A radar-absorbing material for millimeter-wave radar, its preparation method and application

Abstract

This invention provides a microwave absorbing material that can be used in millimeter-wave radar, its preparation method, and its application. The raw materials for preparing the microwave absorbing material include liquid resin and dielectric material, wherein the amount of dielectric material is 2% to 3.5% of the mass of liquid resin; wherein the Shore A hardness of the liquid resin is 20 HA to 30 HA; and the specific surface area of ​​the dielectric material is 500 m². 2 / g~1000 m 2 The dielectric material has a DBP absorption value of 300 mL / 100g to 500 mL / 100g and a particle size ≤100nm. This invention, through simultaneous optimization of the liquid resin and dielectric material, achieves excellent absorption performance in millimeter-wave radar under a simple structure, and can also handle complex operating conditions such as multi-angle incoming waves and wide temperature range applications.

Description

Technical Field

[0001] This invention belongs to the field of absorbing materials, and particularly relates to an absorbing material that can be used in millimeter-wave radar, its preparation method and application. Background Technology

[0002] In the existing technology of absorbing materials for millimeter-wave radar, there are still many key technical bottlenecks that need to be overcome.

[0003] First, millimeter wave frequencies are generally considered to range from 26.5 GHz to 300 GHz. However, due to the extremely short wavelength of millimeter waves (approximately 3.7 to 3.9 mm), extremely high requirements are placed on the impedance matching capability of absorbing materials. The material needs to achieve impedance matching with free space at an extremely thin thickness (approximately 1 to 3 mm), otherwise the absorption efficiency will easily decrease due to interface reflection. Furthermore, traditional absorbing materials (such as ferrites) usually follow the design principle of "thickness approximately equal to one-quarter of the wavelength." However, traditional absorbing materials often require greater thickness to achieve broadband absorption, making it difficult for the material to simultaneously meet the dual requirements of "thin layer" and "broadband."

[0004] Furthermore, the stability of materials in complex operating environments poses a significant challenge, especially in scenarios with drastic temperature changes, such as automotive engine compartments. High temperatures and humidity can easily cause dielectric drift, resulting in a shift in absorption frequency. Therefore, materials must maintain stable performance over a wide temperature range (e.g., -40℃ to 120℃). More importantly, the angle-dependent nature of electromagnetic wave incidence also limits the practical application of existing absorbing materials. When the incident angle deviates from the normal by more than 30°, the absorption performance often decreases significantly. However, automotive radar needs to handle waves from multiple angles during actual operation, placing higher demands on the wide-angle absorption capabilities of absorbing materials.

[0005] In addition, in terms of processing technology, flexible microwave absorbing materials suitable for curved surfaces need to have good flexibility and adhesion strength. However, existing microwave absorbing materials often have insufficient mechanical properties, making it difficult to balance flexibility, durability and microwave absorption functions.

[0006] In summary, these challenges collectively restrict the further application of millimeter-wave radar absorbing materials in high-end equipment and civilian vehicles. Current technologies typically address these issues by constructing absorbing units with multiple layers of absorbing sheets and dielectric layers, or by performing complex modifications to the dielectric material. However, the solutions offered by existing technologies are not only complex in their fabrication processes but also require lengthy research and development time and are costly. Summary of the Invention

[0007] To improve the environmental stability, flexibility, and wide-angle absorption performance of absorbing materials in the millimeter-wave band, this invention provides an absorbing material that can be used in millimeter-wave radar, its preparation method, and its application.

[0008] According to one aspect of the present invention, a microwave absorbing material for use in millimeter-wave radar is provided. The raw materials for preparing the microwave absorbing material include a liquid resin and a dielectric material, wherein the amount of the dielectric material is 2% to 3.5% of the mass of the liquid resin; wherein the viscosity of the liquid resin is 3000 mPa·s to 10000 mPa·s, and the Shore A hardness of the liquid resin is 20 HA to 30 HA; the specific surface area of ​​the dielectric material is 500 m² / s. 2 / g~1000 m 2 The dielectric material has a DBP absorption value of 300 mL / 100g to 500 mL / 100g and a particle size ≤100nm. This invention combines a liquid resin with specific properties and a dielectric material with a special structure to simultaneously achieve excellent microwave absorption performance, environmental stability, mechanical flexibility, and wide-angle absorption capability. On one hand, the high specific surface area and well-developed porosity of the dielectric material increase the interface for electromagnetic wave interaction, promoting efficient interfacial polarization and multiple scattering mechanisms, thereby enhancing the wide-angle absorption performance of the microwave absorbing material. On the other hand, by optimizing the liquid resin, this invention endows the microwave absorbing material with excellent flexibility and bendability, while also enabling it to exhibit good morphological and dielectric stability over a wide temperature range. This effectively suppresses dielectric drift and absorption frequency shift caused by changes in high temperature or humidity, ensuring the reliability of the radar under complex operating conditions. Therefore, by simultaneously optimizing liquid resin and dielectric materials, this invention can achieve excellent absorption performance in millimeter-wave radar with a simple structure, and can also cope with complex working conditions such as multi-angle incoming waves and wide temperature range applications.

[0009] Preferably, the real part of the dielectric constant of the absorbing material is ε', and the real part of the magnetic permeability of the absorbing material is μ'. Specifically, in the range of 75 GHz to 81 GHz, the absorbing material satisfies the following relationship: The inventors discovered that the core challenge in impedance matching under millimeter-wave radar lies in the coordinated control of dielectric constant and permeability. An excessively high dielectric constant hinders electromagnetic waves from penetrating the material, while an excessively low dielectric constant weakens its loss mechanism, making effective absorption difficult within a limited thickness. This invention, by controlling the real parts of the dielectric constant and permeability of the absorbing material in the 75GHz~81GHz range, can improve the magnetic loss capability of the absorbing material at a relatively thin thickness, thus achieving excellent absorption performance.

[0010] Preferably, in the range of 75 GHz to 81 GHz, ε' is 4 to 8.5.

[0011] Preferably, μ' is 1 to 1.5 in the range of 75 GHz to 81 GHz.

[0012] Preferably, the liquid resin includes at least one of liquid silicone rubber, liquid epoxy resin, liquid polyurethane resin, and liquid acrylic resin.

[0013] Preferably, the liquid resin includes a first liquid resin and a second liquid resin, wherein the first liquid resin includes liquid silicone rubber, and the second liquid resin includes at least one of liquid epoxy resin, liquid polyurethane resin, and liquid acrylic resin; the mass ratio of the first liquid resin to the second liquid resin is 6~8:2~4.

[0014] Preferably, the content of liquid resin in the raw materials for preparing the microwave absorbing material is 85% to 93%.

[0015] Preferably, the solid content of the liquid resin is 30% to 60%.

[0016] Preferably, the dielectric material includes at least one of conductive carbon black, graphene, and carbon nanotubes.

[0017] Preferably, the dielectric material has a pH > 7.

[0018] Preferably, the purity of the dielectric material is ≥95%.

[0019] Preferably, the thickness of the absorbing material is 1.15 mm to 2.40 mm.

[0020] A second aspect of the present invention provides a method for preparing the microwave absorbing material as described above, the method comprising the following steps: S1. preparing a first slurry, the first slurry comprising a liquid resin and a dielectric material, and then grinding the first slurry to make the fineness of the first slurry ≤15μm; wherein the viscosity of the liquid resin is 3000 mPa·s ~10000 mPa·s; S2. adding a crosslinking agent and a catalyst to the first slurry and mixing to obtain a second slurry; S3. drying the second slurry at 120℃~140℃ to obtain the microwave absorbing material.

[0021] In the preparation method provided by this invention, the liquid resin is predominantly low-branched and linear in structure, and its viscosity is within the range of 3000 mPa·s to 10000 mPa·s, giving it advantages such as short curing time and low temperature. Therefore, liquid resin at a specific viscosity helps to suppress problems such as particle size increase, uneven coating, and agglomeration in the dielectric material during preparation, thus laying the foundation for uniform dispersion of the dielectric material and improving the microwave absorption stability of the absorbing material. Furthermore, by controlling the fineness of the first slurry and the drying temperature in the preparation method, this invention can not only improve production efficiency but also increase product yield.

[0022] Preferably, the amount of crosslinking agent is 6% to 8% of the mass of the liquid resin; and / or, the amount of catalyst is 1% to 2% of the mass of the liquid resin.

[0023] Preferably, the crosslinking agent includes at least one selected from hydrogen-containing silicone oil, tetraethyl orthosilicate, toluene diisocyanate, diphenylmethane diisocyanate, silane coupling agent KH550, and silane coupling agent KH560.

[0024] Preferably, the catalyst includes at least one of platinum-based catalysts, titanium-based catalysts, tin-based catalysts, bismuth-based catalysts, and zinc-based catalysts.

[0025] Preferably, the platinum-based catalyst includes a platinum complex.

[0026] Preferably, the titanium catalyst includes tetrabutyl titanate.

[0027] Preferably, the tin-based catalyst includes dibutyltin dilaurate.

[0028] Alternatively, the grinding process can be carried out using a calender or open mill, wherein the calender can be a two-roll, three-roll, or five-roll mill.

[0029] Preferably, the grinding process involves grinding ≥3 times.

[0030] Optionally, the fineness of the first slurry is confirmed by scraping it onto a fineness plate.

[0031] Preferably, the second slurry is degassed under vacuum before being dried.

[0032] Preferably, the second slurry is leveled before drying.

[0033] Alternatively, the second slurry can be leveled by casting, scraping, or transfer.

[0034] A third aspect of the present invention provides the application of the above-described absorbing material, or the absorbing material prepared by the above-described method, in millimeter-wave radar.

[0035] A fourth aspect of the invention provides the application of the above-described absorbing material, or the absorbing material prepared by the above method, in automotive millimeter-wave radar. The core operating frequency band of the automotive millimeter-wave radar is 76-81 GHz.

[0036] The absorbing material provided by this invention can be used in advanced driver assistance systems (ADAS) and autonomous driving, such as adaptive cruise control (ACC), short-to-medium range radar, automatic emergency braking (AEB), and intersection assist, in the 76GHz to 81GHz frequency band of millimeter-wave radar. It primarily provides high-precision obstacle detection and environmental perception. The absorbing material provided by this invention features thinness, bandwidth, and peak intensity at high frequencies, and it can solve the problems of environmental stability and angle dependence in practical applications. Attached Figure Description

[0037] Figure 1 This is a reflectivity test diagram of the absorbing material provided in Embodiment 1 of the present invention;

[0038] Figure 2 The image shows the radar echo intensity of the absorbing material provided in Embodiment 1 of the present invention at 76~81GHz.

[0039] Figure 3 This is a photograph of the absorbing material provided in Embodiment 1 of the present invention after bending.

[0040] Figure 4 This is an illustration of the particles appearing in the microwave absorbing material provided in Comparative Example 14 of the present invention;

[0041] Figure 5 This is a partial illustration of the microwave absorbing material provided in Comparative Example 14 of the present invention, showing the presence of air bubbles. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0043] Example 1

[0044] (1) Preparation of raw materials for absorbing materials

[0045] In this embodiment, the raw materials for preparing the microwave absorbing material were weighed according to the following formula (calculated by mass parts): 100 parts liquid silicone rubber (Dow 2881-30, viscosity 5000 mPa·s, Shore A hardness 25 HA), 2.2 parts conductive carbon black (specific surface area 1000 m² / s). 2The composition includes: 7 parts of crosslinking agent (containing hydrosilicone oil), 1.5 parts of catalyst (Karstedt catalyst 2000), 0.8 parts of wetting agent, and 0.8 parts of defoamer. The amounts of dielectric material, crosslinking agent, and catalyst are 2.2%, 7%, and 1.5% of the liquid resin, respectively.

[0046] (2) Preparation of microwave absorbing materials

[0047] In this embodiment, the microwave absorbing material is prepared according to the following method:

[0048] S1. According to the above formula, weigh out the liquid resin and dielectric material and mix them to obtain the first slurry. Then, grind the first slurry. The grinding process involves grinding the liquid resin and dielectric material three times on a two-roll calender to make the fineness of the first slurry ≤10μm.

[0049] S2. The crosslinking agent, catalyst, wetting agent, and defoamer in the above-mentioned formulation are added to the first slurry and mixed and dispersed to obtain the second slurry;

[0050] S3. The second slurry is leveled by casting and then dried at 130°C to obtain a microwave absorbing material with a thickness of 2.2 mm.

[0051] Example 2

[0052] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that the liquid resin used in this embodiment is a mixture of 60 parts of liquid silicone rubber (Dow 2881-30) and 40 parts of liquid acrylic resin (Mitsubishi Chemical BR-80). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0053] Example 3

[0054] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that the liquid resin used in this embodiment is a mixture of 40 parts of liquid silicone rubber (Dow 2881-30) and 60 parts of liquid acrylic resin (Mitsubishi Chemical BR-80). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0055] Example 4

[0056] This embodiment prepares the microwave absorbing material according to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that the conductive carbon black used in this embodiment has a specific surface area of ​​550 m². 2 / g, DBP absorbance is 310mL / 100g. Except for the differences mentioned above, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0057] Example 5

[0058] This embodiment prepares the microwave absorbing material according to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that the conductive carbon black used in this embodiment has a specific surface area of ​​980 m². 2 / g, DBP absorbance is 490mL / 100g. Apart from the differences mentioned above, the preparation steps for the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0059] Example 6

[0060] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that the conductive carbon black used in this embodiment has a particle size of 40 nm. Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0061] Example 7

[0062] This embodiment prepares the microwave absorbing material according to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that, in this embodiment, the mass fraction of conductive carbon black used in the preparation of the microwave absorbing material is 2 parts (the amount of dielectric material is 2% of the mass of liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Embodiment 1.

[0063] Example 8

[0064] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that the conductive carbon black used in this embodiment is 3.5 parts by mass (the amount of dielectric material is 3.5% of the mass of the liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0065] Example 9

[0066] This embodiment prepares the microwave absorbing material according to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that, in this embodiment, graphene is used in place of conductive carbon black in equal parts by mass during the preparation of the microwave absorbing material. The specific surface area of ​​the graphene is 900 m². 2 The absorber has a DBP absorption value of 475 mL / 100 g and a particle size of 500 nm. Apart from the differences mentioned above, the preparation steps for the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0067] Example 10

[0068] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, the crosslinking agent used in the preparation of the microwave absorbing material is 6 parts by mass (the amount of crosslinking agent is 6% of the mass of the liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0069] Example 11

[0070] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, the mass fraction of the crosslinking agent used in the preparation of the microwave absorbing material is 8 parts (the amount of crosslinking agent is 8% of the mass of the liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0071] Example 12

[0072] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, the mass fraction of the catalyst used in the preparation of the microwave absorbing material is 1 part (the amount of catalyst is 1% of the mass of the liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0073] Example 13

[0074] This embodiment prepares the microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, the mass fraction of the catalyst used in the preparation of the microwave absorbing material is 2 parts (the amount of catalyst is 2% of the mass of the liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Example 1.

[0075] Example 14

[0076] This embodiment prepares the microwave absorbing material according to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that in this embodiment, during the preparation of the microwave absorbing material, in step S1, the grinding process involves grinding the liquid resin and dielectric material twice on a two-roll calender to make the fineness of the first slurry ≤15μm. Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Embodiment 1.

[0077] Example 15

[0078] This embodiment prepares the microwave absorbing material according to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that, in step S3, the microwave absorbing material is dried at 120°C. Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Embodiment 1.

[0079] Example 16

[0080] This embodiment prepares the microwave absorbing material according to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that, in step S3, the microwave absorbing material is dried at 140°C. Apart from the above differences, the operation steps for preparing the microwave absorbing material in this embodiment are strictly consistent with those in Embodiment 1.

[0081] Comparative Example 1

[0082] This comparative example prepares microwave absorbing material according to the formulation and method provided in Example 1. The difference from Example 1 is that the liquid resin used in this comparative example is 100 parts of liquid silicone rubber (viscosity 2000 mPa·s, Shore A hardness 15 HA). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0083] Comparative Example 2

[0084] This comparative example prepares microwave absorbing material according to the formulation and method provided in Example 1. The difference from Example 1 is that the liquid resin used in this comparative example is 100 parts of liquid silicone rubber (viscosity 30000 mPa·s, Shore A hardness 40 HA). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0085] Comparative Example 3

[0086] This comparative example prepares the microwave absorbing material according to the formulation and method provided in Example 1. The difference from Example 1 is that, in preparing the microwave absorbing material in this comparative example, 100 parts of solid resin (Lubrizol DIPP119) are mixed with 125 parts of solvent (cyclohexanone) and then mixed with 22 parts of dielectric material as the first slurry. Apart from the above differences, the operating steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0087] Comparative Example 4

[0088] This comparative example prepares microwave absorbing materials according to the formulation and method provided in Example 1. The difference from Example 1 is that the conductive carbon black used in this comparative example has a specific surface area of ​​300 m². 2 / g, DBP absorbance value is 200mL / 100g. Except for the differences mentioned above, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0089] Comparative Example 5

[0090] This comparative example prepares microwave absorbing materials according to the formulation and method provided in Example 1. The difference from Example 1 is that the conductive carbon black used in this comparative example has a specific surface area of ​​1200 m². 2 / g, DBP absorbance is 580mL / 100g. Except for the differences mentioned above, the operating procedures for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0091] Comparative Example 6

[0092] This comparative example prepares microwave absorbing material according to the formulation and method provided in Example 1. The difference from Example 1 is that the conductive carbon black used in this comparative example has a particle size of 150 nm. Apart from the above differences, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0093] Comparative Example 7

[0094] This comparative example prepares microwave absorbing material according to the formulation and method provided in Example 1. The difference from Example 1 is that the conductive carbon black used in this comparative example is 1.5 parts by mass (the amount of dielectric material is 1.5% of the mass of liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0095] Comparative Example 8

[0096] This comparative example prepares microwave absorbing material according to the formulation and method provided in Example 1. The difference from Example 1 is that the conductive carbon black used in this comparative example is 4.5 parts by mass (the amount of dielectric material is 4.5% of the mass of liquid resin). Apart from the above differences, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0097] Comparative Example 9

[0098] This comparative example prepares microwave absorbing material according to the formula and method provided in Example 1. The difference from Example 1 is that no dielectric material is added during the preparation of the microwave absorbing material in this comparative example. Furthermore, 22 parts of ferrite (Dongci 3C90) are added to prepare the first slurry. Apart from the above differences, the operating steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0099] Comparative Example 10

[0100] This comparative example prepares microwave absorbing material according to the formulation and method provided in Example 1. The difference from Example 1 is that in step S1, the grinding process in this comparative example involves grinding the liquid resin and dielectric material once on a two-roll calender to achieve a fineness of 15 μm < fineness ≤ 25 μm in the first slurry. Apart from the above differences, the operational steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0101] Comparative Example 11

[0102] This comparative example prepares the microwave absorbing material according to the formulation and method provided in Example 1. The difference between this comparative example and Example 1 is that, in step S3, the microwave absorbing material in this comparative example is dried at 100°C. Apart from the above differences, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0103] Comparative Example 12

[0104] This comparative example prepares the microwave absorbing material according to the formulation and method provided in Example 1. The difference between this comparative example and Example 1 is that, in step S3, the microwave absorbing material in this comparative example is dried at 160°C. Apart from the above differences, the operation steps for preparing the microwave absorbing material in this comparative example are strictly consistent with those in Example 1.

[0105] Test case

[0106] 1. Test Object

[0107] The microwave absorbing materials prepared in Examples 1-16 and Comparative Examples 1-12.

[0108] 2. Testing Methods

[0109] (1) Shore hardness A: Press the instrument vertically onto the 6mm thick sample and read the instantaneous value.

[0110] (2) Tensile strength: In this test, the test object is cut into a 5cm*20cm sample and then tested by a tensile testing machine. When the tensile strength of the test object is ≥5MPa, it is indicated as "pass".

[0111] (3) Environmental stability: The test sample is placed in an oven at -40℃ and 120℃ for 168 hours. After the test, observe whether the shape and size of the test sample have changed, whether the thickness has increased or decreased, and whether there are cracks or bubbles on the surface. If the test sample does not have any of the above changes, it is indicated as "pass".

[0112] (4) Angle dependence: The product is tested using the arch bridge method by changing the angle of the transmitting signal horn. When the absorption peak change is <10dB in the range of 0°~60°, it is indicated as "pass".

[0113] (5) Appearance: Under natural light or 60W~100W fluorescent lamp illumination, with the naked eye within a distance of 30cm~45cm from the object being tested, the sample is rotated vertically and horizontally, and the entire detection surface is scanned for 5~10 seconds. If the surface of the absorbing material is smooth, flat and free of bubbles, it is indicated as "pass".

[0114] (6) Real part of dielectric constant and real part of permeability: The sample was made into a 3mm*7mm coaxial ring and tested by an Agilent E8363B vector network analyzer.

[0115] 3. Test Results and Analysis

[0116] The test data for this test example are shown in Table 1. In this test example, Shore hardness was used to characterize the material's bendability, verifying that the microwave absorbing material provided by this invention has good processing performance and can be used for processing curved surfaces (generally, microwave absorbing materials with a Shore hardness in the range of 20HA~40HA can be used for curved surfaces greater than 90°). The data in Table 1 demonstrates that the microwave absorbing material provided by this invention achieves excellent microwave absorption performance, environmental stability, wide-angle absorption capability, and good processability in the millimeter-wave frequency band.

[0117] The first aspect is the combination Figure 1 The provided test data shows that the absorbing material provided in Example 1 can achieve good wave absorption performance under millimeter waves; and Figure 2 The provided radar echo intensity map test also verifies that the absorbing material provided in Example 1 exhibits good absorption performance in actual application scenarios, with an average reflection performance of -20dB. Figure 1 The test data matches. Furthermore, combined with... Figure 3This demonstrates that the microwave absorbing material provided in Example 1 did not exhibit surface cracks after being bent at 180°. Based on the data from Examples 1-3 and Comparative Examples 1-3 in Table 1, the selection of the liquid resin used to prepare the microwave absorbing material in this invention is crucial. Specifically, combining the data from Comparative Examples 1-2, it can be seen that this invention, by controlling the viscosity and hardness of the liquid resin, synergistically improves the microwave absorbing material's good and stable appearance and dielectric properties within a wide temperature range of -40℃ to 120℃, thereby ensuring the possibility of applying the microwave absorbing material under complex working conditions. In Comparative Example 2, the high hardness of the liquid resin easily leads to a decrease in the bending performance of the microwave absorbing material. The data from Comparative Example 3 shows that, compared to liquid resin, solid resin, due to its large molecular weight and high branching degree, is difficult to obtain a first slurry with a fineness ≤15μm through simple processes. When the slurry fineness is insufficient, it easily leads to the agglomeration of the dielectric material, resulting in uneven coating and unstable microwave absorption performance. Furthermore, by optimizing the formulation of liquid resins, this invention can further improve the flexibility and bendability of microwave absorbing materials, making them less prone to cracking or falling off when attached to various curved surfaces.

[0118] Secondly, as demonstrated by Examples 4-9 and Comparative Examples 4-10, the special structural and content design of the introduced dielectric material not only affects the frequency of highest reflectivity of the absorbing material but also its angle dependence. The inventors discovered a correlation between the specific surface area and DBP absorption value of the dielectric material. Within a suitable range of specific surface area and DBP absorption value, it can, on the one hand, enhance the promotion of multiple scattering mechanisms, thereby significantly improving absorption performance when the incident angle deviates from the normal by 30° or even larger, meeting the absorption requirements of automotive radar for multi-angle incoming waves in actual operation; on the other hand, it can affect the grinding effect during the preparation process, thus affecting the product's appearance. Furthermore, by comparing the data with Comparative Example 9, it can be proven that compared to traditional absorbing materials, the absorbing material provided by this invention can simultaneously meet the dual requirements of "thin layer" and "wideband".

[0119] Thirdly, as can be seen from the data in Examples 10-13, the amount of crosslinking agent and catalyst used in the preparation of microwave absorbing materials will affect the curing effect and hardness of the product, thereby affecting production and application.

[0120] Fourthly, as can be seen from the data of Examples 14-16 and Comparative Examples 10-12, the particle size and drying temperature of the first slurry both affect the performance and application of the microwave absorbing material during the preparation process. In Comparative Example 12, due to the high drying temperature, severe gas volatilization occurred during the preparation process, resulting in bubbles on the surface of the microwave absorbing material, making it impossible to conduct relevant tests.

[0121] Fifthly, as shown in Table 2, the ε' / μ' of the absorbing material provided by this invention is consistently within the range of 4 to 5.5 at 75 GHz. Meanwhile, combining the data from Examples 1, 7, and 8 in Table 1, and Comparative Example 8, it can be seen that although the reflectivity increases with the increase of dielectric material content, a mismatch between the dielectric constant and permeability occurs at higher dielectric material contents, causing ε' / μ' to deviate outside the 4-5.5 range. This results in a decrease in the reflectivity of the absorbing material provided in Comparative Example 8. Therefore, the above data comparison demonstrates that this invention can control the ratio between the real part of the dielectric constant and the real part of the permeability of the absorbing material by adjusting the amount of dielectric material used, specific surface area, DBP value, and particle size, thereby regulating the interaction between the dielectric constant and permeability and further optimizing the reflectivity of the absorbing material.

[0122] In summary, this invention has successfully prepared a microwave absorbing material with excellent millimeter-wave absorption performance, wide temperature range stability, good processability, and outstanding wide-angle absorption capability by systematically designing and synergistically combining a liquid resin matrix with special dielectric materials.

[0123] Table 1. Test Results

[0124]

[0125] Table 2. Correlation test results of the real part of dielectric constant and the real part of permeability

[0126]

[0127] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A radar-absorbing material that can be used in millimeter-wave radar, characterized in that, The raw materials for preparing the microwave absorbing material include liquid resin and dielectric material, and the amount of dielectric material used is 2% to 3.5% of the mass of the liquid resin; The Shore A hardness of the liquid resin is 20 HA to 30 HA. The viscosity of the liquid resin is 3000 mPa·s to 10000 mPa·s; The dielectric material includes conductive carbon black; The liquid resin includes liquid silicone rubber; The dielectric material has a specific surface area of ​​500 m². 2 / g~1000 m 2 / g, the DBP absorption value of the dielectric material is 300mL / 100g~500mL / 100g, and the particle size of the dielectric material is ≤100nm; The method for preparing the microwave absorbing material includes the following steps: S1. Prepare a first slurry, the first slurry comprising the liquid resin and the dielectric material, and then grind the first slurry to make the fineness of the first slurry ≤15μm; S2. Add a crosslinking agent and a catalyst to the first slurry, and mix to obtain a second slurry; S3. The second slurry is dried at 120℃~140℃ to obtain the microwave absorbing material.

2. The microwave absorbing material as described in claim 1, characterized in that, The real part of the dielectric constant of the absorbing material is ε', and the real part of the magnetic permeability of the absorbing material is μ'. Furthermore, in the range of 75 GHz to 81 GHz, the absorbing material satisfies the following relationship: .

3. The microwave absorbing material as described in claim 1, characterized in that, The liquid resin further includes at least one of liquid epoxy resin, liquid polyurethane resin, and liquid acrylic resin.

4. The microwave absorbing material as described in claim 1, characterized in that, The liquid resin includes a first liquid resin and a second liquid resin, wherein the first liquid resin includes liquid silicone rubber, and the second liquid resin includes at least one of liquid epoxy resin, liquid polyurethane resin, and liquid acrylic resin; the mass ratio of the first liquid resin to the second liquid resin is 6~8:2~4.

5. The microwave absorbing material as described in claim 1, characterized in that, The dielectric material also includes at least one of graphene and carbon nanotubes.

6. The microwave absorbing material according to any one of claims 1 to 5, characterized in that, The thickness of the absorbing material is 1.15 mm to 2.40 mm.

7. The microwave absorbing material as described in claim 1, characterized in that, The amount of the crosslinking agent is 6% to 8% of the mass of the liquid resin; the amount of the catalyst is 1% to 2% of the mass of the liquid resin.

8. The application of the absorbing material as described in any one of claims 1 to 7 in millimeter-wave radar.

9. The application of the absorbing material as described in any one of claims 1 to 7 in automotive millimeter-wave radar.

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