Ultra-wideband absorbing honeycomb sandwich structure and its preparation method

Abstract

This invention discloses an ultra-wideband absorbing honeycomb sandwich structure and its fabrication method. The structure includes an upper panel, an absorbing honeycomb, and a lower panel arranged sequentially from top to bottom. The upper panel is a metamaterial panel, and the absorbing honeycomb is formed by impregnating a honeycomb structure with a high-scattering dielectric conductive paste. The lower panel is a low-dielectric-loss, high-magnetic-loss composite material panel. The fabrication method includes preparing a high-frequency scattering absorbing resin, a metasurface, a metamaterial panel, a high-scattering dielectric conductive paste, an absorbing honeycomb, and a low-dielectric-loss, high-magnetic-loss composite material panel. The metamaterial panel, the absorbing honeycomb, and the low-dielectric-loss, high-magnetic-loss composite material panel are then bonded together to obtain the product. This invention is the first to achieve the design and fabrication of an ultra-wideband absorbing honeycomb sandwich structure, which possesses insensitivity to incident angle and polarization direction, effectively meeting the urgent need for omnidirectional ultra-wideband radar stealth in aircraft.

Description

Technical Field

[0001] This invention belongs to the field of aerospace equipment design and manufacturing, and relates to an ultra-wideband absorbing honeycomb sandwich structure and its preparation method. Specifically, it relates to an ultra-wideband absorbing honeycomb sandwich structure that is insensitive to polarization and incident angle and its preparation method. Background Technology

[0002] As a widely used structural form in new aviation equipment, the radar-absorbing honeycomb sandwich structure plays an important integrated role in load-bearing and radar absorption. That is, this structure is both an integral part of the airframe, serving a load-bearing function, and simultaneously absorbs electromagnetic waves incident on its surface, thus contributing to stealth. Currently, radar detection technology is developing rapidly. If radar-absorbing materials / structures cannot effectively absorb radar waves, it will pose a significant threat to equipment safety. Traditional radar-absorbing materials / structures generally suffer from limited absorption bandwidth and sensitivity to electromagnetic wave incident angles and polarization directions, making it difficult to meet the all-around (0-360°) ultra-wideband (0.1-18GHz) radar stealth requirements of new aviation equipment. Therefore, how to obtain high-performance radar-absorbing materials / structures through composition, structure, and process design is a major challenge facing the field of aviation equipment design and manufacturing.

[0003] To address these issues, extensive research has been conducted: 1. In terms of composition optimization, various novel absorbing materials have been continuously developed, such as carbon materials, ferrite absorbing materials, ceramic absorbing materials, and composite materials. 2. In terms of structural design, multi-layer macroscopic absorbing structure designs, represented by Salisbury screens, impedance-matching absorbing materials, and Jaumann absorbing materials, as well as mesoscopic absorbing structure design methods, represented by two-dimensional frequency-selective surfaces and three-dimensional honeycomb structures, have been developed.

[0004] Specifically, in the field of microwave absorbing powder, patent document CN113249092B discloses a metal-organic framework complex composite microwave absorbing powder and its preparation method. This method combines dielectric SiO2 with a magnetic metal-organic framework to broaden the effective absorption bandwidth, which is 4GHz (8-12GHz). Patent document CN113214787B utilizes cobalt ferrite-iron-cobalt alloy to co-coat hollow glass microspheres and carbon microspheres to prepare a ternary core-shell composite material powder with an effective absorption bandwidth of 4.2GHz (8.2-12.4GHz).

[0005] In the design of two-dimensional absorbing structures, two-dimensional frequency-selective surfaces with periodic structures are widely used. Regarding the materials for these frequency-selective surfaces, published patent documents typically employ high-conductivity shielding materials such as metals, graphene, and ITO. For example, patent document CN109638450B utilizes a graphene frequency-selective surface to fabricate a reconfigurable radome; patent document CN113437531B uses metal patch units to fabricate a miniaturized angle-insensitive absorbing structure with an effective absorption bandwidth of 3.5 GHz (3.5-7 GHz); and patent document CN112928483B utilizes a metal-dielectric-metal combination to form a frequency-selective surface stacked structure with an effective absorption bandwidth of 8 GHz (7-15 GHz). However, frequency-selective surfaces only exhibit excellent electromagnetic wave absorption performance near the resonant frequency point, making it difficult to achieve broadband absorption.

[0006] Regarding the design of three-dimensional periodic structures, patent document CN112519365B utilizes dielectric absorbers such as carbon black and graphene to prepare thermoplastic absorbing honeycomb panels with an effective absorption bandwidth of 10GHz (8-18GHz). Patent document CN112143023B proposes a method for preparing a absorbing honeycomb pyramid / rigid foam composite material with an effective absorption bandwidth of 16GHz (2-18GHz). Patent document CN106469858B proposes a honeycomb / resistive sheet stacked structure with an effective absorption bandwidth of 21.6GHz (2.4-24GHz). However, the above three representative patents do not design the absorption performance under different incident angles and polarization directions, and the test frequency band only covers 2-18GHz, making it difficult to achieve ultra-wideband (0.1-18GHz) absorption. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an ultra-wideband absorbing honeycomb sandwich structure that is insensitive to polarization and incident angle and its preparation method. It can effectively solve the problems of poor low-frequency (0.1-4GHz) absorption performance and the large influence of incident angle and polarization direction on absorption performance of the current absorbing honeycomb sandwich structure, and effectively meet the urgent needs of aircraft omnidirectional ultra-wideband radar stealth.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0009] An ultra-wideband absorbing honeycomb sandwich structure includes an upper panel, an absorbing honeycomb, and a lower panel arranged sequentially from top to bottom. The upper panel is a metamaterial panel, which is composed of a quartz fiber reinforced resin matrix composite material and a polymer resin film with a metasurface printed on it disposed in the middle of the quartz fiber reinforced resin matrix composite material. The electrical performance indicators of the metasurface are shown in Table 1. The absorbing honeycomb is formed by impregnating a honeycomb structure with a high-scattering dielectric conductive paste. The electrical performance indicators of the high-scattering dielectric conductive paste are shown in Table 2. The lower panel is a low-dielectric-loss, high-magnetic-loss composite material panel. The electrical performance indicators of the low-dielectric-loss, high-magnetic-loss composite material panel are shown in Table 3. The target quality factor values ​​of the ultra-wideband absorbing honeycomb sandwich structure are shown in Table 4.

[0010] Table 1 Electrical performance indicators of metasurfaces

[0011] Frequency band (GHz) Average value of the real part of the impedance (Ω) Average value of the imaginary part of impedance (Ω) Thickness (mm) P(0.1-1) 400-600 40-90 0.3-0.6 L(1-2) 350-550 30-80 0.3-0.6 S(2-4) 310-540 40-90 0.3-0.6 C(4-8) 340-570 50-100 003-0.6 X(8-12) 310-510 40-90 0.3-0.6 Ku(12-18) 300-500 50-100 0.3-0.6

[0012] Table 2 Electrical Performance Indicators of High-Scattering Dielectric Conductive Paste

[0013] Frequency band (GHz) Electrical frequency dispersion Dielectric constant amplitude Alternating current conductivity (S / m) Electric loss tangent P(0.1-1) 10-20 50-80 0.3-0.5 0.1-0.4 L(1-2) 10-20 40-70 0.3-0.6 0.1-0.4 S(2-4) 10-20 30-60 0.4-0.6 0.2-0.6 C(4-8) 10-20 20-40 0.4-0.7 0.8-1.2 X(8-12) 10-20 15-30 0.5-0.7 1-1.5 Ku(12-18) 5-10 10-25 0.6-0.8 1-1.5

[0014] Table 3 Electrical Performance Indicators of Low Dielectric Loss and High Magnetic Loss Composite Material Panels

[0015] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 0-0.1 3-8 10-20 8-15 0.01-0.05 / 0.1-0.3 L(1-2) 0-0.1 2-5 10-20 6-12 0.01-0.05 / 0.2-0.5 S(2-4) 0-0.1 1-3 10-20 5-10 0.01-0.05 / 0.3-0.5 C(4-8) 0-0.1 1-3 10-20 4-8 0.05-0.1 / 0.3-0.6 X(8-12) 0-0.1 1-3 10-20 3-8 0.05-0.1 / 0.5-0.7 Ku(12-18) 0-0.1 1-3 10-20 2-7 0.05-0.1 / 0.6-0.9

[0016] Table 4. Quality Factor Target Values ​​for Ultra-Wideband Absorbing Cellular Sandwich Structures

[0017] Frequency band (GHz) quality factor P(0.1-1) 0.1-0.5 L(1-2) 0.01-0.05 S(2-4) 0.01-0.05 C(4-8) 0.01-0.05 X(8-12) 0.01-0.05 Ku(12-18) 0.01-0.05 .

[0018] Preferably, in the above-mentioned ultra-wideband absorbing honeycomb sandwich structure, the metasurface is made of a high-frequency dissipation absorbing resin, the electrical performance indicators of which are shown in Table 5. The structural units of the metasurface include one or more combinations of sheet-like structures, open ring structures, closed ring structures, and cross structures. The structure of the metasurface is usually an array structure composed of multiple structural units.

[0019] Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins

[0020] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent p(01-1) 300-400 50-100 400-600 150-300 0.5-1.5 / 0.2-1 L(1-2) 40-50 10-30 80-150 50-80 1-3 / 0.1-1 S(2-4) 20-40 5-15 50-70 20-40 1-3 / 0.1-1 C(4-8) 10-20 5-10 30-50 10-20 1-2 / 0.1-1 X(8-12) 5-10 2-5 20-40 5-15 1-3 / 0.1-1 Ku(12-18) 5-10 25 10-15 3-8 1-3 / 0.1-1 .

[0021] In the aforementioned ultra-wideband absorbing honeycomb sandwich structure, preferably, the quartz fiber reinforced resin matrix composite material uses one or more of epoxy resin, phenolic resin, bismaleimide resin, polyimide resin, and cyanate ester resin, and the polymer resin film includes one or more of polyetheretherketone resin film, epoxy resin film, bismaleimide resin film, and polyimide resin film.

[0022] Preferably, in the aforementioned ultra-wideband absorbing honeycomb sandwich structure, the hexagonal lattice of the honeycomb structure has a side length of 2mm to 5mm, a thickness of 15mm to 25mm, and a bulk density of 90kg / m³. 3 ~120kg / m 3 ;

[0023] The high-scattering dielectric conductive paste is made by mixing dielectric absorbing powder with epoxy resin. The dielectric absorbing powder includes one or more of zero-dimensional dielectric loss absorbing powder, one-dimensional dielectric loss absorbing powder, and two-dimensional dielectric loss absorbing powder. The zero-dimensional dielectric loss absorbing powder includes one or more of carbon spheres, carbon black, and fullerene. The one-dimensional dielectric loss absorbing powder includes one or more of carbon nanowires, carbon nanorods, carbon nanotubes, and carbon nanofibers. The two-dimensional dielectric loss absorbing powder includes one or more of graphene, Mxene, and MoS2.

[0024] In the aforementioned ultra-wideband absorbing honeycomb sandwich structure, preferably, the low dielectric loss and high magnetic loss composite material panel is obtained by curing and molding short-cut fibers, magnetic powder, and epoxy resin as raw materials. The short-cut fibers are short-cut carbon fibers or short-cut silicon carbide fibers, and the magnetic powder includes one or more of carbonyl iron powder, magnetic metal-organic framework, and magnetic core-shell structure.

[0025] In the aforementioned ultra-wideband absorbing honeycomb sandwich structure, preferably, the thickness of the upper panel is 2mm to 4mm, and the thickness of the lower panel is 3mm to 5mm.

[0026] As a general technical concept, the present invention also provides a method for preparing the above-mentioned ultra-wideband absorbing honeycomb sandwich structure, comprising the following steps:

[0027] (1) Preparation of high-frequency scattering effect absorbing resin: High scattering absorber powder is dispersed in epoxy resin to obtain high-frequency scattering effect absorbing resin. The high-frequency scattering effect absorbing resin needs to meet the electrical performance indicators shown in Table 5. The high scattering absorber powder includes one or more of metal-organic framework, carbonyl iron powder, acetylene black, short-cut carbon fiber, graphene and carbon nanotubes.

[0028] Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins

[0029] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 300-400 50-100 400-600 150-300 0.5-1.5 / 0.2-1 L((1-2) 40-50 10-30 80-150 50-80 1-3 / 0.1-1 S(2-4) 20-40 5-15 50-70 20-40 1-3 / 0.1-1 C(4-8) 10-20 5-10 30-50 10-20 1-2 / 0.1-1 X(8-12) 5-10 2-5 20-40 5-15 1-3 / 0.1-1 Ku(12-18) 5-10 2-5 10-15 3-8 1-3 / 0.1-1 ;

[0030] (2) Preparation of metasurface (i.e. frequency selective surface): The high-frequency scattering effect absorbing resin obtained in step (1) is prepared into a metasurface according to the required structure so that the metasurface meets the electrical performance indicators shown in Table 1.

[0031] (3) Preparation of metamaterial panel: The metasurface obtained in step (2) is printed onto a polymer resin film, the polymer resin film with the metasurface is laid onto the middle layer of quartz fiber reinforced resin base prepreg, and cured and shaped using a vacuum bag-autoclave curing process to obtain metamaterial panel.

[0032] (4) Preparation of high-scattering dielectric conductive paste: The dielectric absorbing powder is mixed with epoxy resin. The dielectric absorbing powder includes one or more of zero-dimensional dielectric loss absorbing powder, one-dimensional dielectric loss absorbing powder and two-dimensional dielectric loss absorbing powder to obtain a high-scattering dielectric conductive paste. The high-scattering dielectric conductive paste needs to meet the electrical performance indicators shown in Table 2.

[0033] (5) Preparation of absorbing honeycomb: The honeycomb structure is immersed in the high-scattering dielectric conductive paste obtained in step (4) for 3 min to 5 min, and then pre-cured by turning over at a temperature of 80℃ to 120℃ to coat the inner wall of the honeycomb structure with conductive paste. The immersion and coating are repeated until the bulk density of the absorbing honeycomb is 90 kg / m³. 3 ~120kg / m 3 ;

[0034] (6) Preparation of low dielectric loss and high magnetic loss composite material panel: Magnetic absorbing powder is dispersed in epoxy resin. The magnetic absorbing powder includes short-cut fibers and magnetic powder. The panel is cured and formed by vacuum bag-autoclave curing process to obtain low dielectric loss and high magnetic loss composite material panel. The low dielectric loss and high magnetic loss composite material panel needs to meet the electrical performance indicators shown in Table 3.

[0035] (7) Preparation of ultra-wideband absorbing honeycomb sandwich structure: The metamaterial panel obtained in step (3) is used as the upper panel, the absorbing honeycomb obtained in step (5) is used as the sandwich layer, and the low dielectric loss and high magnetic loss composite material panel obtained in step (6) is used as the lower panel. The upper panel, absorbing honeycomb and lower panel are bonded together with adhesive film to obtain ultra-wideband absorbing honeycomb sandwich structure.

[0036] The preferred method for preparing the ultra-wideband absorbing honeycomb sandwich structure described above is as follows: in step (3), the vacuum bag-autoclave curing process is as follows: under a vacuum of not less than 0.095 MPa, the temperature is increased to 80℃ to 120℃ at a heating rate of 1℃ / min to 3℃ / min, while the pressure is increased to 0.5MPa to 0.7MPa, and the temperature is maintained for 2h to 3h. The temperature is then increased to 130℃ to 150℃ and maintained for 1h to 2h. Finally, the temperature is increased to 180℃ to 200℃ and maintained for 3h to 5h. Then, the temperature is cooled to 40℃ to 60℃ at a cooling rate of 1℃ / min to 3℃ / min, and the pressure is released from the autoclave.

[0037] In the preferred embodiment of the above-mentioned method for preparing ultra-wideband absorbing honeycomb sandwich structure, the vacuum bag-autoclave curing process in step (6) is as follows: under a vacuum of not less than 0.095 MPa, the temperature is raised to 80℃ to 120℃ at a heating rate of 1℃ / min to 3℃ / min, and held for 3h to 5h. Then, the temperature is cooled to 40℃ to 60℃ at a cooling rate of 1℃ / min to 3℃ / min, and the pressure is released from the autoclave.

[0038] In the preferred embodiment of the above-mentioned method for preparing ultra-wideband absorbing honeycomb sandwich structure, the adhesive bonding process of the adhesive film in step (7) is as follows: the vacuum degree is not less than 0.095 MPa, the temperature is raised to 80℃ to 120℃ at a heating rate of 1℃ / min to 3℃ / min, the temperature is kept for 2h to 4h, and then the temperature is cooled to 40℃ to 60℃ at a cooling rate of 1℃ / min to 3℃ / min.

[0039] Compared with the prior art, the advantages of the present invention are as follows:

[0040] (1) This invention provides an ultra-wideband absorbing honeycomb sandwich structure that is insensitive to polarization and incident angle. Compared with traditional frequency-selective surfaces made of shielding materials, this invention uses high-frequency dispersion-effect absorbing resin to prepare a metasurface (frequency-selective surface) and uses composite material structure integration technology to combine it with the upper panel of the honeycomb sandwich structure (quartz fiber reinforced epoxy resin). A low dielectric loss and high magnetic loss composite material is selected as the lower panel of the honeycomb sandwich structure. Based on the resonance effect of the composite material, the honeycomb sandwich structure is insensitive to the incident angle of electromagnetic waves. The optimized impedance matching performance helps to achieve ultra-wideband omnidirectional stealth. The effective absorption bandwidth (reflection loss < -10dB) of the ultra-wideband absorbing honeycomb sandwich structure of this invention covers 0.1-18GHz, and the electromagnetic wave absorption performance shows insensitivity to the incident angle (0-70°) and polarization direction (horizontal and vertical polarization), effectively meeting the urgent need for omnidirectional ultra-wideband radar stealth of aircraft.

[0041] (2) This invention provides a method for preparing an ultra-wideband absorbing honeycomb sandwich structure. A high-scattering dielectric conductive paste is prepared and an absorbing honeycomb is prepared by dip-coating process, which can give full play to the honeycomb’s ability to absorb electromagnetic wave energy through multiple scattering. Attached Figure Description

[0042] Figure 1 The diagram shows the reflection loss of the ultrawideband absorbing honeycomb sandwich structure in TE(a,c) and TM(b,d) modes in Embodiment 1 of the present invention.

[0043] Figure 2 This is a schematic diagram of the open-ring periodic metasurface structure unit in Embodiments 1 and 2 of the present invention.

[0044] Figure 3 This is a schematic diagram of the open-ring periodic metasurface structure unit in Embodiment 3 of the present invention. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0046] The method for preparing the ultra-wideband absorbing honeycomb sandwich structure of the present invention includes the following steps:

[0047] (1) Electrical performance indicators of high-frequency scattering effect absorbing resin

[0048] The electrical performance indicators of the high-frequency scattering effect absorbing resin are shown in Table 5. One or more mixtures of materials, including but not limited to metal-organic frameworks, carbonyl iron, acetylene black, short-cut carbon fibers, graphene, and carbon nanotubes, can be dispersed in epoxy resin to achieve the corresponding electrical performance indicators.

[0049] Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins

[0050] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent p(0.1-1) 300-400 50-100 400-600 150-300 0.5-1.5 / 0.2-1 L(1-2) 40-50 10-30 80-150 50-80 1-3 / 0.1-1 S(2--4) 20--40 5-15 50-70 20--40 1-3 / 0.1-1 C(4-8) 10-20 5-10 30-50 10-20 1-2 / 0.1-1 X(8-12) 5-10 2-5 20--40 5-15 1-3 / 0.1-1 Ku(12-18) 5-10 2-5 10-15 3-8 1-3 / 0.1-1 .

[0051] (2) Preparation and electrical performance range of metasurfaces

[0052] In terms of selecting metasurface structural units, single or combined structures can be prepared using sheet-like, open / closed ring-like, and cross-shaped structures, among others. The metasurface can be prepared using screen printing and 3D printing technologies, among others. The high-frequency scattering effect absorbing powder in step (1) is selected to complete the design of the metasurface structural unit size. The prepared metasurface should meet the electrical performance indicators shown in Table 1.

[0053] Table 1 Electrical performance indicators of metasurfaces

[0054] Frequency band (GHz) Average value of the real part of the impedance (Ω) Average value of the imaginary part of impedance (Ω) Thickness (mm) P(01-1) 400-600 40-90 0.3-0.6 L(1-2) 350-550 30-80 0.3-0.6 S(2--4) 310-540 40-90 0.3-0.6 C(4-8) 340-570 50-100 0.3-0.6 X(8-12) 310-510 40-90 0.3-0.6 Ku(12-18) 300-500 50-100 0.3-0.6

[0055] (3) Fabrication of metamaterial panels

[0056] The metasurface designed in step (2) is printed onto a polymer resin film. The resin film is selected from one or more of bismaleimide, epoxy resin film and cyanate ester film. The printed polymer resin film is laid onto the intermediate layer of quartz fiber reinforced epoxy resin prepreg (the prepreg is a layer structure). The metamaterial panel is prepared by vacuum bag-autoclave curing process.

[0057] The vacuum bag-autoclave curing process is as follows: Under a vacuum of not less than 0.095 MPa, the temperature is increased to 80℃ to 120℃ at a heating rate of 1℃ / min to 3℃ / min, while the pressure is increased to 0.5MPa to 0.7MPa. The temperature is held for 2h to 3h, then the temperature is increased to 130℃ to 150℃ and held for 1h to 2h. Finally, the temperature is increased to 180℃ to 200℃ and held for 3h to 5h. Then, the temperature is cooled to 40℃ to 60℃ at a cooling rate of 1℃ / min to 3℃ / min, and the pressure is released from the autoclave.

[0058] (4) Preparation of high-scattering dielectric conductive paste

[0059] In controlling the scattering properties of dielectric conductive pastes, the sensitivity of material scattering characteristics to composition and microstructure is utilized. Zero-dimensional, one-dimensional, and two-dimensional microstructure dielectric loss absorbing powders are mixed. Zero-dimensional dielectric loss absorbing powders include, but are not limited to, one or more of carbon spheres, carbon black, and fullerenes; one-dimensional dielectric loss absorbing powders include, but are not limited to, one or more of carbon nanowires, nanorods, nanotubes, and carbon nanofibers; and two-dimensional dielectric loss absorbing powders include, but are not limited to, one or more of graphene, Mxene, and MoS2. The dielectric absorbing powders are mixed with epoxy resin at a certain mass ratio, and the electrical properties and scattering characteristics of the resulting high-scattering dielectric conductive paste are shown in Table 2.

[0060] Table 2 Electrical Performance Indicators of High-Scattering Dielectric Conductive Paste

[0061] Frequency band (GHz) Electrical frequency dispersion Dielectric constant amplitude Alternating current conductivity (S / m) Electric loss tangent P(0.1-1) 10-20 50-80 0.3-0.5 0.1-0.4 L(1-2) 10-20 40-70 0.3-0.6 0.1-0.4 S(2-4) 10-20 30-60 0.4-0.6 0.2-0.6 C(4-8) 10-20 20-40 0.4-0.7 0.8-1.2 X(8-12) 10-20 15-30 0.5-0.7 1-1.5 Ku(12-18) 5-10 10-25 0.6-0.8 1-1.5

[0062] (5) Fabrication of absorbing honeycomb

[0063] A honeycomb structure (preferably a white honeycomb) with hexagonal cells having a side length of 2-5 mm and a height of 15-25 mm is selected. The absorbing honeycomb is prepared using an impregnation coating process. Specifically, the honeycomb structure is immersed in the high-scattering dielectric conductive paste prepared in step (4) for 3-5 minutes, followed by pre-curing by turning it over in an oven at 80-120℃ to coat the inner wall of the honeycomb structure with the conductive paste. The desired volume density is achieved by controlling the number of impregnation coatings, with a desired volume density of 90-120 kg / m³. 3 between.

[0064] (6) Preparation of low dielectric loss and high magnetic loss composite material panels

[0065] Magnetic absorbing powder is prepared by mixing short-cut carbon fibers or short-cut silicon carbide fibers (including but not limited to those with dielectric loss) with magnetic powders. The magnetic powders include, but are not limited to, one or more of carbonyl iron powder, magnetic metal-organic frameworks, and magnetic core-shell structures. The magnetic absorbing powders are dispersed in epoxy resin at a mass ratio of 3:7 and cured at 120°C using a vacuum bag-autoclave curing process. The electrical properties of the prepared low-dielectric-loss, high-magnetic-loss composite material panel are shown in Table 3.

[0066] The vacuum bag-autoclave curing process is as follows: Under a vacuum of not less than 0.095 MPa, the temperature is increased to 80℃ to 120℃ at a heating rate of 1℃ / min to 3℃ / min, and held for 3h to 5h. Then, the temperature is cooled to 40℃ to 60℃ at a cooling rate of 1℃ / min to 3℃ / min, and the bag is depressurized and removed from the autoclave.

[0067] Table 3 Electrical Performance Indicators of Low Dielectric Loss and High Magnetic Loss Composite Material Panels

[0068] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 0-0.1 3-8 10-20 8-15 0.01-0.05 / 0-1-0.3 L(1-2) 0-0.1 2-5 10-20 6-12 0.01-0.05 / 0.2-0.5 S(2-4) 0-0.1 1-3 10-20 5-10 0.01-0.05 / 0.3-0.5 C(4-8) 0-0.1 1-3 10-20 4-8 0.05-0.1 / 0.3-0.6 X(8-12) 0-0.1 1-3 10-20 3-8 0.05-0.1 / 0.5-0.7 Ku(12-18) 0-0.1 1-3 10-20 2-7 0.05-0.1 / 0.6-0.9

[0069] (7) Bonding of composite material panels to absorbing honeycomb (preparation of ultra-wideband absorbing honeycomb sandwich structure)

[0070] The metamaterial panel prepared in step (3) is used as the upper panel, the microwave absorbing honeycomb prepared in step (5) is used as the interlayer, and the low dielectric loss and high magnetic loss composite material panel prepared in step (6) is used as the lower panel. The upper and lower panels are bonded to the microwave absorbing honeycomb using an adhesive film. The thickness of the upper panel is between 2-4 mm, the thickness of the lower panel is between 3-5 mm, and the honeycomb height is between 15-25 mm.

[0071] The bonding process of the adhesive film in step 7 is as follows: the vacuum degree is not less than 0.095MPa, the temperature is raised to 80-120℃ at a heating rate of 1-3℃ / min, the temperature is held for 2-4 hours, and then the temperature is cooled to 40-60℃ at a cooling rate of 1-3℃ / min.

[0072] Example 1:

[0073] An ultra-wideband absorbing honeycomb sandwich structure of the present invention includes an upper panel, an absorbing honeycomb, and a lower panel arranged sequentially from top to bottom. The upper panel is a metamaterial panel, which is composed of a quartz fiber reinforced resin matrix composite material and a polymer resin film with a metasurface printed on it disposed in the middle of the quartz fiber reinforced resin matrix composite material. The electrical properties of the metasurface meet the indicators in Table 1. The absorbing honeycomb is formed by impregnating a honeycomb structure with a high-scattering dielectric conductive paste. The electrical properties of the high-scattering dielectric conductive paste meet the indicators in Table 2. The lower panel is a low-dielectric-loss, high-magnetic-loss composite material panel. The electrical properties of the low-dielectric-loss, high-magnetic-loss composite material panel meet the indicators in Table 3. The target quality factor value of the ultra-wideband absorbing honeycomb sandwich structure meets the indicators in Table 4.

[0074] Table 1 Electrical performance indicators of metasurfaces

[0075] Frequency band (GHz) Average value of the real part of the impedance (Ω) Average value of the imaginary part of impedance (Ω) Thickness (mm) p(0.1-1) 400-600 40-90 0.3-0.6 L(1-2) 350-550 30-80 0.3-0.6 S(2-4) 310-540 40-90 0.3-0.6 C(4-8) 340-570 50-100 0.3-0.6 X(8-12) 310-510 40-90 0.3-0.6 Ku(12-18) 300-500 50-100 0.3-0.6

[0076] Table 2 Electrical Performance Indicators of High-Scattering Dielectric Conductive Paste

[0077] Frequency band (GHz) Electrical frequency dispersion Dielectric constant amplitude Alternating current conductivity (S / m) Electric loss tangent P(0.1-1) 10-20 50-80 0.3-0.5 0.1-0.4 L(1-2) 10-20 40-70 0.3-0.6 0.1-0.4 S(2-4) 10-20 30-60 0.4-0.6 0.2-0.6 C(4-8) 10-20 20-40 0.4-0.7 0.8-1.2 X(8-12) 10-20 15-30 0.5-0.7 1-1.5 Ku(12-18) 5-10 10-25 0.6-0.8 1-1.5

[0078] Table 3 Electrical Performance Indicators of Low Dielectric Loss and High Magnetic Loss Composite Material Panels

[0079] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 0-0.1 3-8 10-20 8-15 0.01-0.05 / 0.1-0.3 L(1-2) 0-0.1 2-5 10-20 6-12 0.01-0.05 / 0.2-0.5 S(2-4) 0-0.1 1-3 10-20 5-10 0.01-0.05 / 0.3-0.5 C(4-8) 0-0.1 1-3 10-20 4-8 0.05-0.1 / 0.3-0.6 X(8-12) 0-0.1 1-3 10-20 3-8 0.05-0.1 / 0.5-0.7 Ku(12-18) 0-0.1 1-3 10-20 2-7 0.05-0.1 / 0.6-0.9

[0080] Table 4. Quality Factor Target Values ​​for Ultra-Wideband Absorbing Cellular Sandwich Structures

[0081] Frequency band (GHz) quality factor P(0.1-1) 0.1-0.5 L(1-2) 0.01-0.05 S(2-4) 0.01-0.05 C(4-8) 0.01-0.05 X(8-12) 0.01-0.05 Ku(12-18) 0.01-0.05 .

[0082] In this embodiment, the metasurface is made of high-frequency scattering effect absorbing resin, and the electrical performance indicators of the high-frequency scattering effect absorbing resin meet the indicators in Table 5. The structural unit of the metasurface is a combination of two open ring structures.

[0083] Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins

[0084] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 300-400 50-100 400-600 150-300 0.5-1.5 / 0.2-1 L(1-2) 40-50 10-30 80-150 50-80 1-3 / 0.1-1 S(2-4) 20-40 5-15 50-70 20-40 1-3 / 0.1-1 C (4-8) 10-20 5-10 30-50 10-20 1-2 / 0.1-1 X(8-12) 5-10 2-5 20-40 5-15 1-3 / 0.1-1 Ku(12-18) 5-10 2-5 10-15 3-8 1-3 / 0.1-1 .

[0085] In this embodiment, the resin used in the quartz fiber reinforced resin matrix composite material is epoxy resin, and the polymer resin film is an epoxy resin film.

[0086] In this embodiment, the side length of the hexagonal cells in the honeycomb structure is 3mm, the height of the honeycomb structure is 17mm, and the volume density of the absorbing honeycomb is 90kg / m³. 3 .

[0087] In this embodiment, the high-scattering dielectric conductive paste is made by mixing microwave absorbing powder with epoxy resin, wherein the microwave absorbing powder is conductive carbon black and carbon nanotubes.

[0088] In this embodiment, the low dielectric loss and high magnetic loss composite material panel is obtained by curing and molding short-cut fibers, magnetic powder and epoxy resin as raw materials. The short-cut fibers are short-cut silicon carbide fibers and the magnetic powder is ZIF-67 metal-organic framework.

[0089] In this embodiment, the thickness of the upper panel is 2mm and the thickness of the lower panel is 4mm.

[0090] A method for fabricating an ultra-wideband absorbing honeycomb sandwich structure according to this embodiment includes the following steps:

[0091] (1) Preparation of high-frequency scattering effect absorbing resin: Carbonyl iron powder, chopped carbon fiber, and epoxy resin were mixed and stirred at a mass ratio of 3:1:20. The carbonyl iron powder was selected with an average particle size of 1000 mesh, and the chopped carbon fiber had a length of 3 mm and a diameter of 7 μm. The mixture was stirred at room temperature for 30 minutes using a high-speed stirrer at a stirring speed of 800 rpm to obtain the high-frequency scattering effect absorbing resin. The high-frequency scattering effect absorbing resin met the electrical performance indicators shown in Table 5.

[0092] (2) Fabrication of open-ring periodic metasurfaces: Design as follows Figure 2 The open-ring periodic metasurface structure shown is an array structure composed of multiple structural units. Each structural unit is composed of an outer ring 1 and an inner ring 2 (nested together). The outer ring 1 is a rectangular ring structure with a notch, and the inner ring 2 is a rectangular ring structure with a notch. The width a of the outer ring 1 is 1 mm, the envelope width e of the outer ring 1 is 6 mm, the width c of the inner ring 2 is 2 mm, the envelope length d of the inner ring 2 is 3 mm, the distance b between the outer ring 1 and the inner ring 2 is 0.5 mm, and the opening size f of both the outer ring 1 and the inner ring 2 is 2 mm. The high-frequency scattering effect absorbing resin prepared in step (1) is used to prepare an open-ring periodic metasurface according to the above structure. The metasurface meets the electrical performance indicators shown in Table 1.

[0093] (3) Preparation of metamaterial panel: Using epoxy resin film as carrier, the open-ring periodic metasurface prepared in step (2) is printed on epoxy resin film using screen printing technology. Then, the epoxy resin film with the printed metasurface is laid on the middle layer of quartz fiber reinforced resin base prepreg and cured by vacuum bag-autoclave curing process to obtain metamaterial panel. The vacuum bag-autoclave curing process is as follows: under vacuum degree not less than 0.095MPa, the temperature is raised to 100℃ at a heating rate of 2℃ / min, and the pressure is increased to 0.6MPa. The temperature is held for 2h, the temperature is raised to 150℃ and held for 1h, and finally the temperature is raised to 180℃ and held for 3h. Then, the temperature is cooled to 60℃ at a cooling rate of 1.5℃ / min, the pressure is released and the panel is removed from the autoclave, thus completing the preparation of metamaterial panel.

[0094] (4) Preparation of high-scattering dielectric conductive paste: Carbon black, carbon nanotubes and epoxy resin are mixed and stirred in a mass ratio of 2:1:10, wherein the average particle size of carbon black is 100nm and the outer diameter of carbon nanotubes is 10nm. The mixture is stirred for 30 minutes at room temperature using a high-speed stirrer at a stirring speed of 800rpm to obtain high-scattering dielectric conductive paste. The high-scattering dielectric conductive paste meets the electrical performance indicators shown in Table 2.

[0095] (5) Preparation of absorbing honeycomb: White honeycomb with a pore side length of 3mm and a height of 17mm was repeatedly impregnated and pre-cured in the high-scattering dielectric conductive paste prepared in step (4). The impregnation time for each time was controlled at 3min, the pre-curing temperature was 80℃, and the pre-curing time was 5min. Subsequently, by controlling the number of impregnations, the volume density of the absorbing honeycomb was achieved to be 90kg / m³. 3 .

[0096] (6) Preparation of low dielectric loss and high magnetic loss composite material panel: Short-cut silicon carbide fiber, ZIF-67 metal-organic framework and epoxy resin were mixed and stirred in a mass ratio of 1:3:10. The selected short-cut silicon carbide fiber had a length of 3 mm and a diameter of 14 μm. The mixture was stirred at room temperature for 30 minutes using a high-speed stirrer at a stirring speed of 800 rpm. The mixture was then cured using a vacuum bag-autoclave process under a vacuum degree of not less than 0.095 MPa. The temperature was increased to 100℃ at a heating rate of 1.5℃ / min and held for 4 hours. Subsequently, the temperature was cooled to 60℃ at a cooling rate of 1.5℃ / min. The pressure was released from the autoclave to obtain the low dielectric loss and high magnetic loss composite material panel. The low dielectric loss and high magnetic loss composite material panel meets the electrical performance indicators shown in Table 3.

[0097] (7) Preparation of ultra-wideband absorbing honeycomb sandwich structure: The metamaterial panel prepared in step (3) is used as the upper panel, the absorbing honeycomb prepared in step (5) is used as the sandwich layer, and the low dielectric loss and high magnetic loss composite material panel prepared in step (6) is used as the lower panel. The upper panel, absorbing honeycomb and lower panel are bonded together with an adhesive film to obtain an ultra-wideband absorbing honeycomb sandwich structure. The thickness of the upper panel is 2 mm and the thickness of the lower panel is 4 mm. The bonding process is as follows: the vacuum degree is not less than 0.095 MPa, the temperature is raised to 80℃ at a heating rate of 1.5℃ / min, held for 2 hours, and then cooled to 40℃~60℃ at a cooling rate of 1.5℃ / min to complete the bonding.

[0098] Electrical performance characterization of the ultrawideband absorbing honeycomb sandwich structure in this embodiment:

[0099] Figure 1 Demonstrates TE mode ( Figure 1 a, Figure 1 c) and TM ( Figure 1 b, Figure 1 d) The reflection loss of the absorbing honeycomb sandwich structure under different electromagnetic wave incident angles in the 0.1-18GHz frequency band under mode d) is determined by Figure 1 It is known that the absorbing honeycomb sandwich structure of the present invention can achieve a reflection loss of <-10dB under different polarization directions and incident angles, that is, the effective absorption bandwidth covers 0.1-18GHz. The ultra-wideband absorbing honeycomb sandwich structure of the present invention generates resonant loss at a frequency of 0.5GHz, and the reflection loss in other frequency bands besides the resonant frequency point shows insensitivity to the incident angle and polarization direction. Figure 1 (c) is Figure 1 (a) A magnified view of a local area in the 0.1–1 GHz range. Figure 1 (d) is Figure 1 (b) A magnified view of a local area in the 0.1–1 GHz range. Figure 1 (c) Figure 1 (d) indicates that by constructing a resonance in the 0.1-1 GHz frequency band, the absorption performance outside the resonance influence frequency band is not sensitive to the incident angle (as shown by the curves being very close).

[0100] To better illustrate the insensitivity to incident angle and polarization direction, the quality factor Q is used to characterize the resonance characteristics at the resonant frequency. The quality factor can be calculated by the ratio of the resonant frequency to the resonant half-width at half maximum (FWHM). Table 4 shows the target quality factor values ​​for the absorbing honeycomb sandwich structure with insensitivity to incident angle and polarization direction in the 0.1-18 GHz frequency band. This indicates that by constructing resonance in the P-band (0.1-1 GHz) and quantifying and constraining the resonance behavior through the quality factor, this invention ultimately achieves an effective absorption bandwidth covering the 0.1-18 GHz frequency band, realizing ultra-wideband absorption while maintaining insensitivity to electromagnetic wave incident angle and polarization direction.

[0101] Table 4. Quality Factor Target Values ​​for Ultra-Wideband Absorbing Cellular Sandwich Structures

[0102] Frequency band (GHz) quality factor P(0.1-1) 0.1-0.5 L(1-2) 0.01-0.05 S(2-4) 0.01-0.05 C(4-8) 0.01-0.05 X(8-12) 0.01-0.05 Ku(12-18) 0.01-0.05 .

[0103] Example 2

[0104] An ultra-wideband absorbing honeycomb sandwich structure of the present invention includes an upper panel, an absorbing honeycomb, and a lower panel arranged sequentially from top to bottom. The upper panel is a metamaterial panel, which is composed of a quartz fiber reinforced resin matrix composite material and a polymer resin film with a metasurface printed on it disposed in the middle of the quartz fiber reinforced resin matrix composite material. The electrical properties of the metasurface meet the indicators in Table 1. The absorbing honeycomb is formed by impregnating a honeycomb structure with a high-scattering dielectric conductive paste. The electrical properties of the high-scattering dielectric conductive paste meet the indicators in Table 2. The lower panel is a low-dielectric-loss, high-magnetic-loss composite material panel. The electrical properties of the low-dielectric-loss, high-magnetic-loss composite material panel meet the indicators in Table 3. The target quality factor value of the ultra-wideband absorbing honeycomb sandwich structure meets the indicators in Table 4.

[0105] Table 1 Electrical performance indicators of metasurfaces

[0106] Frequency band (GHz) Average value of the real part of the impedance (Ω) Average value of the imaginary part of impedance (Ω) Thickness (mm) P(0.1-1) 400-600 40-90 0.3-0.6 L(1-2) 350-550 30-80 0.3-0.6 S(2-4) 310-540 40-90 0.3-0.6 C(4-8) 340-570 50-100 0.3-0.6 X(8-12) 310-510 40-90 0.3-0.6 Ku(12-18) 300-500 50-100 0.3-0.6

[0107] Table 2 Electrical Performance Indicators of High-Scattering Dielectric Conductive Paste

[0108] Frequency band (GHz) Electrical frequency dispersion Dielectric constant amplitude Alternating current conductivity (S / m) Electric loss tangent P(0.1-1) 10-20 50-80 0.3-0-5 0.1-0.4 L(1-2) 10-20 40-70 0.3-0.6 0.1-0.4 S(24) 10-20 30-60 0.4-0.6 0.2-0.6 C(4-8) 10-20 20-40 0.4-0.7 0.8-1.2 X(8-12) 10-20 15-30 0.5-0.7 l-1.5 Ku(12-18) 5-10 10-25 0.6-0.8 1-1.5

[0109] Table 3 Electrical Performance Indicators of Low Dielectric Loss and High Magnetic Loss Composite Material Panels

[0110] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 0-0.1 3-8 10-20 8-15 0.01-0.05 / 0.1-0.3 L(1-2) 0-0.1 2-5 10-20 6-12 0.01-0.05 / 0.2-0.5 S(2-4) 0-0.1 1-3 10-20 5-10 0.01-0.05 / 0.3-0.5 C(4-8) 0-0.1 1-3 10-20 4-8 0.05-0.1 / 0.3-0.6 X(8-12) 0-0.1 1-3 10-20 3-8 0.05-0.1 / 0.5-0.7 Ku(12-18) 0-0.1 1-3 10-20 2-7 0.05-0.1 / 0.6-0.9

[0111] Table 4. Quality Factor Target Values ​​for Ultra-Wideband Absorbing Cellular Sandwich Structures

[0112] Frequency band (GHz) quality factor P(0.1-1) 0.1-0.5 L(1-2) 0.01-0.05 S(2-4) 0.01-0.05 C(4-8) 0.01-0.05 X(8-12) 0.01-0.05 Ku(12-18) 0.01-0.05 .

[0113] In this embodiment, the metasurface is made of high-frequency scattering effect absorbing resin, and the electrical performance indicators of the high-frequency scattering effect absorbing resin meet the indicators in Table 5. The structural unit of the metasurface is a combination of two open ring structures.

[0114] Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins

[0115] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 300-400 50-100 400-600 150-300 0.5-1.5 / 0.2-1 L(1-2) 40-50 10-30 80-150 50-80 1-3 / 0.1-1 S(2-4) 20-40 5-15 50-70 20-40 1-3 / 0.1-1 C (4-8) 10-20 5-10 30-50 10-20 1-2 / 0.1-1 X(8-12) 5-10 2-5 20-40 5-15 1-3 / 0.1-1 Ku(12-18) 5-10 2-5 10-15 3-8 1-3 / 0.1-1 .

[0116] In this embodiment, the resin used in the quartz fiber reinforced resin matrix composite material is epoxy resin, and the polymer resin film is polyetheretherketone resin film.

[0117] In this embodiment, the hexagonal lattice of the honeycomb structure has a side length of 4mm, the height of the honeycomb structure is 20mm, and the volume density of the absorbing honeycomb is 110kg / m³. 3 .

[0118] In this embodiment, the high-scattering dielectric conductive paste is made by mixing microwave absorbing powder with epoxy resin, wherein the microwave absorbing powder is MXene and carbon nanotubes.

[0119] In this embodiment, the low dielectric loss and high magnetic loss composite material panel is obtained by curing and molding short-cut fibers, magnetic powder and epoxy resin as raw materials. The short-cut fibers are short-cut carbon fibers and the magnetic powder is carbonyl iron powder.

[0120] In this embodiment, the thickness of the upper panel is 3mm and the thickness of the lower panel is 3mm.

[0121] A method for fabricating an ultra-wideband absorbing honeycomb sandwich structure according to this embodiment includes the following steps:

[0122] (1) Preparation of high frequency scattering effect absorbing resin: ZIF-67 metal-organic framework, acetylene black and epoxy resin were mixed and stirred in a mass ratio of 2:3:10. The average particle size of the selected acetylene black was 80 nm. The mixture was stirred for 30 minutes at room temperature using a high-speed stirrer at a stirring speed of 800 rpm to obtain the high frequency scattering effect absorbing resin. The high frequency scattering effect absorbing resin meets the electrical performance indicators shown in Table 5.

[0123] (2) Preparation of metasurface: The preparation method of metasurface in this step is basically the same as step (2) in Example 1, except that the opening size f of outer ring 1 and inner ring 2 is increased from 2 mm to 4 mm.

[0124] (3) Preparation of metamaterial panel: Using epoxy resin film as carrier, the open-ring periodic metasurface prepared in step (2) is printed on epoxy resin film using screen printing technology. Then, the epoxy resin film with the printed metasurface is laid on the middle layer of quartz fiber reinforced resin base prepreg and cured by vacuum bag-autoclave curing process to obtain metamaterial panel. The vacuum bag-autoclave curing process is as follows: under vacuum degree not less than 0.095MPa, the temperature is raised to 100℃ at a heating rate of 2℃ / min, and the pressure is increased to 0.6MPa. The temperature is held for 2h, the temperature is raised to 150℃ and held for 1h, and finally the temperature is raised to 180℃ and held for 3h. Then, the temperature is cooled to 60℃ at a cooling rate of 1.5℃ / min, the pressure is released and the panel is removed from the autoclave, thus completing the preparation of metamaterial panel.

[0125] (4) Preparation of high-scattering dielectric conductive paste: MXene, carbon nanotubes and epoxy resin were mixed and stirred at a mass ratio of 1:3:10. The selected MXene has an accordion-like microstructure with a single layer size of 200-1000 nm and the carbon nanotubes have an outer diameter of 10 nm. The mixture was stirred at room temperature for 30 minutes using a high-speed stirrer at a stirring speed of 800 rpm to obtain the high-scattering dielectric conductive paste. The high-scattering dielectric conductive paste meets the electrical performance indicators shown in Table 2.

[0126] (5) Preparation of absorbing honeycomb: White honeycomb with a pore side length of 4mm and a height of 20mm was repeatedly impregnated and pre-cured in the high-scattering dielectric conductive paste prepared in step (4). The impregnation time for each time was controlled at 4min, the pre-curing temperature was 100℃, and the pre-curing time was 3min. By controlling the number of impregnations, the volume density of the absorbing honeycomb was achieved to be 110kg / m³. 3 .

[0127] (6) Preparation of low dielectric loss and high magnetic loss composite material panel: Short-cut carbon fiber, carbonyl iron powder, and epoxy resin were mixed and stirred in a mass ratio of 1:4:10. The selected short-cut carbon fiber had a length of 3 mm and a diameter of 7 μm. The carbonyl iron powder had an average particle size of 1000 mesh. The mixture was stirred at room temperature for 30 minutes using a high-speed stirrer at a stirring speed of 800 rpm. The mixture was cured using a vacuum bag-autoclave process under a vacuum degree of not less than 0.095 MPa. The temperature was increased to 100℃ at a heating rate of 1.5℃ / min and held for 4 hours. Then, the temperature was cooled to 60℃ at a cooling rate of 1.5℃ / min. The pressure was released from the autoclave to obtain the low dielectric loss and high magnetic loss composite material panel. The low dielectric loss and high magnetic loss composite material panel meets the electrical performance indicators shown in Table 3.

[0128] (7) Fabrication of an ultra-wideband absorbing honeycomb sandwich structure: The metamaterial panel prepared in step (3) is used as the upper panel, the absorbing honeycomb prepared in step (5) is used as the sandwich layer, and the low dielectric loss and high magnetic loss composite material panel prepared in step (6) is used as the lower panel. The upper panel, the absorbing honeycomb, and the lower panel are bonded together with an adhesive film, thus realizing the fabrication of an ultra-wideband absorbing honeycomb sandwich structure that is insensitive to polarization and incident angle. The thickness of the upper panel is 3 mm, the thickness of the lower panel is 3 mm, and the bonding process is as follows: the vacuum degree is not less than 0.095 MPa, the temperature is raised to 80°C at a heating rate of 1.5°C / min, held for 2 hours, and then cooled to 40-60°C at a cooling rate of 1.5°C / min to complete the bonding.

[0129] Example 3

[0130] An ultra-wideband absorbing honeycomb sandwich structure of the present invention includes an upper panel, an absorbing honeycomb, and a lower panel arranged sequentially from top to bottom. The upper panel is a metamaterial panel, which is composed of a quartz fiber reinforced resin matrix composite material and a polymer resin film with a metasurface printed on it disposed in the middle of the quartz fiber reinforced resin matrix composite material. The electrical properties of the metasurface meet the indicators in Table 1. The absorbing honeycomb is formed by impregnating a honeycomb structure with a high-scattering dielectric conductive paste. The electrical properties of the high-scattering dielectric conductive paste meet the indicators in Table 2. The lower panel is a low-dielectric-loss, high-magnetic-loss composite material panel. The electrical properties of the low-dielectric-loss, high-magnetic-loss composite material panel meet the indicators in Table 3. The target quality factor value of the ultra-wideband absorbing honeycomb sandwich structure meets the indicators in Table 4.

[0131] Table 1 Electrical performance indicators of metasurfaces

[0132] Frequency band (GHz) Average value of the real part of the impedance (Ω) Average value of the imaginary part of impedance (Ω) Thickness (mm) P(0.1-1) 400-600 40-90 0.3-0.6 L(1-2) 550-550 30-80 0.3-0.6 S(2-4) 310-540 40-90 0.5-0.6 C(4-8) 340-570 50-100 0.3-0.6 X(8-12) 310-510 40-90 0.3-0.6 Ku(12-18) 300-500 50-100 0.3-0.6

[0133] Table 2 Electrical Performance Indicators of High-Scattering Dielectric Conductive Paste

[0134] Frequency band (GHz) Electrical frequency dispersion Dielectric constant amplitude Alternating current conductivity (S / m) Electric loss tangent P(0.1-1) 10-20 50-80 0.3-0.5 0.1-0.4 L(1-2) 10-20 40-70 0.3-0.6 0.1-0.4 S(2-4) 10-20 30-60 0.4-0.6 0.2-0.6 C(4-8) 10-20 20-40 0.4-0.7 0.8-1.2 X(8-12) 10-20 15-30 0.5-0.7 1-1.5 Ku(12-18) 5-10 10-25 0.6-0.8 1-1.5

[0135] Table 3 Electrical Performance Indicators of Low Dielectric Loss and High Magnetic Loss Composite Material Panels

[0136] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent P(0.1-1) 0-0.1 3-8 10-20 8-15 0.01-0.05 / 0.1-0.3 L(1-2) 0-0.1 2-5 10-20 6-12 0.01-0.05 / 0.2-0.5 S(2-4) 0-0.1 1-3 10-20 5-10 0.01-0.05 / 0.3-0.5 C(4-8) 0-0.1 1-3 10-20 4-8 0.05-0.1 / 0.3-0.6 X(8-12) 0-0.1 1-3 10-20 3-8 0.05-0.1 / 0.5-0.7 Ku(12-18) 0-0.1 1-3 10-20 2-7 0.05-0.1 / 0.6-0.9

[0137] Table 4. Quality Factor Target Values ​​for Ultra-Wideband Absorbing Cellular Sandwich Structures

[0138] Frequency band (GHz) quality factor P(0.1-1) 0.1-0.5 L(1-2) 0.01-0.05 S(2-4) 0.01-0.05 C(4-8) 0.01-0.05 X(8-12) 0.01-0.05 Ku(12-18) 0.01-0.05 .

[0139] In this embodiment, the metasurface is made of high-frequency scattering effect absorbing resin, and the electrical performance indicators of the high-frequency scattering effect absorbing resin meet the indicators in Table 5. The structural unit of the metasurface is a combination of two open ring structures.

[0140] Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins

[0141] Frequency band (GHz) Electrical frequency dispersion Magnetic frequency dispersion Dielectric constant amplitude Permeability amplitude Electromagnetic loss tangent p(0.1-1) 300-400 50-100 400-600 150-500 0.5-1.5 / 0.2-1 L(1-2) 40-50 10-30 80-150 50-80 1-3 / 0.1-1 S(2-4) 20-40 5-15 50-70 20-40 1-3 / 0.1-1 C(4-8) 10-20 5-10 30-50 10-20 1-2 / 0.1-1 X(8-12) 5-10 2-5 20-40 5-15 1-3 / 0.1-1 Ku(12-18) 5-10 2-5 10-15 3-8 1-3 / 0.1-1 .

[0142] In this embodiment, the resin used in the quartz fiber reinforced resin matrix composite material is epoxy resin, and the polymer resin film is an epoxy resin film.

[0143] In this embodiment, the side length of the hexagonal cells in the honeycomb structure is 4mm, the height of the honeycomb structure is 20mm, and the volume density of the absorbing honeycomb is 90kg / m³. 3 .

[0144] In this embodiment, the high-scattering dielectric conductive paste is made by mixing microwave absorbing powder with epoxy resin, wherein the microwave absorbing powder is MXene and carbon black.

[0145] In this embodiment, the low dielectric loss and high magnetic loss composite material panel is obtained by curing and molding short-cut fibers, magnetic powder and epoxy resin as raw materials. The short-cut fibers are short-cut silicon carbide fibers and the magnetic powder is ZIF-67 metal-organic framework.

[0146] In this embodiment, the thickness of the upper panel is 3mm and the thickness of the lower panel is 3mm.

[0147] A method for fabricating an ultra-wideband absorbing honeycomb sandwich structure according to this embodiment includes the following steps:

[0148] (1) Preparation of high-frequency scattering effect absorbing resin: ZIF-67 metal-organic framework, chopped carbon fibers, and epoxy resin were mixed and stirred in a mass ratio of 4:1:10. The selected chopped carbon fibers had a length of 3 mm and a diameter of 7 μm. The mixture was stirred at room temperature for 30 minutes using a high-speed stirrer at a stirring speed of 800 rpm to obtain the high-frequency scattering effect absorbing resin. The high-frequency scattering effect absorbing resin met the electrical performance indicators shown in Table 5.

[0149] (2) Fabrication of metasurfaces: Design such as Figure 3 The open-ring periodic metasurface structure shown is an array structure composed of multiple structural units. Each structural unit is composed of an outer ring 1 and an inner ring 2 (nested together). The outer ring 1 is a notched circular ring structure, and the inner ring 2 is a notched circular ring structure. The width a of the outer ring 1 is 2 mm, and the radius R of the outer ring 1 is 10 mm. The width b of the inner ring 2 is 2 mm, and the radius r of the inner ring 2 is 6 mm. The opening size c of the outer ring 1 is 5 mm, and the opening size of the inner ring 2 is 5 mm. The high-frequency scattering effect absorbing resin prepared in step (1) is used to prepare an open-ring periodic metasurface according to the above structure. The metasurface meets the electrical performance indicators shown in Table 1.

[0150] (3) Preparation of metamaterial panel: Using epoxy resin film as carrier, the open-ring periodic metasurface prepared in step (2) is printed on epoxy resin film using screen printing technology. Then, the epoxy resin film with the printed metasurface is laid on the middle layer of quartz fiber reinforced resin base prepreg and cured by vacuum bag-autoclave curing process to obtain metamaterial panel. The vacuum bag-autoclave curing process is as follows: under vacuum degree not less than 0.095MPa, the temperature is raised to 100℃ at a heating rate of 2℃ / min, and the pressure is increased to 0.6MPa. The temperature is held for 2h, the temperature is raised to 150℃ and held for 1h, and finally the temperature is raised to 180℃ and held for 3h. Then, the temperature is cooled to 60℃ at a cooling rate of 1.5℃ / min, the pressure is released and the panel is removed from the autoclave, thus completing the preparation of metamaterial panel.

[0151] (4) Preparation of high-scattering dielectric conductive paste: MXene, carbon black and epoxy resin were mixed and stirred in a mass ratio of 4:2:10. The selected MXene has an accordion-like microstructure with a single layer size of 200-1000 nm and the carbon black has an average particle size of 100 nm. The mixture was stirred at room temperature for 30 minutes using a high-speed stirrer at a stirring speed of 800 rpm to obtain the high-scattering dielectric conductive paste. The high-scattering dielectric conductive paste meets the electrical performance indicators shown in Table 2.

[0152] (5) Preparation of absorbing honeycomb: White honeycomb with a pore side length of 4mm and a height of 20mm was repeatedly impregnated and pre-cured in the high-scattering dielectric conductive paste prepared in step (4). The impregnation time for each time was controlled at 3min, the pre-curing temperature was 90℃, and the pre-curing time was 4min. By controlling the number of impregnations, the volume density of the absorbing honeycomb was achieved to be 90kg / m³. 3 .

[0153] (6) Preparation of low dielectric loss and high magnetic loss composite material panel: Short-cut carbon fiber, carbonyl iron powder, and epoxy resin were mixed and stirred in a mass ratio of 1:3:10. The selected short-cut carbon fiber had a length of 3 mm and a diameter of 7 μm. The carbonyl iron powder had an average particle size of 1000 mesh. The mixture was stirred at room temperature for 30 minutes using a high-speed stirrer at a stirring speed of 800 rpm. The mixture was cured using a vacuum bag-autoclave process under a vacuum degree of not less than 0.095 MPa. The temperature was increased to 100℃ at a heating rate of 1.5℃ / min and held for 4 hours. Then, the temperature was cooled to 60℃ at a cooling rate of 1.5℃ / min. The pressure was released from the autoclave to obtain the low dielectric loss and high magnetic loss composite material panel. The low dielectric loss and high magnetic loss composite material panel meets the electrical performance indicators shown in Table 3.

[0154] (7) Fabrication of ultra-wideband absorbing honeycomb sandwich structure: The metamaterial panel prepared in step (3) is used as the upper panel, the absorbing honeycomb prepared in step (5) is used as the sandwich layer, and the low dielectric loss and high magnetic loss composite material panel prepared in step (6) is used as the lower panel. The upper panel, absorbing honeycomb and lower panel are bonded together with an adhesive film to obtain an ultra-wideband absorbing honeycomb sandwich structure. The thickness of the upper panel is 3 mm and the thickness of the lower panel is 3 mm. The bonding process is as follows: the vacuum degree is not less than 0.095 MPa, the temperature is raised to 80℃ at a heating rate of 1.5℃ / min, held for 2 hours, and then cooled to 40-60℃ at a cooling rate of 1.5℃ / min.

[0155] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. An ultra-wideband absorbing honeycomb sandwich structure, characterized in that, The structure includes, from top to bottom, an upper panel, a microwave-absorbing honeycomb, and a lower panel. The upper panel is a metamaterial panel, which is composed of a quartz fiber reinforced resin matrix composite material and a polymer resin film with a metasurface printed on it, located in the middle of the quartz fiber reinforced resin matrix polymer composite material. The electrical performance indicators of the metasurface are shown in Table 1. The microwave-absorbing honeycomb is formed by impregnating a honeycomb structure with a high-scattering dielectric conductive paste. The electrical performance indicators of the high-scattering dielectric conductive paste are shown in Table 2. The lower panel is a low-dielectric-loss, high-magnetic-loss composite material panel. The electrical performance indicators of the low-dielectric-loss, high-magnetic-loss composite material panel are shown in Table 3. The target quality factor values ​​of the ultra-wideband microwave-absorbing honeycomb sandwich structure are shown in Table 4. Table 1 Electrical performance indicators of metasurfaces Table 2 Electrical Performance Indicators of High-Scattering Dielectric Conductive Paste Table 3 Electrical Performance Indicators of Low Dielectric Loss and High Magnetic Loss Composite Material Panels Table 4. Quality Factor Target Values ​​for Ultra-Wideband Absorbing Cellular Sandwich Structures 。 2. The ultra-wideband absorbing honeycomb sandwich structure according to claim 1, characterized in that, The metasurface is made of a high-frequency scattering effect absorbing resin. The electrical performance indicators of the high-frequency scattering effect absorbing resin are shown in Table 5. The structural units of the metasurface include one or more combinations of sheet structure, open ring structure, closed ring structure and cross structure. Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins 。 3. The ultra-wideband absorbing honeycomb sandwich structure according to claim 1, characterized in that, The quartz fiber reinforced resin matrix composite material uses one or more of the following resins: epoxy resin, phenolic resin, bismaleimide, polyimide resin, and cyanate ester resin. The polymer resin film includes one or more of the following: polyetheretherketone resin film, epoxy resin film, bismaleimide resin film, and polyimide resin film.

4. The ultra-wideband absorbing honeycomb sandwich structure according to claim 1, characterized in that, The hexagonal lattice of the honeycomb structure has a side length of 2mm to 5mm, the height of the honeycomb structure is 15mm to 25mm, and the bulk density of the absorbing honeycomb is 90kg / m³. 3 ~120kg / m 3 ; The high-scattering dielectric conductive paste is made by mixing dielectric absorbing powder with epoxy resin. The dielectric absorbing powder includes one or more of zero-dimensional dielectric loss absorbing powder, one-dimensional dielectric loss absorbing powder, and two-dimensional dielectric loss absorbing powder. The zero-dimensional dielectric loss absorbing powder includes one or more of carbon spheres, carbon black, and fullerene. The one-dimensional dielectric loss absorbing powder includes one or more of carbon nanowires, carbon nanorods, carbon nanotubes, and carbon nanofibers. The two-dimensional dielectric loss absorbing powder includes one or more of graphene, Mxene, and MoS2.

5. The ultra-wideband absorbing honeycomb sandwich structure according to claim 1, characterized in that, The low dielectric loss and high magnetic loss composite material panel is obtained by curing and molding short-cut fibers, magnetic powder and epoxy resin as raw materials. The short-cut fibers are short-cut carbon fibers or short-cut silicon carbide fibers, and the magnetic powder includes one or more of carbonyl iron powder, magnetic metal-organic framework and magnetic core-shell structure.

6. The ultra-wideband absorbing honeycomb sandwich structure according to any one of claims 1 to 5, characterized in that, The thickness of the upper panel is 2mm to 4mm, and the thickness of the lower panel is 3mm to 5mm.

7. A method for preparing an ultra-wideband absorbing honeycomb sandwich structure as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Preparation of high-frequency scattering effect absorbing resin: High scattering absorber powder is dispersed in epoxy resin to obtain high-frequency scattering effect absorbing resin. The high-frequency scattering effect absorbing resin needs to meet the electrical performance indicators shown in Table 5. The high scattering absorber powder includes one or more of metal-organic framework, carbonyl iron powder, acetylene black, short-cut carbon fiber, graphene and carbon nanotubes. Table 5 Electrical Performance Indicators of High-Frequency Spreading Effect Absorbing Resins ； (2) Preparation of metasurface: The high-frequency scattering effect absorbing resin obtained in step (1) is prepared into a metasurface according to the required structure, so that the metasurface meets the electrical performance indicators shown in Table 1. (3) Preparation of metamaterial panel: The metasurface obtained in step (2) is printed onto a polymer resin film, the polymer resin film with the metasurface is laid onto the middle layer of quartz fiber reinforced resin base prepreg, and cured and shaped using a vacuum bag-autoclave curing process to obtain metamaterial panel. (4) Preparation of high-scattering dielectric conductive paste: The dielectric absorbing powder is mixed with epoxy resin. The dielectric absorbing powder includes one or more of zero-dimensional dielectric loss absorbing powder, one-dimensional dielectric loss absorbing powder and two-dimensional dielectric loss absorbing powder to obtain a high-scattering dielectric conductive paste. The high-scattering dielectric conductive paste needs to meet the electrical performance indicators shown in Table 2. (5) Preparation of absorbing honeycomb: The honeycomb structure is immersed in the high-scattering dielectric conductive paste obtained in step (4) for 3 min to 5 min, and then pre-cured by turning over at a temperature of 80℃ to 120℃ to coat the inner wall of the honeycomb structure with conductive paste. The immersion and coating are repeated until the bulk density of the absorbing honeycomb is 90 kg / m³. 3 ~120kg / m 3 ; (6) Preparation of low dielectric loss and high magnetic loss composite material panel: Magnetic absorbing powder is dispersed in epoxy resin. The magnetic absorbing powder includes short-cut fibers and magnetic powder. The panel is cured and formed by vacuum bag-autoclave curing process to obtain low dielectric loss and high magnetic loss composite material panel. The low dielectric loss and high magnetic loss composite material panel needs to meet the electrical performance indicators shown in Table 3. (7) Preparation of ultra-wideband absorbing honeycomb sandwich structure: The metamaterial panel obtained in step (3) is used as the upper panel, the absorbing honeycomb obtained in step (5) is used as the sandwich layer, and the low dielectric loss and high magnetic loss composite material panel obtained in step (6) is used as the lower panel. The upper panel, absorbing honeycomb and lower panel are bonded together with adhesive film to obtain ultra-wideband absorbing honeycomb sandwich structure.

8. The method for preparing the ultra-wideband absorbing honeycomb sandwich structure according to claim 7, characterized in that, In step (3), the vacuum bag-autoclave curing process is as follows: under a vacuum of not less than 0.095 MPa, the temperature is increased to 80℃ to 120℃ at a heating rate of 1℃ / min to 3℃ / min, while the pressure is increased to 0.5MPa to 0.7MPa, and the temperature is maintained for 2h to 3h. The temperature is then increased to 130℃ to 150℃ and maintained for 1h to 2h. Finally, the temperature is increased to 180℃ to 200℃ and maintained for 3h to 5h. Then, the temperature is cooled to 40℃ to 60℃ at a cooling rate of 1℃ / min to 3℃ / min, and the pressure is released from the autoclave.

9. The method for preparing the ultra-wideband absorbing honeycomb sandwich structure according to claim 7, characterized in that, In step (6), the vacuum bag-autoclave curing process is as follows: under a vacuum of not less than 0.095 MPa, the temperature is raised to 80℃ to 120℃ at a heating rate of 1℃ / min to 3℃ / min, and kept at that temperature for 3h to 5h. Then, the temperature is cooled to 40℃ to 60℃ at a cooling rate of 1℃ / min to 3℃ / min, and the pressure is released from the autoclave.

10. The method for preparing the ultra-wideband absorbing honeycomb sandwich structure according to any one of claims 7 to 9, characterized in that, In step (7), the bonding process of the adhesive film is as follows: the vacuum degree is not less than 0.095MPa, the temperature is raised to 80℃~120℃ at a heating rate of 1℃ / min~3℃ / min, the temperature is kept for 2h~4h, and then cooled to 40℃~60℃ at a cooling rate of 1℃ / min~3℃ / min.

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