Chinese Researchers Develop a Laser-Powered Receiver That Could Keep Drones Flying Without Landing

Every drone needs to land and recharge, constraining its potential. Chinese researchers have developed a new method of aerial recharging. Their simple, lightweight receiver can absorb energy from a laser beam directed at it from the ground while the drone is in flight.

A Receiver That Works Like a Solar Panel, But for Lasers

The new technology is the work of researchers at the Civil Aviation University of China and Tsinghua University, who designed and built a lightweight receiver that could be attached to a drone wing and convert light from a green laser beam into electricity.

Reporting July 29 in the Cell Press journal Matter & Light, the researchers said the receiver converted 38.49% of the laser’s energy into electricity.

That’s an impressive number, beating the roughly 34% peak efficiency of perovskite–silicon tandem solar cells certified by the U.S. Department of Energy, though laser-beam efficiency isn’t directly comparable to solar-cell efficiency under sunlight.

The researchers named their invention a perovskite laser cell–thermoelectric tandem receiver, or PLC-TE. The name is a bit of a mouthful, but the basic idea is simple: the receiver is made of two layers of materials, each of which harvests some of the energy in the laser beam.

The first layer, a thin film of perovskite—a crystalline substance favored by solar-power researchers because it’s better at capturing light than silicon—captures some of the photons in the laser beam and converts them to electricity.

Sandwiched beneath the perovskite layer is a thermoelectric generator, which captures some of the heat generated by the perovskite and converts that to more electricity.

Heat Was the Problem Nobody Had Solved

Beaming laser light at a receiver sounds like an easy way to generate electricity, but researchers had previously encountered a major impediment: the receiver could overheat. This problem proved a major impediment to making laser recharging practical in the wild.

Jianhua Han, a senior author of the paper at the Civil Aviation University of China, said the problem with overheating came as a surprise to them.

“When we were testing the receiver with a fairly powerful laser, a thermal camera showed that the temperature was reaching up to 80 to 90 degrees C (176 to 194 F),” Han said. “This was a far more serious problem than we had imagined.” The other senior author, Hong Lin, is affiliated with Tsinghua University.

So, the researchers added antimony selenide nanocrystals—tiny bits of semiconductor material—between the two layers of the receiver to slow the transfer of heat away from the perovskite layer.

That allowed the perovskite to do its job without being impeded by excessive heat. At the same time, the heat that was transferred to the thermoelectric layer was enough to allow it to generate more electricity.

Meanwhile, the researchers etched some small channels into the wing of the drone to redirect some of the warm air that was flowing past the receiver.

“By exploiting the movement of the propeller, we were able to redirect some of the warm air that would have flowed away from the receiver to across the backside of the receiver,” Han said. “This too helped in cooling the receiver.”

Han said finding a solution to the heating problem involved a combination of materials and mechanical engineering. “It isn’t just a materials science problem,” he said. “It’s an engineering problem.”

Testing the Idea on a Real Wing

The researchers attached their PLC-TE receiver to the underside of a wing of a stationary drone and aimed a green laser beam at the receiver. The light from the laser beam was converted to electricity, which in turn powered the propeller of the drone, enabling it to hover in a lab setup.

This is not the first time a laser beam has been used to power a drone. Three years ago, a research team at Northwestern Polytechnical University in China demonstrated that a laser beam could be used to keep a small quadcopter drone in the air for extended periods.

However, that demonstration was also limited by the inefficiency of the receiver and issues with keeping the laser beam focused on the drone.

The demonstration by the team from the Civil Aviation University of China picks up where the work by the Northwestern Polytechnical University team left off, and goes from there. The researchers hope to eventually develop a practical technology for keeping a drone in the air.

There are still some significant challenges ahead for the technology. The receiver has only been tested on a stationary drone so far. The next challenge—getting the receiver to work on an actual drone while it is hovering or flying—will involve figuring out how to keep the laser beam focused on the drone.

“The receiver has only been tested in a lab so far,” said Han. “We need to test this technology outside, on a lightweight drone, while it is hovering.”

What Longer Drone Flights Could Mean

Most small drones are only able to stay in the air for up to about an hour or two before they have to land to recharge their batteries. That limits their ability to monitor a wildfire or a flooded neighborhood for more than a couple of hours before they have to return to the ground to recharge.

With the new technology, farmers could observe larger fields without interruption, said Han. “It would also enable forestry workers to monitor forest fires for longer periods of time to get a better idea of how fast a fire was spreading,” he said.

“And it would help disaster relief workers to conduct aerial inspections of flooded roads and buildings hit by wildfires without having to stop and recharge.”

Another application of drones capable of staying in the air longer is in logistics. Companies are also considering using drones for commercial delivery. “There are a lot of logistics companies that are eager to have aircraft that can keep flying for longer periods of time,” Han said.

Han summed up the potential impact of his team’s work with a brief phrase. “We’re hoping to one day be able to do refueling aircraft with light,” he said. But turning that concept into a reality will require many years of additional research and development.

The receiver that they’ve developed has to become more efficient and more durable so it can work outside the controlled environment of the lab. Additional research is needed to develop and commercialize a means of keeping a laser beam focused on a moving aircraft.

For now, the researchers have developed a novel receiver that can be attached to the wing of a drone and harvest both the light and the heat from a laser beam to generate electricity—enough electricity to power a propeller. Whether that will be a practical solution for making drones last longer in the field remains to be seen.