Ultra-thin, polarization-insensitive, and conformal metamaterial-based sensor with high Q-factor

This research paper introduces a distinct and ultra-thin metamaterial-based absorber that exhibits near-perfect narrow-band absorption characteristics for sensing refractive index (RI) in the ISM band. The absorber consists of a grounded FR4 (flame retardant) with an engraved metallic structure arranged in a double-cross pattern with triangular extensions at the ends and a central 8-point-star void. Through simulations and measurement, it has been observed that the absorber exhibits a highly concentrated absorbance at 5.7 GHz, achieving an absorbance efficiency of 99.37% with a full width at half maximum bandwidth of 220 MHz. The quality factor of the presented sensor is analytically computed as 25.92, while the evaluated average sensitivity is 0.47 GHz/RIU and the average figure of merit is 2.18. The thickness is less than 0.00826λ₀ and the size of the sub-wavelength unit cell is around 0.228λ₀. Further, it is demonstrated that MMA is suitable for conformal applications under outside bending conditions.