Interfacial delamination detection of multilayer composite structures based on broadband PMUT arrays

Compared to traditional ultrasonic probes, piezoelectric micromechanical ultrasound transducer (PMUT) arrays have many advantages in the field of composite flaw detection owing to their small size, good consistency, and high sensitivity. However, in the actual detection process, the problems of low axial resolution and echo overlap significantly hinder the further development of PMUT devices for composite flaw detection. In this study, a broadband (75 %) PMUT with a center frequency of 2 MHz was designed using a multi-size mixing structure. At the same time, based on the acoustic phase flip phenomenon, a correlation coefficient method of translational window signals is proposed, which can accurately identify tiny (50-μm-thick, 1/10 wavelength) delamination defects by calculating the phase difference of the echo front, and successfully breaks through the half-wavelength detection limit. In addition, the C-scan imaging results of the two types of delamination defects demonstrate the capability of the PMUT device and detection algorithm in the detection of delamination defects in composite materials. This above study provides research ideas for the further development of ultrasonic devices in the field of solid micro-sized defect detection.