Enhancing Guided-Wave-Based Structural Health Monitoring Using Metamaterial Devices Designed by Topology Optimization

Lamb waves inside thin-walled structures have received extensive attention due to their great promise in applications such as structural health monitoring (SHM). Applications point at the common need for effective conditioning and manipulation of the wave propagation in terms of both frequency content and mode components. In this work, the concept of metamaterials is exploited to construct functional meta-devices (MDs). The MDs are designed to deliver prescribed functionalities after they are surface-mounted onto a structure conveying Lamb waves. To this end, a unified inverse-design scheme based on topology optimization is proposed and applied to achieve multifold functions such as frequency filtering and single-mode transmission. Typical scenarios with different frequencies and modes are discussed. Functional MDs with broadband working frequencies are obtained by using the established design strategy. A representative MD with a finite number of unit cells is examined through finite element simulations. Numerical simulations show that, through wave modulation of the designed MD, Lamb waves located in pass bands can transmit through the MD, while the waves within bandgaps are prohibited to propagate by the MD, which agrees well with the predicted dispersion features. An experiment is finally carried out to confirm the prescribed wave manipulation functions of the designed MD from the SHM perspective, which is finally validated experimentally using a metal specimen containing local plasticized incipient damage. This work provides a universal approach for topologically customizing MDs for the precise and tactical control of Lamb wave propagation, especially for SHM applications.