When will this nonsense
end? When will Dr.
Mike Blewett , late of Surrey University, stop
teaching nonsense? Since I mentioned him, he has slipped from no. 2 to no. 9. Searching “self resonant
frequency”, I have Google hit no. 1, and three hits out of the first five out
of 6 million. Mine have been there for years. Yet no professor or text book
writer has approached me. They continue to “teach” their students how to
measure this non-existent “self resonant frequency of a capacitor” Ivor Catt 6 April 2014 Wikipedia
“Electrical resonance occurs in an ceramic
capacitor at a particular resonance frequency where the imaginary parts of the
capacitor impedance and admittances
cancel each other.” • Since a capacitor is a
transmission line, it has no series inductance and so no self resonant
frequency. Although Google for “self resonant frequency” puts Catt’s
observation above Wikipedia’s at the front of two million hits, any link to
Catt’s hit put in Wikipedia is removed. • http://www.ivorcatt.org/ic2603.htm • [September 2013
update. In Google, Catt is still no. 1 hit out of 4 million for “self
resonant frequency”. Wikipedia have removed their web page for “self resonant
frequency”! Yet Wikipedia does not ban entries on what does not exist. See http://en.wikipedia.org/wiki/Ghost .
Ghosts does better with 70 million hits.] • In 2014,
Google continue the nonsense here
. Note; “The smaller the capacitance C
and the inductance L the higher is the resonance frequency.” The “best”
capacitor is the worst capacitor. Electromagnetic Theory breaks down with
Digital Hardware Design Most
of the web pages criticised below have disappeared. I suggest you do a Google
search for “capacitor self resonant frequency” to read today’s culprits. IC
2011 Self-resonant
frequency of a capacitor Unfortunately,
most of the web pages hyperlinked to below have disappeared Nonsense about so-called “self-resonant frequency” of a
capacitor. Wikipedia
suppresses the truth. Also see http://www.ivorcatt.co.uk/2603.htm If you cut off a
capacitor’s legs at the knees, you will double its self-resonant frequency – Ivor Catt Charge spreading out across the plate of a capacitor Martin Eccles takes
the biscuit My 1994 book Electromagnetism 1 is at http://www.ivorcatt.com/em.htm Nigel
Cook on Ivor Catt’s ideas, (London) Electronics
World (was Wireless World), aug02, pp46-49 More
nonsense is at http://www.ivorcatt.com/2605.htm Yet more nonsense
Scandals in Electromagnetic Theory http://www.ivorcatt.com/28scan.htm RIPOSTE
Ivor Catt's view of Capacitors, by Leslie Green
CEng MIEE
http://www.atceramics.com/pdf/technotes/effective_capacitance_vs_fr.pdf talks about self-resonant
frequency. The “parasitic inductance”
does not exist inside the capacitor. However, the article is very primitive,
because the graphs go in the wrong direction, with C increasing with
frequency, anyway. The alleged L reduces the C, not increasing it as the
author seems to think. http://www.capacitors.com/multicap/phase-esr/phase-esr.html “the capacitor can be used
up to the natural self-resonant frequency or” http://www.educatorscorner.com/experiments/pdfs/exp79.pdf Unfortunate students are
made to measure the “self-resonant frequency” of a capacitor. Tell them to
cut off the poor capacitor’s legs! http://www.capacitors.com/consider/consider.htm This guy is stumbling in the right direction, but he gets his number wrong. Inductance caused by the legs should be proportional to the length of the legs. “Lead length alters a capacitor's range of operating frequency. Here a 2 uf capacitor's self-resonance decreases from 490 kHz to 290 kHz when its leads are lengthened from 3/8 inch to 3 inches. In other words, the capacitor's usable operating range is reduced by almost half.” More nonsense; http://www.qsl.net/kf4trd/varactor.htm your
poor capacitor behaves just like an inductor! The frequency at which both
impedances http://www.emf-emi.com/dosanddonts.shtm Ensure that the SRF (self-resonant frequency) of capacitors is above the highest frequency to be bypassed. …. 10.) Select and mount decoupling capacitors having self-resonance (SRF) above logic band-width (1/) http://www.cypress.com/pub/appnotes/decouple.pdf This writer is in a bad way. Pure fantasy. – IC What a pity this poor
fellow has been pulled from the www by his paymasters. The hyperlink now
jumps straight to another page, bypassing the nonsense I saw on 30jan02.
Perhaps I have influence! Ivor Catt. 5may02 http://www.benchmarkmedia.com/appnotes-a/caig/caig06.asp However, all
capacitors have their own self-resonant frequency To avoid series
inductance, a well behaved capacitor keeps its legs together – Ivor Catt Update 12 years later on 14 February 2014. All but one of the above
web pages have been removed! @@@@@@@@@@@@@@@@@@@@@@@@@@@ The amount of nonsense
drifting around the world, of which the above are examples, is vast. See my 1978 article at http://www.electromagnetism.demon.co.uk/z001.htm
; “Series inductance
does not exist. Pace the many
documented values for series inductance in a capacitor, this confirms
experience that when the so-called series inductance of a capacitor is
measured it turns out to be no more than the series inductance of the wires
connected to the capacitor. No mechanism has ever been proposed for an
internal series inductance in a capacitor.” The key point in my article is that “No mechanism has ever been proposed for an internal series inductance in a capacitor.” The IEE and IEEE have
helped to cause the confusion to escalate by suppressing my 1978 article http://www.electromagnetism.demon.co.uk/z001.htm
, which puts an end to a capacitor’s series inductance. Also, competent
experimentation will show that a capacitor has no internal series
inductance. http://www.ivorcatt.com/em_test04.htm – Ivor Catt, 30jan02 @@@@@@@@@@@@@@@@@@@@@@@@@@@ Ivor
Catt 22apr02 In
1963 I bought the EH-125 pulse generator. This delivered a –10v step with a
100picosecond fall time into a 50 ohm load (e.g. 50 ohm coax.). The
pulse generator could also deliver a –ve 10v spike
with a width of 150psec. I decided to try to create a positive 10v spike. I
cut into the 50 ohm coax, and joined the incoming inner to the outgoing outer
via a red 1uF tantalum capacitor. I also joined the incoming outer to the
outgoing inner via another 1uF tantalum capacitor. Further downstream I found
that I had a positive 150psec spike with no discernable degradation (in rise
time or pulse width) compared with the initial –ve
spike. That is, I had a +ve 10v spike with a width
of 150psec. It
is interesting to calculate the physical width of a 150 psec
wide spike travelling down normal coax, which has a dielectric with a
dielectric constant of 2. Whereas light travels one foot in vacuo in one nsec, it would travel
8 inches in material with a dielectric constant of 2. Thus, a 150psec spike
in the coax has a width of about one inch. So I sent a TEM spike with a width
of 1 inch through these 1uF capacitors. [Note 1] Obviously, I kept their legs
short. It is sad that during the ensuing 40 years the New York IEEE and the
London IEE prevented me from informing electronic engineers that they did not
have to add “high frequency” decoupling capacitors to their logic boards, that the 1uF would do perfectly well on its own.
This obstruction has cost the industry many millions of pounds. However, a
bolshie IEEE and a bolshie IEE cost us a lot more than that in other ways. Ivor Catt 22apr02 Note 1. Anyone who wants to play
with frequencies can be told that the fundamental of the 150psec spike will
be around 3GHz. Put that in your “self-resonant” pipe and smoke it! IC Note 2. As the spike passes the
capacitors placed to each side, the situation is as in http://www.ivorcatt.com/2_1.htm
Figure 14. The characteristic impedance of each capacitor is very small, less
than 1% of 50 ohms. Thus, the mismatch is less than 2%, causing a minimal
reflection of less than 1%. At the same time, if the
legs of the capacitors are kept down to a total of one quarter of an inch in
length, and the two parallel legs represent a quarter inch transmission line
of characteristic impedance 150 ohms, then the mismatch will cause a
reflection of 50%, see http://www.ivorcatt.com/1_4.htm
Figure 11 and the reflection formula. This will be reduced by the fact that
the 150psec spike covers a distance of one inch and a half, so that the
reflections on entering the 150 ohms region tends to be masked by the
opposite mismatch on re-entering the 50 ohm impedance of the next section of
coax. This reduces the reflection to one sixth, i.e. 8%. @@@@@@@@@@@@@@@@@@@@@@@@@@@ 18may02 More drivel. Fig. 2 at http://www.ultracad.com/seminar_caps.htm Google Hit no. 7 for “self resonant
frequency” + capacitor This article high on the
Google hit list has row of capacitors, and each one decouples (digital
electronic equipment for) its particular frequency range. This farce is obvious if
one realises that a 2uF capacitor is made by glueing
together two 1uF capacitors. Thus, a supposedly “high frequency capacitor” is
merely the front little bit of a 1uF capacitor. Of course, you can ruin the
performance of either by leaving it with long legs, making a series one-turn
inductor to stifle its performance. However, the idea that a 10pF capacitor
has shorter legs than a 1uF capacitor is based on nothing at all. What is so tragic is that
the formula these clods use for self resonant frequency, 1/ sqrt LC , means that if C is
big, then the resulting calculated “self resonant frequency” is low. This is
a sensible idea if a resonant circuit is being designed out of a discrete C
and a discrete L, where L can be varied. But if, as in our case, we (have
legs of fixed length and) can only vary the value of C, then the calculation
deludes. If we start with a pair of legs of fixed length, that is, with a
fixed external L, then the bigger the C, the lower the resonant frequency
according to the formula w = 1/ sqrt LC. These buffoons are buying capacitors for
the very reason that they have less capacitance, not that they have less L.
They buy these “high frequency capacitors” for the very reason that, lacking
much C but helping the w = 1/ sqrt LC formula, they
are inferior at doing the decoupling job that they have been bought to do.
All their nonsense is counter-productive. This was pointed out in my book
more than 20 years ago. Since digital electronics took over from radio as the
majority of electronic engineering 40 years ago, it is high time the radio
men gave us at least some access to the IEEE, the London IEE and to Cambridge
and MIT. Even a single digital electronics course by someone who understood
the subject at either MIT or Cambridge University would help a lot. I would
love to give it. However, I am sure the radio men will continue to shut me
and my colleagues out, as they have done for a number of decades, hoping that
their antique radio theory will continue to appear to address the needs of
digital electronic equipment. http://www.ivorcatt.com/em_test04.htm Ivor
Catt 18may02 Since a capacitor is a
two-conductor transmission line with very low characteristic impedance, the
transient impedance that it presents to a step is resistive, not reactive.
This is the way it behaves when decoupling digital circuits; as a local
energy store for the 5v supply with a very low resistive source impedance,
not a reactive source impedance. Calculation of the impedance is made by
using the normal formula for
the characteristic impedance of a transmission line made up of two parallel
plates with width a and separation b. See p73 of my
book “Electromagnetics 1”, pub. Westfields
1975. The (resistive) impedance is very low because the dielectric constant
is very high indeed, and the separation b is tiny. Ivor Catt 18may02 In the surreal world created with
inappropriate mathematical stunts by physically ignorant operators, a
capacitor is looked on with disdain, not because it has more L, but because
it has more C. http://www.ivorcatt.com/em_test04.htm Ivor
Catt 18may02 @@@@@@@@@@@@@@@@@@@@@@@@@@@ Recap.
Take the formula for the resonant frequency for an inductor-capacitor tank
circuit. The
frequency (in radians per sec.) squared equals (1/ inductance x capacitance) Thus,
either increase in inductance or increase in capacitance reduces the resonant
frequency. This has led physically ignorant mathematical mugwumps
to think, not that the best capacitor has the least capacitance, which even
they might realise is ridiculous, but that the best capacitor has the least
inductance, making it able to perform to a much higher frequency up to its
higher resonant frequency. They have failed to realise that they would
realise their dream, of a high self resonant frequency, by reducing the
capacitance just as well as by reducing the inductance. They think that it is
an accident that lo value capacitors have the highest self resonant
frequency. They think it is because of the difference in inductance, which it
is not. However,
all this is nonsense when decoupling digital logic. What matters with digital
logic is the transient performance of a decoupling capacitor, when some
switching logic wants to grab as much charge as possible to launch down a
transmission line
towards the next logic gate. The true model, which should have
replaced the series L C R model for a capacitor, was already published in
1978, http://www.electromagnetism.demon.co.uk/z001.htm , and has been ignored for 24 years by
radio men who continue to teach and publish the old model which is
inappropriate and damaging in digital electronics. Note that today, most
capacitors are used in DC voltage decoupling. The
only way out of this impasse is for students to create problems during the
lecture when lecturers continue to pump out the old, wrong drivel. Otherwise
these lecturers and text book writers will continue to copy and repeat each
other from a bygone age when electronics was about radio, and such a misconception
about the physical nature of a capacitor was not so damaging. http://www.ivorcatt.com/em_test04.htm
Students have much to gain by disrupting
their lectures. It is probably more difficult to learn and be examined in
material which is false. Ivor Catt. 18may02. @@@@@@@@@@@@@@@@@@@@@@@@@@@ In
1965, living in the USA, I telephoned the design engineers in Sprague, who
manufactured capacitors. They told me that they tested for the high frequency
performance of a capacitor by testing at 5kHz and 50kHz, and deduced its
performance at 1MHz and above using the series L C R model. Thus, the
published self-resonant frequency of a capacitor is the result of lo
frequency testing extrapolated using the L C R model. By
making this error, engineers in the capacitor manufacturers might have
doubled their companies’ sales, ensuring that a second “high frequency”
capacitor would be added to every 1uF decoupling capacitor in every digital
system. Ivor
Catt 18may02. @@@@@@@@@@@@@@@@@@@@@@@@@@@ @@@@@@@@@@@@@@@@@@@@@@@@@@@ In the Wikipedia case below
the legs were left the same, so L was constant. So-called “self resonant
frequency” duly increased by a factor of 3 each time C was reduced by a
factor 10. Resonance is when ὡ=1/√LC. So with L constant, ὡ
increases by a factor 3 when C falls by a factor 9. The capacitor has nothing
to do with this “self resonant frequency”, which depends on its external
legs. The capacitor itself has no internal series inductance. http://en.wikipedia.org/wiki/Ceramic_capacitor Sample self-resonant
frequencies for one set of C0G and one set of X7R ceramic capacitors are:
@@@@@@@@@@@@@@@@@@@@@@@@@@@ Source of a Capacitor’s so-called “ self resonant frequency “ |
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Riposte Ivor Catt. 18june02 Scandals in electromagnetic theory http://www.ivorcatt.com/28scan.htm x |
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(Possibly we need a
standard word for this. I suggest "Riposte", or the symbol [R] .) Ivor Catt, 30june02. ivor@ivorcatt.com |