Analysis of the Lift-off Effect of Phase Spectra for Eddy Current Sensors

Abstract

This paper presents an analytical model which describes the inductance change when a double air-cored coil sensor is placed next to a conducting plate. Analysis of the analytical model reveals that the phase signature of such sensor is virtually lift-off independent. This finding is verified by numerical evaluations. This paper also finds that the phase signature of a ferrite U-cored sensor can be approximated by that of a double air-cored sensor of similar size, and therefore possesses similar lift-off independent property. Measurements made with a sample U-cored sensor next to plates of non-magnetic and magnetic materials verified the theoretical results