Browsing by Author "Rigas, Evangelos"

Now showing 1 - 7 of 7
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    2D spatially-resolved depth-section microfluidic flow velocimetry using dual beam OCT
    (MDPI, 2020-03-27) Hallam, Jonathan M.; Rigas, Evangelos; Charrett, Thomas O. H.; Tatam, Ralph P.
    A dual beam optical coherence tomography (OCT) instrument has been developed for flow measurement that offers advantages over microscope derived imaging techniques. It requires only a single optical access port, allows simultaneous imaging of the microfluidic channel, does not require fluorescent seed particles, and can provide a millimetre-deep depth-section velocity profile (as opposed to horizontal-section). The dual beam instrument performs rapid re-sampling of particle positions, allowing measurement of faster flows. In this paper, we develop the methods and processes necessary to make 2D quantitative measurements of the flow-velocity using dual beam OCT and present exemplar results in a microfluidic chip. A 2D reference measurement of the Poiseuille flow in a microfluidic channel is presented over a spanwise depth range of 700 μm and streamwise length of 1600 μm with a spatial resolution of 10 μm, at velocities up to 50 mm/s. A measurement of a more complex flow field is also demonstrated in a sloped microfluidic section.
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    '2D Spatially-Resolved Depth-Section Microfluidic Flow Velocimetry Using Dual Beam OCT'
    (Cranfield University, 2020-04-27 15:33) Hallam, Jonathan; Tatam, Ralph; Rigas, Evangelos; Charrett, Tom
    'Data and associated figures and supplementary materials for '2D Spatially-Resolved Depth-Section Microfluidic Flow Velocimetry Using Dual Beam OCT' published in Micromachines special edition 4th Conference on Microfluidic Handling Systems 2-4th October 2019. Update: 27/04/2020. Added 'requirements.txt' listing exact python packages required and clarified 'readme.txt'.'
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    Dual beam swept source optical coherence tomography for microfluidic velocity measurements
    (2018-11) Rigas, Evangelos; Ford, Helen D.; Tatam, Ralph P.
    Microfluidic flows are an increasing area of interest used for “lab-on-a-chip” bioanalytical techniques, drug discovery, and chemical processing. This requires optical, non-invasive flow-visualization techniques for characterising microfluidic flows. Optical Coherence Tomography (OCT) systems can provide three-dimensional imaging through reasonably-opaque materials with micrometre resolution, coupled to a single optical axis point using optical fibre cables. Developed for imaging the human eye, OCT has been used for the detection of skin cancers and endoscopically in the human body. Industrial applications are growing in popularity including for the monitoring of bond-curing in aerospace, for production-line non-destructive-testing, and for medical device manufacturing and drug encapsulation monitoring. A dual beam Optical Coherence Tomography system has been developed capable of simultaneously imaging microfluidic channel structures, and tracking particles seeded into the flow to measure high velocity flows, using only a single optical access point. This is achieved via a dual optical fibre bundle for light delivery to the sample and a custom high-speed dual channel OCT instrument using an akinetic sweep wavelength laser. The system has 10 μm resolution in air and a sweeping rate of 96 kHz. This OCT system was used to monitor microfluidic flows in 800 μm deep test chips and Poiseuille flows were observed.
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    Dual-channel OCT for velocity measurement in microfluidic channels.
    (OSA, 2018-09-28) Rigas, Evangelos; Hallam, Jonathan M.; Ford, Helen D.; Charrett, Thomas O. H.; Tatam, Ralph P.
    A dual-beam Optical Coherence Tomography system has been developed, using a bespoke dual optical fibre, to simultaneously image microfluidic channel structures and measure high velocity flows (presently 250μm/s) from a single optical access point.
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    Metre-per-second microfluidic flow velocimetry with dual beam optical coherence tomography
    (Optical Society of America, 2019-08-19) Rigas, Evangelos; Hallam, Jonathan M.; Charrett, Thomas O. H.; Ford, H. D.; Tatam, Ralph P.
    A novel dual beam Optical Coherence Tomography (OCT) instrument has been developed for high velocity flow measurement, principally in microfluidics applications. The scanned dual beam approach creates a pair of image-frames separated by a small spatiotemporal offset. Metre-per-second flow measurement is achieved by rapid re-imaging by the second beam allowing for particle tracking between each image-frame of the pair. Flow at 1.06 m/s using a single optical access port has been measured, more than two orders of magnitude larger than previously reported OCT systems, at centimetre depth and with millimetre scale depth of field within a microfluidic chip, whilst simultaneously imaging the microfluidic channel structure.
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    Optics Express: "Metre-per-second microfluidic flow velocimetry with dual beam optical coherence tomography" Rigas Hallam Charrett Ford Tatam
    (Cranfield University, 2019-08-06 14:26) Hallam, Jonathan; Tatam, Ralph; Charrett, Tom; Rigas, Evangelos; Ford, Helen
    Images and analysis code associated with Optics Express publication: "Metre-per-second microfluidic flow velocimetry with dual beam optical coherence tomography". The code should be run in a jupyter notebook (or other python implementation).
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    Transmission line method for the simulation of Fiber Bragg Gratings
    (Optical Society of America, 2019-01-04) Stathopoulos, N. A.; Savaidis, S. P.; Simos, H.; Rigas, Evangelos; Correia, Ricardo Goncalves; James, Stephen W.; Tatam, Ralph P.
    A new method for the analysis and design of fiber Bragg gratings (FBGs) based on the theory of transmission lines has been developed and verified both theoretically and experimentally. The method is an extension of the coupled-mode theory and utilizes the equivalent transmission lines in order to simulate any type of grating, with an easy and direct implementation. The method provides the ability to analyze the optical devices without using full wave approaches, while also facilitating the incorporation of core materials with a complex or non-linear refractive index, non-uniform distributions of the grating&\#x2019;s refractive index, and tilted and phase-shifted gratings. The approach also allows the design of the grating for a given reflection spectra. Numerical results of the method&\#x2019;s application on a randomly varied inscription of the refractive index of a FBG have also been simulated and discussed. Using this method, the characteristics of an erbium-doped (ED)-FBG have been simulated and the predictions verified experimentally.