A meta-lens-enhanced framework for localized damage identification through backscattered wave focusing

Guided wave-based structural health monitoring (GWSHM) has high sensitivity to damage in aerospace applications, but is also sensitive to background noise, leading to potential misjudgments of structural health. This underscores the need for signal enhancement techniques that are specifically responsive to damage. Meta-lenses have long been considered as promising for SHM applications, but targeted strategies for practical SHM scenarios remain limited. This paper presents a framework for damage identification with a damage index (DI) directly related to damage and showing noise robustness and sensitivity to damage properties, by utilizing the wave focusing of the meta-lens for enhancing and redistributing the damage-related energy. Firstly, a classical meta-lens is designed as the standard process to realize wave focusing on the aluminium plate. To maximize the enhancement of the obtained signals brought from the meta-lens, a sensor arrangement with the sensor placed at the symmetric focal point is compared to the traditional one, usually with the sensor placed at the focal point. By utilizing the backscattered waves from the damage, the signals can be enhanced by the meta-lens without changing the baseline, resulting the signal difference directly related to the damage. The white noise with three levels of signal-to-noise ratio (SNR) is then added on these signals to compare the detection of them both under the scenarios with and without the meta-lens, and the results show that the characteristic of the enhanced signal emerges clearly under the noise circumstance. The enhanced signal and the manipulated wave field are further utilised for the damage quantification and localisation and show DI values up to 10 times higher sensitivity to the damage size and location than the scenarios without the meta-lens. Manufacturing and assembly errors are also examined, yielding recommended tolerances for the present meta-lens configuration. Simulations and experiments confirm that reflected focal point sensing increases the DI magnitude and its sensitivity to damage parameters under the tested noise conditions. These results establish a sensing principle for applying meta-lens focusing to localized damage identification under noise.