Eddy current testing for thickness measurement has great advantages, such as non-contact, low cost, and high efficiency. It is reported that there is a linear relationship between the tangent of the phase angle of impedance change and the thickness, termed as the approximate linear method (ALM). However, the accuracy of ALM is not very good, especially when the thickness of a specimen is very thin compared with standard penetration depth. The relationship between tangent of phase angle and thickness is simulated by Dodd-Deed model. The first and second derivatives of tangent of phase angle to thickness is consistent with the power function. Thus, the log–log method (LLM) is obtained by taking logarithm of power fitting equation. And, it is found that the change of excitation frequencies and lift-offs hardly affect the slope and linearity of LLM. The correctness and feasibility of LLM are verified by numerical simulation and experiments.

用于厚度测量的涡流测试具有很大的优势，例如非接触，低成本和高效率。据报道，在阻抗变化的相位角的切线与厚度之间存在线性关系，称为近似线性方法（ALM）。但是，ALM的精度不是很好，特别是当样品的厚度与标准穿透深度相比非常薄时。用Dodd-Deed模型模拟了相角切线与厚度之间的关系。相角与厚度的切线的一阶和二阶导数与幂函数一致。因此，通过采用幂拟合方程的对数获得对数-对数方法（LLM）。并且发现，激励频率和升程的变化几乎不影响LLM的斜率和线性。