Electrically Tunable Microwave Absorber Based on Discrete Plasma-Shells

This paper presents the feasibility of deploying a large-scale tunable absorber based on discrete plasma-shells. The proposed conductor-backed absorber is realized by integrating ceramic gas-encapsulating chambers (plasma-shells) and a closely coupled lossy resonant layer that also serves as a biasing electrode to sustain the plasma. Two topologies comprising lossy inductive or capacitive layers are investigated to realize tunable microwave absorbers. The plasma is sustained by a sinusoidal radio frequency (RF) voltage source coupled directly through the walls of the plasma-shells. These active frequency-selective absorbers are analyzed using a transmission line approach to provide the working principle and its frequency tuning capability. By varying the voltage of the sustainer, the plasma can be modeled as a lossy, variable, frequency-dependent inductor, providing a dynamic tuning response of the absorption spectral band. A prototype plasma-tuned absorber is fabricated and measured in a free space environment to validate the concept. A good agreement between the equivalent circuit model, full-wave electromagnetic simulation, and the measurement results is obtained.