ABSTRACT In this work, the second harmonic generation (SHG) technique based on embedded piezoelectric (PZT) sensors is developed for the defect assessment of concrete samples. Three different imperfection forms of concrete including internal capillary void during the curing process, cracking damage due to compression, and bending loads are examined and analyzed. Clear second harmonics are observed by Fourier transform of time domain signal, and the square of fundamental signal amplitude shows a linear relation with the second harmonic amplitude as theoretically expected. The nonlinear parameter presents a good distinction for samples in different states of three cases, indicating the well-round feasibility of SHG technique based on embedded sensors. In addition, the nonlinear parameter presents an excellent correlation with the variation of internal capillary void and cracks in concrete. The high sensitivity of the developed SHG technique is further validated through a comparison between the nonlinear parameter and two traditional linear parameters, namely the phase velocity of Rayleigh wave and the resonance frequency of vibrations. Experimental results in this study demonstrate that the embedded sensors are promising for the nonlinear ultrasonic nondestructive evaluation of concrete structures, particularly as a low-cost alternative of commercial ultrasonic transducers.

中文翻译：

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基于嵌入式压电传感器的混凝土缺陷非线性超声二次谐波评估

摘要 在这项工作中，基于嵌入式压电 (PZT) 传感器的二次谐波生成 (SHG) 技术被开发用于混凝土样品的缺陷评估。检查和分析了混凝土的三种不同缺陷形式，包括固化过程中的内部毛细管空隙、压缩引起的开裂损伤和弯曲载荷。通过时域信号的傅里叶变换观察到清晰的二次谐波，基波信号幅度的平方与理论预期的二次谐波幅度呈线性关系。非线性参数对三种情况下不同状态的样品表现出很好的区分，表明基于嵌入式传感器的SHG技术的全面可行性。此外，非线性参数与混凝土内部毛细管空隙和裂缝的变化具有极好的相关性。通过非线性参数与两个传统线性参数（即瑞利波的相速度和振动的共振频率）之间的比较，进一步验证了所开发的 SHG 技术的高灵敏度。本研究中的实验结果表明，嵌入式传感器有望用于混凝土结构的非线性超声无损评估，特别是作为商用超声换能器的低成本替代品。即瑞利波的相速度和振动的共振频率。本研究中的实验结果表明，嵌入式传感器有望用于混凝土结构的非线性超声无损评估，特别是作为商用超声换能器的低成本替代品。即瑞利波的相速度和振动的共振频率。本研究中的实验结果表明，嵌入式传感器有望用于混凝土结构的非线性超声无损评估，特别是作为商用超声换能器的低成本替代品。