A novel design method of polarization conversion metasurface unit cell based on topology optimization

Abstract Polarization Conversion Metasurfaces (PCM) have increasingly been applied to electromagnetic scattering reduction due to their excellent characteristics, such as low profile, high efficiency and wide operating bandwidth. However, traditional unit cell design methods often rely on design experience and time-consuming parameter optimization. Topology optimization is an effective method for determining the optimal material distribution to achieve the desired performance. Based on this, this paper proposes a novel design method of PCM unit cell that considers both the material distribution of the top metal layer and the size of the dielectric substrate. A PCM unit cell with an F4B substrate and metal layers on both the top and bottom is optimized to achieve the polarization conversion function. Furthermore, PCM unit cells are arranged in a checkerboard pattern to achieve scattering reduction through scattering cancellation technology. For the proposed PCM unit cell, the simulated bandwidth with a polarization conversion ratio (PCR) greater than 0.9 ranges from 6.18 to 13.69 GHz. For the checkerboard PCM, monostatic radar cross sections (RCS) reductions below 10 dB are achieved between 8.9 GHz and 12.7 GHz. Moreover, the mechanism of polarization conversion is revealed, that is, the current loops in the dielectric substrate result in magnetic resonance.