Example measurements

At the figure above the permeability of two samples of polypropylene-iron-compounds versus magnetizing frequency is shown. The two compound samples differ in the size of the particles of the filler material (53µm and 88µm).

In the soft magnetic iron-silicon the magnetic properties are improved by an orientation of the grains in the material; which means that in the metal layer a defined texture (Goss-texture) is adjusted. In polymers filled with soft magnetic particles it is possible to do an alignment of the particles regarding the axis of easy magnetization. This technique also promises an improvement of the magnetic properties. The figure above shows the increase of permeability of a composite material by doing a particle alignment.

A further significant rise of permeability can be reached by increasing the content of magnetic material in the compound.

The plot shows the dependence of the permeability on the content of magnetic filler in a polymer. It can be seen clearly that only at a high level of magnetic content a high permeability can be expected. Additionally to the measurement data (square symbols) a line curve is plotted. This curve was calculated on the basis of theoretical considerations and describes, in acceptable agreement the experimental values.

If the content of magnetic particles in a polymer is low, a high magnetic field is required to reach the maximum permeability of the composite material. By increasing the proportion of magnetic material in the composite a smaller field is necessary to reach the maximum permeability, which can be seen in the following picture.

This is caused by demagnetizing fields, which are generated around and between the particles and weaken the applied magnetic field. With increasing filler content, the demagnetizing field becomes smaller (see figure below). It is defined by the inner demagnetization factor Ni and depends on the filler fraction of soft magnetic material and also on the particle's shape.

 

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