Radar-absorbing coating based on a graphene-polymer composite

Abstract

Radar-absorbing coating comprising a polymer matrix and a carbon filler, characterized in that the filler is a highly concentrated dispersion of graphene a few layers thick, partially intercalated with protons, wherein the coating has a thickness of 1.5-2.0 mm and a damping factor of at least -10 dB in the frequency range of 3-50 GHz and / or at least -35 dB at the resonance frequency in the range of 20-40 GHz.

Description

[0001] The invention relates to the field of radar-absorbing materials (RAM), in particular thin polymeric composite coatings, and can be used to reduce the radar signature of objects (technology, buildings) as well as to ensure the electromagnetic compatibility (EMC) of radio electronics.

[0002] A radar-absorbing coating based on a graphene-polymer composite with a thickness of 1.5–2.0 mm was developed. The coating is available in two variants: narrowband with resonant absorption down to -65 dB at approximately 29 GHz and broadband with absorption from -25 dB to -70 dB in the 3–50 GHz range. The coating exhibits unique operational properties: it maintains its characteristics in the temperature range of -60°C to +120°C and is resistant to moisture, acids, and alkalis. The technical result is the creation of an ultrathin, universal, and environmentally resistant radar-absorbing coating. State of the art:

[0003] Radar-absorbing materials based on carbon fillers (carbon black, carbon nanotubes, graphite) in a polymer matrix (epoxy resins, polyurethanes) are known. The main disadvantages of such analogues are: 1. Large thickness (3-10 mm and more) required to achieve significant absorption. 2. Narrow absorption bandwidth in resonant materials or insufficient effectiveness in broadband materials. 3. Poor operating characteristics: Insufficient resistance to temperature fluctuations, exposure to moisture, and aggressive media.

[0004] The closest prior art (prototype) is a radar-absorbing material based on a composition of polyurethane and multi-walled carbon nanotubes, described in patent US 2019 / 0011519 A1. Disadvantages of this solution include the need for a greater thickness (approximately 3-4 mm) to achieve comparable absorption efficiencies, as well as the lack of data on resistance to aggressive chemical media, which limits its use under harsh operating conditions. Disclosure of the nature of the invention:

[0005] The object of the invention is to eliminate the aforementioned disadvantages and to create an ultra-thin, robust, durable radar-absorbing coating with high performance characteristics and an extended range of operating properties.

[0006] The technical effect is to ensure a record-thin coating with high absorption efficiency and its resistance to extreme thermal, moisture and chemical influences. Nature of the invention:

[0007] The problem is solved by providing a radar-absorbing coating consisting of a layer of a cured polymer composition containing a highly concentrated graphene dispersion as an absorbing filler, with a coating thickness of 1.5 to 2.0 mm and possessing the following properties: • A damping factor of at least -10 dB in the frequency range of 3 to 50 GHz for the broadband version; • A damping factor of at least -35 dB at the resonant frequency in the range of 20-40 GHz for the narrowband version; • Retention of their electrophysical properties in the temperature range from -60°C to +120°C; • Resistance to long-term exposure to moisture, including salt water, as well as to oils, acids and alkalis.

[0008] A synergistic effect is achieved through the use of a highly concentrated and stable graphene dispersion with a graphene content of 7.5–12 wt%, which forms an optimally developed conductive network within the polymer matrix, ensuring high dielectric losses at low layer thickness. The polymer matrix is ​​preferably based on a water-soluble polymer. The graphene dispersion is a few layers thick in which the graphene is partially intercalated with protons. Brief description of the drawings: • Fig. Figure 1 shows a schematic representation of the layer structure of the described radar-absorbing coating applied to a substrate, where 2 is the substrate, 1 is the coating. • Fig. Figure 2 shows the frequency dependence of the imaginary part of the dielectric permittivity (ε'') for the described coating in narrowband version (resonance at ~29 GHz). • Fig. Figure 3 shows the frequency dependence of the transmission coefficient (S21) for the described coating in narrowband version (absorption depth down to -65 dB at ~29 GHz). • Fig. Figure 4 shows the frequency dependence of the real part of the dielectric permittivity (ε') for the described coating in broadband version. • Fig. Figure 5 shows the frequency dependence of the transmission coefficient (S21) for the described coating in broadband version (absorption from -25 dB to -70 dB in the range 3-50 GHz). Exemplary embodiment of the invention:

[0009] The coating is produced by dispersing a few layers of graphene, partially intercalated with protons, in a water-soluble polymer binder up to a concentration of 10 wt%, followed by application to a metal substrate ( Fig. 1) and curing. The thickness of the control sample was 1.6 mm.

[0010] Tests confirmed the conformity with the specified properties: • For the narrowband version: Presence of a resonant peak in dielectric losses at a frequency of ~29 GHz ( Fig. 2) and an absorption depth of up to -65 dB ( Fig. 3). • For the broadband version: Stable high values ​​of dielectric permittivity ( Fig. 4) and absorption in the range of -25...-70 dB at frequencies of 3-50 GHz ( Fig. 5). • The coating retained its properties after thermal (-60...+120°C) and chemical (acids, alkalis, oils) stresses. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2019 / 0011519 A1

[0004]

Claims

[1] Radar-absorbing coating containing a polymer matrix and a carbon filler, characterized by , that a highly concentrated dispersion of graphene, a few layers thick and partially intercalated with protons, is used as filler, the coating having a thickness of 1.5-2.0 mm and a damping factor of at least -10 dB in the frequency range of 3-50 GHz and / or at least -35 dB at the resonance frequency in the range of 20-40 GHz. [2] Coating according to claim 1, characterized by that the polymer matrix is ​​based on a water-soluble polymer. [3] Coating according to claim 1 or 2, characterized by that it maintains the damping factor within the specified limits after exposure to temperatures ranging from -60°C to +120°C. [4] Coating according to one of claims 1-3, characterized bythat it is resistant to the effects of moisture, including salt water, oils, acids and alkalis. [5] Coating according to any one of claims 1-4, characterized by that it is applied to a substrate.

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