Cho Sungjong, Jeong Hyunjo, Park Ik Keun
NDT Research Center, Seoul National University of Science and Technology, Seoul 01811, Korea.
Department of Mechanical Engineering, Wonkwang University, Iksan 54538, Korea.
Materials (Basel). 2020 Dec 6;13(23):5565. doi: 10.3390/ma13235565.
Nonlinear ultrasound has been proven to be a useful nondestructive testing tool for micro-damage inspection of materials and structures operating in harsh environment. When measuring the nonlinear second harmonic wave in a solid specimen in the pulse-echo (PE) testing mode, the stress-free boundary characteristics brings the received second harmonic component close to zero. Therefore, the PE method has never been employed to measure the so-called "nonlinear parameter ()", which is used to quantify the degree of micro-damage. When there are stress-free boundaries, a focused beam is known to improve the PE reception of the second harmonic wave, so phased-array (PA) transducers can be used to generate the focused beam. For the practical application of PE nonlinear ultrasonic testing, however, it is necessary to develop a new type of PA transducer that is completely different from conventional ones. In this paper, we propose a new annular PA transducer capable of measuring with improved second harmonic reception in the PE mode. Basically, the annular PA transducer (APAT) consists of four external ring transmitters and an internal disk receiver at the center. The focused beam properties of the transducers are analyzed using a nonlinear sound beam model which incorporates the effects of beam diffraction, material attenuation, and boundary reflection. The optimal design of the APAT is performed in terms of the maximum second harmonic reception and the total correction close to one, and the results are presented in detail.
非线性超声已被证明是一种有用的无损检测工具，可用于对在恶劣环境中运行的材料和结构进行微观损伤检测。在脉冲回波（PE）测试模式下测量固体试样中的非线性二次谐波时，无应力边界特性会使接收到的二次谐波分量接近零。因此，PE方法从未被用于测量用于量化微观损伤程度的所谓“非线性参数（ ）”。当存在无应力边界时，已知聚焦光束可改善二次谐波的PE接收，因此相控阵（PA）换能器可用于产生聚焦光束。然而，对于PE非线性超声检测的实际应用，有必要开发一种与传统换能器完全不同的新型PA换能器。在本文中，我们提出了一种新型环形PA换能器，它能够在PE模式下以改善的二次谐波接收来测量 。基本上，环形PA换能器（APAT）由四个外部环形发射器和位于中心的一个内部圆盘接收器组成。使用包含光束衍射、材料衰减和边界反射效应的非线性声束模型分析换能器的聚焦光束特性。根据最大二次谐波接收和接近1的总校正对APAT进行优化设计，并详细给出结果。
