A flexible MXene/PVDF nanocomposite piezoresistive sensor for ultra-broadband ultrasonic guided wave sensing

Driven by the growing demand for detecting minor structural damage in structural health monitoring, high frequency guided wave excitation and sensing are urgently needed. Nanocomposite piezoresistive sensors have been selected as a promising solution to meet this need. In this study, a novel flexible piezoresistive sensor was developed, employing MXene as the sole conductive nanofiller and PVDF as the polymer matrix. A vacuum-assisted filtration technique was employed to precisely control the alignment and orientation of MXene nanosheets within the MXene/PVDF composite resulting composite films. SEM images of the MXene/PVDF sensor reveal a layer-by-layer assembly structure, where MXene nanosheets are tightly encapsulated by the PVDF matrix. Both electrical conductivity measurements and ultrasonic guided wave experiments reveal that the MXene/PVDF sensor containing 3 wt% MXene exhibits the most pronounced change in electrical conductivity and the highest sensitivity to ultrasonic guided wave excitation. To the best of our knowledge, this is the first report of a nanocomposite piezoresistive sensor capable of detecting ultrasonic guided waves at frequencies up to 2.0 MHz. These findings not only expand the application scope of MXene-based materials but also demonstrate their promising potential for detecting minor structural damage in structural health monitoring applications.