[SI-LIST] Re: Current Flow
- From: Dave Instone <dave.instone@xxxxxxxxxx>
- To: levinpa@xxxxxxxxxxxxx
- Date: Wed, 10 Aug 2005 16:30:20 +0100
Less transmission line discontinuities?
Paul Levin wrote:
>Dear Agathon,
>
>Perhaps you could give some more thought to this analogy and explain how
>this manages to happen in high school gymnasiums where no beer is sold,
>and where (presumably) very few of the participants have consumed any
>beer at all. Some of the best waves that I have seen occurred in these
>circumstances.
>
>Regards,
>
>Paul
>________________
>
>Ken Cantrell wrote:
>
>
>
>>"BeerWavefront Impedance" - I'll be laughing about that one for a while. If
>>you start doing standup, let me know.
>>
>>-----Original Message-----
>>From: si-list-bounce@xxxxxxxxxxxxx
>>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of HreidmarKailen
>>Sent: Wednesday, August 10, 2005 2:47 AM
>>To: scott@xxxxxxxxxxxxx; doug@xxxxxxxxxx
>>Cc: steve weir; si-list@xxxxxxxxxxxxx
>>Subject: [SI-LIST] Re: Current Flow
>>
>>
>>I have a good analogy...
>>You know "the wave" that's performed ad hoc at football, and other, arenas
>>by the fans?
>>
>>Well, to simplify, each rank of humans, perdendicular to the direction of
>>wave travel, decide in unison to stand up, raise their
>>arms, and think beer-influenced thoughts. They must use some energy to move
>>and wave.
>>
>>Some strange interaction among these humans causes the next rank to do the
>>same, and so forth. Something very human.
>>
>>The result is something that travels around the arena, sure as the sky is
>>blue, well controlled by the gravity block of the floor
>>which serves to make constant the wavefront size, as long as each rank is a
>>clone of the last and has consumed the same requisite
>>portion of beer. Occasionally, a frankfurter outgassing or the tipsy human
>>scattering off a chair can disturb perfection. Anyway,
>>the result is a constant beer to wavefront ratio -- let's call that the
>>BeerWavefront Impedance.
>>
>>Back to the wave... Said wave proceeds, as seen from the Blimp, quite
>>nicely around the bend. All electrons, er ... humans, are
>>happy. It's a community.
>>
>>Well, that's all folks. The wave proceeds --- a flow of energy. It's
>>really cool.
>>
>>The electrons move little, some up/down some towards the ones they're
>>inspiring to imitate them. At the terminus of the arena
>>seats the last rank typically "matches" the wave by terminating it
>>perfectly. At some later time, the same - or other - instigators
>>will try the same thing, to varying degrees of success. The driver must be
>>a low impedance source of beer, or the result is likely
>>to be an under or over-driven Wave.
>>
>>How can it be that electrons and humans are so alike??
>>
>>Yours,
>>Agathon
>>
>>
>>----- Original Message -----
>>From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
>>To: <doug@xxxxxxxxxx>
>>Cc: "steve weir" <weirsi@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
>>Sent: Friday, August 05, 2005 3:51 PM
>>Subject: [SI-LIST] Re: Current Flow
>>
>>
>>
>>
>>
>>
>>>Enough.
>>>Electrons do not flow down a a PCB trace, electromagnetic fields, which
>>>propagate as waves, do. Electrons do not flow across the plates of
>>>capacitors, but an electromagnetic field does. We can model traces,
>>>plates, transmission lines, cables ... etc as resistors, capacitors and
>>>inductors, but do not forget that they are just that, models.
>>>
>>>If we were talking about light traveling down a piece of fiber, between
>>>mirrors, through windows ... etc, no one would have a problem with a
>>>wave or particle scattering model. Nor would anyone invoke capacitor
>>>bucket brigade models to explain the signal propagation and "return
>>>path." It would be intuitively obvious to anyone that the light will
>>>scatter off of, and be constrained by, reflecting boundaries (return
>>>path.) With light, does anyone have a problem understanding how a
>>>signal can be launched and become totally disconnected from the
>>>launching ground reference? Yet, so many people have a problem
>>>understanding that an electronic signal is an electromagnetic wave
>>>(light), traveling through a medium (dielectric), and is constrained by
>>>boundaries (metal), which either guide the signal, or reflect it. Once
>>>the signal is launched as an EM wave, the original ground, and voltage,
>>>that was used by the transistor, does not matter. The signal (wave) has
>>>a life of it's own, and is constrained only by the metal around it. As
>>>long as all the metal used to guide the wave is continuous, you usually
>>>have a very good transmission medium. As soon as there is a break or
>>>disruption in the guiding metal, serious problems arise. Usually this
>>>break or disruption occurs in what we call the "return path." However,
>>>make no mistake. There's no such thing as far as the EM wave is
>>>concerned. All it knows is that it is following a bunch of metal around
>>>in what we call the path of least impedance. Yank the metal out from
>>>under it along the signal conductor or the "return path" conductor, and
>>>it will find a better path, instantaneously.
>>>
>>>One you look at electronic signals as propagating waves, understanding
>>>them becomes much easier than other oversimplified models. As the wave
>>>travels down a trace on a board, it is very easy to envision the EM
>>>field "touching" the plane and trace, which guide it, and enveloping
>>>itself around the trace and extending off into the infinite universe.
>>>One can imagine what happens when a signal passes down a via and past
>>>planes, and how some of the "light" will leak into each of the planar
>>>cavities, and ripple back and forth, like waves on a pond.
>>>
>>>Scott McMorrow
>>>Teraspeed Consulting Group LLC
>>>121 North River Drive
>>>Narragansett, RI 02882
>>>(401) 284-1827 Business
>>>(401) 284-1840 Fax
>>>
>>>http://www.teraspeed.com
>>>
>>>Teraspeed® is the registered service mark of
>>>Teraspeed Consulting Group LLC
>>>
>>>
>>>
>>>Doug Brooks wrote:
>>>
>>>
>>>
>>>
>>>
>>>>At 02:18 PM 8/5/2005, you wrote:
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>Doug,
>>>>>
>>>>>In the fluid model, we would see current propagate down the signal
>>>>>conductor and then later back in the return lead would we not?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>That's why I said I didn't think "fluid" was the best descriptor. As I
>>>>tried to point out the first time, electrons start flowing down the line,
>>>>onto the "plates" of the distributed capacitance, repelling electrons
>>>>
>>>>
>>>>
>>>>
>>(like
>>
>>
>>
>>
>>>>charges repel) from the other "plates" of the distributed capacitance,
>>>>
>>>>
>>>>
>>>>
>>and
>>
>>
>>
>>
>>>>back, completing the loop. As the first "plates" charge up, the current
>>>>flows past them and charges the next "plates". By the time the current
>>>>
>>>>
>>>>
>>>>
>>gets
>>
>>
>>
>>
>>>>to the end if the line, all the "plates" are charged up, and the flow
>>>>
>>>>
>>>>
>>>>
>>looks
>>
>>
>>
>>
>>>>like a DC flow would look. This is exactly what Figure 7-19 in Bogatin's
>>>>book is describing. You describe this from the standpoint of "waves". I
>>>>can equally well (no better, no worse) describe it as electron flow. I
>>>>don't see a difference and I don't see a problem.
>>>>
>>>>The "fluid flow" model breaks down because we can't envision fluid
>>>>
>>>>
>>>>
>>>>
>>crossing
>>
>>
>>
>>
>>>>between the plates of a capacitor. But electron flow CAN cross the plates
>>>>of a capacitor because of the property that "like charges repel each
>>>>other." Electrons don't physically cross the space between the plates,
>>>>
>>>>
>>>>
>>>>
>>but
>>
>>
>>
>>
>>>>they build up on one side and repel those on the other, so that the same
>>>>number of electrons return to the source as left it.
>>>>
>>>>Doug
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>But in real life, we observe that current propagates in one polarity
>>>>>
>>>>>
>>>>>
>>>>>
>>from
>>
>>
>>
>>
>>>>>the signal conductor portion of the wave guide, and simultaneously in
>>>>>
>>>>>
>>>>>
>>>>>
>>the
>>
>>
>>
>>
>>>>>opposite polarity from the return conductor side of the wave guide. The
>>>>>fluid flow model has problems both with time, and with the fact that the
>>>>>wave propagates down an infinitely long open transmission line just as
>>>>>well as it does an end terminated line. In the open, or infinite length
>>>>>line electrons never passed from one conductor to the other.
>>>>>
>>>>>How does a circular fluid flow analogy model this behavior? At the far
>>>>>end of an open transmission line the conduction path is broken, the
>>>>>
>>>>>
>>>>>
>>>>>
>>fluid
>>
>>
>>
>>
>>>>>has no contiguous path.
>>>>>
>>>>>We can agree that electrons in the conductors move in response to the
>>>>>propagating fields, sic wave. But I have to reiterate that back at our
>>>>>switch it is the fields interacting with the conductors that push on
>>>>>
>>>>>
>>>>>
>>>>>
>>those
>>
>>
>>
>>
>>>>>electrons you observe moving in the conductors. When the dv/dt switches
>>>>>direction later in time, the charge will go the other way in each
>>>>>conductor, but as far as charge between the two conductors: never the
>>>>>twain shall meet.
>>>>>
>>>>>Regards,
>>>>>
>>>>>
>>>>>Steve.
>>>>>
>>>>>At 02:12 PM 8/5/2005 -0700, Doug Brooks wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>(I have changed the subject line to better represent what I think we
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>are
>>
>>
>>
>>
>>>>>>talking about.)
>>>>>>
>>>>>>You raise an excellent example. Let me deal with the two points.
>>>>>>
>>>>>>1. I'm not sure I understand what you are getting at here. The focus
>>>>>>should be at the point of the switch.
>>>>>>
>>>>>>2. I have introduced the problem in some of my transmission line
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>classes
>>
>>
>>
>>
>>>>>>that deal with point 2. Assume that (a) there is a propagation time for
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>a
>>
>>
>>
>>
>>>>>>signal, (b) current (i.e. electrons) flows in a closed loop, (c)
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>current
>>
>>
>>
>>
>>>>>>is constant everywhere in that loop ---- aren't these mutually
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>exclusive
>>
>>
>>
>>
>>>>>>conditions? The answer is no! The current flows down the transmission
>>>>>>line from one side to the other through the distributed capacitance (as
>>>>>>suggested in Bogatin's Figure 7-19). This is a current flow (i.e.
>>>>>>electron flow) picture. If you want to call it a wave flow, well that's
>>>>>>fine. But you can also describe it as current (electrons) flowing to
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>the
>>
>>
>>
>>
>>>>>>point of the distributed capacitance, repelling charge away from the
>>>>>>other side of the capacitance back to the beginning of the line,
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>charging
>>
>>
>>
>>
>>>>>>the capacitance up (with electrons) along the way. At the steady state,
>>>>>>current (electrons) is flowing in the DC loop we would expect. If we
>>>>>>don't have a transmission line ---- well, we always have a transmission
>>>>>>line of sorts. The question is whether it's ideal or REAL crummy. There
>>>>>>is always a characteristic impedance, even if it is only that of air.
>>>>>>
>>>>>>So the "fluid" analogy (I don't think that's the best descriptor) can
>>>>>>deal with this issue perfectly fine. Likewise, it can deal with the
>>>>>>crosstalk coupling issue equally as well. (I don't have a figure like
>>>>>>Eric's in my book, but there is a very detailed illustration of how
>>>>>>crosstalk coupling works in my book that doesn't need Maxwell and wave
>>>>>>theory to understand.)
>>>>>>
>>>>>>So I don't see the difficulty here.
>>>>>>
>>>>>>Doug
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>At 01:18 PM 8/5/2005, steve weir wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Doug, in the fluid model, there are two misleading elements:
>>>>>>>
>>>>>>>1. The focus is on the source of EMF, sic the battery,
>>>>>>>2. It implies a time lag between the foward current starting from some
>>>>>>>point and the matching return current closing that path.
>>>>>>>
>>>>>>>If we take the switch example you offered, one might imagine a couple
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>of
>>
>>
>>
>>
>>>>>>>different cases:
>>>>>>>
>>>>>>>a. The switch is located very close to one terminal of the battery and
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>a
>>
>>
>>
>>
>>>>>>>say 300m wire connects it to the other through some load resistor.
>>>>>>>b. The switch is located at the end of two 300m wires back to the
>>>>>>>battery through some load resistor.
>>>>>>>
>>>>>>>Now, what will each the fluid analogy, and wave propagation tell us
>>>>>>>about each case? Where does each model show the propagation beginning
>>>>>>>and ending? How accurate is each? Which model can explain behavior
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>from virtual DC to any frequency we like? I don't think it's the
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>fluid
>>
>>
>>
>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>analogy.
>>>>>>>
>>>>>>>On a PCB with switching I/Os the time and distance scales have changed
>>>>>>>but not the behavior. What we have is in essence case b from
>>>>>>>above. The wave emanates from the switches in our ICs, not from the
>>>>>>>power supply. The wave model makes this clear, as it does the
>>>>>>>propagation path. The wave model makes clear the critical point that
>>>>>>>the return and forward currents propagate together. The fluid analogy
>>>>>>>with its unidirectional emphasis fails us badly.
>>>>>>>
>>>>>>>Where has the fluid analogy brought us? How many times have you seen
>>>>>>>people talk about bone-headed ideas like the PCB planes or bypass
>>>>>>>capacitors supplying current to high speed edges, when the entire edge
>>>>>>>has completed long before the wave front through power pins can reach
>>>>>>>significant charge in the planes, much less even reach the PWB bypass
>>>>>>>caps? Yet this kind of junk mythology sadly makes its way into books
>>>>>>>and other publications on a regular basis. I don't like it one bit.
>>>>>>>
>>>>>>>For my money, I find the fluid analogy terribly misleading, and a
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>source
>>
>>
>>
>>
>>>>>>>of much misunderstanding. One doesn't need to be able to derive
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>Maxwell
>>
>>
>>
>>
>>>>>>>to understand wave propagation. I think that as Eric's book
>>>>>>>demonstrates, most SI concepts are not that difficult to
>>>>>>>understand. Even a dummy like me gets them from time to time.
>>>>>>>
>>>>>>>Regards,
>>>>>>>
>>>>>>>
>>>>>>>Steve.
>>>>>>>At 12:51 PM 8/5/2005 -0700, Doug Brooks wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>A couple of people have interpreted my statement re "flow" of
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>electrons
>>
>>
>>
>>
>>>>>>>>as meaning electron drift. Let's kill that right now.
>>>>>>>>
>>>>>>>>One electron in = one electron out is the flow of electrons. One
>>>>>>>>electron in = SAME electron out is electron drift --- not at all the
>>>>>>>>same thing.
>>>>>>>>
>>>>>>>>Certainly I don't argue against Maxwell's equations. But I don't
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>argue
>>
>>
>>
>>
>>>>>>>>against the fundamental definition of one amp of current either ---
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>the
>>
>>
>>
>>
>>>>>>>>flow of one coulomb of charge (6.25 x 10^18 electrons) across a
>>>>>>>>surface in one second. I spend a lot of time with engineers (and
>>>>>>>>technicians) who never took Maxwell's equations and didn't understand
>>>>>>>>them if they did. My goal has been to take our difficult SI concepts
>>>>>>>>and explain them in terms that these "poor" people can understand. To
>>>>>>>>suggest that you can't explain what happens during planar transitions
>>>>>>>>without Maxwell's equations (I believe) is simply wrong. To say that
>>>>>>>>the classical description of current can't explain the difference
>>>>>>>>between DC and high frequency is also (I believe) flat wrong. To say
>>>>>>>>that one description is "more accurate" than the other --- well I
>>>>>>>>suggest that depends a lot on whose working with them! And while
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>people
>>
>>
>>
>>
>>>>>>>>have been misled by seminar leaders teaching without the benefit of
>>>>>>>>Maxwell's equations, we all know seminar leaders whose ability to
>>>>>>>>mislead wasn't one bit hampered by a thorough knowledge of Maxwell's
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>equations!
>>
>>
>>
>>
>>>>>>>>Don't sell these more basic principles short when it comes to
>>>>>>>>understanding what is happening on circuit boards. They can very
>>>>>>>>effectively explain what is happening, and why one design approach
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>may
>>
>>
>>
>>
>>>>>>>>be more effective than another depending on the important design
>>>>>>>>considerations. Especially for all those board designers who have no
>>>>>>>>knowledge of Maxwell and wave theory.
>>>>>>>>
>>>>>>>>Doug
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>At 12:01 PM 8/5/2005, steve weir wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>Doug, well I am going to argue vehemently that until someone repeals
>>>>>>>>>Maxwell that the wave description is fundamentally more accurate
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>than the
>>
>>
>>
>>
>>>>>>>>>fluid analogy. The E/M fields cause the electron drift in those
>>>>>>>>>wires. From the time you closed the switch the changing E/M field
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>that
>>
>>
>>
>>
>>>>>>>>>resulted propagated outward. Marconi found a useful purpose for
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>that
>>
>>
>>
>>
>>>>>>>>>phenomenon.
>>>>>>>>>
>>>>>>>>>The fluid analogy is certainly easy to understand, but what is the
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>point
>>
>>
>>
>>
>>>>>>>>>when it is so misleading? I can't tell you how many times otherwise
>>>>>>>>>intelligent engineers that I have known have been thrown off
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>understanding
>>
>>
>>
>>
>>>>>>>>>PCB wave guides, because they were intent on following the DC
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>current loop
>>
>>
>>
>>
>>>>>>>>>of the fluid analogy.
>>>>>>>>>
>>>>>>>>>Teaching the fluid analogy requires that we later break that
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>teaching when
>>
>>
>>
>>
>>>>>>>>>we want to explain what happens at significant frequencies.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>Consider for
>>
>>
>>
>>
>>>>>>>>>instance visualization of return current ( which is the original
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>subject
>>
>>
>>
>>
>>>>>>>>>matter ) when we transition planes in a PCB. If we think about it
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>as a
>>
>>
>>
>>
>>>>>>>>>fluid model we are easily misled into searching out a conduction
>>>>>>>>>path. For
>>>>>>>>>ready examples of this mass confusion, just look at some of the
>>>>>>>>>discussions
>>>>>>>>>on splitting-up grounds in the wrong ways for the wrong reasons,
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>with the
>>
>>
>>
>>
>>>>>>>>>wrong results. But if we simply consider waves to begin with, then
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>the
>>
>>
>>
>>
>>>>>>>>>behavior is easy enough to intuit out.
>>>>>>>>>
>>>>>>>>>Eric does a very nice job in his book explaining signal propagation
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>that
>>
>>
>>
>>
>>>>>>>>>does not rely on the fluid analogy. I think his approach is very
>>>>>>>>>accessible.
>>>>>>>>>
>>>>>>>>>Regards,
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>Steve
>>>>>>>>>At 11:21 AM 8/5/2005 -0700, Doug Brooks wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>With all due respect, Steve, if I have a battery connected to a
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>transistor
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>through a switch, I can turn the transistor "on" and "off" with the
>>>>>>>>>>switch. That is easy to explain using the electron flow concept
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>(which I
>>
>>
>>
>>
>>>>>>>>>>hesitate to call an analogy, it in fact describes the physics
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>involved).
>>
>>
>>
>>
>>>>>>>>>>Is your description more complete AND also easier to understand?
>>>>>>>>>>
>>>>>>>>>>And if it is the frequency with which I "flip" the switch that
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>bothers
>>
>>
>>
>>
>>>>>>>>>>you, that simply means that some of the parameters that were not an
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>issue
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>with slow "flipping" (inductance and capacitance, for example)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>start
>>
>>
>>
>>
>>>>>>>>>>becoming more of an issue with faster "flipping!" But the basic
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>nature of
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>what is happening (in particular where the electrons are flowing)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>is not
>>
>>
>>
>>
>>>>>>>>>>changing, just speeding up. (How the electrons are flowing is
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>speeding up,
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>the electrons themselves, of course, don't change speed!)
>>>>>>>>>>
>>>>>>>>>>Doug
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>At 10:45 AM 8/5/2005, steve weir wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>Doug, I have some real heartburn with some of those
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>representations,
>>
>>
>>
>>
>>>>>>>>>>>particularly the fluid analogy that speaks of current as the flow
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>of
>>
>>
>>
>>
>>>>>>>>>>>electrons. When I grew up current was defined as time variation
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>of
>>
>>
>>
>>
>>>>>>>>>>>electric flux. When an E/M field impinges a chunk of metal the
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>resulting
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>interaction concentrates the field forming a wave guide. All
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>practical
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>wave guides leak, be they a microstrip over a plane, a stripline,
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>or
>>
>>
>>
>>
>>>>>>>>>>>whatever. Some, like a good semirigid coax leak only a little
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>tiny
>>
>>
>>
>>
>>>>>>>>>>>bit. When they leak too much creating excessive disturbance in
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>nearby wave
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>guides, we have cross talk problems. I hope that this is what you
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>were
>>
>>
>>
>>
>>>>>>>>>>>trying to convey.
>>>>>>>>>>>
>>>>>>>>>>>Regards,
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>Steve.
>>>>>>>>>>>
>>>>>>>>>>>A
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>Check out UltraCAD's new presentation videos and new skin effect
>>>>>>>>>>calculator at http://www.ultracad.com
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>------------------------------------------------------------------
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>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>field
>>
>>
>>
>>
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>>>>>>>_______________________________________________________________________
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>_____-
>>
>>
>>
>>
>>>>>>>>Check out UltraCAD's new presentation videos and new skin effect
>>>>>>>>calculator at http://www.ultracad.com
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>_________________________________________________________________________
>>>>>
>>>>>
>>>>>
>>>>>
>>___-
>>
>>
>>
>>
>>>>>>Check out UltraCAD's new presentation videos and new skin effect
>>>>>>calculator at http://www.ultracad.com
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>___________________________________________________________________________
>>>
>>>
>>>
>>>
>>_-
>>
>>
>>
>>
>>>>Check out UltraCAD's new presentation videos and new skin effect
>>>>
>>>>
>>>>
>>>>
>>calculator
>>
>>
>>
>>
>>>>at http://www.ultracad.com
>>>>
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