Optimisation of flux concentrator-coil design for application in magnetic hyperthermia

Abstract

This study investigates some key optimisation aspects of applicator coils with ferrite-based flux concentrators for magnetic hyperthermia treatment. We found that the enhancement of the magnetic field flux from the coil with the aid of flux concentrators comes at a cost of increased inductance - which demands lower capacitance counterparts in a high-frequency resonance LC circuit - and higher AC resistance, which generates unwanted Joules heating. Positioning the coil at the application end of the flux concentrator increases the magnetic field strength dramatically, whilst reducing inductance and AC resistance. Preliminary experiments indicate that the increased magnetic field strength from flux concentrators of higher aspect ratio saturates above a certain concentrator-to-coil length ratio of around 15. Using a high degree of perforation of the core results in negligible difference in magnetic field progression. By optimising the relative coil-to-concentrator dimensions, AC resistance can be limited as proximity effects resulting from ferrite concentrator and coil interaction are reduced. The latter two findings enable new opportunities to improve the cooling efficiency. © Published under licence by IOP Publishing Ltd.