Ultra-broad band plasma–graphene absorber at millimeter-wave frequency bands

Abstract

This paper introduces a new absorber that can effectively absorb millimeter wave frequencies. The design involves stacking foam, plasma, and laminated graphene sheets on a perfect electric conductor substrate. The absorber can generate a wideband effect on electromagnetic waves by combining graphene layers and a plasma medium. The absorption and bandwidth of the plasma slab depend on various parameters like plasma frequency, collisional rate, and thickness. By tuning the plasma frequency ωp (rad/s), average collision frequency υp(Hz), Fermi energy of graphene sheets, and thickness of the foam and plasma layers, the benefit of wideband and good absorption considering reflection amplitude lower than −15 dB, an ultra-bandwidth from 32 to 150 GHz can be achieved. This structure has multiple layers that have bandgap and band-stop regions. These regions are associated with the cavities of dielectric slabs that have graphene sheets. These regions are identified as coupled Fabry–Pérot resonances, which can induce multiple interference effects in multi-reflection for the incident electromagnetic waves, resulting in high-level absorption. Understanding and controlling these resonances is crucial for optimizing the performance of such systems. An equivalent circuit model has been used to predict the absorber's performance. The proposed absorber has a symmetrical structure that reacts similarly to transverse-electric and transverse-magnetic waves. The frequency range of the absorber has been studied to determine the effects of the graphene sheets' relaxation time and voltage biasing. The absorber offers advantages such as being thin, having a wide bandwidth, and being insensitive to polarization.