Visible–Infrared Transparent Ultra-Thin Frequency-Tunable Microwave Absorber Based on a Nanometer-Thick Patterned VO₂ Film

Designing an ultra-thin microwave absorber that can simultaneously realize tunable absorption and broadband optical transparency remains a crucial challenge. In this work, we present a visible–infrared transparent ultra-thin frequency-tunable microwave absorber based on a nanometer-thick patterned vanadium dioxide (VO 2 ) film. The thermally variable sheet resistance of the nanometer-thick VO 2 film enables different percentages of equivalent resistance in the equivalent impedance of the patterned VO 2 film, which induces the absorbing mode to transform from pure Fabry–Perot (FP) cavity resonant to FP cavity and LC electrical co-resonant. The measured thermally peak absorption frequency modulation range is 15.42–12.99 GHz, while the ultra-thin thickness is only 0.071 of the central wavelength of this range. Moreover, the absorber can achieve high optical transparency from 380 to 6000 nm. Therefore, the proposed absorber has diverse applications in optics and modern intelligent platforms.