# Material regions in 3D applications

## Introduction

A region is always defined:

• in a geometric approach, (regrouping of geometric entities)
• in a physical approach, (definition of the physical properties)

## Geometric point of view

From a geometric point of view we distinguish, in 3D, three types of regions, corresponding to three types of geometric entities: volumes, faces, and lines.

These three types of regions are listed in the table below.

A region … is used to describe … Example
volume

a volume part

of any shape

main elements
face

a thin part

(of small thickness)

contact air-gaps, thin sheets, current sheets, …
line

a filiform part

(of small cross-section)

bus-bars, …

In 3D studies:

• all the volumes (except in specific cases ) belong to volume regions
• only few faces (and/or lines) belong to face regions (and/or line regions )

## Physical approach

A material region is used to model a material medium. A material region must be comprised of a material. The physical properties of the material medium are those of the material of the region.

A region is defined…
geometrically by … physically by…
volume a group of volumes a type, a material
face a group of faces

a type, a material

and a thickness

line a group of lines

a type, a material

and a cross-section

## Use of the face regions (or line regions)

It is recommended that the face regions (or line regions ) be used when the shape of the volumes (in the 3D domain) is such that the mesh quality is poor. It is the case of volumes with one dimensions that is small in relation to the others, or to the surrounding volumes.

The process is as follows:

• replacement of the related volume by a face (or a line)
• use of a face region (or line region)

## Additional comments about the face regions (or line regions)

In 3D studies, the volume regions are used to model the main parts of the device. The field, computed by Flux, depending on the physical application, has a random direction. There is no particular restriction on the direction of the field.

For the face and line regions, the user has the ability to impose the direction of the field. The different examples are presented in the table below.

Region Field (or current density)
face normal to the face: tangent to the face:
line radial to the line: tangent to the line: