Radar stealth technology primarily involves the reduction of radar cross-section (RCS) in the frequency range of 3 MHz to 300 GHz, with the centimeter band (2–18 GHz) being a critical area for detection. This band is also a major focus for current research on ultra-wideband radar stealth technology. As radar detection capabilities and target shaping techniques become more advanced, traditional radar-absorbing materials are increasingly limited by their narrow bandwidth, low efficiency, and high density. Therefore, there is an urgent need to develop new wave-absorbing materials and corresponding stealth technologies that offer strong absorption, wide frequency coverage, light weight, and thin thickness.
Conductive polymer-based absorbing materials have emerged as a promising solution. By blending conductive fibers into conventional powder absorbers, the material's absorption performance can be significantly enhanced. However, the optimal blending ratio must be determined to achieve broadband absorption. Despite this, such materials often exhibit poor performance at lower frequencies, which remains a challenge for further research. Conductive polymers like polyaniline, polypyrrole, and poly(3-octylthiophene) have been widely studied due to their low density and good thermal stability. For instance, iodine-doped polyphenylacetylene has shown a reflection loss of -15 dB with an absorption bandwidth of up to 3 GHz. Similarly, polypyrrole-based materials have demonstrated over 8 dB absorption in the 3 cm band. Researchers like TruongVT et al. have developed 2.5 mm-thick materials with less than -10 dB reflectance between 12–18 GHz, while Kong Deming’s work with doped polyaniline showed an average attenuation of 13.37 dB in the 8–14 GHz range.
Magnetic particle-based materials, such as ferrites and metal micropowders, rely on magnetic losses including hysteresis, domain wall resonance, and interfacial polarization. Ferrites, particularly hexagonal magnetoplumbite types, exhibit excellent high-frequency absorption properties. MeshramMR et al. reported a maximum absorption of 16.5 dB within 8–12 GHz, while Zhang Yongjing’s 2 mm thick ferrite absorber achieved over 10 dB absorption in the 8–18 GHz range. Nano-ferrite particles, with their unique surface properties and smaller size, enhance absorption through mechanisms like hysteresis loss and multiple scattering. Ruan et al. found that 65 nm ferrite samples achieved a reflectance of -28.5 dB with a 5 GHz bandwidth below -10 dB. Smaller Fe₃O₄ particles were also shown to improve absorption efficiency across a wide frequency range.
Magnetic metal micropowders, such as carbonyl iron, are used in stealth aircraft like the F/A-18C/D "Hornet" due to their high magnetic permeability and thermal stability. Polycrystalline iron fibers, on the other hand, generate eddy currents and hysteresis losses when exposed to electromagnetic waves, converting energy into heat. 3M’s iron fiber coating can attenuate signals by up to 30 dB in the 5–16 GHz range. Combining conductive polymers with magnetic particles offers a dual mechanism of dielectric and magnetic loss, but challenges remain in optimizing material composition, structure, and fabrication processes to achieve lightweight, broadband, and high-performance absorbing materials. Further research should focus on understanding the interaction between macro and micro structures, selecting suitable materials, and refining preparation techniques.
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