Dot-matrix sandwiched metamaterial cladding and method of making same

Abstract

The application discloses a dot array sandwich metamaterial cover layer and a manufacturing method thereof, which is composed of a surface flexible wave absorbing layer, a dot array sandwich metamaterial layer and a bottom flexible wave absorbing layer from top to bottom. The surface flexible absorbing layer is a mixed layer composed of a flexible PDMS composite material and a nano-scale carbon-based absorbing agent. The material of the dot array sandwich metamaterial layer comprises a flexible PDMS composite material and a nano-scale carbon-based composite material 3D printing dot array metamaterial layer. The bottom flexible wave absorbing layer has the same structure and material as the surface flexible absorbing layer. The application has the advantages of excellent wave absorbing performance, good impact absorbing performance, flexible design, easy production and assembly and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of anti-radar detection of underwater vehicles, in particular to an anti-impact stealth integrated metamaterial covering layer for underwater vehicles to resist radar detection and have anti-impact performance and a manufacturing method thereof. BACKGROUND

[0002] In recent years, the acoustic covering layer technology is the key to realize the acoustic stealth of underwater vehicles, and the research on the acoustic characteristics thereof has become a popular research field. With the proposal of the concept of lattice sandwich metamaterial, many acoustic metamaterials / structures with special physical properties have emerged. However, due to the complexity and particularity of the underwater propagation of sound waves, the application of lattice sandwich metamaterial in the direction of underwater sound absorption and insulation is limited, and relatively less research is conducted. The existing metamaterial wave-absorbing structure can generally only absorb waves in a single frequency range, and the flexible and elastic metamaterial lattice structure has been verified to have the functions of wave absorption and impact resistance, but the flexible and elastic metamaterial terahertz absorption material is generally in the form of a film or a foam, which cannot guarantee excellent mechanical properties in the case of achieving the expected absorption rate, especially when dealing with fragments and other possible impacts, and cannot achieve good anti-impact and energy absorption effects. Therefore, a reasonably designed metamaterial structure can have the functions of wideband stealth wave absorption and anti-impact protection, and is expected to become an effective means for underwater vehicles to realize anti-impact and stealth integration. SUMMARY

[0003] The present application provides a lattice sandwich metamaterial covering layer and a manufacturing method thereof to overcome the defects of the prior art. The covering layer material has the dual functions of wave absorption and impact resistance, effectively combines stealth wave absorption and impact absorption, and provides a new protection design scheme for underwater vehicles to realize anti-impact and stealth integration.

[0004] In order to achieve the above application purposes, the technical solutions adopted by the present application are as follows:

[0005] A lattice sandwich metamaterial covering layer, which is composed of a surface flexible wave absorption layer, a lattice sandwich metamaterial layer and a bottom flexible wave absorption layer from top to bottom.

[0006] The surface flexible absorption layer is a mixed layer composed of a flexible PDMS (polydimethylsiloxane) composite material and a nano-scale carbon-based absorber;

[0007] The material of the lattice sandwich metamaterial layer includes a flexible PDMS composite material and a nano-scale carbon-based composite material 3D printed lattice metamaterial layer;

[0008] The structure and material of the bottom flexible wave absorption layer are the same as those of the surface flexible absorption layer.

[0009] As preferred, the surface layer flexible absorbing layer is prepared by adding nanoscale carbon-based absorbent into PDMS solution, mixing and preparing through 3D printing.

[0010] As preferred, the specific preparation method of the surface layer flexible absorbing layer is: mixing low-viscosity PDMS composite solution and high-viscosity composite solution at a mass ratio of 7:3, stirring uniformly through a magnetic stirrer for 1h to obtain PDMS composite solution; then adding photo-curing initiator according to the weight ratio of PDMS composite solution: photo initiator = 49:1. Then, nanoscale carbon-based absorbent is added, and the nanoscale carbon nanotubes are ultrasonically dispersed for 300s through an ultrasonic machine, and then stirred for 30min through a paddle stirrer, and then placed in a vacuum machine for air extraction and defoaming, and the vacuum is maintained for 15min, and then the 3D printing slurry is obtained. Then, a DLP (Digital Light Processing) 3D printer is used for printing to prepare a flexible PDMS composite material and nanoscale carbon-based absorbent mixed layer.

[0011] As preferred, the nanoscale carbon-based absorbent is a single substance or a mixture of graphene or carbon black.

[0012] As preferred, the dynamic viscosity of the low-viscosity PDMS composite material is 3300 to 3500 centipoise.

[0013] As preferred, the dynamic viscosity of the high-viscosity PDMS composite material is 66000 to 66700 centipoise.

[0014] As preferred, the lattice sandwich metamaterial layer is obtained by slicing a three-dimensional lattice model into a 3D printer, using the 3D printing slurry prepared in the first step, and through layer-by-layer photo-curing.

[0015] As preferred, the lattice structure of the lattice sandwich metamaterial layer is a multilayer cell lattice structure, and is a gradient structure, and the first layer of cells combined with the first layer of medium layer is less than 0.5mm, and the cell single rod is less than 0.3mm. The total thickness of the second layer is not more than 6mm.

[0016] As preferred, the structure and material of the bottom layer flexible wave absorbing layer are the same as those of the surface layer flexible wave absorbing layer.

[0017] As preferred, the thickness of the surface layer flexible wave absorbing layer and the bottom layer flexible wave absorbing layer is not more than 0.5mm.

[0018] The application also discloses a manufacturing method of the lattice sandwich metamaterial covering layer, comprising the following steps:

[0019] First step: mix the low viscosity PDMS composite solution with the high viscosity PDMS composite solution at a mass ratio of 7:3, mix uniformly by a magnetic stirrer for 1h to obtain a PDMS composite solution;

[0020] Then add a photo-curing initiator according to a ratio of the weight of the PDMS composite solution to the weight of the photo initiator = 49:1, the photo initiator is TPO-L (2,4,6-trimethylbenzoyl phenyl phosphonic acid ethyl ester) to obtain a resin base;

[0021] Then add graphene and carbon black particles with a particle size less than 20nm, the mass ratio of the resin base to the particles is 10:2;

[0022] Ultrasonically disperse the nanoscale carbon nanotubes for 300s by an ultrasonic machine, and then stir for 30min by a paddle stirrer;

[0023] Then put into a vacuum machine to perform air extraction and defoaming, keep vacuum for 15min, and take out to obtain a 3D printing paste;

[0024] Print by using a digital light processing 3D printer, print two pieces of a flexible PDMS composite layer mixed with nanoscale carbon-based absorbent layers with a thickness of 0.4mm, and the length and width size is 50mm*50mm.

[0025] Second step: spray a graphene aluminum mixed coating on the lower surface of the 0.4mm thick flexible PDMS composite layer mixed with the nanoscale carbon-based absorbent layer to form a bottom layer flexible wave absorption layer and a surface layer flexible absorption layer.

[0026] Third step: use the 3D printing paste configured in the first step at a proportion, print a 3D gradient dot matrix structure, set the printing slice thickness to 10um, the first layer unit cell of the dot matrix structure is 0.5mm, the rod thickness is 0.1mm, the pore size range is 120um to 300um, the unit cell structure is a body-centered cubic structure, the total layer thickness is 6mm, the length and width size is 50mm*50mm, and the printing is completed to form a dot matrix sandwiched metamaterial layer.

[0027] Fourth step: after the printing is completed, place the surface layer flexible absorption layer on a heating table, coat the low viscosity PDMS composite solution, place the printed dot matrix sandwiched metamaterial layer on the surface layer flexible absorption layer, heat to 100 DEG C and solidify for 45min, take off the heating table, then place the bottom layer flexible wave absorption layer on the heating table, coat the low viscosity PDMS composite solution on the surface, turn over the dot matrix sandwiched metamaterial layer and place it on the heating table, and also heat to 100 DEG C and solidify for 45min. Finally, a dot matrix sandwiched metamaterial cover layer is formed.

[0028] Compared with the prior art, the advantages of the present application are that:

[0029] 1. Excellent wave absorption performance: By combining the surface flexible absorption layer and the lattice sandwich metamaterial layer, high absorption rate of terahertz waves can be achieved, and the absorption rate can reach more than 74%. At the same time, the multiple-angle reflection and loss design of the lattice sandwich metamaterial layer can significantly reduce the reflection and transmission of terahertz waves, achieving almost no reflection effect.

[0030] 2. Impact energy absorption performance: The gradient design of the lattice sandwich metamaterial layer can realize high energy absorption and deceleration effect when facing impact waves and other loads, and has good impact resistance.

[0031] 3. Flexible design: The cover layer is prepared by using flexible PDMS composite material, which has good flexibility and plasticity, and can realize the adhesion and adaptability to complex surfaces.

[0032] 4. Easy to produce and assemble: The preparation method of the cover layer is relatively simple, and it can be quickly prepared by 3D printing technology. At the same time, the flexible design and the easy handling of the material make the assembly and production of the cover layer easier, with lower production cost and time cost. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a longitudinal section view of the lattice sandwich metamaterial cover layer of the embodiment of the present application;

[0034] Figure 2 is a structure schematic view of the second layer of the lattice sandwich metamaterial layer of the embodiment of the present application;

[0035] Figure 3 is a flow chart of the design optimization method of the embodiment of the present application;

[0036] Figure 4 is an energy absorption schematic view of the lattice sandwich metamaterial cover layer of the embodiment of the present application obtained by simulation in the process of impact of an impact wave below 10MPa;

[0037] Figure 5 is an absorption rate schematic view of the lattice sandwich metamaterial cover layer of the embodiment of the present application to terahertz waves in the range of 0.1THz-1.6THz. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the following according to the drawings and examples, further detailed description of the present application.

[0039] As Figure 1As shown, the lattice sandwich metamaterial covering layer of the present invention consists of a surface flexible wave absorbing layer 1, a lattice sandwich metamaterial layer 2, and a bottom flexible wave absorbing layer 3. The first surface flexible absorbing layer 1 is a mixture of flexible PDMS (polydimethylsiloxane) composite material and nanoscale carbon-based absorbent; the second layer is the lattice sandwich metamaterial layer 2, which is mainly a 3D-printed lattice metamaterial layer of flexible PDMS composite material and nanoscale carbon-based composite material; the third bottom flexible wave absorbing layer 33 is the same as the first layer.

[0040] Example:

[0041] Step 1: Apply low-viscosity PDMS composite solution (Sylagard, USA) TM Type 184) and high-viscosity PDMS composite solution (DOWSIL, USA) TM SE 1700 was mixed at a mass ratio of 7:3 and stirred with a magnetic stirrer for 1 hour to obtain a homogeneous PDMS composite solution. Then, a photocuring initiator, TPO-L (ethyl 2,4,6-trimethylbenzoylphenylphosphonate), was added at a weight ratio of 49:1 to obtain a resin base. Graphene and carbon black particles with a particle size of less than 20 nm were then added, with a resin base to particle mass ratio of 10:2. The nanoscale carbon nanotubes were first ultrasonically dispersed for 300 seconds, followed by stirring with a paddle stirrer for 30 minutes. Then, the mixture was placed in a vacuum chamber for degassing and defoaming, and the vacuum was maintained for 15 minutes. The resulting 3D printing slurry was obtained. The optimal absorption thickness of the PDMS composite material and nanoscale carbon-based absorber was calculated to be 0.4 mm. Two flexible PDMS composite material and nanoscale carbon-based absorber mixed layers with a thickness of 0.4 mm and dimensions of 50 mm × 50 mm were printed using a digital light processing 3D printer.

[0042] Step 2: Spray a graphene-aluminum hybrid coating onto the lower surface of a 0.4 mm thick flexible PDMS composite material mixed with a nano-scale carbon-based absorbent.

[0043] Step 3: Using the 3D printing paste prepared in Step 1, print the 3D gradient lattice structure. Set the printing slice thickness to 10µm. The lattice structure is as follows: Figure 2 As shown, the first layer has a unit cell thickness of 0.5 mm, a rod thickness of 0.1 mm, and a pore size ranging from 120 μm to 300 μm. The cell structure is BCC (body-centered cubic structure). The lattice sandwich metamaterial layer is prepared with a total layer thickness of 6 mm and a length and width of 50 mm × 50 mm.

[0044] Fourth step: after printing, the first layer of 0.4mm thick flexible PDMS composite material and nanoscale carbon-based absorbent mixed layer is placed on the heating table, and then the printed dot matrix sandwich metamaterial layer is placed on the low viscosity PDMS composite material solution (SYLAGARDTM 184 type in the United States) and heated to 100℃ for 45min. Then remove the heating table, and then place another 0.4mm thick flexible PDMS composite material and nanoscale carbon-based absorbent mixed layer on the heating table, and then place the dot matrix sandwich metamaterial layer on the heating table, and then heat to 100℃ for 45min. Then form the shock-resistant stealth integrated dot matrix sandwich metamaterial cover layer.

[0045] From Figure 4 and Figure 5 it can be seen that the shock-resistant stealth integrated dot matrix sandwich metamaterial cover layer obtained in this embodiment has a minimum absorption rate of more than 75% for terahertz waves within 0.1THz-1.6THz, and an absorption rate of more than 83% within 0.5THz-1.1THz, and can effectively reduce the impact wave load intensity acting on the back plate when the back plate is subjected to an impact of less than 10MPa.

[0046] The specific design and optimization method steps of the shock-resistant stealth integrated dot matrix sandwich metamaterial cover layer obtained in this embodiment are as follows:

[0047] First step: select materials and determine material parameter information.

[0048] Measure the parameters of the prepared materials, including the basic mechanical parameters of the materials such as elastic modulus, bulk density, ultimate tensile strength, bending strength, and other material parameters; and the impedance, dielectric constant, etc. of the materials.

[0049] Second step: according to the selected materials, design and calculate the thickness of each layer, and design the dot matrix structure configuration, and preset the thickness of each layer.

[0050] First, calculate the material wave absorption performance and the optimal wave absorption thickness by theoretical calculation, and the calculation formula is as follows:

[0051] Z in =Z0(μ r / ε r ) 1 / 2 tanh[j(2fπd / c)(μ r ε r ) 1 / 2 ]

[0052] RL=20log|(Z in -Z0) / (Z in +Z0)|

[0053] where Z in is the input impedance of the wave absorber, μ r and ε r are the relative complex permeability and permittivity of the composite material, f, d and c are the frequency of the incident wave, the thickness of the composite material and the speed of light, respectively.

[0054] According to the calculation result dmm, the thicknesses of the first layer and the third layer are preset, the point matrix sandwich layer structure of the middle second layer is designed considering the impact load pressure p. The first layer and the second layer are modeled by a three-dimensional modeling software (the third layer is the same as the first layer).

[0055] The initial thicknesses of the first layer and the third layer are set as a mm, and the thickness of the point matrix sandwich layer structure of the second layer is b mm, and the thickness of a single layer of the adhesive layer is c mm. Requirements: a = dmm, c ≤ 0.5 mm, and (2a + b + 2c) ≤ 20dmm.

[0056] Step 3: Prepare the cover layer and carry out model impact simulation experiment.

[0057] During the 3D printing preparation process, the model needs to be sliced first, and the slicing thickness precision can reach 10 um per layer. Therefore, when preparing ultra-thin composite materials, the layer thickness can be accurately prepared and controlled, so that the prepared sample can be more accurate in subsequent experiments.

[0058] The relationship between light intensity, exposure time and curing thickness can be represented by Jacobs equation:

[0059]

[0060] where C P is the absolute curing thickness (um), D P is the characteristic curing thickness (um), E i and E c . are the energy density transmitted to the slurry (or input energy density) and the critical energy density (mJ / cm2), respectively.

[0061] where E i = I·t, I refers to the irradiance of incident light (i.e. light intensity, uW / cm2), and t refers to exposure time (s).

[0062] 3.1 Slice the first layer model and the second layer model. Since the model thickness is small, a slicing thickness of 15 um is adopted to ensure printing processing precision.

[0063] 3.2 Assemble the cover layer and carry out wave absorption test to verify the theoretical calculation. The preset back plate material can be selected from metal materials such as aluminum alloy and stainless steel. The back plate material can be preset as a flat layer, and all material layers are laid flat and attached. It can also be set as a complex arc layer according to actual needs. Through the test of wave absorption performance in the 0.1 THz to 2.0 THz band, the design material, thickness and structure are determined for the wave absorption performance in the 0.1 THz to 1.6 THz band. The structure shown in this embodiment can achieve more than 74% wave absorption in the 0.1 THz to 1.6 THz band, especially in the 0.5 THz to 1.1 THz band, the absorption rate can reach more than 83%; after the theoretical calculation and test results of the cover layer show that the absorption rate in the 0.1 THz to 1.6 THz band is higher than 70%, the next step of impact resistance verification is carried out.

[0064] 3.3 Finite element modeling, impact resistance simulation calculation of the model.

[0065] Under the action of air explosion, the peak value of explosion impact load acting on the cover layer structure has little difference in time, therefore, according to the different spatial shapes of the cover layer, the explosion load is uniformly distributed on the outer surface of the cover layer. The explosion load is converted into energy equivalent uniform load, that is, the spherical wave is regarded as a plane wave.

[0066] ① TNT air explosion equivalent static load theoretical model

[0067] According to the TNT explosion mechanics theory, the calculation formula of the plane equivalent static load P is:

[0068] P = (E / V)·K

[0069] Wherein, E is the explosion energy, V is the explosion volume, and K is the equivalent static load coefficient.

[0070] ② Super-elasticity model constitutive

[0071] The impact-resistant and stealthy cover layer is a flexible cover layer with super-elasticity, and the Ogden form constitutive model is used for simulation calculation. Ogden is a model based on the principal elongation (λ), and the strain energy density function is as follows:

[0072]

[0073] ③ Whole structure modeling

[0074] According to the existing material performance parameters and explosion equivalent static load sequence parameters, a finite element model of the integrated lattice sandwich metamaterial cover layer is established. The model is assumed to be axisymmetric, the model size is set to a rectangle with a side length not less than 5 cm, and the explosion equivalent static load is loaded to simulate the impact damage process of the integrated lattice sandwich metamaterial cover layer. Combined with the loaded equivalent static load, the structure model size and other parameters, the deformation and failure relationship of the integrated lattice sandwich metamaterial cover layer under the explosion equivalent static load is observed.

[0075] Fourth step: test the impact resistance and stealth performance of the covering layer.

[0076] In combination with the 3.2 THz wave absorption experiment verification and the 3.3 finite element calculation result, the impact resistance range of the covering layer is verified.

[0077] Case 1: the first layer outer layer is broken, but the sandwich layer is not failed or the first layer and the second layer sandwich layer are both failed.

[0078] The equivalent static load pressure value of explosion is preferentially reduced, and the third step of finite element calculation process is re-performed until the critical impact resistance bearing pressure of the covering layer is obtained.

[0079] Case 2: the first layer and the second layer sandwich layer are both not failed.

[0080] After the critical design thickness a0 and b0 of the integrated lattice sandwich metamaterial covering layer are obtained, according to the requirements: a = dmm, c ≤ 0.5mm and (2a+b+2c) ≤ 20dmm, the thickness of the lattice sandwich layer is improved, and the second step and the third step are repeated to obtain the thickness (2a+b+2c) of the actual optimal integrated lattice sandwich metamaterial covering layer.

[0081] The first layer of the present application is a surface flexible absorption layer, and the transmittance of the first layer to the terahertz wave can reach 99.4%, almost no reflection, and has good terahertz high frequency response. The second layer is a lattice sandwich metamaterial layer, and after the terahertz wave passing through the first layer enters the second layer, due to the gradient design of the second layer lattice structure, the terahertz wave will be reflected and lost multiple times at multiple angles, realizing high absorption of the terahertz wave of a specific frequency. At the same time, the gradient design of the second layer lattice structure can realize high-efficiency energy absorption through the layer-by-layer deformation and crushing of the cells when facing the impact of shock waves and other loads. Through the wave absorption formula: absorption rate = 1-transmittance-reflectivity, the present application can achieve an absorption rate of more than 74% for the incident terahertz wave in the range of 0.1THz-1.6THz through extremely low surface reflection and extremely strong internal multiple-angle reflection and loss. At the same time, through the gradient lattice structure design, the effect of slowing down and absorbing the energy of the shock wave of the fragments can be realized while realizing wave absorption.

[0082] Those skilled in the art will appreciate that the embodiments described herein are presented to help the reader understand the implementation method of the present application and should be understood as the protection scope of the present application not being limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations according to the technical inspiration disclosed in the present application without departing from the essence of the present application, and these modifications and combinations are still within the protection scope of the present application.

Claims

1. A dot-matrix sandwich metamaterial cladding, characterized by: It is composed of a surface flexible wave absorbing layer, a lattice sandwich metamaterial layer, and a bottom flexible wave absorbing layer from top to bottom. The surface flexible wave absorbing layer is a mixed layer composed of a flexible PDMS (polydimethylsiloxane) composite material and a nanoscale carbon-based absorber. The material of the lattice sandwich metamaterial layer includes a flexible PDMS composite material and a nanoscale carbon-based composite material 3D printing lattice metamaterial layer. The structure and material of the bottom flexible wave absorbing layer are the same as those of the surface flexible absorbing layer. The lattice structure of the lattice sandwich metamaterial layer is a multilayer cell lattice structure, and is a gradient structure. The first layer of cells combined with the first layer of dielectric layers is less than 0.5mm, and the cell single rod is less than 0.3mm. The total thickness of the second layer is not more than 6mm.

2. The metamaterial cladding of claim 1, wherein: The surface flexible absorbing layer is prepared by adding a nanoscale carbon-based absorber to a PDMS solution, mixing, and 3D printing.

3. The metamaterial cladding of claim 1, wherein: The specific preparation method of the surface flexible absorbing layer is as follows: mix the low-viscosity PDMS composite material solution and the high-viscosity PDMS composite material solution in a mass ratio of 7:3, stir uniformly for 1h by a magnetic stirrer to obtain a PDMS composite material solution; then add a photoinitiator according to a ratio of PDMS composite material solution weight: photoinitiator weight = 49:1; then add a nanoscale carbon-based absorber, first disperse the nanoscale carbon nanotubes by an ultrasonic machine for 300s, then stir for 30min by a paddle stirrer, then put it into a vacuum machine for vacuum degassing, keep vacuum for 15min, and then take it out to obtain a 3D printing slurry; then use a DLP (digital light processing) 3D printer to print and prepare a flexible PDMS composite material and nanoscale carbon-based absorber mixed layer. The dynamic viscosity of the low-viscosity PDMS composite material is 3300 to 3500 centipoise. The dynamic viscosity of the high-viscosity PDMS composite material is 66000 to 66700 centipoise.

4. The metamaterial cladding of claim 1, wherein: The material of the nanoscale carbon-based absorber is a single substance or a mixture of graphene or carbon black.

5. The metamaterial cladding of claim 1, wherein: The lattice sandwich metamaterial layer is obtained by slicing a three-dimensional lattice model into a 3D printer, using the 3D printing slurry prepared in the first step, and then obtaining it by layer-by-layer photopolymerization.

6. The metamaterial cladding of claim 1, wherein: The structure and material of the bottom flexible wave absorbing layer are the same as those of the surface flexible wave absorbing layer; the thickness of the surface flexible wave absorbing layer and the bottom flexible wave absorbing layer is not more than 0.5mm.

7. A method of manufacturing a dot-matrix sandwich metamaterial cover layer according to one of claims 1 to 6, characterized in that, The steps include: First step: mix the low-viscosity PDMS composite material solution and the high-viscosity PDMS composite material solution in a mass ratio of 7:3, stir uniformly for 1h by a magnetic stirrer to obtain a PDMS composite material solution; Then add a photoinitiator according to a ratio of PDMS composite material solution weight: photoinitiator weight = 49:1, the photoinitiator is TPO-L (2,4,6-trimethylbenzoyl phenyl phosphonic acid ethyl ester) to obtain a resin base; Then add graphene and carbon black particles with a particle size of less than 20nm, and the mass ratio of the resin base to the particles is 10:2; Disperse the nanoscale carbon nanotubes by an ultrasonic machine for 300s, then stir for 30min by a paddle stirrer; Then put into the vacuum machine for pumping and defoaming, vacuum for 15 min, take out the 3D printing paste; The digital light processing 3D printer is used for printing, and two 0.4 mm thick flexible PDMS composite and nano-scale carbon-based absorbent mixed layers are printed, with a size of 50 mm x 50 mm; Second step: spray graphene mixed aluminum coating on the lower surface of the 0.4 mm thick flexible PDMS composite and nano-scale carbon-based absorbent mixed layer to form a bottom flexible wave absorbing layer and a surface flexible absorbing layer; Third step: use the 3D printing paste with the first step configuration ratio to print the 3D gradient lattice structure, with a printing slice thickness of 10 um, a first layer cell of 0.5 mm, a rod thickness of 0.1 mm, a pore size range of 120 um to 300 um, a cell structure of body-centered cubic structure, a total layer thickness of 6 mm, a size of 50 mm x 50 mm, and a printed lattice sandwich metamaterial layer; Fourth step: after printing, place the surface flexible absorbing layer on the heating table, coat the low viscosity PDMS composite solution, align the printed lattice sandwich metamaterial layer on it, heat to 100℃ and solidify for 45 min, then take off the heating table, place the bottom flexible wave absorbing layer on the heating table, coat the low viscosity PDMS composite solution on the surface, turn over the lattice sandwich metamaterial layer and place it on the heating table, and heat to 100℃ and solidify for 45 min; Finally, the lattice sandwich metamaterial cover layer is formed.

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