Wireless power transfer (WPT) has been the subject of intense interest, bordering on folklore, for over a century. The arrival of the modern cell phone with its innumerable “apps” and rising battery consumption, has recently sparked off a huge upsurge in consumer demand for wireless chargers.
WPT is still maturing as we speak. Mysterious signs have started popping up all around us — in airport kiosks, hotels, coffee shops, inside our cars, even on branded furniture. These aren’t teasers placed surreptitiously by Night Shyamalan, but logos of the three dominant, competing standards shown in Figure 1. We also see a high-level diagram of modern WPT technology in the same figure, showing the basic process of wireless power transfer through coupled coils as per these standards. All the three standards, despite some differences, are broadly called “inductive MPT” in this article, because they share the same underlying physical principle: the law of induction, as we will learn shortly.
And we are just getting started! Soon we may start hearing about exotic techniques such as “evanescent wave coupling” and “dielectric resonators”. We may even find ourselves immersed 24/7 in fields of “ubiquitous energy”. Then again, we may not, for health reasons. So, while the debate is still on, and our future speculative, surprisingly, so is our past. Only one thing seems to be certain: WPT as we know it today, didn’t start in its current form, despite appearances. The story has enough twists and turns to keep us on the edges of our seats for a while.
Tracing back the history of WPT is tricky business. We may stumble over some misleading hype strewn along the way. There are potholes of hyperbole too. We may even start to wonder whether a part of us somehow wants to believe in the unbelievable: in the mysterious, the mythical, the magical — in light sabers, wormholes, powerful beams of inter-galactic energy, and fanciful stuff like that. That tendency of ours may indeed have helped to some extent, nominate Nikola Tesla (1856-1943), a brilliant engineer in his own right, as the rockstar of WPT today. In a rather quaint move, a certain company at the forefront of wireless power technology refers to their CTO as the Chief Tesla Officer.
Really? You can almost visualize him driving around in a Model S sedan, dressed in a black shirt emblazoned with bolts of lightning to complete the picture. Tesla must surely be glowing from far beyond upon hearing of all this. But the truth is, we still don’t know the truth. We need to ask: What fraction of the legend is fact? How much of it is just that: a legend? How exactly did we get here? And where are we headed? This article tries to answer that, and also serve as a high-level review of the current state of WPT.