Abstract

Although global damage detection might be achieved via changes of natural frequency, guided wave-based techniques are usually needed to sensitively locate small damages. However, compared to the vibration-based methods, the acoustic or ultrasonic waves in real structures are easily contaminated with environmental noises and careful data analysis and trained experts are usually required. Unlike conventional structures, periodic structures such as phononic crystals (PCs) or metamaterials have the phenomenon of band gaps whose frequency characteristics are quite sensitive to the lattice parameters. When defects such as a mismatch of a unit cell exist in PCs, defect modes can be seen in the band gaps and elastic or acoustic waves will be localized near the defects. The frequencies of the defect modes are even more strongly affected by the variation of lattice parameters of the periodic structures. Thus, sensitive damage detection might be achieved after introducing periodicity on purpose to the detected structure and examining the defect modes in the band gaps. In this talk, I will first show how we came up with introducing periodicity to structures then detect the damage based on the defect modes. Then, I will present some applications other than damage detections with the defect modes in our group. Finally, I will introduce some other periodic-structure applications in which metamaterials are used to enhance the performance of nonlinear ultrasonics-based structural health monitoring.