An investigation on the electromagnetic design optimization of rotary micromachines with double-layer permanent magnets

Electromagnetic design optimization of axial-flux rotary micromachines utilizing double-layer permanent magnets is presented and applied to a micro-scale generator/spirometer currently under development. Double-layer magnet configuration enables the use of two stators in a rotary micromachine, and hence offers performance enhancements in such devices. For an efficient transduction, number of magnetic poles should be carefully selected to obtain maximum flux density in a given device geometry, where magnetic reluctance and leakage act as two competing effects. This optimization has been performed through electromagnetic finite element simulations over a range of MEMS geometries. It was shown that the optimum number of magnetic poles varies from 22 to higher than 32 depending on specific magnet dimensions. Experiments on a manufactured magnet were performed and compared with simulation results. The analysis and results reported here shed light on the efficient design of magnetic micromachines in similar scales.