Miniaturized ultra-thin metamaterial absorber for low frequency using the technique of shifted opposite layers

Abstract

A technique of interdigital shifted opposite layers (SOLs) to design the miniaturized ultra-thin metamaterial absorber (MA) is proposed in this article. To meet the demanding requirements of small dimensions at low frequency, SOLs are first employed in MAs to achieve superior miniaturization. They consist of two identical layers printed on both sides of a thin substrate with relative lateral displacement. Compared with previously published MAs, the displacement substantially increases the equivalent capacitance of the unit cell, thus leading to a lower resonant frequency. To further miniaturize the unit cell, an ultra-thin MA using interdigital SOLs is optimized with a small cell size of 0.036λ0 × 0.036λ0 and a low profile of 0.0053λ0 (where λ0 corresponds to the free-space wavelength at a resonant frequency), exhibiting perfect absorption at 0.868 GHz. The equivalent circuit model shows that the dramatically increased equivalent capacitance and inductance down-shift the resonant frequency. Meanwhile, the current flow and field distribution are investigated to explain the absorption mechanism. Finally, to validate the design concept, the fabricated prototype of the proposed MA has been measured and compared with the simulation result. The measured and simulated results show good agreement.