Wasted energy can keep smartphone running 30 percent longer

May 27, 2015 // By Jean-Pierre Joosting

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The Ohio State University has found a way to make smartphone batteries last up to 30 percent longer on a single charge, by capturing wasted RF energy and feeding it back to battery.

The patented circuitry converts some of the radio signals emanating from a phone into direct current (DC) power, which then charges the phone’s battery. This technology can be built into a smartphone case, without adding more than a trivial amount of bulk and weight.

Some of the inventors, all engineering researchers at Ohio State, are working with a spin-off company to further develop the technology and will launch a Kickstarter campaign in June for market validation and fund development.

“When we communicate with a cell tower or Wi-Fi router, so much energy goes to waste,” explained Chi-Chih Chen, research associate professor of electrical and computer engineering. “We recycle some of that wasted energy back into the battery.”

There are some products newly on the market that harvest stray radio signals to charge tiny wireless devices such as temperature sensors. But the Ohio State invention is many times more powerful and efficient, said Robert Lee, professor of electrical and computer engineering.

“These other devices are trying to harvest little bits of energy from the air,” Lee said. “Our technology is based on harvesting energy directly from the source. They can capture microwatts or even nanowatts (millionths or billionths of a watt), but cell phones need milliwatts (thousandths of a watt) or higher.”

By Lee’s reckoning, nearly 97 percent of cell phone signals never reach a destination and are simply lost. Not all of it can be recaptured, but some can.

“No one can charge a cell phone from the air, but we can reduce power consumption by retrieving some of those lost milliwatts. Think of it as a battery extender rather than a charger,” Lee said.

The idea of converting radio signals into battery power may not seem straightforward, but the basic technology is almost as old as commercial electricity. It relies on the fact that radio waves are actually just a very high-frequency form of alternating current (AC).

To communicate, today’s portable devices broadcast radio signals — that is, high-frequency AC — a portion of which the Ohio State rectifier system captures and converts back to DC. Its trick is to siphon off just enough of the radio signal to noticeably slow battery drain, but not enough to degrade voice quality or data transmission.

Still, there’s a good bit of wasted radio signal to be had. For our convenience, cell phones broadcast in all directions at once as this is the fastest way for a portable device to reach the nearest cell tower or Wi-Fi router.