Monday, 22 May 2017

Paper published in Journal of the Acoustical Society of America

Our work on acoustic and optical trapping of microbubbles has been published as G. Memoli, C. R. Fury, P. N. GĂ©lat, K. O. Baxter & P. H. Jones.  'Acoustic force measurements on polymer-coated microbubbles in a microfluidic device', Journal of the Acoustical Society of America 141 3346 (2017).

From the abstract:  This work presents an acoustofluidic device for manipulating coated microbubbles, designed for the simultaneous use of optical and acoustical tweezers. A comprehensive characterization of the acoustic pressure in the device is presented, obtained by the synergic use of different techniques in the range of acoustic frequencies where visual observations showed aggregation of microbubbles. In absence of bubbles, the combined use of laser vibrometry and finite element modelling supported a non-invasive measurement of the acoustic pressure and an  enhanced understanding of the system resonances. Calibrated holographic optical tweezers were then used for a direct measurement of the acoustic forces acting on an isolated microbubble at low driving pressures and to confirm the spatial distribution of the acoustic field. This allowed quantitative pressure measurements by particle tracking using polystyrene beads and an evaluation of the related uncertainties. The extension of the tracking technique to polymer-coated microbubbles allowed acoustic force measurements at higher pressures, highlighting four peaks in the acoustic response of the device. Results and methodologies are relevant to acoustofluidic applications requiring a precise characterization of the acoustic field and, in general, to biomedical applications with microbubbles or deformable particles.

Tuesday, 7 February 2017

Paper published in IEEE Photonics Journal

Our work on a novel optical trapping system using fractal optics and spatially inhomogneous polarisation of light has been published as Zhirong Liu and P. H. Jones, 'Fractal conical lens optical tweezers', IEEE Photonics Journal 9 6500111 (2017)

From the abstract: We propose a novel optical tweezers composed of an annular beam with alternate radially and azimuthally polarized rings modulated by a fractal conical lens (FCL) and demonstrate its optical forces on Rayleigh dielectric particles both analytically and numerically. Owing to the optical system's particular focusing properties, which could generate a dark-centered or peak-centered intensity distribution in the focal region when selecting an appropriate truncation parameter in front of the focusing lens, the proposed FCL optical tweezers could selectively trap and manipulate dielectric mesoscopic particles with low- or high-refractive indices by appropriately adjusting the radius of the pupil or the beam. Finally, the stability conditions for effective trapping and manipulation Rayleigh particles are analyzed.