Particle separation via the hybrid application of optical and acoustic forces

  • Paul O'Mahoney

    Student thesis: Doctoral ThesisDoctor of Philosophy


    Non-contact manipulation technologies present a useful and powerful means of handling particles or cells. Such techniques are of interest in regenerative medicine applications, and in particular the scalability of these techniques is an area of active research.

    Optical trapping is a precise and dextrous method of manipulating particles with the forces exerted by a laser beam, while acoustic trapping is a scalable technique capable of exerting a force on particles through standing wave resonance. These complimentary modalities can be utilised in a hybrid system to give a resultant technique that borrows from the strengths of each individual method. In this thesis, methods of force balancing, using optics and acoustics, are explored, both independently and in combination with each other.

    A technique for 3D acoustic trapping in glass capillaries is shown, utilising the two pairs of opposing channel walls and the air-water interfaces of two air bubbles as acoustic reflectors. Standing waves set up between these surfaces show discrete acoustic trapping sites for varying lengths of fluid cavity.

    A method of optical radiation force balancing is observed in a 3D potential energy landscape, using similar principles as seen in particle trapping with counter-propagating beams. Tuning of the radiation force balance in this system allows particles to, instead of being pinned to the surface by the radiation force from the optical pattern, become localised at discrete planes of trapping sites throughout the fluid volume.

    A hybrid force balance separation method using the optical and acoustic forces is devised using a single laser beam as the primary deflection mechanism with acoustic trapping providing both localisation and a force balance with the optics. Separation of different sized particles is observed, with larger scale optical deflection mechanisms and their resultant thermal effects demonstrated.
    Date of Award2015
    Original languageEnglish
    SponsorsScottish Funding Council
    SupervisorMichael MacDonald (Supervisor)


    • Optical
    • Optical trapping
    • Acoustic
    • Sorting
    • Hybrid

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