The great technological advancement in wireless communication systems and devices generated the problem of electromagnetic pollution. Developing lightweight, sustainable, and low-cost materials is necessary to minimize electromagnetic pollution. A sustainable porous carbon (PC) absorber material was obtained from the crude black liquor by a simple and low-cost synthesis, and combined with carbon nanotube (CNT), presenting excellent microwave attenuation results. The PC absorber at 20 wt.% filling ratio exhibited an intense reflection loss of ‑35.7 dB at 15.5 GHz, and bandwidth of 1.15 GHz for a thickness of 5.90 mm. By adding 0.2 wt.% of CNT, the reflection loss was -34.6 dB at 17.9 GHz, and a bandwidth of 1.54 GHz for 4.90 mm. The study reveals that the combination of PC and CNT improves the attenuation capacity, allows adjustment in the frequency range of the attenuation peak, and promotes thickness reduction. The results obtained allow us to advance studies in developing high-performance, sustainable, and low-cost microwave-absorbing materials.

Abstract Carbonaceous porous materials are strong candidates for producing low-cost, lightweight, and sustainable electromagnetic (EM) absorbing materials. This work investigates the production of radar-absorbing materials (RAM) by a simple method. Sustainable carbon xerogel (CX) was synthesized from tannin, a biosourced molecule. CX and commercial carbon nanotube (CNT) were embedded in a silicone matrix at proportions of 10 and 15 wt.% of CX and 0.1 wt.% of CNT to produce flexible composites. The morphology and structure of the carbonaceous materials were evaluated by field-emission scanning electron microscopy (FEG-SEM), Raman spectroscopy, X-ray diffraction (XRD), textural properties by N2 adsorption-desorption isotherms, and mercury porosimetry. The electromagnetic characterization of the composites was analyzed by a vector network analyzer (VNA) in the Ku-band. The results demonstrated that an increased concentration of CX in the composite improved reflection loss reaching -43.19 dB at 13.79 GHz.

ABSTRACT Radar absorbing materials (RAMs) are composites made with a polymeric matrix and an electromagnetic absorbing filler, such as carbon black (CB), silicon carbide (SiC) or manganese zinc ferrite (MnZn). To enhance their performances to attenuate an incident wave through reflection loss (RL), RAMs can be produced in multilayer structures. Usually, the RL analysis is done theoretically and experimentally validated with free space analysis. Here, it was demonstrated that multilayer structure can be designed and easily validated using rectangular waveguide, using a simpler setup and small samples. Three composites were produced using 2 wt% of CB (CB2), 40 wt% of SiC (SiC40) and 60 wt% of MnZn (MnZn60). They were characterized over the Ku-band and used to validate the multilayer structures, that were prepared by simply stacking each material inside the waveguide sample holder. One of the best results was obtained with structure SiC40+CB2 with 5.85 mm thickness, that presented a calculated RL of -21 dB at 17.8 GHz and a measured RL of -36 dB at the same frequency. In conclusion, using rectangular waveguide has been proven to be an easy, cheap, precise and fast approach to validate multilayer structures designs.

RESUMO Este trabalho apresenta as propriedades eletromagnéticas de um Material Absorvedor de Radiação Eletromagnética (MARE) feito a partir de Carbeto de Silício (SiC) e Negro de Fumo (NF) como aditivos. O compósito SiC/NF foi produzido utilizando 70 %(m/m) de matriz de silicone, e variando as concentrações do aditivo em 3 %(m/m), 2 %(m/m) e 1 %(m/m) de NF com 27 %(m/m), 28 %(m/m) e 29 %(m/m) de SiC, respectivamente. A estrutura química e a morfologia das partículas de SiC e NF foram analisadas através de espectroscopia Raman e Microscopia Eletrônica de Varredura (MEV). As propriedades dielétricas dos MAREs foram obtidas por meio do analisador de rede vetorial na faixa de frequência de 12,4 a 18,0 GHz. Os resultados de refletividade mostraram que o compósito SiC/NF com 1 %(m/m) de NF apresentou a melhor absorção de radiação eletromagnética, chegando a -47,9 dB em 16,8 GHz com uma amostra de aproximadamente 5,5 mm de espessura.

ABSTRACT Este trabalho apresenta as propriedades eletromagnéticas de um Material Absorvedor de Radiação Eletromagnética (MARE) feito a partir de Carbeto de Silício (SiC) e Negro de Fumo (NF) como aditivos. O compósito SiC/NF foi produzido utilizando 70 %(m/m) de matriz de silicone, e variando as concentrações do aditivo em 3 %(m/m), 2 %(m/m) e 1 %(m/m) de NF com 27 %(m/m), 28 %(m/m) e 29 %(m/m) de SiC, respectivamente. A estrutura química e a morfologia das partículas de SiC e NF foram analisadas através de espectroscopia Raman e Microscopia Eletrônica de Varredura (MEV). As propriedades dielétricas dos MAREs foram obtidas por meio do analisador de rede vetorial na faixa de frequência de 12,4 a 18,0 GHz. Os resultados de refletividade mostraram que o compósito SiC/NF com 1 %(m/m) de NF apresentou a melhor absorção de radiação eletromagnética, chegando a -47,9 dB em 16,8 GHz com uma amostra de aproximadamente 5,5 mm de espessura.