Experimental study on multi-point wireless energy transmission at 950 MHz band

Recently wireless sensor networks have gained more interests. However limited life-time of sensor nodes has long been an issue in wireless sensor networks. On the other hand, wireless energy transmission at 950MHz band has been applied to many applications, especially RFID (Radio Frequency IDentification) systems. However, the problems of restricted transmit power defined by radio regulation and the standing-wave occurred in indoor propagation environments still limit the coverage of wireless energy transmission. In this study, we propose a multi-point wireless energy transmission system with carrier-shift diversity to widen the coverage of wireless energy transmission without decreasing the efficiency of energy charging compared to the conventional method which requires some kinds of channelization schemes when performing multi-point transmission. We also conduct an experiment to show the benefits of the proposed scheme in terms of coverage enhancement. In this experiment, we employ multiple RFID Reader/Writers to perform wireless energy transmission, an IC tag antenna to receive energy, and a phase shifter to perform carrier offset. The experimental results show that the coverage of single-point and multi-point wireless energy transmission without carrier-shift diversity are both 96 percent to activate sensors with a required consumption power of 100μW. On the other hand, the coverage of proposed scheme achieves 100 percent in that environment.