Frequency-Tunable Absorber Using Liquid Crystal at 140 GHz

This letter presents a new class of frequency-tunable sub-terahertz absorbers using liquid crystal (LC) exemplified at 140 GHz. More than 90% absorption of incident EM wave is obtained around the frequency of 140 GHz. The 90% absorption frequency band can be electronically tuned between 137 and 147 GHz by varying the applied biasing voltage across the LC in the range of peak-to-peak voltage 0–30 V. The absorption frequency band is stable with respect to oblique incidence in TE mode for incident angle variation in the range of ± 40°. In TM mode, the leftward frequency shifting is observed for oblique incidence in the range of ± 80° while maintaining more than 90% absorption of the incident EM wave. This tunable absorber can be used to design a multifunctional reconfigurable intelligent surface with absorption and reflection reconfigurability for sub-terahertz wireless applications. This design features one of the widest tunable absorption bandwidths, and incident angle ranges to be reported in the literature.