Ultrathin / broadband / bearing wave-absorbing honeycomb sandwich multilevel structure and preparation method thereof

Abstract

The invention discloses an ultrathin / broadband / bearing wave-absorbing honeycomb sandwich multilevel structure and a preparation method thereof. The ultrathin / broadband / bearing wave-absorbing honeycomb sandwich multilevel structure is formed by connecting unit bodies of rectangular structures. Each unit body comprises a reflecting plate, a square hole honeycomb core body and a metasurface, the square hole honeycomb core body is made of a functional fiber reinforced composite material, and the reflecting plate is made of a carbon fiber composite material; wherein the metasurface and the reflecting plate are arranged on the upper surface and the lower surface of the core body respectively, the square hole honeycomb core body comprises an external square hole and a honeycomb arranged in the square hole, and the inner surface of the square hole is provided with a coating; a lattice structure made of a thermoplastic material is arranged in the honeycomb in the square hole, and the metasurface is a periodic array pattern and is made of a conductive carbon-based nano material; and each unit body is connected with the adjacent unit body in a clamping groove interlocking manner. The broadband electromagnetic absorption effect within the frequency band of 4-40 GHz is achieved, meanwhile, the high specific strength and specific stiffness of the whole sandwich structure are achieved, and an efficient way is provided for achieving a high-performance electromagnetic function structure.

Description

Technical Field

[0001] The invention belongs to the research field of functional composite materials, and specifically relates to an ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure and a preparation method thereof. Background Art

[0002] In recent years, one of the criteria for measuring a country's comprehensive national strength is its military armed forces. Among them, the high concealment and strong anti-reconnaissance capabilities of weapons and equipment can greatly enhance the strength of the army, and it always has a leading strength in the performance of national defense. At present, the concealment technology of weapons and equipment mainly relies on the following two aspects: the first aspect is the aerodynamic shape structure design; the second aspect is the material structure design. It mainly designs the impedance and electromagnetic loss capacity of the material structure, thereby greatly satisfying the complete absorption of the incident electromagnetic wave. At present, functional composite sandwich structures are often used in aircraft structural components to achieve the electromagnetic functionality of the load-bearing components. The traditional wave-absorbing honeycomb sandwich structure mainly uses paper honeycombs as the load-bearing matrix, and its surface homogeneous loss medium has a contradiction between thickness and absorption capacity or adds a frequency selective surface film as an artificial tuning method. If the loss medium content is increased, it will lead to losses in structural weight, strength and other aspects, greatly reducing the efficiency of structural use; if too much frequency selective surface film is added to the structure, a weak interlayer interface will appear inside the structure, which will greatly reduce the overall structural mechanical properties.

[0003] In addition, although domestic and foreign researchers have also carried out diversified innovative research on the unit cell geometry configuration, fiber types and other aspects of the sandwich structure, how to achieve the simultaneous enhancement of the mechanical and electromagnetic properties of the sandwich structure is still one of the difficult problems to be solved. The main reason is that the sandwich structure is a type of structural / functional integrated composite material, and its mechanical and electromagnetic performance constraints are very complex and mutually coupled, which makes it difficult for the structure to take into account both electromagnetic and mechanical properties at the same time. It can only achieve the improvement of a single performance and cannot meet actual engineering needs. Summary of the invention

[0004] The purpose of the present invention is to provide an ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure and a preparation method thereof, so as to overcome the problems existing in the prior art.

[0005] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0006] An ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure is composed of mutually connected rectangular unit bodies; each unit body comprises a reflector, a square-hole honeycomb core and a super surface, the square-hole honeycomb core body adopts a functional fiber-reinforced composite material, and the reflector is a carbon fiber composite material; wherein: the super surface and the reflector are respectively arranged on the upper and lower surfaces of the core body, the square-hole honeycomb core body comprises an external square hole and a honeycomb arranged in the square hole, and the inner surface of the square hole has a coating; a lattice structure of thermoplastic material is arranged in the honeycomb in the square hole, the super surface is a periodic array pattern and the material is a conductive carbon-based nano material; each unit body is connected to an adjacent unit body by a card slot interlocking method.

[0007] Furthermore, the metasurface is of a band-stop type, and the surface resistance of the metasurface is 300 to 700 ohms / □.

[0008] Furthermore, the resistance of the coating on the inner surface of the square hole is in the range of 200 to 600 ohms / □, and the thickness of the coating is in the range of 10 to 12 μm.

[0009] Furthermore, the honeycomb structure wall thickness of the square-cell honeycomb core is in the range of 0.375 to 0.75 mm; the functional fiber-reinforced composite material used in the square-cell honeycomb core is glass fiber, quartz fiber or aramid fiber.

[0010] Furthermore, the lattice structure of the thermoplastic material includes Walled TMPS, Diamond and honeycomb-like lattice configurations, the wall thickness of the lattice structure is in the range of 0.5 mm to 1 mm, the matrix material of the lattice structure is polylactic acid, nylon acrylonitrile-butadiene-styrene terpolymer or polyetheretherketone; the filler of the lattice structure is a multidimensional carbon-based material or a carbon-based magnetic material, including graphene, carbon nanotubes, and graphene-loaded ferrite.

[0011] Furthermore, the characteristic impedance value of the metasurface in the low-frequency band of 4 to 17 GHz is between 377 and 300 ohms, and the characteristic impedance value of the core part in the low-frequency band of 4 to 17 GHz is between 300 and 225 ohms.

[0012] A design method for an ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure, comprising:

[0013] Step 101, using finite element software to model and optimize the square hole honeycomb core, the parameters in the optimization process include honeycomb wall thickness d, height H, unit cell period size L and square hole inner surface coating resistance Rs; the optimization goal is to reduce the honeycomb wall thickness d and height H as much as possible under the condition of meeting the frequency range of 2 to 40 GHz, so as to obtain the optimal size parameters of the optimized square hole honeycomb core;

[0014] On the basis of determining the size of the square-hole honeycomb core, a transmission line theoretical model of the unit body is constructed. Based on the S-parameter inversion method and the calculation formula of the transmission coefficient and reflection coefficient of the unit body, the characteristic impedance of the unit body corresponding to different frequencies is solved, thereby determining the distribution relationship between the characteristic impedance of the unit body and the frequency.

[0015] Step 102, on the basis of determining the size of the square hole honeycomb core, designing a super surface pattern on the fiber reinforced composite material surface on the upper surface of the square hole honeycomb core, thereby forming a super surface; wherein the super surface unit on the super surface includes an internal square and a rectangular wire frame arranged around the square, the width of the wire frame is Q, the width of the square is W, and the spacing between adjacent super surface units is S; combining the transmission line theoretical model of the unit body, and based on the distribution relationship between the characteristic impedance of the unit body and the frequency, using finite element simulation software to further optimize the parameters Q, W and S of the super surface unit and the resistance value of the super surface material, to obtain the optimal size parameters and corresponding impedance that reduce the impedance gradient formed between the incident electromagnetic wave, the super surface and the unit body;

[0016] Step 103, filling a matrix structure filler with a wall thickness of N and a height of h into the honeycombs of the square-hole honeycomb core to form a honeycomb sandwich multi-level structure; comparing the maximum compression strength of the lattice structure under different wall thicknesses and heights through a quasi-static compression test, and selecting the wall thickness and height of the lattice structure that can achieve the best mechanical coupling enhancement effect of the honeycomb sandwich multi-level structure as the optimal size parameters of the lattice structure.

[0017] A method for preparing an ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure, comprising:

[0018] Step 201, using the optimal size parameters of the square-hole honeycomb core optimized in the design method, first prepare a square-hole honeycomb core of glass fiber reinforced composite material, and then prepare a conductive carbon-based coating on the inner wall surface of the square hole by screen printing, and the coating is 10-12 μm; then put it into a 100° C.-120° C. oven for drying for 1-3 hours; after cooling, put the square-hole honeycomb core into a fine-tuning machine tool for fixing, use a 0.1mm-0.6mm diameter cutter head, and control the spindle speed at 2000-4000 rap / min to prepare strips on the outer wall of the square-hole honeycomb core; finally, the processed strips are slotted and locked to complete the preparation of the square-hole honeycomb core part;

[0019] Step 202, using the optimal size parameters of the lattice structure optimized in the design method, the lattice structure is prepared by FDM 3D printing process; the material of the lattice structure is thermoplastic polylactic acid filament, the nozzle temperature is set to 200° C. to 350° C., the hot bed temperature is set to 50° C. to 100° C., and the printing speed is 10 mm / s to 100 mm / s; after the printing is completed, the lattice structure is nested in the prepared square hole honeycomb core;

[0020] Step 203, preparing a fiber-reinforced composite material surface on the upper surface of the square-hole honeycomb core, using the optimal size parameters of the super surface optimized in the design method, mixing a conductive carbon-based slurry corresponding to the surface impedance, and using a screen printing process to prepare a super surface unit pattern on the surface of the fiber-reinforced composite material to form a super surface structure, and then putting it into a 100° C. to 120° C. oven to dry for 1 to 3 hours, and then cooling and taking it out;

[0021] Step 204, prepare a reflective plate on the lower surface of the square hole honeycomb core, and then use a vacuum bag process to integrate the super surface, the square hole honeycomb core and the filled lattice structure and the reflective plate to obtain a prepared ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure.

[0022] Compared with the prior art, the present invention has the following technical features:

[0023] The present invention adopts a convenient and efficient multi-process manufacturing method to replace the traditional frequency selective film. By constructing the interaction relationship between the conductive coating, the metasurface configuration and the lattice structure, the transmission line theory and the electromechanical decoupling model are used to optimize the impedance gradient design of the equivalent model to achieve a broadband electromagnetic absorption effect in the 4-40GHz frequency band. At the same time, the multi-level coupling effect of the honeycomb sandwich structure and the lattice filling structure is utilized to achieve high specific strength and specific energy absorption of the overall sandwich structure, and further obtain a broadband load-bearing integrated functional sandwich structure; the present invention provides an efficient way to achieve high-performance electromagnetic functional structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is an ultra-thin / broadband / load-bearing integrated absorbing honeycomb sandwich multi-level structure and its unit cell periodic model;

[0025] Figure 2 It is a schematic diagram of the transmission line theory model of the unit body periodic model;

[0026] Figure 3 Impedance distribution diagram of the ultra-thin / broadband / load-bearing integrated absorbing honeycomb sandwich multi-level structure;

[0027] Figure 4 This is a comparison chart of the actual test absorption rate and the simulated absorption rate in the 4-40GHz frequency band;

[0028] Figure 5 The stress-strain curves of the lattice structure and its ultra-thin / broadband / load-bearing integrated absorbing honeycomb sandwich structure. DETAILED DESCRIPTION

[0029] The technical problem to be solved by the present invention is to overcome the problems of narrow absorption band, large thickness and poor mechanical properties of existing electromagnetic functional structures, and provide a broadband / load-bearing integrated absorbing honeycomb sandwich multi-level structure based on conductive coating / supersurface and a multi-process preparation method, thereby achieving 35.30GHz broadband effective electromagnetic absorption (absorption rate>87%) in the 4-40GHz frequency band and 21.94MPa maximum compression strength and 6.43MJ·m-3 specific energy absorption effect at a thickness of 9mm, effectively overcoming the problem that the mechanical properties and electromagnetic properties of traditional absorbing structures cannot be taken into account at the same time. At the same time, the volume density of the structure is less than 0.55kg / m -3 , achieving the lightweight effect of the structure.

[0030] The present invention constructs the electromechanical interaction relationship between the functional square-hole honeycomb core, the metasurface configuration and the lattice structure, and uses the transmission line theoretical model to perform a gradient design on the impedance of each layer in the equivalent multi-layer model of the multi-level structure of the absorbing honeycomb sandwich, so that a large number of electromagnetic waves enter the structure to form multiple reflections and scattering, effectively overcoming the problem of the narrow absorption band of the structure; at the same time, the multi-level coupling effect of the square-hole honeycomb sandwich structure and the filling small-size lattice configuration is used to achieve the mechanical enhancement of the overall sandwich structure, and further obtain a broadband / load-bearing integrated functional sandwich structure.

[0031] See attached Figure 1 The present invention provides an ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure, which is composed of rectangular structured unit bodies connected to each other; each unit body includes a reflector, a square hole honeycomb core and a super surface, the square hole honeycomb core body adopts a functional fiber reinforced composite material, and the reflector is a carbon fiber composite material; wherein: the super surface and the reflector are respectively arranged on the upper and lower surfaces of the core body, the square hole honeycomb core body includes an external square hole and a honeycomb arranged in the square hole, and the inner surface of the square hole has a coating; a lattice structure of thermoplastic material is arranged in the honeycomb in the square hole, the super surface is a periodic array pattern and the material is a conductive carbon-based nanomaterial; each unit body is connected to an adjacent unit body by a card slot interlocking method.

[0032] In this solution, the metasurface is of band-stop type, and the surface resistance of the metasurface is controlled to be 300-700 ohms / □; the resistance of the surface coating inside the square hole is controlled to be 200-600 ohms / □, and the coating thickness is in the range of 10-12 μm.

[0033] In this solution, the honeycomb structure wall thickness of the square-cell honeycomb core is in the range of 0.375 to 0.75 mm; the functional fiber-reinforced composite material used in the square-cell honeycomb core may be glass fiber, quartz fiber, aramid fiber, or the like.

[0034] In this embodiment, the lattice structure of the thermoplastic material can be a lattice configuration such as Walled TMPS, Diamond, and honeycomb. The wall thickness of the lattice structure is in the range of 0.5 mm to 1 mm. The matrix material of the lattice structure can be polylactic acid, nylon acrylonitrile-butadiene-styrene terpolymer, polyetheretherketone and other thermoplastic materials. The filler of the lattice structure can be a multidimensional carbon-based material or a carbon-based magnetic material, including graphene, carbon nanotubes, graphene-loaded ferrite, etc.

[0035] In this solution, the characteristic impedance value of the metasurface in the low-frequency 4-17 GHz frequency band is between 377 and 300 ohms, and the characteristic impedance value of the core part in the low-frequency 4-17 GHz frequency band is between 300 and 225 ohms.

[0036] The present invention further provides a design method for an ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure, comprising the following steps:

[0037] Step 101, optimizing electromagnetic loss and impedance matching of a square-cell honeycomb core.

[0038] like Figure 1 As shown in the figure, the square hole honeycomb core is modeled and optimized using CST microwave studio finite element software. The parameters in the optimization process include the honeycomb wall thickness d, height H, unit cell period size L and the resistance Rs of the inner surface coating of the square hole. The optimization goal is to reduce the honeycomb wall thickness d and height H as much as possible under the condition of meeting the frequency range of 2 to 40 GHz, so as to obtain the optimal size parameters of the optimized square hole honeycomb core.

[0039] At the same time, if Figure 2 As shown in the figure, on the basis of determining the size of the square hole honeycomb core, a transmission line theoretical model of the unit body is constructed, and based on the S parameter inversion method, the distribution relationship between the characteristic impedance of the unit body and the frequency is determined:

[0040]

[0041] Where S 21 (S 12 ) and S 11 (S 22 ) represent the transmission coefficient and reflection coefficient of the unit cell, n represents the refractive index, k represents the wave number, Z r represents characteristic impedance, d represents the maximum thickness, and i represents the imaginary unit.

[0042] The characteristic impedance Z at different frequencies can be solved by the above formula r , thus obtaining the distribution relationship between characteristic impedance and frequency.

[0043] Step 102, optimizing the metasurface electromagnetic loss and impedance matching.

[0044] On the basis of determining the size of the square-hole honeycomb core, a super surface pattern is designed on the surface of the fiber-reinforced composite material on the upper surface of the square-hole honeycomb core, thereby forming a super surface; wherein the super surface unit pattern on the super surface is as follows Figure 1 As shown, it includes an internal square and a rectangular wireframe arranged around the block, the width of the wireframe is Q, the width of the square is W, and the spacing between adjacent metasurface units is S; combined with the transmission line theoretical model of the unit body, and based on the distribution relationship between the unit body characteristic impedance and frequency obtained in step 1, the CST microwave studio finite element simulation software is used to further optimize the parameters (Q, W and S) of the metasurface unit and the resistance value of the metasurface material, and the optimal size parameters and corresponding impedance that reduce the impedance gradient formed between the incident electromagnetic wave (air impedance), the metasurface (surface impedance), and the unit body (characteristic impedance) are obtained, thereby further realizing the effective electromagnetic loss of the incident electromagnetic wave in the square hole honeycomb core, and obtaining the ultra-thin and broadband absorption effect.

[0045] Step 103, the mechanical properties of the honeycomb sandwich multi-level structure are enhanced.

[0046] A small-sized lattice structure filler with a wall thickness of N and a height of h is filled into the honeycomb of the square-hole honeycomb core to form a honeycomb sandwich multi-level structure. The maximum compression strength of the lattice structure under different wall thicknesses and heights is compared through a quasi-static compression test, and the wall thickness and height of the lattice structure that can achieve the best mechanical coupling enhancement effect of the honeycomb sandwich multi-level structure are selected as the optimal size parameters of the lattice structure.

[0047] Since the mechanical and electrical properties of the multi-level structure model of the wave-absorbing honeycomb sandwich are decoupled, the lattice structure filler mainly affects the bearing performance of the overall structure, but has a smaller effect on the electromagnetic performance. Therefore, the present invention combines the square hole honeycomb core with a small-sized lattice structure filler (thin-walled TMPS, Diamond, honeycomb-like) with a wall thickness in the range of N (0.5mm to 1mm) and a height of h to optimize the mechanical properties.

[0048] The present invention further provides a method for preparing an ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure, comprising the following steps:

[0049] The present invention adopts a variety of composite processing and manufacturing technologies such as screen printing technology and additive and subtractive technology (CNC machine tool processing and 3D printing) to achieve the rapid and efficient preparation of an ultra-thin / broadband / load-bearing integrated absorbing honeycomb sandwich structure, as follows:

[0050] Step 201, using the optimal size parameters of the square-hole honeycomb core optimized in the design method, first prepare a square-hole honeycomb core of glass fiber reinforced composite material, and then prepare a conductive carbon-based coating on the inner wall surface of the square hole by screen printing, and the coating is 10-12 μm; then put it into an oven at 100°C to 120°C (preferably 120°C) for drying for 1-3 hours; after cooling, put the square-hole honeycomb core into a fine-tuning machine for fixing, use a 0.1mm to 0.6mm (preferably 0.4mm) diameter cutter head, and control the spindle speed at 2000 to 4000rap / min (preferably 3500rap / min) to prepare the strips on the outer wall of the square-hole honeycomb core; finally, the processed strips are slotted and locked to complete the preparation of the square-hole honeycomb core part.

[0051] Step 202, using the optimal size parameters of the lattice structure optimized in the design method, preparing the lattice structure through the FDM 3D printing process; the material of the lattice structure is selected as thermoplastic polylactic acid filament, the nozzle temperature is set to 200°C to 350°C (preferably 215°C), the hot bed temperature is set to 50°C to 100°C (preferably 50°C), and the printing speed is 10mm / s to 100mm / s (preferably 50mm / s); after printing is completed, the lattice structure is nested into the prepared square hole honeycomb core.

[0052] Step 203, prepare a fiber reinforced composite material surface on the upper surface of the square hole honeycomb core, use the optimal size parameters of the super surface optimized in the design method, mix a conductive carbon-based slurry with corresponding surface impedance, and use a screen printing process to prepare a super surface unit pattern on the surface of the fiber reinforced composite material to form a super surface structure, and then put it into an oven at 100°C to 120°C (preferably 120°C) to dry for 1 to 3 hours, and cool and take it out.

[0053] Step 204, prepare a reflective plate on the lower surface of the square hole honeycomb core, and then use a vacuum bag process to integrate the super surface, the square hole honeycomb core and the filled lattice structure and the reflective plate to obtain a prepared ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure.

[0054] Example:

[0055] In a specific example of the present invention, see Figure 1As shown in the figure, the specific dimensions of the wave-absorbing honeycomb sandwich multi-level structure obtained by the optimization method of the present invention are: L (unit period size) in the square hole honeycomb core is 9 mm, d (honeycomb wall thickness) is 0.375 mm, H (honeycomb height) is 8 mm, and the surface resistance Rs of the coating is 200 ohms / ￡; the filling body is a hexagonal honeycomb lattice structure, whose wall thickness N is 1 mm and height h is 8 mm; S (super surface unit spacing) in the super surface unit graph is 1 mm, Q (wire frame width) is 0.6 mm, W (block width) is 6 mm, and the surface resistance K of the super surface is 500 ohms / □; the corresponding square hole honeycomb core, super surface and air impedance distribution with frequency, see the attached Figure 3 shown.

[0056] The invention discloses a multi-process hybrid preparation method for an ultra-thin / broadband / load-bearing integrated absorbing honeycomb sandwich multi-level structure. A continuous glass fiber reinforced composite material is selected as a square hole honeycomb structure skeleton. A conductive coating is prepared on the surface of a glass fiber board by screen printing, and the preparation thickness is controlled at 10 to 12 μm. The assembled parts of the square hole honeycomb structure are processed by a CNC engraving machine, the drill diameter is 0.4 mm, and the spindle speed is controlled at 3500 rap / min. The obtained parts are then prepared by a card slot locking process to realize the preparation of a square hole absorbing honeycomb core. The FDM 3D printing process is used to prepare a hexagonal honeycomb lattice structure with a length×width×height of 8.6×8.6mm×8mm, and the printing material is selected as polylactic acid. The printing nozzle temperature is set to 215°C, the hot bed temperature is 50°C, and the printing rate is set to 50 mm / s. After the printing is completed, the lattice structure is nested in the square hole honeycomb core. The metasurface was prepared by screen printing process, and the thickness of the metasurface was controlled at 10um. After the screen printing was completed, the sample was placed in a 120℃ oven for drying for 1 hour, cooled and taken out, and then integrated into an integrated absorbing honeycomb sandwich multi-level structure under room temperature through a vacuum bag.

[0057] The performance of the honeycomb structure prepared by the present invention is tested. Figure 4-Figure 5 As shown in the figure, it can be seen from the data in the figure that the structural sample prepared by the present invention can achieve 35.30GHz broadband effective electromagnetic absorption (absorption rate>87%) at 4-40GHz. In addition, by using quasi-static compression test, the maximum compressive strengths of the hexagonal lattice structure sample and the final absorbing honeycomb sandwich structure sample (9mm thickness) were obtained as 15.42MPa and 21.94MPa, respectively, which are 200% higher than the compressive strength of the honeycomb sandwich structure without hexagonal lattice structure. At the same time, the final absorbing honeycomb sandwich structure sample (9mm thickness) can achieve a specific energy absorption effect of 6.43MJ·m-3 under a stress of 0.4, verifying the effectiveness and advancement of the present invention.

[0058] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. An ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure, characterized in that: The multi-level structure is composed of mutually connected rectangular unit bodies; each unit body includes a reflector, a square-hole honeycomb core and a super surface, the square-hole honeycomb core body adopts a functional fiber-reinforced composite material, and the reflector is a carbon fiber composite material; wherein: the super surface and the reflector are respectively arranged on the upper and lower surfaces of the core body, the square-hole honeycomb core body comprises an external square hole and a honeycomb arranged in the square hole, and the inner surface of the square hole has a coating; a lattice structure of thermoplastic material is arranged in the honeycomb in the square hole, the super surface is a periodic array pattern and the material is a conductive carbon-based nano material; each unit body is connected to an adjacent unit body by a card slot interlocking method.

2. The ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure according to claim 1, characterized in that: The metasurface is of band-stop type, and the surface resistance of the metasurface is 300 to 700 ohms / □.

3. The ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure according to claim 1, characterized in that: The resistance of the coating on the inner surface of the square hole is in the range of 200 to 600 ohms / □, and the thickness of the coating is in the range of 10 to 12 μm.

4. The ultra-thin / broadband / load-bearing and wave-absorbing honeycomb sandwich multi-level structure according to claim 1, characterized in that: The honeycomb structure wall thickness of the square-hole honeycomb core is in the range of 0.375-0.75 mm; the functional fiber-reinforced composite material used in the square-hole honeycomb core is glass fiber, quartz fiber or aramid fiber.

5. The ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure according to claim 1, characterized in that: The lattice structure of the thermoplastic material includes Walled TMPS, Diamond and honeycomb-like lattice configurations. The wall thickness of the lattice structure is in the range of 0.5 mm to 1 mm. The matrix material of the lattice structure is polylactic acid, nylon acrylonitrile-butadiene-styrene terpolymer or polyetheretherketone; the filler of the lattice structure is a multidimensional carbon-based material or a carbon-based magnetic material, including graphene, carbon nanotubes, and graphene-loaded ferrite.

6. The ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure according to claim 1, characterized in that: The characteristic impedance value of the metasurface in the low-frequency 4-17 GHz frequency band is between 377 and 300 ohms, and the characteristic impedance value of the core part in the low-frequency 4-17 GHz frequency band is between 300 and 225 ohms.

7. A design method for an ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure, characterized in that: include: Step 101, using finite element software to model and optimize the square hole honeycomb core, the parameters in the optimization process include honeycomb wall thickness d, height H, unit cell period size L and square hole inner surface coating resistance Rs; the optimization goal is to reduce the honeycomb wall thickness d and height H as much as possible under the condition of meeting the frequency range of 2 to 40 GHz, so as to obtain the optimal size parameters of the optimized square hole honeycomb core; On the basis of determining the size of the square-hole honeycomb core, a transmission line theoretical model of the unit body is constructed. Based on the S-parameter inversion method and the calculation formula of the transmission coefficient and reflection coefficient of the unit body, the characteristic impedance of the unit body corresponding to different frequencies is solved, thereby determining the distribution relationship between the characteristic impedance of the unit body and the frequency. Step 102, on the basis of determining the size of the square hole honeycomb core, designing a super surface pattern on the fiber reinforced composite material surface on the upper surface of the square hole honeycomb core, thereby forming a super surface; wherein the super surface unit on the super surface includes an internal square and a rectangular wire frame arranged around the square, the width of the wire frame is Q, the width of the square is W, and the spacing between adjacent super surface units is S; combining the transmission line theoretical model of the unit body, and based on the distribution relationship between the characteristic impedance of the unit body and the frequency, using finite element simulation software to further optimize the parameters Q, W and S of the super surface unit and the resistance value of the super surface material, to obtain the optimal size parameters and corresponding impedance that reduce the impedance gradient formed between the incident electromagnetic wave, the super surface and the unit body; Step 103, filling a matrix structure filler with a wall thickness of N and a height of h into the honeycombs of the square-hole honeycomb core to form a honeycomb sandwich multi-level structure; comparing the maximum compression strength of the lattice structure under different wall thicknesses and heights through a quasi-static compression test, and selecting the wall thickness and height of the lattice structure that can achieve the best mechanical coupling enhancement effect of the honeycomb sandwich multi-level structure as the optimal size parameters of the lattice structure.

8. A method for preparing an ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure, characterized in that: include: Step 201, using the optimal size parameters of the square-hole honeycomb core optimized in the design method, first prepare a square-hole honeycomb core of glass fiber reinforced composite material, and then prepare a conductive carbon-based coating on the inner wall surface of the square hole by screen printing, and the coating is 10-12 μm; then put it into a 100° C.-120° C. oven for drying for 1-3 hours; after cooling, put the square-hole honeycomb core into a fine-tuning machine tool for fixing, use a 0.1mm-0.6mm diameter cutter head, and control the spindle speed at 2000-4000 rap / min to prepare strips on the outer wall of the square-hole honeycomb core; finally, the processed strips are slotted and locked to complete the preparation of the square-hole honeycomb core part; Step 202, using the optimal size parameters of the lattice structure optimized in the design method, to prepare the lattice structure through an FDM 3D printing process; The material of the lattice structure is thermoplastic polylactic acid filament, the nozzle temperature is set to 200℃~350℃, the hot bed temperature is set to 50℃~100℃, and the printing speed is 10mm / s~100mm / s; After printing is completed, the lattice structure is nested into the prepared square-hole honeycomb core; Step 203, preparing a fiber-reinforced composite material surface on the upper surface of the square-hole honeycomb core, using the optimal size parameters of the super surface optimized in the design method, mixing a conductive carbon-based slurry corresponding to the surface impedance, and using a screen printing process to prepare a super surface unit pattern on the surface of the fiber-reinforced composite material to form a super surface structure, and then putting it into a 100° C. to 120° C. oven to dry for 1 to 3 hours, and then cooling and taking it out; Step 204, prepare a reflective plate on the lower surface of the square hole honeycomb core, and then use a vacuum bag process to integrate the super surface, the square hole honeycomb core and the filled lattice structure and the reflective plate to obtain a prepared ultra-thin / broadband / load-bearing absorbing honeycomb sandwich multi-level structure.

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