Wideband tunable absorber breaking the trade-off between absorption efficiency and tuning range

Tunable absorbers have attracted much attention due to their smart control of electromagnetic wave absorption. Despite much effort to enhance their performance, the absorption performance remains restricted by the conflict between absorption efficiency and tuning range. In this study, a wideband tunable absorber breaking the trade-off between the absorption efficiency and the tuning range is presented and investigated. First, an improved frequency-dependent resistance model is proposed and analyzed, in which the real part of input impedance varies with frequency. Subsequently, based on the frequency-dependent resistance circuit, a frequency tunable absorber (FTA) with a wide frequency tuning range is constructed by loading voltage-controlled varactors, which exhibits wide tuning bandwidth from 0.613 to 1.816 GHz with reflection coefficients below -10 dB. Additionally, by changing the location of varactor, a varactor-controlled amplitude tunable absorber (ATA) is further explored and designed. The prototypes of FTA and ATA are fabricated and measured, respectively, and good agreements between the simulated and measured results are observed.