Archive of April 2012
The Wireless Power Consortium (WPC) announces that a Qi charger can deliver 5 Watt through a 40mm table top into a Qi receiver.
Resonant Qi charger
Magnetic resonance transmitter delivers power into a magnetic induction receiver
The Qi specification is an 'interface specification'. That means that products on both sides of the interface are free to use whatever technology they like as long as the behavior on the interface is correct.
That freedom is real. 12 different transmitter designs have been approved in the mean time. (Don't confuse "transmitter design" with "transmitter". A "transmitter" is a product that you can use the charge a receiver. A "transmitter design" is a specification.)
Most of these 12 transmitters designs limit the transfer distance to a couple of millimeters. That distance is not a limit of the Qi specification. It is a choice that produces low-cost, highly efficient, transmitters.
The Qi specification allows larger distances. The Wireless Power Consortium has created a Qi transmitter that delivers 5 Watt into a Qi receiver through a 40mm table top. Interestingly, that transmitter uses magnetic resonance operating conditions. This illustrates that magnetic resonance and magnetic induction use the same physics: The magnetic resonance transmitter delivers power into a magnetic induction receiver.
The design of this magnetic resonance transmitter is available for members only. They can find it in the Qi Wiki: http://wiki.wirelesspowerconsortium.com/ (search for CR#123). This transmitter design will be published on the WPC website (as free public download) after the review by the WPC members.