Yes, I need a lot more information.
I'm trying to build something based on this paper:
https://web.stanford.edu/group/Zarelab/publinks/798.pdf with some changes.
The important things to understand are that the output is meant to be in peak-peak Voltage, not in Power-at-some-impedance and that both the isolation from ground and of the two "ends" of the amplifier from each other are important.
I attached a sketch I made.
The changes I would make:
- Trying to push the working frequency up to 2 MHz (though lower is probably tolerable, and it's intended to be changeable)
- Using a low tuning capacitance, or none at all, to achieve resonance (other than the actual load)
- No automated stepper motor tuning
- Using variable inductor-transformers to tune to resonance.
- Replacing the expensive and probably unneccesary Apex power amp with a much cheaper boosted op-amp
- Possibly boosting the primary voltage to reduce the required transformer ratio
- Crystal-controlled frequency source
Anyway, the linked work uses a cylindrical air-core transformer consisting of 3 turns primary over a secondary that isn't fully specified but has an inductance of 300 uH and looks like it probably has a secondary of around 300 turns on a 20mm former (this gives the proper numbers and dimensions that agree with the picture, as well as providing a transformer ratio of about 10 which agrees with my simulations).
Since I want to go to a higher frequency, the combination of inductance and capacitance needs to be reduced. Getting rid of the tuning capacitor (which only makes things worse) is a first step.
(I was somewhat resisting using ferrites because as far as I could tell, the need to baby the flux in the ferrite leads to adding another constraint -> even more headaches.
Another possible idea: Minimal-inductance air core transformer (probably very small diameter to allow the combination of high turns ratio and low inductance) with the center tap / split, and the ends leading off to roller inductors (in series) that are not used as transformers.
Anyway the target inductance for roller inductors would be in the 20 to 100 uH range.