Proposition of Novel Evaluation Method and Values for Wireless Power Transfer With Modulated Waves

Flexible DC power supplying is necessary for the practical use of IoT. There are two main techniques for the power supply. One is the wireless power transfer (WPT) technique and the other is energy harvesting(EH). This paper focuses on WPT with modulated waves and radio-frequency(RF) energy harvesting. Both techniques use rectifiers for the conversion from modulated electromagnetic waves to direct current(DC) power. In recent research, it is revealed that the characteristics of rectifiers with modulated input are calculated with power probability distribution and rectifiers’ own CW characteristics. Herein, we can make the general discussion of the modulated waves for WPT and EH.Previous research show that the modulated waves with high peak-to-average power ratio(PAPR) can improve the RF-DC conversion efficiency of rectifiers when the average input power is low. More strictly speaking, this fact means that the modulation improves the efficiency when the average input power is lower than 1 / PAPR times of the optimum CW input for each rectifier. This is absolutely correct and consistent with much experimental results. However, this is only the sufficient condition and not useful for the practical design. Herein, We focused on the practical and novel evaluation method for the WPT and EH with general modulations. This paper proposes the novel evaluation method for modulations. Our method uses a weighted power probability distribution(PPD). The average and variance of the weighted PPD are practical evaluation parameters for the modulations. The former value approximately equals to the optimum design power for the rectifier with modulated waves and we defined the value as "representative power". The other value can evaluate the modulation quality for WPT. We also show the consistency of these values by comparing with the simulation results.