Amplitude and frequency analysis of multi-sine wireless power transfer

Transmitting multi-sine signals with high peak-to-average power ratio (PAPR) has emerged as an efficient solution to improve the power conversion efficiency (PCE) of wireless power transfer (WPT). This paper analyzes the radio frequency (RF) PCE as a function of the number of tones (N_t) and signal bandwidth (BW) in multi-sine based WPT networks. We show how the energy harvesting efficiency depends on the BW and the non-linear relationship between the instantaneous input amplitude and output voltage. As a result of these, the PCE first increases with increasing N_t and then decreases. We confirm this analysis using measurements. Depending on the circuit chosen for energy harvesting, we can improve PCE of the multi-sine WPT with 25.1% compared to a CW excitation WPT for -5 dBm input power.