Fast and real-time inspection of concrete structures using a rolling 3D ultrasound scanner

A multilayer piezoelectric PVDF (Polyvinylidene fluoride) array transducer is used to develop an ultrasonic rolling scanner for concrete structure inspection. The eight-element transducer array units are assembled in two separate rollers to operate in transmission and receiver modus (pitch-catch mode). The scanner is equipped with a rotational encoder that keeps track of positional information with reference to a starting point during scanning. A large area of concrete surface can be scanned and inspected in a relatively short time. An image of good quality is acquired using a customized electronics platform and an adaptation of the SAFT (Synthetic Aperture Focusing Technique) algorithm. The system setup yields easy interpretation of real time 3D images showing the concrete's internal state. The broadband characteristics of the PVDF transducer made it possible to use a wide range of adjustable operating frequencies. This is highly beneficial for concrete imaging where typical ly aggregates with a large variation in sizes will limit the image quality and enforce a trade-off between penetration depth and required resolution.