Here is an idea based on the work of J L Naudin et al .Take a simple parallel tuned circuit [tank circuit] consisting of a coil and a variable capacitor . I understand that it can be made to oscillate by varying either the inductance or capacitance in a rhythmic manner at twice the frequency of the tank circuit . So we are altering a parameter of the oscillator in the same manner that a child maintains oscillation of a swing by rhythmically altering the center of gravity . One way to do this is to have a center tap on the coil,and provide a switch that will short circuit half the windings . Then we open and close this switch at twice the resonant frequency of the tank circuit . In an initial trial , the resonant frequency of the tank could be kept low ,say 50 Hz .Thus the switching could be done mechanically by a variable speed motor driven cam or commutator . I believe that the amplitude of the oscillation is dependent on the magnitude of change in the inductor and possibly the Q of the tank . I think the amount of energy that could be extracted from the tank could exceed the energy needed to do the switching .I favour mechanical switching initially , it saves argument as to where any excess energy comes from . Is it possible for someone to simulate this please?

This is an old research area.

http://jnaudin.free.fr/html/paraconv.htm

I was looking at parametric converters a few days ago.
Then I fell in to the area of multi-filar windings.

Shorting the inductor would change its resistance, thereby altering the current.  Naudin's writes that the parametric-effect is a result of the change in inductance (dL/dt), not current (di/dt) and where the magic lies - at least that's my reading of it!  What pisses me off about Naudin is that his website is full of mouth-watering stuff like this, followed by a "more to come..." statement, but it never does - that parametric posting is from '97 and was never followed up! 

One of those magnetic-amplifier chokes in place of the inductor might be a better way to go.

OK let me crack you head open!

Oscillations in systems with non-linear reactance By R. V. L. Hartley
http://www.alcatel-lucent.com/bstj/vol15-1936/articles/bstj15-3-424.pdf

Also: How about some power Amplification:
http://www.freepatentsonline.com/7808124.pdf

Broli post :

http://www.energeticforum.com/renewable-energy/5811-parametric-excitation.html#post98702

A couple of questions here . Does anybody know if the oscillation amplitude in a parametric oscillator would depend on frequency? I want to keep the resonant frequency low so that I can use mechanical switching . Also , can anyone offer a wild guess as to the inductance in Henrys of a microwave oven transformer . This transformer is  220 volt to 2000 volt step up transformer and is quite large . Please estimate both the primary and secondary windings .

hi Nep

how's the knee?  recovering nicely after that impact with the poynt gonads?

AC signals across effectively 'unloaded' LC pairs will vary in amplitude with 'f', having a maxima or minima at the res. freq. depending on the LC pair being parallel or series respec.

i seem to remember from seeing one of woopys recent vids that he wrote the Iy / IIy inductances on the MOT which was featured

hope this helps - good aim, btw, obviously touched a nerve or two
np


http://docsfreelunch.blogspot.com
 

@Sprocket . Re the knee ,LOL .Many thanks for those values of inductance.Re my question regarding Frequency . What I meant was , assuming this oscillator idea works , would it give more power out if the frequency was say 1Mhz as opposed to 50 Hz . There would be advantages in 50Hz , One could use a standard transformer and not have issues with the core materials .Also , if mechanical switching was used , a switching rate of 100Hz is feasible ,whereas this is not true at 1Mhz .My idea was to use the primaries of 2 transformers across a capacitor . then use a switch to short out one transformer at the right frequency .A meter or scope across one of the secondaries would detect oscillation .