Post-processing of ultrasonic phased array data for optimal performance

One of the most significant changes over recent years in many areas of NDE has been the move away from monolithic transducers and towards array devices. The existing processing for ultrasonic arrays typically uses the array to emulate a monolithic transducer. This is based on having independently controlled parallel transmission circuits that enable staggered firing of transmitter elements so that the physical wave front injected into a specimen can be translated, steered or focused. Similarly, received signals may be manipulated to perform related operations. This paper describes an alternative approach in which the complete raw data set is collected, containing the time domain signals from every transmitter-receiver pair. Linear post-processing of this data set enables a number of conventional test techniques to be used and compared. Simulated data has been produced for single-point reflectors and an array performance indicator has been used to characterise the point spread function for a number of standard test procedures. Experimental results are also presented and these show good quantitative agreement with the simulated data sets. In addition, an advanced processing algorithm has been implemented which allows the array to be focused at every point in the target in both transmission and reception. This method is proposed as a superior alternative to the conventional test techniques.