Modeling of single turn coil impedance including wiring effects

Because of their robustness, eddy current sensors are widely used in harsh environments. For the extraction of measurement quantities such as distances or material properties, a proper understanding of the magnetic filed distribution and of the impedance of the sensor is required. Thereby the calculation of the absolute impedance of eddy current sensors is still a difficult problem, because many analytical models in literature only allow the calculation of the impedance change due to a target material, but not the absolute impedance. Furthermore, models using geometry discretization for the calculation of absolute impedance values require long calculation times. In this contribution, an analytical impedance model for the calculation of the absolute impedance of a single turn coil is discussed. The impedance model is based on the magnetic vector potential. It allows the fast calculation of the impedance and does not require any methods for geometry discretization. Special efforts are made to analyze the effects of wiring. Wiring effects due to the coil wire itself and the connection wire are considered. A very good agreement between model and measurement is observed.