Broadband stealth material based on active regulation and control metasurface and preparation method

Abstract

The invention provides a broadband stealth material based on an active regulation and control metasurface and a preparation method. A cross structure resistive frequency selection surface, a first dielectric layer, a second dielectric layer, a square ring structure resistive frequency selection surface, a third dielectric layer, a fourth dielectric layer, a multi-fractal structure active frequency selection surface, a fifth dielectric layer, a multi-fractal structure active frequency selection surface, a sixth dielectric layer and a metal backboard are sequentially arranged from top to bottom. The problem that low-frequency wave absorption of a passive absorber and high-frequency wave absorption of an active absorber are difficult to realize at the same time is solved. Resistance type frequency selective surfaces of a cross structure and a square ring structure are adopted for cascade connection, a wide absorption frequency band is generated at high frequency, and a centrosymmetric pattern is adopted, so that polarization stability is achieved. A double-layer multi-fractal structure frequency selective surface is adopted, and a variable capacitance diode and a chip resistor are loaded, so that active tuning of an absorption frequency band can be realized at low frequency. The working range covers the P-K wave band, and the application potential is achieved in the aspects of electromagnetic regulation and control, radar stealth and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and relates to a broadband stealth material based on actively regulated metasurfaces and a preparation method thereof, and is mainly used for radar camouflage and stealth of ground mobile target components and aircraft target components. Background Art

[0002] Microwave absorbers are periodic structure stealth materials that can absorb incident electromagnetic waves in a specific frequency band. They are widely used in electromagnetic shielding, antennas, military stealth, etc. In radar stealth, in order to effectively reduce or suppress RCS, microwave absorbers often need to have broadband absorption characteristics. In recent years, as radar detection technology has gradually developed towards broadband and low frequency, the operating frequency of radar detection equipment has been expanded to the Ultrahigh-Frequency (UHF) Band below 2 GHz, which has put forward more stringent requirements on the absorption bandwidth of microwave absorbers. The present invention can solve the difficult problems of low-frequency wave absorption of traditional passive passive absorbers, broadband wave absorption of low-frequency active active absorbers, and stability design of wave absorption polarization angles through the design of broadband stealth materials based on active control of metasurfaces, thereby improving the radar stealth performance of the target.

[0003] At present, most of the publicly designed passive broadband absorbing structures cover above the C band, and it is difficult to cover the lower frequency P, L, and S bands, and there is a disadvantage of large thickness; active absorbing structures can achieve absorption band tuning at low frequencies, but at the same time it is difficult to take into account high-frequency absorbing performance. Therefore, designing and preparing an absorber that works in the PK ultra-wideband range, has excellent angle stability, low profile thickness, light weight, and stable absorbing performance is the focus of this field. Summary of the invention

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

[0005] The structural design and preparation method provided by the present invention can enable this type of absorbing structure to achieve ultra-wideband electromagnetic wave absorption effects in the P, L, S, C, X, Ku, and K bands, and has the advantages of miniaturization, low profile, polarization insensitivity, good stability in a large angular range, simple preparation method, and light weight.

[0006] To achieve the above-mentioned purpose of the invention, the technical solution of the present invention is as follows:

[0007] A broadband stealth material based on an actively controlled metasurface comprises a plurality of square structure layers of the same size and coincident centers stacked in sequence from top to bottom, which are: a cross structure resistive frequency selective surface 1, a first dielectric layer 2, a second dielectric layer 3, a square ring structure resistive frequency selective surface 4, a third dielectric layer 5, a fourth dielectric layer 6, a multi-fractal structure active frequency selective surface A7, a fifth dielectric layer 8, a multi-fractal structure active frequency selective surface B9, a sixth dielectric layer 10, and a metal back plate 11; the cross structure resistive frequency selective surface 1 and the square ring structure resistive frequency selective surface 4 are both centrally symmetrical figures, and the multi-fractal structure active frequency selective surface B9 is obtained by rotating the multi-fractal structure active frequency selective surface A7 counterclockwise by 90°; definition: the direction from bottom to top is the positive direction of the z-axis, the direction in which the long strip structure 72 of the multi-fractal structure active frequency selective surface A7 extends is the x-axis; the y-axis is perpendicular to the z-axis and the x-axis;

[0008] The cross-structure resistive frequency selective surface 1 comprises four cross structures 101 in two rows and two columns that are not connected to each other; the four cross structures 101 are of the same size and symmetrical about the center, and there is the same gap between adjacent cross structures;

[0009] The square ring structure resistive frequency selective surface 4 includes two square ring structures with overlapping centers: an inner square ring 41 and an outer square ring 42;

[0010] The multi-fractal structure active frequency selective surface A7 includes four fractal units 71 and two long strip structures 72. 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. 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 bending line 711 connected to the long strip structure 72, and a trapezoidal structure 712 connected to the bending line 711; a varactor diode 73 is provided between the two adjacent fractal units 71 on the left along the y-axis direction, and a chip resistor 74 is provided between the two adjacent fractal units 71 on the right along the y-axis direction.

[0012] The multi-fractal structure active frequency selective surface B9 is obtained by rotating the multi-fractal structure active frequency selective surface A7 by 90° counterclockwise around the z-axis;

[0013] It also includes a control system for achieving regulation of the electromagnetic wave absorption frequency band range below 2 GHZ.

[0014] As a preferred embodiment, the control system includes: an external bias power supply A1201, a circuit conductor A1202, a positive feed circuit A1203, a negative feed circuit A1204, and a control structure A1205;

[0015] The control structure A1205 includes a plurality of periodically arranged multi-fractal structure active frequency selective surfaces A7; a positive electrode feeding circuit A1203 is connected to the cathode of the varactor diode 73 of the multi-fractal structure active frequency selective surface A7, a negative electrode feeding circuit A1204 is connected to the anode of the varactor diode 73 of the multi-fractal structure active frequency selective surface A7, and an external bias power supply A1201 is respectively connected to the positive electrode feeding circuit A1203 and the negative electrode feeding circuit A1204 through a circuit conductor A1202;

[0016] It also includes an external bias power supply B1301, a circuit conductor B1302, a positive feed circuit B1303, a negative feed circuit B1304, and a control structure B1305;

[0017] The control structure B1305 includes a plurality of periodically arranged multi-fractal structure active frequency selective surfaces B9; the positive feeding circuit B1303 is connected to the cathode of the varactor diode 73 of the multi-fractal structure active frequency selective surface B9, the negative feeding circuit B1304 is connected to the anode of the varactor diode 73 of the multi-fractal structure active frequency selective surface B9, and the external bias power supply B1301 is respectively connected to the positive feeding circuit B1303 and the negative feeding circuit B1304 through the circuit conductor B1302.

[0018] As a preferred embodiment, 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 multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9 is selected from one of copper, aluminum, gold, and silver.

[0019] As a preferred embodiment, the material of the first dielectric layer 2, the second dielectric layer 3, the third dielectric layer 5, the fourth dielectric layer 6, the fifth dielectric layer 8, and the sixth dielectric layer 10 is selected from one of polymethacrylimide foam, polyimide foam, polyurethane foam, polyvinyl chloride foam, phenolic foam plastic, polyethylene foam plastic, and polyethylene terephthalate plastic.

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

[0021] The second object of the present invention is to provide a method for preparing the broadband stealth material based on active control metasurface, comprising the following steps:

[0022] ① Select the substrate material and use the magnetron sputtering method to plate the resistor film on the surface of the substrate material;

[0023] ② Use a four-probe tester to test the surface resistance of the continuous resistor film and prepare a series of continuous resistor films with a resistance value of 140-160Ω / sq;

[0024] ③ Patterning is performed on the series of resistor films by laser etching technology to prepare a cross-structure resistive frequency selective surface 1 with a resistance range of 140-160Ω / sq and a square-ring structure resistive frequency selective surface 4 with a resistance range of 140-160Ω / sq;

[0025] ④ Select substrate materials, use printed circuit board technology to pre-plate a layer of lead-tin anti-corrosion layer on the multi-fractal structure part, and then chemically corrode the remaining metal that is not pre-plated with the lead-tin anti-corrosion layer to prepare multi-fractal structure active frequency selective surface A7 and multi-fractal structure active frequency selective surface B9 respectively;

[0026] ⑤ Using the soldering method, the varactor diode 73 and the chip resistor 74 are soldered to the designated positions of the multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9;

[0027] ⑥ Select dielectric materials, bond each layer of materials in sequence to form a whole, and bond a metal back plate 11 at the bottom;

[0028] ⑦Finally, through cutting and shaping, a broadband stealth material based on actively controlled metasurface is obtained.

[0029] The third object of the present invention is to provide a method for preparing the broadband stealth material based on active control metasurface, comprising the following steps:

[0030] ① Select substrate materials and obtain a cross-structure resistive frequency selective surface 1 and a square ring-structure resistive frequency selective surface 4 by screen printing;

[0031] ② Use a four-probe tester to test the surface resistance of the continuous resistor film and prepare a series of continuous resistor films with a resistance value of 140-160Ω / sq;

[0032] ③ Select substrate materials, use printed circuit board technology to pre-plate a layer of lead-tin anti-corrosion layer on the multi-fractal structure part, and then chemically corrode the remaining metal that is not pre-plated with the lead-tin anti-corrosion layer to prepare multi-fractal structure active frequency selective surface A7 and multi-fractal structure active frequency selective surface B9 respectively;

[0033] ④ Using the soldering method, the varactor diode and the chip resistor are soldered to the designated positions of the multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9;

[0034] ⑤ Select dielectric materials, bond each layer of materials in sequence to form a whole, and bond a metal back plate 11 at the bottom;

[0035] ⑥Finally, through cutting and shaping, a broadband stealth material based on actively controlled metasurface is obtained.

[0036] The beneficial effects of the present invention are as follows: compared with the traditional passive absorber or low-frequency active absorber structure, the present invention solves the problem that it is difficult to achieve low-frequency wave absorption of the passive passive absorber and high-frequency wave absorption of the active active absorber at the same time. The resistive frequency selective surface cascade of the cross and square ring structures is adopted to make it highly matched with the free space wave impedance at high frequency, produce a wide absorption band, and adopt a central symmetric pattern to make it have polarization stability. The double-layer multi-fractal structure FSS is adopted, and the varactor diode and the patch resistor are loaded, so that it can realize the active tuning of the absorption band at low frequency. The simulation results show that the absorption band of the design is 0.52~24.97GHz, of which the first actively regulated absorption band has a regulation range of 0.52-1.62GHz, and the second fixed absorption band is 1.62-24.97GHz. The relative bandwidth is 191.8%, and the working range covers the P to K bands, and the profile thickness is thin, the weight is light, and the processing is simple. The samples were processed and prepared, and the experimental test results showed that the experimental and simulation results were consistent, and it has application potential in electromagnetic control, radar stealth, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0038] Figure 2 It is a schematic diagram of the structure of a cross-structure resistive frequency selective surface of the present invention;

[0039] Figure 3 It is a schematic diagram of the structure of the square ring structure resistive frequency selective surface of the present invention;

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

[0041] Figure 5 yes Figure 4 Structural schematic diagram of the bending line unit and the trapezoidal structure unit;

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

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

[0044] Figure 8 This is a graph showing the change in normalized impedance real and imaginary part curves for different varactor diode capacitances in Example 4 of the present invention.

[0045] Fig. 94 is a graph showing the change in reflection coefficient curves of different varactor diode capacitance values ​​according to Example 4 of the present invention.

[0046] Fig.10 This is a graph showing the change in the incident angle versus absorptivity curve under TE polarization of Example 4 of the present invention.

[0047] Fig.11 This is a graph showing the change in the incident angle versus absorptivity curve under TM polarization of Example 4 of the present invention.

[0048] 1- cross structure resistive frequency selective surface, 101- cross structure, 2- first dielectric layer, 3- second dielectric layer, 4- square ring structure resistive frequency selective surface, 41- inner square ring, 42- outer square ring; 5- third dielectric layer, 6- fourth dielectric layer, 7- multi-fractal structure active frequency selective surface A, 71- fractal unit; 711- curved line, 712- trapezoidal structure, 72- long strip structure, 73- varactor diode, 74- chip resistor; 8- fifth dielectric layer, 9-multi-fractal structure active frequency selective surface B, 10-sixth dielectric layer, 11-metal backplane, 1201-external bias power supply A, 1202-circuit conductor A, 1203-positive feed line A, 1204-negative feed line A, 1205-control structure A, 1301-external bias power supply B, 1302-circuit conductor B, 1303-positive feed line B, 1304-negative feed line B, 1305-control structure B. DETAILED DESCRIPTION

[0049] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0050] Example 1

[0051] The present embodiment provides a broadband stealth material based on an actively regulated metasurface, comprising a plurality of square structural layers of the same size and coincident centers stacked in sequence from top to bottom, which are: a cross-structure resistive frequency selective surface 1, a first dielectric layer 2, a second dielectric layer 3, a square ring structure resistive frequency selective surface 4, a third dielectric layer 5, a fourth dielectric layer 6, a multi-fractal structure active frequency selective surface A7, a fifth dielectric layer 8, a multi-fractal structure active frequency selective surface B9, a sixth dielectric layer 10, and a metal back plate 11; the cross-structure resistive frequency selective surface 1 and the square ring structure resistive frequency selective surface 4 are both centrally symmetrical figures, and the multi-fractal structure active frequency selective surface B9 is obtained by rotating the multi-fractal structure active frequency selective surface A7 counterclockwise 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 A7 extends is the x-axis; the y-axis is perpendicular to the z-axis and the x-axis;

[0052] The cross-structure resistive frequency selective surface 1 comprises four cross structures 101 in two rows and two columns that are not connected to each other; the four cross structures 101 are of the same size and symmetrical about the center, and there is the same gap between adjacent cross structures;

[0053] The square ring structure resistive frequency selective surface 4 includes two square ring structures with overlapping centers: an inner square ring 41 and an outer square ring 42;

[0054] The multi-fractal active frequency selective surface A7 includes four fractal units 71 and two long strip structures 72. 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. The four fractal units 71 are located between the two long strip structures 72.

[0055] The four fractal units 71 are mirror-symmetric about the x-axis and the y-axis respectively, and each fractal unit 71 includes: a bending line 711 connected to the long strip structure 72, and a trapezoidal structure 712 connected to the bending line 711; a varactor diode 73 is provided between the two adjacent fractal units 71 on the left along the y-axis direction, and a chip resistor 74 is provided between the two adjacent fractal units 71 on the right along the y-axis direction.

[0056] The multi-fractal structure active frequency selective surface B9 is obtained by rotating the multi-fractal structure active frequency selective surface A7 by 90° counterclockwise around the z-axis;

[0057] It also includes a control system for achieving regulation of the electromagnetic wave absorption frequency band range below 2 GHZ.

[0058] The control system includes: an external bias power supply A1201, a circuit conductor A1202, a positive feed circuit A1203, a negative feed circuit A1204, and a control structure A1205;

[0059] The control structure A1205 includes a plurality of periodically arranged multi-fractal structure active frequency selective surfaces A7; a positive electrode feeding circuit A1203 is connected to the cathode of the varactor diode 73 of the multi-fractal structure active frequency selective surface A7, a negative electrode feeding circuit A1204 is connected to the anode of the varactor diode 73 of the multi-fractal structure active frequency selective surface A7, and an external bias power supply A1201 is respectively connected to the positive electrode feeding circuit A1203 and the negative electrode feeding circuit A1204 through a circuit conductor A1202;

[0060] It also includes an external bias power supply B1301, a circuit conductor B1302, a positive feed circuit B1303, a negative feed circuit B1304, and a control structure B1305;

[0061] The control structure B1305 includes a plurality of periodically arranged multi-fractal structure active frequency selective surfaces B9; the positive feeding circuit B1303 is connected to the cathode of the varactor diode 73 of the multi-fractal structure active frequency selective surface B9, the negative feeding circuit B1304 is connected to the anode of the varactor diode 73 of the multi-fractal structure active frequency selective surface B9, and the external bias power supply B1301 is respectively connected to the positive feeding circuit B1303 and the negative feeding circuit B1304 through the circuit conductor 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 multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9 is selected from one of copper, aluminum, gold, and silver.

[0063] The material of the first dielectric layer 2, the second dielectric layer 3, the third dielectric layer 5, the fourth dielectric layer 6, the fifth dielectric layer 8 and the sixth dielectric layer 10 is selected from polymethacrylimide 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 copper, aluminum, gold and silver.

[0065] Example 2

[0066] This embodiment provides a method for preparing the broadband stealth material based on active control metasurface, comprising the following steps:

[0067] ① Select the substrate material and use the magnetron sputtering method to plate the resistor film on the surface of the substrate material;

[0068] ② Use a four-probe tester to test the surface resistance of the continuous resistor film and prepare a series of continuous resistor films with a resistance value of 140-160Ω / sq;

[0069] ③ Patterning is performed on the series of resistor films by laser etching technology to prepare a cross-structure resistive frequency selective surface 1 with a resistance range of 140-160Ω / sq and a square-ring structure resistive frequency selective surface 4 with a resistance range of 140-160Ω / sq;

[0070] ④ Selecting a substrate material, using a printed circuit board process to pre-plate a layer of lead-tin anti-corrosion layer on the multi-fractal structure part, and then chemically corroding the remaining metal that is not pre-plated with the lead-tin anti-corrosion layer, to prepare multi-fractal structure active frequency selective surface 7 and multi-fractal structure active frequency selective surface 9 respectively;

[0071] ⑤ Using the soldering method, the varactor diode 73 and the chip resistor 74 are soldered to the specified positions of the multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9;

[0072] ⑥ Select dielectric materials, bond each layer of materials in sequence to form a whole, and bond a metal back plate 11 at the bottom;

[0073] ⑦Finally, through cutting and shaping, a broadband stealth material based on actively controlled metasurface is obtained.

[0074] Example 3

[0075] This embodiment provides a method for preparing a broadband stealth material based on an actively regulated metasurface, comprising the following steps:

[0076] ① Select substrate materials and obtain cross-structure resistive frequency selective surface FSS1 and square-ring resistive frequency selective surface FSS4 by screen printing;

[0077] ② Use a four-probe tester to test the surface resistance of the continuous resistor film and prepare a series of continuous resistor films with a resistance value of 140-160Ω / sq;

[0078] ③ Select substrate materials, use printed circuit board technology to pre-plate a layer of lead-tin anti-corrosion layer on the multi-fractal structure part, and then chemically corrode the remaining metal that is not pre-plated with the lead-tin anti-corrosion layer to prepare multi-fractal structure active frequency selective surface A7 and multi-fractal structure active frequency selective surface B9 respectively;

[0079] ④ Using the soldering method, the varactor diode and the chip resistor are soldered to the specified positions of the multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9;

[0080] ⑤ Select dielectric materials, bond each layer of materials in sequence to form a whole, and bond a metal back plate 11 at the bottom;

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

[0082] Example 4

[0083] This embodiment provides a broadband stealth material based on active control of the metasurface and a preparation method thereof, the preparation method is specifically as follows:

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

[0085] ② The surface resistance of the continuous resistor film was tested using a four-probe tester, and continuous resistor films with resistance values ​​of 140-160Ω / sq were prepared respectively;

[0086] ③ Patterning is performed on a series of ITO resistor films by laser etching technology to prepare a cross-structure resistive frequency selective surface 1 with a resistance range of 140-160Ω / sq and a square-ring structure resistive frequency selective surface 4 with a resistance range of 140-160Ω / sq;

[0087] ④ A 0.508 mm thick Rogers 4350B dielectric substrate is selected as the fifth dielectric layer 8, and a lead-tin anti-corrosion layer is pre-plated on the upper and lower multi-fractal structure parts of the substrate using printed circuit board technology, and then the remaining copper foil is chemically etched away to prepare multi-fractal structure active frequency selective surface A7 and multi-fractal structure active frequency selective surface B9 respectively;

[0088] ⑤ Using the soldering method, the varactor diode and the chip resistor are soldered to the specified positions of the multi-fractal structure active frequency selective surface A7 and the multi-fractal structure active frequency selective surface B9;

[0089] ⑤ Select PMI foam with a dielectric constant of 1.15 and a loss tangent of 0.0037 as the second, fourth and sixth dielectric layer materials, with thicknesses of 4.6mm, 10mm and 5mm respectively. Use epoxy resin to bond each layer of material into a whole in sequence, and bond a 0.035mm thick metal copper film to the bottom.

[0090] ⑤Finally, through cutting and shaping, a broadband stealth material based on actively controlled metasurface with an area of ​​300mm×300mm was produced.

[0091] The other detailed structural parameters of the broadband stealth material based on active control metasurface of this embodiment are as follows:

[0092]

[0093] The key technology of this scheme is: a low-frequency adjustable ultra-wideband microwave absorber is proposed to optimize the electromagnetic wave absorption performance. The structure adopts a cross and square ring structure of the resistive frequency selective surface to achieve good impedance matching in the high-frequency broadband and improve the absorption performance at high frequencies. A double-layer multi-fractal structure active frequency selective surface is adopted to achieve tunable absorption characteristics at low frequencies by loading varactor diodes and patch resistors. The structures are separated by PMI foam to reduce the overall weight and the influence of interlayer electromagnetic coupling on the absorption characteristics. The resistive frequency selective surface unit of the microwave absorber adopts a central symmetrical structure, and the multi-fractal structure frequency selective surfaces can be obtained by rotating 90°, so it has 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 Fig. 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, of which the first resonance peak can be dynamically tuned in 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 range below -10dB is 1.62-24.97GHz, which has ultra-wideband microwave absorption characteristics.

[0096] like Fig.10 As shown, 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 Fig.11 As shown in the figure, in the TM polarization mode, when the incident angle changes in the range of 0°-45°, the low-frequency absorption peak slightly shifts to 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 embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A broadband stealth material based on active control metasurface, characterized in that: The invention comprises a plurality of square structure layers with the same size and coincident centers, which are stacked in sequence from top to bottom, and are: a cross structure resistive frequency selective surface (1), a first dielectric layer (2), a second dielectric layer (3), a square ring structure resistive frequency selective surface (4), a third dielectric layer (5), a fourth dielectric layer (6), a multi-fractal structure active frequency selective surface A (7), a fifth dielectric layer (8), a multi-fractal structure active frequency selective surface B (9), a sixth dielectric layer (10), and a metal back plate (11); the cross structure resistive frequency selective surface (1) and the square ring structure resistive frequency selective surface (4) are both centrally symmetrical figures, and the multi-fractal structure active frequency selective surface B (9) is obtained by rotating the multi-fractal structure active frequency selective surface A (7) counterclockwise by 90 degrees; Definition: The direction from bottom to top is the positive direction of the z-axis, 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; The cross-structure resistive frequency selective surface (1) comprises four cross structures (101) in two rows and two columns that are not connected to each other; the four cross structures (101) are of the same size and symmetrical about the center, and there is the same gap between adjacent cross structures (101); The square ring structure resistive frequency selective surface (4) comprises two square ring structures with overlapping centers: an inner square ring (41) and an outer square ring (42); The multi-fractal structure active frequency selective surface A (7) comprises four fractal units (71) and two long strip structures (72), wherein the long strip structures (72) extend 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). The four fractal units (71) are mirror-symmetrical about the x-axis and the y-axis respectively, and each fractal unit (71) comprises: a bending line (711) connected to the long strip structure (72), and a trapezoidal structure (712) connected to the bending line (711); a variable capacitance diode (73) is arranged between two adjacent fractal units (71) on the left along the y-axis direction, and a chip resistor (74) is arranged between two adjacent fractal units (71) on the right along the y-axis direction. The multi-fractal structure active frequency selective surface B (9) is obtained by rotating the multi-fractal structure active frequency selective surface A (7) 90 degrees counterclockwise around the z-axis; It also includes a control system for achieving regulation of the electromagnetic wave absorption frequency band range below 2 GHz.

2. The broadband stealth material based on active control metasurface according to claim 1, characterized in that: The control system includes: an external bias power supply A (1201), a circuit conductor A (1202), a positive feed circuit A (1203), a negative feed circuit A (1204), and a control structure A (1205); The control structure A (1205) comprises a plurality of periodically arranged multi-fractal structure active frequency selective surfaces A (7); a positive electrode feeding circuit A (1203) is connected to the negative electrode of a variable capacitance diode (73) of the multi-fractal structure active frequency selective surface A (7); a negative electrode feeding circuit A (1204) is connected to the positive electrode of a variable capacitance diode (73) of the multi-fractal structure active frequency selective surface A (7); an external bias power supply A (1201) is respectively connected to the positive electrode feeding circuit A (1203) and the negative electrode feeding circuit A (1204) through a circuit conductor A (1202); It also includes an external bias power supply B (1301), a circuit conductor B (1302), a positive feed circuit B (1303), a negative feed circuit B (1304), and a control structure B (1305); The control structure B (1305) comprises a plurality of periodically arranged multi-fractal structure active frequency selective surfaces B (9); a positive electrode feeding circuit B (1303) is connected to the negative electrode of a variable capacitance diode (73) of the multi-fractal structure active frequency selective surface B (9); a negative electrode feeding circuit B (1304) is connected to the positive electrode of the variable capacitance diode (73) of the multi-fractal structure active frequency selective surface B (9); and an external bias power supply B (1301) is respectively connected to the positive electrode feeding circuit B (1303) and the negative electrode feeding circuit B (1304) through a circuit conductor B (1302).

3. The broadband stealth material based on active control metasurface according to claim 1, characterized in that: 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 multi-fractal structure active frequency selective surface A (7) and the multi-fractal structure active frequency selective surface B (9) is selected from one of copper, aluminum, gold, and silver.

4. The broadband stealth material based on active control metasurface according to claim 1, characterized in that: The material of the first dielectric layer (2), the second dielectric layer (3), the third dielectric layer (5), the fourth dielectric layer (6), the fifth dielectric layer (8) and the sixth dielectric layer (10) is selected from one of polymethacrylimide foam, polyimide foam, polyurethane foam, polyvinyl chloride foam, phenolic foam plastic, polyethylene foam plastic and polyethylene terephthalate plastic.

5. The broadband stealth material based on active control metasurface according to claim 1, characterized in that: The material of the metal back plate (11) is selected from copper, aluminum, gold and silver.

6. The method for preparing a broadband stealth material based on active control of a metasurface according to any one of claims 1 to 5, characterized in that The steps include: ① Select the substrate material and use the magnetron sputtering method to plate the resistor film on the surface of the substrate material; ② Use a four-probe tester to test the surface resistance of the continuous resistor film and prepare a series of continuous resistor films with a resistance value of 140-160Ω / sq; ③ Patterning is performed on the series of resistor films by laser etching technology to prepare a cross-structured resistive frequency selective surface (1) with a resistance range of 140-160Ω / sq and a square-ring-structured resistive frequency selective surface (4) with a resistance range of 140-160Ω / sq; ④ Selecting a substrate material, using a printed circuit board process to pre-plate a layer of lead-tin anti-corrosion layer on the multi-fractal structure part, and then chemically corroding the remaining metal that is not pre-plated with the lead-tin anti-corrosion layer to prepare a multi-fractal structure active frequency selective surface A (7) and a multi-fractal structure active frequency selective surface B (9); 5. Using a soldering method, the varactor diode (73) and the chip resistor (74) are soldered at designated positions of the multi-fractal structure active frequency selective surface A (7) and the multi-fractal structure active frequency selective surface B (9); ⑥ Select dielectric materials, bond each layer of materials in order to form a whole, and bond a metal back plate (11) at the bottom; ⑦Finally, through cutting and shaping, a broadband stealth material based on actively controlled metasurface is obtained.

7. The method for preparing a broadband stealth material based on active control of a metasurface according to any one of claims 1 to 5, characterized in that The steps include: ① Selecting a substrate material, and obtaining a cross-structure resistive frequency selective surface (1) and a square ring-structure resistive frequency selective surface (4) by screen printing; ② Use a four-probe tester to test the surface resistance of the continuous resistor film and prepare a series of continuous resistor films with a resistance value of 140-160Ω / sq; ③ Select a substrate material, use a printed circuit board process to pre-plate a layer of lead-tin anti-corrosion layer on the multi-fractal structure part, and then chemically corrode the remaining metal that is not pre-plated with the lead-tin anti-corrosion layer to prepare a multi-fractal structure active frequency selective surface A (7) and a multi-fractal structure active frequency selective surface B (9); ④ Using a soldering method, the varactor diode and the chip resistor are soldered to the designated positions of the multi-fractal structure active frequency selective surface A (7) and the multi-fractal structure active frequency selective surface B (9); ⑤ Select dielectric materials, bond each layer of materials in order to form a whole, and bond a metal back plate (11) at the bottom; ⑥Finally, through cutting and shaping, a broadband stealth material based on actively controlled metasurface is obtained.

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