Air-gap effects in inductive energy transfer

A transformer with a separation between the primary and secondary windings can be used to transfer power to artificial organs, pacemakers or robot joints without electrical contacts or wires. This paper examines the impact of the gap fringing field in the operation of the dc-dc converter. As has been implied in previous work the power losses and EMI generated by the fringing field can have a significant impact on the converter operation. This paper presents the mechanism behind the winding power losses using FEA tools and actual measurements. Furthermore the effect of the field vector in electromagnetic emissions of the converter is investigated. A reduction of EMI by means of adjusting the air-gap length is demonstrated and the benefit is quantified using field measurements.