MIT’s light bulb moment

Researchers at MIT have made a significant breakthrough in making batteries and power cords a thing of the past through the use of wireless electricity.

A team from MIT’s Department of Physics, Department of Electrical Engineering and Computer Science, and Institute for Soldier Nanotechnologies (ISN) has been looking for a way to charge battery-powered appliances without having to connect them with leads to a power source.

After a series of experiments, they were able to light a 60W light bulb from a power source 2.13m away without a physical connection to bind the two, achieving what the team has dubbed WiTricity.

The WiTricity was created by using two resonant objects of the same resonant frequency known as coupled resonators to exchange energy. Objects of a different resonant frequency would not interfere with the transfer, resulting in a more efficient energy transfer.

Of the many types of resonances available, the researchers decided to investigate electromagnetic resonators that were joined through their magnetic fields.

Using two copper coils, they connected one coil, the sending unit, to the power source, which transmitted the power by filling the space around it with a non-radiative magnetic field oscillating at MHz frequencies. The other coil, the receiving unit, was designed to resonate with this field and receive the power.

In any system of coupled resonators, there is a ‘strongly coupled’ regime of operation. The MIT scientists were able to identify this regime and make their device operate in it.

This meant that even when the distance between the resonant objects were several times larger than their sizes, an efficient level of energy transfer was maintained.

The main advantage of magnetic coupling is that it has little interaction with most common materials, which means that there is little interference with the power transfer.

According to Andre Kurs, a graduate student in physics working on the project, there is also a health benefit.

He said: ‘The fact that magnetic fields interact so weakly with biological organisms is also important for safety considerations.’

The researchers found that the smaller the receiver, the shorter the range, but for laptop-sized coils, power levels high enough to run a laptop could be transferred over room-sized distances, in almost any direction, even when objects were placed between the two coils.

Prof Peter Fisher said: ‘As long as the laptop is in a room equipped with a source of such wireless power, it would charge automatically, without having to be plugged in. In fact, it would not even need a battery to operate inside of such a room.’

Although wireless power transmission already exists, certain types can be too inefficient, such as electromagnetic radiation, which spreads in all directions, meaning that most of the power would be wasted, and directed electromagnetic radiation, such as lasers, need an uninterrupted line of sight between the source and the device.