In the 1890s, Nikola Tesla captured the imagination of the world with his invention of the Tesla coil, a device that could transmit electricity through the air, no wires required. More than 100 years later, the world has responded by adapting this breakthrough technology... mainly to recharge their electric toothbrushes.
But things are changing rapidly in the world of wireless power, with some new ideas coming to the forefront in the last few years. As more and more gadget makers get hip to the idea of a world without power bricks, this is a technology category that's about to explode.
How will your phone, your lights, and even your electric car someday be powered without a wire? Here's a primer on how wireless power works.
Today: Short-range inductive coupling
Take a device that has a battery inside and rest it on a special charging station or place it on a charging pad: This type of wireless power — which most of us have at least seen over the past few years — is known as inductive coupling. It involves two devices, but there are no visible electrodes or obvious contact points. The technology revolves around the use of magnetic fields to create an electric current.
Run electricity through a coil of wire, and it creates a magnetic field. In the typical inductive coupling scenario, this coil is found inside the base station or charging unit, which is plugged into the wall. Now take another coil of wire and place it in close proximity to (but not touching) the first coil.
In our example, this second coil is inside the toothbrush or smart phone. When the magnetic field of the first coil interacts with the second coil, it generates an electrical current. This is called induction. The current isn't much, but then again, your toothbrush doesn't need much power to recharge its internal battery after the couple of minutes you spend brushing your teeth each day. So, as if by magic, the device is always fully charged.
The use of inductive coupling in electric toothbrushes was born of necessity. Exposed electrodes don't work — and in fact could be very dangerous — if they get wet. More recently, as this technology has been improved to provide greater levels of efficiency with smaller components, its primary utility is becoming one of convenience. No need to plug your phone in at home or in the car, inductive couplings located strategically in your house and vehicle can take care of it for you, automatically.
Tomorrow: Long-range inductive coupling
Inductive coupling is a neat idea, but its extremely short range — often on the scale of a few millimeters — makes it minimally useful in the real world. (The distance the current can travel depends on the diameter of the coils and the number of windings.) The bulk of research today has focused on maximizing the distance at which current can be induced, and minimizing the loss of power over that distance.
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