Ma Botao, Liu Chen, Sun Shupeng, Zhang Lin
Department of Engineering Mechanics, School of Civil Engineering, Shandong University, Jinan 250061, China.
Materials (Basel). 2025 Aug 11;18(16):3753. doi: 10.3390/ma18163753.
Lock-in thermography is a widely adopted infrared nondestructive testing technique that detects subsurface defects by applying modulated thermal waves and analyzing the resulting surface temperature variations. However, quantitatively characterizing subsurface defects at varying depths remains a significant challenge. This study explores the lateral resolution of subsurface defect detection using phase-based lock-in thermography, integrating analytical modeling, finite element simulation, and phase difference analysis. The results demonstrate that defect visibility and boundary definition are highly influenced by the excitation frequency. The thermal diffusion length, which is inversely proportional to the square root of the excitation frequency, governs both the penetration depth and the lateral spread of thermal energy. Higher frequencies enhance lateral resolution, whereas lower frequencies improve the detectability of deeper defects. Detection becomes particularly difficult for defects with small radii or low radius-to-depth ratios. A critical radius-to-depth threshold of 2 is identified as essential for reliable boundary delineation. These findings offer practical guidance for selecting excitation frequencies to achieve an optimal balance between depth sensitivity and lateral resolution in thermal-wave-based nondestructive evaluation.
锁相热成像技术是一种广泛应用的红外无损检测技术，它通过施加调制热波并分析由此产生的表面温度变化来检测地下缺陷。然而，对不同深度的地下缺陷进行定量表征仍然是一项重大挑战。本研究利用基于相位的锁相热成像技术，结合解析建模、有限元模拟和相位差分析，探索地下缺陷检测的横向分辨率。结果表明，缺陷的可见性和边界清晰度受激励频率的影响很大。热扩散长度与激励频率的平方根成反比，它控制着热能的穿透深度和横向扩散。较高的频率提高了横向分辨率，而较低的频率则提高了对较深缺陷的检测能力。对于半径较小或半径与深度比低的缺陷，检测变得特别困难。确定临界半径与深度阈值为2对于可靠的边界描绘至关重要。这些发现为在基于热波的无损评估中选择激励频率以实现深度灵敏度和横向分辨率之间的最佳平衡提供了实用指导。
