Attenuation of a Sinusoidal Magnetic Field in a Halfspace Conductor

conductor medium

copper

iron

brine

frequency f (MHz)

0.1

observation time ωt (°)

0

When a block of conductor is subjected to a changing magnetic field, a current is induced inside the conductor. This Demonstration shows this phenomenon when a sinusoidal magnetic field is applied to a halfspace conductor. The magnetic field of moderate frequency (and therefore, regarded as a near field) is assumed to be parallel to the conductor surface. The skin depth is determined by the frequency

f

as well as the conductor parameters of conductivity

σ

and relative permeance

μ

r

. Taking the direction of the magnetic field as the

z

-axis, the current is directed along the

y

-axis. The spatial distributions of

H

z

and

i

y

(to which the electric field is proportional:

E

y

=

i

y

σ

) are shown graphically.

You can choose copper, iron, or brine (sea water) as the conducting medium. The amplitude of the exciting magnetic field is fixed at 1 A/m, but the frequency and the observation time (or phase) are variable. You can see an animation of the spatial distribution by changing the observation time.