Antenna Design
This model was developed for a pacemaker communication system where two pancake coils were coupled through a Titanium casing.
When a pancake coil with a series resistance of Rs
is placed over a conducting plate,
a mirror coil is induced in the conductor with opposite polarity
and series resistance Rl.
When the coupling factor k
is perfect (σ = 0)
the impedance is real and varies between Rs
and Rs + Rl.
When there is no coupling (σ = 1)
the impedance is that of a coil with a series resistance.
Measurements were taken on two coils between 100 Hz and 15 kHz. At the higher frequencies we expect a divergence from the model because of the skin-effect, which increases the resistance of the mirror coil.