Design and Optimization of a Multifunctional Phased Array Search Unit

Abstract

<p>Dual-element angle beam transducers exhibit operating characteristics suitable for a large range of practical field applications, particularly for the interrogation of highly attenuative materials such as stainless steel. These capabilities can be improved by operating such transducers as phased array search units, consisting of many transducer elements. Each of the array elements is pulsed with the appropriate time delays, thus controlling the shape and the sound beam direction on a large scale. This study describes the design and optimization of a multi-mode T/R (transmit/receive) phased array search unit generating longitudinal, shear and subsurface longitudinal (’creeping’) waves. The elaborated design can be operated with 12 or 16 transducer elements generating multiple wave modes for certain inspection ranges. This search unit is particularly suited for detection of surface connected planar discontinuities associated with circumferential or vertical weld seams of pressure vessels or pressure vessel components (core shroud) in the range of 1.5 inches (~ 40 mm) wall thickness. Based on the well-known physical processes inherent to ultrasound generation in isotropic media, the Generalized Point-Source-Synthesis method (GPSS) [1,2] has been used to model and optimize the probe. The three-dimensional transducer build-up simulation includes the reflection/refraction process at the wedge-to-material sound entry interface considering fluid coupling. The established search unit parameters consist of wedge angle, roof angle, transducer element length and width by given search unit housing dimension and a fixed inspection frequency.</p>