Electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial and preparation method thereof

Abstract

The present invention discloses an electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial, comprising a slanted honeycomb five-mode material, a rotationally stacked pyramid absorber array, and an anisotropic cross-scale micro-nano superhydrophobic surface. The slanted honeycomb five-mode material comprises slanted honeycomb cells; the rotationally stacked pyramid absorber array comprises a plurality of evenly spaced rotationally stacked pyramid absorber units; and the anisotropic cross-scale micro-nano superhydrophobic surface comprises a plurality of flow-direction grooves and flow-direction ridges. The present invention also discloses a method for preparing the material, comprising: bonding the rotationally stacked pyramid absorber array to the slanted honeycomb five-mode material; filling the spaces between the rotationally stacked pyramid absorber units with a wave-transmitting resin material; and forming the flow-direction grooves and flow-direction ridges using a 3D printing method. The present invention can achieve functions such as aerial stealth, underwater noise reduction, and underwater drag reduction, and realizes the miniaturization and lightweighting of the metamaterial structure, thus having broad application prospects in the field of cross-medium aircraft structure design.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing and relates to an integrated metamaterial of electromagnetic stealth, underwater sound absorption and super-hydrophobic drag reduction. Background Art

[0002] Cross-medium aircraft, combining the high speed of aerial vehicles with the stealth of underwater vehicles, represent a key area where my country urgently needs to achieve breakthroughs in the field of new cross-domain aircraft, and they hold enormous potential for future applications. Essential features of future cross-medium aircraft include improving electromagnetic stealth in the air, achieving low underwater noise levels, and achieving high underwater speeds.

[0003] Traditional electromagnetic absorbing materials include electrically lossy coatings, magnetically lossy coatings, and conductively lossy coatings. However, these materials, such as non-magnetic metal oxides, carbonyl iron, ferrites, carbon nanotubes, and graphene compounds, suffer from shortcomings such as narrow absorption bandwidths, high spray precision requirements, high density, and inability to adjust. The absorption mechanism of traditional underwater sound-absorbing materials primarily utilizes the dissipation of energy as sound waves propagate through the material as heat. In polymer-based materials, sound waves typically cause intramolecular friction during propagation, and energy is dissipated at various interfaces. This primarily results in poor absorption of low-frequency sound waves and poor absorption performance at great depths and high static pressures. Frictional drag can account for up to 70% of the total drag in underwater vehicles. Conventional drag reduction methods primarily optimize the vehicle's shape to reduce pressure differential drag. However, the impact force of the water surface during trans-medium entry can damage the surface structure of the vehicle. Conventional drag reduction methods such as supercavitation, microbubble, and flexible wall drag reduction cannot be directly applied to the underwater navigation of trans-medium vehicles. At present, the integrated structural design of electromagnetic stealth, underwater sound absorption and drag reduction has not been realized, which cannot meet the needs of future cross-medium aircraft. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects and provide an electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial and a preparation method, which solves the technical problem that traditional materials cannot simultaneously possess electromagnetic stealth, underwater sound absorption and superhydrophobic drag reduction functions, and cannot meet the needs of cross-media aircraft. The present invention can achieve multiple functions such as air stealth, underwater noise reduction, underwater drag reduction, etc., and realize the miniaturization and lightweight of metamaterial structures, and has broad application prospects in the field of cross-media aircraft structure design.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] An electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial, comprising a five-mode oblique honeycomb material, a rotationally stacked pyramid absorber array, and an anisotropic cross-scale micro-nano superhydrophobic surface arranged in sequence;

[0007] The oblique honeycomb five-mode material contains a number of oblique honeycomb cells arranged in an array;

[0008] The rotating stacked pyramid absorber array includes a plurality of evenly arranged rotating stacked pyramid absorber units;

[0009] The anisotropic cross-scale micro-nano superhydrophobic surface comprises a plurality of flow-direction grooves and flow-direction ridges between adjacent flow-direction grooves.

[0010] Furthermore, the oblique honeycomb cell is a hexagonal structure surrounded by 4 long beams and 2 short beams; the angle 2α between two adjacent long beams is greater than 120°, the length l of the long beam is greater than twice the length h of the short beam, and the angle θ between the short beam and the incident direction of the sound wave is m =0~90°.

[0011] Furthermore, the rotationally stacked pyramid absorber unit includes a metal film as a substrate, a plurality of metal patches stacked on the metal film, and a photosensitive resin covering the metal film and the plurality of metal patches.

[0012] Assume that there are n layers of metal patches, the metal patch close to the substrate is recorded as the first layer, and the other metal patches are recorded in order as the second to n layers; the line connecting the centers of the metal patches in the first to n layers is perpendicular to the substrate, the size of the metal patches in the first to n layers decreases layer by layer, and the metal patches in the first to n layers are rotated layer by layer around the line by an angle β / n, where β / n is greater than 0°.

[0013] Furthermore, n and β are designable parameters, and preferably, β=125°.

[0014] Furthermore, adjacent metal patches are bonded together using dielectric material, wherein the dielectric material is FR4 material; the metal patches are obtained by drying conductive silver paste;

[0015] The metal film is made of copper.

[0016] Furthermore, let the width of the flow-direction groove be a, the width of the flow-direction ridge be b, the height of the flow-direction ridge be c, and the total height of the anisotropic cross-scale micro-nano superhydrophobic surface be H;

[0017] c<H<100μm;

[0018] a≥2b;

[0019] |bc|≤1μm.

[0020] Furthermore, in the anisotropic cross-scale micro-nano superhydrophobic surface, micron-scale micropillars formed by silica nanoparticles are distributed on the surface of the flow-toward grooves and the flow-toward ridges;

[0021] The particle size of the silicon dioxide nanoparticles is 10 nm to 500 nm.

[0022] Furthermore, the material of the oblique honeycomb five-module is aluminum;

[0023] The material of the anisotropic cross-scale micro-nano super-hydrophobic surface is a wave-transmitting resin material.

[0024] A method for preparing an electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial, comprising:

[0025] S1 uses 3D printing method to form oblique honeycomb five-mode material;

[0026] S2 uses a wave-transparent silicon-based inorganic adhesive to bond a rotating stacked pyramid absorber array onto an oblique honeycomb five-mode material;

[0027] S3: filling a wave-transmitting resin material between the rotationally stacked pyramid absorber units of the rotationally stacked pyramid absorber array so that the upper surface of the resin material forms a plane;

[0028] S4 uses 3D printing method to form flow grooves and flow ridges on the resin material.

[0029] Furthermore, step S4 further includes:

[0030] Ultrasonic cavitation is used to roughen the surfaces of the flow-direction grooves and the flow-direction ridges, and at the same time, silicon dioxide nanoparticles contained in the ultrasonic cavitation jet are anchored on the roughened surfaces.

[0031] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0032] (1) The present invention creatively proposes an integrated metamaterial for electromagnetic stealth, underwater sound absorption, and super-hydrophobic drag reduction, which can be applied to the skin structure of a cross-medium aircraft to achieve multiple functions such as air stealth, underwater noise reduction, and underwater drag reduction, thereby miniaturizing and lightweighting the metamaterial structure.

[0033] (2) The present invention uses an oblique honeycomb five-mode material and specifies the structural parameters of the oblique honeycomb five-mode material to achieve efficient absorption of underwater sound waves while achieving high structural strength, and also serves as a substrate for electromagnetic metamaterials;

[0034] (3) The present invention expands the electromagnetic wave absorption bandwidth by designing a rotating stacked pyramid absorber;

[0035] (4) Based on electromagnetic metamaterials, the present invention uses 3D printing technology and ultrasonic cavitation to form anisotropic surface super-hydrophobic structures of different micro-nano scales, thereby reducing underwater resistance and achieving flow control. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1This is a schematic diagram of the overall structure of the electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial of the present invention;

[0037] Figure 2 This is a schematic diagram of the structure of the oblique honeycomb five-mode material of the present invention;

[0038] Figure 3 Schematic diagram of a rotating stacked pyramid electromagnetic metamaterial; (a) is a stereoscopic diagram of a conventional structure, (b) is a front view of a conventional structure, (c) is a stereoscopic diagram of the structure of the present invention, and (d) is a top view of the structure of the present invention;

[0039] Figure 4 Schematic diagram of the super-hydrophobic cross-scale micro-nano surface of the present invention;

[0040] Figure 5 Graphs showing the electromagnetic absorption test results of the material obtained in Example 1 of the present invention; wherein, (a) TE polarization S11 test results, (b) TE polarization absorptivity test results, (c) TM polarization S11 test results, and (d) TM polarization absorptivity test results;

[0041] Figure 6 This is the sound transmission loss curve of the material obtained in Example 1 of the present invention;

[0042] Figure 7 This is a diagram showing the contact angle measurement results of the material obtained in Example 1 of the present invention;

[0043] Among them, 1- oblique honeycomb five-mode material, 2-rotationally stacked pyramid absorber array, 3-anisotropic cross-scale micro-nano superhydrophobic surface, 4-oblique honeycomb substrate, 5-oblique honeycomb cell, 6-traditional pyramid absorber unit, 7-rotationally stacked pyramid absorber unit, 8-photosensitive resin, 9-metal film, 10-metal patch, 11-dielectric material, 12-flow-directed ridges, 13-flow-directed grooves, 14-silica particles. DETAILED DESCRIPTION

[0044] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0045] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0046] Metamaterials are a new class of materials that achieve extraordinary properties through artificial structures. They possess extraordinary physical properties that natural materials do not possess and are expected to become the source of a series of transformative technologies. In recent years, metamaterials have shown great application potential and development space in the fields of electromagnetics, thermal engineering, acoustics, etc. Therefore, the present invention proposes a metamaterial structure suitable for electromagnetic stealth in the air, sound absorption underwater, and super-hydrophobic drag reduction in cross-medium aircraft, enabling cross-medium aircraft to achieve radar stealth, low underwater noise, and high-speed underwater navigation, further improving the overall performance of the aircraft. The present invention is of great significance for achieving low detectability in the wide frequency domain, light weight, high strength, and high efficiency of cross-medium aircraft.

[0047] In terms of electromagnetic stealth in the air, the resonant broadband absorber with a metal-dielectric stacked structure mainly utilizes the continuous superposition of narrowband absorption peaks to form a design concept of broadband absorption. This method is often used in conical structures such as pyramids and frustums. However, due to the height of the conical structure itself, it is difficult to further increase the bandwidth of the absorber. These structures all show the defect that the size increases with the performance. The present invention can effectively expand the high-frequency absorption bandwidth of the structure by rotating the pyramid structure layer by layer along the central axis, that is, introducing a certain rotation angle for each layer of metal patches. In terms of underwater sound absorption, 3D printed oblique honeycomb microstructures are used to utilize cavity resonance, waveform conversion and the intrinsic properties of the material to achieve effective absorption of sound waves and generate lower acoustic impedance. At the same time, the lattice structure can also realize the lightweight load-bearing function of the structure, serving as a bearing substrate for electromagnetic metamaterials. In terms of superhydrophobic drag reduction structures, 3D printing and ultrasonic cavitation are used to prepare a multi-level rough micro-nano structure that imitates the surface of a rice leaf. Based on the 3D printed micron-scale flow structure, the principle of ultrasonic cavitation is used to project a large number of nano-scale silica particles, which are etched and anchored on the surface of the flow structure to achieve anisotropic fluid wettability. At the same time, the lateral fluid flow is regulated to achieve efficient drag reduction.

[0048] Specifically, the present invention provides an integrated electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction material, which mainly includes an oblique honeycomb five-mode material, a rotationally stacked pyramid absorber array and an anisotropic cross-scale micro-nano superhydrophobic surface. The oblique honeycomb five-mode material is formed by 3D-printed aluminum metal, the rotationally stacked pyramid absorber array is generated by stacking several layers of metal patches and dielectric materials, and the anisotropic cross-scale micro-nano superhydrophobic surface is a multi-level rough surface structure prepared by using the ultrasonic cavitation principle on the basis of the 3D-printed flow microscale structure.

[0049] In a specific embodiment, an integrated structure of electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction is not limited to a flat plate structure and can be designed into different three-dimensional curved surface structures according to actual needs.

[0050] In a specific embodiment, the angle between the short beam of the oblique honeycomb cell and the incident direction of the sound wave is greater than 0° and less than 90°, the angle between the two long beams is greater than 120°, the length of the long beam should be more than twice the length of the short beam, and the thickness of the beam can be determined according to the actual structural strength verification requirements. The flat substrate is the incident surface of the sound wave, and the whole is prepared by 3D metal printing technology, and the material is preferably aluminum.

[0051] In a specific embodiment, each layer of metal patches is rotated around the central axis by a certain angle, and the overall rotation angle of all metal patches is preferably 125°; the metal patches are arranged layer by layer in a vertical direction with a side tilt angle of preferably 60°; dielectric material is used to bond each layer of metal patches; the metal patches are made of conductive silver paste, and the dielectric material is FR4 material.

[0052] In a specific embodiment, the anisotropic cross-scale micro-nano superhydrophobic surface is composed of a micron-scale structure consisting of a plurality of flow-direction ridges and flow-direction grooves. The ridges and grooves are etched by ultrasonic cavitation, and a large number of nano-scale silica particles are mixed in the ultrasonic jet, projected and anchored on the rough surface, forming a multi-level superhydrophobic structure of micron-scale flow structure + nano-scale rough surface.

[0053] In a specific embodiment, the flow direction of the ridges and grooves is determined according to the direction of the actual extreme streamline of the aircraft surface. The ridges and grooves are prepared using 3D printing. The size of the ridges and grooves is recommended to be less than 100 microns. This can form strong hydrophobicity along the flow direction, while regulating the lateral fluid flow, which can play a role in flow control.

[0054] The present invention can achieve stable absorption of radar waves across a wide frequency band (2-22 GHz) and a wide angle of incidence (>80°), maintaining an absorption rate above 90%. Sound insulation is greater than 20 dB in the low-frequency range of 200-3500 Hz. It also exhibits drag-reducing super-hydrophobic properties, with a contact angle greater than 145°.

[0055] Example:

[0056] like Figure 1 As shown, the integrated electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction skin structure is primarily composed of an oblique honeycomb five-mode material 1, a rotationally stacked pyramid absorber array 2, and an anisotropic cross-scale micro-nano superhydrophobic surface 3. Specifically, the oblique honeycomb five-mode material 1 is primarily composed of an oblique honeycomb substrate 4 and oblique honeycomb cells 5; the rotationally stacked pyramid absorber array 2 is primarily composed of a photosensitive resin material 8, a metal film 9, a metal patch 10, and a dielectric material 11; and the anisotropic cross-scale micro-nano superhydrophobic surface 3 is primarily composed of flow-directed ridges 12, flow-directed grooves 13, and silica particles 14.

[0057] The oblique honeycomb five-mode material 1 and the rotated stacked pyramid absorber array 2 are glued together with a wave-transparent silicon-based inorganic adhesive, and a wave-transparent resin material is filled between the absorber arrays to form a plane on the surface of the absorber array. 3D printing technology is used to form flow ridges 12 and flow grooves 13 along the flow direction on the surface of the absorber array, and the anisotropic cross-scale micro-nano super-hydrophobic surface 3 is prepared using the principle of ultrasonic cavitation.

[0058] like Figure 2 As shown, the oblique honeycomb five-mode material 1 is prepared by 3D metal printing technology. The selected metal is aluminum. The oblique honeycomb cell 5 is composed of two long beams of length l and a short beam of length h intersecting at the vertex. The two long beams are symmetrically distributed and form an angle of 2α. The thickness of the long beam and the short beam is e. The angle between the short beam and the oblique honeycomb base 4 in the vertical direction is θ m , that is, the angle with the incident direction of the sound wave is θ m In order to achieve better sound absorption effect, the long beam angle 2α should be greater than 120°, the long beam length l is recommended to be greater than twice the short beam length h, and the beam thickness e can be determined according to the actual structural strength verification requirements. m The value range is 0-90°, which can be given according to the isolated sound wave frequency range.

[0059] like Figure 3 As shown, the rotated stacked pyramid absorber array 2 is composed of a plurality of evenly arranged rotated stacked pyramid absorber units 7. The rotated stacked pyramid absorber units 7 are formed by rotating the traditional pyramid absorber units 6 layer by layer along the central axis. Specifically, each layer of metal patches 10 is rotated about the central axis by an angle β / n, where n is the total number of metal patches and the overall rotation angle is β. Numerical calculations show that the absorption rate is higher when β = 125°. In particular, when n = 20 and β = 125°, ultra-wideband absorption can be added to the high-frequency region beyond the basic absorption bandwidth, with the absorption rate maintained above 90%, significantly enhancing the absorption bandwidth. Dielectric material 11 is bonded between each layer of metal patches. The dielectric material 11 can be FR4. The thickness of each metal patch layer is w1, and the thickness of the dielectric layer between the patches is w2. The metal patches are arranged layer by layer in the vertical direction with a side tilt angle α. The absorber unit uses a metal film 9 as a base, and the selected material is copper. The stacked metal-dielectric patches are covered and filled with photosensitive resin 8 to play a role of protection and isolation.

[0060] like Figure 4As shown, the anisotropic cross-scale micro-nano superhydrophobic surface 3 is a micron-scale ribbed groove structure composed of several flow-directed ridges 12 and grooves 13 along the flow direction, where a is the groove width, b is the ridge width, c is the ridge height, and H is the overall superhydrophobic surface height. The micron-scale structure is fabricated using 3D printing technology, with the superhydrophobic surface height H recommended to be below 100 μm. Based on the superhydrophobic structure of a rice leaf surface, the dimensions of the grooves and ridges in the fabricated surface satisfy a ≥ 2b ≈ c. Using the principle of ultrasonic cavitation, and by rationally selecting ultrasonic parameters such as ultrasonic vibration power and ultrasonic direction, tiny cavitation bubbles are generated in the etchant, causing the surface to repeatedly undergo etching as the bubbles collapse, ultimately forming a micro-nano composite hierarchical roughened structure. Simultaneously, a large number of silica nanoparticles 14 are entrained in the cavitation jet, projected by the cavitation jet and anchored to the rough surface, forming a strong bond with the surface. The silica particles range in size from 10 nm to 500 nm. The direction of flow toward the ridges 12 and the grooves 13 can be determined based on the surface streamline direction in the actual application scenario. At the same time, the lateral movement of the fluid is restricted by the direction of the ridges and grooves, which makes it difficult to generate cross flow, ensuring the consistency of the flow direction and playing a certain role in flow control.

[0061] In the design and research of resonant broadband absorbers, metal-dielectric stacking structures have long been a popular design concept. They primarily utilize the continuous superposition of narrowband absorption peaks to form a broadband absorption design concept. This method is often applied to conical structures such as pyramids and frustums. However, due to the inherent height of the conical structure, further increasing the absorber's bandwidth is difficult, and these structures exhibit the drawback that size increases with performance. This invention proposes a new method for effectively increasing the absorption bandwidth of pyramid absorbers. By rotating a conventional pyramid structure layer by layer along its central axis, thereby introducing a certain rotation angle to each layer of metal patches, the high-frequency absorption bandwidth of the structure can be effectively expanded. Compared to the conventional pyramid structure in the control group, the twisted pyramid structure using this layer-by-layer rotation method can add an ultra-broadband absorption region in the high-frequency region beyond the basic absorption bandwidth, and the absorption rate remains above 90%. Experimental samples were prepared and tested, and the results show that this layer-by-layer rotation design concept has a very significant positive effect on expanding the absorption bandwidth of the pyramid absorber.

[0062] In terms of sound-absorbing metamaterial design, traditional cavity resonant sound-absorbing materials form structures with different sound absorption capabilities by introducing spherical, cylindrical, conical, and trumpet-shaped acoustic cavity structures inside homogeneous sound-absorbing materials. In order to reduce low-frequency underwater sound waves, the present invention uses an oblique honeycomb structure based on a five-mode material. The five-mode material does not rely on the resonance mechanism and therefore has wide-band applicability and excellent underwater sound control capabilities. The periodically arranged oblique honeycomb metamaterial structure utilizes the anisotropic resonance of the honeycomb pores of the incident sound wave to absorb sound energy. The main direction of the material is oblique to the interface, so that the transverse wave velocity should be as small as possible. The longitudinal wave velocity is as small as possible, thereby realizing an anisotropic structure with extremely small acoustic impedance.

[0063] In terms of super-hydrophobic drag reduction structure design, traditional super-hydrophobic surface preparation methods, such as template method, solution gel method, chemical etching method, etc., have problems such as high cost, low efficiency, and weak bonding force. Therefore, the present invention proposes a cross-scale micro-nano surface preparation method based on 3D printing metamaterials. First, high-precision 3D printing technology is applied to print a periodically arranged micron-scale prism structure along the surface limit streamline direction with the highest flow efficiency on a photosensitive resin plate, forming anisotropic wettability with the flow direction as the main direction. On this basis, the ultrasonic cavitation phenomenon is utilized, and the cavitation jet effect and shock wave generated by underwater ultrasound are used. A large number of micro-nano cavitation bubble groups impact the solid surface during the periodic expansion and contraction process to produce cavitation, forming a surface nanoscale structure. The cavitation jet then forms a multi-stage composite micro-nano rough surface on the surface of the silica particles. The anisotropic super-hydrophobic performance is not only conducive to achieving low resistance in the flow direction, but also conducive to controlling the flow direction to move only along the flow direction, avoiding flow loss in the lateral direction, and contributing to the flow control of the fluid.

[0064] The three electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction technologies described above use a five-mode sound-absorbing material as the substrate. Rotating stacked pyramid absorbers are affixed to the five-mode material's surface using a wave-transmitting silicone-based inorganic adhesive. The absorber surface is then filled with a photosensitive resin to form a solid surface, upon which the superhydrophobic surface structure is fabricated. In this integrated, multifunctional structure, the five-mode sound-absorbing material not only effectively regulates underwater sound waves but also serves as the primary load-bearing structure. The rotating stacked pyramid absorbers primarily reduce detectability to airborne radar. The anisotropic micro-nano roughened surface effectively increases the contact angle between water and the surface, reducing wettability and achieving superhydrophobic drag reduction and flow control.

[0065] Example 1:

[0066] In this embodiment, the parameter settings of the five-mode oblique honeycomb layer of the sound insulation layer (such as Figure 2 (shown): e = 2 mm, h = 2.08 mm, l = 8.33 mm, 2α = 148°, θ m =28.67°.

[0067] Parameter setting of rotating stacked pyramid electromagnetic absorbing layer ( Figure 3 As shown): resin flat layer height h1 = 1mm, resin cone layer height h2 = 5mm, α = 60°, w1 = 0.02mm, w2 = 0.04mm, width of the bottom metal patch q = 10.61mm, β = 125°, metal film thickness t = 0.1mm, n = 99.

[0068] Parameter settings of the hydrophobic surface layer (such as Figure 4 (As shown): a = 200 μm, b = c = 50 μm, H = 100 μm. The grooves are covered with countless micron-sized micropillars, approximately 3 to 5 μm wide and 5 to 8 μm high, formed from silicon dioxide nanoparticles.

[0069] Through data processing, we can get Figure 5 The electromagnetic absorption test results are shown in Figure 1, where (a) is the TE polarization S11 test result, (b) is the TE polarization absorption rate test result, (c) is the TM polarization S11 test result, and (d) is the TM polarization absorption rate test result. It can be seen from the figure that the absorption rate of the absorber is greater than 80% in the entire working frequency band and is insensitive to changes in the polarization state of the incident wave. Figure 6 The sound insulation test results are shown in the (sound transmission loss curve). In the range of 250Hz-1600Hz, the sound insulation of the structure is greater than 20dB; the low-frequency sound insulation effect is better than the high-frequency sound insulation effect, with an average sound insulation of 37dB, which can achieve good low-frequency broadband sound insulation effect. Figure 7 The hydrophobicity results shown in the (Contact angle measurement results figure) show that the contact angle is greater than 145°.

[0070] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

[0071] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. An electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial, characterized in that: The invention comprises a slanted honeycomb five-mode material (1), a rotationally stacked pyramid absorber array (2), and an anisotropic cross-scale micro-nano super-hydrophobic surface (3) arranged in sequence; The oblique honeycomb five-mode material (1) comprises a plurality of oblique honeycomb cells (5) arranged in an array; The rotating stacked pyramid absorber array (2) includes a plurality of evenly arranged rotating stacked pyramid absorber units (7); The anisotropic cross-scale micro-nano super-hydrophobic surface (3) comprises a plurality of flow direction grooves (13) and flow direction ridges (12) between adjacent flow direction grooves (13); The oblique honeycomb cell (5) is a hexagonal structure formed by 4 long beams and 2 short beams; the angle 2α between two adjacent long beams is greater than 120°, the length l of the long beam is greater than twice the length h of the short beam, and the angle θ between the short beam and the incident direction of the sound wave is m =0~90°; The rotating stacked pyramid absorber unit (7) comprises a metal film (9) as a base, a plurality of metal patches (10) stacked and arranged on the metal film (9), and a photosensitive resin (8) covering the metal film (9) and the plurality of metal patches (10). Assuming that there are n layers of metal patches (10), the metal patch (10) that is in close contact with the substrate is recorded as the first layer, and the other metal patches (10) are recorded in order as the second to n layers; the line connecting the centers of the first to n layers of metal patches (10) is perpendicular to the substrate, the size of the first to n layers of metal patches (10) decreases layer by layer, and the first to n layers of metal patches (10) are rotated layer by layer around the line by an angle β / n, and β / n is greater than 0°; The metal patch (10) is obtained by drying the conductive silver paste; The metal film (9) is made of copper.

2. The electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial according to claim 1, characterized in that: β＝125°。 3. The electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial according to claim 1, characterized in that: Adjacent metal patches (10) are bonded together using a dielectric material (11), and the dielectric material (11) is made of FR4 material.

4. The electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial according to claim 1, characterized in that: Assuming that the width of the flow-direction groove (13) is a, the width of the flow-direction ridge (12) is b, the height of the flow-direction ridge (12) is c, and the total height of the anisotropic cross-scale micro-nano superhydrophobic surface (3) is H; c<H<100μm; a≥2b; |bc|≤1μm.

5. The electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial according to claim 1, characterized in that: In the anisotropic cross-scale micro-nano super-hydrophobic surface (3), micron-scale micro-pillars formed by silicon dioxide nanoparticles (14) are distributed on the surface of the flow-toward groove (13) and the flow-toward ridge (12); The particle size of the silicon dioxide nanoparticles (14) is 10 nm to 500 nm.

6. The electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial according to claim 1, characterized in that: The material of the oblique honeycomb five-mode material (1) is aluminum; The material of the anisotropic cross-scale micro-nano super-hydrophobic surface (3) is a wave-transmitting resin material.

7. The method for preparing an electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial according to any one of claims 1 to 6, characterized in that: include: S1 uses 3D printing method to form oblique honeycomb five-mode material (1); S2 uses a wave-transmitting silicon-based inorganic adhesive to bond a rotating stacked pyramid absorber array (2) onto an oblique honeycomb five-mode material (1); S3: filling a wave-transmitting resin material between the rotationally stacked pyramid absorber units (7) of the rotationally stacked pyramid absorber array (2) so that the upper surface of the resin material forms a plane; S4 uses a 3D printing method to form flow grooves (13) and flow ridges (12) on the resin material.

8. The method for preparing the electromagnetic stealth-underwater sound absorption-superhydrophobic drag reduction metamaterial according to claim 7, characterized in that: In step S4, it also includes: Ultrasonic cavitation is used to roughen the surfaces of the flow-direction groove (13) and the flow-direction ridge (12), and simultaneously silicon dioxide nanoparticles (14) mixed in the ultrasonic cavitation jet are anchored on the roughened surfaces.

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