Diagnostic ultrasound is widely used in cardiology, radiology, obstetrics, and for guiding biopsy or needle access. Ultrasound imaging resolves soft tissue with fine spatial and temporal resolution, is affordable, is real-time in nature, and does not produce ionizing radiation. Research interest exists in the development of therapeutic and other non-diagnostic applications. This dissertation focuses on the area of transducer design for ultrasound guidance and ultrasound-mediated therapeutic effect.;In the first application, a 3600 element two-dimensional (2D) transducer array operating at 5 MHz is developed. Four array configurations are presented along with comparative finite element analysis simulations. Although the narrow bandwidth observed is acceptable for our application, reverberations existed within the substrate.;In order to address this challenge, temperature-dependent acoustic properties of epoxy blends were assessed in terms of their potential as an acoustically lossy substrate. The acoustic impedance and attenuation of five unfilled epoxy blends and two filled epoxy blends -- tungsten and fiberglass fillers -- were analyzed. An 11dB increase in attenuation was observed in tungsten-compared to the fiberglass-filled epoxy in the context of our application.;The increasing interest in ultrasound-mediated drug delivery offers an appealing therapeutic application for ultrasound. A dual-frequency capacitive micromachined ultrasonic transducer (CMUT) is presented as a combined diagnostic and therapeutic device. The primary challenge inherent in the design of this device is the generation of ultrasound at 1-2MHz to rupture drug-loaded microbubbles, and at 20-40MHz to perform high-resolution intravascular imaging. Based on FEA results, the designed dual-frequency CMUT is capable of achieving acoustic peak-negative-pressure greater than 190kPa in un-focused transmit at a center frequency of 2.1MHz with a -6dB bandwidth of 93%. The same device, in high-frequency mode, has been shown in simulation to generate ultrasound centered at 44.1 MHz with a -6dB bandwidth of 42%.;Further variations upon the core, dual-frequency CMUT device design were explored. This includes the demonstration of a CMUT capable of operating in three separate frequency bands, and a device capable of operating at both 1-2MHz and approximately 100MHz. The demonstrated flexibility of hybrid CMUT transducer design could reveal new areas of investigation within ultrasound research and transducer technology.
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