A girl on a swing is a good example. Onl y when the child pumps her legs at the natural frequency of the swing is she able to impart substantial energy and swing higher.
The MIT team focused on one particular type: magnetically coupled resonators, consisting of electromagnetic coils, to broadcast energy. The team explored a system of two electromagnetic resonators coupled mostly through their magnetic fields to transfer electrical energy.
Magnetic coupling is particularly suitable for everyday applications because most common materials interact onl y very weakly with magnetic fields.
"The fact that magnetic fields interact so weakly with biological organisms is also important for safety considerations," said Andre Kurs, a graduate student in physics.
The idea came to Prof Marin Soljacic when he was awoken by his mobile as it beeped to signal it was about to expire.
By Roger Highfield
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