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Cutting the final cord: How wireless power and wireless charging works

Christopher Null | March 4, 2015
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.

More recent research has found that you can extend the useful range of an inducted current by using materials with the same resonant frequencies. All objects have a natural resonant frequency at which they vibrate. Think of a tuning fork. It doesn't matter how hard you hit it, it always vibrates at the same frequency, emitting a tone with the same pitch every time. When you match the resonant frequencies of the two coils in an inductive-coupling scenario, you get better efficiencies from the configuration.

The design of resonant inductive coupling circuits is a bit more complex than this, involving the attachment of a capacitor to each of the two inducting coils. Engineers can fine tune both the design of the coils and the plates to alter the resonant frequency. Ultimately, when the system is energized, an electromagnetic wave is generated that can travel from one resonant coil to the next, over much greater distances than have been capable before.

The most iconic experiments along these lines occurred at MIT in 2006 and 2007, when researchers powered a 60-watt light bulb from a range of two meters using resonant induction. The technology was given a name: WiTricity. One of the researchers, Marin Soljai, would later go on to found a wireless power company by the same name. Today, the company sells a development kit of its Prodigy system for $995: "Your gateway to a future of a world without wires."

Commercial endeavors

The market is already stuffed to the gills with companies that are putting these technologies to use, and standards bodies are rapidly maturing.

The Qi specification is being developed by a massive group called the Wireless Power Consortium that includes Microsoft, Panasonic, Samsung, Sony, Toshiba, Verizon, and more. Qi (pronounced chee) is really a simple implementation of inductive coupling, designed to work mainly through devices in physical contact with one another.

With the goal of encouraging "snack charging" in vehicles, at desks, and during brief stops at coffee shops and cafes, the consortium now lists a total of 692 certified, compatible products on the market, mainly charging plates and cell-phone sleeves. Ikea recently announced that it would be introducing furniture with built-in charging plates for smartphones and tablets. A new version of the Qi standard extends its range from 7mm to 45mm through the use of resonant coupling. That may not sound like much, but it does make the technology much more flexible in the types of places it is implemented.

The other two groups creating wireless power specifications — the Alliance for Wireless Power (A4WP) and the Power Matters Alliance (PMA) — recently announced that they would merge . This brings together A4WP member companies such as Asus, Dell, Fujitsu, HP, Intel, and Witricity with PMA member companies Duracell, Proctor & Gamble, LG, and Starbucks.


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