K Factor & Mutual Inductance

To: tesla-at-poodle.pupman-dot-com
Subject: K Factor & Mutual Inductance
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 01 Apr 1997 09:51:48 -0600
Approved: tesla-at-stic-dot-net

Subject: 
        K Factor & Mutual Inductance
  Date: 
        Tue, 1 Apr 1997 06:29:47 +0000
  From: 
        "John H. Couture" <couturejh-at-worldnet.att-dot-net>
    To: 
        tesla-at-poodle.pupman-dot-com

The K Factor and mutual inductance of a Tesla coil can be found by tests
after the Tesla coil is built. This test is shown in the Tesla Coil
Design
Manual. However, at the time of design these two parameters are unknowns
and
must be calculated. The K Factor can be found if the mutual inductance
is
known. 

One equation for the mutual inductance of air core concentric solenoids
is
shown in Terman's "Radio Engineers Handbook". Once the mutual inductance
Lm
is found the K Factor can be found by the equation
          K Factor = Lm/(sqrt(LpLs))
where Lp and Ls are the inductances of the primary and secondary coils.

Note that the K Factor or coupling is not only dependent on the physical
location of the coils but also on several other parameters such as
resonant
frequency, Q Factor, log decrement, etc. Also, the critical coupling can
be
found when these parameters are coordinated to give Rp = Rs where Rp and
Rs
are the primary and secondary effective resistances.

The JHCTES computer program determines the K Factor and other parameters
in
this manner. The results have been found to agree closely with tests of
actual coils. To my knowledge this is the only computer program
presently
available that utilizes this method of finding these parameters. 

 John Couture