Ultrasonic Imaging through Solids
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Ultrasonic testing is a widely used method, in the industry, for non destructive inspection of materials. The most commonly used technique is the pulse-echo technique where ultrasound is introduced into a test object and reflections from discontinuities inside the object are returned to the receiver. In many situations it is more desirable to look through the object than inside it. For example during oil and gas production in the North Sea, where possible plugging or restricted fluid flow can lead to big expenses. Ultrasonic imaging through solids is feasible, but have some challenges. The main issue is usually large impedance mismatch between materials. In this thesis, beamforming adapted for imaging through solids was implemented and the achieved image quality was investigated. The beamforming was tested on plates of aluminium, plexiglass and steel with a needle used as a line scatterer. A Verasonics Vantage system was utilized for recording the experimental data and the achieved image quality was evaluated based on the point spread function. Results showed that the line scatterer was visible through all materials, but the intensity of the signal varied between the materials. The line scatterer was especially hard to see through steel, which was the material with highest density in the experiments.Based on the point spread function, the image quality was bad for all materials. As the resulting lateral resolution was very similar for all experiments, undetected errors in the implementation are likely.