A stealthy metasurface compatible with radar, infrared, and acoustic fields

Abstract

This invention discloses a stealthy metasurface compatible with radar, infrared, and acoustic fields, relating to the field of electromagnetic stealth technology. The invention involves placing a resonant metal square ring on the top surface of a dielectric substrate, with metal patches of varying sizes placed on both the inner and outer regions of the resonant metal square ring on the top surface of the dielectric substrate, and a metal backplate on the bottom surface of the resonant metal square ring. Quarter-circle arcs are formed at the four corners of the dielectric substrate and the metal backplate. Multiple dielectric substrates are rotated in different directions to alternately arrange them into a metasurface. A cavity structure is then formed on the bottom surface of the metasurface, with multiple cylindrical cavities formed at the intersections of the dielectric substrates communicating with the cavity structure to form a micro-perforated plate structure. When electromagnetic waves and acoustic waves are incident on the metasurface, radar stealth, infrared stealth, and sound absorption and noise reduction functions can be achieved simultaneously. The invention also achieves a coupling design of electromagnetic and acoustic fields to simultaneously modulate electromagnetic and acoustic fields.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic stealth technology, and in particular to a stealth metasurface that is compatible with radar, infrared and acoustic fields. Background Technology

[0002] Metamaterials, as artificial functional materials with periodic or quasi-periodic subwavelength arrays, have attracted much attention and have been widely applied due to their novel properties not found in natural materials. As components of metamaterials, small scatterers or structural units possess the ability to flexibly manipulate physical waves. Metasurfaces, a novel type of two-dimensional metamaterial, have received extensive research and continuous attention due to their excellent resonant properties, such as ultra-thinness, light weight, and high absorption rate, and are often designed as subwavelength composite microstructures. For electromagnetic waves, metamaterials greatly enhance the controllability of electromagnetic waves across different frequency ranges, resulting in some fascinating applications in theory and practice, such as negative refractive index, perfect absorbers, and polarization control devices. In the field of acoustics, metamaterials can be used to exhibit novel and unique properties, generating negative equivalent mass density and negative bulk modulus, and achieving functions such as noise absorption and negative refraction. In the infrared band, incident light can achieve almost perfect absorption efficiency at the subwavelength scale. Therefore, this phenomenon gives metamaterials enormous potential for development in areas such as noise reduction, sound insulation, electromagnetic stealth, and thermal camouflage.

[0003] Currently, most metamaterial designs achieve their functions by modulating waves within the same physical field. However, metamaterial applications typically involve multiple physical domains, making functional compatibility between different domains crucial for material adaptability. Furthermore, effective detection methods have evolved from single-spectrum and single-physical-field detection to comprehensive detection using multiple spectra and physical fields, including optical, microwave, infrared, and acoustic waves. Researchers have proposed a digital metasurface platform that enables electromagnetic functions through optical programming, integrating electronic variable capacitors and photodiodes to achieve microwave stealth, polarization, and eddy current generation. Another researcher has proposed a thermally stable visible-light transparent infrared selective emitter with a four-layer composite film, achieving both visible light transmittance and sound insulation. Finally, a sandwich-structured composite material with resonant acoustic metamaterials has been proposed, exhibiting excellent sound insulation performance in the low-frequency range.

[0004] However, the visible light, infrared light and microwaves involved in the current research are still limited to the electromagnetic field, and the design of sound field insulation performance is limited to the design of generating a single field; therefore, the current design is difficult to achieve the coupling design of multiple physical fields. Summary of the Invention

[0005] This invention provides a stealth metasurface compatible with radar, infrared, and acoustic fields. It can solve the problem that in the current stage of research, the visible light, infrared light, and microwave involved are still limited to the electromagnetic field. At the same time, when considering the sound insulation performance design, it is limited to the design of generating a single field. Therefore, the current design is difficult to achieve the coupling design of multiple physical fields.

[0006] This invention provides a stealthy metasurface compatible with radar, infrared, and acoustic fields, including a dielectric substrate, wherein a resonant metal square ring is disposed on the top surface of the dielectric substrate, and the resonant metal square ring is provided with an opening;

[0007] The top surface of the dielectric substrate has metal patches of different sizes disposed in both the inner and outer regions of the resonant metal square ring.

[0008] The bottom surface of the dielectric substrate is provided with a metal back plate. Quarter-circle arcs are formed at the four corners of the dielectric substrate and the metal back plate. Multiple dielectric substrates are rotated in different directions to form a metasurface by alternating arrangement of multiple dielectric substrates. Cylindrical cavities are formed at the intersection of the dielectric substrates. A cavity structure is provided on the bottom surface of the metasurface. Multiple cylindrical cavities are connected to the cavity structure to form a micro-perforated plate structure.

[0009] Preferably, the period of the metasurface unit formed by the resonant metal square ring, the metal patches of different sizes located in the inner and outer regions of the resonant metal square ring, the dielectric substrate, and the metal backplate is a = 8.00 mm.

[0010] Preferably, the diameter of the cylindrical cavity is r = 0.30 mm.

[0011] Preferably, the thickness of the cavity structure is D = 35 mm, and the wall thickness of the cavity structure is h = 2.00 mm.

[0012] Preferably, the resonant metal square ring, metal patch, and metal backplate are all made of copper.

[0013] Preferably, both the dielectric substrate and the cavity structure are made of polytetrafluoroethylene F4B board, which has a dielectric constant of 2.65 and a loss tangent of 0.001.

[0014] Preferably, when the aperture of the cylindrical cavity is increased, the absorption frequency of the micro-perforated plate structure shifts to a higher frequency.

[0015] As the wall thickness of the cavity structure increases, the absorption frequency of the micro-perforated plate structure shifts to lower frequencies.

[0016] As the thickness of the cavity structure increases, the absorption frequency of the micro-perforated plate structure shifts to lower frequencies.

[0017] This invention provides a stealthy metasurface that is compatible with radar, infrared, and acoustic fields. Compared with the prior art, its advantages are as follows:

[0018] This invention achieves electromagnetic and acoustic fields by placing a resonant metal square ring on the top surface of a dielectric substrate with an opening in the ring, and placing metal patches of different sizes on both the inner and outer regions of the resonant metal square ring on the top surface of the dielectric substrate. A metal backplate is placed on the bottom surface of the resonant metal square ring, and quarter-circle arcs are formed at the four corners of the dielectric substrate and the metal backplate. Multiple dielectric substrates are rotated in different directions to form a metasurface by alternating arrangements of the substrates. A cavity structure is then formed on the bottom surface of the metasurface, and multiple cylindrical cavities formed at the intersections of the dielectric substrates communicate with the cavity structure to form a micro-perforated plate structure. The coupling design involves several steps: First, when microwave electromagnetic waves are incident on the metasurface, they are scattered from different directions, achieving radar stealth. Second, when infrared electromagnetic waves are incident on the metasurface, the metasurface achieves a gradient change in the infrared emissivity of the infrared electromagnetic waves to achieve infrared stealth. Then, when sound waves are incident on the metasurface, they enter the cavity of the micro-perforated plate structure formed by the cylindrical cavity and the hollow structure. The sound waves vibrate and are lost within the cavity of the micro-perforated plate structure, achieving sound absorption and noise reduction. This allows for the simultaneous modulation of electromagnetic waves and acoustics while achieving the coupling design of electromagnetic and acoustic fields. Attached Figure Description

[0019] Figure 1 A schematic diagram of the overall structure of a stealth metasurface compatible with radar, infrared, and acoustic fields provided in an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the overall architecture of a stealthy metasurface compatible with radar, infrared, and acoustic fields, provided for an embodiment of the present invention; wherein (a) is a schematic diagram of the overall functional design; wherein (b) is a schematic diagram of the unit top view design; and wherein (c) is a schematic diagram of the unit cross-sectional front view design.

[0021] Figure 3 This invention provides a functional analysis schematic diagram of a polarization rotator for a stealthy metasurface compatible with radar, infrared, and acoustic fields, according to an embodiment of the present invention. (a) is a schematic diagram of the overall effect; (b) is a schematic diagram of the principle; (c) is a schematic diagram of the performance of the polarization rotator; (d) is a schematic diagram comparing the reflection amplitudes of coded 0 and coded 1; (e) is a schematic diagram comparing the cross-polarization phases of coded 0 and coded 1; and (f) is a schematic diagram of the cross-polarization reflection phase difference between coded 0 and coded 1.

[0022] Figure 4This invention provides a schematic diagram of microwave infrared performance compatibility analysis for a radar, infrared, and acoustically compatible stealth metasurface. (a) shows the overall infrared design; (b) shows the microwave performance of modes 0, 1, and 2 under co-polarization reflectivity, cross-polarization reflectivity, PCR, and cross-polarization reflection phase; (c) shows the surface current distribution of modes 0, 1, and 2 at frequencies of 8 GHz, 9 GHz, and 10 GHz; and (d) shows the electric field distribution of modes 0, 1, and 2 at frequencies of 8 GHz, 9 GHz, and 10 GHz.

[0023] Figure 5 This is a schematic diagram illustrating the compatibility optimization of the infrared and microwave performance of a radar, infrared, and acoustic field compatible stealth metasurface provided for an embodiment of the present invention; wherein (a) shows the specific optimization design of mode 1 and mode 2; wherein (b) shows the microwave performance comparison of mode 1 before and after optimization; and wherein (c) shows the microwave performance comparison of mode 2 before and after optimization.

[0024] Figure 6 A schematic diagram of the sound absorption principle of a micro-perforated plate of a stealth metasurface compatible with radar, infrared and sound fields provided for an embodiment of the present invention; wherein (a) is a schematic diagram of the structure of the micro-perforated plate; wherein (b) is a schematic diagram of the sound absorption principle; wherein (c) is a schematic diagram of the electric field distribution on the surface of the micro-perforated plate element;

[0025] Figure 7 This is a schematic diagram of the design optimization of acoustic structure parameters of a stealthy metasurface compatible with radar, infrared and sound fields provided for an embodiment of the present invention; wherein (a) represents the acoustic structure parameters; wherein (b) represents the influence of aperture size d on acoustic performance; wherein (c) represents the influence of plate thickness on acoustic performance; and wherein (d) represents the influence of cavity depth D on acoustic performance.

[0026] Figure 8 The following are schematic diagrams illustrating the simulation results of a radar, infrared, and acoustically compatible stealth metasurface provided in this embodiment of the invention: (a) is a schematic diagram of the overall design concept of the micro-perforated plate element surface; (b) is a schematic diagram of two sample designs of the micro-perforated plate; (c) is a schematic diagram comparing the far-field simulation results of the element surface and the copper plate; (d) is a schematic diagram of the sound pressure level (SPL) distribution of rectangular and cylindrical samples; (e) is a schematic diagram of the sound absorption coefficient of the micro-perforated plate element surface and the traditional element surface; and (f) is a schematic diagram of infrared thermal imaging simulated in Matlab.

[0027] Figure 9This is a schematic diagram of experimental results for a radar, infrared, and acoustic field compatible stealth metasurface provided in an embodiment of the present invention; (a) is a schematic diagram of the experimental sample and microwave experimental environment; (b) is a simulated RCS of the metasurface and copper plate in the incident direction; (c) is the average infrared emissivity of mode 0, mode 1, and mode 2; (d) is a schematic diagram of the overall infrared imaging of the sample; (e) is a schematic diagram of the thermal robustness test of infrared digital camouflage imaging at 50℃, 90℃, and 120℃; and (f) is a schematic diagram of the acoustic experimental setup and a comparison of simulated and experimental values ​​of acoustic absorption rate.

[0028] Figure 10 This is a schematic diagram of the operation of a stealth metasurface that is compatible with radar, infrared, and acoustic fields, provided as an embodiment of the present invention.

[0029] Among them: 1. resonant metal square ring, 2. metal patch, 3. dielectric substrate, 4. metal backplate, 5. cavity structure, 6. cylindrical cavity. Detailed Implementation

[0030] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0033] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0035] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0036] See Figures 1-2 This invention provides a stealth metasurface compatible with radar, infrared, and acoustic fields. It consists of two parts: the upper part is a multi-spectral metasurface layer composed of an open-ended resonant metal square ring and non-invasive embedded metal patches. The resonant ring achieves broadband linear polarization cross-rotation by forming a 45-degree angle with the linear polarization direction of the incident electromagnetic wave, thereby achieving specific modulation of the reflected electromagnetic wave; metal patches of varying sizes are embedded in the non-metallic regions in the middle and around the open-ended resonant metal square ring. Without affecting microwave performance, the infrared emissivity of different units can be adjusted to achieve macroscopic infrared digital camouflage. Simultaneously, a quarter-circle arc is carved out around each unit to form multiple Helmholtz cavities. The cavity portion is located below the metasurface, forming a micro-perforated plate structure. Sound waves entering the cavity are attenuated by the vibration of the cavity, thereby achieving sound absorption and noise reduction.

[0037] When electromagnetic waves in the microwave band are incident on the top surface of the dielectric substrate 3, the electron-excited motion moves along the resonant metal square ring 1, causing a change in the phase of the reflected wave. Multiple dielectric substrates 3 are rotated in different directions to form a metasurface by alternating arrangements of multiple dielectric substrates 3. When electromagnetic waves in the microwave band are incident on the metasurface, the metasurface elements scatter the electromagnetic waves in the microwave band from different directions, realizing cross-polarization conversion of the electromagnetic waves in the microwave band to achieve radar electromagnetic stealth function.

[0038] Multiple dielectric substrates 3 are placed on the inner and outer regions of the resonant metal square ring 1, and metal patches 2 of different sizes are filled on their top surfaces. The multiple dielectric substrates 3 are rotated in different directions to form a metasurface by alternating arrangement of the multiple dielectric substrates 3. When an infrared electromagnetic wave is incident on the metasurface, the metasurface realizes a gradient change in the infrared emissivity of the infrared electromagnetic wave to achieve infrared stealth function.

[0039] Meanwhile, when the sound wave is incident on the metasurface, it enters the cavity of the micro-perforated plate structure formed by the cylindrical cavity 6 and the cavity structure 5. The sound wave is lost in the vibration during transmission within the cavity of the micro-perforated plate structure, thus achieving the function of sound absorption and noise reduction.

[0040] The upper metasurface unit consists of a metal backplate, a dielectric layer, and metal patterned units from bottom to top. A single metasurface unit comprises a metal backplate, a dielectric layer, a resonant metal square ring, and metal patches of varying sizes. Specific parameters are as follows: the period of the upper metasurface unit is a = 8.00 mm; the side length of the open resonant metal square ring is b = 6.00 mm; the width of the ring is d = 0.5 mm; the width of the opening is l = 2.00 mm; the aperture around the opening is r = 0.30 mm; and the thickness of the metal pattern is h1 = 0.0 mm. The base plate has a thickness of 18mm, a dielectric layer h2 = 3.50mm, and a metal backplate h3 = 0.018mm. Underneath the metal baseplate is a Helmholtz cavity with a thickness D = 35mm and a wall thickness h = 2.00mm. The Helmholtz cavity material has almost no impact on acoustic performance. Considering the overall consistency of the metasurface, the cavity material is the same dielectric layer as the metasurface. All metals are copper, and all dielectrics are F4B (dielectric constant 2.65, loss tangent 0.001).

[0041] I. Multiphysics Compatibility Design.

[0042] 1. Encoded microwave reflectivity based on polarization conversion.

[0043] By setting the angle between the polarization direction of the incident electromagnetic wave and the open-circuit resonator to 45 degrees in the simulation software CST, a highly efficient polarization rotator is formed, which can realize the polarization conversion of the reflected electromagnetic wave, with the effect as shown in the figure. Figure 3As shown in (a) and (b) in the figure; when an x-polarized electromagnetic wave is incident, strong resonance occurs at three frequency points: 5.2 GHz, 7.9 GHz, and 11.5 GHz. The polarization rotation rate reaches over 90% in the range of 7.1 GHz to 12.5 GHz, and the reflected electromagnetic wave changes from its original x-polarization to y-polarization; the formula for calculating the polarization conversion rate is:

[0044]

[0045] Where: r xx =r yy Indicates co-polarized reflectivity; r xy =r yx This represents the cross-polarization reflectance; based on the above formula, PCR can be calculated; PCR from 7.1 GHz to 12.5 GHz is close to 90%; due to the symmetry of the structural design, r xx =r yy and r xy =r yx .

[0046] To explain the polarization transformation process, taking input y-polarization and output x-polarization as examples, we introduce the u-coordinate system and the v-coordinate system; such as Figure 3 As shown in (b), the u-axis is at 45° to the y-axis and perpendicular to the v-axis; then consider the incident electromagnetic wave polarized along the y-axis; the electric field can be decomposed into two orthogonal components (directions). and Therefore, the electric field of the incident electromagnetic wave can be expressed as follows:

[0047]

[0048] in: and These are the unit vectors on the u-axis and v-axis, respectively; the electric field of the reflected wave can be written as follows:

[0049]

[0050] Where ru and rv are the reflection coefficients along the u-axis and v-axis, respectively.

[0051] When an electromagnetic wave is incident on the surface, the electrons excited by the electromagnetic wave will move along the path of the copper surface, with the equivalent direction being the u-axis. This means that the z-axis in other directions will not affect the performance of the electromagnetic wave (equivalent to a perfect electrical conductor), therefore Δj_v = 0 and ru = rv. However, in the u-axis direction, due to the resonant oscillation between the surface current and the bottom current, the reflected wave will change. When Δφ = π, the field synthesized by Eru and Erv will change to the x-direction. Therefore, the direction of the reflected polarization rotates by 90°. If the open square ring is rotated by 90 degrees while the polarization direction of the incident electromagnetic wave remains unchanged, according to the above formula, the new reflected electromagnetic wave can be expressed in the following form:

[0052]

[0053] This means that the new reflected electromagnetic wave still underwent cross-polarization rotation, but the reflection phase changed by 180 degrees while the amplitude remained unchanged. To verify this theory, the phase and amplitude of the reflected electromagnetic wave before and after the square ring rotation were compared on the CST, and the results are as follows: Figure 3 As shown in (d), (e), and (f), it is consistent with the theoretical analysis; according to the coding element theory, the element before rotation is represented as code 0, and the element after rotation is represented as code 1; by arranging two coding elements, specific modulation of the reflected electromagnetic wave can be achieved, thereby reducing the RCS.

[0054] 2. Infrared digital camouflage design based on non-invasive embedded metal patches.

[0055] According to Kirchhoff's laws, at a given temperature and wavelength, the ratio of the spectral emissivity to the spectral absorptivity of any object is independent of the object's properties and is always equal to the emissivity of a blackbody at the transmission temperature. That is, in thermal equilibrium, the emissivity and absorptivity of an object are numerically equal. For materials that are opaque to wavelengths, reflectivity can be obtained by measuring reflectivity.

[0056] ε=α=1-ρ

[0057] Emissivity is an inherent property of materials. Most common metals are high-reflectivity materials with low absorptivity, thus they are widely used in coated infrared low-emissivity materials, especially noble metals such as Au, Pt, and Ag, which have excellent low emissivity. Some common metals also have low emissivity and low cost, such as aluminum, copper, and zinc. The emissivity of copper powder coating at room temperature is 0.1, and that of aluminum powder coating at room temperature is 0.15. For a mixture of metal and non-metal surfaces, on a macroscopic scale of infrared detection, an approximate average can be achieved using the following formula:

[0058] ε=ε m·f m +ε d ·(1-f m )

[0059] Where: ε is the emissivity symbol; ε m Represents metallic emissivity; ε d Represents dielectric emissivity; f m This represents the duty cycle.

[0060] The open-ring resonator has a large amount of non-metallic space around it, which makes it possible to design the infrared radiation characteristics of the metasurface unit. By embedding metal patches of the same thickness in the non-metallic region, the occupancy ratio of the unit surface can be changed, thereby achieving the gradient design of infrared emissivity.

[0061] The specific design concept is as follows: Figure 4 As shown in (a), based on the gradient design requirements of infrared digital camouflage effect, three unit design schemes with infrared emissivity of 0.8, 0.6, and 0.4 were proposed, corresponding to duty cycles of 0.125, 0.375, and 0.625, respectively. To ensure the infrared gradient emissivity effect while minimizing the impact on microwave performance, the embedded metal patch was cut to stagger the resonant frequencies of the metal patch and the polarization rotator, preventing the incident electromagnetic wave from forming large-scale eddy currents within the metal patch and affecting the function of the main polarization converter. According to... Figure 4 The simulation results in (b) show that the same polarization reflectivity, cross-polarization reflectivity, polarization conversion rate, and cross-polarization reflection phase of the cells with three duty cycles maintain good performance above 8-10 GHz, and the difference in cross-polarization reflection phase between 4-16 GHz is less than 40 degrees, achieving compatibility between infrared and microwave performance; Figure 4 As can be seen from the surface currents of the three units in (c) and (d) at the resonant frequency, the embedded metal patch tightly confines the induced current within a limited area, reducing the coupling resonance with the open metal resonant ring and effectively weakening the impact on microwave performance.

[0062] 3. Optimized design for compatibility between infrared digital camouflage design and microwave control performance.

[0063] To maximize the infrared modulation range of the metasurface unit, it is necessary to maximize and maximize the metal duty cycle of the unit. When the metal patch is embedded in the non-metallic region of the open resonant square ring surface, the surface current excited by the metal patch will inevitably affect the open resonant square ring. To better balance infrared and microwave performance, the metal blocks inside and outside the resonant square ring are cut, dividing the interior of the metal block into four small parts and the exterior into two parts, with a slit width of 0.1 mm. In this way, by staggering the resonant frequencies of the square patch and the rotating unit, compatibility between microwave and infrared performance is achieved. The specific design process is as follows: Figure 5 (a) In order to test the microwave performance of the optimized metasurface unit, modes 1 and 2 before and after optimization were simulated in the microwave frequency band; the simulation results are as follows. Figure 5 As shown in (b) and (c) in the figure; the simulation results show that if the metal patch is not cut, the microwave polarization rotation performance of the entire unit is greatly reduced, while the microwave polarization performance of the unit is greatly maintained after the metal patch is cut.

[0064] 4. Acoustic absorption rate based on micro-perforated plates.

[0065] The sound-absorbing structure of the micro-perforated plate consists of three parts: a micro-perforated plate, a rigid wall, and a cavity. Figure 6 As shown in (a); based on acoustic knowledge and the transfer matrix method, the relationship between the upper sound pressure P1, lower sound pressure P2, upper particle vibration velocity V1, and lower particle vibration velocity V2 of the micro-perforated plate can be expressed by the following formula:

[0066]

[0067] Where T1 is the transfer matrix of the micro-perforated plate.

[0068] Similarly, as Figure 6 As shown in (b), the relationship between the upper sound pressure P2, the lower sound pressure P3, the vibration velocity V2 of the upper left particle, and the vibration velocity V3 of the lower particle can be expressed by the following formula:

[0069]

[0070] Where: T2 is the transfer matrix of the cavity behind the plate; k is the wavenumber. Combining the above two equations, the following equation can be obtained using the transfer matrix method:

[0071]

[0072] Where: D is the cavity depth, which is the distance from the microporous plate to the rigid wall.

[0073] At this point, considering the rigid wall surface of the micro-perforated plate sound-absorbing structure, i.e., the boundary condition V3 = 0, the acoustic impedance Z of the micro-perforated plate sound-absorbing structure can be obtained:

[0074]

[0075] Under normal incident conditions, the sound absorption coefficient of the micro-perforated plate can be obtained from the above two formulas:

[0076]

[0077] When the resonant frequency f meets the requirements, the sound absorption coefficient can reach its maximum value:

[0078]

[0079] 5. Acoustic performance optimization.

[0080] The main factors affecting the acoustic performance of micro-perforated plates are the pore diameter d, the perforated plate thickness t, the distance between pores b, and the cavity thickness D; the structural parameters of micro-perforated plates are simplified as follows: Figure 7 As shown in (a) of the diagram; it can be seen from the schematic diagram of the unit that the distance b between the apertures is fixed at 8 mm. Therefore, the study of the acoustic properties of metamaterials is mainly carried out through three factors: aperture diameter d, plate thickness t, and cavity thickness D.

[0081] With a plate thickness t = 3.5 mm and a cavity thickness D = 40 mm, the aperture d is varied from 0.2 mm to 1.0 mm in increments of 0.2 mm. The resulting sound absorption coefficient curve is shown below. Figure 7 (b) In the figure, it can be seen that when d<1, the sound absorption effect is better as the aperture d increases, but the absorption peak corresponding to the frequency shifts to the high frequency. When d<0.8, the change in aperture diameter has a greater impact on the sound absorption coefficient.

[0082] With an aperture d = 0.6 mm and a cavity thickness D = 40 mm, the plate thickness t is gradually increased from t = 1 mm to t = 4.5 mm in increments of 0.5 mm. The resulting sound absorption coefficient curve is shown below. Figure 7 (c) In the figure, it can be seen that the sound absorption coefficient decreases with the increase of plate thickness, the absorption peak shifts to the low frequency direction, the peak value of the absorption peak decreases, and the absorption band narrows.

[0083] With an aperture d = 0.6 mm and a plate thickness t = 3.5 mm, the cavity thickness D is varied, increasing from 10 mm in 10 mm increments to 80 mm. The sound absorption coefficient curve is shown below. Figure 7 (d) In the figure, it can be seen that as the cavity depth increases, the absorption peak shifts to lower frequencies, the peak value increases, and the overall sound absorption effect is better. When the cavity depth is small, changing the cavity depth can effectively affect the acoustic effect, but when the cavity depth increases to a certain value, the change in cavity depth has little effect on the acoustic effect.

[0084] The main parameter involved in the contradiction between acoustic and electromagnetic properties is the aperture size d. From an acoustic point of view, the larger the aperture of the electromagnetic metasurface, the better the acoustic performance; the smaller the aperture, the more stable the electromagnetic performance, which is contradictory. Therefore, we choose an intermediate value as a reasonable aperture size, namely d = 0.6 mm, to ensure that both acoustic and electromagnetic properties have better performance.

[0085] II. Coupling of electromagnetic field and sound field.

[0086] To gain a deeper understanding of the compatibility modulation mechanism of the meta-atom design with electromagnetic and acoustic fields, the electric field distribution at three frequency points—8, 9, and 10 GHz—was observed using CST; the results are as follows: Figure 6 As shown in (c), the metal backplate located between the micro-perforated plate cavity and the element surface effectively confines the electromagnetic field to a specific portion of the element surface; this framework ensures that the presence of the cavity does not impede the modulating capability of reflected microwaves, nor does it affect its infrared camouflage emission performance; the sound absorption characteristics of the micro-perforated plate are independent of the material stiffness, enabling its structure to be seamlessly integrated with traditional multispectral metasurfaces; this integration facilitates multiphysics modulating compatibility.

[0087] III. Methods and Validation.

[0088] 1. Integral structure simulation.

[0089] Figure 8 (a) illustrates the overall design concept of the micro-perforated plate element surface: In the microwave band, by introducing the PB phase theory and the design concept of the coded element surface, the element atoms before the resonator rotation are memorized as coded "0", and the element atoms after rotation are memorized as coded "1". Through "000001111100000", in the infrared band, element atoms with three duty cycles of 0.8, 0.6, and 0.4 (referred to as mode 0, mode 1, and mode 2, respectively) are randomly arranged in a ratio of 1:2:1, forming a digital camouflage infrared imaging effect throughout the infrared band; in the acoustic band, multiple element atoms are combined and arranged to form a micro-perforated plate structure, with a cavity below, thereby achieving a sound absorption effect; Figure 8 The simulation performance in the microwave, acoustic, and infrared bands is shown in turn.

[0090] The simulation was performed using COMSOL Multiphysics software. Since the experimental verification of this invention uses the impedance tube method to measure the sound absorption coefficient, and the impedance tube method limits the shape and parameters of the metamaterial, to facilitate comparison with experimental results, this invention extracted some metamaterial structures from the simulation process, forming rectangular and cylindrical metasurfaces, such as... Figure 8 As shown in (b); to demonstrate that rectangular and cylindrical metasurfaces have exactly the same acoustic properties, the sound pressure level (PSL) distribution was simulated, as shown in [image 1]. Figure 8 As shown in (c), the sound pressure level distributions of the two are exactly the same; the sound absorption coefficient curves of the micro-perforated metasurface and the traditional metasurface are as follows. Figure 8 As shown in (d), the simulation results show that the micro-perforated plate metasurface has a certain sound absorption effect in the range of 20-1600Hz, while the traditional electromagnetic metasurface material has no sound absorption effect at all. This structure enables electromagnetic metamaterials to achieve a breakthrough in acoustic performance, with a sound absorption coefficient greater than 0.5 in the range of 191.1-326.4Hz, showing good sound absorption effect.

[0091] In the microwave frequency band, far-field simulations of the entire metasurface were performed using CST, such as... Figure 8 As shown in (e), the overall RCS distribution and beam fractal diagram were obtained. It can be seen that the reflected electromagnetic wave becomes a double-beam fractal, and the RCS in the vertical direction is significantly reduced. In the infrared band, the infrared distribution of the metasurface was simulated using Matlab combined with the empirical formula for infrared emissivity, and the results are as follows: Figure 8 As shown in (f), the metasurface exhibits a typical digital infrared distribution.

[0092] 2. Experimental verification.

[0093] To further verify the compatibility performance of the metasurface, a prototype was fabricated using traditional printed circuit board (PCB) technology. First, glass cloth and polytetrafluoroethylene (PTFE) resin were scientifically formulated to obtain a customized PTFE sheet under strict processing. Then, the PTFE sheet underwent a series of processes including machining, cutting, and drilling to obtain several PTFE rings and two PTFE sheets. These were then glued together to create the experimental prototype. The resulting prototype is shown below. Figure 9 As shown in (a) in the figure; in order to meet the microwave and acoustic wave test conditions, two types of samples, square and cylindrical, were made respectively. The square sample was used for microwave and infrared band performance testing. It has a size of 320mm*320mm and is composed of 1600 metasurface units, which is consistent with the simulation conditions in CST. The cylindrical sample was used for acoustic wave testing. The sample inner diameter is 9.8cm, which is consistent with the simulation conditions in COMSOL.

[0094] Microwave experimental measurement system such as Figure 9 As shown in (a); the measurement was performed in a microwave anechoic chamber based on a network analyzer (Agilent E8363B) equipped with two pairs of broadband antennas in the 2-6 GHz and 6-12 GHz bands, respectively; to maintain consistency with the simulation setup, the sample was rotated 45 degrees and placed on the detection platform; under perpendicular incidence, the antenna was first aligned with the metal backplate, and then the RCS data was normalized and calibrated; then, the antenna was aligned with the sample surface to measure the co-polarized reflection coefficient, directly obtaining the reduced RCS data of the element surface, as shown in (a). Figure 9 As shown in (b), the simulated RCS of the element surface and the copper plate in the incident direction is given. The simulated RCS reconstruction can be obtained from the difference between them. The measured results are roughly the same as the simulation results, but there is a slight frequency deviation, which is caused by the manufacturing precision, experimental environment and the limited number of cells in the test sample.

[0095] First, the infrared emissivity at different duty cycles was measured using a TSS-5X infrared emissivity meter. The infrared probe acted as the detector, and the element surface was horizontally fixed on the platform. The infrared detector was placed on the element surface, and the infrared emissivity for modes 0, 1, and 2 was obtained respectively. The results are as follows: Figure 9 As shown in (c), a clear gradient infrared emissivity characteristic is displayed, which is in good agreement with the theoretical value. A slight deviation exists between the data from the TSS-5X infrared emissivity meter and the theoretical value, which may be due to limitations in background environment and instrument accuracy. Furthermore, sample roughness also significantly affects the actual infrared emissivity. Then, infrared imaging of the sample was achieved using an infrared imager (Thermao GEAR), as shown... Figure 9 As shown in (d) in the figure; due to the different infrared emissivity of the sample surface, the sample has a significant digital infrared camouflage effect.

[0096] To further verify the robustness of the designed sample, the infrared digital camouflage performance of the sample at different temperatures was tested; three temperature gradients of 50℃, 90℃ and 120℃ were selected to observe the infrared characteristics of the sample. Figure 9 (e) shows the infrared imaging results of the sample after heating at 50°C, 90°C and 120°C for 4 minutes, 8 minutes and 12 minutes respectively. At each temperature, the sample is gradually heated over time, which helps to better realize the camouflage function of the sample. At the same time, the sample can still maintain infrared digital camouflage characteristics at different temperatures, indicating that the sample has good thermal robustness and thermal stability, proving that the sample can still maintain stable performance under extreme temperature conditions.

[0097] In the field of acoustics, the sound absorption coefficient of the physical model in the 50-1000Hz frequency band was measured using the AWA6290T transfer function measurement system. The experimental values ​​were recorded and compared with the simulation results.

[0098] The sound absorption mechanism of the micro-perforated plate structure is unaffected by the material; the polytetrafluoroethylene material used in the experiment is a rigid material, and the influence caused by the vibration of the structure itself is not considered, so it can be regarded as a rigid body; the acoustic impedance of air is 400 kg / (m²). 2 The acoustic impedance of polytetrafluoroethylene (PTFE) is 1.3 × 10⁻⁶ Ω·s. 6 Kg / (m 2The acoustic impedance difference between two objects is defined as impedance mismatch. The greater the acoustic impedance mismatch, the more energy is reflected at the boundary between the two media, i.e., the better the reflection effect. The acoustic impedance of air is negligible compared to that of steel, and therefore can be ignored. During the processing of the physical prototype, the selection of prototype parameter values ​​is consistent with the structural design parameters. During the experiment, three 10 cm diameter sponge pads are added to one end of the impedance tube to calibrate the equipment, improve the accuracy of experimental measurements, and reduce the influence of errors. One end of the impedance tube is the input end, and the other end is the absorption end. The experimental sample is placed in the impedance tube, and the sponge pad is placed at the absorption end to absorb the sound waves. The white noise generated at the data acquisition front end is transmitted to the speaker through the power amplifier, and the sound pressure signal in the pipe is captured by the sensor. The data is transmitted to the acoustic analyzer, and the software on the computer analyzes and calculates the data to obtain the experimental data. The experimental process is as follows: Figure 9 As shown in (f) in the figure.

[0099] The measured sound absorption coefficient of the sample is as follows: Figure 9 As shown in (f), although the measured values ​​of the physical experiment do not completely match the simulation results, the curve trends are consistent and the overall data consistency is high. The experimental results have better performance than the simulation results, so the experimental results can be considered to be effective. The simulation results are consistent with the actual results, which proves the effectiveness of the simulation. It is feasible to judge the performance of materials through simulation. The reasons for the error between the simulation experiment and the physical experiment are: (1) When the experimental sample is made by multi-level processing and splicing process, the amount of glue used at the bonding point is too large, which leads to the actual size being too large and changes the actual volume of the inner cavity; (2) When using glue for multi-level bonding, the polytetrafluoroethylene rings are not well bonded, which leads to the inner wall of the metamaterial not forming a smooth state. During the processing, the surface of the polytetrafluoroethylene plate is rough and the inner wall is uneven, which increases the sound loss, resulting in the actual measurement results being better than the simulation results; (3) There are certain systematic errors in the measurement system, which are difficult to eliminate, but will not cause a significant change in the sound absorption coefficient; (4) Due to process errors such as processing precision, the hole spacing and hole diameter are difficult to achieve accurately, which has a certain impact on the acoustic performance.

[0100] This invention seamlessly integrates a micro-perforated plate structure with an electromagnetic metasurface, simultaneously achieving electromagnetic and acoustic modulation. Within the microwave spectrum, the metasurface achieves cross-polarization rotation of linearly polarized waves through a polarization rotator with a unit structure. Furthermore, a 0-1 coded metasurface is constructed using PB phase theory, thereby reducing the RCS in the 8-10 GHz frequency range. In the infrared domain, while maintaining microwave performance, metasurface units with different duty cycles are randomly and discretely arranged to form a camouflage layer with infrared digital characteristics. Finally, in the acoustic range, the aperture of the electromagnetic metasurface combines with the underlying cavity to form a micro-perforated plate structure composed of multiple Helmholtz cavities. This design effectively dissipates incoming sound waves, thus achieving sound absorption and noise reduction. The micro-perforated plate structure in the acoustic band has no requirements for the material medium, therefore it can be combined with an electromagnetic metasurface to achieve simultaneous modulation of electromagnetic and acoustic multi-physics fields. Its working principle is illustrated below. Figure 10 As shown.

[0101] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A stealthy metasurface compatible with radar, infrared, and acoustic fields, characterized in that, include: A dielectric substrate (3) is provided with a resonant metal square ring (1) on its top surface, and the resonant metal square ring (1) is provided with an opening. The top surface of the dielectric substrate (3) is provided with metal patches (2) of different sizes in both the inner and outer regions of the resonant metal square ring (1); and multiple dielectric substrates (3) are rotated in different directions to form a metasurface by alternating arrangement of multiple dielectric substrates (3). When an infrared electromagnetic wave is incident on the metasurface element, the metasurface realizes a gradient change in the infrared emissivity of the infrared electromagnetic wave to achieve infrared stealth function; when a microwave electromagnetic wave is incident on the metasurface, the metasurface element scatters the microwave electromagnetic wave from different directions to achieve cross-polarization conversion of the microwave electromagnetic wave to achieve radar electromagnetic stealth function. There is a non-metallic region around the resonant metal square ring (1). By embedding metal patches (2) of the same thickness in the non-metallic region and cutting the metal blocks inside and outside the resonant metal square ring (1), the inside of the metal blocks is divided into 4 small parts and the outside is divided into 2 parts, so as to change the duty cycle of the surface of the metasurface unit and thus realize the gradient change of infrared emissivity. In the infrared band, the duty cycles of the metasurface unit surface are designed to be 0.125, 0.375 and 0.625, respectively, with corresponding infrared emissivity of 0.8, 0.6 and 0.4, respectively. The elementary atoms, referred to as mode 0, mode 1 and mode 2, are randomly arranged in a ratio of 1:2:1, forming a digital camouflage infrared imaging effect throughout the infrared band. The bottom surface of the dielectric substrate (3) is provided with a metal back plate (4). Quarter-circular arcs are opened at the four corners of the dielectric substrate (3) and the metal back plate (4). Multiple dielectric substrates (3) are rotated in different directions to form a metasurface by alternating arrangement of multiple dielectric substrates (3). A cylindrical cavity (6) is formed at the intersection of the dielectric substrates (3). A cavity structure (5) is provided on the bottom surface of the metasurface. Multiple cylindrical cavities (6) are connected to the cavity structure (5) to form a micro-perforated plate structure, thereby achieving a sound absorption effect.

2. The stealth metasurface compatible with radar, infrared, and acoustic fields according to claim 1, characterized in that, The period of the metasurface unit formed by the resonant metal square ring (1), the metal patches (2) with different sizes in the inner and outer regions of the resonant metal square ring (1), the dielectric substrate (3) and the metal back plate (4) is a=8.00mm.

3. The stealth metasurface compatible with radar, infrared, and acoustic fields according to claim 1, characterized in that, The diameter of the cylindrical cavity (6) is r=0.30mm.

4. The stealth metasurface compatible with radar, infrared, and acoustic fields according to claim 1, characterized in that, The thickness of the cavity structure (5) is D=35mm, and the wall thickness of the cavity structure (5) is h=2.00mm.

5. The stealth metasurface compatible with radar, infrared, and acoustic fields according to claim 1, characterized in that, The resonant metal square ring (1), metal patch (2) and metal backplate (4) are all made of copper.

6. The stealth metasurface compatible with radar, infrared, and acoustic fields according to claim 1, characterized in that, Both the dielectric substrate (3) and the cavity structure (5) are made of polytetrafluoroethylene F4B plate, with a dielectric constant of 2.65 and a loss tangent of 0.

001.

7. The stealth metasurface compatible with radar, infrared, and acoustic fields according to claim 1, characterized in that, When the aperture of the cylindrical cavity (6) is enlarged, the absorption frequency of the micro-perforated plate structure shifts to a higher frequency. As the wall thickness of the cavity structure (5) increases, the absorption frequency of the micro-perforated plate structure shifts to lower frequencies. As the thickness of the cavity structure (5) increases, the absorption frequency of the micro-perforated plate structure shifts to lower frequencies.

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