In this study, transverse heat flow suppression (THFS) technique was proposed to enhance the ability of thermal-wave radar thermography (TWRT) to resist lateral thermal diffusion and uneven heating. The enhanced TWRT was used to detect subsurface defects of carbon fiber reinforced plastic (CFRP) laminates. The principle of THFS was described in detail by the optical flow analogy. The three-dimension (3-D) thermal-wave model stimulated by the uneven linear frequency modulation (LFM) thermal flow was introduced. The thermal-wave signal was processed by several different postprocessing characteristic extraction algorithms [Cross-correlation algorithm (CC), dual-orthogonal demodulation algorithm (DOD), fractional Fourier transform (FrFT), and principal component analysis (PCA)]. The comparison between normalized DOD amplitude/phase and normalized DOD-THFS amplitude/phase was carried out. The simulation results depicted THFS can significantly improve the difference between defect location and nondefect location. Nine CFRP specimens with artificial flat-bottom holes (FBHs) were prepared for nondestructive testing and evaluation (NDT&E) by enhanced TWRT. Seventy-two FBHs were prepared to test the probability of detection (PoD) of the enhanced TWRT. Hit/miss method was used to count defect information. The results demonstrated that the enhanced TWRT can realize the effective detection of defects (90% detection probability) with a diameter depth ratio of 5.06 under 95% confidence level. Compared with two state-of-the-art approaches, the proposed DOD-THFS phase has a better defect detection signal-to-noise ratio (SNR).

中文翻译：

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利用横向热流抑制技术优化热波雷达热成像以准确检测 CFRP 层压板缺陷

在这项研究中，横向热流抑制（THFS）技术被提出来增强热波雷达热成像（TWRT）抵抗横向热扩散和不均匀加热的能力。增强型 TWRT 用于检测碳纤维增强塑料 (CFRP) 层压板的亚表面缺陷。THFS的原理通过光流类比详细描述。介绍了由不均匀线性频率调制 (LFM) 热流激发的三维 (3-D) 热波模型。热波信号通过几种不同的后处理特征提取算法[互相关算法 (CC)、双正交解调算法 (DOD)、分数傅立叶变换 (FrFT) 和主成分分析 (PCA)] 进行处理。进行了归一化 DOD 幅度/相位和归一化 DOD-THFS 幅度/相位之间的比较。THFS 所描述的仿真结果可以显着改善缺陷位置和非缺陷位置之间的差异。通过增强型 TWRT 制备了九个带有人工平底孔 (FBH) 的 CFRP 试样，用于无损检测和评估 (NDT&E)。准备了 72 个 FBH 来测试增强型 TWRT 的检测概率 (PoD)。命中/未命中方法用于计算缺陷信息。结果表明，增强型TWRT可以在95%置信水平下实现直径深度比为5.06的缺陷的有效检测（检测概率为90%）。与两种最先进的方法相比，所提出的 DOD-THFS 相位具有更好的缺陷检测信噪比 (SNR)。