Unconventional waveform design forwireless power transfer

Continuous wave RF signals have been traditionally used in wireless power transmission systems. This chapter considers RF signals with a time varying envelope and specifically multi-sine signals, and investigates the effect on the obtained RF-dc conversion efficiency of wireless power transmission. The timevarying envelope characteristic of such signals leads to a peak-to-average-power ratio (PAPR) greater than 1 (0 dB) and can have a profound effect in the RF-dc conversion efficiency performance. The chapter begins with a presentation of typical RF-dc converter circuits and modeling of the nonlinear rectifier circuit used to convert RF power in dc electrical power. A description of multi-sine signals and their characteristics is then provided, followed by a theoretical analysis of the rectification process of such signals. Finally, a circuit rectifier prototype is presented and measurements of the RF-dc conversion efficiency are shown demonstrating the fact that it is possible under certain load conditions to obtain an improved efficiency performance over continuous wave signals of the same average power, which increases with higher PAPR.