TSSP: List Archives

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.