Fabrication of CoFe/C@polypyrrole composites with efficient electromagnetic wave absorption properties

Abstract

Recently, increasingly severe electromagnetic radiation has caused harm to precision equipment and human health, which requires the development of effective electromagnetic wave (EMW) absorption materials. These materials require both a strong absorption and a broad bandwidth at low filling rates and small thicknesses. To meet this requirement we have constructed a cobalt-iron/carbon@polypyrrole (CoFe/C@PPy) composite by a two-step synthesis process. The first is the fabrication of magnetic CoFe/C fibers, followed by their coating with a PPy layer with a controlled thickness. This combination of materials results in a magnetic loss from CoFe/C and a dielectric loss from PPy which improves both impedance matching and EMW dissipation. An optimized material has a PPy layer with a thickness of 2.0 mm and a loading of 10% and has a minimum reflection loss (RLmin) of −45.6 dB at 14.64 GHz, and the corresponding effective absorption bandwidth is 5.12 GHz. Furthermore, CST Studio simulations and far-field radar cross-section (RCS) analysis validate its practical use, showing a notable RCS reduction of up to 37.5 dBm2 for a perfect electric conductor.

1. Introduction

With the advancement of wireless technology, the application of electromagnetic wave (EMW) technology has considerably expanded in the military and civilian sectors, remarkably enhancing the quality of human life[1–6]. However, this progress has caused severe EMW pollution, which has emerged alongside water, air, and soil pollution. Severe electromagnetic radiation disrupts the operation of precision equipment and poses health risks to humans[7–9]. The escalating severity of electromagnetic radiation urges the development of thin, light, broadband and strong wave-absorbing materials.

Based on material compositions, widely studied wave-absorbing materials primarily include ferrite-based materials (such as nickel–zinc ferrite[10] and high-entropy spinel ferrite[11]), carbon-based materials (including graphene[12], carbon nanotubes[13] and carbon nanofibers[14]), ceramic-based materials (for example, silicon carbide[15]), and polymer-based materials (for example, polypyrrole [PPy][16]). Among them, recently, carbon-based materials have gained widespread attention because of their low density, excellent corrosion resistance, high conductivity, wide availability, low cost and high chemical stability[17]. However, single-component carbon materials often exhibit poor impedance matching, limiting their applications. Magnetic metals such as iron (Fe)[18], cobalt (Co)[19] and nickel (Ni)[20], along with their alloys, exhibit excellent magnetic loss and high saturation magnetization (Ms). However, single-component magnetic materials often possess high density and poor stability. Therefore, incorporating magnetic components into carbon materials is an effective strategy for enhancing wave absorption performance. For instance, Guo et al. prepared a Ni@C/porous carbon composite that achieved a minimum reflection loss (RLmin) of −37.6 dB at a thickness of 1.9 mm and an effective absorption bandwidth (EAB) of 7.52 GHz at a thickness of 2.0 mm[21]. Similarly, Tang et al. synthesized a Co@C/C-20 composite through acetic acid etching and high-temperature pyrolysis, achieving an RLmin of −49.8 dB and an EAB of 5.0 GHz at only 11% (mass fraction) filling rate[22].

Conductive polymers, such as polyphenylene vinylene, polythiophene, polyaniline (PANI) and PPy, have recently garnered considerable attention in wave-absorbing materials. Compared with traditional inorganic materials, conductive polymers possess conjugated π-bond structures that facilitate the formation of extensive electron-transport networks.