Papers by Trudi-Heleen Joubert
Water Quality Assessment Tool for On-site Water Quality Monitoring
IEEE sensors journal, 2024
How can we maximise operating theatres and reduce waiting lists?
Bulletin of the Royal College of Surgeons of England, Mar 1, 2024
Resource Allocation Optimization in IoT-Enabled Water Quality Monitoring Systems
Sensors, Nov 2, 2023
Proceedings of SPIE, Jun 23, 2014
SU-8/Clay nanocomposite is considered as a candidate material for microcantilever sensor fabricat... more SU-8/Clay nanocomposite is considered as a candidate material for microcantilever sensor fabrication. Organically modified montmorillonite clay nanoparticles are dispersed in the universally used negative photoresist polymer SU-8, for a low cost material, which is also biocompatible. If varying the clay loading of the composite material yields a variation of the Young's modulus, the tailored material stiffness presents an opportunity for fabrication of microcantilevers with tunable sensor sensitivity. With this microcantilever application perspective, mechanical and thermal properties of the material were investigated. SU-8/Clay nanocomposite samples were prepared with clay loadings from 1wt% -10wt%. Tensile test results show a general trend of increase in composite modulus with an increase in the clay loading up to 7wt%, followed by a small drop at 10wt%. The composite material indeed yields moderate variation of the Young's modulus. It was also found that the thermal degradation peak of the material occurred at 300°C, which is beyond the operating temperature of typical microcantilever sensor applications. The fabrication of a custom designed microcantilever array chip with the SU-8/Clay nanocomposite material was achieved in a class 100 cleanroom, using spin-coating and photolithography microfabrication techniques. The optimization of the process for fabricating microcantilever with the SU-8/Clay nanocomposite material is discussed in this paper. The results of this research are promising for cheaper mass production of low cost disposable, yet sensitive, microcantilever sensor elements, including biosensor applications.
IEEE Photonics Technology Letters, Aug 15, 2015
Hot carrier electroluminescence in two junction devices under punch through conditions manufactur... more Hot carrier electroluminescence in two junction devices under punch through conditions manufactured in silicon on insulator nanowires are investigated. Of interest is the spectral content of the light emission, as well as the external power efficiency and the light extraction efficiency. An order of magnitude improvement in external power efficiency was achieved relative to a bulk silicon p-n junction in avalanche.
Eurasip Journal on Wireless Communications and Networking, Jan 8, 2019
In this paper, a new approach to energy harvesting and data transmission optimization in a hetero... more In this paper, a new approach to energy harvesting and data transmission optimization in a heterogeneous-based multi-class and multiple resource wireless transmission wireless sensor network system that focus on monitoring water and its quality is presented. Currently, energy is a scarce resource in wireless sensor networks due to the limited energy budget of batteries, which are typically employed for powering sensors. Once the available energy of a particular sensor node battery is depleted, such sensor node becomes inactive in a network. As a consequence, such node may not be able to participate in the transmission of the application signal in the uplink stage of the network, resulting in a lack of ability to communicate vital signals in a timely manner. Energy scarcity has been a long standing problem in wireless sensor network applications. To address this problem, energy harvesting from intended radiofrequency power source is considered in this work. However, wirelessly powered wireless sensor network systems are confronted by unfairness in resource allocation problem, as well as interference problem in multiple energy resource transmissions. These problems adversely impact the performance of the system in the context of the harvested energy by the sensor nodes, sensors information transmission rates, and the overall system throughput rate. These problems are tackled in this paper by formulating a sum-throughput maximization problem to reduce system energy consumption and enhance the system overall throughput rate. The throughput optimization problem is formulated as a non-convex function. Through the exploitation of the problem structure, it is converted to a convex function. The mathematical models of the optimization problem are validated through numerical simulations. The simulation results reveal that the proposed wireless powered sensor network system outperforms an existing wireless powered sensor network system, by comparison of the numerical simulations of this work to the numerical simulations of the existing WPSN system, regardless of the distances of the sensor nodes to the IPS and the base station. Also, the newly proposed method performs efficiently using parameters that include path-loss exponent impact, performance comparison of systems, convergence based on iteration, comparison based on unequal network distances to the BS, transmission power impact on the attainable throughput and on fraction of energy consumed on information transmissions, and influence of different number of nodes in the network classes.
An air quality sensing system for cool air storage
Proceedings of SPIE, Feb 3, 2017
Cooling and ventilation systems play an important role in human occupied spaces. However, cooling... more Cooling and ventilation systems play an important role in human occupied spaces. However, cooling using reversible air conditioners systems pollutes the environment and consumes a significant amount of energy. With global warming that experiences our environment, the large consumption of electrical energy and the operating instructions for reversible air conditioners, there is a need to find alternatives to those cooling systems. Hence this research project aims to investigate an air storage system, a microsystem reversible ventilation system using natural atmospheric air (renewable energy) for cooling at low consumption of energy. For the variation of the temperature range of comfort due to thermal heat produces by occupants, equipment and environment, an optimal transient automatic regulation of air flow as to be design in order to maintain the temperature of comfort in occupied spaces during peak hours.
High resolution CMOS capacitance-frequency converter for biosensor applications
Proceedings of SPIE, Feb 3, 2017
This paper presents the design of a low-complexity, linear and sub-pF CMOS capacitance-frequency ... more This paper presents the design of a low-complexity, linear and sub-pF CMOS capacitance-frequency converter for reading out a capacitive bacterial bio/sensors with the endeavour of creating a universal bio/sensor readout module. Therefore the priority design objectives are a high resolution as well as an extensive dynamic range. The circuit is based on a method which outputs a digital frequency signal directly from a differential capacitance by the accumulation of charges produced by repetitive charge integration and charge preservation1. A prototype has been designed for manufacture in the 0.35 μm, 3.3V ams CMOS technology. At a 1MHz clock speed, the most pertinent results obtained for the designed converter are: (i) power consumption of 1.37mW; (ii) a resolution of at least 5 fF for sensitive capacitive transduction; and (iii) an input dynamic range of at least 43.5 dB from a measurable capacitance value range of 5 – 750 fF (iv) and a Pearson’s coefficient of linearity of 0.99.
A low input offset voltage operational amplifier using capacitively coupled floating gate (CCFG) MOSFET technology
An operational amplifier has been developed using Capacitively Coupled Floating Gate (CCFG) MOSFE... more An operational amplifier has been developed using Capacitively Coupled Floating Gate (CCFG) MOSFETs. The design is mathematically optimised to achieve good performance from limited silicon area. The resulting operational amplifier operates from low supply voltages, while maintaining wide common mode input range, high gain and low input offset voltage
Enhanced model for MIFG MOSFET devices under switched operation
Multiple input floating gate (MIFG) transistors have been found to be very useful in many analogu... more Multiple input floating gate (MIFG) transistors have been found to be very useful in many analogue applications. We extend the existing MIFG models to cover switched operation and charge injection, extending the usefulness of MIFGs to many new applications
Agriculture
Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ... more Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ticks. Due to misuse in rural dipping pools, some ticks are showing resistance to Taktic. This work presents a low-cost e-nose with commercial sensors to monitor Taktic levels in dipping pool water. The device shows distinctly different measurements for the odours of air, distilled water, farm water, and four levels of Taktic insecticide in farm water. A naive Bayes algorithm with a Gaussian distribution is trained on the data and a validation set achieves a 96.5% accuracy. This work also compares two sol-gel ZnO nanoparticle solutions with an off-the-shelf ZnO nanoparticle ink for use as active material in chemiresistive gas sensors to be employed in an e-nose array. The ZnO solutions are screen-printed onto gold electrodes, auto-sintered with a built in heater, and used with UV illumination to operate as low-power, room temperature gas sensors. All of the screen-printed ZnO sensors sho...
Hot carrier degradation of mixed-mode polysilicon light emitting diodes
Materials Science and Engineering: B
Efficient Resource Allocation in Water Quality Sensor Networks
2019 IEEE 2nd Wireless Africa Conference (WAC)
In this study, an efficient resource allocation scheme that uses an optimization algorithm is put... more In this study, an efficient resource allocation scheme that uses an optimization algorithm is put forward for optimal resource utilization in a wirelessly powered water quality sensor network system. To achieve the wireless powering, energy harvesting from a dedicated radio frequency (DRF) station is introduced, and is aimed to tackle the fundamental energy issues that confronts sensor network systems. Due to the scarceness of energy resource, an energy consumption optimization model is formulated and validated through the numerical simulation results and the Lagrangian solutions. Based on the employed performance evaluation metrics, the proposed system outperforms an existing benchmark system in numerical simulations. The proposed system performs efficiently using parameters such as convergence based on iteration numbers, and performance comparison of systems.
Cooking harvested power manager for natural room cooling controller
Fifth Conference on Sensors, MEMS, and Electro-Optic Systems, 2019
The intention in this work was to generate and store adequate energy to power a natural ambient r... more The intention in this work was to generate and store adequate energy to power a natural ambient room cooling system. A major problem that the automatic air-conditioning industry is facing today has to do with too much power consumption in that the heat and ventilation air conditioning (HVAC) systems are currently using about 50% of all produced electricity. The latter also does not consider the peak time of use, where the desired ambient temperature of an air-conditioned room is greatly affected by the activities of the occupants at a given time. As part of the power management system, the concept of charging a battery to full capacity is explored of exploiting the excess energy available surrounding a cooking pot after, even after the heat source is removed. Thermoelectricity (TE) is used to capture wasted heat from the pot, and the reclaimed thermal energy is optimized for conversion into the electrical power. This is in short what I did. These are my results in summary.
Nanoparticles and organic semiconductors for flexible electronics
Key issues for flexible electronics are low temperature processing, cost-efficient semiconducting... more Key issues for flexible electronics are low temperature processing, cost-efficient semiconducting and dielectric materials, and sufficient performance of the integrated TFT devices. To achieve high performance flexible circuits, contact resistances of today’s transistors must be reduced. Additionally, the parasitic overlap capacitances between the transistor’s electrodes need to be minimized. The inverted staggered transistor setup with self-aligned gate fulfills these requests. Nevertheless, the integrated devices suffer on poor AC characteristics due to limited performance of the common gate dielectric layers. The gate voltage has no direct access to the semiconductor surface, either due to rechargeable surface states and polarization effects or because of low-k values. Consequently, new flexible high-k dielectrics must be implemented in TFT device integration.
Biocompatibility in inkjet-printed paper-based microelectronic biosensors
Inkjet-printing supports environmentally friendly manufacturing of printed electronics and enable... more Inkjet-printing supports environmentally friendly manufacturing of printed electronics and enables rapid prototyping with low material waste. In this work, inkjet-printed conductive tracks on ethyl 2-cyanoacrylate (superglue) is compared to tracks printed on paper. This work will provide solutions for disposable biosensing, where the biocompatibility of versatile superglue is important. The emphasis throughout the work is on developing a biocompatible device. Dog-bone structures with different line widths were printed on paper and superglue, providing comparative results obtained from dimensional and electrical characterisation. On average the tracks printed on superglue have a 2.6 times higher resistivity than those printed on paper, but are acceptable for printed electronics networks. When considering a lumped component ac model, the 500 μm tracks on superglue have a series inductance of 2.6 nH, while the 4-point Kelvin probe characterisation of the 100 μm and 250 μm tracks printe...
International Conference on Competitive Manufacturing (COMA): COMA'16, 6th international conf... more International Conference on Competitive Manufacturing (COMA): COMA'16, 6th international conference Wallenberg Centre(STIAS) Stellenbosch 27th January-29th January 2016. Due to copyright restrictions, the attached PDF file only contains the abstract of the full text item. For access to the full text item, please consult the publisher's website
Undersampling and Saturation for Impedance Spectroscopy Performance
IEEE Sensors Journal, 2021
The development of low-cost impedance spectroscopy devices is limited by the capabilities of low-... more The development of low-cost impedance spectroscopy devices is limited by the capabilities of low-cost hardware. Impedance spectroscopy requires high accuracy over a large bandwidth and dynamic range for most applications. In this paper, back-end signal processing solutions are examined and implemented to improve both the bandwidth and dynamic range of a typical low-cost impedance analyser without modifying the hardware. The bandwidth is improved by undersampling the input waveforms and reconstructing the signals based on the known frequency information. The bandwidth can be increased by multiple orders of magnitude and the limiting factor of the system becomes amplifier bandwidth and the Analog-to-Digital Converter (ADC) sample-and-hold circuit. Despite allowing signals to become orders of magnitude larger than the ADC range, the original signal can be reconstructed based on the measured saturated signal. This saturation technique more than doubles the dynamic range for any given accuracy requirement.
Maximizing the Throughput and Fairness of a Water Quality Monitoring Wireless Sensor Network System
International Journal on Communications Antenna and Propagation (IRECAP), 2018
This work presents a holistic solution for maximizing energy harvesting fairness and information ... more This work presents a holistic solution for maximizing energy harvesting fairness and information throughput in a multi-network wireless sensor network system that could be used for water quality monitoring. Presently, most of the research works on wireless information and power transfer systems employ a single dedicated radio frequency source, while the few ones that have considered multiple dedicated radio frequency sources are faced with interference problems. Due to the doubly near-far problem, unfairness issues are experienced in multiple energy transmissions, energy harvesting and information transmission rate. In this paper, these issues are addressed by investigating a multi-group, multi-source wireless information and power transfer system. A new time-division-multiple-access model is proposed to efficiently timeslot the operation of the sensor nodes and the dedicated radio frequency sources to overcome the interference problems, and to improve the energy efficiency of the network system. Based on the proposed time-division-multiple-access model, an algorithm is developed for fair allocation of energy harvesting and information transmission timing. This work is validated through numerical comparison. The simulation results reveal that the proposed wireless information and power transfer system outperforms an existing state-of-the-art wireless information and power transfer system, regardless of the distance of the sensor nodes to the dedicated radio frequency sources and the sink node.
An air quality sensing system for cool air storage
Fourth Conference on Sensors, MEMS, and Electro-Optic Systems, 2017
Cooling and ventilation systems play an important role in human occupied spaces. However, cooling... more Cooling and ventilation systems play an important role in human occupied spaces. However, cooling using reversible air conditioners systems pollutes the environment and consumes a significant amount of energy. With global warming that experiences our environment, the large consumption of electrical energy and the operating instructions for reversible air conditioners, there is a need to find alternatives to those cooling systems. Hence this research project aims to investigate an air storage system, a microsystem reversible ventilation system using natural atmospheric air (renewable energy) for cooling at low consumption of energy. For the variation of the temperature range of comfort due to thermal heat produces by occupants, equipment and environment, an optimal transient automatic regulation of air flow as to be design in order to maintain the temperature of comfort in occupied spaces during peak hours.
Uploads
Papers by Trudi-Heleen Joubert