Microwave Power dependence of the I-V Characteristics of Submicron and Micron YBCO Constrictions.

Conference paper published by Patrice Umenne Electrical Engineering DepartmentIn this paper, the femtosecond laser technique was used to fabricate micron and submicron sized Josephson Junctions. The influence of an RF signal of frequency 19.5 GHz on the critical current of the micron sized Josephson junction of width 2.1 μm and the sub-micron sized Josephson junction of width 816 nm was analyzed. Both junctions showed the presence of Shapiro-like steps and critical current suppression due an increase in the RF Power. Critical current suppression occurs due to the varying magnetic field produced by the RF signal power.The University of South AfricaCollege of Engineering, Science and Technolog

Micron sized constrictions fabricated using the femtosecond laser technique on YBCO thin films.

In this paper, I report on the fabrication of micron-sized constrictions in YBCO thin films using the femtosecond laser technique. The constrictions are S-shaped superconducting weak links fabricated on YBCO thin films. The constrictions show a measurable superconducting current flowing through them. Current–Voltage (I–V) characteristics were used to determine the critical current IC of the constrictions at 77 K. The width of the constrictions was determined at the narrowest point using SEM (scanning electron microscope). Three micron-sized constrictions were fabricated with a width of 2.88 μm, 1.72 μm, 1.69 μm and a length of 5 μm. Based on the width and length of these constrictions in relation to the coherence length (ξ) of the YBCO, these constrictions should conduct supercurrent by Abrikosov vortices. The SEM images show that the femtosecond laser heats the samples beyond the geometric boundary, damaging some of the superconductive phase of the YBCO constrictions. As a result, the constrictions conduct current by one-dimensional depairing.University of South africaElectrical and Mining Engineerin

Constrictions Fabricated on YBCO Thin Film using the Femtosecond Laser: Limiting Factors.

Journal Article written by Patrice Umenne in the department of Electrical and Mining EngineeringIn this paper we report on the development of a new application of the femtosecond laser, namely, the fabrication of micron, sub-micron and nano sized constrictions on YBCO superconductive thin films. The fabricated micron, sub-micron and nano constrictions have widths of 1.09 um, 705 nm and 394.8 nm, respectively. The thickness of these constrictions ranged from about 160 nm to 190 nm, as defined by the depth profile on the 3D AFM images. The length of these constrictions ranged from 7.2 um to 7.5 um. The length of these constrictions depends on the size of the laser ablation spot used for cutting and on the separation distance between the laser ablation spots along the width of the sample.The University of South AfricaCollege of Engineering, Science and Technolog

Design of a PV Based Power Supply with a NonInverting Buck-Boost Converter

Please follow the link at the top of the record to access the full-text of this item.This paper presents the design of a photovoltaic based power supply using a non-inverting buck-boost converter to charge batteries. The batteries can be used to power a load as back-up power when there is no sunlight. This approach presents a constant output of 48 V charging voltage for the batteries even though the input voltage may vary depending on the amount of solar irradiation falling on the solar panel. Solar charge controllers are important components in such an off-grid system because they can be used to protect the battery bank from overcharging and regulate the charging current. The buck-boost converter is used as a solar charge controller to maximize the charging voltage when the solar irradiation provides less than the required output voltage. The DC-DC converter (buck-boost converter) was modelled using the SIMetrix software to demonstrate the expected output waveforms before building the complete PV power supply.University of South AfricaElectrical and Mining Engineerin

Constrictions Fabricated on YBCO Thin Film using the Femtosecond Laser: Limiting Factors.

Journal Article written by Patrice Umenne in the department of Electrical and Mining EngineeringIn this paper we report on the development of a new application of the femtosecond laser, namely, the fabrication of micron, sub-micron and nano sized constrictions on YBCO superconductive thin films. The fabricated micron, sub-micron and nano constrictions have widths of 1.09 um, 705 nm and 394.8 nm, respectively. The thickness of these constrictions ranged from about 160 nm to 190 nm, as defined by the depth profile on the 3D AFM images. The length of these constrictions ranged from 7.2 um to 7.5 um. The length of these constrictions depends on the size of the laser ablation spot used for cutting and on the separation distance between the laser ablation spots along the width of the sample.The University of South AfricaCollege of Engineering, Science and Technolog

AFM Analysis of Micron and Sub-micron sized Bridges Fabricated Using the Femtosecond Laser on YBCO Thin Films.

The project arose as a result of the need to use the femtosecond laser to fabricate sub-micron and Nano-sized bridges that could be analyzed for the Josephson effect. The femtosecond laser has a low pulse duration of 130 femtoseconds. Hence in an optical setup it was assumed that it could prevent the thermal degradation of the superconductive material during fabrication. In this paper a series of micron and sub-micron sized bridges where fabricated on superconductive YBCO thin film using the femtosecond laser, a spherical convex lens of focal length 30 mm and the G-code control programming language applied on a translation stage. The dimensions of the bridges fabricated where analyzed using the Atomic Force Microscope (AFM). As a result, micron sized superconductive bridges of width 1.68 μm, 1.39 μm, 1.23 μm and a sub-micron sized bridge of width 732 nm where fabricated. The length of this bridges ranged from 9.6 μm to 12.8 μm. The femtosecond laser technique and the spherical convex lens can be used to fabricate bridges in the sub-micron dimension.University of South Africa ESKOM TESP grantElectrical and Mining Engineerin

Design of a smart home system using bluetooth protocol

Abstract: Home automation is an intelligent, functional as a unit system that facilitates home processes without unnecessarily complicating the user’s life. Devices can be connected, which in turn connect and talk through a centralized control unit, which are accessible via mobile phones. These devices include lights, appliances, security systems, alarms and many other sensors and devices. This paper presents the design and implementation of a Bluetooth based smart home automation system which uses a Peripheral interface controller (PIC) microcontroller (16F1937) as the main processer and the appliances are connected to the peripheral ports of the microcontroller via relays. The circuit in the project was designed in Diptrace software. The PCB layout design was completed. The fully functional smart home prototype was built and demonstrated to functional

Emulating Software Defined Network Using Mininet and OpenDaylight Controller Hosted on Amazon Web Services Cloud Platform to Demonstrate a Realistic Programmable Network.

Conference paper written by masters student in satisfaction of masters degreeFollow the link at the top of the record to access the full-text of this item on the publisher's web site.In this paper, a Software Defined Network was created in Mininet using python script. An external interface was added in the form of an OpenDaylight controller to enable communication with the network outside of Mininet. The OpenDaylight controller was hosted on the Amazon Web Services elastic computing node. This controller is used as a control plane device for the switch within Mininet. The OpenDaylight controller was able to create the flows to facilitate communication between the hosts in Mininet and the webserver in the real-life network. In order to test the network, a real life network in the form of a webserver hosted on the Emulated Virtual Environment – Next Generation (EVE-NG) software was connected to Mininet.The University of Johannesburg The University of South AfricaCollege of Engineering, Science and Technolog

The Impact of Virtual Learning Environments on the Practical Skills of Open Distance Learning Students in Electrical Engineering

Open distance learning (ODL) education has been developing rapidly in South Africa. The main reason behind the growth is the demand for online studies created due to the corona pandemic. The ODL system involves study that is not limited by geographical boundaries and extends to many knowledge areas electronically. In practice the study tends to extend to knowledge areas beyond those offered by the standard contact or traditional universities. At the University of South Africa (UNISA), the adoption of the ODL framework to theoretical subjects has been successful by making use of the Sakai virtual learning environment (VLE). The practical subjects or practical knowledge areas on the other hand have previously been taught face-to-face. Therefore, the practical modules have not been effectively taught online particularly in the electrical engineering curriculum. This issue can contribute to graduates who are unskilled in the practical component of a knowledge area, which can lead to unemployment. Virtual learning environments (VLE's) play a vital role when it comes to teaching and learning online. In this paper, the impact of VLE’s on the practical skills of students and practical knowledge is investigated. This is done by analyzing the change in pass rates of students in a practical subject such as Electrical Engineering when taught face-to-face as compared to when taught through a VLE such as Sakai online. Two groups termed as emerging centered learner (ECL) and a developed centered learner (DCL) are investigated. The method evaluates students who study electrical engineering practical module part-time. In this paper the Sakai platform was used as a VLE to teach and then evaluate students in the electrical engineering practical module. The practical guide with the full set of experiments was uploaded on Sakai under additional resources. The students were given the necessary guidelines and tasks via Sakai online, examined and then the pass rates achieved were analyzed at the end of the program and compared to the pass rates achieved using previous face-to-face teaching method used for the same practical’s. It was determined that a VLE can be used to improve the pass rates of a practical module such as electrical engineering taught online in ODL.University of South AfricaElectrical and Mining Engineerin

Access Control with Automated on Duty Notification Tool in air traffic Services

This project provides a solution that alerts management if an Air Traffic Service Unit (ATSU) tower is unmanned during operational hours. The project makes provision for an access control with an automated on duty notification tool. The Air traffic controller activates a report for the on-duty system real time when he accesses the tower. The control system is used to send notification to the line management if the air traffic control tower is unmanned at any time. Escalation to the next level management occurs automatically every 15 minutes if the tower is unmanned until it reaches the senior management of the air traffic services. The project is modelled in Proteus software. The proteus software is interfaced to a Global System for Mobile Communications (GSM) module for communication as an automated notification tool.Air Traffic and Navigation Services University of South AfricaElectrical and Mining Engineerin