Ultrasonic guided wave structural health monitoring: A review of linear and nonlinear methods

Nondestructive testing (NDT), a core component of Structural Health Monitoring (SHM), enables the detection of damage without compromising the structural integrity of engineering systems. Among NDT methods, guided wave techniques have gained increasing prominence due to their capability to inspect relatively large areas with high sensitivity to damage. These techniques, however, face challenges related to mode complexity, environmental variations, and the accuracy of signal interpretation, which require continuous methodological advancements. This review presents a comprehensive evaluation of guided wave–based SHM, with a focus on linear and nonlinear approaches. It examines experimental, numerical, and data-driven developments to clarify the advantages, limitations, and practical applications of each method. The review also identifies existing research gaps particularly in linear and nonlinear effect integration, robust signal processing, and adaptation to complex environments while outlining promising directions for future work. The insights aim to support researchers and practitioners in developing more effective and reliable guided wave techniques for SHM.