MAGNASAT measures the magnetic susceptibility of materials from the change that these materials cause to an alternating current (AC) magnetic field. Changes to the AC magnetic field are caused by a complex mix of eddy currents and the action of magnetic domains and the magnitude of these changes are dependent on the material’s magnetic and electrical properties as well as the quantity of material presented for measurement.
Eddy currents are induced in a conductor when it enters the magnetic field core (inside the coil). Figure 1 shows that a current is produced when a magnet is moved over a copper coil. Figure 2 shows that this process can be reversed ie a current in a coil will produce a magnetic field.
Magnetic domains are used to describe the magnetic characteristics of ferrous materials. A ferromagnetic material consists of magnetic domains, which are small units that align themselves in an applied magnetic field. Figure 3 shows the movement of domains induced by a bar magnet.
When a ferromagnetic material is subjected to an applied magnetic field, the domains align. The alignment of domains cause the material to have considerable magnetic flux density. If the applied magnetic field is changing (i.e. an AC magnetic field) the flux density of the material and the moving of the domains have a significant effect on the applied AC magnetic field.
MAGNASAT subjects the material to be tested to an AC magnetic field and the strength of the eddy currents produced is a function of the magnetic properties of the material in the AC field. The eddy currents produced generate their own magnetic fields which have the effect of altering the electrical properties of the coil applying the magnetic field.
Development of MAGNASAT has included investigations into the effects of all the factors that influence changes in the magnetic field. Studies have included the effect of sample presentation geometry, as well as the development of a measurement coil/reference coil combination for the precise and rapid analysis of samples.