# Choice and definition of the application

## Introduction

The first stage corresponds to the choice and the definition of the application.

The two applications are the applications Supplied conductors and Conductors impedance.

The user defines a material (by default).

## Reference frequency

In practice, the reference frequency is fixed via the scenario of the solving process. (see § Solving process (according to the scenario)).

The reference frequency is the maximum frequency of the scenario.

## Materials

The materials are electric conductive materials characterized by their resistivity in Ω.m.

Only unidirectional conductors of tube type and whose cross-section is rectangular or hollow can be made of a linear homogeneous and isotropic magnetic material characterized by its relative permeability.

The characteristics of available materials are presented in the table below.

Material | Resistivity (20°C) |
---|---|

Aluminum | ρ_{Al} = 2,74.10^{-8} Ω.m |

Copper | ρ_{Cu} = 1,72.10^{-8} Ω.m |

Gold | ρ_{Au} = 2,21.10^{-8} Ω.m |

Silver | ρ_{Ag} = 1,63.10^{-8} Ω.m |

## Skin depth: definition

For a linear homogeneous and isotropic material the average value of “skin” depth, in which the electric currents flow, can be calculated using the following formula:

where:

- f is the frequency
- ρ is the resistivity of the material
- μ
_{0}is the permeability of vacuum; μ_{0}= 4 π 10^{-7}H/m - μ
_{r}is the relative permeability of the material