From: "Terrell W. Fritz"
Date: Fri, 25 May 2001 17:34:36 -0600
Subject: Re: [TSSP] Loss due to ultrasonic mechanical vibration of
Hi Paul, At 12:18 AM 5/26/2001 +0100, you wrote: >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. I would think the frequency is equal, not two times but... > >> 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. I think the RF generator has a 80Hz input bandwidth. I should be able to hear that. Have to figure out which input pin controls that. I also posted a note to the Tesla list on this. We'll see what turns up. > >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. F=MA, V=FT (?) and all the physics stuff I forget at the moment. But that is all for freely moving objects as opposed to wire imbedded in poly... > >> 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. Oh!! >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. Hmmmmmmmm... > >In the end I'll get my big coil running and see what heats up :) Cheers, Terry > >CHeers, >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.