More is merrier for wireless power supply

Using magnetic induction to send electricity to devices is more efficient when more than one machine is involved.

The notion of transmitting power over the air is at least 100 years old, with methods from high-powered microwaves to focused beams of infrared being tested.

But researchers at the Massachusetts Institute of Technology (MIT), led by physicist Marin Soljacic, think using magnetic fields to induce a current in a distant device is the most promising approach. They tune the transmitter and receiver to magnetically resonate at the same frequency to maximise efficiency. Waves carry energy most effectively between objects that resonate at the same frequency, an effect at work when a singer smashes a nearby glass with the right note.