Nikola Tesla was quite a character. He was an eccentric genius whose work in the late 19th and early 20th centuries revolutionized electronic engineering. He was a pioneer in fields ranging from radio transmissions to developing alternating-current electricity. Tesla also had quite a few rivals -- his work tweaked the noses of some of the greatest inventors of the time, including Thomas Edison and Guglielmo Marconi.
Tesla filed many patents during his lifetime. One of those appeared in the patent office on Jan. 18, 1902. The patent's title was "Apparatus for Transmitting Electrical Energy." In the patent, Tesla describes a device that he believed could transmit electrical power from one conductor to another without the need for wires. Ultimately, Tesla's work in this field failed due to engineering and financial obstacles. But the dream didn't die with Nikola Tesla.
Transmitting power through radio waves at first seemed promising. A good example of how radio waves can transmit power is a crystal radio. This basic radio consists of a long wire as an antenna, a diode, another wire to act as the ground wire and a crystal earphone. By attaching the two wires to either end of the diode, connecting the ground wire to a metal stake in the ground and connecting the crystal earphone to the ends of the diode, this radio can pick up radio waves that you can actually hear, yet you don't need a battery or other power source to hear them -- the radio waves themselves provide the power.
The trouble with radio wave transmissions is they aren't very efficient. Radio waves spread out as they transmit -- only a relatively small percentage of them would make it to reach the antenna for the charging device. But there are other methods to send electricity wirelessly, including through microwaves or magnetism. The magnet approach really resonated with engineers looking for a way to get rid of those extra charging cords.