Inductive thermography is a non-destructive technique for detecting surface cracks in electrically conductive materials. The induced eddy currents and the heat diffusion are disturbed by surface cracks, which makes the defects visible in infrared images. In non-magnetic materials, with high electrical and thermal conductivity, a short heating pulse is necessary, otherwise the thermal signal diminishes too quickly. However, with a short heating pulse only a little amount of heat is induced into the material, so the noise may be too high compared to the signal, causing a too low signal-to-noise (SNR) ratio for reliable defect detection. Applying a sequence of short pulses offers a solution. The evaluation of this multi-pulse excitation is in principle identical to the well-known lock-in technique, which is usually applied for sinusoid modulated heating. The main goal of the paper is to investigate how the temperature and phase noise can be reduced by several factors. The influence of the number of pulses, the heating power, the pulse duration, and the crack depth on the SNR is investigated. Theoretical considerations and experimental results are presented and compared to the derived equations. Aluminum and non-magnetic steel samples with artificial cracks were inspected and compared to the theoretical results.

感应热成像是一种用于检测导电材料表面裂纹的非破坏性技术。感应涡流和热扩散受表面裂纹的干扰，从而使缺陷在红外图像中可见。在具有高电导率和导热率的非磁性材料中，必须有一个短的加热脉冲，否则热信号会很快减小。但是，在短的加热脉冲下，材料中只会产生少量热量，因此与信号相比，噪声可能太高，从而导致信噪比（SNR）太低，无法可靠地进行缺陷检测。施加一系列短脉冲可提供解决方案。这种多脉冲激励的评估原则上与众所周知的锁定技术相同，通常用于正弦调制加热。本文的主要目的是研究如何通过多种因素降低温度和相位噪声。研究了脉冲数，加热功率，脉冲持续时间和裂纹深度对SNR的影响。提出了理论上的考虑和实验结果，并将其与导出的方程进行了比较。检验了带有人工裂纹的铝和非磁性钢样品，并将其与理论结果进行了比较。提出了理论上的考虑和实验结果，并将其与导出的方程进行了比较。检验了带有人工裂纹的铝和非磁性钢样品，并将其与理论结果进行了比较。提出了理论上的考虑和实验结果，并将其与导出的方程进行了比较。检验了带有人工裂纹的铝和非磁性钢样品，并将其与理论结果进行了比较。