Flexible Janus metasurface for multifunctional polarization manipulation

A flexible Janus metasurface (MS) is proposed for the integrated manipulation of multiband polarization wavefronts in reflection and a low-loss transmission window in transmission. The top layer consists of nested circular and polygonal rings with diagonally truncated cuts, which excite multiple resonant modes to achieve broadband and multiband linear-to-linear and linear-to-circular polarization conversion. The bottom metallic structure introduces a low-loss transmission channel within a specific frequency band. Both metallic patterns are printed on ultrathin flexible polyimide (PI) substrates. Under + Z -direction incidence, the proposed metasurface realizes left-handed circular polarization, right-handed circular polarization, and cross-polarized wavefront conversion across the C-, X-bands and part of Ku-bands, while providing high-efficiency transmission with an insertion loss below 1 dB in the Ku-band. Under − Z -direction incidence, the same low-loss transmission characteristics are maintained within the transmission window, whereas co-polarized reflection is obtained outside this band, demonstrating pronounced direction-dependent electromagnetic responses. The physical mechanisms underlying the multiple polarization conversion functionalities are elucidated through u – v orthogonal-mode decomposition and an equivalent circuit model. Furthermore, the extracted polarizability tensors verify that the proposed structure satisfies the omega-type bianisotropic coupling condition, thereby revealing the physical origin of the asymmetric co-polarized reflection for opposite illumination directions. The measured results of the fabricated flexible prototype agree well with the simulations, and stable polarization conversion and transmission performances are maintained under bending conditions. The proposed metasurface therefore shows considerable potential for direction-dependent wavefront manipulation, conformal radar detection, and advanced wireless communication systems.