read the resonant cavity patent, it answers so many questions
it's not an electrical resonance such as that between a capacitor and an inductor, where the waves propagate at the the speed of light, i am not exactly sure how to describe it properly, but it is closer to a mechanical/acoustical/physical resonance of the electrical stress induced in the water that causes them to oscillate, more like an atomic resonance between the covalent bonds as the fluctuate
why doesn't straight high voltage DC work in the cell? well it might, but stan describes this as a static electrical stress on the water, while pulsed DC is a dynamic electrical stress on the water
just think of tesla's earthquake machine, it was the size of a cigar box or something, you set it on a bridge and it does nothing (static), you turn it on and have it vibrate at the right frequency and it'll destroy the bridge (dynamic)
also the term resonant cavity is not Stan's technology, it is something he learned about and put to use, (it's in the dictionary right next to resonant charging chokes too) ... i haven't found many other sources of information on them, but i'll be looking and i bet there is a big book all about them somewhere