Air Power

“Time Reversal” Could Make Wireless Electricity Ubiquitous

Wireless electrical power appeared on the horizon in the late 19th century when Nikola Tesla, the mercurial genius and sworn rival of Thomas Edison, invented an amazing device that could shoot electricity and set light bulbs aglow 100 feet away.

Unfortunately, the Tesla coil, as it was known, emitted alarming lightning bolts and was hugely inefficient. Nearly 130 years later, while electrical wires proliferate, wireless power across distances greater than a few inches remains a kind of holy grail.

A new invention developed jointly by UMD physics Professor Steven Anlage and a group of undergraduates in the Honors College’s Gemstone program stands to make wireless power as ubiquitous as Wi-Fi. The device could someday clear a mess of wires off your desk and offer a groundbreaking way to power mobile devices, pacemakers and an array of futuristic gadgets.

But first, Anlage has to overcome some of the challenges that bedeviled Tesla.

“How do you find something… and get power to it when the target is moving around?”

The answer: time reversal. Put simply, it’s a way to analyze electromagnetic signals, recording and then playing them backward, in order to pinpoint a device in your purse, pocket or implanted in your body. Then, a Wi-Fi router-like device delivers electricity to that device in the form of microwaves.

“The idea is that a box on the wall sends the energy all over the place,” Anlage says. “Little bits of energy go in every possible direction, phased in such a way that when it reverberates all around the room, it does nothing anywhere to speak of except in your phone, and then, boom—it delivers all its energy in a pulse.”

The system was awarded the 2017 UMD Invention of the Year Award in the physical sciences category. The groundbreaking patents and scientific papers the team produced—including a best paper award at the 2016 IEEE International Wireless Power Transfer Conference in Portugal—are rare in the field, because companies hoping to cash in on proprietary discoveries conduct much of their research in secret, says Scott Roman ’16, a former Gemstone student who worked with Anlage.

There should be more collaboration around such a potentially important technology, Roman says.

“It’s clear that a lot of people in the industry have no idea of the science behind what they’re trying to do,” he says. “You can’t magically push out a product without understanding it.”

Efficiency—a measure of how much electricity emitted is being used—is perhaps the biggest challenge. Roman guesses 25 percent efficiency is required for a marketable product, while the Anlage/Gemstone invention is currently below 1 percent.

Low efficiency means lots of electricity wasted, with only a tiny trickle of usable power remaining. (It’s theoretically possible to crank the power way up, Anlage says, but the downside is that microwave energy could become intense enough to injure people.)

The efficiency question is a fascinating subject that Anlage is delving into in his continuing research, pursuing the project as science rather than product development, with funding from the Navy and Air Force. Once the technology is ready, much as Tesla envisioned in the 1890s, it could change the world.

“We might think of it as a way to charge a phone or a tablet now, but when you have ubiquitous power, people will start to think of new uses,” he says. “Health monitoring devices embedded in the body are one possibility. And it will open up other possibilities no one has considered yet.”