Airgap fringing flux reduction in inductors using open-circuit copper screens

In a gapped inductor, airgap fringing flux induces eddy currents in coil conductors in the vicinity of the airgap, producing unwanted power loss and heat in the coil. An open-circuit copper screen placed around the airgap of a ferrite core is shown to reduce the fringing flux around the airgap. The reduction in fringing flux is shown by experiment to reduce the power loss, in the inductor winding, associated with eddy currents induced by airgap fringing flux, and practical results compare favourably with presented finite-element results. The reduction in coil losses reduces the cooling requirement for the inductor, or alternatively, allows an increase in the thermal rating of the inductor. © IEE, 2005.