Electromagnets

Electromagnets produce static, or DC, magnetic fields normally in the range 0-20 kOe, although some of the electromagnets found in the market are able to produce 20-30 kOe.
Fig. 1 shows schematically a cut view of an electromagnet.

It consists of a magnetic circuit composed by a yoke and two cores made of high permeability carbon steel. Two coils of wire having hundreds, or even thousands, of windings are allocated around the cores.

The useful magnetic field is created in the air gap between the pole caps. This magnetic field depends on the current, the permeability and saturation induction of the core and the physical dimensions of the magnetic circuit (in particular, the air gap distance). In many electromagnets air gap is continuously adjustable by means of rotating pole nuts. The maximum current used is limited by the insulating of the cooper wire used for making the coils. The coils, which are connected in series, are water or air cooled in order to avoid damage of the insulating copper wire. Further increase in the magnetic field is possible by using iron-cobalt pole pieces or modifying the shape of the poles (as it is shown in Fig. 2 where the dependence of the magnetic field in the gap for two different pole caps is plotted).

Fig. 3 shows a typical horizontal electromagnet, but in some cases costumers also request vertical electromagnets. For instance, companies that commercialise BH meters and DC hysteresigraphs for the characterization of permanent magnets prefer a vertically designed electromagnet.

The most important specifications of an electromagnets are: maximum magnetic field produced in useful air gap distances (one-inch or one and half inches air gap, for instance), magnetic field uniformity, power consumption, maximum current per coil, magnets resistance, cooling water, or air, flow required and air gap range.

Electromagnet power supply. To operate an electromagnet requires an appropriate bipolar power supply (it has the ability to set either positive or negative current and voltage values). Therefore, each electromagnet model is offered with its corresponding programmable power supply. The electromagnet power supply delivers a high stability and low ripple current. Its most important output parameters are: maximum current and voltage, stability, ripple an noise and temperature coefficient.