or anti-parallel to an applied field, an induced magnetization response will arise.

Magnetic permeability measures the degree to which individual dipole moments of the building blocks can be aligned or moved from their normal orientation by an externally applied magnetic field. The more of the individual moments that can be moved into alignment, the more magnetically polarizable the material. The magnetic properties of materi-als are quantified by magnetic dipole moment density. When an electrical current flows in a closed loop, the mag-netic moments is.

= （3-7）

where M is the dipole moment, I is the current and A is the area of the loop enclosed by the current filament. M has units of Am2 For bulk materials, the material is characterized by dipole moment density

= （3-8）

which has units of A/m. V is volume. When a magnetic field, H, induces a

magnetic moment, the amount of moment is expressed as

（3-9） =

where k is the magnetic susceptibility (and is a dimensionless quantity). There is considerable similarity between induced magnetic moment and induced electric dipole momentdiscussed previously in the displacement current sec-tion.

In the material, the magnetic flux is expressed as

= 0( + ) （3-10）

and magnetic permeability is expressed as

= 0(1+ ) （3-11）

where

0=4 ×10 7 / （3-12）

The term relative magnetic permeability is expressed as

= =(1+ ) （3-13） 0