Twelve years later, the wireless revolution that brought the mobile phone, Bluetooth and WiFi is about to extend its claim to the domain of power. A handful of companies are now trying to beam power directly to mobile phones, PDAs, laptops and other gadgets without our having to remember to plug them in overnight. The promise of wire-free power, though, may run afoul of the current penchant for all things green because it usually involves a loss of efficiency.
The first products on the market won’t force consumers into paroxysms of guilt. A charging pad for the Motorola Razr, made by WildCharge of Boulder, Colorado, doesn’t waste much power because it comes in direct contact with the cell phone.
But it also falls short of Kuennen’s original idea—to charge gadgets from a distance. To do this, he found a way to create a powerful magnetic field in one area of a room—a kind of hot zone within which gadgets receive a charge. The idea is similar to that of a common induction coil: an electric current running through a coiled wire creates a magnetic field, which can induce a current in another coil nearby. Fulton Innovation, which Kuennen helped found, now makes a device that uses a magnetic coil, concealed under a desktop or other surface, to transmit power to a second, smaller coil within the device. Efficiency is 98 percent, Fulton claims, if the device is a few centimeters away, but drops off sharply at greater distances. “I can charge a cell phone or I can charge your [electric] car,” says Dave Baarman, Fulton’s director of advanced technologies.
The most convenient option would be for a phone to charge itself automatically. That requires a charger that can work remotely from just about anywhere in the room or house. One approach is to use radio waves to send power through the air. Powercast, based in Pittsburgh, last year sold an artificial Christmas tree decorated with wireless LED lights, which get their power from a radio transmitter hidden in the trunk. Powercast sold nearly 500 of the trees last year, for $395 each. Because the transmitter sends radio-frequency power in all directions, some gets lost in thin air, reducing efficiency.
Some researchers are conjuring a future without any power cords. Using high-frequency radio waves, Prof. Marin Soljacic at the Massachusetts Institute of Technology can transmit wireless power for several meters sufficient to run toasters, microwave ovens, PCs and vacuum cleaners. Soljacic envisions replacing the electrical outlets in the typical home with coils embedded in the walls, which would beam power to each room.
The prospect presents a difficult choice between convenience and energy efficiency. The greater the distance between the power source and the gadget, the more power is typically lost in the transfer. Replacing power outlets with coils in the wall, for instance, may come at a big cost to efficiency—as much as 50 percent or more, depending on the distance from the outlet to the appliance. The trade-off would surely be worthwhile in a pacemaker or other medical device, but probably not in a toaster or a television. How about a plug-in electric car that didn’t have to be plugged in? That might pass muster. Sometimes convenience makes all the difference between a worthy product’s success and failure.
