Playing about with a couple of QI inductive chargers and receiver.

I was wondering how efficiently the inductive phone chargers worked, so I got a couple of modules off ebay and a receiver plate to take to bits. They do seem to communicate with each other, rather than just pumping current into any coil that comes near.
The transmitters seemed to use what appeared to be a microcontroller controlling an H-bridge driver that then drove the coil via a paralleled cluster of capacitors. The receiver had a modest amount of circuitry in it with what appears to be a dedicated QI receiver chip, possibly by Texas Instruments.
Efficiency was 50% at best and got MUCH worse as the coils were parted.
Both the transmit and receive coils are both backed by a layer of ferrite material. In the case of the transmitter it was a hard ferrite disk and on the receiver it was a thin brittle layer sandwiched between two layers of plastic and with the coil stuck to the front.
Neat enough toy for inductive coupling of power. Perhaps ideal for charging circuits mounted inside waterproof cases.