CN112492867B - Wave-absorbing honeycomb with pyramid-like structure and preparation method thereof - Google Patents

Abstract

The invention discloses a wave-absorbing honeycomb with a pyramid-like structure and a preparation method thereof, belonging to the technical field of microwave absorbing materials. The wave-absorbing honeycomb includes a plurality of pyramid-like wave-absorbing structures arranged in an array, each The wave-shaped wave-absorbing structure is composed of a number of wave-absorbing honeycomb sheets of different sizes and electromagnetic properties that are stacked and bonded from large to small in order from bottom to top. The middle area of each pyramid-like wave-absorbing structure is filled with non-wave-absorbing The honeycomb sheet, the pyramid-like absorbing structure and the non-absorbing honeycomb sheet together form a flat overall shape. The wave-absorbing honeycomb has both excellent wave-absorbing performance and a certain structural bearing capacity. The preparation method is stable and easy to control, and can prepare a wave-absorbing honeycomb with excellent wave-absorbing performance.

Description

A wave-absorbing honeycomb with a pyramid-like structure and its preparation method

technical field

The invention relates to a microwave-absorbing honeycomb with a pyramid-like structure and a preparation method thereof, belonging to the technical field of microwave-absorbing materials.

Background technique

The absorbing honeycomb is mainly obtained by impregnating the absorbing agent and depositing a layer of absorbing agent in the cell wall of the honeycomb to obtain the absorbing characteristics. The honeycomb is processed into the shape of sheet or pyramid, and then impregnated with absorbent to meet the application requirements of different fields. Among them, the microwave-absorbing honeycomb pyramid has excellent microwave-absorbing performance, and is widely used in microwave anechoic chambers or dark boxes. For the wave-absorbing honeycomb pyramid obtained by a single impregnation method, the absorber can easily form a concentration gradient in the thickness direction of the honeycomb, which is not conducive to the stability control of the wave-absorbing performance, and the electrical properties can be designed with fewer variables. The honeycomb pyramid is not easy to process, and the honeycomb in the form of the pyramid cannot be used for structural bearing, which limits the application range and field of the traditional honeycomb pyramid. For example, the utility model patent CN206344528U discloses a pyramidal honeycomb structure wave-absorbing material, which specifically discloses that the pyramid is an inner and outer composite layer structure, the inner layer is a honeycomb matrix layer, and the honeycomb matrix layer is a honeycomb formed by continuous hexagons. There is a flame-retardant absorbent layer on the wall, the outer layer of the pyramid is a polyester panel layer, and the base is composed of a honeycomb matrix layer and a skin layer on its outer surface. The material used is a wave-absorbing honeycomb sheet obtained after impregnation. However, its disadvantage is that four pieces of wave-absorbing honeycomb sheets are bonded to form a single pyramid, and the wave-absorbing pyramid in the final stroke is formed by a square pyramid. array, the absorbing honeycomb pyramid cannot be used as a structural load-bearing member.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a microwave-absorbing honeycomb with a pyramid-like structure with excellent microwave-absorbing performance and structural load-bearing performance and an easy-to-control preparation method.

For realizing the above object, technical scheme of the present invention is:

A wave-absorbing honeycomb with a pyramid-like structure, including a plurality of pyramid-like wave-absorbing structures arranged in an array, each of which is composed of a plurality of wave-absorbing honeycomb sheets of different sizes and electromagnetic properties According to the order from bottom to top, it is stacked and bonded from large to small. The middle area of each pyramid-like absorbing structure is filled with non-absorbing honeycomb sheets, pyramid-like absorbing structures and non-absorbing honeycomb sheets. Together they form a flat overall shape.

Furthermore, the thickness of the wave-absorbing honeycomb sheet is 5-20 mm, and the length and width (also called cell size) are not less than 3.2 mm.

A preparation method of a wave-absorbing honeycomb with a pyramid-like structure, comprising the following steps:

1) impregnating multiple non-absorbing honeycomb sheets with absorbent slurry, vibrating to remove excess slurry, drying, and repeating it several times to obtain wave-absorbing honeycomb sheets with different electromagnetic characteristics;

2) Cutting the wave-absorbing honeycomb sheet and the non-wave-absorbing honeycomb sheet into a certain size and shape;

3) The absorbing honeycomb sheet and the non-absorbing honeycomb sheet are laminated and stacked, and the absorbing honeycomb sheet is stacked from large to small in order from bottom to top to form a pyramid-like wave-absorbing structure, and the non-wave-absorbing honeycomb The sheets are filled between the absorbing honeycomb sheets of the same layer, between the upper and lower surfaces of each layer of absorbing honeycomb sheets, between the upper and lower surfaces of each non-absorbing honeycomb sheet, and between the absorbing honeycomb sheet and the non-absorbing honeycomb sheet. The sides of the honeycomb sheet are bonded with adhesive;

4) The product obtained in step 3) is pressurized and heated to solidify to obtain the final wave-absorbing honeycomb with a pyramid-like structure.

Further, the absorbent slurry is composed of a powdery absorbent, an adhesive system and a solvent, wherein the weight ratio of the powdery absorbent to the adhesive system is 1:1-1:5.

Further, the powder absorbent includes one or more of conductive carbon black, graphene, carbonyl iron powder, and metal oxide powder; the adhesive is selected from acrylic or polyurethane modified epoxy resin; the solvent is selected from plasma water.

Further, the viscosity value of the absorbent slurry is 10-20s.

Further, the thickness of the wave-absorbing honeycomb sheet in step 1) is 5-20 mm, and the length and width (also called cell size) are not less than 3.2 mm.

Further, step 1) is repeated no less than 3 times.

Further, each wave-absorbing honeycomb sheet adopts the same impregnation process or different impregnation processes.

Further, the cut size of the wave-absorbing honeycomb sheet in step 2) is 5mm×5mm˜100mm×100mm.

Further, the adhesive is selected from thermosetting resin.

Further, the drying temperature is 80-120° C., and the drying time is 1-2 hours.

Further, when stacking in step 3), first bond the wave-absorbing honeycomb sheet and the non-wave-absorbing honeycomb sheet of each layer together by applying the adhesive to the side of the wave-absorbing honeycomb sheet, Then embed the wave-absorbing honeycomb sheet into the corresponding position of the non-wave-absorbing honeycomb sheet to achieve bonding to obtain a complete layer; then apply the adhesive evenly on the upper and lower surfaces of the wave-absorbing honeycomb sheet of each layer, Stack and glue together according to the preset stacking order.

Further, the pressurization in step 4) is mold pressing or vacuum bag pressing, the curing temperature is from room temperature to 130° C., and the curing time is 2 to 24 hours.

Combining the characteristics of the wave-absorbing honeycomb sheet and the honeycomb pyramid structure, the invention proposes a wave-absorbing honeycomb with a pyramid-like structure and a preparation method thereof. Using non-absorbing honeycomb sheet as the base material, different impregnation processes are used to obtain wave-absorbing honeycomb sheet with serialized electromagnetic characteristics; according to the electrical performance design, honeycomb sheets with different parameters are stacked to form a pyramid-like wave-absorbing structure array. The present invention uses different sizes of wave-absorbing honeycomb sheets to be stacked and bonded, and the size of the honeycomb sheets gradually decreases from bottom to top, forming a pyramid-like wave-absorbing structure, which has excellent wave-absorbing performance and strong designability in electrical properties. It can meet the requirements of different application conditions. At the same time, the non-absorbing honeycomb sheet can be filled in the area between the pyramids, and co-cured with the absorbing honeycomb to form a multi-layer absorbing honeycomb, which has a flat physical shape and a pyramid-like electrical structure, which can be combined Absorbing performance and structural bearing capacity.

The beneficial effect of the present invention compared with prior art:

(1) The process of the present invention is easy to control, and the microwave-absorbing honeycomb with a pyramid-like structure has high microwave-absorbing performance. By stacking honeycomb sheets of different sizes, a pyramid-like structure is formed, which overcomes the existing wave-absorbing honeycomb pyramid Disadvantages of difficult processing.

(2) The electrical performance of the present invention is highly designable, and the impregnation process can be regulated, and absorbing honeycomb sheets of different sizes and electromagnetic properties can be designed to obtain wave-absorbing honeycombs with pyramid-like wave-absorbing structures with different wave-absorbing performances to meet different requirements. Application requirements.

(3) The present invention can reduce the difference in the wave-absorbing performance of the honeycomb in two directions through the orthogonal stacking of honeycomb sheets, and obtain a wave-absorbing honeycomb with stable performance.

Description of drawings

Fig. 1 is a schematic diagram of a pyramid-like wave-absorbing structure of a wave-absorbing honeycomb with a pyramid-like structure in the present invention;

Fig. 2 is a schematic diagram of the overall structure of the wave-absorbing honeycomb with a pyramid-like structure in the present invention;

Fig. 3 is the preparation flowchart of the wave-absorbing honeycomb with pyramid-like structure of the present invention;

Fig. 4 is the reflectance test curve of embodiment 1 of the present invention;

Fig. 5 is the reflectivity test curve of embodiment 2 of the present invention;

FIG. 6 is a reflectance test curve of Example 3 of the present invention.

Detailed ways

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below through specific embodiments and accompanying drawings.

The present invention proposes a microwave-absorbing honeycomb with a pyramid-like structure, as shown in Figure 1-2, including a plurality of pyramid-like (also known as pyramid-shaped) wave-absorbing structures arranged in an array, each pyramid-like The absorbing structure is composed of multiple absorbing honeycomb sheets of different sizes and electromagnetic properties stacked and bonded from large to small in order from bottom to top, and the middle area of each pyramid-like wave-absorbing structure is filled with non-absorbing honeycomb The sheet, the pyramid-like absorbing structure and the non-absorbing honeycomb sheet together form a flat overall shape.

The present invention also provides a method for preparing a wave-absorbing honeycomb with a pyramid-like structure, as shown in Figure 3, specifically through the following steps:

1. Honeycomb sheet preparation

In this step, the thickness of the non-absorbing honeycomb sheet is determined according to the electrical performance design, generally 5-20 mm. There is no special requirement for the cell size of the honeycomb, generally not less than 3.2mm, and it must be suitable for impregnating the absorbent slurry.

2. Preparation of absorbent slurry

The absorbent slurry is composed of a powdery absorbent, an adhesive system and a solvent, and the weight ratio between the powdery absorbent and the adhesive system is 1:1-1:5. The adhesive is generally water-soluble, which can be acrylic or polyurethane modified epoxy resin, and the solvent is plasma water. In this step, the viscosity of the slurry is adjusted through the amount of solvent added, so that the absorbent slurry has good manufacturability. In order to make it easier for the absorbent to deposit evenly in the cell walls of the honeycomb, the viscosity of the absorbent slurry should not be too high; and in order to prevent the absorbent from settling and agglomerating in the slurry, the viscosity of the absorbent slurry should not be too low. Appropriate absorbent slurry viscosity is an important parameter for the realization of manufacturability. Preferably, the viscosity is measured with a Tu-4 cup, and the viscosity value is 10-20s.

3. Honeycomb sheet impregnation

Use the absorbent slurry to impregnate the honeycomb sheet, vibrate repeatedly to remove excess slurry, and then dry it.

This step adopts the impregnation method known in the art, and those skilled in the art select the impregnation method and impregnation process according to the actual situation.

The drying process is as follows: the temperature is 80-120° C., and the time is 1-2 hours. The temperature should not be too high, otherwise the honeycomb pyramid will be deformed during the drying process; if the temperature is too low and the time is too short, the adhesive cannot be partially cured to play a bonding role, and it is easy to soak out after impregnation again.

4. Repeat the third step several times

In this step, the slurry is impregnated with the honeycomb sheet several times. During each impregnation, the viscosity of the slurry may be the same or may be gradually reduced. The specific process may refer to known techniques in the art. The number of repeated dipping is not less than 3 times to achieve the purpose of high electromagnetic loss, which is specifically designed according to the electrical performance. The honeycomb sheet can be prepared into a wave-absorbing honeycomb sheet with the same electrical properties, and can also be impregnated for different times to obtain a wave-absorbing honeycomb sheet with serialized electrical properties. The absorbent slurry of the present invention is at a lower viscosity level, and through the method of multiple dipping, the content of absorbent deposited by each dipping is less, which is more conducive to uniform deposition.

5. Absorbing honeycomb cutting

According to the electrical performance requirements of the wave-absorbing honeycomb, the wave-absorbing honeycomb array structure is designed, and the number of pyramid-like structures, the number of layers and the size of the wave-absorbing honeycomb sheet in each layer are determined. Cut the wave-absorbing honeycomb sheet into the designed shape and size, usually a square, but also other shapes. When cutting the wave-absorbing honeycomb, it must be parallel or perpendicular to the stretching direction of the honeycomb, and cannot be cut along other directions.

At the same time, the blanking and cutting of the non-absorbing honeycomb is carried out. According to the size and position of each wave-absorbing honeycomb sheet, cut out the honeycomb sheet of the same size at the corresponding position of the non-absorbing honeycomb sheet to obtain the base material inlaid with the wave-absorbing honeycomb sheet. The size of the absorbing honeycomb sheet should be slightly larger than the size of the square holes on the non-absorbing honeycomb sheet to ensure that the absorbing honeycomb can be completely fixed in the honeycomb sheet.

6. Absorbing honeycomb stack bonding

The stacking and bonding of the absorbing honeycomb is carried out according to the array structure design. A thermosetting resin is selected as the adhesive between the absorbing honeycomb layers. First, apply the adhesive on the side of the wave-absorbing honeycomb sheet, insert each layer of wave-absorbing honeycomb sheet into the corresponding position of the non-wave-absorbing honeycomb sheet, and then apply the adhesive evenly on the upper and lower surfaces of the honeycomb sheet , and finally stack the honeycomb sheets together according to the designed stacking sequence.

7. Absorbing honeycomb curing.

Using the corresponding process, the stacked multi-layer absorbing honeycomb is heated and solidified to obtain the absorbing honeycomb with a pyramid-like absorbing structure.

According to the curing conditions of the thermosetting resin, the curing process of the absorbing honeycomb is determined. Vacuum bag pressing or molding process can be used, the curing temperature is from room temperature to 130°C, and the curing time is 2 to 24 hours.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

Step 1: Select a honeycomb block with a density of 48kg/m ³ and a cell size of 3.2mm, and use a cutting machine to cut it into a honeycomb sheet of 300mm×300mm×5mm.

Step 2: Take a certain quality of conductive carbon black, water-soluble honeycomb modified epoxy resin, curing agent and deionized water, wherein the total mass of conductive carbon black and resin (containing curing agent) is 500g, conductive carbon black and resin The weight ratio (including curing agent) is 1:1, and the plasma water is 5000g. Put the conductive carbon black, resin, curing agent and a small amount of plasma water into the container for high-speed mechanical stirring for 10 minutes, then gradually add the remaining plasma water into the container, and get the absorbent slurry after stirring evenly. After the foam on the surface of the slurry is eliminated, use the Tu-4 cup to monitor the viscosity of the absorbent slurry, and the viscosity value is 12-13s. Pour the configured absorbent slurry into a plastic tank of a certain size.

Step 3: Place the honeycomb sheet in the absorbent slurry, and shake it up and down several times for impregnation, so that the honeycomb sheet is fully soaked in the slurry. Take out the honeycomb sheet from the absorbent slurry, perform vibration treatment, discharge the excess slurry in the pores of the honeycomb sheet, air it on the wire mesh, and dry it at 100°C for 1 hour to completely volatilize the water. Fully cured.

Step 4: Repeat step 3 to impregnate and dry the honeycomb pyramid 5 times in total.

Step 5: Design the wave-absorbing honeycomb array structure according to the electrical performance requirements, determine the number of layers of the wave-absorbing honeycomb to be 10 layers, the number of pyramid-like structures to be 6×6, the side length of the first layer (bottom layer) of the pyramid is 50mm, and the second layer Layer 45mm, and so on, the side length of the pyramid decreases by 5mm in each layer, and the side length of the 10th layer (surface) pyramid is 5mm. According to the design parameters of the pyramid structure, the wave-absorbing honeycomb sheet and the non-wave-absorbing honeycomb sheet are cut.

Step 6: Apply epoxy resin adhesive to the side of the wave-absorbing honeycomb sheet, and place it in the corresponding position of each layer of non-wave-absorbing honeycomb sheet to obtain 10 layers of honeycomb sheet. Then apply the epoxy resin adhesive evenly on the top and bottom of the 10-layer honeycomb sheet, wherein the first layer (bottom layer) is only coated with adhesive on the top, and the tenth layer (surface layer) is only coated with adhesive on the bottom. Finally, the 10 layers of honeycomb are stacked in sequence.

Step 7: Curing by vacuum bagging process. A 5mm-thick aluminum plate is placed on the upper and lower sides of the paved multi-layer absorbing honeycomb. After fixing, the whole is placed in a vacuum bag, vacuumed, placed in an oven, and heated to 80°C. After 4 hours of heat preservation, the oven is turned off to cool down. After cooling down to room temperature, open the vacuum bag for demoulding to obtain a microwave-absorbing honeycomb with a pyramid-like microwave-absorbing structure. The reflectivity test curve of the absorbing honeycomb is shown in Figure 4.

Example 2

A honeycomb block with a density of 48kg/m ³ and a cell size of 4.8mm is selected as the base material. A total of 8 honeycomb pyramids were impregnated and dried, and the rest were the same as in Example 1 to obtain a microwave-absorbing honeycomb with a pyramid-like wave-absorbing structure. The reflectivity test curve of the absorbing honeycomb is shown in Fig. 5 .

Example 3

Step 1: Select a honeycomb block with a density of 80kg/m ³ and a cell size of 3.2mm, and use a cutting machine to cut it into honeycomb sheets of 500mm×500mm×10mm.

Step 2: Take a certain quality of conductive carbon black, water-soluble honeycomb modified epoxy resin, curing agent and deionized water, wherein the total mass of conductive carbon black and resin (containing curing agent) is 1200g, and conductive carbon black and resin The weight ratio (including curing agent) is 1:3, and the plasma water is 6000g. Put the conductive carbon black, resin, curing agent and a small amount of plasma water into the container for high-speed mechanical stirring for 10 minutes, then gradually add the remaining plasma water into the container, and get the absorbent slurry after stirring evenly. After the foam on the surface of the slurry is eliminated, use the Tu-4 cup to monitor the viscosity of the absorbent slurry, and the viscosity value is 10-11s. Pour the configured absorbent slurry into a plastic tank of a certain size.

Step 3: Place the honeycomb sheet in the absorbent slurry, and shake it up and down several times for impregnation, so that the honeycomb sheet is fully soaked in the slurry. Take out the honeycomb sheet from the absorbent slurry, perform vibration treatment, discharge the excess slurry in the honeycomb pyramid holes, air it on the wire mesh, and dry it at 100°C for 1 hour to completely volatilize the water, and the absorbent slurry Fully cured.

Step 4: Repeat step 3 to impregnate and dry the honeycomb sheet 1 to 10 times respectively to obtain 10 kinds of wave-absorbing honeycomb sheets with different dielectric properties, which are the wave-absorbing honeycombs of specifications 1 to 10.

Step 5: Design the absorbing honeycomb array structure according to the electrical performance requirements, determine the number of absorbing honeycomb layers to be 10 layers, the number of pyramid-like structures to be 5×5, the side length of the first layer (bottom layer) of the pyramid is 100mm, and the second layer The layer is 90mm, and so on, the side length of the pyramid decreases by 10mm for each layer, the side length of the 10th layer (surface layer) of the pyramid is 10mm, and the size of the absorbing honeycomb is 500mm×500mm×100mm. According to the size of the pyramid structure design, the absorbing honeycomb sheet and the non-absorbing honeycomb sheet are cut, the first layer (bottom layer) uses the specification 10 absorbing honeycomb, the second layer uses the specification 9 absorbing honeycomb, and so on. The 10th layer (surface layer) adopts the specification 1 wave-absorbing honeycomb.

Step 6: Apply epoxy resin adhesive to the side of the wave-absorbing honeycomb sheet, and place them in the corresponding positions of each layer of non-wave-absorbing honeycomb sheet to obtain 10 layers of honeycomb sheet. Then apply the epoxy resin adhesive evenly on the top and bottom of the 10-layer honeycomb sheet, wherein the first layer (bottom layer) is only coated with adhesive on the top, and the tenth layer (surface layer) is only coated with adhesive on the bottom. Finally, the 10 layers of honeycomb are stacked in sequence.

Step 7: Curing by molding process. Place the paved multi-layer absorbing honeycomb in the cavity of the flat mold, the thickness of the limit side strip is 100mm, and place the upper cover. After the mold is closed, place it on the platform of the press, raise the temperature to 130°C, pressurize at 1.5Mpa, keep the temperature for 2 hours, and then close the press. After cooling down to room temperature, the pressure is released, the mold is demoulded, and the burrs are removed to obtain a wave-absorbing honeycomb with a pyramid-like wave-absorbing structure. The reflectivity test curve of the absorbing honeycomb is shown in Figure 6.

Parts not described in detail in the present invention are well-known technologies for those skilled in the art.

The specific embodiments and drawings of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. Those skilled in the art can understand that various alternatives can be made without departing from the spirit and scope of the present invention. , changes and modifications are possible. The present invention should not be limited to the content disclosed in the embodiments of the specification and the accompanying drawings, and the scope of protection of the present invention is subject to the scope defined in the claims.

Claims (10)

1. A wave-absorbing honeycomb with a pyramid-like structure is characterized in that it comprises a plurality of pyramid-like wave-absorbing structures arranged in an array, and each pyramid-like wave-absorbing structure is composed of a plurality of different sizes and electromagnetic properties The wave-absorbing honeycomb sheets are stacked and bonded in order from bottom to top, and the middle area of each non-absorbing honeycomb sheet is filled with wave-absorbing honeycomb sheets, wave-absorbing honeycomb sheets and non-wave-absorbing honeycomb sheets. The sheets together form a flat overall shape. 2. The wave-absorbing honeycomb with pyramid-like structure according to claim 1, characterized in that the thickness of the wave-absorbing honeycomb sheet is 5-20mm, and the length and width are not less than 3.2mm. 3. A preparation method of a wave-absorbing honeycomb with a pyramid-like structure, characterized in that, comprising the following steps: 1) Use absorbent slurry to impregnate multiple non-absorbing honeycomb sheets, vibrate to remove excess slurry, dry, and repeat it several times to obtain wave-absorbing honeycomb sheets with different electromagnetic characteristics; 2) Cut the absorbing honeycomb sheet and non-absorbing honeycomb sheet into a certain size and shape; 3) The absorbing honeycomb sheet and the non-absorbing honeycomb sheet are laminated and stacked, and the absorbing honeycomb sheet is stacked from large to small in order from bottom to top to form a pyramid-like wave-absorbing structure. The middle area of the wave-absorbing honeycomb sheet is filled with wave-absorbing honeycomb sheets. The sides of the honeycomb sheet are bonded with adhesive; 4) The product obtained in step 3) is pressurized and heated to solidify to obtain the final wave-absorbing honeycomb with a pyramid-like structure. 4. preparation method as claimed in claim 3, is characterized in that, absorbent slurry is made up of powdery absorbent, adhesive system and solvent, and wherein the weight ratio of powdery absorbent and adhesive system is 1: 1～1:5; the powder absorbent includes one or more of conductive carbon black, graphene, carbonyl iron powder, and oxidized metal powder; the adhesive is acrylic or polyurethane modified epoxy resin; the solvent is plasma water ; The viscosity value of the absorbent slurry is 10-20s. 5. The preparation method according to claim 3, wherein the thickness of the wave-absorbing honeycomb sheet in step 1) is 5-20mm, and the length and width are not less than 3.2mm; the wave-absorbing honeycomb sheet cut in step 2) The size is 5mm×5mm~100mm×100mm. 6. The preparation method according to claim 3, characterized in that, step 1) is repeated no less than 3 times. 7. The preparation method according to claim 3, characterized in that the same impregnation process or different impregnation processes are used for each wave-absorbing honeycomb sheet. 8. The preparation method according to claim 3, characterized in that the drying temperature is 80-120° C. and the drying time is 1-2 hours. 9. The preparation method according to claim 3, characterized in that, when stacking in step 3), the wave-absorbing honeycomb sheet and the non-wave-absorbing honeycomb sheet of each layer are first bonded together by Apply the adhesive to the side of the wave-absorbing honeycomb sheet, and then embed the wave-absorbing honeycomb sheet into the corresponding position of the non-wave-absorbing honeycomb sheet to achieve bonding to obtain a complete layer; then apply the adhesive evenly The upper and lower surfaces of the wave-absorbing honeycomb sheets of each layer are stacked and bonded together according to the preset stacking sequence. 10. The preparation method according to claim 3, wherein the pressurization in step 4) is mold pressing or vacuum bag pressing, the curing temperature is from room temperature to 130°C, and the curing time is 2-24 hours.

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