Non-destructive Testing by Inovated Approach Using Swept Frequency with Various Eddy Current Probes

摘要

This study deals with innovated eddy current testing - swept frequency eddy current technique, which allows non-destructive evaluation of materials with non-zero conductivity. The basis of this novel method is a change of frequency of exciting signal in a wide range while the testing probe is in a fixed position. The swept frequency technique enables investigation of conductive objects with uneasily scanning surface. A plate of austenitic steel with three artificial EDM notches differing in their depths is inspected in this paper. Various eddy current probes placed above defects and supplied with a time-varying electric current of changing frequency are employed for the testing in order to evaluate the detection and the resolution characteristics concerning the depth of detected notches. Frequency characteristics of the induced voltage for different defect depths are evaluated in order to assess the resolution capabilities. Numerical model of inspection from COMSOL Multiphysics software connects a model of high frequency coil with a measurement chain. The purpose of this study is the confirmation of applicability of swept frequency eddy current technique using experimental results, the verification by numerical simulations and comparison of different types of probes.