Please read the abstract (Summary) in the section 00front of this document / Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

abstract: The human ankle is a critical joint required for mobility and stability of the body during static and dynamic activity. The absence of necessary torque output by the ankle due to neurological disorder or near-fatal injury can severely restrict locomotion and cause an inability to perform daily tasks. Physical Human-Robot Interaction (pHRI) has explored the potential of controlled actuators to positively impact human joints and partly restoring the required torque and stability at the joint to perform a task. However, a trade-off between agility and stability of the control technique of these devices can reduce the complete utilization of the performance to create a desirable impact on human joints. This research focuses on two control techniques of an Active Ankle Foot Orthosis (AFO) namely, Variable Stiffness (VS) and Variable Damping (VD) controllers to modulate ankle during walking. The VS controller is active during the stance phase and is used to restore the ankle trajectory of healthy participants that has been altered by adding a dead-weight of 2 Kgs. The VD controller is active during the terminal stance and early-swing phase and provides augmentative force during push-off that results in increased propulsion and stabilizes the ankle based on user-intuitions. Both controllers have a positive impact on Medial Gastrocnemius (GAS) muscle and Soleus (SOL) muscle which are powerful plantar - flexors critical to propulsion and kinematic properties during walking. The VS controller has recorded an 8.18% decrease in GAS and an 9.63 % decrease in SOL muscle activity during the stance phase amongst participants while decreasing mean ankle position error by 22.28 % and peak ankle position error by 17.43%. The VD controller demonstrated a 7.59 % decrease in GAS muscle and a 10.15 % decrease in SOL muscle activity during push-off amongst the participants while increasing the range-of-motion (ROM) by 7.84 %. Comprehensively, the study has shown a positive impact on ankle trajectory and the corresponding muscle effort at respective stages of the controller activity. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2020

Tato diplomová práce se zabývá teoretickými poznatky a návrhem bikónické antény pracující v kmitočtovém rozsahu 4 až 8 GHz. V rámci práce jsou také popsány způsoby impedančního přizpůsobení a vybrané typy polarizátorů elektromagnetických vln a radioprůzračných krytů. Na základě teoretických poznatků je určena koncepce návrhu bikónické antény a vybrán vhodný polarizátor pro zajištění kruhové polarizace vyzařovaných elektromagnetických vln.

The aim of the thesis is to describe EBG substrate and exminate his influence on some types of antennas and choose one of them for realization. In first part this thesis describes the paramaeters of antenna in generall, in the second part is dedicated to introduction with EBG substrate mainly on the surface with the high impedance (HIES). The third part deals with the simulations of microstrip patch antennas with EBG substrate and without EBG substrate. In the last parts was designed and optimized antenna using superstrate.

Title: Assessment of muscle imbalances in handball players Objectives: The main aim of this work was to evaluate the occurrence of muscle imbalances in the handball players of the first - league team of woman by means of the kinesiological analysis and segmental analysis from the BIA method. Methods: In modified kinesiological analysis, we focused on assessing posture and examining shortened muscles. To segmental analysis by the BIA method, we used the Tanita MC - 980 apparatus, where we first assessed the asymmetry in the distribution of muscle mass on individual body segments. Results: In 80 % of the total, the upper cross syndrome was recorded. Lower cross syndrome was found in 67 % of the players. The results of segmental muscle mass analysis using BIA showed a statistically insignificant difference (p > 0.05) in the distribution of muscle mass in the upper limbs (average difference of 0.05 kg) and a statistically significant difference (p < 0.05) in the distribution of muscle mass at the lower of the limbs (average difference of 0.11 kg). The following significant correlations were found for the whole population (n = 15): m. Iliopsoas right and the amount of muscle mass (BIA) on right upper limb (r = 0.549), iliopsoas on the right and the amount of muscle mass (BIA) on left upper limb (r =...

v anglickém jazyce The subject of the presented work is (the usage of) electroacoustic transducers in physics teaching. Its first part contains an overview of study materials, physics textbooks and a selection of academic studies dealing with the aforementioned topic. The central part of the thesis consists of three experimental activities in which electroacoustic transducers are employed. These activities may be adopted for home or laboratory work of students or in hobby groups. The first activity aims at exploring the principle of operation of or- dinary headphones. The second activity contains instructions for making a simple phone. The third, most extensive activity, focuses on the measurement of electrical properties of various electroacoustic transducers. The results are further used for a more detailed discussion of their operating principles. In the final part of the thesis, the usage and verification of one of these proposed activities in practice are discussed.

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Synchronous machines (SMs) are a vital part of today's world, and precise modeling is important for studying their stability. In this thesis, a small-signal analysis is done on the d-q frame for the AC SM. Starting from formulating the SM's abc frame equations, a d-q transformation is done based on the SM rotor frame so that the inductance from the abc frame representation will be fixed. Then, the SM's fundamental parameters are obtained from standstill frequency response testing. In the interest of having the most complete model possible, a governor controller and an exciter controller have been designed, and their performance has been evaluated according to the International Standard ISO-8628. A d-q steady-state analysis has been carried out and the resulting small-signal perturbation has been added to the steady-state equations. The model has been analyzed with exciter control only, with governor control only, and with both controllers, and in the end, the small-signal d-q impedance model for the SM has been verified by simulations and experiments in the Center for Electronics Systems (CPES) at Virginia Tech. The impedance measurement unit (IMU) was built by CPES. It is designed for measuring three-phase AC power systems and DC systems. Nevertheless, even though the single-phase system can be connected to the IMU, the impedance result in the end is not correct. Modifications have been made to the IMU so that it is able to calculate the single-phase AC power system impedance. The experimental results demonstrate that implementation has been completed. / Master of Science / Emergency diesel generators are critical in the event of widespread blackouts. Generators are typically synchronous machines (SMs), and stability studies are crucial from the standpoint of the power system. With knowledge gained through stability analysis, if instability occurs, a solution can be quickly formulated based on phenomena that has been observed during the event. In order to study the system stability, an accurate model is essential. The small-signal d-q impedance model will be derived by the Center for Power Electronics Systems (CPES) at Virginia Tech based on an AC generator that is rated at 28 kW, and the impedance results will be verified by both MATLAB/Simulink simulations and experiments. The impedance measurement unit (IMU) will serve as the equipment to do the measurement. However, the IMU can only correctly calculate impedance for a three-phase power system. For the single-phase AC power system, due to the three-phase phase locker loop (PLL) calculating the wrong angle, the IMU cannot properly determine the impedance. However, modifications have been applied to the IMU so that it can automatically calculate the impedance for a single-phase AC power system.

Yes / Matching the antenna’s impedance to the RF-front-end of a wireless communications system is challenging as the impedance varies with its surround environment. Autonomously matching the antenna to the RF-front-end is therefore essential to optimize power transfer and thereby maintain the antenna’s radiation efficiency. This paper presents a theoretical technique for automatically tuning an LC impedance matching network that compensates antenna mismatch presented to the RF-front-end. The proposed technique converges to a matching point without the need of complex mathematical modelling of the system comprising of non-linear control elements. Digital circuitry is used to implement the required matching circuit. Reliable convergence is achieved within the tuning range of the LC-network using control-loops that can independently control the LC impedance. An algorithm based on the proposed technique was used to verify its effectiveness with various antenna loads. Mismatch error of the technique is less than 0.2%. The technique enables speedy convergence (< 5 µs) and is highly accurate for autonomous adaptive antenna matching networks. / This work is partially supported by RTI2018-095499-B-C31, Funded by Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (MCIU/AEI/FEDER,UE), and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1.

This dissertation deals with impedance measurements of lead-acid accumulator. Main aim was to study recent problems of impedance measurements of lead-acid accumulator and most importantly to extend difference method and also to interpret its results. The original DC difference method was developed earlier at our Power Sources Laboratory of Department of Electrical and Electronic Technology. The DC difference method and also the new AC difference method are both non-destructive, which means that experimental data can be obtained in situ. New method provides more accurate set of information because of its wide frequency range nature. Electrodes of lead-acid accumulator were analysed with special attention to collector / active mass double layer and to active mass itself. Various states and operation regimes were investigated. Obtained data contributed to better understanding of involved degradation mechanisms. Main aim of other experiment was to observe and interpret corrosion rates of electrode collector composed of various lead alloys. Last but not least charge and discharge regimes e.g. 100% deep of discharge regime, partial state of charge (PSoC) regime and pulse charge regime were analysed. BioLogic VSP was the device used for almost all experimental measurements. It takes a lot of effort to optimise VSP operation regime. Best operation regime of VSP for the difference method was suggested too.