A facet ensemble approach for evaluation of array performance in ultrasonic NDE

The use of ultrasonic array systems, in conjunction with a synthetic aperture focusing technique (SAFT) has recognized potential for flaw characterization in nondestructive evaluation (NDE). However, defect type, location, orientation and geometrical constraints imposed by the test specimen can reduce the effectiveness of nonoptimal array systems. To assist with design, a simulation approach for evaluation of array performance for NDE imaging was developed and is described in this paper. In the development of the model, several key factors were identified as being critical in defining the response of a linear ultrasonic transducer array. These include the ultrasonic wavelet generated by each array element, the directivity of the transducers and the interaction of the ultrasonic wave field with the surface which is to be imaged. Following several simplifying assumptions, and employing a linear systems approach, the cumulative response of all these factors was formulated. Thus a low-cost, yet powerful, interactive model for system design evaluation could be implemented. To illustrate the model, a range of simulation results is presented, concerning the imaging of a fatigue crack in a solid medium. The influence of array element spacing and centre frequency is considered, in conjunction with aperture size, defect orientation and surface roughness. In each case, the principal factors governing final image quality are discussed and where possible, recommendations are made concerning array design and imaging strategy.>