Ultrasound imaging is an important technique utilized for medical diagnosis and damage detection in a variety of industrial applications. In most conventional ultrasound imaging systems, a pulse is emitted from an ultrasonic transducer, and transmitted or reflected ultrasound pulses are measured with a similar transducer. In this project, instead of using a conventional transducer, a laser-based system will be utilized to measure the ultrasound. This is a potentially transformative method that may have unique advantages relative to conventional methods, including reduction of measurement errors, and the ability to create full-field videos of traveling wavefronts. The project will address the fundamental challenges needed to enable laser-based ultrasonic measurements to be utilized for industrial applications and biomedical research. A strong outreach effort will use measured videos of acoustics fields to motivate secondary students to become interested in science and engineering. These videos will allow students to engage in topics such as how ultrasound imaging works, why shock waves produced by pile driving are of concern for marine life near construction sites, and how layering in the ocean is used for long-range communication by both the military and marine mammals.
To detect ultrasonic waves optically, the measurement arm of a laser interferometer is directed at a stationary retroreflective surface. When an acoustic wave passes through the measurement laser beam, the wave?s density variations produce phase shifts that can be detected by the interferometer. This project anticipates a wide range of outcomes. Interferometric measurements of ultrasonic fields have often been performed using a commercial laser Doppler vibrometer. However, vibrometers are engineered to measure vibrating surfaces; they are not optimized for measuring acoustic fields. The project will investigate designs for implementing an Open Source Acoustic Interferometric Detector to enable other researchers to construct a system optimized for interferometric measurements of ultrasound fields. An important outcome will be a protocol to actively monitor and control ultrasonic standing wave formation. This will produce a doubling of the force applied by ultrasound radiation force excitation. Other outcomes will enable multiple measurements to be combined to obtain high-fidelity and depth-sensitive interferometric measurements at higher frequencies than have been obtained in previous studies. These single-point and full-field measurements will not be susceptible to some of the artifacts observed when ultrasound is measured with conventional transducers. Interferometric measurements of ultrasonic fields will be used to investigate the fluid/structure interactions that lead to Mach shock formation when a wave pulse passes through an object.