Design of Wideband Energy Capturing Adapter Based on 3-D Meta-Structure for Wireless Power Transmission Application

A wideband energy capturing adapter based on 3-D meta-structure is presented in this article for wireless power transmission (WPT) system. Compared with conventional planar resonant structure, the proposed 3-D meta-structure for energy collection is designed first. After analyzing the magnetic field magnitude and power loss density distribution of the 3-D meta-structure unit cell, it is found that the induced current lengths are different under ${x}$ -polarization and ${y}$ -polarization, resulting in different equivalent circuits and operating bandwidths. The collecting efficiency of the 3-D meta-structure unit cell under oblique incidence is investigated as well, demonstrating the stable wide-angle reception. Then, a wideband combining network is proposed to collect the alternating current (ac) power from an $8\times8~3$ -D meta-structure array based on multistage T-junction power dividers and impedance transformers. The operating bandwidth of the proposed combining network can cover that of the 3-D meta-structure array. After energy collection, a rectifier circuit based on a multichannel parallel connection is presented for wideband ac-to-direct current (dc) conversion. Due to the nonlinear characteristics of the proposed rectifier circuit, the effects of input power level, load resistance, and operating frequency on rectification efficiency are studied in detail. Finally, a prototype is fabricated and tested for demonstration. Measured results show that the proposed design can achieve over 30% system conversion efficiency $\eta $ at 3.5–8.5 GHz (6.2–6.7 GHz) under ${x}$ -( ${y}$ -) polarization. Simulated and measured results are in good agreement.