In this manuscript, the electromagnetic wave absorption properties of sustainable porous carbon composites were evaluated over the X-band frequency range (8.2-12.4 GHz). The porous carbon material was made from the byproduct of cellulose production and was used as additive on the development of radar absorbing material (RAM) composites. These porous carbon materials have different characteristics, such as porosity size (180 m < Ø 1 < 250 m and 425 m < Ø 2 < 500 m) and particle size (ϕ 1 < 250 m and 250 m < ϕ 2 < 425 m). Composite materials were also studied as frequency selective surface (FSS) structures. It was shown how complex permittivity and reflection loss (RL) can be manipulated over the frequency range using FSS structure. While regular RAM presented RL of 19 dB at ~11.8 GHz, FSS structure presented a RL of 19 dB shifted to 12.4 GHz regarding the same carbon porous material (with particles between 250 and 425 µm and porosity between 180 and 250 µm). It was demonstrated here the potential use of sustainable porous carbon as RAM, and how FSS structure can be used to tune the frequency of the RL maximum peak.

This paper presents the influence of different sizes of carbonyl iron particles on the reflectivity measurements of Radar Absorbing Material (RAM). The electromagnetic characterization was performed with a vector network analyzer and a rectangular waveguide in the frequency range of 12.4 to 18GHz (Ku Band). The influence of different parameters such as thicknesses, particle sizes and concentration of carbonyl iron were evaluated. Reflectivity results showed the influence of these parameters on the performance of the RAM. The best reflectivity values (~-18 dB) were obtained for samples with 60 wt% concentration and 5 mm thickness. We provide information about significantly reflection loss improvement by simply controlling carbonyl iron particulate size. Index Termscarbonyl iron filler, Ku band, microwave absorber. I. INTRODUCTION Radar Absorbing Material (RAM) is a type of material designed to attenuate electromagnetic radiation on specific frequencies. Many researches have been made about RAM due its countless applications in electromagnetic compatibility and interference reduction. These materials can be applied on communication systems, modern electronic devices, anechoic chamber, military stealth technology, and so on [1]. RAMs can be produced in different forms, such as paints or thin films [2]. Usually, RAMs are composite materials made with polymer (matrix) and absorptive material (mean). In the literature, materials with dielectric and/or magnetic losses are commonly used as means. In this matter, materials like ferrite, carbonyl iron (CI), carbonaceous materials and conductive polymers has advantages over lossless materials [2],[3]. Despite their high specific mass, composites made with ferrites or CI have advantages like thin thickness and broadband frequency absorption because of iron on their compositions [4]. Carbonyl iron has a relatively low electrical conductivity, a high Curie temperature, and a high saturation magnetization. These properties make CI a good candidate to be used as absorption mean, especially in the frequency range between 2-18 GHz [5]. The effectiveness of the absorptive material contributes to the reflectivity losses that are determined