Minimization of internal reverberation in acoustic windows used in US inspection systems by numerical simulation

摘要

Most ultrasonic tools for the inspection of pipelines or bore-holes consist of a transducer, separated from the exterior by an acoustic window. This acoustic window protects the device from the potentially hostile exterior and is part of the mechanical construction. Therefore the acoustic window is positioned between the transducer and the region of interest. Due to mechanical constraints and acoustic impedance differences between the window and the in- exterior mediums, the acoustic window will produce unwanted internal reflections. The amplitude of these reflections is normally much higher than the background noise level. These reflections hamper proper defect analysis of the pipeline, such as wall thickness loss. This study is performed to reduce these reflections, while fulfilling the mechanical specifications of the acoustic window. With UMASIS, a fully elastic 2D finite difference modeling tool, several configurations are simulated. UMASIS is a very powerful tool for modeling and interpreting modeling results. The thickness, orientation and shape of the acoustic window are varied. The modeled response provides accurate information about the dominant contributions to the internal reflections. The snapshots generated with UMASIS, enable us to pinpoint the causes of reflection. This drastically decreases the development time of the acoustical window and allows a significant reduction of the distortion of the acoustic window.