A Rectenna is a really obscure electrical device, which currently sees little use. Rectenna stands for RECTifying anTENNA.

It's a simple and cheap device for turning radiowaves into DC power. It basically consists of a wire, a diode and a capacitor.

When placed into a radio beam, it produces a DC electrical voltage which can supply power.

The Rectenna was invented to allow reception of microwave power from geosynchronous orbit, where solar energy is available and can easily be used to drive a microwave generator; the Rectenna can turn microwaves to DC current with extremely high efficiency (more than 90%).