An ultrathin broadband load-bearing wave-absorbing honeycomb sandwich multi-level structure and a preparation method thereof

Abstract

The application discloses a kind of ultrathin broadband bearing wave-absorbing honeycomb sandwich multi-stage structure and preparation method, by the unit body of rectangular structure is connected mutually to constitute;Each unit body includes reflector, square hole honeycomb core and super surface, square hole honeycomb core adopts functional fiber reinforced composite material, and reflector is carbon fiber composite material;Wherein: super surface, reflector are respectively arranged in the upper and lower surfaces of core body, square hole honeycomb core includes the square hole of outside and the honeycomb of being arranged in square hole, and the inner surface of square hole has coating;Dot matrix structure of thermoplastic material is arranged in the honeycomb in square hole, and the super surface is periodic array pattern and material is conductive carbon-based nanomaterial;Each unit body is connected with adjacent unit body by card slot interlocking mode connection.The application realizes the broadband electromagnetic absorption effect in 4~40GHz frequency band, simultaneously realizes the high specific strength and specific rigidity of overall sandwich structure, provides an efficient way for realizing high-performance electromagnetic function structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of functional composite materials, and particularly relates to an ultrathin broadband bearing wave-absorbing honeycomb sandwich multi-level structure and a preparation method thereof. BACKGROUND

[0002] In recent years, one of the standards for measuring the strength of a country's comprehensive national power is military armed forces. Among them, the high concealment and strong anti-detection capability of weapon equipment can greatly enhance the strength of the army and always have leading strength in the performance of national defense forces. At present, the concealment technology of weapon equipment mainly depends 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 capability of the material structure, so as to greatly satisfy the complete absorption of incident electromagnetic waves. At present, functional composite sandwich structures are often used in aircraft structural components, thereby realizing the electromagnetic functionality of the bearing component. The traditional wave-absorbing honeycomb sandwich structure mainly takes paper honeycomb as the bearing matrix, and the surface loss medium exists in the contradiction between thickness and absorption capacity or adds a frequency selective surface film as an artificial coordination method. If the loss medium content is increased, the structure weight, strength and other aspects will be lost, which greatly reduces the structure use efficiency; if too many frequency selective surface films are added in the structure, weak interfacial layers will appear in the structure, thereby greatly reducing the mechanical properties of the overall structure.

[0003] In addition, although domestic and foreign research scholars have carried out multi-innovation research on the unit cell geometric configuration and fiber type of the sandwich structure at the present stage, how to realize the synchronous enhancement design of the mechanical properties and electromagnetic properties of the sandwich structure is still one of the problems to be solved, and the main reason is that the sandwich structure is a kind of structure / function integrated composite material, and the mechanical properties and electromagnetic properties are very complex and coupled, which makes it difficult to simultaneously consider the electromagnetic properties and mechanical properties of the structure, and only the single performance can be improved, which cannot meet the actual engineering needs. SUMMARY

[0004] The purpose of the application is to provide an ultrathin broadband bearing 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-mentioned task, the application adopts the following technical scheme:

[0006] An ultrathin broadband load wave-absorbing honeycomb sandwich multi-level structure is composed of rectangular unit bodies connected with each other; each unit body comprises a reflecting plate, a square-hole honeycomb core and a metasurface, the square-hole honeycomb core 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 and lower surfaces of the core respectively, the square-hole honeycomb core comprises square holes on the outside and honeycombs arranged in the square holes, and the inner surface of the square hole has a coating; a dot matrix structure of thermoplastic material is arranged in the honeycomb in the square hole, the metasurface is a periodic array pattern and the material is a conductive carbon-based nanomaterial; each unit body is connected with the adjacent unit body through a clamping slot interlocking mode.

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

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

[0009] Further, the wall thickness of the honeycomb structure in 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.

[0010] Further, the dot matrix structure of the thermoplastic material comprises Walled TMPS, Diamond and honeycomb-like dot matrix configurations, the wall thickness of the dot matrix structure is in the range of 0.5 mm-1 mm, the matrix material of the dot matrix structure is polylactic acid, a ternary copolymer of nylon acrylonitrile-butadiene-styrene or polyether ether ketone; the filler of the dot matrix structure is a multi-dimensional carbon-based material or a carbon-based magnetic material, including graphene, carbon nanotubes, graphene loaded ferrite.

[0011] Further, 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.

[0012] A design method of an ultrathin broadband load wave-absorbing honeycomb sandwich multi-level structure, comprising:

[0013] Step 101, modeling and optimizing the square-hole honeycomb core by using finite element software, the parameters in the optimization process including the honeycomb wall thickness d , height H , unit body periodic size L and resistance of the coating on the inner surface of the square hole Rs ; the optimization goal is to reduce the honeycomb wall thickness as much as possible under the condition of meeting the frequency range of 2-40 GHzd and height H , 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 unit cell transmission line theoretical model is constructed, the characteristic impedance of the unit cell at different frequencies is calculated based on the S-parameter inversion method and the transmission coefficient and reflection coefficient calculation formula of the unit cell, and the distribution relationship between the characteristic impedance of the unit cell and the frequency is determined;

[0015] Step 102, on the basis of determining the size of the square hole honeycomb core, an ultrathin surface pattern is designed on the fiber-reinforced composite surface of the upper surface of the square hole honeycomb core, so as to form an ultrathin surface; wherein the ultrathin surface unit on the ultrathin surface includes an internal square and a rectangular frame arranged around the square, the width of the frame is Q , the width of the square is W , and the distance between adjacent ultrathin surface units is S ; combining the unit cell transmission line theoretical model, and based on the distribution relationship between the characteristic impedance of the unit cell and the frequency, the parameters Q , W and S of the ultrathin surface unit and the resistance value of the ultrathin surface material are further optimized by using a finite element simulation software, so as to obtain the optimal size parameters and the corresponding impedance which make the impedance gradient between the incident electromagnetic wave, the ultrathin surface and the unit cell decrease;

[0016] Step 103, filling a lattice structure with a wall thickness of N and a height of h 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 which can achieve the optimal mechanical coupling enhancement effect of the honeycomb sandwich multi-level structure are selected as the optimal size parameters of the lattice structure.

[0017] A preparation method of an ultrathin broadband load-bearing wave-absorbing honeycomb sandwich multi-level structure, comprising:

[0018] Step 201, using the optimal size parameters of the square hole honeycomb core obtained by the design method, first, a square hole honeycomb core of glass fiber reinforced composite material is prepared, then a conductive carbon-based coating is prepared on the inner wall surface of the square hole through a screen printing process, and the coating is 10-12 μm; then it is placed in a 100-120 °C oven for 1-3 hours; after cooling, the square hole honeycomb core is fixed in a fine adjustment machine tool, a 0.1-0.6 mm diameter cutter head is used, the spindle speed is controlled at 2000-4000 rap / min, and the strip on the outer wall of the square hole honeycomb core is prepared; finally, the processed strip is locked in the slot to complete the preparation of the square hole honeycomb core part;

[0019] Step 202, the optimal size parameters of the lattice structure obtained by optimization in the design method are used to prepare the lattice structure by FDM 3D printing process; the material of the lattice structure is selected as thermoplastic polylactic acid filaments, the nozzle temperature is set to 200 DEG C~350 DEG C, the hot bed temperature is set to 50 DEG C~100 DEG C, and the printing speed is 10 mm / s~100 mm / s; after printing is completed, the lattice structure is nested into the prepared square hole honeycomb core;

[0020] Step 203, a fiber reinforced composite material surface is prepared on the upper surface of the square hole honeycomb core, the optimal size parameters of the super surface obtained by optimization in the design method are used, the conductive carbon-based slurry corresponding to the surface impedance is proportioned, the super surface unit pattern is prepared on the fiber reinforced composite material surface by using the silk screen printing process to form a super surface structure, and then it is placed into a 100 DEG C~120 DEG C oven and dried for 1~3 hours and then taken out after cooling;

[0021] Step 204, a reflector plate is prepared on the lower surface of the square hole honeycomb core, and then a vacuum bag process is used to integrate the super surface, the square hole honeycomb core, the filled lattice structure and the reflector plate to obtain a prepared ultrathin broadband load absorbing honeycomb sandwich multi-level structure.

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

[0023] The present application 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 super surface configuration and the lattice structure, using the transmission line theory and the force-electric decoupling model, the impedance gradient of the equivalent model is optimized and designed to achieve a broadband electromagnetic absorption effect in the 4~40GHz frequency band. At the same time, by using the multi-level coupling effect of the honeycomb sandwich structure and the lattice filling structure, the high specific strength and specific energy absorption of the overall sandwich structure are realized, and a broadband load integrated functional sandwich structure is further obtained; the present application provides an efficient way to realize a high-performance electromagnetic functional structure. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The ultrathin broadband load integrated absorbing honeycomb sandwich multi-level structure and its unit body periodic model;

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

[0026] Figure 3 The impedance distribution diagram of the ultrathin broadband load integrated absorbing honeycomb sandwich multi-level structure;

[0027] Figure 4A comparison chart of actual test absorption rate and simulation absorption rate in the 4~40GHz frequency band is provided.

[0028] Figure 5 A stress-strain curve of the dot array structure and the ultrathin wideband load integrated wave-absorbing honeycomb sandwich structure. DETAILED DESCRIPTION

[0029] The technical problem to be solved by the present application is to overcome the problems of narrow absorption band, large thickness and poor mechanical performance of the existing electromagnetic function structure, and to provide a wideband / load integrated wave-absorbing honeycomb sandwich multi-level structure and a multi-process preparation method based on a conductive coating / super surface, so as to realize a wideband effective electromagnetic absorption (absorption rate > 87%) of 35.30GHz in the 4~40GHz frequency band and a maximum compression strength of 21.94 MPa and specific energy absorption effect under a thickness of 9mm, effectively overcoming the problem that the mechanical performance and electromagnetic performance of the traditional wave-absorbing structure cannot be considered simultaneously. At the same time, the bulk density of the structure is less than 0.55kg / m -3 , realizing the lightweight effect of the structure.

[0030] By constructing the force-electric interaction relationship between the functional square hole honeycomb core, the super surface configuration and the lattice structure, the impedance of each layer in the equivalent multi-layer model of the wave-absorbing honeycomb sandwich multi-level structure is designed by using the transmission line theory model, so that a large amount of electromagnetic waves enter the structure to form multiple reflections and scattering, effectively overcoming the problem of narrow absorption band of the structure. At the same time, by using the multi-level coupling effect of the square hole honeycomb sandwich structure and the small size dot array configuration, the mechanical enhancement of the overall sandwich structure is realized, and a wideband / load integrated functional sandwich structure is further obtained.

[0031] Referring to the accompanying Figure 1 , the ultrathin wideband load wave-absorbing honeycomb sandwich multi-level structure provided by the present application is composed of rectangular structure unit bodies connected with each other. Each unit body includes a reflecting plate, a square hole honeycomb core and a super surface. The square hole honeycomb core is made of functional fiber reinforced composite material, and the reflecting plate is made of carbon fiber composite material. The super surface and the reflecting plate are arranged on the upper and lower surfaces of the core, respectively. The square hole honeycomb core includes external square holes and honeycombs arranged in the square holes. The inner surface of the square hole has a coating. The honeycombs in the square holes are provided with dot array structures of thermoplastic material. The super surface is a periodic array pattern and is made of conductive carbon-based nanomaterial. Each unit body is connected with the adjacent unit body through a clamping slot interlocking mode.

[0032] In the present scheme, the super surface is a band-stop type, and the surface resistance of the super surface is controlled to be 300~700 ohms ; the resistance of the coating on the inner surface of the square hole is controlled to be 200~600 ohms The coating thickness is in the range of 10-12 μm.

[0033] In the scheme, the wall thickness of the honeycomb structure in the square-hole honeycomb core is in the range of 0.375-0.75 mm; the functional fiber reinforced composite material used by the square-hole honeycomb core can be glass fiber or quartz fiber, aramid fiber, etc.

[0034] In the scheme, the lattice structure of the thermoplastic material can be Walled TMPS, Diamond and lattice configuration such as honeycomb, the wall thickness of the lattice structure is in the range of 0.5 mm-1 mm, the matrix material of the lattice structure can be polylactic acid, nylon acrylonitrile-butadiene-styrene terpolymer, polyether ether ketone and other thermoplastic materials, the filler of the lattice structure can be multi-dimensional carbon-based material or carbon-based magnetic material, including graphene, carbon nanotube, graphene loaded ferrite, etc.

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

[0036] The application further provides a design method of an ultrathin broadband load-bearing wave-absorbing honeycomb sandwich multi-level structure, comprising the following steps:

[0037] Step 101, electromagnetic loss and impedance matching optimization of the square-hole honeycomb core.

[0038] As shown in Figure 1 , the square-hole honeycomb core is modeled and optimized by using CST microwave studio finite element software, and the parameters in the optimization process include the honeycomb wall thickness d , height H , unit cell periodic size L and the resistance of the square-hole inner surface coating 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 2-40 GHz, so as to obtain the optimal size parameters of the optimized square-hole honeycomb core.

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

[0040]

[0041]

[0042] In the formula S 21 ( S 12 ) and S 11 ( S 22 ) respectively represent the transmission coefficient and the reflection coefficient of the unit body, n represents the refractive index, k represents the wave number, Z r represents the characteristic impedance, d represents the maximum thickness, i represents the imaginary unit.

[0043] The characteristic impedance at different frequencies is solved by the above formula Z r , so as to obtain the distribution relationship between the characteristic impedance and the frequency.

[0044] Step 102, super surface electromagnetic loss and impedance matching optimization.

[0045] On the basis of determining the size of the square hole honeycomb core, the super surface pattern is designed on the fiber reinforced composite material surface of the upper surface of the square hole honeycomb core, so as to form a super surface; wherein the super surface unit pattern on the super surface is as shown in Figure 1 , which includes an internal square block and a rectangular frame arranged around the square block, the width of the frame is Q , the width of the square block is W , and the distance 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 unit body characteristic impedance and the frequency obtained in step 1, the parameters Q , W and S of the super surface unit and the resistance value of the super surface material are further optimized by using CST microwave studio finite element simulation software, so as to obtain the optimal size parameters and corresponding impedance which can reduce the impedance gradient formed between the incident electromagnetic wave (air impedance), the super surface (surface impedance) and the unit body (characteristic impedance), so as to further realize the effective electromagnetic loss of the incident electromagnetic wave in the square hole honeycomb core, and obtain the super-thin and wide-band absorption effect.

[0046] Step 103, mechanical property enhancement of honeycomb sandwich multi-level structure.

[0047] The wall thickness is N , and the height is hThe small-size lattice structure filling body with a wall thickness of 0.5mm to 1mm and a height of 0.5mm to 1mm 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 realize the optimal mechanical coupling enhancement effect of the honeycomb sandwich multi-level structure are selected as the optimal size parameters of the lattice structure.

[0048] Since the force-electricity performance of the wave-absorbing honeycomb sandwich multi-level structure model is decoupled, the lattice structure filling body mainly affects the bearing performance of the overall structure and has a smaller influence on the electromagnetic performance, therefore, the square-hole honeycomb core and the small-size lattice structure filling body (thin-walled walled TMPS, Diamond, honeycomb-like) with a wall thickness of 0.5mm to 1mm and a height of 0.5mm to 1mm are combined to optimize the mechanical performance. N h The small-size lattice structure filling body (thin-walled walled TMPS, Diamond, honeycomb-like) with a wall thickness of 0.5mm to 1mm and a height of 0.5mm to 1mm 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 realize the optimal mechanical coupling enhancement effect of the honeycomb sandwich multi-level structure are selected as the optimal size parameters of the lattice structure.

[0049] The application further provides a preparation method of the ultrathin broadband bearing wave-absorbing honeycomb sandwich multi-level structure, which comprises the following steps:

[0050] The application adopts a screen printing process and various composite processing manufacturing technologies such as additive and subtractive processes (numerical control machine tool processing and 3D printing) to realize fast and efficient preparation of the ultrathin broadband bearing integrated wave-absorbing honeycomb sandwich structure, and the specific preparation process is as follows:

[0051] In step 201, the optimal size parameters of the square-hole honeycomb core obtained by the design method are used to first prepare a square-hole honeycomb core of a glass fiber reinforced composite material, then a conductive carbon-based coating with a thickness of 10 to 12 microns is prepared on the inner wall surface of the square hole through a screen printing process, and then the square-hole honeycomb core is placed in a 100 to 120 (preferably 120) degree oven for drying for 1 to 3 hours; after cooling, the square-hole honeycomb core is fixed in a fine adjustment machine tool, a 0.1 to 0.6 (preferably 0.4) millimeter diameter cutter head is used, the spindle speed is controlled at 2000 to 4000 rap / min (preferably 3500 rap / min), and the preparation of the strip on the outer wall of the square-hole honeycomb core is performed; finally, the processed strip is embedded and locked in a slot to complete the preparation of the square-hole honeycomb core part.

[0052] In step 202, the optimal size parameters of the lattice structure obtained by the design method are used to prepare the lattice structure through an FDM 3D printing process; the material of the lattice structure is selected as a thermoplastic polylactic acid wire, the nozzle temperature is set to 200 to 350 (preferably 215) degrees, the hot bed temperature is set to 50 to 100 (preferably 50) degrees, and the printing speed is 10 to 100 (preferably 50) millimeters per second; after printing is completed, the lattice structure is nested into the prepared square-hole honeycomb core.

[0053] ​Step 203, a fiber-reinforced composite material surface is prepared on the upper surface of the square-hole honeycomb core, the optimal size parameters of the super surface obtained by optimization in the design method are used, a conductive carbon-based slurry corresponding to the surface impedance is proportioned, a super surface unit pattern is prepared on the fiber-reinforced composite material surface by using a screen printing process to form a super surface structure, and then the super surface structure is placed into a 100-120°C (preferably 120°C) oven for drying for 1-3 hours and then taken out after cooling.

[0054] Step 204, a reflecting plate is prepared on the lower surface of the square-hole honeycomb core, and then a super surface, a square-hole honeycomb core, a filled lattice structure and a reflecting plate are integrated by using a vacuum bag process to obtain a prepared ultrathin broadband load-bearing wave-absorbing honeycomb sandwich multi-level structure.

[0055] Embodiment:

[0056] In a specific example of the present application, referring to FIG. 1, by using the optimization method of the present application, the specific size of the wave-absorbing honeycomb sandwich multi-level structure obtained is as follows: the square-hole honeycomb core has a cell period size of 9 mm, a cell wall thickness of 0.375 mm and a cell height of 8 mm, the surface resistance of the coating is 200 ohms / square, the filling body is a hexagonal honeycomb lattice structure with a wall thickness of 1 mm and a height of 8 mm, the super surface unit pattern has a super surface unit spacing of 1 mm, a line frame width of 0.6 mm and a square width of 6 mm, and the surface resistance of the super surface is 500 ohms / square. Figure 1 L d H Rs N h S Q W K Figure 3

[0057] In the present application, the ultrathin broadband load-bearing integrated wave-absorbing honeycomb sandwich multi-level structure is prepared by a multi-process mixing method, a continuous glass fiber-reinforced composite material is selected as a square-hole honeycomb structure framework, a conductive coating is prepared on the surface of the glass fiber plate by using screen printing, and the thickness of the coating is controlled to be 10-12 microns; the assembly parts of the square-hole honeycomb structure are processed by using a numerical control engraving machine, the diameter of the drill bit is 0.4 mm, the spindle speed is controlled to be 3500 rap / min, and the obtained parts are then embedded by using a clamping groove locking process to realize the preparation of the square-hole wave-absorbing honeycomb core; a hexagonal honeycomb lattice structure with a length of 8.6 mm, a width of 8.6 mm and a height of 8 mm is prepared by using an FDM 3d printing process, and polylactic acid is selected as the printing material; the printing nozzle temperature is set to be 215​​​​​​​​​​​​​​o C, the heated bed temperature is 50 o C. The printing rate is set to 50 mm / s; after printing is complete, the dot matrix structure is nested into the square-hole honeycomb core. A metasurface is prepared using screen printing, with the metasurface thickness controlled at 10 μm. After screen printing, the sample is placed in a 120°C container. o Dry in an oven at C for 1 hour, cool and remove, then pass through a vacuum bag at room temperature to form an integrated, multi-level, microwave-absorbing honeycomb sandwich structure.

[0058] The performance of the honeycomb structure prepared according to this invention was tested, see Appendix. Figures 4-5 As shown in the figure, the data indicates that the structural sample prepared by this invention can achieve broadband effective electromagnetic absorption of 35.30 GHz (absorption rate > 87%) in the 4~40 GHz range. Furthermore, using quasi-static compression testing, the maximum compressive strengths of the hexagonal lattice structure sample and the final absorbing honeycomb sandwich structure sample (9 mm thickness) were obtained as 15.42 MPa and 21.94 MPa, respectively, which is 200% higher than the compressive strength of the honeycomb sandwich structure without the hexagonal lattice structure. Simultaneously, the final absorbing honeycomb sandwich structure sample (9 mm thickness) can achieve [the desired effect] under a stress of 0.4. The energy absorption effect verifies the effectiveness and advancement of the present invention.

[0059] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. An ultrathin broadband load-bearing wave-absorbing honeycomb sandwich multistage structure, characterized in that, The multi-level structure is composed of rectangular structure unit bodies connected to each other; each unit body comprises a reflecting plate, a square-hole honeycomb core and a metasurface, the square-hole honeycomb core 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 respectively arranged on the upper and lower surfaces of the core, the square-hole honeycomb core comprises square holes on the outside and honeycombs arranged in the square holes, and the inner surface of the square hole has a coating; a dot matrix structure of a thermoplastic material is arranged in the honeycombs in the square holes, the metasurface is a periodic array pattern and is made of a conductive carbon-based nanomaterial; each unit body is connected to an adjacent unit body through a clamping groove interlocking mode.

2. The ultrathin broadband load-carrying wave-absorbing honeycomb sandwich multistage structure according to claim 1, characterized in that, The metasurface is a band-stop type, and the surface resistance of the metasurface is 300-700 ohms .

3. The ultrathin broadband load-carrying wave-absorbing honeycomb sandwich multistage structure according to claim 1, characterized in that, The square hole inner surface coating has a resistance of 200-600 ohms and a coating thickness in the range of 10-12 μm.

4. The ultrathin broadband load-carrying wave-absorbing honeycomb sandwich multistage structure of claim 1, wherein, The wall thickness of the honeycomb structure in 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 ultrathin broadband load-carrying wave-absorbing honeycomb sandwich multistage structure of claim 1, wherein, The dot matrix structure of the thermoplastic material comprises a Walled TMPS, a Diamond and a honeycomb-like dot matrix configuration, the wall thickness of the dot matrix structure is in the range of 0.5 mm-1 mm, the matrix material of the dot matrix structure is polylactic acid, a ternary copolymer of nylon acrylonitrile-butadiene-styrene or polyether ether ketone; the filler of the dot matrix structure is a multi-dimensional carbon-based material or a carbon-based magnetic material, including graphene, carbon nanotubes and graphene loaded ferrite.

6. The ultrathin broadband load-carrying wave-absorbing honeycomb sandwich multistage structure of claim 1, wherein, The characteristic impedance value of the metasurface is between 377-300 ohms in the low-frequency 4-17 GHz frequency band, and the characteristic impedance value of the core part is between 300-225 ohms in the low-frequency 4-17 GHz frequency band.

7. The design method of the ultrathin broadband load-carrying wave-absorbing honeycomb sandwich multi-level structure according to any one of claims 1-6, characterized in that, Comprise: Step 101, using finite element software to model and optimize the square hole honeycomb core, the parameters in the optimization process include the honeycomb wall thickness d , height H , unit cell periodic size L , and the resistance of the square hole inner surface coating 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 2-40GHz, thereby obtaining 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, the characteristic impedance of the unit body at different frequencies is calculated by using the transmission coefficient and the reflection coefficient calculation formula of the unit body based on the S parameter inversion method, so as to determine 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, a super surface pattern is designed on the fiber reinforced composite surface of the upper surface of the square hole honeycomb core, so as to form a super surface; wherein the super surface unit on the super surface comprises an internal square block and a rectangular wire frame arranged around the square block, the width of the wire frame is Q , the width of the square block is W , and the pitch of adjacent super surface units is S ; in combination with 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, the parameters Q , W and S of the super surface unit and the resistance value of the super surface material are further optimized by using a finite element simulation software, so as to obtain the optimal size parameters and the corresponding impedance which make the impedance gradient between the incident electromagnetic wave, the super surface and the unit body decrease. Step 103, filling a lattice structure filling body with a wall thickness of N and a height of h into the honeycomb of the square-hole honeycomb core to form a honeycomb sandwich multi-level structure; through quasi-static compression test, the maximum compression strength of the lattice structure with different wall thicknesses and heights is compared, and the wall thickness and height of the lattice structure that can achieve the optimal mechanical coupling enhancement effect of the honeycomb sandwich multi-level structure are selected as the optimal size parameters of the lattice structure.

8. A method for preparing the ultrathin broadband load-bearing wave-absorbing honeycomb sandwich multi-level structure according to any one of claims 1-6, characterized in that, Comprise: Step 201, using the optimal size parameters of the square-hole honeycomb core obtained by the design method in claim 7, first preparing a square-hole honeycomb core of a glass fiber reinforced composite material, then preparing a conductive carbon-based coating on the inner wall surface of the square hole by a screen printing process, the coating is 10-12 μm; then put into a 100℃-120℃ oven and dry for 1-3 hours; after cooling, put the square-hole honeycomb core into a fine adjustment machine tool for fixation, use a 0.1 mm-0.6 mm diameter tool bit, control the spindle speed at 2000-4000 rap / min, and prepare a strip on the outer wall of the square-hole honeycomb core; finally, the prepared strip is clamped and locked, and the preparation of the square-hole honeycomb core part is completed; Step 202, using the optimal size parameters of the dot matrix structure obtained by the design method, preparing the dot matrix structure by a FDM 3D printing process; The material of the dot matrix structure is thermoplastic polylactic acid wire, the nozzle temperature is set to 200℃-350℃, the hot bed temperature is set to 50℃-100℃, and the printing speed is 10 mm / s-100 mm / s; after printing is completed, the dot matrix 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 obtained by optimization in the design method, matching the conductive carbon-based paste corresponding to the surface impedance, using the screen printing process to prepare a super surface unit pattern on the fiber-reinforced composite material surface to form a super surface structure, and then placing it in a 100-120°C oven for 1-3 hours for drying, and taking it out after cooling; Step 204, preparing a reflector on the lower surface of the square-hole honeycomb core, and then using a vacuum bag process to integrate the super surface, the square-hole honeycomb core and the filled lattice structure, and the reflector to obtain a prepared ultrathin broadband load-carrying wave-absorbing honeycomb sandwich multi-level structure.

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