| This thesis describes the design, fabrication, modeling and device characteristics of ultrasound transducers developed from millimeter size piezoelectric ceramic hollow spheres. Green ceramic hollow spheres were produced using a coaxial nozzle slurry process and a sacrificial core coating process in the size range of 1–6 mm in diameter and 12–200 μm in wall thickness. Ceramic powders with the morphotropic phase boundary compositions of lead zirconate titanate solid solution known as PZT-4 and PZT-5A, and a modified lead titanate composition were used in these two processes.; After sintering, the desired shapes were obtained by drilling, grinding, or polishing. Sphere surfaces were then coated with an electrode material in desired shapes and area of coverage. Two main poling configurations were studied: a radial poling configuration with inside and outside electrodes, and a tangential poling with top and bottom outside electrodes with several different electrode patterns. Dielectric, piezoelectric and ferroelectric properties of these transducers were measured. Vibration modes were determined using the ATILA™ finite element analysis (FEA) code, and associated resonance frequencies were measured and compared to the calculated values. The effect of sphere dimensions, materials and electrode configurations were analyzed using FEA. It was determined from the finite elements analysis of the structure that wall thickness variations do not have a pronounced affect on the vibrations of the structure at lower frequencies (from kHz to low MHz).; Focused transducers were prepared for biomedical ultrasound imaging from dish-shape shell sections of the hollow spheres. Pulse-echo characteristics such as, insertion loss, waveform and bandwidth were measured. These transducers were also modeled using the FEA. Transducer operation frequencies of up to 50 MHz were achieved with f-numbers down to 1.; Omnidirectional miniature hydrophones were prepared from radially poled hollow spheres. Underwater sonar performance was evaluated by measuring free field voltage sensitivity (FFVS), transmit voltage response (TVR), source level and directivity beam patterns of these hydrophones. FFVS of −218 dB re 1V/μPa with a frequency independent response up to 500 kHz, and TVR of 150 dB @1m re 1μPa/V at 500 kHz were obtained from these transducers. These results were compared to that of the finite element analysis of these devices.; Hollow spheres were also placed into multi-element arrays with elements electrically connected to one another in parallel, series or a mix of both. Higher TVR, FFVS and directional beam patterns were obtained from these arrays. |
