This paper describes a novel method for thickness measurement in conducting material by combining the measurement of the decaying induced eddy current and its associated apparent conductivity calculation. In conventional frequency domain NDE (Non-destructive Evaluation), the skin depth is the limiting factor due to the single frequency excitation. In contrast, with a pulsed excitation, the induced eddy currents decay with time and the decay of the eddy current consists of continuum of frequencies and hence the entire thickness of the conducting material could be investigated in a single shot. The time at which the decay of the eddy current is maximum is called diffusion time “t_m” and the corresponding calculated value of apparent electrical conductivity “σ^m_app” both of which can be directly correlated to the thickness of the material. Since the induction of the eddy current and its associated secondary magnetic field measured by using suitable magnetic sensors [h_z α (σ/t)^3/2 for B-field and V_z α (σ^3/2/t^5/2) for an induction coil] is directly related to the conductivity of the materials, one can calculate the apparent conductivity σ_app(t) as a function of decay time. Apparent conductivity calculations have been made for aluminum plates based on the thin conducting sheet model in which the applied magnetic field is uniform throughout the thickness. Subsequently, transient measurements have been performed with stacks of aluminum plates by using pickup coils in the form of an absolute as well as differential configuration. From this, it has been shown that the square root of the ratio of the maximum diffusion time, t_m and the corresponding apparent conductivity, σ^m_app called as maximum diffusion depth, δ_m which is proportional to the plate thickness. The diffusion depth is a parameter derived from standard electromagnetic equations which is analogous to the skin depth in the frequency domain. In this work, induction coil sensors of both types have been used to measure the transients, and the other instruments such as transmitter, transmitter controller and data acquisition system used for this work are the same ones used for TDEM (time domain electro-magnetic) based geophysical applications.

本文结合衰减感应涡流的测量及其相关的视在电导率计算，介绍了一种用于导电材料厚度测量的新方法。在常规的频域NDE（非破坏性评估）中，趋肤深度是单频激励的限制因素。相反，在脉冲激励下，感应的涡流随时间衰减，并且涡流的衰减由连续的频率组成，因此可以单次研究导电材料的整个厚度。在该涡电流的衰减最大被称为扩散时间“的时间吨_米”和表观电导率的相应的计算的值“σ^米_应用两者都可以直接与材料的厚度相关联。由于通过使用合适的磁传感器[测量的涡流和其相关联的次级磁场的感应ħ _Ž α（σ /吨）^3/2对B场和V _ž α（σ ^3/2 /吨^5/2）用于感应线圈]直接相关的材料的导电率，可以计算表观电导率σ_应用程式（吨）作为衰减时间的函数。已经基于薄导电片模型对铝板进行了表观电导率计算，其中所施加的磁场在整个厚度上都是均匀的。随后，通过使用绝对和差分配置形式的拾波线圈对铝板叠堆进行了瞬态测量。由此看来，它已经表明的最大扩散时间，该比值的平方根吨_米和相应的表观电导率，σ^米_应用称为最大扩散深度，δ_米与板厚成正比。扩散深度是从标准电磁方程得出的参数，类似于频域中的趋肤深度。在这项工作中，两种类型的感应线圈传感器都已用于测量瞬变，而用于此工作的其他仪器（例如变送器，变送器控制器和数据采集系统）与用于TDEM（时域电磁）的仪器相同。基础的地球物理应用。