The US military has shown in a test that it is possible to wirelessly transmit electrical energy over a longer distance.

A team from the Naval Research Laboratory (NRL), a US Navy research facility, transmitted 1.6 kilowatts of electrical energy over a distance of one kilometer. According to the NRL, it was “the most significant demonstration of power beaming in nearly 50 years”.

The electricity is converted into microwaves for transmission through the air. These are then sent in a directed beam to a receiver. A dish serves as the transmitting antenna, which makes it possible to precisely focus the beam.

Microwaves become direct current

A rectifying antenna, a rectenna, is used on the receiver side. This consists of an array of many small microwave antennas operating in the X-band. This is the frequency range between 7 and 11.2 gigahertz (GHz). The incoming electromagnetic waves are then converted into direct current by a diode. The NRL team uses 10 GHz because the technology required for this is mature and cheap.

The US Department of Defense wants to use wireless power transmission from space. The idea is to supply energy to deployed troops from space, making them independent of local fuel supplies. The goal of the Safe and Continuous Power Beaming – Microwave (Scope-M) project was to transmit one kilowatt of electrical power over a distance of one kilometer.

The NRL tested the transmission at two locations: at the army compound at Blossom Point, Maryland, it peaked at 1.6 kilowatts. The set target was thus clearly exceeded.