[SI-LIST] Re: FEM/BEM/MoM

Hello Lin

The real switch closes very fast, but not instantaneously.  At some point,
the gap is very small and there is an arc due to the gas breakdown at very
large electric field intensity.  This produces a very rapidly increasing
current with significant high frequency content (GHz).  Gas discharge
produces a lot of interference, as you will see if you wave a scope probe
near a fluorescent light tube.  The frequencies are mainly down in the MHz
range because the tube is larger than the switch.  At the high frequencies
involved in the switch, experience shows that the RF losses are highly
significant, partly due to skin effect and also dielectric losses.  The
result is conducted heat plus high frequency radiation.  As someone pointed
out there could also be a non-reversible (destructive) mechanical change,
but I think we designed the switch and conductors to cope.  I once saw some
high power starting gear down below in a large boat - frightening! 

Cheers
Geoff

> -----Original Message-----
> From: Lin Li [mailto:lilin@xxxxxxxxxxxxx]
> Sent: 28 August 2003 20:31
> To: gary_pratt@xxxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: FEM/BEM/MoM
> 
> 
> Heat transformation is not likely to happen unless the switch 
> cable has very
> large resistance.
> 
> We know at the moment of the electrons transfer, there will 
> be a transient
> which will induce radiation. That is where the energy goes.
> 
> I cannot deny heat effect but it is minor.
> 
> Best,
> 
> Lin
> **********************
> Lin Li
> Ph.D. candidate
> 3123 Glenn Martin Hall
> Mechanical Engineering
> University of Maryland
> College Park, MD 20742
> Ph: 301-405-5588
> ***********************
> 
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Pratt, Gary
> Sent: Thursday, August 28, 2003 1:08 PM
> To: arafi001@xxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: FEM/BEM/MoM
> 
> 
> The quarter-Joule turns into heat when the switch is vaporized into a
> cloud of smoke.
> Whats the paradox?
> 
> Gary L. Pratt, P.E.
> Product Manager
> High-Speed Design Kits
> Mentor Graphics
> (503) 685-1177
> gary_pratt@xxxxxxxxxx
> 
> 
> 
> 
> -----Original Message-----
> From: Abdulrahman Rafiq [ mailto:arafi001@xxxxxxx
> <mailto:arafi001@xxxxxxx> ]
> Sent: Thursday, August 28, 2003 12:36 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] FEM/BEM/MoM
> 
> 
> Geoff,
> 
> Could you ellaborate on this a little more, as I am afraid i
> can't quite see what happened to the 1/4 Joule of energy.
> Perhaps if you could do a quick back of the envelope
> calculation as an example.
> 
> -----------------
> 
> Just a little diversion to show the error in a schematic:
> An old example often quoted is the problem of connecting two
> one farad
> capacitors together by a switch; one is at 1V potential, the
> other zero.
> The initial energy is 1/2 CV**2 =3D 0.5 joule.  After closing
> the switch th=
> ere
> is charge distribution, and energy =3D 1/8 +1/8 =3D 0.25
> joule.  Where did =
> the
> missing 0.25 joule go?  If you did an electrical degree,
> you'd see the
> paradox.  If you studied high frequencies, you'd know the
> answer.  (I did a
> Physics degree, then built RF circuits, so for me a capacitor
> is not a
> capacitor.)
> 
> The answer is
> 1) it's not physically possible to put two capacitors
> together at one point
> 2) therefore they are separated by a distance
> 3) therefore on closing the switch, the discharge current
> travels a distance
> 4) the conductors have finite conductivity
> 5) therefore there is a varying electromagnetic field and
> energy is
> dissipated and radiated
> 6) please don't talk about too much about inductance because
> it's only an
> approximation.
> -------------------
> ---------------------------------------
> Abdulrahman Rafiq
> Department of Physics
> University of California
> Riverside, Ca. 92521
> Email: arafi001@xxxxxxx
> URL: www.geocities.com/arafiq786
> --------------------------------------
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