A Single-Layer Focusing Metasurface Based on Induced Magnetism

A transmissive single-layer Huygens unit cell based on induced magnetism is proposed to design low-profile and multi-focus metasurface. The Huygens unit cell consists of a pair of antisymmetric metal elements and a dielectric substrate with only 1.2 mm thickness (A0/6.8 at 37 GHz). The surface currents flowing in the opposite directions form the circulating electric currents to induce the magnetic currents orthogonal to the electric currents. The full coverage of 27r phase is achieved through optimizing the parameters of the metal elements, which solves the problem of the incomplete phase coverage caused by layer number reduction. With Holographic theory, the compensating phase distribution on the metasurface is calculated. The incident plane wave can be converged to designated points in any desired fashion including focal number, location, and intensity distribution, which exhibits outstanding manipulation capability. As the simulations and measured results show, the designed metasurface can achieve good multi-focus focusing characteristics. The focusing efficiency at the center frequency is 43.78%, and the relative bandwidth with 20% focusing efficiency exceeds 20%. The designed metasurface has the advantages of low profile, simple processing, and high efficiency, which has a wide range of application prospects in the fields of millimeter wave imaging, biomedical diagnosis and detection.