Multi-Frequency Eddy Current Testing of Copper Based Magnetic Alloys Using the Principal Component Analysis

Abstract

  Multi-frequency eddy current measurements are utilized to conduct non-destructive testing of physical and geometric characteristics of products made from magnetic metallic materials. Using the example of magnetic bronzes, the joint effect of several parameters like magnetic permeability, electrical conductivity, the thickness of magnetic material, and the value of the gap between the material surface and the sensor on experimental hodographs of the “controlled sample - eddy current sensor” system is investigated. The influence of magnetic properties on hodograph lines is studied by comparing the results with hodographs of a non-magnetic copper alloy. The measurement results (experimental hodographs) are subjected to mathematical processing using the principal component method to separate the main influencing factors. Thus, the entire set of experimental data describing the hodograph of a particular sample is considered as the coordinates of one point of a multidimensional space. The results of numerical calculations are presented in the form of projections of the plane of the first principal components. This provides a visual separation of simultaneously acting competing factors manifested in the formation of clustered groups of points describing samples with similar physical and geometric properties on the planes of the main components. Obtained results demonstrate that application of the principal component method has expanded the capabilities of eddy current testing of magnetic metallic materials. The proposed approach can be used for development of new eddy current devices for nondestructive diagnosis of products and structures.osis of products and structures.