From: Paul
Date: Wed, 06 Sep 2000 16:45:05 +0100
Subject: Re: [TSSP] Low Q Values
Mark, Lets just clarify this. Your small coil, and all of Malcolm's data, plus your and my calculations all indicate that a decrease of Q with added topload is the norm. The proposal is that increase of Q with added topload, as exhibited by Terry's coil, is a sign of eddy current loss. Mark S. Rzeszotarski, Ph.D. wrote: > I was using less wire spacing than you. I, too, use Medhurst Table > VIII. Are you sure the spacing is .67? It seems a bit off. I calculate the spacing factor as the proportion of winding length spanned by copper, ie turns * wire_diameter / coil_length. For Terry's coil, 1000 * 0.00051m / 0.762m = 0.67 Paul wrote: > >I've been trying to calculate the impact of Terry's foil > >ground plane...throwing my hands up in despair... Mark wrote: > There are several series approximations for estimating mutual > inductance but they work poorly with tesla coil geometries because > you end up subtracting terms with large values in the series. Yes, I've a lovely formula summing products of Legendre polynomials which suffers exactly that problem. > Can you describe the geometry you are looking to solve? That of a single turn circular loop above and parallel to a ground plane. I want to know the change in Q factor of the the loop, as a function of ground plane thickness, conductivity, height of loop, and of course f. Thats the ideal form to be fitted into the computer model of the solenoid - it can just go in as an adjustment to the series resistance of each turn. I'm happy to ignore second order effects such as coupling from a solenoid turn via eddy loops to other solenoid turns. I feel sure that somewhere in a dusty old textbook there's a formula waiting for me to find it. I dont really want to be doing elliptic integrals if it can be avoided. Also, if you have a good formula for mutual inductance between coaxial circular current filaments, please pass it on - I'm not too happy with the one in use at the moment. Regards, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.