Efficiency improvement of the impulsive wireless power transmission through biomedical tissues by varying the duty cycle

It is very challenging to improve the power conversion efficiency (PCE) in wireless power transmission (WPT), especially through the propagation channel of biological tissue. The received power for biomedical applications is usually very weak due to the security regulations of Specific Absorption Rate (SAR) and the propagation attenuation by biological tissues. So the input power (P_IN) of the RF-DC rectifier is usually not high, and the optimal PCE cannot be achieved as conventional efficient rectifiers do. In this paper, we propose an impulsive technique to promote the PCE at a low input power level at -10 dBm and to optimize the performance by varying the duty cycles of the impulsive power waves. Therefore, the dc output voltage (V_out) and PCE can be effectively improved from 1.176 to 1.905 volt (62%) and from 13.83% to 36.29%, respectively. Furthermore, the wireless channels for such wideband power transmission techniques and the biological channel effects are investigated in this paper. Fundamental analysis is setup to predict the tissue attenuation loss. Through the measurements, we found that our proposed techniques can improve the V_out and PCE within the 10 mm thickness of biological tissues (pork) and supply more wireless power for biomedical implantable systems.