Thermal Therapy - RF/Microwave Interaction with Biological Tissues - page 163

Heating object

Deformed ferrite core

A C A C

N S N S

Direction of
eddy current

S N S N

D D

B B

Magnetic field

(a) (b)

FIGURE 4.19 Heating principle.

FIGURE 4.20 Thermographic view after heating by deformed core applicator.

This conductive plate also operates as a magnetic shield plate. It is called
an auxiliary electrode. By attaching the auxiliary electrode to the surface of
the phantom, magnetic couplings between the poles A and C and B and D are
reduced. So, it is considered that only the magnetic field coupling between the
poles A and B and D and C remains. As a result, eddy currents distribute as
shown in Figure 4.21 b . We should notice here that these eddy currents flow
into the auxiliary electrode because it has a conductivity higher than the
phantom. Consequently, the total current flow forms a closed loop, as shown