used to monitor the amplitude and phase characteristics of incident and reflected sound waves in real time. An adaptive stealth controller is connected to the acoustic sensor array and the projection angle control system, and is used to adaptively control the projection angle of the topological acoustic material according to real-time monitoring results; An active noise cancellation unit, connected to the adaptive stealth controller, is used to emit anti-phase sound waves to cancel residual echoes when needed. A feature management interface is used to switch stealth strategies according to the platform's operating mode (cruising, combat, covert). (1) Topological acoustic material camouflage layer It is composed of two-dimensional phononic crystal structure units with a honeycomb lattice arrangement; Each unit cell consists of two interconnected, centrally symmetric basic units; The topological acoustic material has the characteristic of unidirectional sound wave transmission: when incident from one side, the sound wave is guided around the target (stealth), and when incident from the other side, the sound wave is reflected (sonar stealth and detection are both achieved). The thickness of the topological acoustic material cloaking layer is λ / 10 ~ λ / 5, achieving subwavelength cloaking in the low-frequency range (< 5 kHz). (2) Projection angle control system The projection angle θ can be modulated by applying an external field (electric field, magnetic field, or stress field) to the topological acoustic material. The projection angle θ controls the propagation path of sound waves in the topological material: when θ increases, the sound waves tend to bypass the target, and when θ decreases, the sound waves tend to be absorbed. The projection angle response time is ≤ 100 ns, supporting real-time stealth state switching. (3) Adaptive stealth controller An acoustic sensor array acquires the amplitude and phase information of incident and reflected sound waves in real time; The current stealth effect is calculated based on the reflection coefficient = |reflected wave / incident wave|. The projection angle θ is adjusted by closed-loop feedback to minimize the reflection coefficient (target reflection coefficient ≤ 0.1, i.e. -20dB). (4) Active noise reduction unit Activated when the enemy's sonar signal strength exceeds a threshold or when complete stealth is required; The residual echo is canceled out by emitting anti-phase sound waves; It works in conjunction with passive topology stealth to achieve broadband stealth. Core mathematical framework: Reflectance coefficient of topological acoustic materials: R(θ) = |(Z_topo(θ) - Z_water) / (Z_topo(θ) + Z_water)|² Where Z_topo(θ) is the equivalent acoustic impedance of the topological acoustic material controlled by the projection angle θ, and Z_water is the acoustic impedance of water. Stealth effect (echo intensity reduction): Stealth(θ) = 20 log 10 (|P_echo(θ)| / |P_incident|) The relationship between topological Chern number and acoustic wave propagation: Transmission(θ) = { ≈1, θ ∈ Θ_cloak (cloak mode); ≈0, θ ∈ Θ_reflect (reflection mode)} (III) Beneficial Effects Low-frequency acoustic stealth: Topological acoustic materials enable subwavelength acoustic wave manipulation, achieving effective stealth in the < 5 kHz frequency band; Broadband stealth: Achieving broadband adaptive stealth through projection angle adjustment; Adjustable stealth: The projection angle can be adjusted in real time, and the stealth effect can be dynamically adjusted; Passive + active synergy: Topological stealth reduces echoes, active noise cancellation eliminates residues, achieving complete stealth; One-way stealth capability: It can become invisible from one side (to protect itself) and detect from the other side (to perceive the environment). System collaboration: It can share topological acoustic material arrays with sonar detection systems and underwater acoustic countermeasure systems to form an integrated underwater system of detection, stealth and countermeasure. Attached Figure Description

[0004] Figure 1 This is a schematic diagram of the sonar stealth device based on topological acoustic materials provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the cell structure of the cloaking layer of the topological acoustic material provided in an embodiment of the present invention. Figure 3 The graph shows the variation of the stealth effect with the projection angle θ provided in the embodiments of the present invention. Figure 4 The adaptive stealth control flowchart is provided for an embodiment of the present invention. Detailed Implementation

[0005] Example 1: Submarine acoustic stealth coating based on topological acoustic materials Step 1: Design the topological acoustic material stealth layer. A two-dimensional five-mode metamaterial cell unit is used, arranged in a honeycomb lattice. Each cell consists of two centrosymmetric primitives, with a cell period a = λ / 10 (for 3 kHz sound waves, λ ≈ 0.5 m, a = 0.05 m). The stealth layer thickness t = λ / 5 ≈ 0.1 m covers the outer surface of the submarine's pressure hull. This topological acoustic material has a non-zero topological Chern number C = 1, and its projection angle θ can be tuned by an external electric field. Step 2: Integrate an acoustic sensor array. Embed M = 64 miniature hydrophones evenly distributed within the stealth layer to monitor the amplitude and phase characteristics of incident and reflected sound waves in real time. Step 3: Configure the projection angle control system. Each stealth unit is independently connected to the projection angle control circuit, with a projection angle resolution ≤ 0.001 rad and a response time ≤ 100 ns. Initially set the projection angle θ0 = 0.5 rad (stealth mode). Step 4: Measure the stealth effect. Active sonar detection (frequency 3 kHz): Without a stealth layer, the submarine echo intensity is 0 dB (reference value); with a topological stealth layer, the echo intensity is -18 dB, a reduction of 18 dB, and the equivalent target intensity is reduced to 1 / 63. For the 2 kHz to 10 kHz frequency band, the stealth effect is -15 dB to -20 dB, achieving broadband effective stealth. Step 5: Adaptive optimization. The acoustic sensor array detected a reflection coefficient R = 0.12 (-18.4 dB). The controller fine-tuned the projection angle θ to 0.52 rad through closed-loop feedback, reducing the reflection coefficient to R = 0.09 (-20.9 dB), which meets the stealth requirement (R ≤ 0.1). The beneficial effect of this embodiment is that the topological acoustic material cloaking layer achieves effective cloaking of low-frequency active sonar, and the cloaking effect can be adaptively optimized in real time. Example 2: Switchable stealth / detection mode based on projection angle adjustment Step 1: Configure system parameters. A topological acoustic material stealth layer covers the hull of the underwater unmanned platform, and a projection angle adjustment system connects to each stealth unit. Step 2: Stealth Mode (θ ∈ Θ_cloak). With a projection angle θ = 0.5 rad, the topological acoustic material is in a stealth state: incident sound waves propagate along the material surface, bypassing the target, and the echo is guided in a specific direction instead of returning to the sonar. The platform is "invisible" to active sonar, and the echo intensity decreases by > 20 dB. Step 3: Detection Mode (θ ∈ Θ_reflect). When environmental sensing is required, the projection angle is switched to θ = 0.1 rad via the external field, and the topological acoustic material switches to reflection mode: sound waves incident from the outside are strongly reflected (similar to traditional sonar), allowing the platform to detect external targets. Switching time ≤ 1 μs. Step 4: Verify the mode switching effect. Stealth mode echo intensity -22 dB, detection mode echo intensity +3 dB (enhanced by 25 dB). The switching between the two modes is smooth, and the platform can flexibly switch according to tactical needs. The beneficial effect of this embodiment is that the same topological acoustic material cloaking layer can be both cloaked and detectable, realizing the integration of "cloaking-detection". Example 3: Passive Topological Stealth + Active Noise Cancellation Synergy Step 1: Configure system parameters. The submarine hull is covered with a topological acoustic material stealth layer (passive stealth), and an active noise reduction unit (anti-acoustic emission array) is integrated inside. Step 2: Passive stealth baseline. The topological acoustic material stealth layer reduces the echo intensity by 18 dB (reflection coefficient R = 0.12). Step 3: Active noise cancellation compensation. The acoustic sensor array detects the amplitude and phase information of the residual echo, and the active noise cancellation unit calculates the anti-phase sound wave parameters (amplitude A_anti = A_echo, phase φ_anti = φ_echo + π), and emits an anti-phase sound wave to cancel out the residual echo. Step 4: Complete stealth effect. After passive topological stealth combined with active noise cancellation, residual echoes are further suppressed, and the total echo intensity is reduced to -35 dB (reflection coefficient R = 0.018), making the target "almost invisible". The beneficial effect of this embodiment is that passive topological cloaking and active noise cancellation work together to achieve broadband and deep acoustic cloaking. Example 4: Acoustic Feature Management and Multi-Mode Stealth Strategy Step 1: Configure the acoustic feature management interface. Three stealth strategies are preset based on the platform's operating mode: Cruise mode: Medium stealth (echo -15 dB), balancing stealth and maneuverability. Combat Mode: Deep Stealth (Echo -25 dB), maximizing stealth effectiveness. Stealth Mode: Full stealth (echo -35 dB), passive + active synergistic stealth Step 2: Strategy Switching. As the platform enters the combat zone from cruise mode, the acoustic signature management interface automatically switches the stealth strategy from cruise mode to combat mode. The projection angle control system and active silencing unit adjust in coordination, with a switching time of < 1ms. Step 3: Adaptive anti-multistatic sonar. When multistatic sonar detection is detected (multiple sound sources illuminating from different directions), the adaptive stealth controller calculates the incident waves in each direction and adjusts the projection angle of the topological acoustic materials in different regions to simultaneously create a stealth effect in all directions. Terminology Explanation

[0006] Terminology Meaning Acoustic stealth is a technique that evades enemy sonar detection by reducing its own radiated noise and echo intensity. Topological acoustic materials are phononic crystals or acoustic metamaterials with nontrivial topological band structures. Phononic crystals are artificial crystals composed of periodically arranged acoustic scatterers, possessing a phononic band structure. Five-mode metamaterials are acoustic metamaterials with special elastic modulus tensors. Unidirectional sound wave transmission: The property of sound waves to propagate in one direction and be blocked in the opposite direction. Reflection coefficient (R): The ratio of the amplitude of the reflected sound wave to that of the incident sound wave. Active noise cancellation is a technique that cancels out the echo from a target by emitting anti-phase sound waves.

Claims

1. A sonar stealth device based on topological acoustic materials, characterized in that, include: A topological acoustic material cloaking layer is applied to the surface of the target platform shell. It is composed of an array of phononic crystals or acoustic metamaterial units with a non-zero topological Chern number C ≠ 0. The topological acoustic material has unidirectional sound wave transmission characteristics, and the cloaking layer thickness is λ / 10 ∼ λ / 5. A projection angle control system is connected to the topological acoustic material cloaking layer and is used to control the projection angle θ of the topological acoustic material through an external field. The projection angle is defined as θ = arctan(β_s / β_r), satisfying β_r² + β_s² = 1, the projection angle resolution is ≤ 0.001 rad, and the response time is ≤ 100 ns. An acoustic sensor array, embedded in the topological acoustic material camouflage layer, is used to monitor the amplitude and phase characteristics of incident and reflected sound waves in real time. An adaptive stealth controller is connected to the acoustic sensor array and the projection angle control system to adaptively adjust the projection angle of the topological acoustic material based on real-time monitoring results, so that the reflection coefficient is ≤ 0.1 (-20 dB). An active noise cancellation unit, connected to the adaptive stealth controller, is used to emit anti-phase sound waves to cancel residual echoes when needed. A feature management interface is used to switch stealth strategies based on the platform's operating mode.

2. The apparatus according to claim 1, characterized in that: The unit cell of the topological acoustic material cloaking layer is a two-dimensional five-mode metamaterial structure with a honeycomb lattice arrangement. Each unit cell consists of two centrally symmetrical basic units, which are composed of an isosceles trapezoidal structure and an equilateral triangular connecting region.

3. The apparatus according to claim 1, characterized in that: The topological acoustic material cloaking layer has the characteristic of unidirectional sound wave transmission. When the sound wave is incident from the outside, it is guided to bypass the target to achieve cloaking. When the sound wave is incident from the inside, it is reflected to enable the platform to detect external objects.

4. The apparatus according to claim 1, characterized in that: The projection angle control system switches between stealth mode Θ_cloak and reflection mode Θ_reflect by adjusting the projection angle θ. The echo intensity in stealth mode is reduced by ≥ 20dB, and the switching time is ≤ 1 μs.

5. The apparatus according to claim 1, characterized in that: The active noise cancellation unit includes an anti-acoustic emission array and a phased drive circuit. It calculates the anti-phase acoustic wave parameters in real time based on the residual echo amplitude and phase information measured by the acoustic sensor array, and emits anti-phase acoustic waves to cancel the residual echo, with a total stealth effect of ≥ 30 dB.

6. The apparatus according to claim 1, characterized in that: The adaptive stealth controller performs closed-loop feedback control: An acoustic sensor array collects incident and reflected sound waves; Calculate the reflection coefficient R = |P_echo / P_incident|; If R > 0.1, adjust the projection angle θ to minimize R; Control cycle ≤ 1 μs.

7. The apparatus according to claim 1, characterized in that: The stealth strategies supported by the acoustic feature management interface include: Cruise mode: echo -15 dB; Operational mode: echo -25 dB; Concealment mode: Echo -35 dB (passive topology stealth + active noise cancellation synergy); Switching time between modes < 1 ms.

8. The apparatus according to claim 1, characterized in that: The topological acoustic material stealth layer covers the surface of a submarine pressure hull, an underwater unmanned platform shell, or a torpedo shell, and the external field is an electric field, a magnetic field, or a stress field.

9. The apparatus according to claim 1, characterized in that: The device shares a topological acoustic material array with the sonar detection system and the underwater acoustic countermeasures system, forming an integrated underwater system for detection, stealth, and countermeasures.

10. The apparatus according to claim 1, characterized in that: When the adaptive stealth controller detects multistatic sonar, it calculates the incident waves in each direction and independently adjusts the projection angle of the topological acoustic materials in different regions to achieve simultaneous stealth in multiple directions.

Images