Source of a Capacitor’s mysterious
“self resonant frequency”.
In the Wikipedia case below the legs were left the same, so L was
constant. Socalled “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.
Obviously all the capacitors’ legs are of the same length. So with L constant, ὡ
increases by a factor 3 when C falls by a factor 9. The capacitor itself has
nothing to do with this “self resonant frequency”, which depends on its
external legs. The capacitor itself has no internal series inductance, and no
self resonant feqwuency.
http://en.wikipedia.org/wiki/Ceramic_capacitor
Sample
selfresonant frequencies for one set of C0G and one set of X7R ceramic
capacitors are:
10 pF 
100 pF 
1 nF 
10 nF 
100 nF 
1 µF 

C0G (Class 1) 
1550 MHz 
460 MHz 
160 MHz 
55 MHz 

X7R (Class 2) 
190 MHz 
56 MHz 
22 MHz 
10 MHz 
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In
around 1965 I came across a book which had a list of various types of
capacitor, including their manufacturers, their capacitance, and the length of
their legs. It gave their “self resonant frequency”. I mentally formed their
legs into a square of the same total length and treated each pair of opposite
sides as a short transmission line. I then calculated the inductance of the
square. Taking the stated capacitance, I could then calculate the capacitor’s
socalled “self resonant frequency” while ignoring capacitor type. That is, I calculated each capacitor’s “self
resonant frequency” from its stated capacitance and the length of its legs.
This
proved that the socalled “self resonant frequency” Ѡ=1/(LC) related the the capacitor’s legs, and it had no internal series
inductance.
I have
been making this point for more than fifty years, and yet today a Google search
for “self resonant frequency” + capacitor gives us 500,000 hits, with mine
coming at 3, 4 and 7. A Google search for “capacitor self resonant frequency”
gives me hits no. 1, 2, 3 and 8. At hit no. 4, Wikipedia continues to talk
nonchalantly about the nonexistent “self resonant frequency” of a capacitor.
It lets the cat out of the bag with; “The smaller the capacitance C and
the inductance L the higher is the resonance frequency.” This confirms my work in 1965, that socalled “self resonant
frequency” is reduced by reducing C, and is based on an inductance outside the
capacitor,.
The
squalid record on capacitor self resonant frequency, where we can see that an
intellectual infrastructure does not exist anywhere in the world (“ Where
are they? ”) can be extrapolated to
electromagnetic theory, where I have found the same worldwide intellectual void
in a much more important subject. Nobody is thinking about or discussing
electromagnetic theory. They are only copying what others have written, and
teaching what is in the books, replete with timehonoured oversights and errors.
Ivor Catt 29 March
2014