Honeycomb composite wave-absorbing structure based on three-dimensional gradient resistive film and preparation method thereof

Abstract

The invention discloses a honeycomb composite wave-absorbing structure based on a three-dimensional gradient resistive film and a preparation method thereof, and belongs to the field of radar wave-absorbing materials, and the honeycomb composite wave-absorbing structure comprises a composite wave-absorbing body which comprises a foam cylinder and a gradient resistive film attached to the outer surface of the foam cylinder; the sheet resistance value of the gradient resistive film is gradually increased along a first direction, and the first direction is perpendicular to the cross section of the foam column body; the honeycomb structure is provided with a plurality of hole grids, and a composite wave absorbing body is inserted into each hole grid; and the metal bottom plate is positioned on one side of the honeycomb structure, is vertical to the gradient resistance film, and is connected with one side, with the minimum sheet resistance value, of the gradient resistance film. A honeycomb with low density and high mechanical strength is used as a substrate, a three-dimensional gradient resistive film wave-absorbing structure is inserted into the honeycomb, and the broadband wave-absorbing structure with light weight and strong absorption is obtained.

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 the modern battlefield environment, radar detection technology is constantly developing, and important military targets and military equipment are easily exposed to the enemy's attack range. Therefore, the development of radar stealth technology is becoming more urgent, and the requirements for radar stealth effect are becoming more stringent. Absorbing materials can absorb incident electromagnetic waves to a certain extent, converting electromagnetic wave energy into heat energy dissipation or reducing the energy of reflected electromagnetic waves by other means.

[0003] According to the loss mechanism of electromagnetic waves by the absorbing material, it can be divided into three types: resistance loss type absorbing material, dielectric loss type absorbing material and magnetic loss type absorbing material. At the same time, the honeycomb structure is widely used in the field of radar stealth because of its light weight and good mechanical strength. The composite honeycomb structure with the absorbing material can have 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 bandwidth. Therefore, it is still difficult for existing technologies to achieve broadband strong absorption through lightweight structures. Summary of the invention

[0004] In view of the defects and improvement needs of the prior art, 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-mentioned purpose, 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 absorbing body, comprising 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 with a plurality of cells, each of which has one of the composite absorbing bodies inserted therein; and a metal bottom 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 smallest square resistance.

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

[0007] Furthermore, when 3≤N≤5 and 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 regions: 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, there is provided a method for preparing a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film as described above, comprising: dividing a substrate into N printing areas from bottom to top, N≥2; screen-printing a resistive carbon paste on the surface of the 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 are performed 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, wherein one composite absorber is inserted into each cell; and connecting a metal bottom plate to the side with the smallest square resistance in the gradient resistance film, wherein the metal bottom 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, wherein the three-dimensional gradient resistance film is composited with a honeycomb structure, and 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 finally obtain a lightweight and highly absorbing broadband absorber, which can absorb more than 90% of electromagnetic waves in a broadband range of 2-18 GHz and more than 99% of electromagnetic waves in a broadband range of 3-18 GHz.

[0017] Different from the traditional resistive film absorber, which usually places the resistive film at a quarter wavelength away from the metal base plate to lose the electric field, this structure inserts the resistive film into the honeycomb grid and places it perpendicular to the metal base plate. Electromagnetic waves will form multiple standing waves on the three-dimensional resistive film, thereby utilizing the ohmic loss of the resistive film to achieve wave absorption. At the same time, the gradient resistive film structure made of different resistance values ​​forms an impedance gradient design, further enhancing the electromagnetic loss effect, and finally obtaining a lightweight and highly absorbing broadband absorber.

[0018] (2) The absorbing honeycomb structure uses a finished white honeycomb 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 method for preparing a honeycomb composite absorbing structure based on a three-dimensional gradient resistance film is provided. The method has a reasonable design and great scalability. It can prepare resistance films with different gradients, 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 wave absorbing structure based on a three-dimensional gradient resistance film provided in an embodiment of the present invention;

[0021] Figure 2 A top view of a honeycomb composite wave 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 a four-gradient three-dimensional gradient resistor film partition provided in an embodiment of the present invention;

[0023] Figure 4 is a diagram showing the test results of the wave absorbing performance of the third embodiment;

[0024] Figure 5 is a graph showing the test results of the wave absorbing performance of the fourth embodiment;

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

[0026] In all 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 purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can 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 accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0030] Embodiment 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 a plurality of cells and a metal bottom plate.

[0032] The 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 composite absorber is inserted into each cell of the honeycomb structure. The metal bottom plate is 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 smallest square resistance.

[0033] In this embodiment, the gradient resistor film is divided into N different regions, the square resistance values ​​in each region are the same, and the square resistance values ​​between the regions are different, and N≥2.

[0034] Preferably, 3≤N≤5. Further preferably, 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 regions: 100Ω-1000Ω, 200Ω-2000Ω, and 300Ω-3000Ω.

[0035] Preferably, in the honeycomb structure, the honeycomb aperture length is 2.75 mm-8 mm, and the honeycomb density is 30 kg / 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] Embodiment 2

[0039] A method for preparing a honeycomb composite wave absorbing structure based on a three-dimensional gradient resistance film is used to prepare the honeycomb composite wave 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≥2, which are the first printing area, the second printing area, ..., and the Nth printing area from bottom to top.

[0041] Step 2, screen printing the resistive carbon paste on the surface of the printing material, from bottom to top, the square resistance of the resistive carbon paste screen-printed in each printing area gradually increases, and drying and curing are performed after each screen printing 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 by double-sided adhesive or glue. The double-sided adhesive is high temperature resistant double-sided adhesive, and the glue is high temperature resistant glue, which can withstand a maximum temperature of 150° C. in long-term use.

[0046] Step 4: insert the composite absorber into the cells of the honeycomb structure, and insert one composite absorber into each cell.

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

[0048] Embodiment 3

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

[0050] Step (1), dividing the printing material from bottom to top into two areas, 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, and 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 value of 1000Ω corresponding to a height of 18 mm, and after printing, it 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 value of 2000Ω corresponding to a height of 12 mm, and after printing, it is dried and cured at a curing temperature of 160°C and a curing time of 10 minutes to obtain a gradient resistor film.

[0051] Step (2), cutting 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 attaching the patches to the surface of the foam cylinder with high temperature resistant double-sided tape to obtain the absorbing foam.

[0052] Step (3), inserting the absorbing foam into the cells of the paper honeycomb, connecting the first printed area of ​​the resistor film to the metal bottom plate, and obtaining a composite absorbing structure.

[0053] Embodiment 4

[0054] A honeycomb composite wave 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, the heights are 8mm, 10mm and 12mm respectively, the printing material is a PI film with a thickness of 75μm, and 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 value of 400Ω corresponding to a height of 8mm, and is dried and cured after printing, the curing temperature is 160℃, and the curing time is 10min. Then, the second printing area is printed with a resistive carbon paste with a square resistance value of 900Ω corresponding to a height of 10mm, and is dried and cured after printing, the curing temperature is 160℃, and the curing time is 10min. Then, the third printing is performed in the third printing area corresponding to a height of 12mm, and the square resistance value of the printed resistive carbon paste is 2000Ω. Similarly, it is dried and cured after printing, the curing temperature is 160℃, and the curing time is 10min.

[0056] The three-dimensional image of the honeycomb composite wave absorbing structure based on the three-dimensional gradient resistance film prepared in this embodiment is shown in FIG. 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] Embodiment 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 uses resistive carbon pastes with different square resistance values ​​for printing. 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, and each printing needs to be dried and cured to obtain a gradient resistance film.

[0059] Specifically, in this embodiment, N=4, including a first printing area, a second printing area, a third printing area and a 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 microwave absorption performance in a microwave darkroom. The test results of the 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 is shown that the composite structure has a reflectivity below -10dB in the 2-18GHz frequency band and a reflectivity below -20dB in the 3-18GHz frequency band.

[0061] By comparing the wave absorption performance curves of Example 3 and Example 4, it can be found that the reflectivity amplitude of the wave absorption performance curve of Example 3 at the peak position at 5GHz, 10GHz and 15GHz frequency points is higher than -20dB. The reason is that the three-dimensional gradient resistance film structure in Example 3 has only two printing areas, that is, only two layers of gradient, and the impedance between the air and the metal base plate is still relatively discontinuous. Compared with Example 3, the three-dimensional gradient resistance film structure of Example 4 has three layers of printing area, specifically the first printing area, the second printing area and the third printing area, with a total of three layers of gradient design. The three-dimensional gradient resistance film structure of Example 4 makes the impedance transformation between the air and the metal base plate smoother, and the overall structure has better impedance matching with the air, thereby achieving better wave absorption performance.

[0062] Figure 6This is a performance test result diagram of the resistive film composite absorber obtained by preparing the honeycomb by dipping. The process of preparing the resistor film by impregnation to obtain the absorbing honeycomb is as follows: (1) adding an absorbent, a degassing agent and a dispersant to a solvent and mixing them evenly to obtain an absorbing slurry; (2) dividing the aramid honeycomb into N zones in the height direction, N≥3, including a non-impregnated zone, a first impregnated zone, a second impregnated zone and an 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 absorbing aramid honeycomb is cured and formed to obtain an absorbing aramid honeycomb; (3) printing the carbon slurry onto a substrate according to a hexagonal ring array pattern by screen printing, and obtaining a frequency selective surface of the resistor film with a hexagonal ring array pattern after drying and curing; (4) connecting the substrate of the frequency selective surface of the resistor film to the non-impregnated zone of the absorbing aramid honeycomb, and connecting the N-1th impregnated zone of the absorbing aramid honeycomb to a metal base plate to obtain a composite absorber.

[0063] contrast Figure 5 and Figure 6 It can be seen that the reflectivity of the resistive film composite absorber obtained by impregnation of the honeycomb is only lower than -10dB at 2.2-16GHz. Limited by the choice of the impregnation slurry, its impedance matching effect is difficult to be further improved. The reflectivity of the absorber structure in the fourth embodiment is lower than -10dB at 2-18GHz and lower than -20dB at 3-18GHz. 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 bottom plate smoother and more efficiently loses electromagnetic waves, thereby achieving better absorbing performance.

[0064] It will be easily understood by those skilled in the art that the above description is only 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 protection scope of the present invention.

Claims

1. A honeycomb composite absorbing structure based on a three-dimensional gradient resistance film. It is characterized in that include: A composite wave absorbing body, comprising 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 at 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 wave absorbing structure based on the three-dimensional gradient resistance film according to claim 1, It is 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, and N≥2.

3. The honeycomb composite wave absorbing structure based on the three-dimensional gradient resistance film according to claim 2, It is characterized in that 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 regions: 100Ω-1000Ω, 200Ω-2000Ω, and 300Ω-3000Ω.

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

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

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

8. A method for preparing a honeycomb composite wave absorbing structure based on a three-dimensional gradient resistance film according to any one of claims 1 to 7, It is characterized in that include: Divide the printing material into N printing areas from bottom to top, N ≥ 2; Using resistive carbon paste to perform screen printing on the surface of the substrate, from bottom to top, the square resistance value of the resistive carbon paste screen printed in each printing area gradually increases, and drying and curing are 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 bottom plate is connected to the side of the gradient resistance film with the smallest square resistance, and the metal bottom plate is perpendicular to the gradient resistance film to obtain a honeycomb composite wave absorbing structure.

9. The method for preparing the honeycomb composite wave absorbing structure based on the three-dimensional gradient resistance film according to claim 8, It is characterized in that 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 the honeycomb composite wave absorbing structure based on the three-dimensional gradient resistance film according to claim 8, It is characterized in that 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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