# AC/DC Module Glossary

This glossary contains finite element modeling terms in an electromagnetics context. For mathematical terms as well as geometry and CAD terms specific to the COMSOL Multiphysics software, please see the Multiphysics Glossary.

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### anisotropy

Variation of material properties with direction.

### constitutive relation

The relation between the D and E fields and between the B and H fields. These relations depend on the material properties.

### eddy currents

Induced currents normal to a time-varying magnetic flux in a ferromagnetic material.

### edge element

See vector element.

### electric dipole

Two equal and opposite charges +q and q separated a short distance d. The electric dipole moment is given by p = qd, where d is a vector going from q to +q.

### gauge transformation

A variable transformation of the electric and magnetic potentials that leaves Maxwell’s equations invariant.

### magnetic dipole

A small circular loop carrying a current. The magnetic dipole moment is m = IAe, where I is the current carried by the loop, A its area, and e a unit vector along the central axis of the loop.

### Nedelec’s edge element

See vector element.

### phasor

A complex function of space representing a sinusoidally varying quantity.

### quasi-static approximation

The electromagnetic fields are assumed to vary slowly, so that the retardation effects can be neglected. This approximation is valid when the geometry under study is considerably smaller than the wavelength.

### vector element

A finite element often used for electromagnetic vector fields. The tangential component of the vector field at the mesh edges is used as a degree of freedom. Also called Nedelec’s edge element or just edge element.