AbstractSound and light show many similarities because they both propagate as waves. This means they share the same wave properties such as reflection, refraction, scattering, diffraction, and so on. The similarities between them bring a lot of opportunities for translating knowledge of one onto the other. When compared to ultrasound, and particularly in microscopy and micromanipulation, optics is a more-developed and better-understood area, partly due to the difficulty of producing complex ultrasonic beams. Hence it makes perfect sense to explore sound based on the research of optics. Differences between light and sound are mainly due to the nature variety of their mechanisms and different scale of their wavelength. Those difference makes either light or sound suitable for certain applications.
This thesis will focus on the currently technology for beam shaping for acoustic and optical waves, making use of their similarities, especially for imaging and manipulation purposes.
When light scattering and absorption is low, optical scattering is able to provide high resolution and suitable for imaging. A low-cost Light-Sheet Tomography imaging system is built for monitoring the growth of plant roots based on optical scattering from the roots. When optical scattering and absorption is severe it dramatically decreases spatial resolution, optical absorption can be employed to generate less-scattered acoustic signals to form high contrast images of the optical absorbing structure in a sample. A photoacoustic imaging system featuring light sheet illumination is built, along with an automatic data acquisition system. 2D images acquired with this system are reconstructed with inverse Radon transformation.
The short wavelength of optical waves makes them suitable for interaction with micron-scale objects, but less suitable for macro objects because the force does not easily scale up with the size of the targets. On the other hand, ultrasonic waves have the suitable wavelength and power level for interaction with mm- or even cm- size objects.
Various ultrasonic beams with vortex wavefront were generated with a 1000-element phase-control transducer array to levitate and rotate a macro acoustic absorber by transferring linear and angular momentum from the acoustic beam to the absorber. The ratio between linear and angular momentum in the beam was measured simultaneously. With the same ultrasound transducer array, the delivery of a controllable negative radiation force onto prism-shape target is demonstrated to pull the prism towards the sound source. This is the first demonstration of macroscopic and ultrasonic tractor beam.
The study of ultrasound and optical beam shaping has proven that the similarities between sound and light waves can be utilized to extend our existing knowledge on them, and further provides more opportunities on wave-matter interaction applications.
|Date of Award||2014|
|Sponsors||China Scholarship Council & Engineering and Physical Sciences Research Council|
|Supervisor||Michael MacDonald (Supervisor)|