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Life Unplugged

Bundle up your power cords—wireless energy transfer is here

smithsonian.com

When the aliens arrive, they will likely seize the cell phones. And the iPods and laptops and PDAs. Not because they desire the toys, but because these devices accompany us on our walks and drives and subway rides with such little exception that, to a fresh observer, the gizmos might appear to power us.

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In many senses they do. We must remember to slip them into our pockets and purses before leaving the house. More vitally, we must remember to re-charge them every evening. It's only a matter of time before that classic teenage nightmare of being naked in school is replaced by the terror of a Low Battery signal—beeping in one's pocket during Study Hall like the beating of some hideous heart.

So when can we reclaim control of our memories and dreams? When can we cut these modern umbilical cords and have gadgets that power-up wirelessly while we do more important things—like text-message our vote for the next American Idol?

Wireless transfer itself is nothing new. Radio waves have broadcast information to tiny antennas for decades. Lots of energy, in the form of radiation, is lost during these transmissions, however. That's fine for sending data such as cell phone positions, a process that requires little energy. But sending power itself requires conserving as much energy as possible during the transfer.

So, engineers need a more frugal way to send power. One option is through resonance: when one resonant object produces energy at a certain frequency, a nearby resonant object at the same frequency can suck up the power efficiently. Put simply, this type of energy transfer explains why a booming singer might cause a wine glass, filled to the right level, to vibrate visibly—perhaps even to shatter.

But unless you're married to the Fat Lady and call home using stemware, this "acoustic resonance" won't help you charge your mobile phone. Instead, engineers can harness "magnetic resonance" by designing twin coils whose magnetic fields speak to each other, in a sense, across a bedroom or café.

This wireless energy transfer requires that the two coils be set to the same frequency. Then, when one coil is connected to a power source such as a battery or outlet, it will send energy to the other coil implanted in an electronic device.

The system has several benefits. Few everyday items interact with magnetic fields, so it's unlikely for something to unintentionally drain power from the coils. Unlike a laser, resonant coils can transfer energy through obstacles, so your PC continues to charge even if someone plops a grande latte between your laptop and the wall. And because the coils are designed to conserve radiation, the devices pose no harm to people—aside from the potential to help inflate a cell phone bill.

The largest drawback is that wireless power currently works across a moderate-sized room (in one test it lighted a bulb seven feet away), but long-range transfer appears highly difficult, if not impossible. So when the aliens commandeer your Blackberry and take it back to their home planet, the joke's on them. Unless, of course, they probe you first.

The real Wishful Thinker behind this column was Aristeidis Karalis, an engineering graduate student at the Massachusetts Institute of Technology, who predicts the system might be available for products within the next several years.

Have an idea that should be thought about wishfully? Send it to jaffee@si.edu

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