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Magnetic stimulation and therapy 229

exponentially) in depth. That could cause unpleasant, even painful reactions at the
skin surface, a region rich in sensitive nerves.
A possibility to reduce AF values at the skin surface and increase them in depth is
the use of combined coils, made of horizontal and inclined turns. This is the reason
for considering in the model the possibility to rotate the turns (Fig. 7.3) with the alpha
angle to the skin surface. Fig. 7.5 presents the distribution of AF in the depth of the
tissue (z-axis direction) for three cases: case (a) the quadruple coil introduced earlier (it
has eight turns, two per section); case (b) a combination of a similar quadruple coil
with three turns for each section and a quadruple coil with one turn for each section,
with the turns inclined (α 5 π/3) and with opposite current polarity; and case (c) the
same combination as (b), but with double magnitude for the radius of turns.
As Fig. 7.5 shows, the rate of AF values at z 5 0 and at z 5 0.01 m (the con-
sidered target area) is B2.5 in case (a), 1.8 in case (b), and 1.15 in case (c). The incli-
nation and radius of turns could provide good control for the localization of the AF
values in the depth of the tissue.
The quadruple coils produce the best concentration of AF at the target stimulating
area, minimizing the inhibition effects on surrounding regions. The combination of
quadruple coils with horizontal and inclined turns could result into the control of the

Figure 7.5 Distribution of AF in the depth of tissue for three forms of the stimulating coils
(Morega, 2000).