Robert van Zyl

Modeling geomagnetically induced currents in the South African power transmission network using the finite element method

Geomagnetically induced currents (GIC) are a result of time variations of the geomagnetic field, which induce a geoelectric field at the Earths surface. Geomagnetic perturbations are enhanced during adverse space weather events called geomagnetic storms. All ground-based conductor networks can be affected by GIC during such events. As a way of assessing the magnitude of GIC expected in a particular technological system, models are developed, in which the computation of the induced geoelectric field is a key step. Computation of GIC in the South African power transmission network has so far been done using a uniform Earth model and improved using a layered Earth conductivity profile. In this work we present geoelectric field results obtained by using the finite element method (FEM) and improved GIC estimates using a realistic conductivity profile, magnetic field data interpolated from two South African observatories, and a new method for estimating the network coefficients, a and b, which map the north-south and east-west electric fields to their respective GIC components. The performance of the chosen FEM model demonstrates that it is an effective tool for GIC modeling. Unlike previous engineering techniques, our method for estimating the a and b coefficients from GIC and measured magnetic field data gives results that are independent of prior knowledge of the network configuration. The GIC estimated using the a and b coefficients obtained from the proposed method compares well with the measured GIC during the late October 2003 geomagnetic storm.

A review of rectenna models for electromagnetic energy harvesting

Purpose – Distributed wireless sensor networks (DWSNs) are applied in a variety of applications that can enhance the quality of human life. Batteries are the predominant source of energy in DWSNs. One of the key obstacles in the adoption of DWSNs technology is the limited lifetime of batteries in microsensors. Recharging or replacing depleted batteries can significantly increase costs in DWSNs. The purpose of this paper is to address, through a thorough review, this power challenge in DWSNs and to evaluate a 16‐element equiangular spiral rectenna to harvest ambient microwave energy in real‐life scenarios to supply indoor DWSNs.Design/methodology/approach – The paper focuses on the practical implementation of a rectenna that can be used in electromagnetic energy harvesting. The design and measurement of the rectenna follows a broad overview of rectenna designs reported in the literature.Findings – The paper concludes that the 16‐element equiangular spiral rectenna has the potential to generate power that e...

A low cost testbed and test-design methodology for nanosatellite sub-/systems

The architecture of a software-driven testbed is discussed. The test setup has been developed as measurement and instrumentation system to functionally verify and thermally validate the communication subsystems designed and manufactured for the nanosatellite applications. The system is applied for qualification of a communications subsystem currently under consideration for ZA-CUBE-2 mission.

Passive field uniformity enhancement in reverberation chambers

Much has been written on field uniformity enhancement and different types of stirrers for reverberation chambers. We have distilled the theory and applied this to a full-wave electromagnetic simulation of an empty, rectangular cavity with and without the introduction of shaped conductive structures. In anticipation of real-life applications, both dipole and Yagi-Uda antennas, orientated in the vertical and horizontal, were used as radiators. This study presents attempts to passively distribute the fields more evenly inside a reverberation chamber by supporting more modes with the introduction of conductive structures inside the chamber. A brief theoretical background is given to support the simulation-based analysis reported here. Simulations were conducted for a 1.86 × 2.44 × 2.47 m screened room. The results show that passive field enhancement has improved the standard deviation when compared to an empty chamber. The simulated standard deviation of the internal total electric field distribution over a frequency band of 1 – 2 GHz shows marginal improvement in the field uniformity of between 0.6 dB at lower frequencies and 0.1 dB at higher frequencies when introducing static conductive structures in the cavity and employing a horizontally positioned dipole. However, passive “stirring” of the modes alone does not satisfy the requirements for electromagnetic compatibility testing using reverberation chambers, but it does pose an improvement in the performance of reverberation chambers where dynamic mixing of the modes is done through rotating stirrer structures.

Practical electromagnetic compatibility studies of a CubeSat

Purpose Incorporating electromagnetic compatibility (EMC) in the design life of traditional satellites is entrenched in the satellite industry. However, EMC treatment of CubeSats has not been widely pursued, for various possible reasons. CubeSats are a young technology platform initially intended for students and researchers at universities to create awareness and excitement amongst them for space technology. This and other factors limited the need for stringent EMC planning. As CubeSats mature in complexity, the success of future missions will rely on incorporating proper EMC designs in their development. This paper aims to address the experimental investigation of known EMC culprits within a CubeSat’s context. Design/methodology/approach Electromagnetic interference suppression effectiveness of cable trays in CubeSats, as well as crosstalk in high-speed/frequency data links, is investigated, using the PC/104 connector stack. Some recommendations for improving the EMC and, therefore, enhancing satellite mission success are provided. Findings It was found that, if physically feasible in the CubeSat, cable trays are significant radiation suppressors. A further investigation into crosstalk between pins of the PC/104 connector stack showed that grounding a pin in between two signal pins leads to a significant reduction in the coupled signal. Originality/value This paper addresses EMC within the context of a CubeSat and outlines experiments done resulting in cost-effective methods of reducing interference by using already available material (such as unused signal pins available in the PC/104 connector).

Photocurrents obtained from a triple planar probe sensor for in situ extreme ultraviolet (EUV) radiation measurements on low Earth orbiting CubeSats

Purpose In the Earth’s upper atmosphere, damage to satellite electronics is caused by exposure to extreme ultraviolet (EUV) radiation. One particular region where this type of radiation occurs is the South Atlantic Magnetic Anomaly region. As a result, there is a need to design and develop a sensor which could be used to investigate the flux and energy levels of radiation in this region. To do so, the aim of this study is to characterise the sensor and its electric response to typical EUV radiation levels based on the photoelectric effect principle. Design/methodology/approach For this purpose, a copper plate planar sensor prototype with dimensions that fit on the sides of a one-unit (1U) CubeSat was constructed. The sensor prototype was placed in a vacuum chamber and was subjected to continuous radiation from a vacuum ultraviolet deuterium light source at test facilities available in the Western Cape region (South Africa). Subsequently, the terminal voltage of the sensor was measured and compared with theory. Findings The measured time-averaged terminal voltages indicate the generation of photocurrents of the order of 1 μA, which is consistent with theory. Originality/value Conclusively, these results validate the measurement approach and operation of the sensor, which can be used to design a 1U CubeSat sensor that measures EUV radiation in low Earth orbit.

PSIM simulations of a dc SQUID magnetometer

Purpose – This paper aims to report the modelling and simulation work that predicts the behaviours of both a Josephson junction (JJ) and a dc superconducting quantum interference device (SQUID). It is pertinent to predict the SQUID magnetometers’ behaviours via simulations, before subjecting them to real experiments because they are quite expensive to acquire, and can be easily damaged during test analysis. Design/methodology/approach – To achieve this, power simulation (PSIM) was used to model and simulate a JJ, using the basic equation that describes the effective current through it. A dc SQUID magnetometer, which is composed of two JJs, was then modelled and simulated using the modelled JJ. Thermal noise simulation is also included, to observe its effects on the magnetometer’s output. A directly coupled flux-locked loop circuit was later included in the simulation to amplify and linearise the SQUID’s output, which is usually sinusoidal. Findings – When steady bias currents were applied to the JJ, the r...

Empirical investigation of wireless sensor network performance in noisy environments

Purpose – The purpose of this work is to assess the influence of ambient noise on the performance of wireless sensor networks (WSNs) empirically and, based on these findings, develop a mathematical tool to assist technicians to determine the maximum inter-node separation before deploying a new WSN. Design/methodology/approach – A WSN test platform is set up in an electromagnetically shielded environment (RF chamber) to accurately control and quantify the ambient noise level. The test platform is subsequently placed in an operational laboratory to record network performance in typical unshielded spaces. Results from the RF chamber and the real-life environments are analysed. Findings – A minimum signal-to-noise ratio (SNR) at which the network still functions was found to be of the order 30 dB. In the real-life scenarios (machines, telecommunications and computer laboratories), the measured SNR exceeded this minimum value by more than 20 dB. This is due to the low ambient industrial noise levels observed i...