Journal of Magnetism and Magnetic Materials 101 (1991) 286-288 North-Holland Ai lw Some aspects of the design of rotating actuators K. Hameyer and R. Hanitsch Technische Universith't Berlin, Germany Mathematical modelling of the magnetic and mechanical properties can be carried out by different methods. For optimizing or investigation of material-dependent properties, simple models with reasonable accuracies are needed to reduce the computational time. Different methods were used for the solution of the electromagnetic field problem. The design rules for a rotating actuator will be given• 1. Materials 1.1. Permanent magnet material ity of 100. Compared with this, a construction with bonded soft magnetic material expands in volume if we keep the magnetic voltage drop constant [2,3]. The use of powder metallurgy high-energy perma- nent magnets can lead to significantly improved effi- ciency and performance of electrical devices• High remanence and high coercivity at room temperature makes Nd-Fe-B magnet excitation particularly attrac- tive in electromagnetic energy converters• The sensitiv- ity of the coercivity of this material to high tempera- tures calls for increased attention to the thermal as- pects of a new design• With a special heat treatment some temperature stabilization effects can be ob- served. Small additions of Co, Dy or V creates a greater thermal stability. Because of this, applications with Nd-Fe-B under heavy-duty operation are limited to temperatures up to 150 ° C. All sintered Nd-Fe-B magnets are significantly stronger then Sm-Co alloys. The energy product (BH)ma x of Nd-Fe-B magnets was increased by more than 30% compared to that of Sin-Co magnets• The performance gap between fer- rites and rare-earth magnets is completed with plastic- bonded permanent magnets. These grades of bonded Nd-Fe-B or Sin-Co are often hot extruded materials. With respect to the manufacturing process, apart from having good magnetic properties, similar attention to the non-magnetic properties must be given [1-3]. 1.2. Soft magnetic materials To avoid eddy currents in the soft magnetic parts of the magnetic circuit, laminations are used. This part of the construction can be substituted by plastic-bonded ferromagnetic material• This is advantageous because of the better machinability of the moulded pieces• These grades of bonded soft magnetic materials show good magnetic properties. Typical values of saturation flux density are 1.5-1.8 T, coercive field strength 3.5- 4.5 Acm -~ and maximum permeability at 50 Hz, 60-180 (HYPERM. 080p, Krupp). FeCo lamination steel has values of saturation flux density up to 2.3 T, a low coercive field strength and a maximum permeabil- 1.3. Modelling of non-linear characteristics The available information from manufacturers about the non linear characteristics of permanent magnet materials or soft magnetic material are usually given as measured diagrams. Often only the induction against the field strength at room temperature is plotted. To use this information numerically, the plotted values have to be stored in arrays of discrete data samples. Between the data samples, interpolation of the real characteristic has to be done. Good results can be obtained by cubic spline interpolation. In doing the calculation of the magnetic circuits with the presence of permanent magnets it is assumed that the values of remanence and coercivity are at their maximum levels. It can be shown that without complete magnetization the magnetic characteristics in the second quadrant change strongly. These characteristics are a rarity in program libraries• 2. Design of magnetic circuits 2.1. Methods At this point, only a few methods for calculation should be mentioned. In every case the complexity of the field problem itself leads to the best method to use. The following list starts with numerical and ends with the analytical methods: finite-element method (FEM), • boundary element method (BEM), finite difference method (FDM), • magnetic equivalent circuit (MEC), charge simulation method (CSM), • simplified analytical approach (SAA). The numerical methods FEM, BEM and FDM are advantageous for solving electromagnetic field prob- lems with very complex geometries• A general disad- vantage of these methods can be seen in their need for 0312-8853/91/$03.50 © 1991 - Elsevier Science Publishers B.V. All rights reserved