Browsing by Author "Ramokolo, Lesiba R"

Now showing 1 - 8 of 8
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    Celebrating the Year of Light….. from medicine to security with Optical Coherence Tomography
    (CSIR, 2015-10) Singh, A; Sharma, Ameeth; Roberts, T; Khutlang, Rethabile; Ramokolo, Lesiba R; Marome, N; Webb, L; Botha, N; Karsten, A; Strauss, Hencharl J
    This poster Celebrating the Year of Light….. from medicine to security with Optical Coherence Tomography was presented at the CSIR’s 5th Conference, 8-9 October 2015.
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    CSIR National Laser Centre develops a high speed OCT system
    (CSIR, 2016-11) Sharma, Ameeth; Singh, Ann; Roberts, Ted; Ramokolo, Lesiba R; Van der Westhuizen, Corrie
    The optical coherence technique (OCT) technique, which was demonstrated by Fercher and Huang in the early 90s, has made significant strides in bio-medical diagnostic applications in the fields of dermatology, dentistry and ophthalmology. Other impact areas and applications include polymer characterisation, surface and thin-film characterisation and biometrics. The National laser Centre has developed a high speed, large area optical coherence tomography (OCT) prototype for fingerprint scanning. The system, which is not limited to this application, can image a large volume (25mm x 25mm x 11mm) and resultant 3-D images (512 x 512 x 2048 pixels) are acquired in less than three seconds. The heart of the system is a swept laser source and a two-axis scanner. Signal acquisition is made possible through a high-speed analogue-to-digital converter capable of speeds greater than 1GS/s. The system has demonstrated the ability to capture live fingerprints making it a viable alternative for high security access control. Furthermore the ability to capture latent fingerprints, from plastic and glass surfaces, was also demonstrated making it applicable to forensics. This paper will present the system design and some of the initial results.
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    Damage invariant and high security acquisition of the internal fingerprint using optical coherence tomography
    (Infonomics Society, 2016-11) Darlow, Luke N; Singh, Ann; Moolla, Yaseen; Ramokolo, Lesiba R; Van Wyk, R; Botha, Natasha; Webb-Ray, L
    Fingerprints are widely used for biometric authentication, identification, and access control. However, most current acquisition devices obtain fingerprints from the surface of the skin and are thus inherently restricted by the surface 2D representation they offer. Using an emerging fingerprint acquisition technology – optical coherence tomography – to access an internal fingerprint under the skin surface, this paper serves to address two limitations of conventional scanners: fingertip skin damage (owing to eczema, in this case) and presentation attacks. The surface fingerprint was very poorly affected by severe damage, with minutiae detection accuracy diminished from 88.7% to 4.7%. The internal fingerprint was far less affected by severe damage, with minutiae detection accuracy decreased from 81.3% to 40.5%. The internal fingerprint showed improved recovery when eczema abated, with minutiae extraction accuracy improvements of 35.6% for the internal fingerprint yet only 0.6% for the surface fingerprint. Furthermore, the difference between the internal fingerprint of real and fake fingers is distinct and an analysis of the orientation certainty level allowed for fully automated and entirely accurate presentation attack detection.
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    Detecting defects during powder deposition in additive manufacturing
    (2018-11) Hendriks, Adriaan J; Ramokolo, Lesiba R; Ngobeni, Christopher M; Moroko, Matome C; Naidoo, Darryl
    Additive manufacturing applications, in areas such as aerospace and medicine, are limited due to the lack of process stability and quality management. In particular, geometrical inaccuracies and the presence of mechanical defects hinder repeatability of the process. To break into industries with very high quality standards, an important issue to be addressed is in-situ quality control during a build. The work which will be presented here is focused on image based process monitoring of the powder bed after the deposition of a new powder layer. We will also discuss the effects these might have on consolidating the powder with the rest of the part. Preliminary results will be shown of defects identified after a new powder layer has been deposited.
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    Detection and quantification of iodine in biological fluids using photonic-based systems: UV-Vis and Transmission spectroscopy
    (2024-01) Mcotshana, Zenande KS; Thwala, Nomcebo L; Ombinda-Lemboumba, Saturnin; Ramokolo, Lesiba R; Lugongolo, Masixole Y; Van Steen, E; Mthunzi-Kufa, Patience
    Iodine is a crucial trace element that occurs in minute amounts in nature and is necessary for the development of bones, thyroid function, and several metabolic processes. Iodine deficiency, also known as hypothyroidism, affects millions of individuals worldwide, and an overabundance of iodine in the body is known as hyperthyroidism. The early identification of iodine with high sensitivity and selectivity is crucial for physiological impact since the abnormalities caused by iodine disorder can increase the frequency of mortality and mental impairments. This work aims to detect iodine using UV-Vis and Transmission spectroscopy and utilizing selenium nanoparticles as a probe. Selenium nanoparticles (SeNPs) were synthesized by ND: YAG laser method and characterized by Dynamic light scattering (DLS), and High-resolution transmission electron microscopy (HRTEM), while the conjugation of iodine to SeNPs was confirmed by Ultraviolet-visible (UV-vis) spectroscopy. For iodine detection, UV-Vis and Transmission spectroscopy were used and compared and the synthesized colloidal and spherical selenium nanoparticles were utilized as a probe to detect iodine. The absorption peaks and a red shift for SeNPs changed upon the reaction with iodine and this shift may allow for the estimation of iodine concentration. The two methods will enable the detection and monitoring of iodine at different concentrations in the body thus preventing the onset of iodine-related diseases.
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    Detection of viral pathogens using optical photonic techniques with the aid of selenium nanoparticles
    (2024-01) Mcotshana, Zenande KS; Thwala, Nomcebo L; Ombinda-Lemboumba, Saturnin; Ramokolo, Lesiba R; Thobakgale, Setumo L; Lugongolo, Masixole Y; Van Steen, E; Mthunzi-Kufa, Patience
    Viral infections such as HIV and SARS-CoV-2 have significantly increased morbidity in humans and resulted in a significant number of fatalities globally, hence early detection is crucial, particularly at a point-of-care (POC) setting to prevent the spread of these diseases. Localized surface plasmon resonance (LSPR) and green light-based Transmission spectroscopy techniques were used in this study to assess real-time molecular interactions between virus-spiked and non-spiked samples. The current study focuses on integrating selenium nanoparticles (SeNPs) with different optical photonic techniques for enhanced detection of HIV. Selenium nanoparticles were synthesized and functionalized with antibodies specific to HIV. Before and after bioconjugation with viral secondary antibodies, the SeNPs were characterized using Ultraviolet–visible (UV-Vis) spectroscopy, Dynamic light scattering (DLS), High-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy, to elucidate their properties and confirm the presence of functional groups. After that, the NPs were integrated with plasmonic systems and used for the enhanced detection of HIV in comparison to traditional LSPR and Transmission spectroscopy. Colloidal selenium nanoparticles were successfully synthesized, using ND: YAG laser. The orange-colored, spherically shaped nanoparticles were evenly distributed and easily resuspended. Anti-HIV antibodies conjugated to SeNPs were added after HIV-specific antibodies were successfully immobilized on a glass slide substrate to react with HIV pseudovirus. The pseudovirus was effectively identified by the use of Transmission Spectroscopy and LSPR techniques. The two optical techniques for HIV detection were more sensitive after integrating selenium nanoparticles, as compared to the conventional Transmission spectroscopy and LSPR methods. This improved and highly sensitive approach may be utilized to identify viral infections early, thus combating the spread of infectious diseases.
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    A high speed OCT system developed at the CSIR National Laser Centre (paper)
    (The South African Institute of Physics, 2016-07) Sharma, Ameeth; Singh, Ann; Roberts, Ted; Ramokolo, Lesiba R; Strauss, Hencharl J
    Light-based techniques continue to gain momentum in different spheres of diagnostic and therapeutic applications due to their non-invasive, non-contact properties. One such technique is Optical Coherence tomography (OCT). Since first being reported by Huang in 1991, OCT has made significant strides in different fields such as dermatology, ophthalmology, polymer characterisation and biometrics. The type of OCT system employed can be a simple, cost effective solution or a complex, highly specific and fast system depending on the application. As part of a larger project, we have designed and built a high speed OCT system that can image a large surface area (25 by 25 mm) to a depth of 11 mm (sample dependant). Resultant 3-D images (512 x 512 x 2048 pixels) are acquired in less than 3 seconds. The heart of the system is a 200 kHz swept laser source and two-axis galvanometer based scanner. Signal acquisition is made possible through a high-speed analogue-to-digital converter capable of speeds greater than 1GS/s. This paper will give an overview of the system design and the specifications that have been obtained.
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    Layer-wise powder deposition defect detection in additive manufacturing
    (SPIE, 2019-03) Hendriks, Adriaan J; Ramokolo, Lesiba R; Ngobeni, Christopher M; Moroko, Matome C; Naidoo, Darryl
    Additive manufacturing applications, in areas such as aerospace and medicine, are limited due to the lack of process stability and quality management. In particular, geometrical inaccuracies and the presence of mechanical defects hinder repeatability of the process1. A great disadvantage of AM is that verifying the quality of AM produced parts are mainly done after part fabrication which does not allow the operator to act upon defects observed during the actual build. To break into industries with very high quality standards, an important issue to be addressed is in-situ quality control during a build2, 3. If defects on a new powder layer can be detected before laser melting occurs, a new layer may be suitably recoated or the process can be paused for user controlled rectification. The work which will be presented here is focused on image based process monitoring of a powder bed additive manufacturing system using a shadow casting method. As a proof of principle, a few main defects during recoating will be identified and analyzed to establish the severity and possible impact of the defects on metal powder consolidation. Preliminary results of defects identified before and after material consolidation will be shown. For this, a software package is in development to automatically detect defects. This is aimed towards developing a system which in the future will contribute to quality assurance.