Does Displacement Current Exist?
By Jack L. Stone, Publisher
he
November 2002 issue #67 included Part 1 of the feature article “Displacement Current
Does Not Exist” By William C. (Bill) Miller, KT4YE. I advised Bill to be braced for
some strong reactions to his controversial subject. Sure enough, we had a flurry of
messages exchanged with many of them appearing on the Antenna Theory III Forum—a
very appropriate place for this kind of discussion. For those who haven’t yet visited
the Forums, you should take the time to do so as you will certainly find something of
interest among the thousands of postings there within the 23 separate Forums (19
ready-only and 4 are active for postings). One will find just about every conceivable
subject covered since the Forums were started in May 1997. There is also a search tool
that can help you quickly find a subject or key word.
Back to Bill’s article about displacement current. This is a very important aspect of
the premises for the workings of capacitor-type antennas in the efforts to explain how
they work—and if they do work as claimed. There are many assertions about how these
antennas (or devices) work. Specifically, we would be referring to the CFA, EH, etc. that
are considered as classified among the capacitor types. Although the inventors/makers of
the antennas are quick to tell us how they work with convincing confidence about the
theories, some are not yet so sure we have the whole answer which brings up the subject of
displacement current. This is a very interesting area to open up for discussion, for if we
don’t delve into such theories, we will never find the absolute answer(s). Bill is to
be applauded for having the intestinal fortitude (guts!) to write the article as it
generates very healthy discussions, which in turn helps us all better understand such
theories. Granted, feelings may run deep and strong. Bill’s 2-part series is
well-presented and demonstrates how one may easily take a position for or against the
existence of displacement current. One very good response came from Professor D’Amico
and a link is provided here because the response came in the form of a PDF and with its
many equations and Greek symbols, is best kept in that PDF format. You are invited to
first read the Professor’s response to Bill’s article and then read Bill’s
rebuttal to the response reproduced below.
| Michele D’ Amico
is Associate Professor in Electromagnetic Fields at University Politecnico di Milano,
where he teaches Electromagnetic Fields, and “Antennas and Propagation”. He
holds a Ph.D. in Mathematics from the University of Essex (UK). He has authored 2 books
and more than 60 technical and scientific publications. |
>> CLICK HERE FOR COMMENTS BY PROF. D’AMICO << |
Bill Miller’s comments on Professor
D’Amico’s comments about his antenneX article in the November 2002 issue #67:
Displacement
Current Does Not Exist
Part 1: The Capacitor and Displacement Currents
By William C. (Bill) Miller, KT4YE
In the set of equations presented,
Professor D’Amico has established a fascinating proposition. By postulating that
Displacement Current does not exist, and using Maxwell’s Equations to check the
consequences, he has proven that a circular, parallel plate transmission line (and by
extension, all classes of parallel transmission lines) does not exist. After all,
transmission line theory neither requires nor supports the concept of Displacement
Current.
There are several issues here. Professor D’Amico has suddenly introduced an entirely
new phenomenon – “relaxation time” – into the discussion. In the model
we are discussing, this phenomenon does not exist. We would welcome seeing a capacitor
model that incorporates the theoretical basis for this phenomenon, thus proving that
– with the implementation of “relaxation time,” the E fields suddenly
become uniform.
Professor D’Amico is correct in stating that drift velocity is not the phenomenon
that “spreads” the electromagnetic perturbation along the conductor. However,
there are still some people that believe that this is how current flows. (The author is
not one of them.)
By pointing out that perturbations do not move instantaneously, but at near light-speed,
Professor D’Amico is acknowledging that the E Fields between the plates of a
capacitor ARE NOT UNIFORM. If the fields are not uniform, then any derivation using that
assumption is fatally flawed. That is the basis of the author’s proposition, and the
author thanks Professor D’Amico for acknowledging the validity of this basic concept.
Professor D’Amico is correct in assessing this effect as being of secondary value.
But, with differential voltages on the same conductor, E fields from one point on the
conductor to another point on the same conductor MUST exist.
By attacking the author’s knowledge of the phenomenon (or the measurement tools).
Professor D’Amico neatly sidesteps the problem. (Ad homonym arguments are often used
when there is no valid argument to be made against the proposition, aren’t they?)
Classical theory REQUIRES infinite current flow when a step voltage is applied. This flaw
is neither addressed nor explained by Professor D’Amico.
Professor D’Amico’s proposition can be summarized as, “If it works, it must
be OK.” As a graduate engineer himself, the author has no problem with this concept
– as long as the proposition continues to work. In virtually all Electronic
Engineering, the presence or absence of Displacement Current is TOTALLY UNIMPORTANT to the
design’s integrity.
This is NOT TRUE in antenna design. A variety of failed or flawed antenna designs are
based in whole or in part on the existence of Displacement Current. Thousands of man-hours
and much larger sums of money have been invested in (so far) futile attempts to
“use” Displacement Current. The author asserts that one of the following two
propositions must be true:
a) Quite a number of skilled and experienced theoreticians AND artificers are utter fools
at their trades, or
b) The basic theory is flawed
Stateside, when a child loses a tooth, he or she places it under the pillow and, late at
night, the “tooth fairy” retrieves it and leaves some money. This is a
delightful myth. The tooth disappears and the child becomes richer. And the belief in the
tooth fairy does no harm to the child – unless the child decides to get even richer
by pulling all his (or his sibling’s) teeth en masse!
Displacement Current is also a delightful myth. Unlike the tooth fairy myth, it works in
almost all applications. But let us not pretend it exists for ALL applications, lest we be
like the child who, upon pulling his siblings teeth, learns that disappointment and pain
– not riches – is the reward.
As a closing comment, the author would like to welcome Professor D’Amico, and all
other interested parties, to review the second half of the article. In this, we believe
that we demonstrate that the correct model for the capacitor is a transmission line
launching a TEM wave.
William C. (Bill) Miller, KT4YE
Part 2 of Bill’s article appears in this
month’s issue #68 for December 2002:
Part 2: The Transmission Line as a Capacitor
and the Elimination of Displacement Currents
SILENT KEY
L.B. Cebik, W4RNL is not only a good friend, but has been a regular member of the writing
team here for more than five years and more recently became our Technical Editor as well.
It was only a few short months ago in my July 2002 column that I mentioned the passing in
June of LB’s Dad (96), James S. Cebik, ex: 1ATG, W1BUK, KA1TXF Sadly, tragedy has
visited LB’s home again all too soon with the untimely passing of his beloved spouse,
Jean on November 4, 2002.
 In memory of:
Mrs. Jean R. Cebik, N4TZP
SK: November 4, 2002
 Mrs. Jean Robeson Cebik, N4TZP, was the wife of L. B. Cebik,
W4RNL. A life-long resident of the Knox County, Tennessee, she passed away Monday,
November 4, 2002, at the age of 59 after a 13-month struggle with cancer. Jean worked for
many years at the University of Tennessee and at Technology for Energy before returning to
UT and earning a master's degree in French literature. Afterwards, she taught a number of
years at Pellissippi State College and then retired to become a licensed wild songbird
rehabilitator. In addition, she was an accomplished craftsperson and an amateur radio
operator.As her final wish,
Jean requested that individuals plant a tree or shrub in their yards to support the
songbirds that she so much loved and so ably rehabilitated.
The dedication that appears in each of LB's volumes of antenna studies bears witness to
Jean's importance to his life and work:
"All of the volumes of my antenna studies are dedicated to my wife, my friend, my
supporter, and my colleague, all of whom are Jean. Her patience, understanding, and
assistance gave me the confidence to retire early from academic life to undertake
full-time the continued development of my web site (http://www.cebik.com). The site is
devoted to providing, as best I can, information of use to radio amateurs and others--both
beginning and experienced--on various antenna and related topics. Each volume grew out of
that work--and hence, shows Jean's help at every step." |
As a follow-up, LB reports that Jean's wish that folks
plant a shrub or tree for songbirds and other wildlife has really taken root. Perhaps up
to 200 plantings will occur because the note hit both amateur radio and rehabilitation
lists, websites, etc. One Australian Ham is planting a Golden Wattle so that, in
conjunction with US plantings, the sun will never set on her work or memory. A planting by
the regional rehabilitation group at a local nature center was to occur on the first
Saturday of December 2002, with a likely local newspaper story on it to appear as well.
Also, the International Wildlife Rehabilitation Council will publish information on Jean
and her wish in its on-line journal. We only wish that she could be here to see the
outpouring of response to her last wish.
Working closely as I do with LB, I was privy to Jean's
illness to an extent over this past year and my heart truly went out to them in this time
of distress. At times like this, words at best ring hollow in comparison to the feelings
of deep dispair within their home. LB has many friends around the world and I am confident
they join me is wishing him well and extending spiritual support in his time of grief and
healing.
The above is one of LB’s favorite pictures of
Jean. Vaya Con Dios, Jean…..
HOW’S K5CNF?
As many of the readers know, Richard Morrow, K5CNF has been in involved as an experimenter
and technical writer with antenneX since it was founded in 1988. Richard has been
going through some tough times with his own health and we very nearly had another silent
key had he delayed medical attention by a few more hours! Richard was rushed to the
hospital at 3:00am on or about July 15, 2002 and spent the next two months or more there
after undergoing critical major surgery. While he is now back home, he still cannot spend
any time at the office and is scheduled for more surgery soon and another stay at the
hospital. Then, more recovery is needed. Richard hopes to be able to produce some more
articles from much-delayed projects in time for the January or February 2003 issue. We
surely hope so as his contributions are missed.
SEASONS' GOOD WISHES
With over 180 countries counted among the readership, this is indeed an
International audience and I understand that this last month of the year and the turn to
the New Year are celebrated differently. The past year has been filled with struggles,
tragedy and adversity for some while others may have found great enjoyment in various
forms. This marks our 6th season and "turn of the year" together online and no
matter which fate has been dealt you in the past, it is my sincere wish for all to enjoy a
happy and prosperous 2003. This is a wonderful readership and I enjoy making contact when
the opportunity arises—so, to all who celebrate this occasion at this time, I wish a
Merry Christmas and a Happy New Year! — Jack L. Stone
>> Let Santa fill your stocking
from the Shopping Shack Shelves! <<
Buy yourself or a friend an Xmas gift from
our store!
| Subscription | Books | Software | Antennas | Electronics |
Components |
IN THIS ISSUE
This month is our 68th online issue! We again include many fine articles by our
great writing team. Now, allow me now to introduce this month's line-up of content:
THE DECEMBER 2002 ONLINE ISSUE NO. 68 CONTENTS:
OUR MONTHLY COLUMNS (plus this one by yours
truly):
- From the Shack By F.M. Kabbary
Microscopic & Macroscopic Field Reaction & Vortices
In this editorial, Dr. Kabbary proposes to show the difference between the microscopic
and macroscopic field reactions of the radiating antenna. He also believes it explains and
confirms that it is vortices that propagate and not waves that propagate.
- Antenna Modeling By L. B. Cebik, W4RNL
Some Basic Guideline Graphics for NEC
LB says that over the years since starting this column, he has had requests
for a listing of basic guidelines and limits applicable to NEC. LB has had occasion to
create some presentation graphics covering some of this information and presents them in
this column.
- Ham WorkShop By
L. B. Cebik, W4RNL
Notes on Hatted Vertical Dipoles for 10 Meters
The search for compact antennas--especially vertically polarized antennas--has taken many
turns. However, one of the simplest and cheapest to construct is the vertical dipole with
so-called "capacity hats" on each end. This article looks at what is involved in
designing and building such an antenna. The design is based on others that LB has built,
including horizontally polarized 2-element Yagis.
- Propagation By
Marcel H. de Canck, ON5AU
Oblique Angle Propagation Part 2
In part 1 of oblique angled propagation, Marcel made a study of the
critical angles for each HF ham band. That study was made for midday time only and with
TOA’s from zero degrees to forty-five degrees, in five degrees steps. The exercise
gives an idea of how oblique angled propagated waves behave during the midday time. But
the wave behaviors and the critical angles will be completely different at other times of
the day or night. In this month's issue, we study the critical angles during a twenty-four
hours period at the same location. Marcel has included the results via animations with his
propagation wizards.
FEATURE ARTICLES IN THE LIBRARY:
Notes
on 6-Element Wide-Band 2-Meter Yagis
By: L.B. Cebik, W4RNL |
| In several past notes, LB discussed a VHF antenna to which he has some
partiality. The antenna is a 6-element Yagi that covers all of 2-meters with at least 10
dBi free-space gain, at least 20 dB 180- degree front-to-back ratio, and better than 1.2:1
50-Ohm SWR from 144 to 148 MHz. The antenna boom length is less than 56" (1.4 m),
which lends itself to the use of a non-conductive boom, for which the element lengths and
spacings are designed. The use of a direct 50-Ohm feed reduces the number of mechanical
connections in the path between cable and element, thus reducing the number of potential
loss sources. |
LAB NOTES: Unwinding the Coils in Capacitive Antennas:
Dipole Experiments
By Joel C. Hungerford, KB1EGI |
| Last
month in the November 2002 issue #67 of antenneX, Joel investigated the process of varying
the inductive loading of a fixed-wire length monopole by adjusting the portion of the wire
that was wound into the coil and following the change of resonant frequencies that
resulted. This month, Joel added an identical coil/wire system and made a dipole
antenna with the two wires. Both sides of the dipole were unwound together a turn at a
time and the resultant changes in resonant frequencies were compared to the single wire
case. |
Earth
Spots!
By Igor Grigorov, RK3ZK |
| Have you
ever noticed that there were certain areas where radio communications were almost
impossible -- and that these areas were always that way? In Igor's past professional work,
he was responsible for servicing radio stations and making sure everything always worked
well. However, over time he noticed a certain trend of these "voids" and signal
operating problems that would plague certain areas and not others. After extended research
and investigations, Igor believes he has the answers and writes about his discoveries in
this month's article. |
CAGE
DIPOLES & PRISMATICS
By Dan Handelsman & David Jefferies |
As discussed in a group of articles in antenneX, the Prismatic
Polyhedron, or Pn, is a derivative of the simple dipole, albeit with a more complex form
and feed arrangement. The principal characteristic of this antenna is purported to be its
extremely wide bandwidth. Recently, in a discussion between Dan and Dave Cutberth, another
one of antenneX’s contributors, Dave proposed that the Pn was simply a form
of the well-known “cage dipole”. This is understandable due to the superficial
similarity in form between the two antennas. David Jefferies thought this was a reasonable
conjecture, and set a project student to construct a 1-GHz cage dipole. To test this
conjecture further, David suggested that Dan investigate the similarities and differences
between them by NEC simulation, especially in the parameter felt most important --
bandwidth. |
Displacement
Current Does Not Exist
Part 2: The Transmission Line as a Capacitor
& the Elimination of Displacement Currents
By William C. (Bill) Miller, KT4YE |
| Displacement
Current is the critical “ingredient” in recent antenna designs such as the CFA
and EH. Its existence was postulated in the late 1800’s to explain how Alternating
Current (AC) could flow between the plates of a capacitor. In Part 1, we examined the
"classical" model of a capacitor and identified several inconsistencies in its
performance. In this Part 2, we examine the Transmission Line and demonstrate that this
model performs all the functions of the classical capacitor while eliminating the
inconsistencies. Finally, we shall examine the consequences of this revised model on
"standard" engineering designs, high-speed logic, and antennas. |
Homebrew
Antenna Pattern Range for 2.44 GHz
By Ed Lawrence, WA5SWD |
| This
is a continuation of the 2.44GHz Standard Gain Antenna article by the author that appeared
in the October, 2002 online issue #66 of antenneX. To recap, Ed's employer had
asked him to put together a small Antenna Range for 2.44 GHz since they would be doing
some work (passive RFID microtags) in that ISM Band. Ed realized there would be a lot to
learn and he needed to find practical answers to four questions. The fourth question was
unanswered by the prior article. Fourth Question: How can he make valid pattern
measurements and what equipment must I buy or build to do so? |
| |
Well, there you have it, folks—thanks for listening and
remember, the reading lamp is always on for you in the reading rooms. If I can be of
further help, I'm just a Stone's Throw! away. December
2002 antenneX Online Issue #68
reGARDS, Jack L. Stone, Publisher jack@antennex.com
Send mail to webmaster@antennex.com
with questions or comments.
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June 02, 2008