Multi-element ultrasonic scanning of in-service airframes

The search continues for a large-area inspection tool which can rapidly scan aircraft structures to find corrosion in metallic areas, or delaminations in composite parts. In the meantime there is potential for increasing the scan rate of currently, available scanning systems, such as the Defence Evaluation and Research Agency's ANDSCAN® by the use of multi-element probes. A linear-array ultrasonic probe with just eight elements can reduce the total scanning time with ANDSCAN by approximately a factor of eight when compared to a similar single-element scan. This is because the scanning motion required to obtain good coverage becomes a paintbrush-type sweeping action which is far more efficient. This paper presents the results obtained with a special design of multi-element ultrasonic probe and multiplexer for use with a conventional flaw detector on composite structures. In particular, the requirement for a simple portable system -with as few trailing cables as possible - has been addressed. Recommendations for the future design of specialised NDT arrays is included.