A Band Enhanced Tunable Ultra-Broadband Absorber Based on Loading the Lumped Resistors and Cavity Resonance

In this paper, we present and demonstrate a band enhanced tunable ultra-broadband absorber (TUA) based on loading the lump resistors (LRs) and cavity resonance. The absorber’s each cell integrates four split ring-shaped solid state plasma resonators (SSPRs) which are connected by the solid state plasma (SSP) bars separately. The four split ring-shaped SSPRs and external truncated SSP bars are loaded with lump elements, respectively. The entire structure also comprises the dielectric substrate and continuous metallic layer. By simulations, the ultra-broadband absorption goes beyond 90% in the frequency region 11.13–19.81 GHz is realized through loading LRs and cavity resonance. Moreover, the absorber also is polarization-independent for the incident electromagnetic wave. It is remarkable that the absorption bandwidth is further promoted by inserting the air cylinders (ACs). The absorption also is investigated for oblique incidence, which shows that the proposed TUA can work over a wide incident angle. We focus on the distribution of surface current, the electric field, and power loss density to elucidate the physical mechanism. In addition, the tunable spectra can be obtained in such TUA by exciting the different SSPRs.