Impedance-Controllable Embedded Resonator for Switchable High-Selectivity Metamaterial Rasorber

A new technique for designing a dynamically controllable transparent window in the metamaterial absorber is investigated. Active lossy layer and lossless layer are proposed to establish the rasorber. First, the impedance-controllable embedded resonator is presented as a choke to limit the current flowing through the lossy elements. The interdigital and meander lines are applied to independently equivalent the large lumped capacitor and inductor required for low-frequency (L/S-band) resonance. It is demonstrated that the impedance loading of the inductive embedded resonator makes for a miniaturized unit size of 0.086λL. Then, the cascaded embedded resonator on the lossless layer realizes a switchable high-selectivity passband in the reflection band. The transition from transmission band to absorption band is reduced due to the sharp roll-off edges of the passband. Finally, the rasorber prototype is fabricated and validated by the free-space measurement. By switching the bias of the p-i-n diodes, a high-selectivity window at 2.2 GHz can be triggered while it keeps absorbing in the whole band (1.2-3.7 GHz, 102%) at window-off state. Principles of operation and synthesis procedure are presented in this article.