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dc.contributor.advisorVasu, R M
dc.contributor.authorChandran, Sriram R
dc.date.accessioned2017-11-14T07:14:00Z
dc.date.accessioned2018-07-31T06:03:27Z
dc.date.available2017-11-14T07:14:00Z
dc.date.available2018-07-31T06:03:27Z
dc.date.issued2017-11-14
dc.date.submitted2015
dc.identifier.urihttp://etd.iisc.ac.in/handle/2005/2753
dc.identifier.abstracthttp://etd.iisc.ac.in/static/etd/abstracts/3593/G27123-Abs.pdfen_US
dc.description.abstractThis thesis describes the development and applications of an extension of DWS which enables the recovery of ‘localized’ mechanical properties, in a specified region of a complex jelly-like object which is inhomogeneous, marked out by the focal volume of an ultrasound transducer, also called the region-of-interest (ROI). Introduction of the sinusoidal forcing creates a sinusoidal phase variation in the detected light in a DWS experiment which modulates the measured intensity autocorrelation, g2 (τ ). Decay in the modulation depth with τ is used to recover the visco-elastic spectrum of the material in the ROI. En route to this, growth of the mean-squared dis- placement (MSD) with time is extracted from the modulation depth decay, which was verified first by the usual DWS experimental data from an homogeneous object with properties matching those in the ROI of the inhomogeneous object and then those obtained by solving the generalized Langevin equation (GLE) modelling the dynamics of a typical scattering centre in the ROI. A region-specific visco-elastic spectral map was obtained by scanning the inhomogeneous object by the ultrasound focal volume. Further, the resonant modes of the vibrating ROI were measured by locating the peaks of the modulation depth variation in g2(τ ) with respect to the ultrasound frequency. These resonant modes were made use of to recover elasticity of the material of the object in the ROI. Using a similar strategy, it was also shown that flow in pipe can be detected and flow rate computed by ‘tagging’ the photons passing through the pipe with a focussed ultrasound beam. It is demonstrated, both through experiments and simulations that the ultrasound-assisted technique devel- oped is better suited to both detect and quantitatively assess flow in a background of Brownian dynamics than the usual DWS. In particular, the MSD of particles in the flow, which shows forth a super-diffusive dynamics with MSD growing following τ α with α < 2, is captured over larger intervals of τ than was possible using existing methods. On the theoretical front, the main contribution is the derivation of the GLE, with multiplicative noise modulating the interaction ‘spring constant’. The noise is derived as an average effect of the micropolar rotations suffered by the ‘bath’ particles on the ‘system’ particle modelled. It has been shown that the ‘local’ dynamics of the system particle is nontrivially influenced by the dynamics, both translation and rotation, of ‘nonlocal’ bath particles.en_US
dc.language.isoen_USen_US
dc.relation.ispartofseriesG27123en_US
dc.subjectDiffuse Correlation Spectroscopyen_US
dc.subjectSoft Condensed Matteren_US
dc.subjectVisco-Elastic Spectrumen_US
dc.subjectDiffusing Wave Spectroscopy (DWS)en_US
dc.subjectUltrasound Transducersen_US
dc.subjectCondensed Matteren_US
dc.subjectUltrasound Diffuse Correlation Spectrosocpyen_US
dc.subjectElasticityen_US
dc.subjectViscoelasticityen_US
dc.subjectUltrasound Modulated Optical Tomographyen_US
dc.subjectDiffusing-wave Spectroscopyen_US
dc.subjectUltrasound-assisted Diffuse Correlation Spectroscopyen_US
dc.subject.classificationApplied Physicsen_US
dc.titleUltrasound-Assisted Diffuse Correlation Spectroscopy : Recovery of Local Dynamics and Mechanical Properties in Soft Condensed Matter Materialsen_US
dc.typeThesisen_US
dc.degree.namePhDen_US
dc.degree.levelDoctoralen_US
dc.degree.disciplinefaculty of Engineeringen_US


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