# How to Use Magnetostrictive Materials with an Inductor

## Description

This example problem illustrates a coil energized with a current source inducing movement in a rod of magnetostrictive material.

The magnetostrictive rod has a plane of symmetry normal to its axis. The rod can also be represented using an axisymmetric model. Therefore, only a quarter of the cross-sectional area of the rod needs to be used.

In order to use a structured, quadrilateral mesh, enter the geometry as four regions. The bottom-left point is the origin. The total length of the rod is 50mm with a radius of 3.25mm. Taking symmetry into account, the extreme point on the rod is the (25, 3.25). The extreme point for the surrounding air is chosen somewhat arbitrarily as (50, 16.25).

## Materials

Apply the AIR_MAG material to the three outer regions. Use a magnetostrictive material for the rod region.

## Boundary Conditions

The ATILA-GiD interface uses a point boundary condition to define the inductor. (Use the icon to open the boundary conditions.)

The inductor used is a cylindrical one with the following dimensions.

IMPORTANT NOTE: The length of the inductor does not account for symmetry. You must enter the full length of the inductor and set the center point at the origin.

For clarity, apply the inductor condition to the point at the center of the magnetostrictive rod. ATILA will use the center point as defined in the dialog, not the point where the inductor is applied in GiD. Placing the inductor at the correct point in the geometry provides a visual consistency with the information in the dialog.

The external source energizing the coil is also defined in this dialog. The ATILA-GiD interface will supply the correct excitation based on the values entered in the dialog. This coil is energized with a per unit current source.

Inductor Condition

All the magnetic field is assumed to be contained within the air region surrounding the rod. Force the magnetic potential to zero on the lines surrounding the problem.

Magnetic Potential

To enforce the axisymmetric condition, apply a line constraint clamping the y displacement along the centerline of the rod.

To enforce the symmetry condition, apply a line constraint clamping the x displacement along the middle of the rod.

Symmetry Condtions

The polarization direction of the magnetostrictive material is set using a surface condition.

Define the local axis using the X and Angle option.

Pick the center point of the rod as the origin of the axis. Then, enter the point (0, 0, -1) on the command line to indicate the point in the positive x direction. Finally, enter -90 degrees to place the y axis. The local z axis is then oriented along the global x axis, as shown.

Polarization of Magnetostrictive Material

## Mesh Generation

Use a structured, quadrilateral mesh for the rod and the surrounding air.

## Problem Data

Set the problem data to a 2-D, Axisymmetric, Harmonic Analysis. Do not compute losses or stress.

For this example, the frequencies used for calculation are: 100Hz, 10000Hz, 12000Hz, 14000Hz, 16000Hz, 18000Hz, and 20000Hz.

## Post Processing

After calculation, the potential lines at 10000Hz should be similar to the image below.

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