Real-Time B-Scan Ultrasonic Imaging Using a Digital Phased Array System for NDE
Phased array systems for electronically steering and focusing ultrasonic fields have been used extensively in medical imaging since the late 1970’s. Despite the advantages of these systems (rapid redirection of beams, dynamic focusing to improve depth-of-field, and reduced mechanical complexity), phased arrays have been used very little for materials characterization. The reason for this lack of phased array technology in materials characterization is simply the wide range of velocity of sound encountered when working with materials and the resulting complexity in the beam former (the electronic system that appropriately delays and sums signals from individual elements of an array to produce a steered, focused beam) of a phased array system that can image in a wide variety of materials. Most medical phased array systems have analog beam formers which are hard-wired assuming the velocity of sound in soft tissue (1.54 mm/μsec), and therefore cannot be easily used to image in metals where the velocity of longitudinal sound waves is 3 or 4 times the velocity in soft tissue. At GE Corporate Research & Development (CRD) we have constructed a phased array system which uses a completely programmable digital beam former. This system provides exceptional flexibility for phased array imaging in a wide variety of materials; allowing focusing and steering using either the longitudinal or transverse wave velocity for any material.
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