I have been testing for several weeks a new circuit to create a better AC current with a current sensor to adapt the frequency.

Schematic:

By adding coil L7 and capacitor C13, the generation of alternating current is balanced in the negative and positive directions.

Old circuit:

New circuit:

I also added a shunt resistor to measure the current. By changing the frequency we can detect the peak of fog creation which corresponds to the current peak.

And for example for a disk sold with a resonance frequency of 108kHz the peak of fog creation is at 100kHz.

I have ordered the new PCB with the modifications. I will test it before publishing it.