Lightweight ultra-wideband microwave absorbing material and preparation method thereof

Abstract

The present application relates to a kind of lightweight microwave absorbing material based on high aspect ratio conductive fiber and its preparation method.The present application utilizes the unique dispersion characteristics (permittivity changes with frequency) of high aspect ratio conductive fiber, which is mixed with resin to make wave-absorbing layer, and is applied to Jaumann wave-absorbing structure, achieving significant improvement of overall wave-absorbing performance in 2-18GHz.The material is composed of wave-absorbing layer and dielectric layer (porous foam), and the wave-absorbing frequency band is closely related to the impedance characteristics, order and thickness of each layer.The aspect ratio of the conductive fiber in the present application is greater than or equal to 1000, and the electrical conductivity is greater than or equal to 10 4 S / m; the areal density of the microwave absorbing material in the present application is less than or equal to 0.3kg / m 2 , the thickness is less than or equal to 25mm, the microwave reflectivity is less than or equal to -10dB in 2GHz-4GHz, and less than or equal to -25dB in 4GHz-18GHz, which is a lightweight ultra-wideband wave-absorbing material.

Description

TECHNICAL FIELD

[0001] The application relates to a light-weight microwave absorbing material based on high-aspect-ratio conductive fibers and a preparation method thereof, and belongs to the technical field of wave-absorbing materials. BACKGROUND

[0002] In order to reduce the radar signal characteristics of equipment, a wave-absorbing coating or a wave-absorbing patch using carbonyl iron powder as an absorbent is usually used, which has the disadvantage of large density and is not suitable for large-area use. In addition, the wave-absorbing coating and the patch only have a single action frequency band and cannot effectively cope with ultra-wide frequency detection, so it is urgent to develop a light-weight, ultra-wide frequency microwave absorbing material.

[0003] The high-aspect-ratio conductive fiber has the advantages of large electromagnetic parameters, good frequency dispersion characteristics, light weight and high efficiency, and has a broad application prospect in the field of ultra-wideband wave absorption. The present application utilizes the good dielectric dispersion characteristics of the high-aspect-ratio conductive fiber to solve the problem of high and low frequency compatibility, and combines it with the Jaumann wave-absorbing structure. Through reasonable multi-layer structure design and reliable preparation process, a kind of ultra-wideband light-weight microwave absorbing material is successfully obtained. The material has a 2-18GHz full-band microwave absorption characteristic, and has a light weight, which can be used to reduce the radar scattering characteristics of equipment in the 2-18GHz frequency band. SUMMARY

[0004] The technical problem solved by the present application is to overcome the shortcomings of the prior art and provide a light-weight ultra-wideband microwave absorbing material and a preparation method, which can effectively reduce the radar scattering characteristics of equipment in the 2-18GHz frequency band.

[0005] The Jaumann wave-absorbing structure is a kind of wideband wave-absorbing structure, which is usually composed of a multi-layer structure with different impedance characteristics (wave-absorbing layer and dielectric layer). The wave-absorbing frequency band is closely related to the impedance characteristics, arrangement order and thickness of each layer. The Jaumann wave-absorbing structure currently designed and used in engineering adopts a resistance layer with fixed resistance value as the wave-absorbing layer. The electromagnetic characteristics of the wave-absorbing layer cannot change with frequency, which makes the overall material have the problems of incompatible high and low frequencies and excessive thickness (40-60mm).

[0006] The present application utilizes the unique dispersion characteristics (dielectric constant changes sharply with frequency) of the high-aspect-ratio conductive fiber, mixes it with resin to make a wave-absorbing layer, and applies it to the Jaumann wave-absorbing structure, which realizes the significant improvement of the overall wave-absorbing property in the 2-18GHz frequency band.

[0007] The technical solution of the present application is:

[0008] A light-weight ultra-wideband microwave absorbing material is composed of a wave-absorbing layer and a dielectric layer.

[0009] The wave-absorbing layer is composed of conductive fibers and resin, wherein the aspect ratio of the conductive fibers is greater than or equal to 1000 (the aspect ratio = fiber length / fiber diameter) and the conductivity is greater than or equal to 10 S / m 4 S / m. By adopting the technical solution of high-aspect-ratio conductive fibers, the dielectric dispersion characteristics of the wave-absorbing layer can be greatly improved, that is, the dielectric constant of the wave-absorbing layer presents a sharp downward trend with the increase of frequency. The ordinary wave-absorbing filler does not have obvious dielectric dispersion characteristics, that is, the dielectric constant of the wave-absorbing layer made of ordinary wave-absorbing filler changes little with frequency. The significant dielectric dispersion performance is beneficial to expand the wave-absorbing frequency band and improve the high-frequency and low-frequency wave-absorbing compatibility of the wave-absorbing material.

[0010] A light-weight ultra-wideband microwave absorbing material, wherein the dielectric layer is composed of low-dielectric material, and the relative dielectric constant ε' of the dielectric layer is less than or equal to 1.6 and the dielectric loss factor ε'' is less than or equal to 0.4 in the frequency range of 2-18 GHz.

[0011] The absorbing layer and the dielectric layer are arranged in the thickness direction with a spacing (except for the bottom layer and the surface layer, because the bottom layer and the surface layer must have one side adjacent to air).

[0012] The ultra-wideband light-weight wave-absorbing material of the present application is a multi-layer material (Jaumann multi-layer wave-absorbing structure) obtained by compounding the wave-absorbing layer and the dielectric layer in a specific order.

[0013] The wave-absorbing layer is made by mixing high-aspect-ratio conductive fibers and resin and then molding.

[0014] By the above technical solution, the high-aspect-ratio conductive fibers and the Jaumann wave-absorbing structure are combined: the high-aspect-ratio conductive fibers are used as the wave-absorbing layer in the Jaumann structure, and the low-dielectric foam material is used as the dielectric layer in the preparation of the Jaumann structure. The special dispersion characteristics of the high-aspect-ratio conductive fibers are used to improve the high-frequency and low-frequency wave-absorbing compatibility, and the low-dielectric foam material is used to suppress the impedance fluctuation in the whole wave band, so as to finally realize the ultra-wideband wave-absorbing.

[0015] The dispersion characteristics of the dielectric constant of the wave-absorbing layer depend on the aspect ratio, conductivity and content of the conductive fibers in the wave-absorbing layer.

[0016] The wave impedance of the surface layer of the wave-absorbing material is close to the wave impedance of air by adjusting the wave impedance of the material (the microwave reflectivity of the wave-absorbing material is related to the wave impedance) through the multi-layer structure. In the adjustment of the wave impedance, the high-aspect-ratio conductive fibers are used to ensure that the dielectric constant of the wave-absorbing layer presents a nearly cross-order downward trend in the frequency range of 2-18 GHz, thereby improving the high-frequency and low-frequency compatibility of the wave-absorbing layer; the high-impedance characteristics of the dielectric layer are used to suppress the impedance fluctuation in part of the wave band, and the dielectric gradient of the wave-absorbing layer in the thickness direction and the thickness of each layer of the dielectric layer are optimized to realize the wideband wave-absorbing performance of the material in the frequency range of 2-18 GHz.

[0017] A preparation method of a lightweight ultra-wideband microwave absorbing material, comprising:

[0018] 1) According to the reflectivity and thickness requirements, the permittivity of the absorbing layer, the thickness of the dielectric layer, and the arrangement order of each layer in the Jaumann absorbing structure are designed;

[0019] 2) The absorbing layer is prepared according to the design in 1). The content of conductive fibers in the absorbing layer and the thickness of the absorbing layer are adjusted to obtain an absorbing layer with a specific permittivity;

[0020] 3) The dielectric layer is prepared according to the design in 1);

[0021] 4) The absorbing layer and the dielectric layer are compounded according to the structure arrangement order in 1);

[0022] The absorbing layer in the present application relies on high aspect ratio conductive fibers to achieve ideal dielectric dispersion characteristics in the ultra-wide frequency band. The typical characteristics are as follows:

[0023] ① The thickness of a single layer is ≤2mm;

[0024] ② The aspect ratio of the conductive fibers in the absorbing layer is ≥1000;

[0025] ③ The conductivity of the conductive fibers is ≥10 4 S / m;

[0026] ④ The working frequency band is 2-18GHz;

[0027] The absorbing layer in the present application uniformly disperses high aspect ratio conductive fibers in resin and is obtained after molding. The preparation process includes the following steps:

[0028] ① According to the design requirements, a certain amount of conductive fibers is mixed with resin, and the uniform dispersion of the conductive fibers in the resin is ensured;

[0029] ② The mixture of conductive fibers and resin is poured into a mold of a specific thickness, and is cured by heating and pressing;

[0030] ③ After complete cooling, the absorbing layer is obtained after demolding.

[0031] The dielectric layer in the present application is composed of a material with a low permittivity, and its room temperature relative permittivity (2-18GHz) ε' ≤1.6, ε'' ≤0.4.

[0032] The compounding process of the absorbing layer and the dielectric layer in the present application uses epoxy resin as the adhesive, and the curing temperature is 100-130℃. The preparation steps are as follows:

[0033] ① The absorbing layer and the dielectric layer are stacked according to the design order;

[0034] ② evenly coat the epoxy resin adhesive on the surface to be compounded;

[0035] ③ solidify under certain pressure and temperature, and finally obtain the lightweight ultra-wideband microwave absorbing material.

[0036] The final performance of the lightweight ultra-wideband microwave absorbing material in the application is closely related to the wave-absorbing layer, the dielectric layer and the multi-layer structure, and different performance requirements can be met by adjusting the above three aspects.

[0037] Main technical indexes and characteristics:

[0038] The overall performance of the lightweight ultra-wideband microwave absorbing material in the application is as follows:

[0039] ① total thickness ≤ 25 mm;

[0040] ② bulk density ≤ 0.3 g / cm 3 ;

[0041] ③ microwave reflectivity: 2GHz-4GHz ≤-10dB, 4GHz-18GHz ≤-25dB (test method refer to GJB2038A-2001).

[0042] Based on the above, the application at least has the following beneficial technical effects:

[0043] First, the application makes full use of the advantage of the high-aspect-ratio conductive fiber material in dielectric constant adjustment, and greatly improves the dielectric dispersion characteristics of the material by optimizing key parameters such as electrical conductivity and aspect ratio, thereby breaking through the bottleneck of electromagnetic parameters in the ultra-wideband absorbing material.

[0044] Second, the ultra-wideband microwave absorbing material in the application has the characteristic of being lightweight, with a bulk density of ≤ 0.3 g / cm 3 , which is much lower than that of conventional absorbing coating and patch materials (bulk density of about 3.3 g / cm 3 ).

[0045] Third, the application organically combines the high-aspect-ratio conductive fiber material with the Jaumann wave-absorbing structure, thereby significantly expanding the absorbing frequency band of the material (microwave reflectivity: 2GHz-4GHz ≤-10dB, 4GHz-18GHz ≤-25dB), and the traditional absorbing coating and patch material only has single-band absorbing performance (such as X-band). BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The normalized dielectric constant modulus (|ε r | nomalized ) of the three wave-absorbing layers;

[0047] Figure 2Dielectric constant modulus of three wave-absorbing layers r |);

[0048] Figure 3 Microwave reflectivity of Example 1;

[0049] Figure 4 Microwave reflectivity of Example 2;

[0050] Figure 5 Schematic diagram of composite molding of multilayer wave-absorbing material

[0051] Figure 6 SEM of conductive fiber in Example 1;

[0052] Figure 7 Optical photo (partial) of high aspect ratio conductive fiber used in Example 1;

[0053] Figure 8 Physical sample of Example 1 material (top right is cross section). DETAILED DESCRIPTION

[0054] The present application will be further described in detail below in conjunction with the accompanying drawings and specific examples:

[0055] Preparation example

[0056] The preparation method of the wave-absorbing layer comprises:

[0057] According to the design requirements, a specific content of conductive fiber is mixed with resin to ensure uniform dispersion of the conductive fiber in the resin; the mixture of the conductive fiber and the resin is poured into a mold of a specific thickness, and is cured by heating and pressing to form a wave-absorbing layer. The resin used is all epoxy resin. The schematic diagram of the composite molding process is shown in Figure 5 .

[0058] The preparation parameters of the three wave-absorbing layers are listed in the following table:

[0059] Table 1 Preparation parameters of three wave-absorbing layers

[0060]

[0061] As shown in Figure 1 , the dielectric constant of wave-absorbing layer 1#, 2# and 3# samples was tested respectively. To evaluate the dielectric dispersion characteristics of the material, the normalized dielectric constant modulus (|ε r | nomalized ) is usually used as a characterization. The normalization process is to divide the dielectric constant modulus of all frequency points by the dielectric constant modulus at 18 GHz. The normalized dielectric constant modulus data of the three samples is shown in Figure 1 . As can be seen from the figure, in the frequency range of 2-4 GHz, the |ε r |nomalized The descending speed of the curve is significantly greater than that of the wave-absorbing layer 2#; at the same time, the |ε r | nomalized The descending speed of the curve is approximately, the above-mentioned characteristics mean that the aspect ratio has a significant influence on the |ε r | nomalized The trend of change. The high aspect ratio can significantly improve the |ε r | nomalized The descending speed of the curve, while maintaining the high-frequency (8-18 GHz) |ε r | nomalized The descending speed of the curve is basically unchanged. This is exactly what is required for the ultra-wideband wave-absorbing |ε r | nomalized The descending trend of the curve (or the dielectric dispersion characteristic): that is, it urgently needs to descend at the low-frequency band, and the descending speed quickly slows down as the frequency rises.

[0062] As Figure 2 shown, it is worth mentioning that the carbon-based fiber used in the wave-absorbing layer 3# sample has the same aspect ratio as 1#, the conductivity is lower than 1#, but Figure 1 The |ε r | nomalized The curve of the two is basically the same, which shows that the aspect ratio has a decisive influence on the dielectric dispersion characteristic.

[0063] The conductivity of the conductive fiber mainly affects the size of the |ε r (Non-normalized, that is, the absolute value), see Figure 2 . Since the conductivity of 3# is lower than that of 1# and 2#, the |ε r | is low. This means that the conductivity mainly affects the absolute value of the dielectric constant. Since the absolute value of the dielectric constant affects the wave impedance, the conductivity of the conductive fiber is also important for the wave-absorbing performance.

[0064] Example 1

[0065] A lightweight ultra-wideband microwave absorbing material is prepared by the following method:

[0066] The wave-absorbing layer is prepared by the method of the above preparation example, the aspect ratio of the conductive fiber in the wave-absorbing layer is 1143, and the conductivity is 5.8x10 4 S / m. In order to realize the gradient change of the dielectric constant, the fiber content in the wave-absorbing layer is taken as different values. The dielectric layer adopts PMI foam material, the density is 0.11 g / cm 3 , and the dielectric constant is 1.1-0.1j;

[0067] The lightweight ultra-wideband wave-absorbing material in Example 1 is composed of 4 layers of wave-absorbing layers and 5 layers of dielectric layers, and the structure parameters of each layer in Example 1 are shown in Table 2.

[0068] The multi-layer composite process is as follows: first, according to the order of Table 2, stack each layer of material in turn; then evenly coat the epoxy resin adhesive on the surface of each layer to be compounded; finally, cure at 130°C for 2 hours under a pressure of 0.5 MPa to obtain the lightweight ultra-wideband microwave absorbing material of Example 1.

[0069] Table 2 Structure parameters of each layer in Example 1

[0070]

[0071]

[0072] In Table 2, the wave-absorbing layer 1#: short-cut carbon fibers with a length of 8 mm, a diameter of 7 μm, and an electrical conductivity of 5.8×10 4 S / m, the mass percentage of short-cut carbon fibers in the wave-absorbing layer 1# is 1.2%; the SEM of the conductive fibers is shown in Figure 2. Figure 6 ;

[0073] In Table 2, the wave-absorbing layer 2#: short-cut carbon fibers with a length of 8 mm, a diameter of 7 μm, and an electrical conductivity of 5.8×10 4 S / m, the mass percentage of short-cut carbon fibers in the wave-absorbing layer 2# is 0.5%;

[0074] In Table 2, the wave-absorbing layer 3#: short-cut carbon fibers with a length of 8 mm, a diameter of 7 μm, and an electrical conductivity of 5.8×10 4 S / m, the mass percentage of short-cut carbon fibers in the wave-absorbing layer 3# is 0.4%;

[0075] In Table 2, the wave-absorbing layer 4#: short-cut carbon fibers with a length of 8 mm, a diameter of 7 μm, and an electrical conductivity of 5.8×10 4 S / m, the mass percentage of short-cut carbon fibers in the wave-absorbing layer 4# is 0.1%.

[0076] The wave-absorbing layers 1#-4# in Table 2 can be qualitatively evaluated in terms of the dielectric constant by using the sample's wave permeability. The wave permeability is shown in Table 3. Generally, the wave permeability of a sample is related to the dielectric constant and thickness of the sample. When the thickness of the sample is fixed, the change in the wave permeability can indirectly reflect the change in the dielectric constant. The smaller (more negative) the wave permeability is, the larger the dielectric constant is, and the larger (closer to 0) the wave permeability is, the smaller the dielectric constant is. When the thickness of the wave-absorbing layers 1#-4# in Example 1 is 0.2 mm, the wave permeability values at each frequency point are shown in Table 3. As shown in Table 3, the wave permeability of the wave-absorbing layers 1#, 2#, 3# and 4# increases (is closer to 0) layer by layer, which means that the dielectric constant of each wave-absorbing layer in this example decreases layer by layer.

[0077] Table 3: Permeability of each wave-absorbing layer in Example 1 (unit: dB, thickness of wave-absorbing layer is 0.2mm)

[0078]

[0079]

[0080] The mass and volume of Example 1 were tested respectively, and the bulk density of Example 1 was obtained as 0.24 g / cm 3 .

[0081] The microwave reflectivity of Example 1 was tested according to GJB2038A-2001, and the microwave reflectivity was as shown in Figure 3 Figure 2. It can be seen from the figure that Example 1 presents typical super-wideband wave-absorbing characteristics, with reflectivity <-10 dB at 2-4 GHz, and reflectivity <-25 dB at 4-18 GHz (with reflectivity <-30 dB at 4-16 GHz).

[0082] Example 1 effectively solves the problem of lightweight expansion of the wave-absorbing frequency band by means of the special dispersion characteristics of the high aspect ratio conductive fiber, and through the optimization design of the dielectric gradient and the thickness of the dielectric layer in combination with the multi-layer wave-absorbing structure, realizing the super-wideband wave-absorbing performance at 2-18 GHz.

[0083] Example 2

[0084] The difference between Example 1 and Example 2 is that the conductive fiber used in the wave-absorbing layer in Example 2 has an aspect ratio of 429 (the length of the carbon-based fiber is 3 mm, and the diameter is 7 μm).

[0085] In Example 2, the conductivity of the conductive fiber in the wave-absorbing layer is 5.8 x 10 4 S / m. To realize the gradient change of the dielectric constant, the content of the conductive fiber in the wave-absorbing layer is taken as different values. The dielectric layer uses PMI foam material with a density of 0.11 g / cm 3 and a dielectric constant of 1.1-0.1j;

[0086] The microwave wave-absorbing material in Example 2 is composed of 7 wave-absorbing layers and 8 dielectric layers, and the structure parameters of each layer in Example 2 are shown in Table 3.

[0087] The multi-layer composite process is as follows: first, according to the order in Table 3, stack each layer of material in turn; then evenly coat the epoxy resin adhesive on the surface of each layer to be compounded; finally, cure at 0.5 MPa pressure and 130°C for 2 hours to obtain the microwave absorbing material of Example 2.

[0088] Table 3: Structure parameters of each layer in Example 2

[0089] Number of layers Material Thickness (mm) Remarks 1 PMI foam 4.2 Bottom layer 2 Wave absorbing layer 1 0.5 3 PMI foam 3.4 4 Wave absorbing layer 2 0.5 5 PMI foam 2.4 6 Wave absorbing layer 3 0.25 7 PMI foam 1.8 8 Wave absorbing layer 4 0.25 9 PMI foam 1.8 10 Wave absorbing layer 5 0.25 11 PMI foam 3.2 12 Wave absorbing layer 6 0.15 13 PMI foam 2.4 14 Wave absorbing layer 7 0.15 15 PMI foam 4.3 Surface layer

[0090] In Table 3, the short-cut carbon fiber with length of 3mm, diameter of 7μm and conductivity of 5.8x10 4 S / m was used in the wave-absorbing layer 1#, and the mass percentage of the short-cut carbon fiber in the wave-absorbing layer 1# was 5%;

[0091] In Table 3, the short-cut carbon fiber with length of 3mm, diameter of 7μm and conductivity of 5.8x10 4 S / m was used in the wave-absorbing layer 2#, and the mass percentage of the short-cut carbon fiber in the wave-absorbing layer 2# was 3%;

[0092] In Table 3, the short-cut carbon fiber with length of 3mm, diameter of 7μm and conductivity of 5.8x10 4 S / m was used in the wave-absorbing layer 3#, and the mass percentage of the short-cut carbon fiber in the wave-absorbing layer 3# was 1%;

[0093] In Table 3, the short-cut carbon fiber with length of 3mm, diameter of 7μm and conductivity of 5.8x10 4 S / m was used in the wave-absorbing layer 4#, and the mass percentage of the short-cut carbon fiber in the wave-absorbing layer 4# was 0.5%;

[0094] In Table 3, the short-cut carbon fiber with length of 3mm, diameter of 7μm and conductivity of 5.8x10 4 S / m was used in the wave-absorbing layer 5#, and the mass percentage of the short-cut carbon fiber in the wave-absorbing layer 5# was 0.2%;

[0095] In Table 3, the short-cut carbon fiber with length of 3mm, diameter of 7μm and conductivity of 5.8x10 4 S / m was used in the wave-absorbing layer 6#, and the mass percentage of the short-cut carbon fiber in the wave-absorbing layer 6# was 0.2%;

[0096] In Table 3, the short-cut carbon fiber with length of 3mm, diameter of 7μm and conductivity of 5.8x10 4 S / m was used in the wave-absorbing layer 7#, and the mass percentage of the short-cut carbon fiber in the wave-absorbing layer 7# was 0.1%;

[0097] The mass and volume of Example 2 were respectively tested, and the bulk density of Example 2 was 0.28g / cm 3 .

[0098] The microwave reflectivity of Example 2 was tested according to GJB2038A-2001, and the microwave reflectivity was as shown in Figure 2. Figure 4As a comparison, the dashed line in the figure is the reflectivity curve of Example 1. As can be seen from the figure, the reflectivity curves of Example 2 and Example 1 are significantly different in the frequency range of 2-6 GHz. Compared with Example 1, the reflectivity of Example 2 is obviously higher in the frequency range of 2-6 GHz, which means that the wave absorption effect of Example 2 in the frequency range of 2-6 GHz is sharply decreased. In the frequency range of 6-18 GHz, the difference between the reflectivity of the two is narrowed, but the reflectivity of Example 1 is still obviously lower than that of Example 2.

[0099] The difference in reflectivity in the frequency range of 2-6 GHz is mainly related to the aspect ratio of the conductive fiber in the wave absorbing layer. The conductive fiber with high aspect ratio (Example 1) has more ideal dielectric dispersion characteristics (low frequency high, high frequency low), and has more advantages in the compatibility of wave absorbing performance at high and low frequencies, so the reflectivity curve of Example 1 shows obvious super wideband characteristics. When the aspect ratio of the conductive fiber is reduced (Example 2), the dielectric dispersion characteristics of the wave absorbing layer are deteriorated (the speed of the decrease of the dielectric constant from low frequency to high frequency is reduced), and the compatibility of the wave absorbing performance at high and low frequencies is deteriorated, so the reflectivity of Example 2 is rapidly increased at low frequency, and is kept at a low level at high frequency.

[0100] In addition, the influence of the aspect ratio of the conductive fiber is also reflected in the design efficiency of the wave absorbing structure. High aspect ratio only needs 4 layers of wave absorbing layer gradient to achieve wideband wave absorption (Example 1), and small aspect ratio cannot effectively improve the wave absorbing performance at low frequency even if 7 layers of wave absorbing layer gradient are used. This shows that high aspect ratio can quickly adjust the wave impedance and exhibit extremely high impedance matching efficiency.

[0101] Although the present application is disclosed with the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present application, therefore, the protection scope of the present application should be limited by the scope defined by the claims of the present application.

Claims

1. A lightweight ultrawideband microwave absorbing material, characterized in that: It includes an absorbing layer and a dielectric layer. The absorbing layer consists of conductive fibers and resin. The conductive fibers are short-cut carbon-based fibers with an aspect ratio ≥1000 and an electrical conductivity ≥10. 4 S / m; The dielectric layer is made of low-dielectric foam material with a relative permittivity ε'≤1.6 and ε''≤0.4 in the 2-18GHz range; The absorbing layer and the dielectric layer are arranged at intervals in the thickness direction to form a Jaumann absorbing structure.

2. The lightweight ultrawideband microwave absorbing material according to claim 1, characterized in that: Along the thickness direction, the dielectric constant of the absorbing layer exhibits a monotonically gradient distribution, and along the direction from the bottom layer to the top layer of the absorbing material, the dielectric constant of each absorbing layer shows a monotonically decreasing trend.

3. The lightweight ultrawideband microwave absorbing material according to claim 1, characterized in that: The thickness of a single layer of the absorbing layer is ≤2mm.

4. The lightweight ultrawideband microwave absorbing material according to claim 1, characterized in that: The conductive fibers in the absorbing layer are made of conductive materials.

5. The lightweight ultrawideband microwave absorbing material according to claim 1, characterized in that: The resin is made of any one or more of epoxy resin, silicone resin, and polyurethane resin.

6. The lightweight ultrawideband microwave absorbing material according to claim 1, characterized in that: With the mass of the absorbing layer as 100%, the mass percentage of the conductive fibers in the absorbing layer is 0.05%-5%.

7. A method for preparing a lightweight ultrawideband microwave absorbing material according to any one of claims 1-6, characterized in that: include S1: Apply the adhesive evenly to the surfaces of the absorbing layer and the dielectric layer to be laminated; S2: The microwave absorbing layer coated with adhesive and the dielectric layer are stacked in sequence and cured to obtain the absorbing material.

8. The method for preparing a lightweight ultrawideband microwave absorbing material according to claim 7, characterized in that: The method for preparing the microwave absorbing layer includes mixing conductive fibers and resin evenly to obtain a mixture of conductive fibers and resin; pouring the mixture of conductive fibers and resin into a mold, curing, cooling, and demolding to obtain the microwave absorbing layer.

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