First post here.
I have a built a wireless power transmitter that consists of 2 flat spiral coils that transmit about 20 watts across a short distant to power a heating element. The coils inductance is roughly 7uH.
At the moment I have the oscillator circuit so that it is powered off until the receiving coil is placed over the transmitting coil, in order to sense that the coil is real and not a foreign object. To do this, I have placed a Hall effect sensor on the base with the transmitter and a small magnet in the middle of the receiver. Obviously under RF power, the induced magnetic field in the transmitting coil heats the sensing magnet up pretty hot! It works, but it not elegant.
I would like to do something different but not sure how. I'm pretty sure the transmitter coil inductance will slightly change when the receiver coil is near. I would like to detect that change in inductance and trigger the oscillator. I tried to build a RLC circuit which is pinged at a known frequency then measure voltage. This works at low power I found, but now at high power as I damaged my circuit. Can anyone provide any guidance on this?
During transmission, the entire circuit draws 6.5A @ 12V with a load designed for max power transfer.
Also, if there is a better/simpler/elegant method to accomplish this, please tell!