Hydrogel-based underwater cloaking device, design method, and test system

Abstract

The present disclosure provides a hydrogel-based underwater stealth device, a design method and a testing device, the underwater stealth device comprising two symmetrical halves, the two halves forming a ridge structure and defining a triangular prism-shaped shielding space below, each half comprising a plurality of sequentially arranged unit cells, each unit cell comprising a strip-shaped rigid piece and a flexible cover layer wrapped outside the strip-shaped rigid piece, each strip-shaped rigid piece being at an angle with the symmetry plane of the two halves, the strip-shaped rigid piece providing tensile and compressive stiffness to the unit cell, the flexible cover layer providing shear stiffness to the unit cell, the unit cell being suitable for reducing shear wave conversion effect to achieve acoustic diffraction when sub-wavelength scale acoustic waves sweep across the underwater stealth device.

Description

Technical Field

[0001] This disclosure relates to the fields of underwater acoustic control and metamaterials, and in particular to an underwater stealth device based on hydrogel, its design method, and testing system. Background Technology

[0002] With the development of marine sonar observation systems, the demand for acoustic metamaterials has shifted from simple sound-absorbing and sound-insulating metamaterials for controlling underwater acoustics to metamaterials for controlling sound wave paths, such as those for sound diffraction and sound refraction. Acoustic stealth metamaterials are a class of acoustic metamaterials primarily designed to achieve sound diffraction. Their design largely relies on the basic theories of transformation acoustics, using specific microstructures to achieve corresponding properties. The size of the microstructure is determined based on the operating frequency. As the frequency of marine sonar detection systems increases, the wavelength becomes shorter, and the requirements for the size of the microstructure become more stringent. Currently, underwater stealth structures can only achieve stealth functionality below 20kHz; stealth at frequencies above 20kHz remains unachievable. Furthermore, the microstructures within current underwater stealth structures are mostly connected by rigid solids with impedance matching below 0.5. This design is not conducive to achieving sound diffraction when subwavelength scale sound waves pass over the structure. Summary of the Invention

[0003] To address the aforementioned technical issues, this disclosure provides an underwater stealth device and design method based on hydrogel, which can achieve stealth at frequencies of 20kHz and higher.

[0004] According to one aspect of the inventive concept of this disclosure, an underwater stealth device based on hydrogel is provided, comprising two symmetrical halves forming a ridge-like structure and defining a triangular prism-shaped shielding space below. Each half includes multiple layers of sequentially arranged unit cells, each unit cell including a strip-shaped rigid sheet and a flexible covering layer covering the strip-shaped rigid sheet. Each strip-shaped rigid sheet forms an angle with the plane of symmetry of the two halves. The strip-shaped rigid sheet provides tensile and compressive stiffness to the unit cell, and the flexible covering layer provides shear stiffness to the unit cell. The unit cell is adapted to reduce the shear wave conversion effect to achieve acoustic diffraction when subwavelength scale sound waves pass over the underwater stealth device.

[0005] According to some embodiments of this disclosure, the rigid strip is made of stainless steel, and the flexible covering layer is hydrogel.

[0006] According to some embodiments of this disclosure, the included angle is related to the size of the ridge structure, including:

[0007]

[0008] Where α represents the angle between the rigid sheet and the two half-planes of symmetry, a represents the height of the shielding space, b represents the length of half the shielding space, c represents the height difference between the ridge structures, M represents the intermediate parameters of the geometric distribution, and P represents the advanced geometric distribution parameters.

[0009] According to some embodiments of this disclosure, the thickness of the unit cell is less than 1 / 3 of the underwater 100kHz acoustic wavelength.

[0010] According to some embodiments of this disclosure, adjacent unit cells are connected by flexible weak connections to reduce the intralayer shear modulus and extralayer tensile modulus of the unit cells, wherein the spacing between two adjacent rigid strips in the same layer is 1 to 3 mm.

[0011] According to some embodiments of this disclosure, the thickness of the unit cell is 3-5 mm, the thickness of the strip rigid sheet is 0.5-1 mm, and the width of the strip rigid sheet is 20-22 mm.

[0012] According to some embodiments of this disclosure, the length of the shielding space: the height of the shielding space: the height of the ridge structure = 2: (1±10%)*0.202857: (1±10%)*0.808571.

[0013] According to another aspect of the inventive concept of this disclosure, a design method for an underwater stealth device based on hydrogel as described above is provided, comprising:

[0014] Construct a uvw coordinate system and an xyz coordinate system. The uvw coordinate system contains a uniform acoustic fluid medium, while the xyz coordinate system contains an anisotropic first and second acoustic fluid medium. The symmetry planes of the two halves of the underwater stealth device are located on the yz plane, and the bottom surface of the shielding space is located on the xz plane.

[0015] The first attribute of the region containing the two halves in the xyz coordinate system is obtained based on the geometric parameters of the underwater stealth device and the property parameters of the first and second acoustic fluid media.

[0016] The second attribute of the underwater stealth device is obtained by orthogonalizing the first attribute of the region where the two halves are located. The second attribute includes bulk modulus information and density information.

[0017] The bulk modulus information and the density information are scaled;

[0018] The second property of one phase material in the flexible cover layer and the strip rigid sheet is defined, and the second property of the other phase material is obtained by combining acoustic lamination theory.

[0019] The second property of the obtained phase material is matched with data in the natural and synthetic materials library to obtain the material properties that satisfy the transformation acoustics and the theory of laminated equivalent media.

[0020] According to some embodiments of this disclosure, the property parameters of the first acoustic fluid medium and the second acoustic fluid medium are obtained through acoustic transformation theory transformation formulas and uniform acoustic fluid medium parameters in the uvw coordinate system, including:

[0021]

[0022]

[0023]

[0024]

[0025] Where a represents the height of the shielding space, b represents the length of half the shielding space, and c represents the height difference between the two ridge structures. The coordinate system transformation matrix ρ represents the first half of the ridge structure. 1 K1 represents the density matrix of the first half of the ridge structure, and K1 represents the bulk modulus of the first half of the ridge structure. The coordinate system transformation matrix ρ represents the second half of the ridge structure. 2 K1 represents the density matrix of the second half of the ridge structure, and K2 represents the bulk modulus of the second half of the ridge structure.

[0026] According to some embodiments of this disclosure, the acoustic lamination theory includes:

[0027]

[0028] Where, ρ ⊥ Represents vertical density, which is one of the 11 components of the density tensor; <·> represents the table volume-weighted average, ρ ρ denoted by parallel density, which is the 22nd component of the density component, and K represents the bulk modulus;

[0029] The second property of the other phase material obtained by combining acoustic lamination theory calculations includes:

[0030]

[0031]

[0032] Where ρ1 represents the density of the defined phase material, ρ2 represents the density of the other phase material, and ρ 11 ρ represents the 11 density components in the principal coordinate system. 22f2 represents the density component in the principal coordinate system, f1 represents the filling rate of the other phase material, K1 represents the bulk modulus of the defined phase material, and K2 represents the bulk modulus of the other phase material.

[0033] According to some embodiments of this disclosure, the density matrix of the attributes of the two halves has the same first invariant, second invariant and third invariant, and the z-direction is naturally its eigenvector direction. Based on the other two eigenvectors, the rotation angle α of the xy-axis plane about the z-axis can be obtained, where counterclockwise rotation is the positive direction.

[0034] According to some embodiments of this disclosure, the background uniform material is water, the underwater stealth device is laminated into a two-phase material layer, one phase material is fixed as stainless steel, the properties and proportion coefficient of the other phase material are calculated, and the hydrogel material is matched with data in a natural synthetic material library to obtain a hydrogel material that meets the requirements of transformation acoustics and the theory of laminated equivalent medium.

[0035] According to another aspect of the inventive concept of this disclosure, a testing system is provided, suitable for testing the stealth effect of the hydrogel-based underwater stealth device as described above. The testing system includes:

[0036] A steel plate is placed on the bottom of the water to support the sample to be tested, wherein the underwater stealth device is adapted to be installed on the sample;

[0037] A transducer suitable for emitting a Gaussian wave packet with a frequency range of 5000Hz to 100000Hz and the Gaussian wave packet having four periods;

[0038] Multiple hydrophone linear array elements are arranged in an array above the steel plate. The multiple hydrophone linear array elements are used to acquire scattered echo signals, which are used to evaluate the stealth effect of the underwater stealth device.

[0039] According to the embodiments of this disclosure, an underwater stealth device, design method and testing system based on hydrogel are proposed. Based on hydrogel material, a new flexible weak connection method is proposed. Combined with transformation acoustic theory, a novel underwater stealth structure is designed to achieve acoustic diffraction when subwavelength scale sound waves pass over the structure, and can achieve ultra-high frequency stealth function. Attached Figure Description

[0040] Figure 1 The schematic diagram and enlarged partial structure of the hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure are intended to illustrate the structure.

[0041] Figure 2 This is a schematic diagram of the structure of a single cell of a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure;

[0042] Figure 3 This is a front view and an enlarged schematic diagram of a partial structure of a hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure;

[0043] Figure 4 This is a schematic diagram of the structure and dimensions of a single cell of a hydrogel-based underwater stealth device according to another exemplary embodiment of the present disclosure;

[0044] Figure 5 This is a schematic diagram of the overall structure and dimensions of a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure;

[0045] Figure 6 This is a flowchart of a design method for a hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure;

[0046] Figure 7 yes Figure 6 Methods for constructing coordinate systems in flowcharts;

[0047] Figures 8(a) to (d) are equivalent acoustic properties of a single cell of a hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure;

[0048] Figure 9 This is a simulated configuration of an underwater stealth device according to exemplary embodiments of the present disclosure;

[0049] Figure 10 yes Figure 9 3D plot of the sound source modulation function for the simulated configuration shown;

[0050] Figure 11 This is a schematic diagram of the structure of a test system for a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure;

[0051] Figure 12 This is a sound field distribution diagram of a test system with and without a cloak, according to an exemplary embodiment of the present disclosure;

[0052] Figure 13 This is a test result diagram of a test system for a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure;

[0053] Figure 14 This is a schematic diagram of the structure of a rigid strongly connected unit cell and a flexible weakly connected unit cell according to exemplary embodiments of the present disclosure;

[0054] Figure 15 yes Figure 14 The diagram shows a rigid strongly connected unit cell and a flexible weakly connected unit cell, along with their property parameters.

[0055] Figure 16 yes Figure 14 The figures show the finite element simulation results of rigid strongly connected unit cells and flexible weakly connected unit cells.

[0056] Figure 17 yes Figure 14 The figure shows the results of the wave property study of rigid strongly connected unit cells and flexible weakly connected unit cells.

[0057] The meanings of the reference numerals in the above figures are as follows:

[0058] 1-Shielded space;

[0059] 2-unit cell;

[0060] 21-Strip rigid sheet;

[0061] 22- Flexible covering layer;

[0062] 3-Acrylic sheet;

[0063] 4-Underwater stealth device;

[0064] 5-Steel plate;

[0065] 6-Transducer;

[0066] 7- Hydrophone linear array element. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0068] Currently, underwater stealth structures can only achieve stealth capabilities below 20kHz; stealth at frequencies above 20kHz remains unachievable. Furthermore, the microstructures within current underwater stealth structures are mostly connected by rigid solids with impedance matching below 0.5. This design is unfavorable for achieving acoustic diffraction when subwavelength sound waves pass over the structure. Hydrogels, a novel synthetic material, possess both fluid and solid properties. Dynamically, they resemble water, while statically they exhibit certain load-bearing characteristics and high flexibility, offering the potential to solve current technical problems and overcome bottlenecks. Based on hydrogel materials, we propose a new flexible weak connection method and, combined with transformation acoustics theory, design a novel underwater stealth structure capable of achieving ultra-high frequency stealth capabilities.

[0069] Figure 1 The schematic diagram and enlarged partial structure of the hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure are intended to illustrate the structure. Figure 2 This is a schematic diagram of the structure of a single cell of a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure; Figure 3These are a front view and an enlarged schematic diagram of a partial structure of a hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure.

[0070] According to one aspect of the inventive concept of this disclosure, an underwater stealth device based on hydrogel is provided, such as... Figures 1 to 3 As shown, the underwater stealth device includes two symmetrical halves, which form a ridge-like structure and define a triangular prism-shaped shielding space 1 below. Each half includes multiple layers of sequentially arranged unit cells 2. Each unit cell 2 includes a strip-shaped rigid plate 21 and a flexible covering layer 22 covering the strip-shaped rigid plate 21. Each strip-shaped rigid plate 21 forms an angle with the plane of symmetry of the two halves. The strip-shaped rigid plate 21 provides tensile and compressive stiffness to the unit cell 2, and the flexible covering layer 22 provides shear stiffness to the unit cell 2. The unit cell 2 is suitable for reducing the shear wave conversion effect so as to achieve acoustic diffraction when subwavelength scale sound waves pass over the underwater stealth device.

[0071] In this embodiment, a novel flexible weak connection method is proposed for the underwater stealth device based on hydrogel. Combined with transform acoustic theory, a novel underwater stealth structure is designed to achieve acoustic diffraction when subwavelength scale sound waves pass over the structure, thus enabling ultra-high frequency stealth function.

[0072] According to some embodiments of this disclosure, a template is used to position and define the rigid strip 21, and then liquid hydrogel is filled into the gaps of the rigid strip 21 and cured. Optionally, the template is constructed from an acrylic sheet 3. The acrylic sheet 3 can be retained during the inspection process, or it can be removed before inspection.

[0073] According to some embodiments of this disclosure, the strip-shaped rigid sheet 21 is a long strip-shaped rigid sheet, and the underwater stealth device and its defined shielding space are presented as a horizontally placed triangular prism.

[0074] Figure 4 This is a schematic diagram of the structure and dimensions of a single cell of a hydrogel-based underwater stealth device according to another exemplary embodiment of the present disclosure.

[0075] According to some embodiments of this disclosure, such as Figure 4 As shown, the rigid strip is made of stainless steel, and the flexible covering layer is made of hydrogel. The material parameters of the stainless steel and hydrogel are shown in Table 1.

[0076] Table 1 Material Parameters

[0077]

[0078]

[0079] In this embodiment, the rigid strip is a reinforcing material (stainless steel) that provides the main tensile and compressive stiffness of the unit cell, thus providing a large static load-bearing capacity for the underwater stealth device. The flexible covering layer is a matrix material (hydrogel) that provides the main shear stiffness of the unit cell. The design of this material distribution greatly reduces the shear wave conversion effect and also provides a certain shear load-bearing capacity for the underwater stealth device.

[0080] According to some embodiments of this disclosure, the included angle is related to the size of the ridge structure, including:

[0081]

[0082] Where α represents the angle between the rigid sheet and the two half-planes of symmetry, a represents the height of the shielding space, b represents the length of half the shielding space, c represents the height difference between the ridge structures, M represents the intermediate parameters of the geometric distribution, and P represents the advanced geometric distribution parameters.

[0083] According to some embodiments of this disclosure, the thickness of a single cell is less than 1 / 3 of the underwater 100kHz acoustic wavelength.

[0084] According to some embodiments of this disclosure, adjacent unit cells are connected by flexible weak connections to reduce the intralayer shear modulus and extralayer tensile modulus of the unit cells. Optionally, the spacing between two adjacent rigid strips in the same layer is 1 to 3 mm; more preferably, the spacing between two adjacent rigid strips in the same layer is 1 mm, 1.5 mm, 2 mm, 2.5 mm, or 3 mm.

[0085] According to some embodiments of this disclosure, the thickness of the unit cell is 3-5 mm, the thickness of the strip rigid sheet is 0.5-1 mm, and the width of the strip rigid sheet is 20-22 mm.

[0086] Figure 5 This is a schematic diagram of the overall structure and dimensions of a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure.

[0087] According to some embodiments of this disclosure, such as Figure 5 As shown, the height of the shielding space is (1±10%)*0.060857m, the length of the shielding space is (1±10%)*0.6m, and the height of the ridge structure is (1±10%)*0.181713m.

[0088] Figure 6 This is a flowchart of a design method for a hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure.

[0089] According to another aspect of the inventive concept of this disclosure, a design method for an underwater stealth device based on hydrogel as described above is provided, such as... Figure 6As shown, the design method includes operations S601 to S606.

[0090] According to some embodiments of this disclosure, operation S601 includes: constructing a uvw coordinate system and an xyz coordinate system, wherein a uniform acoustic fluid medium is distributed in the uvw coordinate system, and an anisotropic first acoustic fluid medium and a second acoustic fluid medium are distributed in the xyz coordinate system, the symmetry planes of the two halves of the underwater stealth device are located on the yz plane, and the bottom surface of the shielding space is located on the xz plane.

[0091] According to some embodiments of this disclosure, operation S602 includes: obtaining the first attribute of the region where the two halves of the underwater stealth device are located in the xyz coordinate system based on the geometric parameters of the underwater stealth device and the property parameters of the first acoustic fluid medium and the second acoustic fluid medium.

[0092] According to some embodiments of this disclosure, operation S603 includes: orthogonalizing the first attribute of the region where the two halves are located to obtain the second attribute of the underwater stealth device, the second attribute including bulk modulus information and density information.

[0093] According to some embodiments of this disclosure, operation S604 includes scaling the bulk modulus information and the density information.

[0094] According to some embodiments of this disclosure, operation S605 includes: defining a second property of one phase material in the flexible cover layer and the strip rigid sheet, and calculating the second property of the other phase material in conjunction with acoustic lamination theory.

[0095] According to some embodiments of this disclosure, operation S606 includes: matching the second property of another phase material obtained with data in a library of natural and synthetic materials to obtain material properties that satisfy transformation acoustics and the theory of laminated equivalent media.

[0096] Figure 7 yes Figure 6 Methods for constructing coordinate systems in flowcharts.

[0097] According to some embodiments of this disclosure, such as Figure 7 As shown, the ridge structure in the upper figure is an underwater stealth device, and the space below the ridge structure is a shielding space; the lower left figure is the uvw coordinate system; the lower right figure is the xyz coordinate system; in the uvw coordinate system, a uniform acoustic fluid medium is distributed, which has parameters ρ0 and K0; the xyz coordinate system is distributed with anisotropic acoustic fluid medium 1 (first acoustic fluid medium) and acoustic fluid medium 2 (second acoustic fluid medium).

[0098] According to some embodiments of this disclosure, the property parameters of the first acoustic fluid medium and the second acoustic fluid medium are obtained through acoustic transformation theory transformation formulas and uniform acoustic fluid medium parameters in the uvw coordinate system, including:

[0099]

[0100]

[0101]

[0102]

[0103] Where a represents the height of the shielding space, b represents the length of half the shielding space, and c represents the height difference between the two ridge structures. The coordinate system transformation matrix ρ represents the first half of the ridge structure. 1 K1 represents the density matrix of the first half of the ridge structure, and K1 represents the bulk modulus of the first half of the ridge structure. The coordinate system transformation matrix ρ represents the second half of the ridge structure. 2 K1 represents the density matrix of the second half of the ridge structure, and K2 represents the bulk modulus of the second half of the ridge structure.

[0104] In this embodiment, the density is orthogonally anisotropic, and the xy component of the density property in region 2 even exhibits negative density. Such a demanding property is difficult to achieve and requires the use of various materials to construct complex microstructures to realize this orthogonal anisotropic density property. In this embodiment, the transformation used is a standard linear transformation. Optionally, the dimensions of the underwater stealth device are assigned values, for example, b = 300 mm, a = 0.202857 b, c = 0.808571 b, and substituted into formulas (4) and (5), to obtain the following relationship between regions 1 and 2 in the xyz system under these geometric parameters:

[0105]

[0106] K1 = 0.749117K0

[0107]

[0108] K2 = 0.749117K0

[0109] Analyzing the above relationship, based on the characteristics of real symmetric second-order tensors, these two density matrices possess the same first, second, and third invariants, and therefore their eigenvalues ​​are also the same. The z-direction is naturally the direction of its eigenvector and does not need to be changed. Through the other two eigenvectors, the rotation angle α of the xy-axis plane about the z-axis can be obtained (counterclockwise rotation is the positive direction).

[0110] Orthogonalizing the above relationships yields the properties of underwater stealth devices, including:

[0111] α1 = 22.7867 [deg]

[0112]

[0113] α² = -22.7867 [deg]

[0114]

[0115] Analysis of the properties of the aforementioned underwater stealth device reveals that achieving such properties remains difficult. Therefore, we scale it down; for example, by introducing a scaling factor L = 0.61, we scale both the density tensor and the bulk modulus simultaneously, obtaining the following results:

[0116]

[0117]

[0118]

[0119]

[0120] Analysis of the above results shows that, in essence, formula (2) is transformed into the following mapping relationship:

[0121]

[0122] Clearly, the resulting impedance mismatch will negatively impact stealth performance. To achieve the desired effect by simultaneously scaling the density tensor and bulk modulus, and incorporating acoustic lamination theory, a uniform background material of water (ρ0 = 1000 kg / m³) is used. 3 K0 = 2.2 × 10 9 The underwater stealth device is a two-phase material laminate, with one phase material fixed as stainless steel (ρ1=7850kg / m). 3 K1 = 156.06 × 10 9 The properties and proportion coefficients of the other phase material can be obtained by solving for Pa).

[0123] According to some embodiments of this disclosure, the acoustic lamination theory includes:

[0124]

[0125] Where, ρ ⊥ Represents vertical density, which is one of the 11 components of the density tensor; <·> represents the table volume-weighted average, ρ ρ denoted by parallel density, which is the 22nd component of the density component, and K represents the bulk modulus;

[0126] The second property of another phase material obtained by combining acoustic lamination theory calculations includes:

[0127]

[0128]

[0129] Where ρ1 represents the density of the defined phase material, ρ2 represents the density of the other phase material, and ρ `1 ρ represents the 11 density components in the principal coordinate system. 22 f2 represents the density component in the principal coordinate system, f1 represents the filling rate of the other phase material, K1 represents the bulk modulus of the defined phase material, and K2 represents the bulk modulus of the other phase material.

[0130] In this embodiment, the properties of the first phase material (stainless steel) are substituted into formulas (7) and (8) to obtain ρ2 = 931.135 kg / m 3 K2 = 2.1614 × 10 9 Pa, f2 = 0.7934. Matching the calculated phase material property parameters with those in a natural and synthetic materials library revealed that the hydrogel material satisfies this theoretical property, with a density of 1000 kg / m³. 3 The bulk modulus is 2.21 × 10⁻⁶. 9 Pa approximately satisfies the second-phase material property requirements of transformation acoustics and the theory of laminated equivalent media.

[0131] At the subwavelength scale, the structural size of acoustic metamaterials is much smaller than the wavelength. This characteristic makes it impossible to distinguish the structure of the metamaterial when waves propagate within it, allowing the metamaterial to be considered a homogeneous medium based on the layered equivalence theory and subwavelength scale effects. In the embodiments disclosed herein, the unit cell is in the form of stainless steel encapsulated by hydrogel, with a characteristic size of a total unit cell thickness of 4 mm, less than 1 / 3 of the underwater 100 kHz sound wave wavelength. The rotation angle of the unit cell is α, which can be expressed as follows through the orthogonalization process of the anisotropic density matrix:

[0132]

[0133] Where M represents the intermediate parameter of the geometric distribution, and P represents the advanced geometric distribution parameter.

[0134] Analysis of the above formula shows that the rotation angle α is a nonlinear function that is only related to the geometric dimensions of the underwater stealth device structure. Once we determine a, b, and c, the rotation angle α of the unit cell is determined. The rotation angles of the unit cells on both sides of the cloak are symmetrically distributed. Therefore, we introduce a sign function into the formula. Hydrogel is a flexible material that has a certain load-bearing capacity in static state and properties similar to solids. In dynamic state, its acoustic response is similar to that of water, and it also has the characteristics of a fluid. This encapsulation structure reduces the slip effect caused by the discontinuity of the solid-liquid interface, effectively reducing mass loss.

[0135] Figures 8(a) to (d) show the equivalent acoustic properties of a single cell of a hydrogel-based underwater stealth device according to exemplary embodiments of the present disclosure.

[0136] According to some embodiments of this disclosure, the transmittance and reflectance coefficient method was used for verification, as shown in Figures 8(a) to (d). The dynamic properties of the unit cell were initially verified to be consistent with the theoretical requirements, with errors of less than 5% in the range of 2500Hz to 35kHz.

[0137] Figure 9 This is a schematic diagram of the structure of a test system for a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure; Figure 10 yes Figure 9 The 3D plot of the sound source modulation function for the simulated configuration is shown.

[0138] According to some embodiments of this disclosure, the unit cell is further periodically extended to design an underwater stealth device such as... Figure 9 As shown, the stealth effect of this underwater stealth device was simulated using COMSOL simulation software. The 3D graph of the sound source modulation function of the simulated configuration is shown below. Figure 10 As shown, the top and left and right sides are perfectly matched layers, and the scatterer contains air (density 1.29 kg / m³). 3 Bulk modulus 0.000151767×10 9 A hard, thin-walled aluminum shell (Pa) with a stainless steel bottom interface is used in the simulation, employing impedance boundaries. The underwater stealth device utilizes... Figure 9 The structure shown has a unit cell as follows: Figure 4 The structure shown is a line sound source controlled by a Gaussian time modulation function and a quadratic spatial modulation function. The specific modulation function form is shown below:

[0139] p(x,t)=exp(-π(t-t0) / 0.0003) 2 cos(2πf(t-t0))(-x 2 +λ 2 )

[0140] Where P(x,t) represents the excitation sound source, f represents the excitation frequency, t0=2 / f, λ=c / f, c is the sound speed of the background fluid water, c=1480m / s.

[0141] Figure 11 This is a schematic diagram of the structure of a test system for a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure.

[0142] According to another aspect of the inventive concept of this disclosure, a testing system is provided, suitable for testing the stealth effect of hydrogel-based underwater stealth devices as described above. Figure 11 As shown, the test system includes: steel plate 5, transducer 6, and hydrophone linear array element 7.

[0143] According to some embodiments of this disclosure, a steel plate is placed on the bottom of the water to support the sample to be tested, wherein an underwater stealth device is suitable for covering the sample.

[0144] According to some embodiments of this disclosure, the transducer is adapted to emit a Gaussian wave packet with a frequency range of 5000 Hz to 100000 Hz and the Gaussian wave packet having four cycles.

[0145] According to some embodiments of this disclosure, multiple hydrophone linear array elements are arranged in an array above a steel plate. The multiple hydrophone linear array elements are suitable for acquiring scattered echo signals, and the echo signals are suitable for evaluating the stealth effect of the underwater stealth device.

[0146] In this embodiment, a multi-threaded underwater acoustic testing system with separate transmit and receive functions is used. The system also includes a semi-automatic positioning trolley, a signal generator, a signal monitor, a power amplifier, a signal preamplifier, and a Ni computer, etc., which will not be described in detail again.

[0147] According to some optional embodiments of this disclosure, there are three test scenarios for the test device: with underwater stealth device (covering the test piece), without underwater stealth device (exposing the test piece), and in an empty field (without the test piece).

[0148] When an underwater cloak is in place, the cloak covers the scatterer (test piece) and is placed on a stainless steel plate. Then, the corresponding parameters are set on the motor system control software on the computer, so that the spherical transducer emits Gaussian wave packets with four periods from 5000Hz to 100000Hz, for example, a total of 20 frequency wave packets. The monitoring data of ten hydrophones from left to right are selected to evaluate the sound field changes. The sampling frequency is 400000, and each frequency is tested three times.

[0149] Without underwater cloaking devices, the scatterer (test piece) is placed on a stainless steel plate. Then, the corresponding parameters are set on the motor system control software on the computer to make the spherical transducer emit Gaussian wave packets with four periods from 5000Hz to 100000Hz, for example, a total of 20 frequency wave packets. The monitoring data of ten hydrophones from left to right are selected to evaluate the sound field changes. The sampling frequency is 400000, and each frequency is tested three times.

[0150] In the empty field (plane), no scattering body (test piece) is placed on the stainless steel plate. Then, the corresponding parameters are set on the motor system control software on the computer so that the spherical transducer emits Gaussian wave packets with four periods from 5000Hz to 100000Hz. For example, a total of 20 frequency wave packets are used. The monitoring data of ten hydrophones from left to right are selected to evaluate the sound field changes. The sampling frequency is 400000, and each frequency is tested three times.

[0151] Then, the multi-frequency stealth effect of the stealth cloak is evaluated by comprehensively analyzing the sound field experimental data with, without, and in empty fields.

[0152] Figure 12 This is a sound field distribution diagram of a test system with and without a cloak, according to an exemplary embodiment of the present disclosure.

[0153] According to some embodiments of this disclosure Figure 9 The simulated configuration can excite a Gaussian wave packet containing 3.5 periods, which is beneficial to... Figure 9 The simulation configuration continues to simulate the scattered sound field at 10kHz. By comparing the sound field in the empty field (plane), with underwater stealth device (cloak), and without underwater stealth device (nocloak), the sound field conditions at time T = 8.375e(-4)s under the condition of emitting the same Gaussian wave are as follows. Figure 12 As shown, from Figure 12 It can be clearly seen that the sound field when the underwater cloak is present is basically the same as the sound field when the plane is in the air, which greatly reduces the scattering of the interface of the hidden object. In other words, the underwater cloak has a good cloaking effect.

[0154] Figure 13 This is a test result diagram of a test system for a hydrogel-based underwater stealth device according to an exemplary embodiment of the present disclosure.

[0155] According to some optional embodiments of this disclosure, a total of 20 frequencies (5000Hz to 100000Hz, measured once every 5000Hz) were tested, and each frequency was tested three times. The average was taken as the raw data for post-processing. A total of 180 sets of data were obtained from the tests for three scenarios: plane, cloak, and nocloak, and were then processed, including:

[0156]

[0157] NewRCS represents the stealth effect of the underwater stealth device, P i The mean(P) represents the hydrophone weights. cloak-reflected The mean(P) represents the time-domain average of the reflected sound pressure data when an underwater stealth device is present. plane-reflected The mean(P) represents the time-domain average of the reflected sound pressure data in the open field. nocloak-reflected () represents the time-domain average value of the reflected sound pressure data without underwater stealth devices.

[0158] In this embodiment, P i The selection of the hydrophone is related to its location. Hydrophones closer to the central axis of the structure can better reflect the actual scattering effect of the structure and will have a larger weight. Hydrophones farther away have weaker echo signals and will have a relatively smaller weight.

[0159] According to some optional embodiments of this disclosure, such as Figure 13 As shown, the total weight of the first 5 hydrophones near the center is 0.995, and the total weight of the last 5 hydrophones far from the center is 0.005. The NewRCS value, which characterizes the stealth effect of the underwater stealth device, is calculated by formula (9). If the value is less than or equal to 0.3, it means that there is a certain stealth effect at the corresponding frequency. If it is less than or equal to 0.2, it means that there is a certain stealth effect at the corresponding frequency and the effectiveness is high.

[0160] In this embodiment, the underwater stealth device of this disclosure has broadened and improved the operating frequency of the underwater acoustic diffraction stealth structure. The multi-frequency test results in the range of 25kHz-50kHz are good, proving that the structure has broken through the previous low-frequency limitation of 20kHz and greatly broadened the application frequency band of the stealth function.

[0161] Figure 14 This is a schematic diagram of the structure of a rigid strongly connected unit cell and a flexible weakly connected unit cell according to exemplary embodiments of the present disclosure; Figure 15 yes Figure 14 The diagram shows a rigid strongly connected unit cell and a flexible weakly connected unit cell, along with their property parameters. Figure 16 yes Figure 14 The figures show the finite element simulation results of rigid strongly connected unit cells and flexible weakly connected unit cells. Figure 17 yes Figure 14 The figure shows the results of the wave property study of rigid strongly connected unit cells and flexible weakly connected unit cells.

[0162] According to some embodiments of this disclosure, the connection methods between units include, for example: Figure 14 The rigid strong connection shown in (a) and as shown in Figure 14 The flexible weak connection shown in (b) is shown in the middle.

[0163] In rigidly connected unit cells, the discontinuity at the solid-liquid interface causes anisotropy, but the strong scattering of shear waves from the solid layer significantly affects the stealth effect. To mitigate this effect, the connection method between unit cells is changed as follows: Figure 14 The flexible weak connections shown in (b) significantly reduce the intralayer shear modulus and extralayer tensile modulus of the unit cell, making it more fluid-phase.

[0164] like Figure 15 As shown, the simulation was performed using the COMSOL finite element method in the frequency domain, and the results are as follows. Figure 16 As shown, through Figure 16 It can be seen that the underwater stealth device with flexible weakly connected unit cells has a better stealth effect and also has a wider stealth angle.

[0165] For the study of the wave properties of these two types of unit cells, 20*10 unit cells were arranged into a supercell intermediate layer, and their wave properties were simulated using COMSOL to obtain the reflection coefficient and transmission coefficient, as shown below. Figure 17 As shown, it can be seen that the supercell layer using flexible weakly connected units effectively reduces sound reflection and improves sound transmission underwater.

[0166] The embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. It should be noted that implementations not illustrated or described in the drawings or the main text of the specification are forms known to those skilled in the art and have not been described in detail. Furthermore, the definitions of the various components described above are not limited to the specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can easily modify or substitute them.

Claims

1. An underwater stealth device based on hydrogel, characterized in that, The device comprises two symmetrical halves that form a ridge-like structure and define a triangular prism-shaped shielding space below. Each half includes multiple layers of sequentially arranged unit cells. Each unit cell includes a rigid strip and a flexible covering layer covering the rigid strip. Each rigid strip forms an angle with the plane of symmetry of the two halves. The rigid strip provides tensile and compressive stiffness to the unit cell, and the flexible covering layer provides shear stiffness to the unit cell. The unit cell is suitable for reducing shear wave conversion effects to achieve acoustic diffraction when subwavelength scale sound waves pass over the underwater stealth device.

2. The underwater stealth device according to claim 1, characterized in that, The rigid strip is made of stainless steel, and the flexible covering layer is made of hydrogel.

3. The underwater stealth device according to claim 2, characterized in that, The included angle is related to the size of the ridge structure, including: Where α represents the angle between the rigid sheet and the two half-planes of symmetry, a represents the height of the shielding space, b represents the length of half the shielding space, c represents the height difference between the ridge structure and the shielding space, M represents the intermediate parameter of the geometric distribution, and P represents the advanced geometric distribution parameter.

4. The underwater stealth device according to claim 3, characterized in that, The thickness of the unit cell is less than 1 / 3 of the underwater 100kHz sound wavelength.

5. The underwater stealth device according to claim 3, characterized in that, The adjacent unit cells are connected by flexible weak connections to reduce the intralayer shear modulus and extralayer tensile modulus of the unit cells. The spacing between two adjacent rigid strips in the same layer is 1 to 3 mm.

6. The underwater stealth device according to claim 3, characterized in that, The thickness of the unit cell is 3-5 mm, the thickness of the strip rigid sheet is 0.5-1 mm, and the width of the strip rigid sheet is 20-22 mm.

7. The underwater stealth device according to claim 5 or 6, characterized in that, The length of the shielding space: the height of the shielding space: the height of the ridge structure = 2: (1±10%)*0.202857: (1±10%)*0.808571.

8. A design method for an underwater stealth device based on hydrogel as described in any one of claims 1 to 7, characterized in that, include: Construct a uvw coordinate system and an xyz coordinate system. The uvw coordinate system contains a uniform acoustic fluid medium, while the xyz coordinate system contains an anisotropic first and second acoustic fluid medium. The symmetry planes of the two halves of the underwater stealth device are located on the yz plane, and the bottom surface of the shielding space is located on the xz plane. The first attribute of the region containing the two halves in the xyz coordinate system is obtained based on the geometric parameters of the underwater stealth device and the property parameters of the first and second acoustic fluid media. The second attribute of the underwater stealth device is obtained by orthogonalizing the first attribute of the region where the two halves are located. The second attribute includes bulk modulus information and density information. The bulk modulus information and the density information are scaled; The second property of one phase material in the flexible cover layer and the strip rigid sheet is defined, and the second property of the other phase material is obtained by combining acoustic lamination theory. The second property of the obtained phase material is matched with data in the natural and synthetic materials library to obtain the material properties that satisfy the transformation acoustics and the theory of laminated equivalent media.

9. The method according to claim 8, characterized in that, The property parameters of the first and second acoustic fluid media are obtained through the transformation formulas of acoustic transformation theory and the parameters of the uniform acoustic fluid media in the uvw coordinate system, including: Where a represents the height of the shielding space, b represents the length of half the shielding space, and c represents the height difference between the two ridge structures. The coordinate system transformation matrix ρ represents the first half of the ridge structure. 1 K1 represents the density matrix of the first half of the ridge structure, and K1 represents the bulk modulus of the first half of the ridge structure. The coordinate system transformation matrix ρ represents the second half of the ridge structure. 2 K1 represents the density matrix of the second half of the ridge structure, and K2 represents the bulk modulus of the second half of the ridge structure.

10. The method according to claim 9, characterized in that, The acoustic layering theory includes: Where, ρ ⊥ Represents vertical density, which is one of the 11 components of the density tensor; <·> represents the table volume-weighted average, ρ ρ denoted by parallel density, which is the 22nd component of the density component, and K represents the bulk modulus; The second property of the other phase material obtained by combining acoustic lamination theory calculations includes: Where ρ1 represents the density of the defined phase material, ρ2 represents the density of the other phase material, and ρ `1 ρ represents the 11 density components in the principal coordinate system. 22 f2 represents the density component in the principal coordinate system, f1 represents the filling rate of the other phase material, K1 represents the bulk modulus of the defined phase material, and K2 represents the bulk modulus of the other phase material.

11. The method according to claim 8, characterized in that, The density matrices of the properties of the two halves have the same first, second, and third invariants, and the z-direction is naturally... Based on the direction of its characteristic vector, the rotation angle α of the xy-axis plane around the z-axis can be obtained, where counterclockwise rotation is the positive direction.

12. The method according to claim 8, characterized in that, The background material is water, and the underwater stealth device is laminated into a two-phase material layer. One phase material is fixed as stainless steel. The properties and proportion coefficients of the other phase material are calculated and matched with data in a natural and synthetic material library to obtain a hydrogel material that meets the requirements of transformation acoustics and the theory of laminated equivalent media.

13. A testing system suitable for testing the stealth effect of hydrogel-based underwater stealth devices as described in any one of claims 1 to 7, characterized in that, The testing system includes: A steel plate is placed on the bottom of the water to support the sample to be tested, wherein the underwater stealth device is adapted to be installed on the sample; A transducer suitable for emitting a Gaussian wave packet with a frequency range of 5000Hz to 100000Hz and the Gaussian wave packet having four periods; Multiple hydrophone linear array elements are arranged in an array above the steel plate. The multiple hydrophone linear array elements are used to acquire scattered echo signals, which are used to evaluate the stealth effect of the underwater stealth device.

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