Optimisation of a non contact coil / magnet actuator: Geometry, nonlinearities and thermal heating

This article presents the optimisation of an electromagnetic actuator composed of a toroidal coil and a cylindrical magnet positioned along the coil’s axis that may be used for non-contact measurement of excitation of structures, for vibration testing, electromagnetic shunts or energy harvesting. The originality of this work lies in proposing a generalised optimisation of such electromagnetic systems to maximise the axial force for a given volume or mass, while aiming for the most linear behaviour possible. A semi-analytical and dimensionless computation method is introduced and compared with existing approaches. The influence of each geometric parameter of the coil and the magnet on the axial force is investigated. Furthermore, the non-linearities induced by the displacement of the magnet in the coil’s magnetic field are quantified, and the effect of design parameters on limiting these non-linearities is analysed to identify optimal geometries. The axial force and non-linearity computations are validated through finite element simulations and experimental measurements. Finally, a study on the influence of the coil wire diameter on the force output and allowable current is also presented.