Honeycomb composite absorbing structure based on three-dimensional gradient resistance film and its preparation method

Abstract

The present invention discloses a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film and a preparation method thereof, belonging to the field of radar absorbing materials. The honeycomb composite absorbing structure comprises: a composite absorber comprising a foam column and a gradient resistance film attached to the outer surface of the foam column; the gradient resistance film having a square resistance that gradually increases along a first direction perpendicular to the cross-section of the foam column; a honeycomb structure having multiple cells, each of which has a composite absorber inserted therein; and a metal base plate located on one side of the honeycomb structure, perpendicular to the gradient resistance film, and connected to the side of the gradient resistance film with the lowest square resistance. Using a low-density, high-mechanical-strength honeycomb as a substrate, the three-dimensional gradient resistance film absorbing structure is inserted into the honeycomb, resulting in a lightweight, highly absorbing, broadband absorbing structure.

Description

Technical Field

[0001] The present invention belongs to the field of radar absorbing materials, and more specifically, relates to a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film and a preparation method thereof. Background Art

[0002] In modern battlefield environments, radar detection technology continues to advance, making it easier for important military targets and equipment to be exposed to enemy strikes. Consequently, the development of radar stealth technology is becoming increasingly urgent, and the requirements for radar stealth effectiveness are becoming more stringent. Absorbing materials can absorb incident electromagnetic waves to a certain extent, dissipating the energy of these waves into heat or reducing the energy of reflected electromagnetic waves through other means.

[0003] According to the loss mechanism of electromagnetic waves by the absorbing material, it can be divided into three types: resistive loss type absorbing material, dielectric loss type absorbing material and magnetic loss type absorbing material. At the same time, honeycomb structure has a wide range of applications in the field of radar stealth due to its light weight and good mechanical strength. Combining honeycomb structure with absorbing material can ensure good absorbing performance while ensuring mechanical strength. Traditional absorbing honeycombs usually use an impregnation process to absorb electromagnetic waves through the dielectric loss of the absorbing slurry, but it is difficult to accurately control the electromagnetic parameters of the absorbing slurry, and it is not easy to achieve strong absorption of electromagnetic waves in a wide frequency band. Therefore, it is still difficult to achieve strong broadband absorption through lightweight structures with existing technologies. Summary of the Invention

[0004] In response to the defects of the existing technology and the need for improvement, the present invention provides a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film and a preparation method thereof, the purpose of which is to obtain a lightweight and highly absorbing broadband absorbing structure.

[0005] To achieve the above objectives, according to one aspect of the present invention, a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film is provided, comprising: a composite absorber comprising a foam column and a gradient resistance film attached to the outer surface of the foam column; the gradient resistance film having a sheet resistance that gradually increases along a first direction perpendicular to the cross-section of the foam column; a honeycomb structure having a plurality of cells, each cell having one of the composite absorbers inserted therein; and a metal base plate located on one side of the honeycomb structure, perpendicular to the gradient resistance film, and connected to the side of the gradient resistance film having the smallest sheet resistance.

[0006] Furthermore, the gradient resistance film is divided into N different regions, the square resistance values ​​in each region are the same, and the square resistance values ​​between each region are different, and N≥2.

[0007] Furthermore, when 3≤N≤5 and N=3, the square resistances of the three regions gradually increase along the first direction, and the resistances of the three regions are respectively within the following three ranges: 100Ω-1000Ω, 200Ω-2000Ω, and 300Ω-3000Ω.

[0008] Furthermore, in the honeycomb structure, the honeycomb aperture length is 2.75mm-8mm, and the honeycomb density is 30kg / m 3 -80kg / m 3 , the plane compression strength is 0.6MPa-4.2MPa.

[0009] Furthermore, the honeycomb structure adopts para-aramid honeycomb or meta-aramid honeycomb.

[0010] Furthermore, the material of the foam column is PMI foam.

[0011] Furthermore, the foam column is a foam cylinder.

[0012] According to another aspect of the present invention, a method for preparing a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film as described above is provided, comprising: dividing a printing substrate into N printing areas from bottom to top, where N ≥ 2; screen-printing a resistive carbon paste on the surface of the printing substrate, wherein the square resistance of the resistive carbon paste screen-printed in each printing area gradually increases from bottom to top, and drying and curing the paste after each screen printing to obtain a gradient resistance film; attaching the gradient resistance film to the outer surface of a foam column to obtain a composite absorber; inserting the composite absorber into cells of a honeycomb structure, with one composite absorber inserted into each cell; and connecting a metal base plate to the side of the gradient resistance film with the smallest square resistance, wherein the metal base plate is perpendicular to the gradient resistance film, to obtain a honeycomb composite absorbing structure.

[0013] Furthermore, each time the drying and curing is performed, the drying and curing temperature is 120° C.-200° C., and the drying and curing time is 10 min-30 min.

[0014] Furthermore, the gradient resistor film is attached to the outer surface of the foam column by using double-sided tape or glue.

[0015] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0016] (1) A honeycomb composite absorbing structure based on a three-dimensional gradient resistance film is provided. The three-dimensional gradient resistance film is composited with a honeycomb structure. A honeycomb with low density and high mechanical strength is used as a substrate. The high loss effect of the three-dimensional gradient resistance film structure is utilized to ultimately obtain a lightweight and highly absorbing broadband absorber. The structure achieves an absorption of more than 90% of electromagnetic waves in a broadband range of 2-18 GHz and an absorption of more than 99% of electromagnetic waves in a broadband range of 3-18 GHz.

[0017] Unlike traditional resistive film absorbers, which typically place the film a quarter wavelength away from the metal base to dissipate the electric field, this structure inserts the film into the honeycomb cells and places it perpendicular to the metal base. Electromagnetic waves form multiple standing waves on the three-dimensional resistive film, thus utilizing the ohmic loss of the resistive film to achieve wave absorption. At the same time, the use of gradient resistive film structures made of different resistance values ​​creates an impedance gradient design, further enhancing the electromagnetic loss effect, ultimately resulting in a lightweight, highly absorbing broadband absorber.

[0018] (2) The absorbing honeycomb structure uses finished white honeycombs with high structural strength and low mass. The supporting foam is polymethacrylimide (PMI) foam with low density, which achieves broadband strong absorption through a lightweight structure, thereby solving the technical problem that traditional absorbing materials are heavy and have certain limitations in practical application areas.

[0019] (3) A preparation method for a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film is provided. The method has a reasonable design and great scalability. Resistance films with different gradients can be prepared, which can meet the actual working conditions and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A three-dimensional diagram of a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film provided by an embodiment of the present invention;

[0021] Figure 2 A top view of a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film provided in an embodiment of the present invention;

[0022] Figure 3 A schematic diagram of the four-gradient and three-dimensional gradient resistor film partitioning provided by an embodiment of the present invention;

[0023] Figure 4 1 is a graph showing the test results of the wave absorption performance of Example 3;

[0024] Figure 5 1 is a graph showing the test results of the wave absorbing performance of Example 4;

[0025] Figure 6 This is a performance test result diagram of the resistive film composite absorber obtained by dipping the honeycomb.

[0026] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0027] 1 is the first printing area, 2 is the second printing area, 3 is the third printing area, 4 is the metal base plate, 5 is the aramid paper honeycomb, 6 is the printing material polyimide film, and 7 is the PMI foam cylinder. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0029] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0030] Example 1

[0031] A honeycomb composite wave absorbing structure based on a three-dimensional gradient resistance film comprises a composite wave absorbing body, a honeycomb structure with multiple cells and a metal bottom plate.

[0032] The composite absorber comprises a foam column and a gradient resistor film attached to the outer surface of the foam column. The gradient resistor film has a square resistance that gradually increases along a first direction perpendicular to the cross-section of the foam column. Each cell of the honeycomb structure has a composite absorber inserted into it. A metal base plate is located on one side of the honeycomb structure, perpendicular to the gradient resistor film, and connected to the side of the gradient resistor film with the lowest square resistance.

[0033] In this embodiment, the gradient resistance film is divided into N different regions, each region has the same square resistance value, and each region has different square resistance values, where N≥2.

[0034] Preferably, 3≤N≤5. Further preferably, N=3, the square resistances of the three regions gradually increase along the first direction, and the resistances of the three regions are respectively within the following three ranges: 100Ω-1000Ω, 200Ω-2000Ω, and 300Ω-3000Ω.

[0035] Preferably, in the honeycomb structure, the honeycomb aperture length is 2.75mm-8mm, and the honeycomb density is 30kg / m 3 -80kg / m 3 , the plane compression strength is 0.6MPa-4.2MPa.

[0036] Preferably, the honeycomb structure adopts para-aramid honeycomb or meta-aramid honeycomb.

[0037] Preferably, the foam column is made of PMI foam, which has a low dielectric constant and a low density. The foam column is a foam cylinder. It should be noted that the foam column can also be made of other foam materials and shapes, such as a cubic column.

[0038] Example 2

[0039] A method for preparing a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film is used to prepare the honeycomb composite absorbing structure based on a three-dimensional gradient resistance film in Example 1. The preparation method includes the following steps 1 to 5.

[0040] Step 1: Divide the printing material into N printing areas from bottom to top, where N is greater than or equal to 2. From bottom to top, the printing area is the first printing area, the second printing area, ..., and the Nth printing area.

[0041] Step 2: screen-print the resistive carbon paste on the surface of the printing material. From bottom to top, the square resistance of the resistive carbon paste in each printing area gradually increases. After each screen printing, the resistive carbon paste is dried and solidified to obtain a gradient resistive film.

[0042] Specifically, the first printing area prints the lowest square resistance carbon paste, the second printing area prints the higher square resistance carbon paste, and the Nth printing area prints the highest square resistance carbon paste. That is, as the printing area number increases, the square resistance of the printed carbon paste also increases.

[0043] Preferably, each time the drying and curing is performed, the drying and curing temperature is 120° C.-200° C., and the drying and curing time is 10 min-30 min.

[0044] Step 3: attaching the gradient resistor film to the outer surface of the foam column to obtain a composite absorber.

[0045] Preferably, the gradient resistor film is attached to the outer surface of the foam column using double-sided tape or glue. The double-sided tape is heat-resistant double-sided tape, and the glue is heat-resistant glue that can withstand a maximum temperature of 150°C in long-term use.

[0046] Step 4: inserting the composite absorber into the cells of the honeycomb structure, with one composite absorber inserted into each cell.

[0047] Step 5: Connect a metal base plate to the side of the gradient resistor film with the smallest square resistance, with the metal base plate being perpendicular to the gradient resistor film, to obtain a honeycomb composite absorbing structure.

[0048] Example 3

[0049] A honeycomb composite absorbing structure based on a three-dimensional gradient resistance film is prepared by the following method.

[0050] Step (1): Divide the printing material into two areas from bottom to top, namely the first printing area and the second printing area, with heights of 18 mm and 12 mm respectively. The printing material is a PI film with a thickness of 75 μm. Screen printing is performed using resistive carbon pastes with different square resistances. The first printing area is printed with a resistive carbon paste with a square resistance of 1000 Ω corresponding to a height of 18 mm. After printing, the resistive carbon paste is dried and cured at a curing temperature of 160° C. and a curing time of 10 min. Then, the second printing area is printed with a resistive carbon paste with a square resistance of 2000 Ω corresponding to a height of 12 mm. After printing, the resistive carbon paste is dried and cured at a curing temperature of 160° C. and a curing time of 10 min to obtain a gradient resistor film.

[0051] Step (2) is to cut the gradient resistor film into patches with a length equal to the height of the foam and a width equal to the circumference of the cross section of the foam cylinder, and to attach the patches to the surface of the foam cylinder with high-temperature resistant double-sided tape to obtain the absorbing foam.

[0052] In step (3), the absorbing foam is inserted into the cells of the paper honeycomb, and the first printed area of ​​the resistor film is connected to the metal base plate to obtain a composite absorbing structure.

[0053] Example 4

[0054] A honeycomb composite absorbing structure based on a three-dimensional gradient resistance film. The difference between this embodiment and the third embodiment is that the steps (1) of the two are different. The specific steps (1) of this embodiment are as follows.

[0055] Step (1): The printing material is divided into three areas from bottom to top, namely the first printing area, the second printing area, and the third printing area, with heights of 8 mm, 10 mm, and 12 mm, respectively. The printing material is a PI film with a thickness of 75 μm. Resistive carbon pastes of different square resistances are used for screen printing. The first printing area is printed with a resistive carbon paste with a square resistance of 400 Ω corresponding to a height of 8 mm. After printing, the resistive carbon paste is dried and cured at a curing temperature of 160° C. and a curing time of 10 minutes. Then, the second printing area is printed with a resistive carbon paste with a square resistance of 900 Ω corresponding to a height of 10 mm. After printing, the resistive carbon paste is dried and cured at a curing temperature of 160° C. and a curing time of 10 minutes. Then, the third printing is performed in the third printing area corresponding to a height of 12 mm. The resistive carbon paste has a square resistance of 2000 Ω. Similarly, after printing, the resistive carbon paste is dried and cured at a curing temperature of 160° C. and a curing time of 10 minutes.

[0056] The three-dimensional image of the honeycomb composite absorbing structure based on the three-dimensional gradient resistance film prepared in this embodiment is as follows: Figure 1 As shown, the top view is Figure 2 As shown, it includes a first printing area 1, a second printing area 2, a third printing area 3, a metal base plate 4, an aramid paper honeycomb 5, a printing material polyimide film 6 and a PMI foam cylinder 7.

[0057] Example 5

[0058] The difference between this embodiment and the third embodiment is that this embodiment divides the printing material into N areas from bottom to top, including a first printing area, a second printing area, a third printing area, and up to the Nth printing area, where N is a positive integer greater than 2, and printing is performed using resistive carbon pastes with different square resistance values. The first printing area prints the resistive carbon paste with the lowest square resistance, the second printing area prints the resistive carbon paste with a higher square resistance, and the Nth printing area prints the resistive carbon paste with the highest square resistance. That is, as the printing area number increases, the square resistance of the printed resistive carbon paste also increases. Each printing needs to be dried and cured to obtain a gradient resistance film.

[0059] Specifically, in this embodiment, N=4, including the first printing area, the second printing area, the third printing area and the fourth printing area, as shown in FIG. Figure 3 As shown, the corresponding heights are h1, h2, h3 and h4 respectively.

[0060] Furthermore, the above embodiment was tested. The composite structure of the obtained three-dimensional gradient resistance film and honeycomb was tested for its wave absorbing performance in a microwave darkroom. The test results of embodiment 3 are as follows: Figure 4 As shown, Figure 4 It shows that the composite structure has a reflectivity below -10dB in the 2.0-18GHz frequency band. Figure 5 As shown, Figure 5 It shows that the composite structure has a reflectivity below -10dB in the 2-18GHz frequency band and below -20dB in the 3-18GHz frequency band.

[0061] Comparing the absorption performance curves of Example 3 and Example 4 reveals that the reflectivity amplitude of Example 3 at the peak position at the 5 GHz, 10 GHz, and 15 GHz frequencies is higher than -20 dB. This is because the 3D gradient resistive film structure in Example 3 has only two printed areas, meaning only two gradient layers, resulting in a significant impedance discontinuity between the air and the metal substrate. Compared to Example 3, the 3D gradient resistive film structure in Example 4 has three printed areas: the first, second, and third printed areas, resulting in a three-layer gradient design. This 3D gradient resistive film structure in Example 4 achieves a smoother impedance transition between the air and the metal substrate, providing a better impedance match between the overall structure and the air, thereby achieving superior absorption performance.

[0062] Figure 6This is a performance test result diagram of the resistive film composite absorber obtained by dipping the honeycomb. The process of preparing the resistive film by impregnation to obtain the absorbing honeycomb is as follows: (1) adding the absorbent, degassing agent and dispersant to the solvent and mixing them evenly to obtain the absorbing slurry; (2) dividing the aramid honeycomb into N zones in the height direction, N≥3, including the non-impregnated zone, the first impregnated zone, the second impregnated zone and the N-1th impregnated zone, and impregnating them with the absorbing slurry. The non-impregnated zone does not need to be impregnated, the first impregnated zone is impregnated once, the second impregnated zone is impregnated twice, and the N-1th impregnated zone is impregnated N-1 times. After the impregnation is completed, the resistive film is cured and formed to obtain the absorbing aramid honeycomb; (3) the carbon slurry is screen-printed onto the printing material according to the hexagonal ring array pattern, and after drying and curing, a resistive film frequency selective surface with the hexagonal ring array pattern is obtained; (4) the printing material of the resistive film frequency selective surface is connected to the non-impregnated zone of the absorbing aramid honeycomb, and the N-1th impregnated zone of the absorbing aramid honeycomb is connected to the metal base plate to obtain a composite absorber.

[0063] contrast Figure 5 and Figure 6 As can be seen, the reflectivity of the resistive film composite absorber obtained by impregnation of the honeycomb is only below -10 dB in the 2.2-16 GHz range. Due to the choice of impregnation slurry, its impedance matching effect is difficult to further improve. The absorber structure in Example 4 has a reflectivity below -10 dB in the 2-18 GHz range and below -20 dB in the 3-18 GHz range. This is due to the three-layer impedance gradient design and the strong absorption effect of the three-dimensional resistive film, which makes the impedance transformation between the air and the metal base plate smoother, more efficiently dissipates electromagnetic waves, and thus achieves better absorbing performance.

[0064] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A honeycomb composite absorbing structure based on a three-dimensional gradient resistance film, characterized in that: include: A composite absorber includes a foam column and a gradient resistance film attached to the outer surface of the foam column; The square resistance of the gradient resistance film gradually increases along a first direction, and the first direction is perpendicular to the cross section of the foam column; A honeycomb structure having a plurality of cells, wherein one of the composite absorbers is inserted into each cell; The metal bottom plate is located on one side of the honeycomb structure, is perpendicular to the gradient resistance film, and is connected to the side of the gradient resistance film with the smallest square resistance.

2. The honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 1, characterized in that: The gradient resistance film is divided into N different regions, each region has the same square resistance value, and each region has different square resistance values, where N≥2.

3. The honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 2, wherein: 3≤N≤5； When N=3, the square resistance values ​​of the three regions gradually increase along the first direction, and the resistance values ​​of the three regions are respectively in the following three ranges: 100Ω-1000Ω, 200Ω-2000Ω, and 300Ω-3000Ω.

4. The honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 1, wherein: In the honeycomb structure, the honeycomb aperture length is 2.75mm-8mm, and the honeycomb density is 30kg / m 3 -80kg / m 3 , the plane compression strength is 0.6MPa-4.2MPa.

5. The honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 1 or 4, characterized in that: The honeycomb structure adopts para-aramid honeycomb or meta-aramid honeycomb.

6. The honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 1, characterized in that: The material of the foam column is PMI foam.

7. The honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 1, characterized in that: The foam column is a foam cylinder.

8. A method for preparing a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to any one of claims 1 to 7, characterized in that: include: Divide the printing material into N printing areas from bottom to top, N ≥ 2; Screen printing is performed on the surface of the printing material using a resistive carbon paste, with the square resistance of the resistive carbon paste screen-printed in each printing area gradually increasing from bottom to top, and drying and curing is performed after each screen printing to obtain a gradient resistive film; Attaching the gradient resistance film to the outer surface of the foam column to obtain a composite absorber; Inserting the composite absorber into the cells of the honeycomb structure, with one composite absorber inserted into each cell; A metal base plate is connected to the side of the gradient resistance film with the smallest square resistance, and the metal base plate is perpendicular to the gradient resistance film to obtain a honeycomb composite wave absorbing structure.

9. The method for preparing a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 8, wherein: Each time of drying and curing, the drying and curing temperature is 120°C-200°C, and the drying and curing time is 10min-30min.

10. The method for preparing a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film according to claim 8, wherein: The gradient resistor film is attached to the outer surface of the foam column by using double-sided tape or glue.

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