This is an advanced inductive charging system into which [David McIntosh] has put a lot of hard work. It uses the same coil-based concepts that we’ve seen in other DIY systems, but the game changer is a communications function that just isn’t found in home brew versions of the hardware. It lets the receiver (device being charged) give feedback to the transmitter by rolling another signal into the EM field being generated.
Do why would you need feedback? Well, if the two coils are not positioned well, the power produced on the receiving end can vary greatly. For instance, you may have the wrong voltage because the coils are not balanced. Or there may not be enough current to properly start charging. The feedback system is designed to let the sending unit change frequency to try to account for physical orientation, or to shut itself off if the charge is just not possible. This is done in expensive commercial devices, and that’s what [David] used as his model.