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Acousto-optical trapping and manipulation of microbubbles

Fury, CR; (2016) Acousto-optical trapping and manipulation of microbubbles. Doctoral thesis , UCL (University College London).

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Abstract

Encapsulated microbubbles, widely used as ultrasound contrast agents, exhibit acoustic emissions that are highly dependent upon the physical properties of their environment. This sensitivity could allow for the development of microscopic environmental sensors if the acoustic emission's dependent parameters can be quantified. In this thesis an instrument capable of dual-method micro-manipulation, centred around a microfluidic device (MFD), was built and characterised for the manipulation forces applied to microbubbles, with the goal of engaging the instrument in future work to study microbubble emission in isolation. Acoustic tweezers provided high magnitude, long range, forces capable of aggregating microbubbles. Laser vibrometry and microbubble position tracking were used to characterise the acoustic trapping field and pressures. Pressure was found to be a function of frequency, where modes of the MFD were selectively excited. A Laguerre-Gaussian mode holographic optical tweezer gave fine spatial control of microbubble positions and a force balancing method with which to measure acoustic forces. This trap was parameterised for the first time in terms of trap stiffness, and an optimum set of parameters was found enabling greater acoustic force balancing. Trap stiffness increased with laser power, trap diameter and microbubble diameter. Force balancing measurements agreed with the acoustic characterisation, critically in that force was dependent upon channel-mode frequencies, and that lipid-shelled microbubbles experienced a greater force than co-polymer shelled microbubbles. A unique micro-horned transducer was built to excite microbubbles into acoustic resonance. This transducer was capable of insertion into the MFD and was characterised for its emission with laser vibrometry and hydrophone tomography.

Type: Thesis (Doctoral)
Title: Acousto-optical trapping and manipulation of microbubbles
Event: UCL
Language: English
UCL classification: UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: http://discovery.ucl.ac.uk/id/eprint/1521370
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