Comb excitation method for single guided wave modes in complex cross sections

Abstract

Irregular and complex cross-sectional waveguide structures exhibit numerous guided wave modes, which become mixed at high frequencies and hinder mode identification and application in damage monitoring. To address the need for single mode excitation in nondestructive testing and structural health monitoring, this study presents a comb excitation method based on group velocity that aims to excite a single guided wave mode in irregular and complex cross-sectional waveguides. Using rails as a case study for simulation and validation of the excitation effect, array comb sensors are arranged along the rail web. By adjusting the time delay and phase compensation of the comb excitation sensors, the single excitation of the rail head, rail web, and rail base detection modes is achieved over a wide frequency range. This study also establishes the modal singularity index, employing the higher-order elements SAFE method, and proposes a target modal selection rule for a wider frequency range. In addition, an evaluation index is defined to quantify the guided wave modal excitation effect is defined. Finite element simulations are used to investigate the influence of sensor spacing and number of sensor points on the array comb excitation effect, and suggestions are made for optimising the array comb excitation. Finally, experimental verification demonstrates the high accuracy of the higher-order elements SAFE method and confirms the effectiveness of the proposed comb excitation method.