Wireless powering by magnetic resonant coupling: Recent trends in wireless power transfer system and its applications

Wireless power transfer (WPT) concept offers users the freedom from annoying wires, and allowing seamless powering and charging of portable devices in an unburdened mode. Since Nikola Tesla's early experiment, the WPT technology has observed the remarkable technological advancement on transmission methods which previously deemed unfeasible. This review paper outlines recent research activities on wireless power technology covering the history, the basic principle of magnetic resonant coupling, and early works on resonant coupled WPT. The two fundamental concepts of power transmission, the maximum power transfer and maximum energy efficiency principles, are summarized in terms of their energy efficiency and transmission distance capabilities. This paper also reviews the comparative study between coupled-mode theory (CMT) and reflected load theory (RLT) in case of analyzing the power transmission model of conventional 2-coil resonant coupled WPT with frequency splitting modes. The study shows that circuit-based RLT provides accurate results as CMT while predicting the average power transmission efficiency in steady-state analysis and is more convenient. This paper explains the effectiveness of advance 4-coil resonant coupled system adopting maximum power transfer principle in extending the operating range of WPT with better power transmission. Various efficiency enhancement techniques for resonant coupled WPT including system with multiple receivers are demonstrated in this paper. The review implies that the adaptive impedance matching using LC circuits is more prolific in practical terms to improve the efficiency of coupled coils. Moreover, the benefits of resonant coupled WPT, its implementation in both consumer and non-consumer applications, and the commercial journey of WPT along with the safety consideration to human exposure issues are also addressed in this paper. (C) 2015 Elsevier Ltd. All rights reserved.