Automated transducer deployment for Lamb wave-based nondestructive evaluation of plates

Lamb wave-based inspection methods show promise in long range Nondestructive Evaluation (NDE) of thin metallic and composite plates. This NDE strategy is typically implemented in a pitch-catch configuration of one actuator and at least one sensor. Despite non-contact methods such as laser ultrasonics and air-coupled transducers, the most common approach relies on contact transducers. Transducer placement is usually performed manually and positional errors and variations in contact conditions are therefore inevitable. Thus, this study investigates the potential improvement in measurement reliability and repeatability through the use of an automated deployment system. The system is comprised of two subsystems: 1) A gel deployment subsystem to deposit the desired amount of couplant at the target location. 2) A transducer deployment subsystem to lower the transducer onto test article. In addition to a detailed description of the developed prototype systems, their combined reliability is demonstrated for experiments on an aluminum panel in a broad frequency range. The results are compared to those obtained via transducers positioned by multiple different human operators. These benchmark experiments are conducted with varying degree of aids, such as placement templates and weights. Furthermore, measurements from manual placement are processed both manually as well as automatically to further illustrate the need for fully automated NDE capabilities. It is shown that the automated prototype transducer deployment system not only reduces manual labor but achieves slightly improved repeatability as compared to an experienced human operator with positioning aids.