Qi (pronounced CHEE) is a manufacturer-agnostic standard for wirelessly charging small, battery-powered devices. Qi, which means life energy in Chinese, was developed and is maintained by the Wireless Power Consortium, a group of manufacturers that includes Apple, Dell, LG Electronics and Verizon Wireless.
The Qi standard ensures that any device that meets Qi specifications can be charged by being placed on any charging surface that meets Qi specifications, regardless of the device's manufacturer or brand. The Qi charging surface transfers the required energy to the compatible battery-powered device through electromagnetic induction.
The Serbian-American scientist Nikola Tesla first observed electromagnetic induction in the latter part of the 19th century. He noticed that when a strong alternating current (AC) passed through a coil of wire, a nearby coil acquired a weaker AC at the same frequency, even when the two coils were not physically connected. The extent of this effect depends on the distance between the coils and also on their relative positioning.
The Qi standard permits the transmitting coil and the receiving coil to be positioned two different ways: guided positioning and free positioning. Guided positioning requires the end user to place the battery-powered device in direct alignment with the transmitting coil. Close spacing of the two coils, as well as shielding on their surfaces, ensures the inductive power transfer is efficient. Free positioning bundles coils in a charging pad to generate a magnetic field around the battery-powered device. This way gives the charging device a workable service over separations as far as 15cm, which has made it easier for retailers and transportation service providers to embed charging surfaces in such things as counter surfaces, furniture and lamp bases.
The Qi standard competes with AirFuel, a proposed standard overseen by the AirFuel Alliance. The AirFuel Alliance was formed by the merger of the Alliance for Wireless Power (AW4P) and the Power Matters Alliance (PMA); its members include AT&T, Samsung and Intel. Both the Wireless Power Consortium and the AirFuel Alliance are experimenting with inductive charging, resonance charging and radio charging to provide mobile end users with ubiquitous charging. In such a scenario, an end user's device might issue a permission-based alert indicating the availability of wireless charging.