Switchable and Tunable Salisbury Screen Microwave Absorber Based on a Uniform Vanadium Dioxide Film

Vanadium dioxide (VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) has generated extensive interest in switchable and reconfigurable microwave devices because of its reversible insulator-to-metal transition, which leads to large changes in its electrical and optical properties. This work reports a Salisbury screen-based switchable microwave absorber that uses uniform VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film as the top resistive layer. The screen acts as a reflector or an absorber layer in the insulating and metallic states of VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>, respectively. As a proof of concept, we design and experimentally demonstrate an X-band microwave absorber. The fabricated microwave absorber has a center frequency of ∼10.55 GHz with a bandwidth of 2 GHz. It shows a high reflection of −2 dB in the VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> insulating state and a low reflection (high absorption) of ∼−36 dB in the VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> metallic state. During the phase transition, the microwave absorber shows wide range of reflection intensity variation and resonance frequency tuning as a function of temperature due to changes in the VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> electrical properties. We also present an equivalent circuit model to explain and validate the measurement results. Thermally controlled switchable and tunable absorbers have the potential to be used in a wide range of applications, including electromagnetic shielding, stealth technology, medical applications, etc.