Thermally tunable absorbers using vanadium dioxide (VO₂) composites

Thermally tunable absorbers using vanadium dioxide (VO₂) composites offer a promising approach for controlling electromagnetic (EM) absorption in microwave systems. VO₂ exhibits a reversible phase transition near 68 °C, changing from an insulating to a metallic state. This property allows precise tuning of absorption characteristics when integrated into metamaterial structures. Two VO₂ compositions (L50 and LM1090) were deposited in varying masses onto carbon-based substrates. A custom-fabricated printed circuit board (PCB) heater was developed to provide spatially uniform thermal activation. The absorbers were evaluated in the 16–19.9 GHz and 20–25 GHz bands using a WR-62 waveguide and vector network analyzer. Scattering parameters (S₁₁ and S₂₁) were measured at temperatures ranging from 25 °C to 90 °C. Infrared thermal imaging confirmed the quality and consistency of heat distribution during phase transitions. The results demonstrated that L50 samples provided sharp switching and deeper absorption, while LM1090 offered broader bandwidth tuning. The best-performing absorber achieved a minimum transmission (S₂₁) of –21.3 dB and a tunable bandwidth greater than 3 GHz. Heating uniformity, mechanical alignment, and modular sample mounting contributed to improved repeatability and measurement accuracy. These findings confirm the effectiveness of VO₂ as a thermally responsive material for reconfigurable absorbers. The integration of efficient thermal control, material optimization, and waveguide-based measurement enables practical development of tunable EM devices. Such absorbers have potential applications in radar cross-section reduction, adaptive sensing, and frequency-selective filtering for communication systems.