Wide-frequency-domain wide-angle-domain RCS continuous dynamic adjustable curved surface conformal active metasurface

Abstract

The invention discloses a wide-frequency-domain wide-angle-domain RCS continuous dynamic adjustable curved surface conformal active metasurface, and relates to the technical field of metasurface design, in particular to a wide-frequency-domain wide-angle-domain RCS continuous dynamic adjustable curved surface conformal active metasurface, a metasurface structure unit is sequentially provided with a metal structure layer, an F4B dielectric substrate, an ABS dielectric layer and a metal backboard layer from top to bottom, the metal structure layer and the metal backboard layer are connected through a circular through hole technology and are used for forming a tunable electromagnetic resonance structure. According to the wide-frequency-domain wide-angular-domain RCS continuous dynamic adjustable curved surface conformal active metasurface, an active metasurface structure unit with robustness to an incident angle and deformation is designed through theoretical analysis and simulation calculation, and the curved surface conformal active metasurface is machined and manufactured by adopting an innovative method combining 3D printing and a PCB technology. And the design method of the curved surface conformal metasurface is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of metasurface design, and in particular to a wide-frequency-domain and wide-angle-domain RCS continuous dynamically adjustable curved surface conformal active metasurface. Background Art

[0002] Metasurface is a material with a subwavelength structure that can manipulate the amplitude, phase and polarization of electromagnetic (EM) waves through microscopic structural design. Due to its small size, low loss, simple manufacturing and unique electromagnetic properties, metasurfaces have aroused great interest and have shown diverse applications in various fields from microwaves to visible light, such as achromatic lenses, vortex beam generators, surface wave couplers, super holograms, etc. Among them, radar stealth technology based on metasurfaces is favored by scientists from all over the world. A series of multifunctional metasurface absorbers with strong absorption rates have been designed. By optimizing their performance in specific frequency bands and fixed angles, researchers have been able to achieve strong broadband absorption at normal incidence.

[0003] Existing metasurface stealth design schemes are mostly based on planar metasurfaces. For targets with curved surface features, they are mostly implemented by splicing and assembling planar metasurface structures. There are inevitably edge geometric features, and the metasurface has a low degree of adaptability to curved targets, making it difficult to conform to targets of any shape. This not only reduces the stealth effect, but also cannot be applied to flying targets with strict aerodynamic layout requirements. In addition, in many design schemes, the normal incident angle is an important indicator for evaluating its performance, but in actual applications, most of them are oblique incident angles. Traditional planar metasurface stealth design schemes often face problems such as narrow frequency band and strong angle dependence. More importantly, in the process of dynamic adjustment of the electromagnetic wave scattering characteristics of curved targets, the frequency and angle coupling effects brought about by different curvatures make the design more complicated. These limitations seriously restrict the promotion and application of metasurface technology in the fields of stealth technology and communications. Summary of the invention

[0004] The present invention provides a conformal active metasurface with continuously dynamically adjustable curved surface RCS in a wide frequency domain and a wide angle domain, which solves the problems raised by the above-mentioned background technology.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a wide-frequency domain and wide-angle domain RCS continuously dynamically adjustable curved conformal active metasurface, wherein the metasurface structural unit is sequentially arranged from top to bottom as a metal structure layer, an F4B dielectric substrate, an ABS dielectric layer, and a metal backplane layer, and the metal structure layer and the metal backplane layer are connected in the middle by circular through-hole technology to form a tunable electromagnetic resonance structure.

[0006] Optionally, the period of the metasurface structure unit is set to p=10 mm.

[0007] Optionally, the metal structure layer and the metal backplane layer are both made of copper, and their thicknesses are both set to 0.018 mm, and the diameters of the circular through holes on the metal structure layer and the metal backplane layer are set to s=1 mm.

[0008] Optionally, the metal structure layer is composed of two rectangular structures on the left and right, a PIN diode is integrated between the two rectangular structures on the left and right, and an equivalent circuit is set for the PIN diode of each structural unit.

[0009] Optionally, the width of the left rectangular metal structure of the metal structure layer is set to a=3.7mm, and the length is set to b=9mm, the width of the right rectangular metal structure of the metal structure layer is set to c=3.7mm, and the length is set to d=10mm, and the gap between the right rectangular metal structure of the metal structure layer and the left rectangular metal structure of the metal structure layer is set to f=0.6mm.

[0010] Optionally, the PIN diode of the metal structure layer is set to SMP1321-040LF, and the width of the metal structure connecting the two sides of the PIN diode is set to aa=0.2mm, and the length is set to bb=0.8mm, and the metal structures on the left and right sides of the PIN diode are set accordingly.

[0011] Optionally, the equivalent circuit of the PIN diode is a fixed capacitor and a variable resistor in parallel, the fixed capacitor is set to C=0.15pF, the variable resistor is set to R=1-10000Ω, and the resistance value of the variable resistor can be controlled by a bias voltage.

[0012] Optionally, the F4B dielectric substrate is set to be a F4B flexible dielectric substrate with a thickness of 0.1 mm, and the relative dielectric constant of F4B is set to 2.67, and the loss tangent is set to 0.001, and the ABS dielectric layer is a resin medium with a thickness of 2.5 mm, and the relative dielectric constant is set to 2.65, and the loss tangent is set to 0.005.

[0013] The wide frequency domain and wide angle domain RCS continuously dynamically adjustable curved surface conformal active metasurface comprises the following operation steps: S1. Structural unit impedance matching When an electromagnetic wave is incident on a conformal active metasurface unit from free space, part of the electromagnetic wave is reflected back into the free space to form a reflected wave, while the electromagnetic wave that enters the unit continues to propagate in the form of a transmitted wave or is converted into other forms of energy due to loss. Therefore, the unit's absorption rate of electromagnetic waves A (ω) can be expressed as: (1) In the formula, ω is the angular frequency of the incident wave, R (ω) and S11 are the reflectivity and reflection amplitude respectively, T (ω) and S21 are the transmittance and transmission amplitude respectively. The reflective unit with a metal backplane can eliminate the transmission of electromagnetic waves, so its absorption rate A (ω) for electromagnetic waves can be expressed as: (2) Among them, the reflection amplitude S11 of the unit can also be written as: (3) Using the reflection coefficient S11 and the transmission coefficient S21, the effective impedance is calculated (4) In the formula, Z in is the input impedance of the unit, and Z0 is the wave impedance of free space. When the unit satisfies the impedance matching relationship Z in =Z0, its reflectivity is 0 and its absorptivity is maximum. When the unit does not satisfy the impedance matching relationship, its reflectivity becomes larger and its absorptivity becomes smaller.

[0014] S2. Surface area control design When an electromagnetic wave is incident obliquely on the surface of a medium and is reflected or refracted, its polarization characteristics do not change. However, in the case of oblique incidence, the angle of the incident wave The influence on impedance matching is significant. In different polarization modes, as the oblique incident angle changes, the free space wave impedance of the mode will change. The wave impedance expression of TM polarization under different oblique incident angles can be derived from the vector transmission line equation: (5) in is the characteristic impedance of free space, which is about 377Ω. As the oblique incident angle changes, the wave impedance in the TM mode decreases as the incident angle increases. Therefore, when designing an oblique incident absorbing structure, it is necessary to optimize the design according to the incident wave angle.

[0015] S3. Design and simulation of reconfigurable metasurfaces Based on the design and analysis of the above-mentioned wide-frequency and wide-angle dynamically adjustable curved conformal active metasurface structural units, an active metasurface composed of 20×20 structural units was constructed. The control resistors in each column can be dynamically adjusted and accurately modeled according to the theoretically calculated values. The arc length of the curved surface was set to 200 mm and the central angle was set to 114°.

[0016] S4. Experimental operation Firstly, a measurement sample with the same curvature as the simulation model is set, and the specifications of the sample are set to 256mm×200mm. Compared with the simulation model, the measurement sample is designed with an additional 56mm area, which is mainly used to arrange the control circuit. The curved conformal active metasurface is processed and manufactured by combining 3D printing with low-cost printed circuit board PCB technology. The top structure layer is processed on the F4B ultra-thin flexible medium using PCB technology, and the F4B thickness is set to 0.1mm. Then, 3D printing technology is used to process the ABS resin medium board with the middle thickness set to 2.5mm. The middle through-hole technology uses copper wire for conduction. Subsequently, the above parts are glued together. Finally, the assembled sample is experimentally verified. The experimental device includes a time-domain RCS test and analysis system, a linearly polarized LP horn antenna, an FPGA and a turntable bracket.

[0017] The present invention has the following beneficial effects: 1. This wide-frequency and wide-angle RCS continuously dynamically adjustable curved conformal active metasurface has designed an active metasurface structural unit that is robust to incident angle and deformation through theoretical analysis and simulation calculations. It also uses an innovative method that combines 3D printing and PCB technology to complete the processing and production of the curved conformal active metasurface, broadening the design method of curved conformal metasurfaces.

[0018] 2. This wide-frequency and wide-angle RCS continuously dynamically adjustable curved conformal active metasurface, in view of the complexity of the curved target, adopts a regional control strategy to accurately control the PIN diode bias voltage in different regions, thereby achieving impedance matching for electromagnetic waves with different incident angles. A series of simulation calculations and experimental test results jointly confirm the effectiveness of the proposed reconfigurable metasurface and verify the dynamic control capability of the curved conformal active metasurface on electromagnetic waves in wide-frequency and wide-angle domains.

[0019] 3. This wide-band and wide-angle RCS continuously dynamically adjustable curved conformal active metasurface, through the coordination between the metal structure layer, F4B dielectric substrate, ABS dielectric layer, and metal backplane layer, can flexibly adjust the electromagnetic response of the curved conformal active metasurface compared with the traditional design scheme. It shows stronger adaptability and optimization capabilities in wireless communication, detection sensing, intelligent stealth and other technologies that make extensive use of curved structures, and expands the application field of existing metasurface technology. At the same time, the designed metasurface has a simple structure and a small number of layers, which reduces the manufacturing cost and improves the integration and stability of the system, providing a solid foundation for future practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A conceptual diagram of a curved conformal active metasurface (CAM) of the present invention; Figure 2 The design and simulation diagram of the super surface structure unit in the present invention; Figure 3 This is a comparison diagram of impedance matching and reflectivity of the super surface structural unit of the present invention for electromagnetic waves at different incident angles; Figure 4 This is a design diagram of impedance matching of curved surface targets for electromagnetic waves with different incident angles in different regions in the present invention; Figure 5 This is a comparison diagram of the RCS simulation of the curved conformal active metasurface (CAM) in the present invention at an incident angle of θ = 0°-50° in the wide frequency domain; Figure 6 This is a comparison diagram of RCS simulation in a wide reflection angle range of the curved conformal active metasurface (CAM) of the present invention at an incident angle of θ=0°-50°; Figure 7 This is a diagram of the RCS test results in the present invention. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] See also Figures 1 to 7 The present invention provides a technical solution: a wide-frequency-domain and wide-angle-domain RCS continuously dynamically adjustable curved conformal active metasurface, wherein the metasurface structural unit is sequentially arranged from top to bottom as a metal structure layer, an F4B dielectric substrate, an ABS dielectric layer, and a metal backplane layer, wherein the metal structure layer and the metal backplane layer are connected in the middle by a circular through-hole technology to form a tunable electromagnetic resonance structure.

[0023] The period of the metasurface structure unit is set to p = 10 mm.

[0024] The metal structure layer and the metal back plate layer are both made of copper, and the thickness is set to 0.018 mm. The diameter of the circular through holes on the metal structure layer and the metal back plate layer is set to s=1 mm.

[0025] The metal structure layer consists of two rectangular structures on the left and right, with a PIN diode integrated in the middle of the two rectangular structures. The PIN diode of each structural unit is set with an equivalent circuit. By precisely controlling the bias voltage of the PIN diode, dynamic regulation of the electromagnetic wave reflectivity and radar scattering cross section RCS in the wide frequency domain and wide angle domain is achieved, so that each area of ​​the metasurface can meet the impedance matching conditions under different incident angles, thereby ensuring the effective absorption of electromagnetic waves.

[0026] The width of the rectangular metal structure on the left side of the metal structure layer is set to a=3.7mm, the length is set to b=9mm, the width of the rectangular metal structure on the right side of the metal structure layer is set to c=3.7mm, the length is set to d=10mm, and the gap between the rectangular metal structure on the right side of the metal structure layer and the rectangular metal structure on the left side of the metal structure layer is set to f=0.6mm.

[0027] The PIN diode of the metal structure layer is set to SMP1321-040LF, and the width of the metal structure on both sides connecting the PIN diode is set to aa=0.2mm, and the length is set to bb=0.8mm. The metal structures on the left and right sides of the PIN diode are set accordingly.

[0028] See also Figure 1 The equivalent circuit of the PIN diode is a parallel connection of a fixed capacitor and a variable resistor. The fixed capacitor is set to C=0.15pF, and the variable resistor is set to R=1-10000Ω. The resistance value of the variable resistor can be controlled by the bias voltage. By analyzing the interaction between the incident wave and different superatoms in the CAM at different incident angles, the CAM is divided into three different areas. The impedance matching theory is used to analyze and optimize the resistance value of the PIN diode in each area. By adjusting the applied bias voltage, the CAM can achieve continuous and dynamic control of the radar cross-section RCS in a wide frequency range and a wide angle range. The simulation and experimental results show that the proposed CAM can continuously modulate the RCS of the curved target in a wide angle range of 0° to 50° and a wide frequency range of 8GHz to 15GHz. Compared with the existing technology, the dynamic modulation bandwidth and angle range of the CAM in electromagnetic wave absorption are significantly improved, and it has the advantages of simple structure, few layers, and easy processing.

[0029] The F4B dielectric substrate is set to be an F4B flexible dielectric substrate with a thickness of 0.1 mm, and the relative dielectric constant of F4B is set to 2.67, and the loss tangent is set to 0.001. The ABS dielectric layer is a resin dielectric with a thickness of 2.5 mm, and the relative dielectric constant is set to 2.65, and the loss tangent is set to 0.005.

[0030] The RCS continuous dynamic adjustable curved surface conformal active metasurface in wide frequency domain and wide angle domain includes the following operation steps: S1. Structural unit impedance matching When an electromagnetic wave is incident on a conformal active metasurface unit from free space, part of the electromagnetic wave is reflected back into the free space to form a reflected wave, while the electromagnetic wave that enters the unit continues to propagate in the form of a transmitted wave or is converted into other forms of energy due to loss. Therefore, the unit's absorption rate of electromagnetic waves A (ω) can be expressed as: (1) Where ω is the angular frequency of the incident wave, R(ω) and S 11 are the reflectivity and reflection amplitude, T(ω) and S 21 are transmittance and transmission amplitude respectively. The reflective unit with a metal backplane can eliminate the transmission of electromagnetic waves, so its absorption rate A (ω) for electromagnetic waves can be expressed as: (2) Among them, the reflection amplitude of the unit S 11 It can also be written as: (3) Using the reflection coefficient S 11 and the transmission coefficient S 21 , calculate the effective impedance (4) In the formula, Z in is the input impedance of the unit, and Z0 is the wave impedance of free space. When the unit satisfies the impedance matching relationship Z in =Z0, its reflectivity is 0 and its absorptivity is maximum. When the unit does not satisfy the impedance matching relationship, its reflectivity becomes larger and its absorptivity becomes smaller.

[0031] When Z in The closer the impedance matching of / Z0 is to 1, the better the impedance matching of the material is, and the electromagnetic wave can enter the metasurface without reflection, effectively reducing the reflectivity. The designed curved conformal active metasurface unit adjusts the resistance value R of the loaded PIN diode to make the unit input impedance Z in changes when the input impedance Z of the structural unit in =Z0, the absorption rate reaches the maximum and becomes a high absorption state. When the PIN diode resistance R is adjusted to make Z in When the matching relationship is not satisfied, it becomes a high-reflection state, thereby realizing dynamic adjustment of reflectivity and absorptivity. Figure 2 As shown in, (a) Schematic diagram of a wide-frequency and wide-angle RCS dynamically adjustable metasurface structure unit, where p=10mm, h=2.5mm, a=3.7mm, b=9mm, c=3.7mm, d=10mm, f=0.6mm, aa=0.2mm, bb=0.8mm, s=1mm; (b) The reflectivity of the metasurface structure unit varies with the resistance R; (c) The input impedance Z of the metasurface structure unit in / Z0 changes with the resistance R; (d) the reflectivity of the metasurface structure unit changes with the incident angle θ; (e) the input impedance Z of the metasurface structure unit in / Z0 changes with the incident angle θ; (f) The influence of the deformation of the metasurface structural unit on the reflectivity performance. Figure 2(b) shows the simulation results of the reflectivity of the designed wide-band reflectivity dynamic control active metasurface structure unit changing with the resistance R. It can be seen that: in the 7-15GHz frequency band, when R gradually increases from 1Ω to 50Ω, the reflectivity decreases from approximately 0dB to approximately -15dB (minimum is -29dB); when R increases from 50Ω to 70Ω, the reflectivity gradually increases from approximately -15dB (minimum is -29dB). Correspondingly, as shown in Figure 2 (c) shows the input impedance Z of the designed broadband reflectivity dynamic control active metasurface structure unit in From the simulation results of the change of / Z0 with the resistance R, it can be known that: in the 7-15GHz frequency band, when the PIN diode resistance value R=1Ω, the input impedance Z of the structural unit in The wave impedance Z0 of free space does not meet the matching relationship, Z in / Z0 changes greatly, and the curve shows large fluctuations, achieving efficient reflection of electromagnetic waves; as the resistance value of R increases, Z in / Z0 changes gradually decrease. When R=50Ω, in the 7-15GHz frequency band, Z in / Z0 changes gradually approaching 1, achieving high absorption of electromagnetic waves. It can be seen that in the 7-15GHz wide band, by controlling the resistance value R of the PIN diode (SMP1321-040LF), the reflectivity of electromagnetic waves can be dynamically adjusted. Selecting R=1Ω and R=50Ω can achieve dynamic conversion from high-efficiency reflection of electromagnetic waves to high-efficiency absorption of electromagnetic waves.

[0032] At the same time, the curved conformal active metasurface designed in this paper is also robust to the incident angle and deformation, as shown in the figure. Figure 2 (d) shows the reflectivity of the metasurface structure unit changing with the incident angle θ. Figure 2 (e) shows the input impedance Z of the metasurface structure unit. in / Z0 changes with the incident angle θ. It can be seen that at the same resistance value R=50Ω, as the incident angle of the electromagnetic wave increases, within the incident angle range of θ=0°-θ=50°, the reflectivity of the metasurface structure unit decreases, but it can still maintain a low reflectivity; the input impedance Z of the metasurface structure unit in / Z0 As the incident angle θ increases, Z in Although / Z0 increases, it still approaches 1, which proves that the designed structural unit has a certain robustness to the electromagnetic wave incident angle θ; Figure (f) is the simulation result of the reflectivity changing with the curvature of the structural unit. It can be seen that the designed structural unit has good adaptability to changes within a certain curvature. When the central angle δ corresponding to the surface is less than 10°, the structural unit can still maintain a low reflectivity within the frequency band of 7-15GHz, which also lays the foundation for the dynamic control design of curved conformal active metasurfaces.

[0033] S2. Surface area control design When an electromagnetic wave is incident obliquely on the surface of a medium and is reflected or refracted, its polarization characteristics do not change. However, in the case of oblique incidence, the angle of the incident wave The influence on impedance matching is significant. In different polarization modes, as the oblique incident angle changes, the free space wave impedance of the mode will change. The wave impedance expression of TM polarization under different oblique incident angles can be derived from the vector transmission line equation: (5) in is the characteristic impedance of free space, which is about 377Ω. As the oblique incident angle changes, the wave impedance in the TM mode decreases as the incident angle increases. Therefore, when designing an oblique incident absorbing structure, it is necessary to optimize the design according to the incident wave angle.

[0034] In order to achieve the optimal impedance matching for different incident waves, the resistance values ​​corresponding to electromagnetic waves at different incident angles were selected through theoretical calculation and simulation optimization, such as Figure 3 As shown in the figure, the input impedance Z of the designed structural unit with different resistances R when the incident angle θ=0°, θ=30°, and θ=50° in The real and imaginary parts of are compared with the absorption rate. Figure 3 (a)-(b) are comparative analyses of the designed structural unit with an incident angle of θ=0°, where: Figure 3 In (a), when the incident angle θ = 0°, the resistance R = 1Ω, R = 55Ω, the input impedance Z in The real and imaginary parts of ; (b) Comparison of electromagnetic wave reflectivity when the incident angle θ=0°, the resistance R=1Ω, R=55Ω; (c) When the incident angle θ=30°, the resistance R=60Ω, R=55Ω, the input impedance Z in The real and imaginary parts of ; (d) Comparison of electromagnetic wave reflectivity when the incident angle θ=30°, the resistance R=60Ω, R=55Ω; (e) When the incident angle θ=50°, the resistance R=60Ω, R=80Ω, the input impedance Z in The real and imaginary parts of the input impedance; (f) When the incident angle θ = 50°, the resistance R = 60Ω, R = 80Ω, the electromagnetic wave reflectivity is compared. It can be seen that when the resistance R = 1Ω, the real and imaginary parts of the input impedance do not satisfy the matching relationship, Z in / Z0 changes greatly, with higher reflectivity; when the resistance R=55Ω, in the 7-15GHz frequency range, the input impedance Z in The real part of / Z0 gradually approaches 1, and the imaginary part gradually approaches 0, which satisfies the impedance matching condition, has a low reflectivity, and can achieve wide-band absorption. Figure 3(c) is the comparison of the input impedance of the designed structural unit with an incident angle of θ = 30°, R = 55Ω and R = 60Ω. It can be seen that the Z in The real part of / Z0 is closer to 1 in the range of 8-15GHz, and the input impedance Z in / The imaginary part of Z0 is closer to 0; Figure 3 (d) shows the comparison of the absorption rate of the designed structural unit with an incident angle of θ = 30°, R = 55Ω and R = 60Ω. Compared with R = 55Ω, the resistance R = 60Ω can achieve better absorption effect while ensuring a wide bandwidth. Figure 3 (e)-(f) are the comparison of the input impedance and absorption rate of the designed structural unit with an incident angle of θ=50°, R=60Ω and R=80Ω. It can be seen that Z in / Z0 real part is closer to 1 in the 9-12GHz range, and the input impedance Z in / The imaginary part of Z0 is closer to 0; Figure 3 (f) From the reflectivity comparison, it can be seen that the resistor R = 80Ω can achieve better absorption effect while ensuring a wide bandwidth compared to R = 65Ω.

[0035] S3. Design and simulation of reconfigurable metasurfaces Based on the design and analysis of the above-mentioned wide-frequency and wide-angle dynamically adjustable curved conformal active metasurface structural units, an active metasurface composed of 20×20 structural units was constructed. The control resistors in each column can be dynamically adjusted and accurately modeled according to the theoretically calculated values. The arc length of the curved surface was set to 200 mm and the central angle was set to 114°.

[0036] Simulation model such as Figure 4 As shown. Figure 4 (a)-(c) are schematic diagrams of the change in the electromagnetic wave incident angle distributed in different areas of the cylindrical surface when the electromagnetic wave incident angle (angle with the normal) is different: θ=0°, θ=30°, and θ=50°. Taking the center of the curved target as the reference, when the incident angle is 0°, the electromagnetic wave incident angle (angle with the normal) on both sides of the curved target gradually increases, and the outermost incident angle becomes 57°; when the incident angle is 30°, the electromagnetic wave incident angles on both sides of the curved target are no longer symmetrically distributed, the incident angle on the far right becomes 27°, and the incident angle on the left side of the curved surface becomes 87°; when the incident angle is 50°, the electromagnetic wave incident angles on both sides of the curved target become more complicated, the incident angle on the far right becomes 77°, and the area on the left side of the curved surface after the incident angle becomes 90° cannot be directly irradiated by electromagnetic waves.

[0037] Due to the complexity of the target shape and the significant influence of the incident angle on the scattering of electromagnetic waves, it is particularly necessary to study the regional division and control design based on the incident angle. Figure 4As shown in (d)-(f), in the process of studying the interaction between electromagnetic waves and curved targets, the surface of the curved target can be divided into three main control areas according to the different electromagnetic wave incident angle domains: Region I (0°≤θ<30°) mainly exhibits specular scattering, and the electromagnetic waves are almost directly reflected according to the law of reflection. Region II (30°≤θ<50°) is a transitional region, where electromagnetic waves experience both specular scattering and creeping wave scattering. In this region, the performance of traditional absorbing materials gradually deteriorates with the increase of the incident angle, especially showing obvious sensitivity to electromagnetic waves in different polarization states. In region III (θ≥50°), electromagnetic waves are mainly propagated in the form of creeping waves, and the scattering characteristics are very different from those in the first two regions. The scattering characteristics of this region are complex, and the design of the absorber requires targeted optimization.

[0038] Through the above analysis, we know that for curved targets, targeted designs are needed for different incident angles in order to achieve impedance matching more efficiently and realize effective absorption of electromagnetic waves. To this end, based on the particularity of the angular domain when electromagnetic waves are incident on curved targets, the idea of ​​regional regulation is adopted to flexibly adjust the electromagnetic characteristics of the metasurface structural unit according to the change of the incident angle, so that it can maintain good absorption performance at different incident angles, and realize the wide-band and wide-angle efficient absorption of the curved conformal active metasurface. Figure 4 According to the analysis, for the curved surface area I, R=55Ω is selected, and the wave absorption performance in the wide frequency domain is used to ensure that scattering can still be effectively reduced at small angles of incidence. In area II, R=60Ω is selected to achieve adaptive regulation of changes in the incident angle. For area III, when the incident angle is greater than 50°, considering that creeping waves are mainly present at this time, R=80Ω is selected to further improve the absorption efficiency. Based on the theoretical analysis of the surface regional control design, according to the different incident angle domains of electromagnetic waves, the key angle domains such as incident angle θ=0°, 30°, and 50° are distinguished, and the incident angle value of each column of metasurface structure units is calculated respectively, and the corresponding resistance value R is selected. The specific values ​​are as follows: Figure 4 As shown in (g)-(i).

[0039] In CST commercial simulation software, the frequency domain solver was used to simulate the design CAM model in the 2-18GHz wide frequency domain and incident angles θ = 0°, 30°, and 50°. Figure 4 (g)-(i) Set the resistance value of each of the 20 columns as the high absorption state of the curved conformal active metasurface, and set the resistance value of 20 columns R=1Ω as the high reflection state of the curved conformal active metasurface. At the same time, as a comparison, the RCS of curved metal plates of equal size and curvature is simulated and calculated. The simulation results are shown in Figure 5As shown, (a)-(c) respectively represent the RCS far-field 3D diagrams of the curved metal plate with equal size and curvature, the curved conformal active metasurface in high reflection state and high absorption state; (d)-(f) are the broadband RCS simulation comparisons at incident angles θ=0°, 30° and 50°. (g)-(i) are the broadband RCS simulation comparisons of different resistance value combinations at the same incident angle. Figure 5 It can be clearly seen from the three-dimensional far-field images of (a)-(c) that when the conformal active metasurface (CAM) is in an efficient reflection state, its reflection characteristics are similar to those of a curved copper plate, showing efficient reflection performance. In contrast, when the CAM is in an efficient absorption state, it can effectively absorb electromagnetic waves, thereby significantly reducing the radar cross-section (RCS) of the target. In addition, by adjusting the control parameters of the PIN diode, the CAM can dynamically switch between the efficient reflection state and the efficient absorption state. Figure 5 (d)-(f) show the RCS simulation results of the curved copper plate, efficient reflection state and efficient absorption state at incident angles θ = 0°, 30° and 50°. Figure 5 As shown in (d), when the CAM is in the high-efficiency reflection state (R = 1Ω), its reflectivity is very close to that of the curved copper plate. Figure 4 (g) shows that the CAM achieves broadband absorption in the 8-15 GHz band, and the average RCS is reduced by more than 10 dB compared with the high-efficiency reflection state. Figure 5 As shown in (e)-(f), when the metasurface is in a highly efficient reflection state (R = 1Ω), the reflectivity of the CAM is very close to that of the curved copper plate. When the CAM is adjusted to the absorption state, it achieves broadband absorption in the 8-15 GHz frequency band. Figure 5 As shown in (g)-(i), by adopting a regional control strategy and selecting different resistance value combinations, CAM can continuously and dynamically adjust the RCS in the frequency band of 8GHz to 15GHz and the incident angle range of 0° to 50°. It is known that the designed regional control CAM can not only improve the wave absorption effect, but also does not require the design of special structures in different regions. The metasurface structural unit is simple in design. The impedance value of the active metasurface in different regions is adjusted by electrical control to achieve impedance matching, forming an electromagnetic wave absorption effect in a wide frequency domain and wide angle domain, realizing the dynamic adjustment of the RCS of curved targets, and significantly improving the stealth performance of complex targets.

[0040] At the same time, the designed curved conformal active metasurface still has a certain wave absorption effect in a wide reflection angle domain. In order to further analyze the RCS dynamic control effect of the designed curved conformal active metasurface in a wide reflection angle domain, the RCS values ​​in the angle domain of -90° to 90° for electromagnetic waves with different incident angles (0°, 30°, 50°) at the same frequency point were simulated and calculated. The simulation results are shown in the figure below. Figure 6As shown, (a)-(c) wide frequency domain RCS simulation comparison when the incident angle θ=0°, θ=30°, θ=50° at 8GHz; (d)-(f) wide frequency domain RCS simulation comparison when the incident angle θ=0°, θ=30°, θ=50° at 15GHz; Figure 6 From (a) to (c), we know that when the 8 GHz electromagnetic wave is incident at 0°, the curved conformal active metasurface is in a high reflection state (R=1), which is highly consistent with the RCS curve of the curved metal plate. When it is in a high absorption state, the RCS values ​​in the angular range of -30° to 70° are reduced by more than 10 dB, and it also has a good absorbing effect in a wide angle range. When the 8 GHz electromagnetic wave is incident at 30°, it is in a high absorption state, and the RCS values ​​in the wide angle range of -30° to 70° are reduced by more than 10 dB. When the 8 GHz electromagnetic wave is incident at 50°, it is in a high absorption state, and the RCS values ​​in the wide angle range of -20° to 80° are reduced by more than 10 dB, which also has a good absorbing effect. Similarly, from Figure 6 It can be seen from (d)-(f) that when the incident wave frequency is 15 GHz and is incident on the designed curved conformal active metasurface at 0°, 30°, and 50° respectively, the curved conformal active metasurface is in a high reflection state (R=1) and has a high degree of consistency with the RCS curve of the curved metal plate. When it is in a high absorption state, it can achieve an effective reduction in the RCS value in a wide angle range of -30° to 70°. At the same time, from the 3D graphs of electromagnetic waves representing the high reflection state RCS and the high absorption state RCS, it can be seen that by adjusting the control parameters, the designed curved conformal active metasurface can achieve dynamic adjustment of the RCS in a wide reflection angle range.

[0041] S4. Experimental operation first, Figure 7 In the figure, (a) is the actual sample picture; (b) is the actual test picture; (c) is the RCS test result when the incident angle θ=0°; (d) is the RCS test result when the incident angle θ=0°; (e) is the RCS test result when the incident angle θ=0°, as shown in Figure 7 As shown in (a), a measurement sample with the same curvature as the simulation model is set, and the specification of the sample is set to 256mm×200mm. Compared with the simulation model, the measurement sample is designed with an additional 56mm area mainly used for arranging the control circuit. The curved conformal active metasurface is processed and manufactured by combining 3D printing with low-cost printed circuit board PCB technology. The top structure layer is processed on the F4B ultra-thin flexible medium using PCB technology, and the F4B thickness is set to 0.1mm. Then, the ABS resin medium board with the middle thickness set to 2.5mm is processed by 3D printing technology. The middle through-hole technology uses copper wire for conduction. Subsequently, the above parts are glued together. Finally, the assembled sample is experimentally verified. The experimental device includes a time-domain RCS test and analysis system, a linearly polarized LP horn antenna, an FPGA and a turntable bracket.

[0042] like Figure 7 (b) As shown. In order to accurately measure the RCS value under normal LP wave conditions, an FPGA for controlling voltage was made, and the control voltage of each column of the sample was accurately controlled by FPGA. At the same time, in order to reduce the test error, the control circuit part and FPGA and other control devices in the sample were shielded with absorbing materials. Figure 7 (c)-(e) show the test results. In the figure, the reflective state control voltage is 0.01v, and the absorptive state control voltage coding sequence is the same as the voltage coding sequence calculated by the resistance inversion in the simulation, corresponding to 0.7v, 0.75v, and 0.8v respectively. The above control voltages are dynamically controlled by the connected FPGA. Figure 7 From (c)-(e), we know that when the curved conformal active metasurface is in a highly reflective state, the reflectivity of the metasurface to electromagnetic waves is close to 1, which is highly consistent with the RCS curve of the curved metal plate. When the curved conformal active metasurface is in a highly absorptive state, broadband absorption is achieved in the 6-15GHz frequency range. Compared with the highly reflective state, the RCS is reduced by an average of more than 10dB, and some frequencies can reach -20dB, which is basically consistent with the theoretical results and simulation results. The deviation of the experimental results is mainly due to the imperfect placement of the experimental device, the inaccurate performance of the PIN diode, and the inevitable manufacturing errors in PCB processing and PIN diode welding. But overall, the experimental results are consistent with the theoretical predictions and strongly prove the effectiveness of the proposed PCM.

[0043] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance. In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, it can be indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific circumstances. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus.

[0044] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A conformal active metasurface with continuous and dynamic adjustable RCS in wide frequency and angle domains, characterized by: The metasurface structure unit is sequentially arranged from top to bottom as a metal structure layer, an F4B dielectric substrate, an ABS dielectric layer, and a metal backplane layer. The metal structure layer and the metal backplane layer are connected in the middle by circular through-hole technology to form a tunable electromagnetic resonance structure.

2. The wide frequency domain and wide angle domain RCS continuously dynamically adjustable curved surface conformal active metasurface according to claim 1, characterized in that: The period of the metasurface structure unit is set to p=10 mm.

3. The wide frequency and wide angle RCS continuously dynamically adjustable curved surface conformal active metasurface according to claim 1, characterized in that: The metal structure layer and the metal back plate layer are both made of copper, and the thickness is set to 0.018 mm. The diameter of the circular through holes on the metal structure layer and the metal back plate layer is set to s=1 mm.

4. The wide frequency and angle RCS continuously dynamically adjustable curved surface conformal active metasurface according to claim 3, characterized in that: The metal structure layer is composed of two rectangular structures on the left and right, a PIN diode is integrated between the two rectangular structures on the left and right, and an equivalent circuit is set for the PIN diode of each structural unit.

5. The wide frequency and wide angle RCS continuously dynamically adjustable curved surface conformal active metasurface according to claim 4, characterized in that: The width of the left rectangular metal structure of the metal structure layer is set to a=3.7mm, and the length is set to b=9mm. The width of the right rectangular metal structure of the metal structure layer is set to c=3.7mm, and the length is set to d=10mm. The gap between the right rectangular metal structure of the metal structure layer and the left rectangular metal structure of the metal structure layer is set to f=0.6mm.

6. The wide frequency and wide angle RCS continuously dynamically adjustable curved surface conformal active metasurface according to claim 4, characterized in that: The PIN diode of the metal structure layer is set to SMP1321-040LF, and the width of the metal structure connecting the two sides of the PIN diode is set to aa=0.2mm, and the length is set to bb=0.8mm. The metal structures on the left and right sides of the PIN diode are set accordingly.

7. The wide frequency and wide angle RCS continuously dynamically adjustable curved surface conformal active metasurface according to claim 6, characterized in that: The equivalent circuit of the PIN diode is a parallel connection of a fixed capacitor and a variable resistor, the fixed capacitor is set to C=0.15pF, the variable resistor is set to R=1-10000Ω, and the resistance value of the variable resistor can be controlled by a bias voltage.

8. The wide frequency and wide angle RCS continuously dynamically adjustable curved surface conformal active metasurface according to claim 1, characterized in that: The F4B dielectric substrate is set to be an F4B flexible dielectric substrate with a thickness of 0.1 mm, and the relative dielectric constant of F4B is set to 2.67, and the loss tangent is set to 0.

001. The ABS dielectric layer is a resin dielectric with a thickness of 2.5 mm, and the relative dielectric constant is set to 2.65, and the loss tangent is set to 0.

005.

9. The wide frequency domain and wide angle domain RCS continuously dynamically adjustable curved surface conformal active metasurface according to claims 1-8, characterized in that: The steps include: S1. Structural unit impedance matching When an electromagnetic wave is incident on a conformal active metasurface unit from free space, part of the electromagnetic wave is reflected back into the free space to form a reflected wave, while the electromagnetic wave that enters the unit continues to propagate in the form of a transmitted wave or is converted into other forms of energy due to loss. Therefore, the unit's absorption rate of electromagnetic waves A (ω) can be expressed as: （1） In the formula, ω is the angular frequency of the incident wave, R (ω) and S11 are the reflectivity and reflection amplitude respectively, T (ω) and S21 are the transmittance and transmission amplitude respectively, and the reflective unit with a metal backplane can eliminate the transmission of electromagnetic waves, so its absorption rate A (ω) for electromagnetic waves can be expressed as: （2） Among them, the reflection amplitude S11 of the unit can also be written as: （3） Using the reflection coefficient S11 and the transmission coefficient S21, the effective impedance is calculated （4） In the formula, Z in is the input impedance of the unit, Z0 is the wave impedance of free space, when the unit satisfies the impedance matching relationship Z in =Z0, its reflectivity is 0 and its absorptivity is maximum, while when the unit does not satisfy the impedance matching relationship, its reflectivity becomes larger and its absorptivity becomes smaller; S2. Surface area control design When an electromagnetic wave is incident obliquely on the surface of a medium and is reflected or refracted, its polarization characteristics do not change. However, in the case of oblique incidence, the angle of the incident wave The influence on impedance matching is significant. In different polarization modes, as the oblique incident angle changes, the free space wave impedance of the mode will change. The wave impedance expression of TM polarization under different oblique incident angles can be derived from the vector transmission line equation: （5） in is the characteristic impedance of free space, which is about 377Ω. As the oblique incident angle changes, the wave impedance in the TM mode decreases as the incident angle increases. Therefore, when designing an oblique incident absorbing structure, it is necessary to optimize the design according to the incident wave angle. S3. Design and simulation of reconfigurable metasurfaces According to the design and analysis of the above-mentioned wide-band and wide-angle dynamically adjustable curved conformal active metasurface structural unit, an active metasurface consisting of 20×20 structural units was constructed, in which each column of control resistors can be dynamically adjusted and accurately modeled according to the theoretically calculated values, where the arc length of the curved surface is set to 200 mm and the central angle is set to 114°; S4. Experimental operation Firstly, a measurement sample with the same curvature as the simulation model is set, and the specifications of the sample are set to 256mm×200mm. Compared with the simulation model, the measurement sample is designed with an additional 56mm area, which is mainly used to arrange the control circuit. The curved conformal active metasurface is processed and manufactured by combining 3D printing with low-cost printed circuit board PCB technology. The top structure layer is processed on the F4B ultra-thin flexible medium using PCB technology, and the F4B thickness is set to 0.1mm. Then, 3D printing technology is used to process the ABS resin medium board with the middle thickness set to 2.5mm. The middle through-hole technology uses copper wire for conduction. Subsequently, the above parts are glued together. Finally, the assembled sample is experimentally verified. The experimental device includes a time-domain RCS test and analysis system, a linearly polarized LP horn antenna, an FPGA and a turntable bracket.

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