Can portable electronic devices (like my phone) be recharged wirelessly?

Yes, but those little devices use a lot more power than you might think…

By Sarah Jensen

Everything from calculators to keyboards to mice are easily recharged these days using solar power. No extra wires or connectors or USB ports required. But we still connect our handsets to an electric power supply at end of the day — and try to remember to pack all the necessary cables and cradles and ports when we travel.

“In devices with smaller power levels, you can use solar or wireless power,” says Yogesh Ramadass, who received his PhD in energy harvesting and low-power electronic design from MIT in 2009. “But that’s not possible with a cell phone because the power levels are orders of magnitude higher than in simpler devices. The area necessary to capture enough solar power to recharge a smart phone indoors would be humungous.”

And while data is easily transferred wirelessly to cell phones by satellite signal, that method can’t provide the oomph necessary for recharging, either. “Cell phones contain very sensitive receivers that easily pick up data,” says Ramadass. “But again, you’d need something much larger than a phone’s antenna to channel enough energy to charge a battery.”

That’s not to say users have no alternatives to traditional plug-in chargers. Currently on the market are wireless charging pads for repowering not only phones but other devices as well, such as electric toothbrushes. The pad relies on inductive charging, which uses electromagnetic energy to induce a transfer of energy to the gadget, no wires attached. The pad is placed on a tabletop and the phone is either inserted into a special sleeve or set directly atop the pad. The recharging is accomplished through communication between a transmitter coil in the pad and a receiver coil in the phone.

“Research is currently under way to increase the distance between the pad and your cell phone,” says Ramadass, now an electrical design engineer with Texas Instruments. “In another three to four years, we’ll be able to charge our phones from a foot or more away from the pad.”

Next on the horizon may be universal wireless chargers, he predicts. “Very soon,” he says, “we’ll see various cell phone companies come out with chargers that can be used with different brands of cell phones.” That’s good news for hotel guests who can leave their charger at home and the social butterfly who needs to recharge their phone halfway through a party. “Multiple people will be able to put their cell phones on the charger, and they’ll all recharge,” explains Ramadass.

But a completely wireless way of boosting your battery no matter where you are? “I don’t foresee the day when your phone will just continually charge from wherever you happen to be,” says Ramadass. “That’s not going to happen anytime soon.”

Thanks to Avaneesh Rastogi of Lucknow, India, for this question.

Posted: October 2, 2012

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