Unless you are particularly organized and good with tie wrap, you probably have a few dusty power cord tangles around your home. You may have even had to follow one particular cord through the seemingly impossible snarl to the outlet, hoping that the plug you pull will be the right one. This is one of the downfalls of electricity. While it can make people's lives easier, it can add a lot of clutter in the process.

For these reasons, scientists have tried to develop methods of wireless power transmission that could cut the clutter or lead to clean sources of electricity. While the idea may sound futuristic, it isn't particularly new. Nicola Tesla proposed theories of wireless power transmission in the late 1800s and early 1900s. One of his more spectacular displays involved remotely powering lights in the ground at his Colorado Springs experiment station.

Tesla's work was impressive, but it didn't immediately lead to widespread, practical methods for wireless power transmission. Since then, researchers have developed several techniques for moving electricity over long distances without wires. Some exist only as theories or prototypes, but others are already in use. If you have an electric toothbrush, for example, you probably take advantage of one method every day.

Everyday Energy The wireless transmission of energy is common in much of the world. Radio waves are energy, and people use them to send and receive cell phone, TV, radio and WiFi signals every day. The radio waves spread in all directions until they reach antennae that are tuned to the right frequency. A similar method for transferring electrical power would be both inefficient and dangerous.

A toothbrush's daily exposure to water makes a traditional plug-in charger potentially dangerous. Ordinary electrical connections could also allow water to seep into the toothbrush, damaging its components. Because of this, most toothbrushes recharge through inductive coupling.

Photo courtesy Amazon.com Most electric toothbrushes recharge through inductive coupling.

Inductive coupling uses magnetic fields that are a natural part of current's movement through wire. Any time electrical current moves through a wire, it creates a circular magnetic field around the wire. Bending the wire into a coil amplifies the magnetic field. The more loops the coil makes, the bigger the field will be.

An electric toothbrush's base and handle contain coils that allow the battery to recharge.

If you place a second coil of wire in the magnetic field you've created, the field can induce a current in the wire. This is essentially how a transformer works, and it's how an electric toothbrush recharges. It takes three basic steps:

1. Current from the wall outlet flows through a coil inside the charger, creating a magnetic field. In a transformer, this coil is called the primary winding.
2. When you place your toothbrush in the charger, the magnetic field induces a current in another coil, or secondary winding, which connects to the battery.
3. This current recharges the battery.

You can use the same principle to recharge several devices at once. For example, the Splashpower recharging mat and Edison Electric's Powerdesk both use coils to create a magnetic field. Electronic devices use corresponding built-in or plug-in receivers to recharge while resting on the mat. These receivers contain compatible coils and the circuitry necessary to deliver electricity to devices' batteries.

© Copyright Splashpower 2006 A Splashpower mat uses induction to recharge multiple devices simultaneously.

Thank You Thank you to Josh Senecal for his assistance with this article.

A newer theory uses a similar setup to transmit electricity over longer distances. We'll look at how it works in the next section.