MIT researchers have discovered that a wireless electricity delivery technique they invented three years ago works better when it's used to charge multiple devices at the same time.
In 2007, they demonstrated a transmitter and receiver consisting of coils about two feet across. When placed more than six feet apart, they were used to light a 60-watt bulb — even with people sitting in between.
But the new system uses a slightly larger transmitter, with receivers that are only about a foot across – moving closer to a size that could eventually be built into a PC or a television set, they say. The transmitting coil could be built into a wall or ceiling, and the transfer of power works over distances comparable to the size of an ordinary room.
Lead author André Kurs says this reduction in size of the receiving coil is an ongoing process. With a bit more work, he says, "we could embed it in a portable device," he says.
The system, based on work by Nikola Tesla, works by creating a strong electromagnetic resonance between the sending and receiving coils.
Although predicted by theory, it's the first time anyone has actually demonstrated the increase in efficiency when powering two devices at the same time. The MIT team found that when powering two devices at once, which individually could achieve less than 20 percent efficiency in power transfer, the combined efficiency climbed to more than 30 percent.
The two receiving coils resonate with each other as well as with the transmitting coil, and help to reinforce the strength of the magnetic field. Kurs says that the efficiency should continue to rise as more devices are added, climbing toward a theoretical limit of 100 percent.
The amount of power transmitted in the latest experiment was just 100 watts, but Kurs says that is only limited by the amplifier used for the transmitting coil, and can easily be increased.
"It could be several hundred watts, or a kilowatt," he says. "You could feed power to a medium-sized room, and power a dozen devices."