An integrated systems approach to automated scanning and analysis of engineering structures

This paper describes the development and application of an integrated scann ing system consisting of a dry-coupled wheel probe linked to an ultrasonic instrument capable of digitising and processing the received time domain si gnals on-line. The wheel probe operates at a centre frequency of 10 MHz wit h energy up to 14 MHz, allowing good spatial resolution to be obtained. The rubber type of the wheel probe has extremely low loss, is durable and soft enough such that good coupling can be achieved at relatively low applied l oads if the surface finish of the test structure is not excessively rough. The ultrasonic instrument contains an embedded PC which has been programmed to perform on-line advanced signal processing tasks such as inverse adapti ve filtering. This combination allows rapid, dry-coupled, scanning of relat ively large areas. The advanced signal processing allows the inspection of complex/difficult geometries to be automated. Two application studies are p resented. Firstly, the system is used to inspect an automotive adhesively-b onded joint using inverse adaptive filtering to characterise the bond quali ty. Secondly, the system is used to inspect rapidly a 100 mum-thick sealant layer in an aerospace wet-wing structure.