Metasurface-Based Generation of Solid and Hollow Near-Field Patterns Using the Method of Maximum Power Transmission Efficiency

Near-field-shaped focusing has broad applications in wireless power transfer and microwave imaging. Traditional near-field focusing antenna arrays have a large size and require the design of complex feeding networks. This paper proposes a scheme for near-field-shaped focusing using a radiation-type metasurface, which offers a low-profile, compact structure and simplifies the corresponding feeding network design. The proposed scheme is based on the method of maximum power transmission efficiency, which determines the amplitude and phase distributions required to generate preset field patterns on a target plane. For solid-pattern shaping, different weights are assigned to the constraints to flexibly control the field distribution, enabling multiple solid patterns to be synthesized using the same set of sampling points. For hollow-pattern shaping, sampling points are uniformly distributed along the inner sides of the edges defining the outer contour of the target pattern. Given the sampling-point locations and weighting matrix, the required amplitude and phase distributions are obtained by solving a constrained optimization problem. These distributions are then implemented using the radiation-type metasurface to realize the desired near-field patterns. To validate the proposed method, a circularly polarized radiation-type metasurface operating at 9.4 GHz is designed and evaluated through full-wave simulations. A 16 × 16 metasurface is used to demonstrate near-field-shaped focusing for solid and hollow square, circular, and triangular patterns. The results verify the effectiveness of the proposed scheme in realizing near-field focusing with diverse solid and hollow patterns.