Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate

An equivalent-circuit model is used to analyse the improvement of the wave absorbing performance of the lossy frequency selective surface (FSS) absorber by using a magnetic substrate, showing that it is possible to widen the wave absorbing bandwidth. Three pieces of magnetic substrates are prepared. According to the complex permittivity and permeability, the reflectivity of the corresponding absorber is calculated by the finite difference time-domain (FDTD) method, and the bandwidth of the reflectivity below -10 dB is optimized by genetic algorithm. The calculated results indicate that the wave absorbing performance is significantly improved by increasing the complex permeability of the substrate; the reflectivity bandwidth below -10 dB of the single layer FSS absorber can reach 3.6-18 GHz with a thickness of 5 mm, which is wider than that with a dielectric substrate. The density of the FSS absorber is only 0.92 g/cm(3). Additionally, the absorption band can be further widened by inserting a second lossy FSS. Finally, a double layer lossy FSS absorber with a magnetic substrate is fabricated based on the design result. The experimental result is consistent with the design one.