A transparent flexible metasurface absorber based on a bio-inspired water-based structure and graphene for RCS...

A switchable bifunctional metasurface absorber (MA) with optical transparency and flexibility is proposed by integrating a bio-inspired water-based structure (BIWBS) with graphene. The proposed design can be switched between ultra-broadband and dual-band absorption mode by controlling the water-filling state of the BIWBS, and the absorptivity (A(ω)) and the relative bandwidth (RB) are dynamically manipulated by changing the sheet resistance (R_s) of graphene. When the BIWBS is filled with water and the R_s is 800 Ω sq^-1, A(ω) > 90% is achieved in the 14.22-67.48 GHz band (Ku-V band), corresponding to an RB of 130.38%. When the BIWBS is in the dry state and R_s = 150 Ω sq^-1, A(ω) exceeds 90% in the dual bands of 15.07-28.02 GHz (Ku-Ka band) and 65.02-75.46 GHz (V band) bands, with corresponding RBs of 60.11% and 14.86%, respectively. Especially, the designed MA enables radar cross section reduction (RCSR). In the planar case, an ultra-broadband and dual-band RCSR exceeding 10 dB are obtained in 14.79-64.32 GHz (RB = 125.22%) and 16.46-28.64 GHz (RB = 54.01%)/64.14-73.34 GHz (RB = 13.38%), respectively. The frequency ranges of RCSR are in good agreement with those of the absorption bands. Moreover, it maintains superior RCSR performance in the conformal case. The proposed MA exhibits excellent flexibility and optical transparency, which provides an effective approach to realizing switchable ultra-broadband and dual-band RCSR and has significant application potential in conformal electromagnetic (EM) radar stealth and electromagnetic compatibility.