# RF Module Glossary

This glossary contains finite element modeling terms in an electromagnetic waves 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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### absorbing boundary

A boundary that lets an electromagnetic wave propagate through the boundary without reflections.

### 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.

### cutoff frequency

The lowest frequency for which a given mode can propagate through, for example, a waveguide or optical fiber.

### edge element

See vector element.

### eigenmode

A possible propagating mode of, for example, a waveguide or optical fiber.

### 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.

### perfect electric conductor

A material with high electric conductivity, modeled as a boundary where the electric field is zero.

### perfect magnetic conductor

A material with high permeability, modeled as a boundary where the magnetic field is zero.

### 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.