In what it describes as the most significant demonstration of its kind in half a century, the US Naval Research Laboratory (NRL) beamed 1.6 kW of power over a kilometer (3,280 ft) using a microwave beam at the US Army Research Field in Maryland.
The idea of transmitting power over long distances without wires has been around for well over a century. By the 1970s, the technology was mature enough to make it a key component in a concept by American physicist Gerard K. O'Neil that proposed establishing space colonies to build huge solar collector stations to beam power back to Earth.
The principle is simple enough. Electricity is converted to microwaves, which are then focused in a tight beam at a receiver made up of what are called rectenna elements. These are very simple components that consist of an x-band dipole antenna with an RF diode. When microwaves strike the rectenna, the elements generate DC current.
