how to transfer 2 Volts on 2 coupled inductors?

Sorry to bother, that's a question I met in the company and nobody can answer it, I guess maybe sb. here can help me.



We are working on an inductive charging board. The primary and secondary board are only communicating via two coupled inductors.
The mainvoltage going from primary winding to the secondary winding is about 15V and 20k Hz. Now I need to get another 3.3V, 100Hz voltage signal from a microcontroller on the secondary board and feedback to the primary board via the same pair of windings. I wonder how can I realize this? Thank you for any suggestion.


I thought before that maybe i can use a low-pass filter to do that. But the magnitude and frequency of the main voltage is changing a little with the resonant frequency on the secondary board. Thus maybe it's somewhat inaccurate.

here the secondary would have a voltage due to the primary.... if you want to transmit a signal from secondary to primary then you would have to apply it in parallel to the coils of the secondary.... since there is already an voltage due to primary this is not possible since a node cannot have two values of voltage at the sametime....

so my idea is to time slice and transmit... transmit for sometime from primary and then for sometime from secondary and so on.....