A Minimized 2-D Left-Handed Material Spiral Unit Cell With Rotation Symmetry for Midrange Wireless Power Transfer

This letter presents a technique for designing left-handed material (LHM) unit cell, and a minimized 2-D low-loss LHM square spiral unit cell (38 mm × 38 mm × 1.6 mm) with rotation symmetry is developed in the frequency band 13.56-14 MHz. Two LHM slabs with 5×5 unit cell array are added to the transmission and receiving antennas, respectively, and the power transfer efficiency has increased greatly.