Broadband Magnetic Absorber Based on Double-Layer Frequency-Selective Surface

A thin and broadband frequency-selective surface (FSS)-based magnetic absorber is presented for low-microwave frequency applications. The design consists of double layers of FSS with the combination of two different magnetic substrates, which provides a much broader bandwidth compared to existing single-layered designs. The magnetic materials are in-house made by mixing different ratios of carbonyl-iron powder with silicone elastomer polydimethylsiloxane (PDMS). The simple single-square loop (SSL) structure is used for both FSSs that are printed on a standard FR4 material using lossy resistive sheet. This configuration allows the use of a closed-form equivalent-circuit model for a fast and efficient bandwidth optimization. A genetic algorithm (GA) is utilized to obtain the design parameters for broadband absorption with minimum overall thickness. The measured results confirm that the proposed absorber operates from 0.78 to 4.8 GHz with −10 dB reflectivity. The design achieves 144% fractional bandwidth with a 10.12 bandwidth-to-thickness ratio.