Mesh-free modeling of ultrasonic fields generated by transducers and acoustic microscopes

With the gain in momentum of the structural health monitoring field in the last two decades, the popularity of ultrasonic nondestructive testing (NDT) has rapidly grown. However, ultrasonic NDT requires an expert to perform the tests that can be time consuming and expensive for complex structures. A computer simulation of these tests can be utilized as a guide during actual evaluations or as a tool to train technicians. Presented in this dissertation is the development of models which simulate ultrasonic fields in front of flat transducers and focused acoustic lenses that are commonly used during NDT experiments. These models are developed using the distributed point source method (DPSM) for its proven capability to simulate ultrasonic fields.;Four sets of boundary conditions that arise from different types of commonly used acoustic transducers are modeled, enabling the visualization of the ultrasonic fields produced by the transducers. The transducer models exhibit good agreement with existing analytical solutions.;In addition, the effect of a small cavity located at or near the focal point of an acoustic microscope is studied. For this application, the conventional DPSM technique is modified so that the inversion of a large global matrix can be avoided, significantly improving the computational efficiency. The model shows that the pressure goes to zero and that the velocity increases at the cavity location. Simulations demonstrate that the microscope is able to sense changes in position of the cavity by variations in the measured ratio of reflected to incident acoustic force.;The field generated by a three-element acoustic microscope lens is also presented. Qualitative agreement between the DPSM model prediction and the experimentally generated fields in a homogeneous fluid is obtained. It is also investigated how the ultrasonic field generated by the acoustic lens is affected in the presence of a solid interface.