Software control of an active magnetic shield

An active shield is designed to reduce the stray magnetic field of an induction heater, which heats a workpiece using a strong magnetic excitation field. The shield consists of a number of coils at well-chosen positions and generates a magnetic field that is opposite to the induction heater stray field in a defined target area. The presented software controller maximises the field reduction by using amplitude and phase information of the relevant frequency components in the spectrum of the excitation current and of the Euclidian space components of the magnetic field at a point. The average field reduction in the target area is equal to 25 dB.