Two Novel Information Entropy Indices for Analysis of the Eddy Current Distribution

Abstract

The Koch curve exciting coil eddy current sensor is a kind of novel flexible planar eddy current probe. In this study, an intersection angle spectrum entropy index and a radial direction energy spectrum entropy were proposed to evaluate the eddy current distribution. Eddy current distributions induced by one turn of a circular coil and one turn of a second order Koch curve coil feed with different exciting frequency alternative currents and at different lift-off distances, were simulated and the eddy current distributions varying with lift-off distance in different exciting frequencies were compared by the two proposed indices. With the increase of the lift-off distance or the decrease of exciting frequency, the similarity between the shape of the Koch curve and the eddy current distribution became weakened and the degree of the concentration of the eddy current distribution in the specimen under the exciting coil was loosened.

Quantitative evaluation of eddy current distribution by relative entropy and cross entropy

“…The entropy of the TIAS of the two exciting coils is shown in Figure 3. The result of entropy of the TIAS is similar to the result in the literature, 19 the angle is split to 18 intervals by the step 5°, but 30 intervals by the step 3°in this work to refine the results.…”

“…Thus, with the increase of the lift-off distance and decrease of the exciting frequency, the difference of the EC distribution of the two exciting coils is increasingly smaller. Combined the literature, 19 the ''lift-off effect'' of the EC testing can be summarized as follows:…”

“…In this paper, the eddy current distributions are extracting by FEMs calculated by commercial software COMSOL multi-physics and the entropies are calculated by the MATLAB which are same to that in the literature. 19 In order to fast get the information of the FEMs and the method, the parameter of specimen and the coil are rewrite here. All FEMs have three part: coil, specimen and air domain.…”

“…Thus, many indices were proposed to quantitatively evaluate the EC distribution, such as interaction efficiency, information entropy of angular spectrum, information entropy of intersection angle spectrum entropy, and a radial direction energy spectrum. [19][20][21] The information theory was first used to evaluate the EC distribution, but there are many different indices in the information theory. Thus, in this study, the relative entropy and the cross entropy are considered as quantitative indices to evaluate the EC distribution, because the relative entropy measures the ''distance'' between the two EC distribution, and the cross entropy can prove the correctness of the relative entropy and the information entropy.…”

A Novel Rotational Field Eddy Current Planar Probe with Two-Circular Sector Pickup Coils

“…Weimin Zhang proposed the fractal Koch curve structure to be an exciting coil-inducing eddy current distribution in many directions in a small region [15]. Then, in order to quantitatively evaluate the eddy current distribution, the angular spectrum and other indices based on information entropy have been proposed [16,17,18]. Those methods can be thought of as a space domain method.…”