Microwave Absorbing Properties of Carbonyl Iron Particle Composites with Frequency Selective Surface

With the increased use of diverse electronics in the high frequency spectrum, high-performance absorbing and shielding materials are needed to ensure electromagnetic compatibility. Microwave absorbance of polymer composites of carbonyl iron powders with frequency selective surface (FSS) is investigated, focusing on the frequency of 5.8 GHz. Composite sheets were prepared by hot pressing a mixture of carbonyl iron powders and silicone rubber. FSS with a square-loop geometry and surface resistance close to the optimum value was fabricated by a screen printing method using carbon black paste as conductive ink. The microwave absorbance for both normal and oblique incidence angles was determined using the commercial computational tool (ANSYS-HFSS). The particulate composites show a reflection loss of -21 dB at 5.8 GHz, with a small thickness of 2.5 mm. Further enhancement of microwave absorbance (less than -40 dB reflection loss) can be realized by attaching a resistive square-loop FSS on the grounded magnetic composite, which is attributed to the enhanced impedance matching driven by the additional resistive component of the attached FSS. The experimental results, obtained with a test sample of optimized composite structure with FSS, are in good agreement with the simulation results. In addition, it was found that the angular stability of the carbonyl iron absorber improved by attachment of FSS, particularly for TM polarization.