MST-Department of Physics

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Browsing MST-Department of Physics by Author "Ambusso, Willis Jakanyango"

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    Design and Fabrication of Aperture Coupled Microstrip Patch Antennas with Arbitrarily Shaped Apertures
    (2014-02-19) Kitur, Stanley Kibet; Ambusso, Willis Jakanyango; Konditi, D. B. O.
    A linearly-polarized aperture coupled microstrip antenna design is characterized and optimized using FEKO antenna simulation software. One of the major drawbacks of these microstrip antennas is their narrow bandwidth. Aperture coupled being one of the feeding technique has proven to be a solution to this problem. In this research a patch antenna that is coupled to a microstrip-line by an aperture in the intervening ground plane has been designed and fabricated and implemented. The shape and the size of the aperture and the location of the patch relative to the aperture are the crucial parameters for the aperture coupled microstrip antennas. Arbitrarily shaped coupling apertures have been considered by investigating their contributing effect on the radiation characteristics of the antenna. The goal of this thesis is to explore the shape and the size and location of the patch relative to the aperture. These have been considered by investigating their performance effects through electromagnetic principles. The aim of this study was to investigate an aperture shape that provides better coupling of the radiated power from the feed line to the patch element while at the same time giving lower back- lobe radiation level from the aperture. The aperture shapes investigated were rectangular shaped, H-shaped and Diamond shaped. It was found that H-shaped aperture coupled antenna provides higher coupling and reduced backward radiation levels as compared to the other aperture shapes. It was also found that the signal coupling level is greatest when the patch is centered over the aperture. The numerical analysis was carried out using the Electrical Field Integral Equation technique with moment method using software called FEKO. This software uses the triangular patch modeling as the basis function. The antenna characteristics such as the VSWR, S-parameters, radiation pattern, and input impedance were simulated for the various shapes of coupling apertures. The antennas prototypes using each of these aperture shapes were fabricated using FR4 PC boards joined together. Ideally the antenna was to be characterized in an echoic chamber and the result compared with the simulated data. However due to lack of an echoic chamber, the data obtained in an open space was compared with the simulated ones for similarity of patterns. The obtained results were found to be in good correlation.
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    Geophysical Investigation of Mbeu Iron Ore Deposit in Meru County using Gravity Method
    (2014-03-06) Abuga, Vincent Onyancha; Migwi, C. M.; Ambusso, Willis Jakanyango
    Gravity survey was used to detect metallic bearing rocks and dense bodies of rocks within host formations in Mbeu area of Tigania. From the study, there is a clear indication of the presence of iron ore in the region. The ground based gravimeter was used to precisely measure variation in the gravity fields at different points. A total of 86 gravity stations were surveyed. The data obtained was corrected for drift, latitude, Free Air and Bouguer corrections from where the Free Air Anomaly and Bouguer Anomaly were computed. The contour map was drawn to represent this information and the profiles were created. Four profiles were chosen which were oriented in the directions NE-SW, NW-SE, nearly E-W and N-S for the purpose of fitting model to the observed data. Spherical model was employed to estimate the sought parameters of the anomaly. These include: depth from the surface to the centre, Z, radius, R, depth to surface T and the mass of the body, M. The depth from the surface was found to range from 0-140 m and mass ranging from 8.6x 109to 3.2x 10"kg.
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    Groundwater investigation and characterisation in Marigat area, Baringo county, using vertical electrical sounding resistivity surveys
    (2014-07-31) Cherop, Komen Hezekiah; Ambusso, Willis Jakanyango; Githiri, John Gitonga
    Resistivity surveys will be carried out to investigate groundwater potentials and to characterise water bearing layer in Marigat area, Baringo County. This study aims at obtaining useful information on the rock type and fault lines that are conduits to groundwater within the area based on the response of the earth to the flow of regulated input current source. The information obtained will constitutes a knowledge base which is fundamental to water resource assessment and decision making in the study area. In this study, Vertical electrical sounding (VES) method will be applied using Schlumberger electrode configuration. About 60 VES points will be probed along ten traverses within an area of 10 km2 using an ABEM SAS 300 C terameter and the field stations will be positioned using Global positioning system (GPS) device. The field data will be analysed using Winsev software and the information obtained interpreted in order to define the aquifer distribution and to delineate the lithological changes of different layers. The interpreted results of YES will furnish information of resistivities and thickness of different layers at the sounding point. This study will help in selecting a possible site that boreholes can be drilled for potable and sustainable water supply and reduce the risks of drilling dry boreholes.
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    A numerical simulator to estimate hydrological parameters of a fractured porous medium using fluorescein thermal decay correction
    (2012-04-17) Ng'ang'a, Benson Wang'ombe; Ambusso, Willis Jakanyango; Omenda, Peter
    A method that can be used to estimate hydrological parameters of a fracture using fluorescein thermal decay correction is presented. These parameters are porosity, permeability, fracture size, entire reservoir pore volume and reservoir recharge rate. A tracer was pumped into an injection well and its arrival characteristics with respect to time in the production wells monitored. The data was used to generate breakthrough curves which gives tracer effluent history. These curves yielded important information about the reservoir. Resulting fluorescein decays were accounted for by application of numerical modelling and properties of the geothermal system were estimated. The estimates were used to simulate a fracture connecting two wells. A mathematical model describing the flow of the tracer was solved to generate its flow profile in a fracture. This was done by developing a computer package in Microsoft Visual C++. The profile was matched with the field data by trying out different values of the fracture parameters. The values that almost matched the profile on the field data curve were the required parameters. Porosity was observed to vary between 13 % to 15 %, permeability was found to be 1.8 mm" and permeability thickness of 950 m2. The fracture thickness was estimated to vary between 3 m and 10 meters. Rate of aquifer flow was 1.956 x 10-9 kglm3/sec while entire reservoir pore volume was obtained to be 653520 lit res/sec
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    Radionuclide content of sand used for construction in Kakamega county and associated indoor radon diffusion doses
    (2014-04-25) Shikali, N. Collins; Ambusso, Willis Jakanyango; Munji, M. K.
    The greatest portion of radiation received by world‟s population comes from natural radioactive sources. Everyone on earth receives natural radiation; some get much more than others depending on where they live. Primordial radionuclide in building sand and gravels from quarries are some of the sources of radiation hazards common in dwellings and working places. In this study, activity concentrations of naturally occurring radionuclide in mineral sand used for construction collected in old gold mining belt of Kakamega County were measured using gamma ray spectrometry technique, [NaI(Tl)]. The results of the concentrations of naturally occurring radionuclide were as follows: 226Ra ranged from 36.79±8.89 to185.21±5.89 Bqkg-1, 232Th ranged from 51.12±2.56 to 158.92±7.95 Bqkg-1 and 40K ranged from 322.38±16.12 to 960.53±48.03 Bqkg-1. The calculated radium equivalent activity (Raeq), the absorbed dose rate (D), and the external hazard index (Hex) were within the international recommended values. Hence construction sands from the study region do not pose any risk to the inhabitants in terms of the acceptable limits. The movement of radon by diffusion from the walls of classrooms constructed from such sand into indoor air was modeled based on radiological parameters. The posed model predicted an ambient indoor radon concentration of 9 Bqm-3, 15.6 Bqm-3 and 28.7 Bqm-3 in three monitoring stations (classrooms) in the region. The modeled radon concentrations were lower than measured; the model reproduced the general trends associated with diffused indoor radon fluxes. Thus it can be helpful in estimating radon concentrations for other similar processes such as estimating radon concentration in caves and mines.
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    Studies of Effects of Petroleum Products Spillage on Water and Soil at Mwavumbo in Kilifi County, Kenya.
    (2014-03-06) Ketko, Augustine; Migwi, C. M.; Ambusso, Willis Jakanyango
    Oil spills on land and sea are environmental disasters that can cause both short and long-term pollution. These effects are very deleterious though several oil remediations have been developed, but still a wide spectrum of biotic community suffers the impact. This study sought to determine the effects of petrol, diesel and kerosene blend on both water and land. Blend of petrol, diesel and kerosene were poured into fixed volume of water and soil by consistently varying their quantities of volume. The pH of sampled soil and water with petrol, diesel and kerosene blend spillage were determined periodically over three months at interval of one month. Thermal pollution on land and water were determined by carrying out a set of experiments involving measurements of temperature. Absorbance and transmittance of the petroleum products blend was determined using spectrophotometer. The model of analysis of absorbance and transmittance of electromagnetic radiation was Beer's Lambert law. Porosities of pure soil samples together with soil blended with petrol, diesel and kerosene were determined using porosity model method. Permeability of pure soil samples together with soil blended with petrol, diesel and kerosene were determined using Darcy's method and analyzed using Darcy's law. From the analysis, petroleum products blend spillage on water and soil was found to raise temperature and pH of soil and water and also absorbance and transmittance of water. It was also established that petroleum products blend spillage on soil lowers porosity and soil aeration but increases permeability of soil. Use of solutions of surfactant to remediate soil with petroleum products spillage was effective in lowering permeability of soil