Broadband invisibility cloaking based on active regulation of metasurface and preparation method thereof

Abstract

The application provides a kind of wideband stealth material based on active regulation super surface and preparation method, from top to bottom in turn: cross structure resistance type frequency selective surface, first, second dielectric layer, square ring structure resistance type frequency selective surface, third, fourth dielectric layer, multi-fractal structure active frequency selective surface, fifth layer dielectric layer, multi-fractal structure active frequency selective surface, sixth layer dielectric layer, metal back plate;The application solves the problem that low-frequency wave absorption of passive absorber and high-frequency wave absorption of active absorber are difficult to realize simultaneously. The cascading of cross and square ring structure resistance type frequency selective surface generates wide absorption frequency band at high frequency, and the central symmetry pattern makes it have polarization stability. The double-layer multi-fractal structure frequency selective surface is loaded with varactor diode and patch resistor, so that it can realize active tuning of absorption frequency band at low frequency. The working range covers P to K band, and has application potential in electromagnetic regulation, radar stealth and other aspects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of functional materials, and relates to a wideband stealth material based on active regulation of a super surface and a preparation method thereof, and is mainly used for radar camouflage stealth of ground mobile target components and aircraft target components. BACKGROUND

[0002] A microwave absorber is a kind of periodic structure stealth material, which can realize absorption of incident electromagnetic waves in a specific frequency band. It is widely used in electromagnetic shielding, antennas, military stealth, etc. In radar stealth, in order to effectively reduce or suppress RCS, the microwave absorber often needs to have wideband absorption characteristics. In recent years, with the gradual development of radar detection technology towards wideband and low frequency, the working frequency of radar detection equipment has been expanded to the Ultrahigh-Frequency (UHF) Band below 2GHz, which puts forward more stringent requirements on the absorption bandwidth of the microwave absorber. The wideband stealth material based on active regulation of a super surface designed by the application can solve the problems of low-frequency absorption of traditional passive absorbers, wideband absorption of low-frequency active absorbers, and stability design of absorption polarization angle, and further improve the radar stealth performance of the target.

[0003] At present, most of the disclosed passive and wideband absorption structures cover the C band and above, and it is difficult to cover the P, L and S bands with lower frequencies, and there is the disadvantage of large thickness; the active absorption structure can realize absorption band tuning at low frequencies, but it is difficult to consider high-frequency absorption performance at the same time. Therefore, designing and preparing an absorber working in the P-K ultra-wideband range, with excellent angle stability, low profile, light weight and stable absorption performance, is an important work in the field. SUMMARY

[0004] The purpose of the application is to solve the problems of narrow active regulation range in low frequency band and narrow absorption frequency band in high frequency band of the current metamaterial wideband absorption structure, improve the wideband absorption effect of the current absorption structure in the frequency range of 0.5-25GHz, and design and prepare an ultra-wideband absorption structure based on a low-frequency adjustable ultra-wideband microwave absorber. The structure has the characteristics of light weight, low profile, excellent polarization and incident angle stability, and can realize wideband absorption effect in the P-K band.

[0005] The structure design and preparation method provided by the application can realize ultra-wideband electromagnetic wave absorption effect in the P, L, S, C, X, Ku and K bands, and has the advantages of miniaturization, low profile, polarization insensitivity, good large-angle stability, simple preparation method, light weight, etc.

[0006] To achieve the above-mentioned purposes, the technical solutions of the application are as follows:

[0007] The wide-band stealth material based on active regulation of super surface includes a plurality of square structure layers with the same size and center overlap, which are stacked from top to bottom, and are sequentially: a cross structure resistance type frequency selective surface 1, a first layer of dielectric layer 2, a second layer of dielectric layer 3, a square ring structure resistance type frequency selective surface 4, a third layer of dielectric layer 5, a fourth layer of dielectric layer 6, a multi-fractal structure active frequency selective surface A 7, a fifth layer of dielectric layer 8, a multi-fractal structure active frequency selective surface B 9, a sixth layer of dielectric layer 10, and a metal back plate 11; the cross structure resistance type frequency selective surface 1 and the square ring structure resistance type frequency selective surface 4 are center-symmetric patterns, and the multi-fractal structure active frequency selective surface B 9 is obtained by counterclockwise rotation of the multi-fractal structure active frequency selective surface A 7 by 90°; definition: the direction from bottom to top is the positive direction of the z-axis, and the direction in which the long strip structure 72 of the multi-fractal structure active frequency selective surface A 7 extends is the x-axis; the y-axis is perpendicular to the z-axis and the x-axis;

[0008] The cross structure resistance type frequency selective surface 1 includes two rows and two columns of four cross structures 101 that are not connected to each other; the four cross structures 101 are the same size and are center-symmetric, and have the same gap between adjacent cross structures;

[0009] The square ring structure resistance type frequency selective surface 4 includes two center-overlapping square ring structures: an inner square ring 41 and an outer square ring 42;

[0010] The multi-fractal structure active frequency selective surface A 7 includes four fractal units 71 and two long strip structures 72, and the long strip structure 72 extends along the x-axis; each fractal unit 71 is perpendicular to the long strip structure 72; the direction perpendicular to the long strip structure 72 is the y direction, and the four fractal units 71 are located between the two long strip structures 72;

[0011] The four fractal units 71 are mirror-symmetric about the x-axis and the y-axis, respectively, and each fractal unit 71 includes: a curved line 711 connected to the long strip structure 72, and a trapezoidal structure 712 connected to the curved line 711; a varactor diode 73 is arranged between the two fractal units 71 adjacent in the y-axis direction on the left side, and a chip resistor 74 is arranged between the two fractal units 71 adjacent in the y-axis direction on the right side.

[0012] The multi-fractal structure active frequency selective surface B 9 is obtained by counterclockwise rotation of the multi-fractal structure active frequency selective surface A 7 by 90° about the z-axis;

[0013] Further including a control system for realizing regulation and control of an electromagnetic wave absorption frequency band range below 2GHz.

[0014] As a preferred mode, the control system includes: an external bias power supply A1201, a circuit wire A1202, a positive electrode feeding circuit A1203, a negative electrode feeding circuit A1204, and a control structure A1205.

[0015] The control structure A1205 comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces A7; the positive electrode feed line A1203 is connected with the negative electrode of the varactor diode 73 of the multifractal structure active frequency selective surface A7, the negative electrode feed line A1204 is connected with the positive electrode of the varactor diode 73 of the multifractal structure active frequency selective surface A7, and the external bias power supply A1201 is connected with the positive electrode feed line A1203 and the negative electrode feed line A1204 through the circuit lead A1202.

[0016] The control structure B1305 comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces B9; the positive electrode feed line B1303 is connected with the negative electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, the negative electrode feed line B1304 is connected with the positive electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, and the external bias power supply B1301 is connected with the positive electrode feed line B1303 and the negative electrode feed line B1304 through the circuit lead B1302.

[0017] The control structure B1305 comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces B9; the positive electrode feed line B1303 is connected with the negative electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, the negative electrode feed line B1304 is connected with the positive electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, and the external bias power supply B1301 is connected with the positive electrode feed line B1303 and the negative electrode feed line B1304 through the circuit lead B1302.

[0018] As a preferred mode, the frequency selective surface FSS on the cross structure resistance type frequency selective surface 1 and the square ring structure resistance type frequency selective surface 4 is selected from one of tin-doped indium oxide, conductive carbon paste, indium tin oxide, graphene conductive paste, carbon nanotube conductive paste and conductive silver paste; the frequency selective surface FSS on the multifractal structure active frequency selective surface A7 and the multifractal structure active frequency selective surface B9 is selected from one of copper, aluminum, gold and silver.

[0019] As a preferred mode, the materials of the first layer medium layer 2, the second layer medium layer 3, the third layer medium layer 5, the fourth layer medium layer 6, the fifth layer medium layer 8 and the sixth layer medium layer 10 are selected from one of polymethyl methacrylimide foam, polyimide foam, polyurethane foam, polyvinyl chloride foam, phenolic foam plastic, polyethylene foam plastic and polyethylene terephthalate plastic.

[0020] As a preferred mode, the material of the metal back plate 11 is selected from one of copper, aluminum, gold and silver.

[0021] The second object of the application is to provide a preparation method of the active regulation super surface based wideband stealth material.

[0022] 1. Selecting a substrate material, and using a magnetron sputtering method to coat a resistance film on the surface of the substrate material;

[0023] ②Surface resistance of continuous resistance film is tested by using a four-probe tester, and a series of continuous resistance films with resistance value of 140-160 Ω / sq are prepared;

[0024] ③Cross structure resistance type frequency selective surface 1 with resistance value range of 140-160 Ω / sq and square ring structure resistance type frequency selective surface 4 with resistance value range of 140-160 Ω / sq are respectively prepared by laser etching technology on the series of resistance films;

[0025] ④Multi-fractal structure active frequency selective surface A7 and multi-fractal structure active frequency selective surface B9 are respectively prepared by selecting a substrate material, pre-plating a lead-tin resist layer on the multi-fractal structure part by using a printed circuit board process, and then chemically etching the remaining metal without pre-plating the lead-tin resist layer;

[0026] ⑤The varactor diode 73 and the patch resistor 74 are welded at the specified positions of the multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9 by using tin soldering;

[0027] ⑥The layers of materials are sequentially bonded into a whole by selecting a dielectric material, and a metal back plate 11 is bonded at the bottom;

[0028] ⑦Finally, the wideband stealth material based on the active control metasurface is obtained through cutting and shaping.

[0029] The third object of the present application is to provide a preparation method of the wideband stealth material based on the active control metasurface, comprising the following steps:

[0030] ①The cross structure resistance type frequency selective surface 1 and the square ring structure resistance type frequency selective surface 4 are respectively obtained by selecting a substrate material and using silk screen printing;

[0031] ②Surface resistance of continuous resistance film is tested by using a four-probe tester, and a series of continuous resistance films with resistance value of 140-160 Ω / sq are prepared;

[0032] ③Multi-fractal structure active frequency selective surface A7 and multi-fractal structure active frequency selective surface B9 are respectively prepared by selecting a substrate material, pre-plating a lead-tin resist layer on the multi-fractal structure part by using a printed circuit board process, and then chemically etching the remaining metal without pre-plating the lead-tin resist layer;

[0033] ④The varactor diode and the patch resistor are welded at the specified positions of the multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9 by using tin soldering;

[0034] ⑤The layers of materials are sequentially bonded into a whole by selecting a dielectric material, and a metal back plate 11 is bonded at the bottom;

[0035] VI. Finally, the wideband invisibility material based on the active regulation super surface is obtained by cutting and shaping.

[0036] The application has the advantages that compared with the traditional passive absorber or low-frequency active absorber structure, the application solves the problem that the low-frequency wave absorption of the passive absorber and the high-frequency wave absorption of the active absorber are difficult to be realized simultaneously. The cross and square ring two-structure resistance type frequency selective surface is cascaded, so that the resistance type frequency selective surface can be highly matched with the wave impedance of the free space at high frequencies, a wide absorption frequency band is generated, the central symmetry pattern is adopted, so that the resistance type frequency selective surface has polarization stability. The double-layer multi-fractal structure FSS is adopted, the varactor diode and the patch resistor are loaded, so that the resistance type frequency selective surface can realize active tuning of the absorption frequency band at low frequencies. The simulation results show that the design absorption frequency band is 0.52-24.97 GHz, the first active regulation absorption band is 0.52-1.62 GHz, the second fixed absorption band is 1.62-24.97 GHz, the relative bandwidth is 191.8%, the working range covers the P to K band, the profile thickness is thin, the mass is light, and the processing is simple. The sample is processed and prepared, the test results show that the experimental and simulation results are consistent, and the application has application potential in electromagnetic regulation, radar stealth and the like. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a schematic diagram of the overall structure of the application;

[0038] Figure 2 is a schematic diagram of the cross structure resistance type frequency selective surface of the application;

[0039] Figure 3 is a schematic diagram of the square ring structure resistance type frequency selective surface of the application;

[0040] Figure 4 is a schematic diagram of the multi-fractal structure active frequency selective surface of the application;

[0041] Figure 5 is a schematic diagram of the multi-fractal structure active frequency selective surface of the application; Figure 4

[0042] Figure 6 is a schematic diagram of the control structure A of the application;

[0043] Figure 7 is a schematic diagram of the control structure B of the application;

[0044] Figure 8 is a graph showing the change of the normalized impedance real part and imaginary part of different varactor diode capacitance values in the embodiment 4 of the application.

[0045] Figure 9 ​is a graph of the change of the reflection coefficient curve of different capacitance values of the variable capacitance diode of embodiment 4 of the present application.

[0046] Figure 10 is a graph of the change of the absorption rate curve of the incident angle under TE polarization of embodiment 4 of the present application.

[0047] Figure 11 is a graph of the change of the absorption rate curve of the incident angle under TM polarization of embodiment 4 of the present application.

[0048] 1-cross structure resistive frequency selective surface, 101-cross structure, 2-first layer dielectric layer, 3-second layer dielectric layer, 4-square ring structure resistive frequency selective surface, 41-inner square ring, 42-outer square ring; 5-third layer dielectric layer, 6-fourth layer dielectric layer, 7-multifractal structure active frequency selective surface A, 71-fractal unit; 711-bending line, 712-ladder structure, 72-strip structure, 73-variable capacitance diode, 74-surface mount resistor; 8-fifth layer dielectric layer, 9-multifractal structure active frequency selective surface B, 10-sixth layer dielectric layer, 11-metal back plate, 1201-external bias power supply A, 1202-circuit wire A, 1203-positive electrode feeding circuit A, 1204-negative electrode feeding circuit A, 1205-control structure A, 1301-external bias power supply B, 1302-circuit wire B, 1303-positive electrode feeding circuit B, 1304-negative electrode feeding circuit B, 1305-control structure B. DETAILED DESCRIPTION

[0049] The present application is herein described, by way of example only, with reference to certain embodiments thereof. It is construed that persons skilled in the art can easily understand other advantages and functions of the present application from the contents disclosed in the present description. The present application can also be implemented or applied by other different embodiments, and each detail in the present description can be modified or changed based on different viewpoints and applications without departing from the spirit of the present application.

[0050] Embodiment 1

[0051] The embodiment provides a wideband stealth material based on active regulation of a super surface, which comprises a plurality of square structure layers with the same size and center overlap stacked in sequence from top to bottom, namely, a cross structure resistance type frequency selective surface 1, a first layer of dielectric layer 2, a second layer of dielectric layer 3, a square ring structure resistance type frequency selective surface 4, a third layer of dielectric layer 5, a fourth layer of dielectric layer 6, a multi-fractal structure active frequency selective surface A 7, a fifth layer of dielectric layer 8, a multi-fractal structure active frequency selective surface B 9, a sixth layer of dielectric layer 10 and a metal back plate 11; the cross structure resistance type frequency selective surface 1 and the square ring structure resistance type frequency selective surface 4 are both center-symmetric patterns, and the multi-fractal structure active frequency selective surface B 9 is obtained by counterclockwise rotation of the multi-fractal structure active frequency selective surface A 7 by 90 degrees; definition: the direction from bottom to top is the positive direction of the z axis, and the direction in which the strip structure 72 of the multi-fractal structure active frequency selective surface A 7 extends is the x axis; the y axis is perpendicular to the z axis and the x axis;

[0052] The cross structure resistance type frequency selective surface 1 comprises four cross structures 101 which are not connected to each other and arranged in two rows and two columns; the four cross structures 101 have the same size and are center-symmetric, and have the same gap between adjacent cross structures;

[0053] The square ring structure resistance type frequency selective surface 4 comprises two center-overlapping square ring structures, namely, an inner square ring 41 and an outer square ring 42;

[0054] The multi-fractal structure active frequency selective surface A 7 comprises four fractal units 71 and two strip structures 72, and the strip structure 72 extends along the x axis; each fractal unit 71 is perpendicular to the strip structure 72; the direction perpendicular to the strip structure 72 is the y direction, and the four fractal units 71 are located between the two strip structures 72.

[0055] The four fractal units 71 are mirror-symmetric about the x axis and the y axis, and each fractal unit 71 comprises a curved line 711 connected with the strip structure 72 and a trapezoidal structure 712 connected with the curved line 711; a varactor diode 73 is arranged between two fractal units 71 adjacent in the y axis direction on the left side, and a chip resistor 74 is arranged between two fractal units 71 adjacent in the y axis direction on the right side.

[0056] The multi-fractal structure active frequency selective surface B 9 is obtained by counterclockwise rotation of the multi-fractal structure active frequency selective surface A 7 by 90 degrees around the z axis;

[0057] Further comprising a control system for realizing regulation and control of an electromagnetic wave absorption frequency band range below 2GHz.

[0058] The control system comprises an external bias power supply A1201, a circuit wire A1202, a positive electrode feeding circuit A1203, a negative electrode feeding circuit A1204 and a control structure A1205.

[0059] The control structure A1205 comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces A7; the positive electrode feeding circuit A1203 is connected with the negative electrode of the varactor diode 73 of the multifractal structure active frequency selective surface A7, the negative electrode feeding circuit A1204 is connected with the positive electrode of the varactor diode 73 of the multifractal structure active frequency selective surface A7, and the external bias power supply A1201 is connected with the positive electrode feeding circuit A1203 and the negative electrode feeding circuit A1204 through the circuit lead A1202.

[0060] The control structure B1305 comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces B9; the positive electrode feeding circuit B1303 is connected with the negative electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, the negative electrode feeding circuit B1304 is connected with the positive electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, and the external bias power supply B1301 is connected with the positive electrode feeding circuit B1303 and the negative electrode feeding circuit B1304 through the circuit lead B1302.

[0061] The control structure B1305 comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces B9; the positive electrode feeding circuit B1303 is connected with the negative electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, the negative electrode feeding circuit B1304 is connected with the positive electrode of the varactor diode 73 of the multifractal structure active frequency selective surface B9, and the external bias power supply B1301 is connected with the positive electrode feeding circuit B1303 and the negative electrode feeding circuit B1304 through the circuit lead B1302.

[0062] The frequency selective surface FSS on the cross structure resistive frequency selective surface 1 and the square ring structure resistive frequency selective surface 4 is selected from one of tin-doped indium oxide, conductive carbon paste, indium tin oxide, graphene conductive paste, carbon nanotube conductive paste and conductive silver paste; the frequency selective surface FSS on the multifractal structure active frequency selective surface A7 and the multifractal structure active frequency selective surface B9 is selected from one of copper, aluminum, gold and silver.

[0063] The material of the first layer dielectric layer 2, the second layer dielectric layer 3, the third layer dielectric layer 5, the fourth layer dielectric layer 6, the fifth layer dielectric layer 8 and the sixth layer dielectric layer 10 is selected from one of polymethyl methacrylimide foam, polyimide foam, polyurethane foam, polyvinyl chloride foam, phenolic foam plastic, polyethylene foam plastic and polyethylene terephthalate plastic.

[0064] The material of the metal back plate 11 is selected from one of copper, aluminum, gold and silver.

[0065] Embodiment 2

[0066] The embodiment provides a preparation method of the wide-band stealth material based on the active regulation super surface.

[0067] ①A substrate material is selected, and a resistive film is plated on the surface of the substrate material by using a magnetron sputtering method;

[0068] ②Surface resistance of continuous resistance film is tested by using four-probe tester to prepare series of continuous resistance films with resistance value of 140-160 Ω / sq;

[0069] ③Cross structure resistance type frequency selective surface 1 with resistance value range of 140-160 Ω / sq and square ring structure resistance type frequency selective surface 4 with resistance value range of 140-160 Ω / sq are prepared by laser etching technology for patterning etching on series of resistance films;

[0070] ④Multifractal structure active frequency selective surface 7 and multifractal structure active frequency selective surface 9 are prepared by selecting substrate material, pre-plating a layer of lead-tin resist layer on the multifractal structure part by using printed circuit board technology, and then chemically etching the remaining metal without pre-plating the lead-tin resist layer;

[0071] ⑤Varactor diode 73 and patch resistor 74 are welded at specified positions of multifractal structure active frequency selective surface A7 and multifractal structure active frequency selective surface B9 by using tin soldering method;

[0072] ⑥Each layer of material is bonded in sequence to become a whole by selecting dielectric material, and a metal back plate 11 is bonded at the bottom;

[0073] ⑦Finally, the wideband stealth material based on active control metasurface is obtained through cutting and shaping.

[0074] Embodiment 3

[0075] The embodiment provides a preparation method of a wideband stealth material based on active control metasurface, comprising the following steps:

[0076] ①Cross structure resistance type frequency selective surface FSS1 and square ring structure resistance type frequency selective surface FSS4 are obtained by selecting substrate material and respectively through silk screen printing;

[0077] ②Surface resistance of continuous resistance film is tested by using four-probe tester to prepare series of continuous resistance films with resistance value of 140-160 Ω / sq;

[0078] ③Multifractal structure active frequency selective surface A7 and multifractal structure active frequency selective surface B9 are prepared by selecting substrate material, pre-plating a layer of lead-tin resist layer on the multifractal structure part by using printed circuit board technology, and then chemically etching the remaining metal without pre-plating the lead-tin resist layer;

[0079] ④Varactor diode and patch resistor are welded at specified positions of multifractal structure active frequency selective surface A7 and multifractal structure active frequency selective surface B9 by using tin soldering method;

[0080] 5. Selecting medium materials, bonding each layer of materials in sequence to form a whole, and bonding a metal back plate 11 at the bottom;

[0081] 6. Finally, through cutting and shaping, a wideband stealth material based on actively controlled metasurface is obtained.

[0082] Example 4

[0083] The embodiment provides a wideband stealth material based on actively controlled metasurface and a preparation method.

[0084] 1. Selecting 0.125mm thick PET medium sheet as the first layer of medium layer 2 and the third layer of medium layer 5, with a dielectric constant of 3 and a loss tangent of 0.016, using a magnetron sputtering method to coat ITO film on the surface of the PET sheet,

[0085] 2. The surface resistance of the continuous resistance film is tested by a four-probe tester, and a continuous resistance film with a resistance of 140-160Ω / sq is prepared;

[0086] 3. The laser etching technology is used to pattern and etch the series of ITO resistance films, and a cross-shaped structure resistance type frequency selective surface 1 with a resistance range of 140-160Ω / sq and a square ring structure resistance type frequency selective surface 4 with a resistance range of 140-160Ω / sq are prepared;

[0087] 4. Selecting 0.508mm thick Rogers 4350B medium substrate as the fifth layer of medium layer 8, using printed circuit board technology to pre-plate lead-tin resist layer on the upper and lower layers of the substrate, and then chemically etching the remaining copper foil, to prepare a multifractal structure active frequency selective surface A7 and a multifractal structure active frequency selective surface B9;

[0088] 5. The varactor diode and the chip resistor are welded to the multifractal structure active frequency selective surface A7 and the multifractal structure active frequency selective surface B9 at specified positions by using tin soldering method.

[0089] 5. Selecting PMI foam with a dielectric constant of 1.15 and a loss tangent of 0.0037 as the second layer of medium layer, the fourth layer of medium layer and the sixth layer of medium layer, with thicknesses of 4.6mm, 10mm and 5mm respectively, and using epoxy resin to bond each layer of materials in sequence to form a whole, and bonding a 0.035mm thick copper film at the bottom.

[0090] 5. Finally, through cutting and shaping, a wideband stealth material based on actively controlled metasurface with an area of 300mm×300mm is prepared.

[0091] The wideband stealth material based on actively controlled metasurface of the embodiment has the following detailed structure parameters:

[0092]

[0093] The key technologies of this solution are: a low-frequency tunable ultra-wideband microwave absorber is proposed to optimize electromagnetic wave absorption performance. This structure uses a resistive frequency selective surface with a cross and square ring structure to achieve good impedance matching in a high-frequency broadband, improving absorption performance at high frequencies. A double-layer multi-fractal active frequency selective surface is loaded with varactor diodes and chip resistors to achieve tunable absorption characteristics at low frequencies. PMI foam is used to separate the structures, reducing overall weight and the impact of interlayer electromagnetic coupling on absorption characteristics. The resistive frequency selective surface unit of this microwave absorber adopts a centrosymmetric structure. The multi-fractal frequency selective surface can be rotated 90 degrees, resulting in good polarization stability.

[0094] like Figure 8 As shown in the figure, under normal incidence, when the capacitance of the varactor diode increases from 0.53pf to 7.2pf, the real part of the normalized impedance of the structure basically fluctuates around 1, and the imaginary part basically fluctuates around 0, indicating that the structure can achieve good matching with the free space wave impedance within a wide frequency range and has excellent absorption performance.

[0095] like Figure 9 As shown in the figure, under normal incidence, when the capacitance of the varactor diode increases from 0.53pf to 7.2pf, the structure produces five resonance peaks. The first resonance peak can be dynamically tuned within the range of 0.52-1.62GHz, and the remaining four resonance peaks are at 3.29GHz, 11.8GHz, 17.87GHz, and 23.22GHz. In addition, the fixed bandwidth below -10dB ranges from 1.62-24.97GHz, demonstrating ultra-wideband microwave absorption characteristics.

[0096] like Figure 10 As shown in the figure, in the TE polarization mode, when the incident angle varies in the range of 0°-45°, the absorption rate decays with the increase of the incident angle. When the incident angle varies between 0-30°, the absorption rate of most frequency bands is above 90%, until the incident angle increases to 45°, the absorption rate of some frequency bands drops to about 85%.

[0097] like Figure 11 As shown in the figure, in the TM polarization mode, when the incident angle varies from 0° to 45°, the low-frequency absorption peak shifts slightly toward the high frequency, but remains stable overall, and the absorption rate is almost always maintained above 90%. This proves that the proposed absorber has good angular stability in the range of 0-45°.

[0098] The above examples only illustrate the principles of the present application and its efficacy, and are not intended to limit the application. Any modification or change on the above examples made by any person skilled in the art, without departing from the spirit and scope of the present application, shall be covered by the claims of the present application.

Claims

1. A broadband invisibility material based on actively regulated metasurface, characterized in that, It comprises a plurality of square structure layers with the same size and center overlapping, which are stacked from top to bottom in turn, namely: cross structure resistive frequency selective surface (1), first layer dielectric layer (2), second layer dielectric layer (3), square ring structure resistive frequency selective surface (4), third layer dielectric layer (5), fourth layer dielectric layer (6), multifractal structure active frequency selective surface A (7) fifth layer dielectric layer (8), multifractal structure active frequency selective surface B (9), sixth layer dielectric layer (10), metal back plate (11); the cross structure resistive frequency selective surface (1) and the square ring structure resistive frequency selective surface (4) are both center-symmetric patterns, and the multifractal structure active frequency selective surface B (9) is obtained by counterclockwise rotation of the multifractal structure active frequency selective surface A (7) by 90°; Definition: the direction from bottom to top is the positive direction of the z-axis, and the direction in which the strip structure (72) of the multifractal structure active frequency selective surface A (7) extends is the x-axis; the y-axis is perpendicular to the z-axis and the x-axis; The cross structure resistive frequency selective surface (1) comprises two rows and two columns of four cross structures (101) not connected to each other; the four cross structures (101) are the same in size and are center-symmetric, and have the same gap between adjacent cross structures (101); The square ring structure resistive frequency selective surface (4) comprises two center-overlapping square ring structures: an inner square ring (41) and an outer square ring (42); The multifractal structure active frequency selective surface A (7) comprises four fractal units (71) and two strip structures (72), and the strip structure (72) extends along the x-axis; each fractal unit (71) is perpendicular to the strip structure (72); the direction perpendicular to the strip structure (72) is the y direction, and the four fractal units (71) are located between the two strip structures (72), The four fractal units (71) are respectively mirror-symmetric about the x-axis and the y-axis, each fractal unit (71) comprises: a curved line (711) connected with the strip structure (72), and a trapezoidal structure (712) connected with the curved line (711); a varactor diode (73) is arranged between the two fractal units (71) adjacent along the y-axis direction on the left side, and a chip resistor (74) is arranged between the two fractal units (71) adjacent along the y-axis direction on the right side, The multifractal structure active frequency selective surface B (9) is obtained by counterclockwise rotation of the multifractal structure active frequency selective surface A (7) by 90° around the z-axis; It also comprises a control system for realizing the regulation and control of the electromagnetic wave absorption frequency band range below 2GHz.

2. The active metasurface-based broadband invisibility material of claim 1, wherein: The control system comprises: an external bias power supply A (1201), a circuit wire A (1202), a positive electrode feeding circuit A (1203), a negative electrode feeding circuit A (1204), and a control structure A (1205). The control structure A (1205) comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces A (7); the positive electrode feeding circuit A (1203) is connected with the negative electrode of the varactor diode (73) of the multifractal structure active frequency selective surface A (7), the negative electrode feeding circuit A (1204) is connected with the positive electrode of the varactor diode (73) of the multifractal structure active frequency selective surface A (7), and the external bias power supply A (1201) is connected with the positive electrode feeding circuit A (1203) and the negative electrode feeding circuit A (1204) through the circuit lead A (1202) respectively; It also comprises an external bias power supply B (1301), a circuit lead B (1302), a positive electrode feeding circuit B (1303), a negative electrode feeding circuit B (1304) and a control structure B (1305); The control structure B (1305) comprises a plurality of periodically arranged multifractal structure active frequency selective surfaces B (9); the positive electrode feeding circuit B (1303) is connected with the negative electrode of the varactor diode (73) of the multifractal structure active frequency selective surface B (9), the negative electrode feeding circuit B (1304) is connected with the positive electrode of the varactor diode (73) of the multifractal structure active frequency selective surface B (9), and the external bias power supply B (1301) is connected with the positive electrode feeding circuit B (1303) and the negative electrode feeding circuit B (1304) through the circuit lead B (1302) respectively.

3. The active metasurface-based broadband invisibility material of claim 1, wherein: The frequency selective surface FSS on the cross structure resistive frequency selective surface (1) and the square ring structure resistive frequency selective surface (4) is selected from one of tin-doped indium oxide, conductive carbon paste, indium tin oxide, graphene conductive paste, carbon nanotube conductive paste and conductive silver paste; the frequency selective surface FSS on the multifractal structure active frequency selective surface A (7) and the multifractal structure active frequency selective surface B (9) is selected from one of copper, aluminum, gold and silver.

4. The active metasurface-based broadband invisibility material of claim 1, wherein: The material of the first layer dielectric layer (2), the second layer dielectric layer (3), the third layer dielectric layer (5), the fourth layer dielectric layer (6), the fifth layer dielectric layer (8) and the sixth layer dielectric layer (10) is selected from one of polymethyl methacrylimide foam, polyimide foam, polyurethane foam, polyvinyl chloride foam, phenolic foam plastic, polyethylene foam plastic and polyethylene terephthalate plastic.

5. The active metasurface-based broadband invisibility material of claim 1, wherein: The material of the metal back plate (11) is selected from one of copper, aluminum, gold and silver.

6. The method for preparing the wideband invisibility material based on the active modulation super surface according to any one of claims 1 to 5, characterized in that The method comprises the following steps: ①A substrate material is selected, and a resistive film is plated on the surface of the substrate material by using a magnetron sputtering method; ②A four-probe tester is used to test the surface resistance of the continuous resistive film, and a series of continuous resistive films with a resistance value of 140-160 Ω / sq are prepared; ③A laser etching technology is used to perform patterned etching on the series of resistive films, and a cross structure resistive frequency selective surface (1) with a resistance value range of 140-160 Ω / sq and a square ring structure resistive frequency selective surface (4) with a resistance value range of 140-160 Ω / sq are prepared respectively; (4) Selecting substrate material, using printed circuit board technology to pre-plate a layer of lead-tin resist layer on the part of the multi-fractal structure, and then chemically etching the rest of the metal without pre-plating lead-tin resist layer to prepare multi-fractal structure active frequency selective surface A (7) and multi-fractal structure active frequency selective surface B (9) respectively; (5) Using tin soldering method, soldering varactor diode (73) and patch resistor (74) at the specified position of multi-fractal structure active frequency selective surface A (7) and multi-fractal structure active frequency selective surface B (9); (6) Selecting dielectric material, bonding each layer of material in sequence to form a whole, and bonding metal back plate (11) at the bottom; (7) Finally, through cutting and shaping, the wideband stealth material based on active regulation super surface is obtained.

7. The method for preparing the broadband invisibility material based on the active metasurface of claim any one of claims 1 to 5, characterized in that The steps include: (1) Selecting substrate material, respectively obtaining cross structure resistance type frequency selective surface (1) and square ring structure resistance type frequency selective surface (4) by silk screen printing; (2) Using four-probe tester to test the surface resistance of continuous resistance film, preparing a series of continuous resistance films with resistance of 140-160Ω / sq; (3) Selecting substrate material, using printed circuit board technology to pre-plate a layer of lead-tin resist layer on the part of the multi-fractal structure, and then chemically etching the rest of the metal without pre-plating lead-tin resist layer to prepare multi-fractal structure active frequency selective surface A (7) and multi-fractal structure active frequency selective surface B (9) respectively; (4) Using tin soldering method, soldering varactor diode and patch resistor at the specified position of multi-fractal structure active frequency selective surface A (7) and multi-fractal structure active frequency selective surface B (9); (5) Selecting dielectric material, bonding each layer of material in sequence to form a whole, and bonding metal back plate (11) at the bottom; (6) Finally, through cutting and shaping, the wideband stealth material based on active regulation super surface is obtained.

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