Developing 3D-CMUT for Ultrasonic Guided Wave-Based Damage Imaging Applications: A Comprehensive Theory and Simulation Study

It is widely recognized that the use of multimode ultrasonic guided waves holds the potential for a comprehensive evaluation of structural damages, including their locations, sizes, and types, in the realm of damage imaging. Recently, a micro-electromechanical system (MEMS) sensor, named 3-D capacitive micromachined ultrasonic transducer (3D-CMUT), has emerged as a promising candidate for detecting 3-D vibrations of multimode ultrasonic guided waves. In this work, 3D-CMUT is introduced for the first time in ultrasonic guided wave-based damage imaging. Initially, for analytical convenience, an idealized design of 3D-CMUT is substituted with a simplified configuration comprising a piston-type cell (sensing z-directional signals) and two orthogonally positioned identical comb-type cells (sensing x- and y-directional signals). Subsequently, finite element method (FEM) simulations are employed to establish models of “a damaged aluminum plate with a circular through-hole” and “an undamaged aluminum plate.” By using the transfer function-based effective method, 3-D scattered signals captured by an array of 3D-CMUTs are rapidly extracted to characterize the circular through-hole. Ultimately, the scattered data are transformed into intuitive damage images using the decomposition of the time-reversal operator and multiple signal classification (DORT-MUSIC) algorithm. The results not only affirm the viability of applying 3D-CMUT in damage imaging but also underscore the advantages of integrating 3-D ultrasonic guided wave information for a more accurate assessment of structural damages. This research may contribute significantly to advancing the applications of 3D-CMUT in nondestructive testing (NDT).