TABLE OF CONTENTS For fields with time variation of exp( i ?t) we may replace the ? / ? t operator by i ? so Maxwell's curl equations may be written as
| (6.12) |  |
| (6.13) |  |
where E and B are now complex phasors. The conduction current will be much greater than the displacement current for frequencies ? = ?/ ?. In biological tissue the conductivity is ? ? S/m with effective relative dielectric constants ? ? 10 6 ? 0. In metals ? = 10 7 10 8 S/m with ? ? ? 0 displacement currents are negligible up to 10 MHz.
The simplest example of AC current induction is that produced by a time-harmonic magnetic field tangential to conducting half-space with ? r = 1. This field can be thought of as being produced by an infinite sheet with a uniform surface current density that is parallel to the conducting half-space shown in Figure 6.1. Neglecting the displacement current we have
| (6.14) |  |
where J e = ? E inside the metal. Taking the curl of this equation
| (6.15) |  |
and using the identity
| (6.16) |  |
with ? B = 0 and ? E= -i ? B we have
| (6.17) |  |
On the CD Four color images for many of the figures may be found on the CD-ROM.
