# Describing the material media

## Introduction

Material media are modeled by material regions :

• mainly volume regions in 3D problems; surface regions and line regions are also possible in 3D
• mainly surface regions in 2D problems; line regions and point regions are also possible in 2D

For additional information about the role of regions, see the chapter Physics: principles.

## Material regions: overview

Volume, surface or line material regions allow the modeling of the material media (with materials). The physical properties of the medium are those of the corresponding material region.

A region … enables the modeling …
air or vacuum

of the air or of the vacuum

(permeability μr =1)

(hard material or

soft material)

magnetic non conducting

of a medium:

magnetic (permeability μr)

non conducting

coil

conductor1

of a medium:

conducting with source1

non magnetic (permeability μr =1)

this medium represents a coil:

• constituted of a number of turns
• passed through by a current Js
laminated magnetic non conducting2

of a laminated medium:

magnetic (permeability μr)

non conducting

This medium represents

a stacked magnetic sheets :2

• plane (2D plane / 3D) or cylindrical (3D)
• simplified via a homogenization technique
(soft material)
Note: 1* See § Describing the sources
Note: 2 See Best Practices document “The modeling of magnetic core made of laminations in Flux”. This document is available from the Supervisor (Help / Documents).

## Thin regions

Thin regions enable the modeling of regions of slight thickness.

In the most general case, the magnetic field direction within a thin region is not known. It depends on the medium properties and on those of the surrounding medium.

In 3D, for certain particular cases, the direction of the magnetic field can be selected by the user. Examples are presented in the table below.

Thin region Direction of fields H and B
no restriction quasi normal quasi tangential
magnetic

soft magnetic material with:

μ2 ≈ μ1

soft magnetic material with:

μ2 << μ1

soft magnetic material with:

μ2 >> μ1

## Filiform regions

Filiform regions enable the modeling of small cross-section regions.

The filiform regions (of Magnetic region type) are used to model magnetic bars with high permeability, or small cross section permanent magnets with the direction of magnetization following the direction of the bar.

In 3D, the direction of the magnetic field in a filiform region is imposed by Flux. The magnetic field is considered tangent to the line that models the filiform region.