A design methodology for 2D sparse NDE arrays using an efficient implementation of refracted - ray TFM

2D sparse ultrasonic NDE array designs would benefit from a real-time simulation package in which the array transducer parameters and inspection scenario were fully integrated to optimise the array design for a specific application. Importantly, this process is not straight-forward for many applications, due to the conflicting requirements of conventional array theory (inter-element spacing and element beam characteristics) and the physical demands of the inspection scenario (refraction at non-planar interface). A novel algorithm has been developed that allows extremely efficient calculation of the total time of flight of an acoustic ray through two layer media, taking into account the effects of refraction through a 3D surface. The approach has been implemented on GP-GPU hardware, and embedded within the Total Focussing Method imaging algorithm. This new software module supports arbitrary location of probe elements, array element directivity, arbitrary curved interface between two media, arbitrary transmit/receive sequences and any 1D/2D/3D image size for reconstructing the ultrasonic image from raw RF ultrasonic data. The measured performance for the implemented algorithm is >23 GPaths/second on a Fermi-class GPU. For example, a 640x960 pixel image and 128-element probe requires ~5e9 transmit-receive path calculations and the GP-GPU system performs the entire calculation in 0.22 seconds (subject to data acquisition and other constraints). An example 2D array design is presented for the inspection of composite material, with the principal design objective to maximise the array aperture to ensure greatest volumetric coverage from a single inspection point. The final array configuration comprised 128 array elements, within a 35mm aperture, with each array element 1.5mm in diameter. Moreover, this array operated through a column of water and provided coverage of an area roughly equivalent to 40mm in diameter. The array transducer has been fabricated and tested on composite fan blade samples with a thickness variation between 5mm and 50mm and shown to detect simulated defects and impact damage locations.