Wireless power system shown off

A system that can deliver power to devices without the need for wires has been shown off at hi-tech conference. The technique exploits simple physics and can be used to charge a range of electronic devices over many metres. They had showed mobile phones and televisions charging wirelessly. This system could replace the miles of expensive power cables and billions of disposable batteries.
The system is based on work by physicist Marin Soljacic at the Massachusetts Institute of Technology (MIT). It exploits “resonance”, whereby energy transfer is markedly more efficient when a certain frequency is applied. When two objects have the same resonant frequency, they exchange energy strongly without having an effect on other, surrounding objects.
The system uses two coils – one plugged into the mains and the other embedded or attached to the gadget. Each coil is carefully engineered with the same resonant frequency. When the main coil is connected to an electricity supply, the magnetic field it produces is resonant with that of with the second coil, allowing “tails” of energy to flow between them. As each “cycle” of energy arrives at the second coil, a voltage begins to build up that can be used to charge the gadget. The main coil could be embedded in the “ceiling, in the floor, or underneath your desktop”. Devices using the system would automatically begin to charge as soon as they were within range. And you never have to worry about plugging these things in again.”
The system is able to operate safely because the energy is largely transferred through magnetic fields. Humans and the vast majority of objects around us are non-magnetic in nature. It is able to do this by exploiting an effect that occurs in a region known as the “far field”, the region seen at a distance of more than one wavelength from the device. In this field, a transmitter would emit mixture of magnetic and potentially dangerous electric fields. But crucially at a distance of less than one wavelength, the “near field” is almost entirely magnetic. Hence Witricity uses low frequency electromagnetic waves, whose waves are about 30m long. Shorter wavelengths would not work.