Underwater acoustic invisibility cloak

Abstract

The underwater acoustic stealth cloak comprises at least 36 half-moon-shaped liquid crystal blocks, side electrodes, outer electrodes, inner electrodes, a first power supply and a second power supply, the half-moon-shaped liquid crystal blocks are bonded to the outer circumference of a spherical stealth object assembly area, the half-moon-shaped liquid crystal blocks are surrounded by a titanium alloy frame, seven titanium alloy partitions divide the half-moon-shaped liquid crystal blocks into a first cavity, a second cavity, a third cavity, a fourth cavity, a fifth cavity, a sixth cavity, a seventh cavity and an eighth cavity from outside to inside along the spherical radius direction, the first cavity, the second cavity, the third cavity, the fourth cavity and the fifth cavity are filled with liquid crystal materials with decreasing densities, the sixth cavity, the seventh cavity and the eighth cavity are filled with air, the outer electrodes are bonded to the outer side of the first cavity arc, the inner electrodes are bonded to the inner side of the eighth cavity arc, the side electrodes are bonded to the left and right sides of the first cavity, the second cavity, the third cavity, the fourth cavity and the fifth cavity, and the first power supply is connected with the inner electrodes and the outer electrodes; a wire is led out from one side of the half-moon-shaped liquid crystal blocks and connected with the second power supply.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic stealth, and in particular relates to an underwater acoustic stealth cloak.

[0002] Existing underwater acoustic stealth technologies using sound-absorbing metamaterials suffer from poor sound absorption at low frequencies and under high hydrostatic pressure. Existing underwater acoustic stealth technologies using sound-insulating and decoupling metamaterials are characterized by high cost and weight. Existing underwater acoustic stealth technologies based on sound absorption and sound insulation decoupling principles leave acoustic shadow zones. Existing underwater acoustic stealth technologies using acoustically conductive metamaterials have a narrow operating frequency range. The underwater acoustic stealth technology based on liquid crystal materials proposed in this invention effectively solves the above problems, meeting the requirements for flexible, wide-bandwidth, low-cost, and efficient underwater acoustic stealth. Background Technology

[0003] For underwater acoustic equipment, the application of underwater acoustic metamaterials is a prerequisite for ensuring and improving the performance of underwater acoustic communication, acoustic stealth, and sonar detection. Due to limitations imposed by the mass density law and high hydrostatic pressure, traditional underwater acoustic materials cannot effectively absorb low-frequency sound waves, exhibiting low elastic energy conversion efficiency. Traditional underwater acoustic stealth methods primarily utilize acoustic materials with thicknesses matched to the corresponding wavelengths, allowing sound waves to be fully reflected and absorbed by the incident surface, thereby reducing sound wave penetration and providing good sound insulation. However, traditional acoustic materials have many drawbacks. The main disadvantages include limited application range, high cost, large size, and excessive space occupation. In recent years, with the development of acoustic metamaterial technology, various underwater acoustic metamaterials have been proposed. Compared to sound waves propagating in air, underwater sound is more difficult to control than airborne sound of the same frequency, thus making the design of underwater acoustic metamaterials more complex.

[0004] Underwater acoustic metamaterials used in underwater acoustic equipment are mainly divided into three categories according to their functions: (1) Sound absorption metamaterials (SAM): They absorb sound waves through small surface reflection and high loss factor. They are mainly used to absorb near-field self-noise generated by the equipment body and active sonar detection sound waves. (2) Sound insulation decoupling metamaterials (SIDM): Through impedance mismatch between the structure and water, the self-noise caused by internal structural vibration is prevented from propagating into the water. (3) Underwater acoustic guided metamaterials (UAGM): They achieve stealth by guiding sound waves along a specific path to change their reflection path.

[0005] Due to the inherent limitations of local resonance theory, sound-absorbing metamaterials have a narrow absorption bandwidth, resulting in poor sound absorption at low frequencies and under high hydrostatic pressure. Their sound absorption capabilities for underwater applications still need improvement. In high hydrostatic pressure environments, sound-insulating and decoupling metamaterials are typically designed to be thicker and heavier. Furthermore, underwater acoustic control based on sound absorption and insulation principles inevitably leaves a "sound shadow zone," making it difficult to resist multi-dimensional detection technologies such as multi-static sonar. Guiding sound waves along a specific path through metamaterial structural design is the basic idea for achieving stealth capabilities. Due to material limitations, the operating bandwidth of underwater acoustic guiding metamaterials can only be designed to a fixed value, which can only play a diffraction modulation role for incident waves at specific frequencies.

[0006] Liquid crystal materials, as metamaterials with tunable dielectric properties, have continuous tunability, low loss, and high linearity. In fact, the tunable dielectric constant of liquid crystal materials can be maintained over a wide frequency range, including tens of Hz to hundreds of kHz for underwater acoustic detection. As the frequency of the incident sound wave increases, the speed of sound wave propagation in the medium increases, and the reflection and refraction change accordingly. In order to keep the reflection and refraction behavior of the incident sound wave unchanged, the dielectric constant of the liquid crystal can be appropriately increased to correspond to the frequency of the incident sound wave.

[0007] As an anisotropic material, liquid crystal materials have molecular orientation axes that are strongly dependent on surface effects and ambient temperature, and their modulation characteristics are particularly sensitive to changes in external fields (such as electric fields, magnetic fields, and light fields).

[0008] How to flexibly adjust the operating frequency band of underwater acoustic guiding metamaterials according to changes in the incident wave frequency, and achieve active guidance and adaptive control of the incident sound wave, is a problem that needs to be solved for underwater acoustic guiding metamaterials to be better applied to underwater acoustic stealth. To solve this problem, liquid crystal material was used as the acoustic guiding metamaterial to design an underwater acoustic stealth cloak, which can flexibly adjust the operating frequency band to adapt to different underwater acoustic detection equipment while achieving acoustic stealth. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide an underwater acoustic cloak.

[0010] To achieve the purpose of this invention, the following technical solution is adopted:

[0011] The present invention discloses an underwater acoustic cloak, comprising: at least 36 crescent-shaped liquid crystal blocks, side electrodes, outer electrodes, inner electrodes, a first power source, and a second power source. The crescent-shaped liquid crystal blocks are bonded to the outer circumference of a spherical cloak assembly area. Each crescent-shaped liquid crystal block is enclosed by a titanium alloy frame. The crescent-shaped liquid crystal blocks are evenly distributed along the outer circumference of the spherical cloak assembly area. Seven titanium alloy partitions, along the direction of the extension line of the radius of the spherical cloak assembly area, divide each crescent-shaped liquid crystal block from the outside to the inside into a first cavity, a second cavity, a third cavity, a fourth cavity, a fifth cavity, a sixth cavity, a seventh cavity, and an eighth cavity. The first, second, third, fourth, and fifth cavities are filled with liquid crystal materials of decreasing density, while the sixth, seventh, and eighth cavities are filled with air. An external electrode is attached to the outer side of the arc of the first cavity, and an internal electrode is attached to the inner side of the arc of the eighth cavity. Side electrodes are attached to the left and right sides of the first, second, third, fourth, and fifth cavities, respectively. After at least 36 semi-circular crescent-shaped liquid crystal blocks are attached to the outer circumference of the spherical stealth assembly area, the positive and negative terminals of the first power supply are connected to the internal and external electrodes, respectively, through wires. The wires are led out from one side of the semi-circular crescent-shaped liquid crystal block and connected to the second power supply.

[0012] The underwater acoustic cloak of the present invention comprises 72 semi-circular crescent-shaped liquid crystal blocks.

[0013] The underwater acoustic cloak of the present invention, wherein: the titanium alloy partition is an arc segment centered on the center of the spherical cloak assembly area.

[0014] The underwater acoustic cloak of the present invention comprises the following: along the radial extension line of the spherical cloak assembly area, the width of the first cavity is 0.166a; the width of the second cavity is 0.152a; the width of the third cavity is 0.1396a; the width of the fourth cavity is 0.128a; the width of the fifth cavity is 0.1174a; the width of the sixth cavity is 0.1076a; the width of the seventh cavity is 0.0988a; and the width of the eighth cavity is 0.0906a, where a is the radius of the spherical cloak assembly area.

[0015] The underwater acoustic cloak of the present invention, wherein the density of the liquid crystal material filling the first to fifth cavities is calculated using the following formula: Where ρ0 = 1000 kg / m 3 r i These represent the radii from the center of the spherical stealth assembly area to the outer edges of the first to fifth cavities, respectively, and the densities of the sixth to eighth cavities are expressed as the density ρ of the titanium alloy frame. 框架 =536.12kg / m 3 calculate.

[0016] The underwater acoustic cloak of the present invention, wherein: the first power supply and the second power supply are DC power supplies, and their voltages are between 0-20V.

[0017] The underwater acoustic stealth cloak of this invention conforms to the development trend of underwater acoustic stealth achieved by new materials and technologies. It achieves active guidance of incident sound waves through reasonable acoustic guide structure design and adaptive control of incident sound waves through filling with liquid crystal material. The designed underwater acoustic cloak meets the requirements of flexible, wide-bandwidth, low-cost and efficient underwater acoustic stealth, and broadens the application scope of liquid crystal materials in the field of underwater acoustic stealth.

[0018] The underwater acoustic cloak of the present invention has the following advantages:

[0019] (1) For the acoustic stealth analysis of underwater acoustic conductive metamaterials, a constant mode mapping coordinate transformation theory is proposed and a coordinate transformation mapping function is constructed.

[0020] (2) For the eight-layer acoustic guide structure material unit, the size, density and modulus parameters of each unit block were reasonably designed to achieve the equivalent of water medium and achieve the purpose of acoustic stealth.

[0021] (3) In view of the narrow frequency range of existing acoustic stealth and the inability to adapt to various acoustic detection devices to achieve stealth, the liquid crystal filling material broadens the working frequency band of acoustic duct structure stealth.

[0022] (4) To meet the actual needs of liquid crystal regulation in acoustic guide structures, a liquid crystal regulation microstructure based on five circular electrodes and inner and outer spherical electrodes was designed to realize continuous regulation of the dielectric constant of liquid crystal.

[0023] (5) The acoustic cloak was built in COMSOL software. Simulation results show that the echo cross-section of the target object can be significantly reduced in the range of 200Hz to 20kHz. Attached Figure Description

[0024] Figure 1 This is a cross-sectional schematic diagram of the underwater acoustic cloak of the present invention, in which all the semi-circular crescent-shaped liquid crystal blocks are longitudinally cut open.

[0025] Figure 2 for Figure 1 A three-dimensional schematic diagram of a semi-circular crescent-shaped liquid crystal block;

[0026] Figure 3 for Figure 1 Enlarged schematic diagram of the semi-circular crescent-shaped liquid crystal block;

[0027] Figure 4 From Figure 1 A schematic diagram of the entire circular cross-section formed by cutting open two semi-circular crescent-shaped liquid crystal blocks at point AA.

[0028] exist Figures 1 to 4 In the diagram, 1 represents the first cavity; 2 represents the second cavity; 3 represents the third cavity; 4 represents the fourth cavity; 5 represents the fifth cavity; 6 represents the sixth cavity; 7 represents the seventh cavity; 8 represents the eighth cavity; 9 represents the titanium alloy frame; 10 represents the side electrode; 11 represents the external electrode; 12 represents the internal electrode; 13 represents the first power source; 14 represents the semi-circular crescent-shaped liquid crystal block; 15 represents the spherical stealth device assembly area; 16 represents the second power source; and 17 represents the titanium alloy partition. Detailed Implementation

[0029] like Figures 1 to 4 As shown, the underwater acoustic cloak of the present invention includes: 72 crescent-shaped liquid crystal blocks 14, side electrodes 10, outer electrodes 11, inner electrodes 12, a first power supply 13, and a second power supply 16. The crescent-shaped liquid crystal blocks 14 are bonded to the outer circumference of the spherical cloak assembly area 15. Each crescent-shaped liquid crystal block 14 is surrounded by a titanium alloy frame 9. The crescent-shaped liquid crystal blocks 14 are evenly distributed along the outer circumference of the spherical cloak assembly area 15. Seven arc-shaped titanium alloy partitions 17 divide each crescent-shaped liquid crystal block 14 from the outside to the inside into a first cavity 1, a second cavity 2, a third cavity 3, a fourth cavity 4, a fifth cavity 5, a sixth cavity 6, a seventh cavity 7, and an eighth cavity 8, along the direction of the radius extension line of the spherical cloak assembly area 15. The fourth cavity 4 and the fifth cavity 5 are filled with liquid crystal materials with decreasing densities, respectively. The sixth cavity 6, the seventh cavity 7 and the eighth cavity 8 are filled with air, respectively. An external electrode 11 is attached to the outer side of the arc of the first cavity 1, and an internal electrode 12 is attached to the inner side of the arc of the eighth cavity 8. Side electrodes 10 are attached to the left and right sides of the first cavity 1, the second cavity 2, the third cavity 3, the fourth cavity 4 and the fifth cavity 5, respectively. After at least 36 semi-circular crescent-shaped liquid crystal blocks 14 are attached to the outer circumference of the spherical stealth assembly area 15, the positive and negative terminals of the first power supply 13 are connected to the internal electrode 12 and the external electrode 11 through wires, respectively. The wires are led out from one side of the semi-circular crescent-shaped liquid crystal block 14 and connected to the second power supply 16. The first power supply 13 and the second power supply 16 are DC power supplies with voltages between 0-20V.

[0030]

[0031] In formula (1), η i H is the ratio of the liquid crystal block formed in the i-th cavity to the liquid crystal block formed in the 1i-th cavity. i Let L be the height of the i-th cavity in the radial direction. iThe thickness is perpendicular to the radius, a is the radius of the spherical stealth assembly area 15, b is the radius of the underwater acoustic stealth cloak, b = 2a, and the outer radius of the liquid crystal block formed in the i-th cavity is equal to the cloak radius b minus the width of the first i-1 layers of liquid crystal blocks; based on the above formulas, the following formulas (2) and (3) are derived:

[0032] r2=b-H1

[0033]

[0034]

[0035] r3=b-H1-H2

[0036]

[0037]

[0038] Similarly, H4, H5, H6, H7, and H8 can all be expressed as expressions containing only the unknown quantity H1, while ∑H i ≤ba, let ∑H i =ba, where b = 2a, solving for H1 ≈ 0.166a, H i We can also find that i = 2, 3, ..., 8.

[0039] It is found that: along the radius extension line of the spherical stealth assembly area 15, the width of the first cavity 1 is 0.166a; the width of the second cavity 2 is 0.152a; the width of the third cavity 3 is 0.1396a; the width of the fourth cavity 4 is 0.128a; the width of the fifth cavity 5 is 0.1174a; the width of the sixth cavity 6 is 0.1076a; the width of the seventh cavity 7 is 0.0988a; and the width of the eighth cavity 8 is 0.0906a, where a is the radius of the spherical stealth assembly area 15.

[0040] The density of the liquid crystal material filled in the first cavity 1 to the fifth cavity 5 is calculated using the following formula:

[0041] Where ρ0 = 1000 kg / m 3 r i These are the radii from the center of the spherical stealth assembly area 15 to the outer sides of the first cavity 1 to the fifth cavity 5, respectively, and the densities of the sixth cavity 6 to the eighth cavity 8 are expressed as the density ρ of the titanium alloy frame. 框架 =536.12kg / m 3 calculate.

[0042] A 0-20V DC current is applied to the side electrode 10, inner electrode 12, and outer electrode 11. Voltage can only be applied to the side electrode 10 or to both the inner and outer electrodes 12 at the same time; simultaneous application of voltage to all three electrodes would place the liquid crystal materials in the first cavity 1 to the fifth cavity 5 in an irregular electric field, preventing ordered deflection. When the applicable acoustic frequency is in the range of 200Hz to 20kHz, the voltage applied to the side electrode 10 is approximately V = 0.001*lg(f) - 0.2. When a lower operating frequency is required, only the voltage applied to the inner and outer electrodes 12 needs to be approximately V = 0.001*lg(f) - 0.2, at which point the frequency f is the adjusted highest operating frequency. Since the liquid crystal response time is in the millisecond range, frequency adaptation can be achieved simply by ensuring that the side electrode 10, inner electrode 12, and outer electrode 11 are not powered simultaneously.

[0043] The above content is one of the preferred embodiments of the present invention. The present invention is not limited to the cases implemented as described above. In the implementation scheme, the structures and principles that are not described in detail are all common implementation methods in the art.

Claims

1. An underwater acoustic cloak, comprising: At least 36 crescent-shaped liquid crystal blocks (14), side electrodes (10), outer electrodes (11), inner electrodes (12), a first power supply (13), and a second power supply (16) are attached to the outer circumference of the spherical stealth assembly area (15). The key feature is that each crescent-shaped liquid crystal block (14) is surrounded by a titanium alloy frame (9), and the crescent-shaped liquid crystal blocks (14) are evenly distributed along the outer circumference of the spherical stealth assembly area (15). Seven titanium alloy partitions (17) along the direction of the radius extension line of the spherical stealth assembly area (15) divide each crescent-shaped liquid crystal block (14) from the outside to the inside into a first cavity (1), a second cavity (2), a third cavity (3), a fourth cavity (4), a fifth cavity (5), a sixth cavity (6), a seventh cavity (7), and an eighth cavity (8). The first cavity (1), second cavity (2), third cavity (3), fourth cavity (4), and fifth cavity (8) are... Cavity (5) is filled with liquid crystal material of decreasing density. Cavity 6 (6), Cavity 7 (7) and Cavity 8 (8) are filled with air. An external electrode (11) is attached to the outer side of the arc of Cavity 1 (1), and an internal electrode (12) is attached to the inner side of the arc of Cavity 8 (8). Side electrodes (10) are attached to the left and right sides of Cavity 1 (1), Cavity 2 (2), Cavity 3 (3), Cavity 4 (4) and Cavity 5 (5). After at least 36 semi-circular crescent-shaped liquid crystal blocks (14) are attached to the outer circumference of the spherical stealth assembly area (15), the positive terminal of the first power supply (13) is connected to the internal electrode (12) through a wire, and the negative terminal of the first power supply (13) is connected to the external electrode (11) through a wire. The wire is led out from one side of the semi-circular crescent-shaped liquid crystal block (14) and connected to the second power supply (16). The density of the liquid crystal material filled in Cavity 1 (1) to Cavity 5 (5) is calculated using the following formula: ,in r i The radii from the center of the spherical stealth assembly area (15) to the outer side of the first cavity (1) to the fifth cavity (5) are respectively the equivalent density of the sixth cavity (6) to the eighth cavity (8) in terms of the titanium alloy frame density. calculate.

2. The underwater acoustic cloak as described in claim 1, characterized in that: There are 72 semi-circular crescent-shaped liquid crystal blocks (14).

3. The underwater acoustic cloak as described in claim 2, characterized in that: The titanium alloy partition (17) is an arc segment with the center of the sphere of the spherical stealth assembly area (15) as the center.

4. The underwater acoustic cloak as described in claim 3, characterized in that: Along the radius extension line of the spherical stealth assembly area (15), the width of the first cavity (1) is 0.166a, the width of the second cavity (2) is 0.152a, the width of the third cavity (3) is 0.1396a, the width of the fourth cavity (4) is 0.128a, the width of the fifth cavity (5) is 0.1174a, the width of the sixth cavity (6) is 0.1076a, the width of the seventh cavity (7) is 0.0988a, and the width of the eighth cavity (8) is 0.0906a, where a is the radius of the spherical stealth assembly area (15).

5. The underwater acoustic cloak as described in claim 4, characterized in that: The first power supply (13) and the second power supply (16) are DC power supplies with voltages between 0 and 20V.

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