School of Information Engineering, Wuhan University of Technology, Wuhan 430070, China.
Shaanxi ERC of NDT and Structural Integrity Evaluation, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an 710049, China.
Sensors (Basel). 2023 Jan 7;23(2):694. doi: 10.3390/s23020694.
Thin multi-layered materials are widely used in key structures of many high technology industries. To ensure the quality and safety of structures, layer thickness measurement by non-destructive testing (NDT) techniques is essential. In this paper, a novel approach for the measurement of each layer's thickness in thin multi-layered material is proposed by using ring-shaped laser generated focused ultrasonic bulk waves. The proposed method uses a ring-shaped laser with a variable radius to generate shear waves with variable focus inside the structure. By analyzing the signal characteristics at the ring center when the laser radius varies from zero to maximum, the direct measurement of layer thickness can be realized, considering that only when the focal depth and the layer thickness satisfy the specific relationship, the reflected shear waves converge and form a peak at the ring center. This straightforward approach can increase the pulse-echo SNR and prevent the processing of aliasing signals, and therefore provides higher efficiency and accuracy for the layer thickness measurement. In order to investigate the feasibility of this method, finite element simulations were conducted to simulate the ring-shaped laser generated ultrasonic waves in multi-layered structure in detail. Following the principle of the proposed method, the layer thickness of a bi-layer and 3-layer structure were respectively measured using simulation data. The results confirm that the proposed method can accurately and efficiently measure the layer thickness of thin multi-layered material.
薄型多层材料广泛应用于许多高科技产业的关键结构中。为了确保结构的质量和安全，使用无损检测（NDT）技术对层厚进行测量是必不可少的。本文提出了一种利用环形激光产生聚焦超声体波测量薄型多层材料各层厚度的新方法。该方法采用可变半径的环形激光在结构内部产生具有可变焦点的剪切波。通过分析激光半径从 0 到最大值变化时环形中心处的信号特征，可以实现层厚的直接测量，因为只有当焦点深度和层厚满足特定关系时，反射剪切波才会汇聚并在环形中心形成峰值。这种直接的方法可以提高脉冲回波 SNR，防止处理混叠信号，从而为层厚测量提供更高的效率和准确性。为了研究该方法的可行性，进行了有限元模拟，以详细模拟多层结构中环形激光产生的超声波。根据所提出方法的原理，分别使用仿真数据测量了双层和三层结构的层厚。结果证实，该方法可以准确、高效地测量薄型多层材料的层厚。
