Circumferential phased array of shear-horizontal wave magnetostrictive patch transducers for pipe inspection.

Several investigations report effective uses of magnetostrictive patch transducers to generate and measure longitudinal and torsional guided waves in a pipe. They can be used to form a phased array for the circumferential inspection of pipes. Although there are circumferential phased arrays employing piezoelectric transducers or EMAT's, no magnetostrictive patch transducer based array system has been attempted. In this investigation, we aim to develop a circumferential phased magnetostrictive patch transducer (PMPT) array that can focus shear-horizontal waves at any target point on a cylindrical surface of a pipe. For the development, a specific configuration of a PMPT array employing six magnetostrictive patch transducers is proposed. A wave simulation model is also developed to determine time delays and amplitudes of signals generated by the transducers of the array. This model should be able to predict accurately the angular profiles of shear-horizontal waves generated by the transducers. For wave focusing, the time reversal idea will be utilized. The wave focusing ability of the developed PMPT array is tested with multiple-crack detection experiments. Imaging of localized surface inspection regions is also attempted by using wave signals measured by the developed PMPT array system.