Hybrid SRR-Based Stacked Metamaterial for Miniaturized Dual-Band Wireless Power Transfer System

A novel stacked wideband metamaterial is proposed for a robust and compact dual-band wireless power transfer (WPT) system. The proposed metamaterial employs split-ring resonator (SRR) unit cells loaded by nonuniform capacitors. First, two types of unit cells that exhibit two resonance frequencies are analyzed. The results show that it can only improve the coupling between the transmitter (Tx) and the receiver (Rx) at the single band. Then, each unit cell is sandwiched with each other, and a hybrid unit cell that indicates three resonance frequencies is finally proposed. The hybrid SRR exhibits near-zero permeability within the wide frequency range of interest. Therefore, the proposed metamaterial is effective at both bands simultaneously. The system was fabricated and tested, including a compact dual-band WPT system. The size of the Tx (Rx) and the metamaterial is $15\times15$ and $20\times20$ mm, respectively. The measured figures of merit (FOM) are 0.92 at 390 MHz and 0.85 at 770 MHz at a power transfer distance of 20 mm, which is a significant improvement over recently proposed dual-band WPT systems with metamaterials.