Depends if there is resonance. One thing that seems to be unclear is that the coil and the ultrasound are actually there to intensify the plasma, not the other way around.
The coil is fixed at 100 Hz and so has less utility in targeting specific conditions.
The ultrasonic is there to add harmonics of the plasma, being either 1/16th (fast) or 1/256th (slow) of the frequency sent to plasma.
For more details, please check the link: