Prestack reverse-time migration in structural health monitoring

This paper presents an approach to quantitatively detect and image multiple damages in a plate-like structure. A structural health monitoring system (SHMS) with a linear array of active, distributed actuators/sensors is proposed. The integrated actuators/sensors are used to activate/receive lowest order antisymmetric A₀ mode Lamb waves. A migration technique used in geophysical exploration and seismic prospecting is adopted to interpret the back-scattering wave field and to image the flaws in the structure. The proposed approach is modeled by finite difference method both in simulating the reflection waves and in implementing the prestack migration. An analytical solution based on Mindlin plate theory is derived to verify the accuracy of the numerical algorithm. An excitation time imaging condition specifically for the migration of waves in a plate is introduced based on ray tracing concept, and prestack reverse-time migration is proceeded to propagate the reflection energy back to the damages. The plate is imaged in terms of the velocity of transverse deformation after migration, thus the locations, dimensions and seriousness of the flaws could be visually displayed. The numerical results show that multiple damages can be successfully detected and the image of the damages coincides well with the target damages. The conclusion is that prestack migration can be a prospective technique in SHMS applications.