Free-space transmission

The renaissance of serious interest^26–28 in the transfer of power by radio waves is doubtless the result of technological gains in microwave radar and communication systems over the past 25 years, and also the more recent demonstration that microwave energy should be generated at power levels appropriate to some applications of wireless power transfer. In turn, the availability of microwave power focused attention upon the problems of developing an efficient RF-to-dc converter and upon antenna systems suitable for efficient power transfer. When the problems were solved, modest laboratory experiments were set up for the first time in the efficient transfer of meaningful amounts of power by means of a microwave beam and associated conversion components.