A universal standard for charging devices wirelessly is close to becoming a reality, as the Wireless Power Consortium finalized the interface definition for a low-power specification this past Friday. That interface definition is already available internally and will be published publicly on August 30, though WPC said that performance requirements and compliance testing documents will only be available to consortium members.

The current spec maxes out at 5 Watts of power. That should be sufficient for most common mobile devices, many of which already charge via USB ports that max out at 2.5W (5V at 500mA). The spec is open enough to allow a wide variety of design solutions, such as a magnetically aligned coil that is used for the Palm Pre's Touchstone charger, or an array of coils activated individually depending on device placement.

In addition to the standard, however, WPC has a series of tests for specification compliance. Devices purporting to comply with the standard will have to pass third-party certification before the manufacturer is allowed to use the trademarked "Qi" logo on the device or its packaging. This is designed to make it easy for consumers to find interoperable chargers and devices.

"Our customers will see the Qi logo and know: this product works with my other Qi products," wrote Menno Treffers, a senior director of standardization at Philips who works with the consortium. "Publishing a standard is not enough. Without test documentation, certification services, and a logo license agreement, interoperability is an illusion."

Certification testing services will begin in August, meaning products supporting the standard could start appearing this fall.