The Design Of Wireless Power Transmission System Based On Retro-Reflective Beamforming And Near-Field Focusing

In recent years, with the rapid development of portable and implanted electronic devices, as well as the emerging technologies such as internet of things and body area networks, there has been an increasing demand for the wireless charging technology. Microwave power transmission is one of the potential solutions to wireless charging in the mid-to-long range. However, due to the free space loss, microwave power supply has the problem of low transmission efficiency and uninsured safety.To address the above problems, a wireless power transmission scheme based on retro-reflective beamforming and near field focusing is proposed and studied in this work. The scheme employs the retro-reflective antenna array to produce a microwave beam that tracks and focus power onto the target position, so that wireless power can be accurately delivered to mobile devices with improved efficiency. In addition, The concept of near field focusing using distributed antenna arrays is introduced, which proves able to reduce the far field radiation intensity that could be unsafe to human body and cause interference to other electronic systems. Specifically, the work accomplished includes the follows:(1) The retro-reflective structure and its implementation is studied in detail, based on which, a microwave power transmission architecture based on retro-reflective beamforming is designed. In this architecture, the wireless power transmitter receives a pilot signal broadcasted by the mobile device. The pilot signal is then converted to digital domain and analyzed by DSP to obtain the conjugate phase information with respect to each element of the transmitting antenna array. After that, the feeding phases of the antenna array are properly controlled, and the power transmitter is able to deliver focused power beam to the mobile device.(2) Based on the above architecture, a retro-reflective microwave power transmission demonstration system is designed and built, including the transmitting antenna array, pilot signal analysis module, retro-reflective control software and a rectenna in the power receiver. Experimental demonstration of the wireless powering to a mobile device 1.5m away is successfully accomplished, with the real-time tracking capability.(3) A design of wireless power transmission based on near field focusing with distributed antenna array is presented. In this design, the power transmitter consists of two 1′4 antenna arrays, well separated in space. By using the retro-reflective scheme, all the 8 antenna elements, jointly focus the wireless power to the mobile device. Simulation and experiment results show that the scheme of distributed retro-reflective beamforming can accurately focus the power to the mobile device’s location within a certain region, whereas reduce the power distribution in other locations of the area.