Wirelessly powered drone achieves flight with microwave beam

Rockets typically use about 90 per cent of their fuel escaping the Earth’s atmosphere. Researchers at the University of Tsukuba in Japan believe this limitation could be overcome by wirelessly transmitting the necessary power to the rocket.

Previous analyses of this kind were carried out decades ago and mostly considered microwaves of a frequency in the low gigahertz (GHz) range. Given that the power transmission efficiency increases as the operating frequency is raised, the team behind this latest research used microwaves with a relatively high frequency (28GHz).

The team managed to get a drone weighing roughly 0.4kg to hover for 30 seconds at a height of 0.8m above the source of the microwave beam.

“We used a sophisticated beam-tracking system to ensure that the drone received as much of the microwave power as possible,” said Kohei Shimamura, lead author. “Moreover, to further increase the transmission efficiency, we carefully tuned the phase of the microwaves using an analogue phase shifter that was synchronised with GPS units.”

The researchers measured the efficiencies of the power transfer through the beam (4 per cent); the capture of microwaves by the drone (30 per cent); the conversion of microwaves to electricity for propulsion (40 per cent), and other relevant processes.

Based on this information and an analytical formula, they calculated the overall power transmission efficiency in their experiment was around 0.43 per cent. For comparison, in a previous study the team measured the total transmission efficiency for a fixed-position (rather than free-flying) drone to be 0.1 per cent.

“These results show that more work is needed to improve the transmission efficiency and thoroughly evaluate the feasibility of this propulsion approach for aircraft, spacecraft and rockets,” Shimamura said. “Future studies should also aim to refine the beam-tracking system and increase the transmission distance beyond that demonstrated in our experiment.”

The researchers hope that although microwave-powered rocket propulsion is still in its early stages, it could someday become a superior way to launch rockets into orbit given the high onboard-fuel demands of conventional propulsion techniques.

Last year, engineers demonstrated a wireless charging solution that can power objects in motion that could one day allow electric cars to be charged while they are driving.