Study on the Inductance of Micro Planar Coil for Eddy Current Detection

Abstract-A noncontact inductive sensor was designed for the eddy current detection, the main structure of the inductive sensor is single-layer micro-planar coil. Two groups of micro-planar coils with different wire width, wire distance and wire thickness are fabricated by using electrochemical and MEMS technology in order to make the detection. We establish the inductance and impedance mathematic models to describe the near-field eddy current effect of the micro-planar coil according to the structure of the coil. When alternate current in certain frequency circulates in the micro-planar coil, alternate magnetic field will generate around the coil. The effect of eddy current can be mainly reflected by the signal of inductance. This paper describes the fabrication of the micro-planar coil, and proposes an approach to calculate the inductance. Through the experiment of testing the inductance and impedance of the coil by using Agilent 4294A Precision Impedance Analyzer and Solartron Electro-chemical Impedance System, we make a comparison between the inductance and impedance. The experimental results indicate the signal of the inductance and impedance of the micro-planar coil can be well used in the study of eddy current field while in a certain condition, but the inductance has good sensitivity and linearity and high interference immunity. The comparison between the inductance and impedance reveals that the experimental results and the theoretical calculation results are almost consistent, and the deviation is between 3 % and 12%. So the mathematical model of the inductance has shown to be effective, and the intensity of the eddy current field around the coil can be better expressed by the signal of the inductance while it is more stable and sensitive