From: Paul
Date: Sat, 26 May 2001 00:18:28 +0100
Subject: Re: [TSSP] Loss due to ultrasonic mechanical vibration of secondary?
Terrell W. Fritz wrote: > Magnetostriction I think is the term and there is the magnetic > attraction between wires with opposing currents. Not too clear on it myself. I think the coil tries to expand, and the mechanical vibration would be at 2 times the RF frequency. > My SS coil does not seem to vibrate the secondary but it would > be at 350kHz which is hard to hear :-)) Can you modulate the carrier with an audio tone - try putting some into your sonotube coil - you might hear it? I'm sure there must be some mechanical coupling, its a question of whether the energy lost in a tightly formed, well coated, Tesla secondary is significant. What about a less well made one? Would only take less than 1% loss per cycle to help fix up the energy budget. Wish I could think of a way to measure it. You're right, I think the forces could be calculated, but I don't know how to go on to calculate the movement and energy loss. > There is also corona around the coils and stuff here and there (like off > the tope edge of the secondary) that is a loss that may be significant. > the field stress plots coming up will show these points. No, in this case the un-accounted loss is present for small signals. One way or another the measured Q almost always comes out well below the figure based just on the Medhurst resistance and an allowance for drive impedance and ground resistance. There's a portion, in my case around 40%, that remains unknown. Marco has a similar portion, and we still have the mystery of your sonotube loss. Can Medhurst be out by a factor of two? Have to think about some AC resistance measurements. In the end I'll get my big coil running and see what heats up :) CHeers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.