SUMMARY

Capacitive Micromachined Ultrasonic Transducers (CMUTs) consist of small membranes that use a capacitive mechanism for transmitting and sensing ultrasonic pressure waves. They have significant potential to advance medical ultrasound imaging beyond the capabilities of current technology. Using well-established micromachining techniques, they can achieve complex geometries, densely populated arrays, and tight integration with electronics, all of which are required for advanced intravascular ultrasound applications such as high-frequency or forward-looking catheters. Before CMUTs can be effectively used, they must be characterized and optimized through experimentation and modeling. Unfortunately, immersed CMUT arrays are difficult to simulate due to acoustic crosstalk. This refers to the mutual dependence between every membrane in an array due to the interactions of their respective pressure waves. Consequently, the entire array must be modeled simultaneously for complete accuracy. Finite element models (FEMs) are very accurate for simulating CMUTs but become computationally expensive for large arrays. For this thesis, a more efficient method is investigated that still provides accuracy comparable to FEM. It models membrane stiffness using a finite difference approximation of thin plate equations. For fluid coupling effects, a Boundary Element Matrix (BEM) is employed that is based on the Green’s function for a baffled point source in a semi-infinite fluid. These effects are incorporated into the model by meshing the array surface and solving a system of nodal force balance equations. The entire CMUT array can thus be modeled with a surface mesh, allowing for drastic improvement in computation time over FEM. This thesis will focus on development and characterization of the model through comparison with FEM and experiments. It will also use the model to explore methods for reducing acoustic crosstalk and optimizing CMUT array performance.