Flexible broadband ultrathin radar and infrared compatible stealth metasurface and preparation method thereof

Abstract

The application discloses a flexible wide-band ultrathin radar and infrared compatible stealth metasurface and a preparation method, and belongs to the field of electromagnetic metasurfaces and micro-electro-mechanical systems. The metasurface is sequentially provided with an ultrathin multi-resonant spectrum selection layer, an anti-reflection impedance matching layer, a resonant loss layer, a magnetic medium attenuation layer and a coherent enhancement total reflection layer along the direction of electromagnetic wave incidence. The multi-resonant spectrum selection layer is designed with a geometric scale gradient change wave-absorbing pattern, the resonant loss layer is designed with a four-fold rotating arrow and a circular ring combined pattern, and the magnetic loss layer and the dielectric loss layer with low to high dielectric constants are combined to achieve a synergistic absorption mechanism, so that the radar-infrared compatible stealth effect of an ultrawide working frequency band is finally realized. The metasurface structure has high-efficiency wide-band absorption performance and excellent mechanical flexibility, the preparation process is simple and reliable, large-area, low-cost and repeatable manufacturing can be realized, and the metasurface structure has a wide application prospect in the fields of multi-band stealth and flexible electromagnetic devices.

Description

Technical Field

[0001] This invention belongs to the fields of electromagnetic metasurfaces and microelectromechanical systems, specifically relating to a flexible broadband ultrathin radar and infrared compatible stealth metasurface and its preparation method. Background Technology

[0002] As target detection methods gradually shift from traditional single-mode approaches to modern radar-infrared multi-band combinations, the risk of being tracked and identified has significantly increased, urgently requiring the development of multi-band stealth technologies that can drastically reduce target identification and tracking. Metasurfaces are functional array structures composed of subwavelength-scale artificial microstructure units arranged according to specific rules. By precisely designing the geometric parameters and arrangement of these units, precise control over the amplitude, phase, and polarization of electromagnetic waves can be achieved, thereby endowing the material with diverse electromagnetic response characteristics. Therefore, designing electromagnetic stealth metasurfaces with wide bandwidth, ultra-thin structures, and conformal attachment capabilities is of great significance for achieving integrated radar-infrared multi-band stealth.

[0003] To meet the needs of multi-band stealth in radar and infrared applications, research on electromagnetic metasurfaces has developed rapidly. However, current technologies still face the challenge of balancing the expansion of operating frequency bands with the improvement of mechanical flexibility. Radar-band stealth typically requires surfaces with high absorption and low reflection characteristics to effectively weaken radar echo signals; while infrared stealth relies on low absorption and high reflection characteristics to reduce the infrared radiation signature of targets. This constraint leads existing research to employ multi-layer integrated structure designs to improve overall stealth performance. Currently, these methods suffer from insufficient optimization of absorbing pattern design and magnetic and dielectric loss layers, resulting in metasurfaces exhibiting large structural thicknesses (up to 10 mm), complex designs, and insufficient flexibility. To improve the mechanical flexibility of electromagnetic metasurfaces and enhance their conformal adhesion capabilities, it is often necessary to sacrifice operating bandwidth. For example, a typical 3 mm thick absorbing structure often has an effective absorption bandwidth limited to 8–20 GHz, making it difficult to balance wide bandwidth and thinness requirements, which severely restricts its engineering application potential. Therefore, there is an urgent need for a radar-infrared compatible stealth metasurface that combines ultra-thin structure, high absorption efficiency, and flexible attachability to achieve high-performance, manufacturable engineering application solutions. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a flexible, broadband, ultrathin radar-infrared compatible stealth metasurface. This technical solution integrates an ultrathin multi-resonance spectrum selection layer, an anti-reflection impedance matching layer, a resonant loss layer, a magnetic medium attenuation layer, and a coherent enhanced total reflection layer, arranged sequentially along the electromagnetic incidence direction, to achieve flexible, broadband, ultrathin radar-infrared compatible stealth, with a radar operating frequency band of 7.8 ~ 42.3 GHz.

[0005] This invention provides a flexible, broadband, ultrathin radar and infrared compatible stealth metasurface, comprising a multi-resonance spectrum selection layer, an anti-reflection impedance matching layer, a resonant loss layer, a magnetic medium attenuation layer, and a coherent enhanced total reflection layer arranged sequentially along the electromagnetic incident direction;

[0006] The multi-resonance spectrum selection layer is a flexible PET substrate with a patterned ITO film on its surface; it includes an ITO film that is rectangular in shape, with a cross-shaped cutout in the middle of the rectangular film, dividing the rectangular film into four quadrant rectangular sub-regions; each of the four quadrant rectangular sub-regions has a circular cutout with the corner as the center, the circular cutouts are coaxially arranged and the radius of the circular cutouts varies in a gradient.

[0007] The anti-reflection impedance matching layer is a porous PDMS (polydimethylsiloxane) with preset pores.

[0008] The resonant loss layer is a flexible PET substrate with a patterned ITO film on its surface; it includes an ITO film that is rectangular in shape, with obliquely open square ring cutouts at the four corners of the rectangle (the four sides are not connected end to end, but have gaps at adjacent corners); the rectangle has open circular ring cutouts (the rings are not closed, but have gaps on the four quadrant axes), and arrow-shaped cutouts extending from the quarter arc of the rings with their tips pointing towards the center, the four arrow-shaped cutouts being 90° quadruple rotationally symmetrical;

[0009] The magnetic media attenuation layer is PDMS (polydimethylsiloxane) doped with magnetic particles.

[0010] Furthermore, the thickness of the flexible PET substrate of the multi-resonance spectrum selection layer is 0.1~0.2 mm; the sheet resistance of the ITO film is 5~10Ω / sq; the side length of the ITO film forming a rectangle is 0.1~0.3 mm shorter than the side length of the metasurface unit period; the side length of the rectangular sub-region is 3.3~4.3 mm, and the width of the cross-shaped slit is 0.1~0.3 mm.

[0011] Furthermore, in the gradient-changing rings, the outer diameter of the first-level ring is 0.8~1.2 mm, increasing radially; the outer diameter of the second-level ring is 2.4~2.7 mm; and the outer diameter of the third-level ring is 3.5~3.7 mm. The inner diameter of each level of ring is 0.05~0.15 mm smaller than the outer diameter. The inner and outer diameters of the same level of rings in the different gradient-changing rings are the same.

[0012] Further, in the resonant loss layer, the flexible PET substrate has a thickness of 0.1~0.2 mm; the ITO film has a sheet resistance of 90~120 Ω / sq; the side length of the ITO film forming a rectangle is 0.8~0.95 times the side length of the metasurface unit period; the outer diameter of the ring is 3~4 mm, and the inner diameter is 0.1~0.2 mm smaller than the outer diameter; the width of the unclosed region of the ring is 0.1~0.3 mm, located on the X and Y axes of the ring; the width of the arrow-shaped hollowed-out arrow shaft is 0.1~0.3 mm, and the distance between the arrows is equal to the width of the unclosed region of the ring; the side length of the square ring is 0.4~0.9 mm, and the width of the hollowed-out square ring is 0.05~0.15 mm; the width of the oblique unclosed region of the square ring is 0.05~0.15 mm, located at the corner facing the center of the ITO film.

[0013] Furthermore, the porous PDMS of the anti-reflection impedance matching layer has a thickness of 0.8~1.2 mm and a porosity of 30%~60%; the magnetic dielectric attenuation layer has a thickness of 0.9~1.3 mm and a mass fraction of doped magnetic particles of 10%~40%; and the magnetic nanoparticles have a diameter of 50~100 nm.

[0014] Furthermore, the coherent enhanced total reflection layer is a flexible PET substrate with a continuous ITO film coated on its surface; the thickness of the PET substrate is 0.1~0.2 mm; and the sheet resistance of the ITO film is 5-10 Ω / sq.

[0015] Furthermore, the metasurface unit has a periodic side length of 7~9 mm and a thickness of 2~3.1 mm; the metasurface is capable of efficient absorption in the ultra-wideband range of 7.8~42.3 GHz.

[0016] This invention also provides a method for fabricating a flexible broadband ultrathin radar and infrared-compatible stealth metasurface, comprising the following steps:

[0017] Step 1: Patterning of ITO functional structures on the PET surface is achieved by using sputtering ITO and photolithography humidification etching or electrospraying ITO ink printing to prepare a multi-resonance spectrum selection layer and a resonant loss layer;

[0018] Step 2: Prepare the anti-reflection impedance matching layer and the magnetic medium attenuation layer using PDMS casting process;

[0019] Step 3: Prepare an ITO thin film layer by sputtering ITO or electrospraying ITO ink onto the surface of a flexible PET substrate to obtain a coherent enhanced total reflection layer;

[0020] Step 4: The multi-resonance spectrum selection layer, anti-reflection impedance matching layer, resonant loss layer, magnetic medium attenuation layer and coherent enhancement total reflection layer are integrated and packaged using oxygen plasma room temperature bonding process.

[0021] Furthermore, when preparing the anti-reflection impedance matching layer, NaCl or nano-PS particles are used as additives for the PDMS precursor; when NaCl is used as an additive for the PDMS precursor, it is rinsed in deionized water after curing to remove NaCl; when nano-PS particles are used as an additive for the PDMS precursor, they need to be rinsed in N-methylpyrrolidone after curing to dissolve and remove the nano-PS particles.

[0022] Furthermore, in preparing the magnetic dielectric attenuation layer, magnetic nanoparticles are used as additives for the PDMS precursor; the magnetic nanoparticles are selected from nano Fe3O4, carbonyl iron powder, or nano nickel powder.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) Through the above-mentioned multi-layer structure design, this invention achieves efficient synergy between spatial impedance matching and multi-element loss mechanism. First, at the electromagnetic wave incident port, the surface multi-resonance spectrum selection layer adopts a gradient multi-scale design with gradient internal hollow circular ring geometry. This not only effectively disperses the resonant frequency, allowing electromagnetic waves to smoothly enter the structure with higher transmittance, but also takes into account the low surface emissivity to achieve infrared stealth. Second, when broadband electromagnetic waves are transmitted into the interior, the middle resonant loss layer plays a core role in energy attenuation. The ingenious combination pattern of four rotating arrows and rings on the surface of this layer, through complex etching gaps and conductive structure edges, introduces rich equivalent distributed capacitance and inductance in space, successfully constructing a multi-band cascaded LC resonant circuit. Specifically, the internal four rotating arrow structure establishes the basic high-frequency absorption band, while the circular etched gaps and the outer hollow decorative units further excite additional resonant modes, effectively broadening and significantly enhancing the low-frequency resonant absorption. These multi-scale geometric features are coupled with each other, which not only ensures the structure's insensitivity to the polarization of incident electromagnetic waves, but also stimulates a powerful dielectric loss mechanism, thereby efficiently absorbing and dissipating the energy of transmitted broadband electromagnetic waves.

[0025] (2) This invention proposes for the first time a transverse anti-reflection impedance matching layer and a bottom magnetic dielectric attenuation layer, which together construct a gradient dielectric constant and impedance gradient system from top to bottom. The upper anti-reflection impedance matching layer significantly reduces the equivalent dielectric constant of the layer by introducing porous PDMS with a specific porosity, making its surface wave impedance as close as possible to the free space wave impedance, effectively eliminating the impedance abrupt change at the interface and greatly suppressing in-situ reflection. As the electromagnetic wave continues to propagate to the bottom layer through the dielectric loss of the middle layer, after entering the dense PDMS magnetic dielectric attenuation layer doped with nano Fe3O4 particles, the equivalent dielectric constant and equivalent permeability increase significantly. This gradient distribution of dielectric constant from top to bottom continuously guides the electromagnetic wave to penetrate deep into the structure, and combined with the Fabry-Perot resonator formed by the continuous conductive film at the bottom layer, it undergoes multiple reflections, greatly extending the propagation path of the electromagnetic wave. Finally, the transmitted electromagnetic wave is completely converted into heat energy dissipation under the combined action of the strong magnetic loss induced by Fe3O4 particles and other mechanisms. It is precisely by relying on the deep synergy of the above-mentioned functional layers that this invention achieves excellent broadband radar wave absorption and infrared-compatible stealth performance with an extremely thin thickness.

[0026] (3) Each layer of this invention is made of stretchable and flexible material, giving the overall structure excellent flexibility and conformality. By designing a geometrically gradient absorption pattern in the multi-resonance spectrum selection layer and combining it with the synergistic absorption mechanism of the magnetic loss layer and the dielectric loss layer, efficient electromagnetic energy absorption is achieved. The overall thickness of this invention is 2.0 ~ 3.1 mm. Under the preferred size (e.g., an overall thickness of approximately 2.575 mm), the device can cover an ultra-wide operating frequency band of 7.8 ~ 42.3 GHz, possessing both wideband absorption performance and excellent mechanical flexibility. In addition, the PDMS, PET, and ITO materials selected in this invention have good chemical stability and process compatibility, enabling large-area, low-cost, and reproducible manufacturing, and have significant engineering application potential. Attached Figure Description

[0027] Figure 1 This is an exploded view of the layered structure of the metasurface of the present invention;

[0028] Figure 2 This is a schematic diagram of the geometric gradient change annular pattern after the ITO patterning of the multi-resonance spectrum selection layer in Embodiment 1 of the present invention;

[0029] Figure 3 This is a schematic diagram of a square patch array after the ITO resonant loss layer is patterned in Embodiment 1 of the present invention;

[0030] Figure 4 This is a schematic diagram of the bandwidth of the metasurface according to an embodiment of the present invention. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] A flexible, broadband, ultrathin radar-infrared compatible stealth metasurface comprises five parts: a multi-resonance spectrum selection layer 1, an anti-reflection impedance matching layer 2, a resonant loss layer 3, a magnetic medium attenuation layer 4, and a coherent enhanced total reflection layer 5. The metasurface unit cell period size is 7~9 mm. Details are as follows:

[0033] (1) Multi-resonance spectrum selection layer 1: Composed of a PET layer with ITO resonant units on the surface. The thickness of the PET is 0.1~0.2 mm, and the sheet resistance of the ITO film is 5~10Ω / sq to achieve low infrared emissivity. The resonant unit is a quadruple rotating rectangular patch array containing a hollowed-out circular ring pattern. The main body of the array consists of four square ITO patches of the same size arranged in a 2×2 configuration. The difference between the side length of the overall ITO pattern and the size of the metasurface unit period is 0.1~0.3 mm, and the side length of a single square ITO patch ranges from 3.3~4.3 mm. Adjacent square ITO patches are separated by a cross-shaped PET gap (the substrate is not coated with ITO film at the gap), and the gap width is 0.1~0.3 mm. Each square ITO patch contains concentrically distributed hollowed-out circular ring patterns with gradient geometric dimensions to excite multi-frequency resonance and broaden the radar absorption bandwidth. The outer diameter of the first-level ring ranges from 0.8 to 1.2 mm, the second-level ring from 2.4 to 2.7 mm, and the third-level ring from 3.5 to 3.7 mm. The radial width of each level of the hollowed-out ring is 0.05 to 0.15 mm. The geometric dimensions of the internal hollowed-out rings exhibit a gradient change to stimulate multi-frequency resonance and broaden the radar absorption bandwidth.

[0034] (2) Anti-reflection impedance matching layer 2: This layer serves as both an impedance matching layer and a wave-transmitting layer. It is made of porous PDMS with a thickness of 0.8~1.2 mm, a side length of 8~9 mm, and a porosity of 30%~60%. This reduces the equivalent dielectric constant, minimizes electromagnetic wave reflection at the surface, and promotes the wave vector's entry into the internal structure. Simultaneously, the low thermal conductivity and high transmittance of the porous PDMS reduce surface temperature rise, thereby indirectly suppressing infrared radiation intensity. The porosity is designed to match the equivalent wave impedance of this layer with free space, achieving low reflection over a wide frequency band.

[0035] (3) Resonant Loss Layer 3: This layer consists of a PET layer with ITO on the surface, wherein the thickness of the PET layer is 0.1~0.2 mm; the sheet resistance of the ITO film is 90~120 Ω / sq, so as to generate appropriate dielectric loss and consume the incident electromagnetic wave energy. The ITO surface is periodically patterned, with a square ITO patch as the base. The side length of the square patch is 0.8~0.95 times the periodic size of the metasurface unit. It is divided into a main ring, an internal arrow array and an outer corner feature by fine etching gaps (the gaps expose the PET substrate). Specifically, there is a concentric annular etching gap inside the patch, with an outer diameter of 3~4 mm and a radial ring width (i.e., the width of the etching gap) of 0.1~0.2 mm. The annular gap surrounds its internal area and is divided into four quadrants by cross-shaped intersecting gaps with a width of 0.1~0.3 mm. Within each quadrant, the retained ITO pattern is presented as an arrow shape extending from the bottom edge of a quarter-circle arc, with its tip pointing towards the center of the patch. The width of the arrow shaft is 0.1–0.3 mm, and the four arrows are arranged in a 90° quadruple rotational symmetry, collectively forming a polarization-insensitive core absorbing structure. Furthermore, at each of the four corners of the outer perimeter of the square ITO patch ring, a miniature square unit for exciting multiple resonances is added. The outer edge length of this unit is 0.4–0.9 mm, and the etched square ring linewidth is 0.05–0.15 mm. The inner corner of this square ring facing the patch center has a slanted break opening with a width of 0.05–0.15 mm. Through the coherent arrangement of these multi-scale features, the entire pattern introduces abundant equivalent capacitance and inductance in space, thereby constructing a highly efficient multi-band resonant network for efficiently dissipating incident electromagnetic wave energy in specific frequency bands.

[0036] (4) Magnetic dielectric attenuation layer 4: This layer is composed of PDMS doped with a predetermined mass fraction of nano-magnetic particles, with a thickness of 0.9~1.3 mm and a side length of 8~9 mm. The diameter of the magnetic particles is 50~100 nm, and the doping mass fraction is 10~40 wt%. By controlling the content of magnetic particles, a magnetic loss mechanism is introduced, which works in conjunction with dielectric loss to achieve ultra-wideband absorption, especially enhancing the absorption performance of low-frequency electromagnetic waves.

[0037] (5) Coherent Enhanced Total Reflection Layer 5: It is composed of PET with a continuous ITO film on the surface, wherein the thickness of PET is 0.1~0.2 mm and the sheet resistance of ITO film is 5~10Ω / sq; the continuous conductive film serves as the total reflection surface, and together with the above absorbing structure, it forms a Fabry-Perot resonant cavity to enhance the absorption efficiency of transmitted electromagnetic waves.

[0038] The metasurface has an overall thickness of 2.0 ~ 3.1 mm and a side length of 7 ~ 9 mm, and can cover an ultra-wide operating frequency band of 7.8 ~ 42.3 GHz.

[0039] Example 1

[0040] This embodiment provides a flexible broadband ultrathin radar-infrared compatible stealth metasurface.

[0041] like Figure 1 As shown, the metasurface is integrated from an ultrathin multiresonant spectrum selection layer 1, an anti-reflection impedance matching layer 2, a resonant loss layer 3, a magnetic medium attenuation layer 4, and a coherent enhanced total reflection layer 5, arranged sequentially along the electromagnetic incident direction, with an overall thickness of 2.575 mm. The parameters of each layer are as follows:

[0042] (a) Multi-resonance spectrum selection layer 1, which uses a flexible PET substrate with ITO resonant units on the surface, has a thickness of 0.125 mm, and the sheet resistance of the ITO film is 7 Ω / sq. The resonant unit is a quadruple rotating rectangular patch array containing a hollowed-out circular ring pattern, and the PET substrate has a side length of 8 mm. The main body of the array consists of four square ITO patches of the same size arranged in a 2×2 pattern, and the side length of each square ITO patch is 3.75 mm. Adjacent square ITO patches are separated by cross-shaped PET gaps with a gap width of 0.25 mm. Each square ITO patch has a radially gradient hollowed-out circular ring pattern inside. The outer diameter of the first-level ring is 1 mm, the outer diameter of the second-level ring is 2.5 mm, the outer diameter of the third-level ring is 3.5 mm, and the radial width of each level of hollowed-out ring is 0.1 mm.

[0043] (b) Anti-reflection impedance matching layer 2: This layer serves as an impedance matching layer and a wave-transmitting layer. It is made of porous PDMS with a thickness of 1 mm and a porosity of about 40% to reduce electromagnetic wave reflection on the surface.

[0044] (c) Resonant Loss Layer 3: This layer uses a flexible PET substrate with ITO resonant units on the surface, with a thickness of 0.125 mm and a sheet resistance of 100 Ω / sq for the ITO film. For example... Figure 3 As shown, the PET substrate has a side length of 8 mm. The layer pattern uses a square ITO patch with a side length of 7.3 mm as its base. Inside the patch is a concentric annular etched slit with an outer diameter of 3.5 mm and a radial width of 0.15 mm. This annular slit surrounds its internal area and is divided into four quadrants by cross-shaped slits with a width of 0.2 mm. Within each quadrant, the arrow shaft has a width of 0.15 mm. Simultaneously, the outer edge of the micro-square unit has a side length of 0.65 mm, and the etched square ring line has a width of 0.1 mm, with a 0.1 mm wide oblique break opening.

[0045] (d) Magnetic dielectric attenuation layer 4: This layer is composed of PDMS doped with a predetermined mass fraction of Fe3O4 nanoparticles, with a thickness of 1.2 mm. According to the loss requirements, the particle diameter is 50 nm, the Fe3O4 mass fraction is 10 wt%, and ultra-wideband absorption is achieved.

[0046] (e) Coherent Enhanced Total Reflection Layer 5: This layer, together with the layered structure above, forms a Fabry-Perot resonant cavity, reflecting the transmitted electromagnetic waves back for secondary absorption. A PET with a continuous ITO film on its surface, approximately 0.125 mm thick, is used. The sheet resistance of the ITO film is 7 Ω / sq.

[0047] Example 2

[0048] A method for fabricating a flexible broadband ultrathin radar-infrared compatible stealth metasurface:

[0049] (a) Fabrication of multi-resonance spectrum selection layer 1

[0050] First, an ITO thin film with a sheet resistance of 7 Ω / sq is magnetron sputtered onto the PET surface, where the PET thickness is approximately 0.125 mm. Then, the ITO is etched using photolithography and wet etching processes. Figure 2 The gradient circular pattern shown is patterned, with the photolithography parameters being BP212 photoresist, a film thickness of approximately 2.2 μm, and an exposure dose of 230 mJ / cm². 2 The wet etching parameters were: aqua regia as the etchant and an etching time of 30-32 seconds. After rinsing and drying with deionized water, a PET multi-resonant spectrum-selective layer with gradient-varying circular ITO rings on the surface was obtained.

[0051] (b) Fabrication of anti-reflection impedance matching layer 2

[0052] PDMS prepolymer and curing agent were mixed at a ratio of 10:1, and then 40 wt% of soluble NaCl crystal particles were added as a pore-forming agent. The mixture was then poured onto a PMMA substrate at a thickness of 1 mm and allowed to stand for 20 min, followed by curing in an oven at 85 °C for 2 h. After curing, the NaCl was removed by immersion in deionized water, resulting in porous PDMS with a porosity of approximately 40%. This porous PDMS was then peeled off to obtain the anti-reflection impedance matching layer.

[0053] (c) Fabrication of resonant loss layer 3

[0054] The fabrication method is the same as that for the multi-resonance spectral selective layer 1, except that the ITO sputtering thickness is controlled to a sheet resistance of 100 Ω / sq, and the patterned feature pattern is changed to... Figure 3 The periodic square patch shown has an etching time of approximately 25-28 seconds.

[0055] (d) Fabrication of magnetic media attenuation layer 4

[0056] The PDMS prepolymer and curing agent were mixed at a ratio of 10:1, and then 10% by mass of Fe3O4 nanoparticles (50 nm in diameter) were added and stirred until homogeneous. Next, a 1.2 mm thick layer was poured onto a PMMA substrate and allowed to stand for 20 minutes, followed by curing in an oven at 85 °C for 2 hours. After curing, the PDMS was peeled off to obtain the magnetic dielectric attenuation layer.

[0057] (e) Fabrication of coherent enhanced total reflection layer 5

[0058] ITO films with a sheet resistance of 7 Ω / sq can be directly magnetron sputtered onto PET surfaces, with a PET thickness of approximately 0.125 mm. Alternatively, ITO films can be obtained by electrospraying on PET surfaces using ethylene glycol methyl ether precursor ink containing 6 wt% ITO at a voltage of 1200 V.

[0059] (f) Bonding assembly

[0060] The surfaces of the multi-resonance spectrum selection layer 1, the anti-reflection impedance matching layer 2, the resonant loss layer 3, the magnetic medium attenuation layer 4, and the coherence-enhanced total reflection layer 5 were treated with oxygen plasma. The treatment power for the multi-resonance spectrum selection layer 1, the resonant loss layer 3, and the coherence-enhanced total reflection layer 5 was 30 W, and the treatment time was 1 min; the treatment power for the anti-reflection impedance matching layer 2 and the magnetic medium attenuation layer 4 was 30 W, and the treatment time was 30 s. After oxygen plasma treatment of each layer, they were sequentially bonded and repeatedly rolled with rollers to improve the bonding strength.

[0061] Example 3

[0062] In the embodiment of step (a) multi-resonant spectrum selection layer 1, firstly, an ITO film with a sheet resistance of 7 Ω / sq is magnetron sputtered onto the PET surface, wherein the PET thickness is approximately 0.125 mm; electrospraying technology is used, employing an ethylene glycol methyl ether precursor ink with 6 wt% ITO, and the process is carried out at an operating voltage of 1200 V. Figure 2 The graphic path shown is patterned using electrospray printing.

[0063] Example 4

[0064] In the embodiment of step (b) anti-reflection impedance matching layer 2, nano PS particles are used as pore-forming agents to replace NaCl. After curing, it needs to be immersed in N-methylpyrrolidone solution to rinse and dissolve and remove the PS particles, thereby forming a porous PDMS structure.

[0065] Example 5

[0066] In the embodiment of the magnetic media attenuation layer 4 in step (d), the nano Fe3O4 powder in the magnetic media attenuation layer 4 can also be replaced with other magnetic nano absorbers such as carbonyl iron powder or nano nickel powder of equal mass fraction, which can also introduce effective magnetic loss to achieve broadband absorption.

[0067] To verify the electromagnetic performance of the flexible broadband ultrathin radar-infrared compatible stealth metasurface described in this invention, the metasurface unit was modeled and numerically simulated using CST Studio Suite 2022 electromagnetic simulation software based on the structural parameters of Example 1. During the simulation, a frequency domain solver was selected to balance computational accuracy and efficiency, and the boundary conditions were set to a unitcell periodic structure to simulate an infinitely periodic metasurface array. X-polarized and Y-polarized electromagnetic waves incident along the +z direction were excited through Floquet ports, and simulation analysis was performed in the frequency range of 5–45 GHz. As shown in Figure 4, the overall thickness of this invention ranges from 2.0 to 3.1 mm. Under the preferred dimensions (e.g., an overall thickness of approximately 2.575 mm), simulation results show that the metasurface achieves efficient radar wave absorption in the 7.8–42.3 GHz frequency band. Simultaneously, the low infrared emission characteristics of the ITO gradient pattern in the top multi-resonant spectrum selection layer enable the entire metasurface structure to possess radar-infrared dual-band compatible stealth capabilities. In addition, metasurfaces exhibit excellent conformal adhesion capabilities, enabling conformal wave absorption on curved or non-metallic carrier surfaces, and have significant potential for engineering applications.

[0068] Comparative Example 1

[0069] The ITO thin film pattern of the intermediate resonant loss layer 3 in Example 1 is replaced with a continuous conductive thin film or a single complete patch without structural features. In this comparative example, the resonant loss layer 3 loses its ability to introduce multiple equivalent capacitances and equivalent inductances. Due to the lack of multi-scale structural support, the metasurface in this comparative example cannot construct multi-band LC resonant circuits, and its electromagnetic response degenerates into an extremely narrow single resonant peak. Therefore, broadband electromagnetic waves cannot excite a strong, polarization-insensitive dielectric loss effect in this layer, and the energy attenuation mechanism of transmitted electromagnetic waves is severely weakened. This results in a sharp deterioration of the broadband absorption characteristics of this invention in the 7.8~42.3 GHz frequency band, failing to meet the broadband stealth requirements of modern multi-band radar.

[0070] Comparative Example 2

[0071] Reducing the geometric size of the quadruple rotating arrows in the ITO thin film pattern of the resonant loss layer 3 in Example 1 will cause this layer to lose the wideband coupling capability brought about by the multi-scale (micro square, ring, and arrow) geometric features. In the electromagnetic wave transmission mechanism, the specific combination of quadruple rotating arrows and rings in this invention precisely corresponds to cascaded LC resonant circuits of different frequency bands (wherein the inner arrows establish the high-frequency absorption basis, and the rings and corner units further excite and broaden the low-frequency resonance). If the pattern features are missing or the proportions are mismatched, the distributed equivalent capacitance and equivalent inductance will change drastically, causing the original multi-band resonant network to break or the resonant frequency to shift severely.

[0072] Comparative Example 3

[0073] The anti-reflection impedance matching layer 2 and the magnetic dielectric attenuation layer 4 in Example 1 are swapped, resulting in a multi-resonance spectrum selection layer 1, a magnetic dielectric attenuation layer 4, a resonant loss layer 3, an anti-reflection impedance matching layer 2, and a coherent enhanced total reflection layer 5 arranged sequentially along the electromagnetic incident direction. This comparative example disrupts the gradient design of "dielectric constant from low to high" from the wave-facing surface to the bottom layer, adopting an inverted arrangement of "large at the top and small at the bottom" (placing the magnetic dielectric attenuation layer 4 with high dielectric constant and equivalent permeability on the wave-facing surface, while placing the porous anti-reflection impedance matching layer 2 with low dielectric constant in the deeper layer), causing a severe impedance mismatch. When the high dielectric layer is in direct contact with free space, the equivalent wave impedance of the metasurface layer and the free space wave impedance (approximately 377 Ω) will produce a huge impedance step. This extreme impedance mismatch will induce strong specular reflection at the gas-solid interface, causing most of the incident electromagnetic wave energy to be directly rejected and reflected back to free space, making it impossible for it to penetrate into the internal resonant layer and magnetic dielectric layer for cooperative dissipation. This inverted structure will cause a significant increase in the target's radar cross section (RCS), putting the overall electromagnetic stealth performance at risk of failure.

[0074] Any equivalent structure or process that utilizes the content of this invention and its accompanying drawings, or is directly or indirectly applied to other related technical fields, is similarly included within the scope of patent protection of this invention.

Claims

1. A flexible, broadband, ultrathin radar- and infrared-compatible stealth metasurface, characterized in that, It includes a multi-resonance spectrum selection layer (1), an anti-reflection impedance matching layer (2), a resonant loss layer (3), a magnetic medium attenuation layer (4), and a coherent enhancement total reflection layer (5) arranged sequentially along the electromagnetic incident direction. The multi-resonance spectrum selection layer (1) is a flexible PET substrate with a patterned ITO film on its surface; including an ITO film that is rectangular in shape, with a cross-shaped cutout in the middle of the rectangular film, dividing the rectangular film into four quadrant rectangular sub-regions; each of the four quadrant rectangular sub-regions has a circular cutout with the corner as the center, the circular cutouts are coaxially arranged and the radius of the circular cutouts varies in a gradient. The anti-reflection impedance matching layer (2) is a porous PDMS with preset pores; The resonant loss layer (3) is a flexible PET substrate with a patterned ITO film on its surface; including an ITO film that is rectangular in shape, with obliquely open square ring cutouts at the four corners of the rectangle; and an open circular ring cutout inside the rectangle, with arrow-shaped cutouts extending from a quarter arc of the ring towards the center, the four arrow-shaped cutouts being 90° quadruple rotational symmetry. The magnetic media attenuation layer (4) is PDMS doped with magnetic particles; The coherent enhanced total reflection layer (5) is a flexible PET substrate with a continuous ITO film on its surface.

2. The flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 1, characterized in that, The thickness of the flexible PET substrate of the multi-resonance spectrum selection layer (1) is 0.1~0.2 mm; the sheet resistance of the ITO film is 5~10 Ω / sq; the side length of the ITO film forming a rectangle is 0.1~0.3 mm shorter than the side length of the metasurface unit period; the side length of the rectangular sub-region is 3.3~4.3 mm, and the width of the cross-shaped slit is 0.1~0.3 mm.

3. The flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 2, characterized in that, In the gradient-changing rings, the outer diameter of the first-level ring is 0.8~1.2 mm, increasing radially; the outer diameter of the second-level ring is 2.4~2.7 mm; and the outer diameter of the third-level ring is 3.5~3.7 mm. The inner diameter of each level of ring is 0.05~0.15 mm smaller than the outer diameter. Within the four four-quadrant rectangular sub-regions, the outer and inner diameters of the same level of rings are kept consistent.

4. The flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 1, characterized in that, In the resonant loss layer (3), the thickness of the flexible PET substrate is 0.1~0.2 mm; the sheet resistance of the ITO film is 90~120Ω / sq; the side length of the ITO film forming a rectangle is 0.8~0.95 times the side length of the metasurface unit period; the outer diameter of the ring is 3~4 mm, and the inner diameter is 0.1~0.2 mm smaller than the outer diameter; the width of the unclosed area of ​​the ring is 0.1~0.3 mm, located on the X and Y axes of the ring; the width of the arrow-shaped hollowed-out arrow shaft is 0.1~0.3 mm, and the distance between the arrows is equal to the width of the unclosed area of ​​the ring; the side length of the square ring is 0.4~0.9 mm, and the width of the hollowed-out square ring is 0.05~0.15 mm; the width of the oblique unclosed area of ​​the square ring is 0.05~0.15 mm, located at the corner facing the center of the ITO film.

5. The flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 1, characterized in that, The porous PDMS thickness of the anti-reflection impedance matching layer (2) is 0.8~1.2 mm, and the porosity is 30%~60%; the thickness of the magnetic medium attenuation layer (4) is 0.9~1.3 mm, and the mass fraction of the doped magnetic particles is 10%~40%; the diameter of the magnetic nanoparticles is 50~100 nm.

6. The flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 1, characterized in that, The thickness of the PET substrate is 0.1~0.2 mm; the sheet resistance of the ITO film is 5~10 Ω / sq.

7. The flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 1, characterized in that, The metasurface unit has a periodic side length of 7-9 mm and an overall thickness of 2-3.1 mm; the metasurface is capable of efficient absorption in the ultra-wideband range of 7.8-42.3 GHz.

8. A method for fabricating a flexible broadband ultrathin radar and infrared compatible stealth metasurface as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Patterning of ITO functional structures on the PET surface is achieved by using a combination of sputtering ITO and photolithography humidification etching or electrospraying ITO ink printing, and a multi-resonance spectrum selection layer (1) and a resonant loss layer (3) are prepared. Step 2: The anti-reflection impedance matching layer (2) and the magnetic medium attenuation layer (4) are prepared by PDMS casting process. Step 3: Sputter ITO or electrospray ITO ink is used to spray ITO on the surface of a flexible PET substrate to prepare an ITO thin film layer to obtain a coherent enhanced total reflection layer (5). Step 4: The multi-resonance spectrum selection layer (1), anti-reflection impedance matching layer (2), resonant loss layer (3), magnetic medium attenuation layer (4) and coherent enhancement total reflection layer (5) are integrated and packaged using oxygen plasma room temperature bonding process.

9. The method for fabricating the flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 8, characterized in that, When preparing the anti-reflection impedance matching layer (2), NaCl or nano PS particles are used as additives for the PDMS precursor. When NaCl is used as an additive for the PDMS precursor, it is rinsed in deionized water after curing to remove NaCl. When nano PS particles are used as an additive for the PDMS precursor, they need to be rinsed in N-methylpyrrolidone after curing to dissolve and remove the nano PS particles.

10. The method for fabricating the flexible broadband ultrathin radar and infrared-compatible stealth metasurface according to claim 8, characterized in that, When preparing the magnetic dielectric attenuation layer (4), magnetic nanoparticles are used as additives for the PDMS precursor; the magnetic nanoparticles are selected from nano Fe3O4, carbonyl iron powder or nano nickel powder.

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