# High capacitance oscillator circuit to produce longitudinal waves

I’m trying to figure out a suitable oscillator circuit to produce longitudinal electric field waves (like in a Tesla Coil) to experiment and produce any mechanical or EM effects on various materials. A conductive sphere will be driven with AC. So the sphere will be pulsing with –q , +q , -q , ... with an isometric pure electrodynamic field with all magnetic field cancelled out.

A 50 Mhz fixed frequency oscillator circuit with weak or no harmonic distortion to oscillate relatively high amount of charges back and forth to a high capacitance sphere antenna (sphere, because i know the self-capacitance equation of a sphere only). I think a crystal/Pierce oscillator would fit best for a fixed high frequency without harmonic distortions. The problem is, I would need to oscillate high amount of charges (about 10^-5 – 10^-4 Coulombs) to produce a decent, mechanical or EM effect.

To drive such high amplitude of oscillations with peak voltages low enough to be safely measured even with a 10x oscilloscope probe, I would need a high capacitance oscillator circuit and I think that even if I connected many crystals in parallel, I would need thousands of them.

Could I use a thick crystal with low fundamental frequency and produce only a higher harmonic (50MHz) by a band-pass circuit? But then again, why would I need a crystal when I used a resonant LC circuit with high capacitance?

Also I would need to be able adjust the amplitude of the oscillations (amount of oscillating charges) which makes things even more complicated. Should I vary the collector voltage of the transistor or the resistance?

Any suggestions are welcome.

• Maxwell's equations pretty much say that for a electromagnetic field to propagate,the electromagnetic field will be orthogonal to the direction of propagation–ie. not longitudinal. You can of course let an electric field oscillate linearly,but that is not going to be a wave,but an excited oscillation within a conductor.Note that from Maxwell it's clear as daylight there can not be something like a electrodynamic wave without the matching magnetic one–that'd directly contradict Faraday's Law of induction. – Marcus Müller Nov 4 '16 at 13:14
• You can try to achieve $\mathbf J = - \epsilon_0 \frac{\partial\mathbf E}{\partial t}$, but I'd a bit curious about the material where that would happen. – Marcus Müller Nov 4 '16 at 13:14
• Point is that this will only happen in extremely interesting plasmas, metamaterial, or, classically, as longitudinal modes in cavities/waveguides. – Marcus Müller Nov 4 '16 at 13:16