Wireless energy transfer is a method of getting useful electricity from one place to another without the need for electrical conducting media. Usually, this process involves a phenomenon known as electromagnetic induction. Other methods, particularly radio-frequency (RF) microwaves and laser beams, have also been used.
The Serbian-American scientist Nikola Tesla first observed electromagnetic induction in the latter part of the 19th century. He noticed that when a strong alternating current (AC) passed though a coil of wire, a nearby coil acquired a weaker AC at the same frequency, even when the two coils were not physically connected. The extent of this effect depended on the distance between the coils, and also on their relative orientation. The greatest electromagnetic induction occurred when the coils lay along a common axis in close proximity. This discovery led to the development of the transformer, a major component of electrical systems today.
Microwaves concentrate RF electromagnetic fields into powerful beams that can travel over greater distances than simple induction coils (such as the ones used by Tesla) allow. However, for public safety reasons, the Federal Communications Commission (FCC) limits the maximum amount of power that such systems can use in the United States. A receiving antenna, usually a dish, picks up the transmitted microwave energy, and a converter circuit changes it into usable electricity.
Lasers can concentrate considerable energy in an extremely narrow beam that travels over great distances through space or clear air. A photovoltaic cell (PV cell) can intercept the visible or infrared (IR) rays from a distant laser and convert that energy to direct-current (DC) electricity. The DC can, in turn, charge the batteries for a consumer device such as a personal computer (PC), eBook reader, or cell phone. However, even this technology cannot yet convey the massive amounts of energy needed to electrify cities. For that purpose, high-voltage utility transmission lines remain the option of choice.
Continue reading about wireless energy transfer:
PowerBeam explains the basics of wireless energy transfer.
Pure Energy Systems describes several methods for wireless transmission of electrical energy.
Singularity Hub speculates about the future of wireless energy transfer.