Mon January 19th 2009
Seminar A path from low to high frequency with a detour into transducer land
Jeff Ketterling


This seminar will commence with a brief summary of Dr. Ketterling's thesis work related to the phase space of sonoluminescence. This work involved the acoustic levitation of gas-filled bubbles at 20 kHz and examined at what gas ratios, drive pressure, and ambient radii the bubbles were stable and emitting light. The theoretical work of Profs. Lohse and Hilgenfeldt was essential and complementary to these experiments. The seminar will then focus on more recent work involving high-frequency ultrasound (HFU) transducers (>20 MHz) that are widely used for fine-resolution ophthalmic and small-animal imaging. Most HFU imaging is now performed with single-element, focused transducers. These devices have excellent lateral resolution, but a fairly limited depth of field (DOF). Array devices are an obvious approach to improving image quality for HFU, but it has proven difficult to fabricate and fully instrument linear array devices. An annular array provides a simplified approach to improving DOF while still maintaining excellent lateral resolution. The design, fabrication, and testing of 40 and 20 MHz annular arrays will be discussed. Examples of ophthalmic and small-animal images will be presented and compared to the current state of the art. The results reveal that annular arrays lead to a significant improvement in image quality versus currently utilized single-element devices. Finally, the seminar will summarize ongoing work related to HFU excitation of ultrasound contrast agents (UCAs). UCAs designed for use with (HFU) would permit the visualization of slow-moving microcirculation in ophthalmic and small-animal applications. Polymer-shelled UCAs were examined for their single-bubble backscatter when excited with 40 MHz tone bursts of 1, 3, 5-10, 15, and 20 cycles. The backscatter signals were then examined to determine if a 20 MHz subharmonic component was present. The subharmonic was initiated between 8-10 cycles and then increased in magnitude as the number of cycles
Go back to the agenda.

The 10th Complex Motion in Fluids 2021
Max Planck Gesellschaft
Centre for Scientific Computing