Cut the Cord: Low-Power Far-Field Wireless Powering

Although the idea of eliminating cords seems attractive, the efficiency will always be better when a wire or cable is used to deliver power. So, what are the applications that warrant wireless powering, and especially wireless powering at longer ranges? It might be appropriate to remember a quote by Rudyard Kipling in this introduction: I keep six honest serving men (they taught me all I knew) Their names are What and Why and When And How and Where and Who Let us start by answering the main questions related to wireless powering. There are essentially three types, Figure 1(a) inductive, capacitive or resonant reactive near-field coupling; (b) far-field directive power beaming; and (c) far-field nondirective power transfer.