Sub-Wavelength Characterisation of Defects
In an increasing number of industries , plant is extended beyond its original design life and there is a need to ascertain the integrity of areas that were not originally anticipated to require inspection. Guided acoustic waves provide the necessary range (tens of metres) for remote inspection and commercially available systems are routinely used for rapid screening of pipework. Recent research has led to the development of guided wave synthetic focusing techniques for pipe inspection, which have been shown to give an order of magnitude improvement in the sensitivity to small defects. However, the quantitative information in the images is still not of sufficient resolution to enable sizing of critical defects to the accuracy required for structural integrity assessment. The reason why accurate sizing cannot be achieved is because, like other imaging systems, the resolvable detail is diffraction-limited by the wavelength of the probing wave. Resolution can be increased by operating at higher frequency but this is achieved at the expense of reduced range due to the increased attenuation and scattering. In many imaging fields so-called super-resolution techniques have been investigated that enable detail below the diffraction limit to be extracted. Although the benefits of super-resolution have been demonstrated in certain applications, its exploitation is highly case-specific. This is because it must be tailored according to a priori knowledge of the interaction of the probing wave with the features likely to be encountered. The purpose of this project is to develop the use of sub-wavelength (super-resolution) characterisation techniques for the characterisation of otherwise inaccessible defects in safety-critical pipes using guided waves. The principal goal will be to determine the maximum penetration depth of a crack or corrosion patch, and also its orientation or shape. You can view a presentation here.
Carandente, R., Ma, J. and Cawley, P. 'The scattering of the fundamental torsional mode from axi-symmetric defects with varying depth profile in pipes', J Acoust Soc Am, Vol 127, pp3440-3448, 2010.
Ma, J. and Cawley, P. 'Low-frequency pulse echo reflection of the fundamental shear horizontal mode from part-thickness elliptical defects in plates', J Acoust Soc Am, Vol 127, pp3485-3493, 2010.
EPSRC, E.ON, Shell, EDF