The feasibility of synthetic aperture guided wave imaging to a mobile sensor platform

A mobile sensor platform that features a non-contact guided wave piezoelectric composite transducer payload for rapid inspection of large plate-like structures is presented. The paper begins with results from an experimental B-scan of an aluminium plate. Since the current guided wave payload uses 30 mm square transducers (9λ9λ wide) the system provides fairly course lateral resolution that in this case is approximately equal to the width of the transducer. The paper goes on to use simulation tools to examine the practical SNR and resolution limits of this approach. When using narrow aperture transducers that provide a wide field of view it is important to apply the synthetic aperture focusing technique to maximise image resolution. It is shown that resolution is a function of both transducer aperture and robot positional uncertainty since the effectiveness of synthetic aperture techniques is directly dependent on positional accuracy. It is also shown that since systems utilising larger aperture transducers with a narrow field of view are not as dependent on synthetic array reconstruction, they can outperform systems with narrower transducers in cases where there is relatively large positional uncertainty. Lastly the resolution and relative SNR are modelled as functions of transducer aperture for the cases of B-scan and synthetic array processing.