RF inductor modeling for the 21st century

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "B2 by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bensonbd-at-erols-dot-com>

Hi All,
    Found an interesting article in the September 27, 2001 issue of EDN
magazine on page 67.  Click on the URL below and look under "Design
Feature" to read the article or download a PDF version.

http://www.e-insite-dot-net/ednmag/index.asp?layout=issueTOC&pubdate=9/27/2001

The new model uses an inductor in series with a resistor.  This is in turn
in parallel with a capacitor in series with a resistor.  The core is
represented by a resistor in parallel with it all.

    The article finds inaccuracy with the Coilcraft model on their website.
 The Coilcraft data is considered to be accurate, though.

    The main features of the article are the graphs.  They are very
interesting graphs of impedance and Q vs frequency.  There is an impedance
peak at the self resonant frequency.  The Q drops but does not go to zero
at the self resonant frequency (we know this from measurements).  Below the
coil's self resonant frequency the impedance drops precipitously and the Q
reaches a peak.  This implies that there is a definite size (huge) for the
toroid to maximize the coil's Q (if the model obtains).  There could be
drawn further inference that the best primary should have a peak Q where
the secondary Q peaks to minimize system losses.  This may seem trivial in
light of spark gap loss investigations.  It may be useful, though, when the
art of designing triggered pressurized spark gaps is perfected.  The new
1kA, 15 kV SCRs are also interesting.

    This article may or may not apply to larger inductors like Tesla coil
resonators.  It would be interesting if such a simple model could be
"adjusted" to work.

Cheers,
B2