Compressed Sensing in Material Diagnostics via Ultrasound Imaging (CoSMaDU)

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Non-destructive testing (NDT) is a core tool to ensure the absence of critical flaws in fabrication and enable maintenance of large infrastructure such as railroad tracks. With growing demands in both areas, the importance of fast and reliable NDT techniques has increased aiming at examining a component throughout its entire life.Ultrasound is, due to its simple and safe applicability, one of the most established NDT techniques. However, so far ultrasound testing is performed mostly on a qualitative basis (i.e., is a specimen is flawed or not). The quantitative assessment of defects is in fact limited, since the exact interpretation of ultrasound data is difficult. Due to the complex nature of ultrasonic wave propagation, the acquired data can be highly ambiguous which necessitates a large amount of a priori knowledge on the component or structure under test and the measurement setup to allow for a reliable interpretation.To facilitate this, appropriate post-processing becomes indispensable. Notwithstanding, the post-processing methods currently used in commercial ultrasound NDT products are quite rudimentary or are used only together with the inspection of the raw data in a complementary fashion for lack of reliability. The main reason advanced signal processing techniques have not been applied is the lack of appropriate forward models that account for the complexity of the ultrasonic wave propagation and yet are still suitable for signal processing applications. The proposed project aims at improving the state-of-the-art by pursuing two goals: The first objective is to investigate forward models for ultrasonic wave propagation with the goal to find the best compromise between the realistic modeling of physical propagation effects such as dispersion, acoustic shadowing and speckle noise on the one hand and the suitability for signal processing methods in terms of the model complexity on the other hand. Our investigations will consider the measurement setup and the post-processing stage jointly. Based on this, the second objective of this project is to design measurement architectures that capture relevant (for post-processing) information efficiently. To achieve this, the state-of-the-art in sub-Nyquist-Sampling techniques such as Compressed Sensing or Finite Rate of Innovation Sampling will be applied to ultrasonic NDT. In particular, our proposal aims at closing the gap between novel theoretical results (that usually rely on idealized algebraic formulations) and the physics of ultrasonic wave propagation to make these results applicable to real setups.