In non-destructive testing (NDT) applications, Full Waveform Inversion (FWI) is a high-resolution imaging technique that uses complete ultrasonic wavefields to reconstruct material properties. Unlike most ultrasonic inspection approaches, FWI does not rely on primitive assumptions; rather, it reduces the difference between the measured and simulated wavefields, hence using full information for detailed material characterization. This thesis focuses on developing a two-dimensional frequency domain FWI framework. Wave propagation is modeled with the Helmholtz equation, while gradients for model updates are calculated using the adjoint-state method. BFGS optimization is used to ensure stable and efficient convergence. The Inversion is accomplished via multi-frequency techniques for increased robustness with two approaches: sequential frequency stepping from low to high frequencies and simultaneous inversion using all frequencies in each iteration. The work illustrates the capabilities of frequency domain FWI as a concrete and accurate method for ultrasonic inspection, demonstrating its potential for high-resolution material characterization in NDT applications.     «

In non-destructive testing (NDT) applications, Full Waveform Inversion (FWI) is a high-resolution imaging technique that uses complete ultrasonic wavefields to reconstruct material properties. Unlike most ultrasonic inspection approaches, FWI does not rely on primitive assumptions; rather, it reduces the difference between the measured and simulated wavefields, hence using full information for detailed material characterization. This thesis focuses on developing a two-dimensional frequency doma...     »