Page 125 - The Art and Science of Analog Circuit Design

Analog Breadboard-rig

INDUCTANCE
Figure 9-8.

A loop of conductor has inductance -
two adjacent loops have mutual inductance.

If two such coils are close to each other we must consider their mutual
inductance as well as their self-inductance. A change of current in one
will induce an EMF in the other. Defining the problem, of course, at once
suggests cures: reducing the area of the coils by more careful layout, and
increasing their separation. Both will reduce mutual inductance, and re-
ducing area reduces self inductance too.
It is possible to reduce inductive coupling by means of shields. At LF
shields of mu-metal are necessary (and expensive, heavy and vulnerable
to shock, which causes loss of permittivity) but at HF a continuous
Faraday shield (mesh will not work so well here) blocks magnetic fields
too, provided that the skin depth at the frequency of interest is much less

Figure 9-9.

Inductance is reduced by reducing loop area -
mutual inductance is reduced by reducing loop area
and increasing separation.
Since the magnetic fields around coils are dipole fielcte they attenuate with the cube of the
distance - so increasing separation is a very effective way of reducing mutual inductance.

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