Abstract
A printed spiral resonator without external lumped elements is proposed. Instead of employing surface-mount device (SMD) capacitors, series-parallel capacitive plates are designed and etched on the same substrate to achieve simultaneous conjugate matching between a pair of symmetrical near-field coupled resonators. Simulations are conducted with the aid from CST Microwave Studio. The proposed design displayed satisfactory tolerance towards planar displacement at z-axis plane, lateral displacement at x- and y-axis planes as well as concurrent planar and lateral displacement. Positioned at perfect alignment with a transfer distance of 15 mm, the simulated and measured maximum power transfer efficiency achieved are 79.54% and 74.96% respectively. The variation ratio for planar displacement acquired is 0.29% when receiving resonator is rotated from -180º till 180º with step size of 15º. Under rotational angle from 0º till 180º, the measured average variation ratio for lateral displacement at x- and yaxis up to 15 mm is 20.14%. Feasibility of sustaining power transfer efficiency under various offsets depicts the possibility of integrating the proposed simple design for low power wireless energy transfer applications such as wireless charging for handheld devices in consumer electronics and implanted biomedical devices.