Nesta pesquisa de doutorado foi desenvolvida uma metodologia de análise e interpretação de dados GPR (Ground Penetrating Radar) empregando a tomografia de micro-ondas. Esta ferramenta foi empregada com o objetivo de detectar e estimar a geometria de alvos que simulam artefatos comumente encontrados em sítios arqueológicos brasileiros e de um alvo orgânico que simula um corpo humano em decomposição visando estudos forenses sob condições controladas. Os dados de interesse arqueológico foram adquiridos sobre o Sítio Controlado de Geofísica Rasa (SCGR) do IAG/USP. Os dados de interesse forense foram adquiridos sobre um experimento controlado conduzido no campus da USP em Pirassununga (SP), onde um porco de aproximadamente 80 kg foi enterrado e a sua decomposição foi monitorada com o método GPR ao longo de 18 meses. Os cálculos necessários para a execução da inversão dos dados GPR através da tomografia foram implementados em linguagem Matlab, juntamente com ferramentas de remoção de background que se mostraram úteis para auxiliar a interpretação dos resultados. O programa de imageamento tomográfico foi validado a partir de dados sintéticos gerados no software GprMax a partir de modelos que simulam os alvos de interesse arqueológico instalados no SCGR. A geometria dos alvos do SCGR pôde ser bem estimada, exceto pelo alvo representado pelo muro de tijolos. Feições no solo associadas às escavações para instalação dos alvos puderam ser observadas com clareza nas imagens tomográficas. A geometria do porco, bem como o processo de decomposição foram mapeados através da tomografia mesmo em condições de baixo contraste entre as suas propriedades elétricas e as do solo. Em ambos os casos estudados as imagens tomográficas de dados GPR de 270 MHz, 400 MHz e 900 MHz permitiram extrair mais informações acerca dos alvos do que pelo uso do processamento convencional. Os resultados mostram que a tomografia de micro-ondas possui um grande potencial para aplicação em sítios arqueológicos brasileiros, bem como para aplicações forenses. / In this research a methodology for analysis and interpretation of GPR (Ground Penetrating Radar) data using microwave tomography was developed. This tool was used for detection and geometry evaluation of targets which simulate artifacts usually found at Brazilian archaeological sites and also of one organic target which simulates a decomposing human body for forensic studies under controlled conditions. The data of archaeological interest were acquired on the Geophysical Test Site (SCGR) at IAG/USP. The data of forensic interest were acquired on an experiment developed at the USP campus in Pirassununga (SP) city. In this experiment a pig with about 80 kg was buried and its decomposition was monitored through GPR profiles during 18 months. The calculations required for the GPR data inversion through microwave tomography were implemented in Matlab language, with background removal tools which were helpful for the interpretation of resulting images. The tomographic imaging program was validated using synthetic data generated by the software GprMax. The models simulate targets of archaeological interest buried at the SCGR. The geometry was well estimated for all the targets, except for the brick wall. Ground features associated to excavations done for the installation of the targets were clearly observed in the tomographic images. The pig geometry and its decomposition process were mapped through microwave tomography even under conditions of low contrast between its electric properties and those from the soil. In both studied cases the tomographic images from GPR data of 270 MHz, 400 MHz and 900 MHz allowed to extract more information about the targets than just using the conventional processing. The results show that microwave tomography has a great potential to be applied at Brazilian archaeological sites, as well as for forensic applications.

Nesta pesquisa de doutorado foi desenvolvida uma metodologia de análise e interpretação de dados GPR (Ground Penetrating Radar) empregando a tomografia de micro-ondas. Esta ferramenta foi empregada com o objetivo de detectar e estimar a geometria de alvos que simulam artefatos comumente encontrados em sítios arqueológicos brasileiros e de um alvo orgânico que simula um corpo humano em decomposição visando estudos forenses sob condições controladas. Os dados de interesse arqueológico foram adquiridos sobre o Sítio Controlado de Geofísica Rasa (SCGR) do IAG/USP. Os dados de interesse forense foram adquiridos sobre um experimento controlado conduzido no campus da USP em Pirassununga (SP), onde um porco de aproximadamente 80 kg foi enterrado e a sua decomposição foi monitorada com o método GPR ao longo de 18 meses. Os cálculos necessários para a execução da inversão dos dados GPR através da tomografia foram implementados em linguagem Matlab, juntamente com ferramentas de remoção de background que se mostraram úteis para auxiliar a interpretação dos resultados. O programa de imageamento tomográfico foi validado a partir de dados sintéticos gerados no software GprMax a partir de modelos que simulam os alvos de interesse arqueológico instalados no SCGR. A geometria dos alvos do SCGR pôde ser bem estimada, exceto pelo alvo representado pelo muro de tijolos. Feições no solo associadas às escavações para instalação dos alvos puderam ser observadas com clareza nas imagens tomográficas. A geometria do porco, bem como o processo de decomposição foram mapeados através da tomografia mesmo em condições de baixo contraste entre as suas propriedades elétricas e as do solo. Em ambos os casos estudados as imagens tomográficas de dados GPR de 270 MHz, 400 MHz e 900 MHz permitiram extrair mais informações acerca dos alvos do que pelo uso do processamento convencional. Os resultados mostram que a tomografia de micro-ondas possui um grande potencial para aplicação em sítios arqueológicos brasileiros, bem como para aplicações forenses. / In this research a methodology for analysis and interpretation of GPR (Ground Penetrating Radar) data using microwave tomography was developed. This tool was used for detection and geometry evaluation of targets which simulate artifacts usually found at Brazilian archaeological sites and also of one organic target which simulates a decomposing human body for forensic studies under controlled conditions. The data of archaeological interest were acquired on the Geophysical Test Site (SCGR) at IAG/USP. The data of forensic interest were acquired on an experiment developed at the USP campus in Pirassununga (SP) city. In this experiment a pig with about 80 kg was buried and its decomposition was monitored through GPR profiles during 18 months. The calculations required for the GPR data inversion through microwave tomography were implemented in Matlab language, with background removal tools which were helpful for the interpretation of resulting images. The tomographic imaging program was validated using synthetic data generated by the software GprMax. The models simulate targets of archaeological interest buried at the SCGR. The geometry was well estimated for all the targets, except for the brick wall. Ground features associated to excavations done for the installation of the targets were clearly observed in the tomographic images. The pig geometry and its decomposition process were mapped through microwave tomography even under conditions of low contrast between its electric properties and those from the soil. In both studied cases the tomographic images from GPR data of 270 MHz, 400 MHz and 900 MHz allowed to extract more information about the targets than just using the conventional processing. The results show that microwave tomography has a great potential to be applied at Brazilian archaeological sites, as well as for forensic applications.

The objective of the proposed research is to develop structural changes to the design and application of electromagnetic (EM) sensing models to more efficiently and accurately invert EM measurements to extract parameters for applications such as landmine detection. Two different acquisition modalities are addressed in this research: ground-penetrating radar (GPR) and electromagnetic induction (EMI) sensors. The models needed for practical three-dimensional (3D) spatial imaging typically become impractically large, with up to seven dimensions of parameters that need to be extracted. These parameters include, but are not limited to target type, 3D location, and 3D orientation. The new special structures for these models exploit properties such as shift invariance and tensor representation, which can be combined with strategic inversion techniques, including the Fast Fourier Transform and semidefinite programming. The structures dramatically reduce the amount of computation and can eliminate the need to store up to five dimensions of parameters while still accurately estimating them.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Synthetic-aperture microwave imaging with ground penetrating radar systems has become a research topic of great importance for the potential applications in sensing and profiling of civil and geophysical structures. It allows us to visualize subsurface structures for nondestructive evaluation with microwave tomographic images. This paper provides an overview of the research program, ranging from the formation of the concepts, physical and mathematical modeling, formulation and development of the image reconstruction algorithms, laboratory experiments, and full-scale field tests.

The advancement of technologies that interface with electrically excitable tissues, such as the cortex and muscle, has the potential to lend greater mobility to the disabled, and facilitate the study of the central and peripheral nervous systems. Myoelectric interfaces are currently limited in their signal fidelity, spatial resolution, and interfacial area. Such interfaces are either implanted in muscle or applied to the surface of the muscle or skin. Thus far, the former technology has been limited in its applications due to the stiffness (several orders of magnitude greater than muscle) of its substrates, such as silicon and polyimide, whereas the latter technology suffers from poor spatial resolution and signal quality due to the physical separation between the electrodes and the signal source. We have developed a stretchable microneedle electrode array (sMEA) that can function while stretching and flexing with muscle tissue, thereby enabling multi-site muscle stimulation and electromyography (EMG) measurement across a large interfacial area. The scope of this research encompassed: (i) the development of a stretchable and flexible array of penetrating electrodes for the purposes of stimulating and measuring the electrical activity of excitable tissue, (ii) the characterization of the electrical, mechanical, and biocompatibility properties of this electrode array, (iii) the measurement of regional electrical activity of muscle via the electrode array, (iv) the study of the effect of spatially distributed stimulation of muscle on the fatigue and ripple of muscle contractions, and (v) the assessment of the extent to which the stretch response of electrically stimulated muscle behaves in a physiological manner.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2003. / The imaging of platiniferous reefs in the Bushveld Igneous Complex (BIC) is of great economical and sociological importance. Borehole radar technology has been identified as a viable mapping tool to be used in day-to-day mining operations, but a critical assessment has to be made on the feasibility of this postulation. The system analysis made of the borehole radar deployed in the BIC is presented in this dissertation. The analysis is done using a specific example - the GeoMole borehole radar system. A novel procedure, based on the basic theory of electromagnetic radiation and propagation, is proposed by which the entire physical radar system can be characterized. The power transmitted by an unconventional borehole-deployed transmitter is estimated by a sequence of free space measurements, numerical simulations and theoretic derivations and approximations. Antenna transfer functions (magnitude and phase) are numerically simulated for a variety of deployment configurations. The total system transfer function of the receiver analogue and digital chain is determined. This enables the calculation of the radar's performance figures necessary to determine the applicability of the radar in a specific geological setting. A radar system is only complete when considered in its environment. The BIC is a stratified system of numerous rock layers. An in-depth study is done on the propagation of radiowaves in stratified lossy media. Only the case for non-magnetic media is discussed in this dissertation. The developed theory is used to predict the system response to a typical transmitted radar pulse in the UG1 - UG2 stratigraphy of the BIC, determine the maximum detection range of reef horizons and estimate the reflectivity of the reefs. Resolution is one of the key parameters that determine the performance and accuracy of imaging. An algorithm is proposed, developed and tested by which the resolution of the system is increased and overlapping echoes become resolvable. Even though some of the techniques are developed with a specific system in mind, the applicability of the concepts and algorithms is universal.

Thesis (PhD (Surgical Sciences. Ophthalmology))--Stellenbosch University, 2008. / Purpose: To evaluate the outcome of primary adult optical penetrating keratoplasty (PKP) at a public health service hospital of a developing country. Patients and Methods: A retrospective review was performed of the medical records of every patient 12 years of age or older who underwent PKP for keratoconus, corneal edema, stromal scarring, or stromal dystrophy at King Khaled Eye Specialist Hospital in the Kingdom of Saudi Arabia between January 1, 1997, and December 31, 2001, and for whom a minimum of 3 months’ follow-up was available. Results: Of 910 eyes that met the inclusion criteria, there were 464 eyes with keratoconus, 188 eyes with corneal edema, 175 eyes with stromal scarring, and 83 eyes with stromal dystrophy. For the entire group, the probability of graft survival was 96.7% at 1 year, 86.2% at 3 years, and 80.9% at 5 years. Five-year survival probability was best with keratoconus (96.1%), followed by stromal dystrophy (85.9%), stromal scarring (71.1%), and corneal edema (40.3%). The probability of graft survival differed significantly among the surgical indications at all postoperative intervals (P<0.001). Factors associated with a significantly increased risk of graft failure on multivariate Cox proportional hazard regression analysis included increasing donor tissue age (P = 0.005) and decreasing recipient graft size (P = 0.02). Final visual acuity of 20/40 or better was obtained in 409 (44.9%) eyes. Visual acuity of 20/40 or better was obtained in 336 (72.4%) eyes with keratoconus and in 53 (63.9%) eyes with stromal dystrophy but in only 11 (6.3%) eyes with stromal scarring and 9 (4.8%) eyes with corneal edema (P<0.001). Overall, improvement in vision occurred in 750 (82.4%) eyes, remained the same in 97 (10.7%) eyes, and worsened in 63 (6.9%) eyes. Conclusions: The present study has conclusively demonstrated that primary adult optical PKP can be performed at a public health facility in the Kingdom of Saudi Arabia with graft survival and visual results that are comparable to those obtained in welldeveloped Western facilities. This success is attributed to the presence of a suitable infrastructure that provides modern eye care facilities, donor tissue, and pharmaceuticals to patients who have access to preoperative screening and evaluation, surgical intervention, and postoperative care by well-trained ophthalmologists and ancillary support personnel.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2004. / The use of ground penetrating radar, and especially borehole radar in underground mines, is becoming increasingly attractive. This is due to the improvements in the user friendliness of this system. Borehole radar is able to sense accurately geological faults and structures hidden inside the rock body and this information is of value to geologists. In the quest to increase the accuracy of the radar, it was realized that the borehole trajectory and surrounding rock properties are needed. This thesis discusses a rock permittivity and loss sensor which is designed to be deployed in cylindrical hard rock boreholes with diameter of about 50 mm. The sensor consists of electrodes to produce capacitance that is dependant on the rock properties, and electronics to measure this dependency. The biggest problem foreseen is that the probe will not be in direct contact with the rock body. Cylindrical Electrodes were designed using numerical simulations and physical models. Sensitivity and noise attributes received attention. Electronic components were used to sense the small capacitance produced by the electrodes. The resulting signals are slow changing "DC• voltages from which an indication of the needed properties could be extracted. The system was integrated and tested in both laboratory and mine conditions. Test-result-b,ased improvements were introduced and led to satisfactory working of the probe. However, the deployment method will need attention before this probe can be used in field conditions.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2003. / Ground penetrating radar is currently proving itself as an invaluable tool for the prediction of geological structures in the mining environment. Borehole radar is a specific application of this technology, useful in the prediction of the course of rock layers between boreholes ahead of mining. Establishing borehole radar as an industrial tool requires a system that is more userfriendly and easier to deploy than the bi-static radar systems currently available. The development of a monostatic radar system is discussed. It is an ultra wide band, pulse radar system that operates at VHF (10-100 MHz). The system is required to detect reflections from objects 5 m away and further. This translates to a total electromagnetic propagation time of approximately 100 ns or more in the rock medium. The complete design process - from fundamental requirements, through a conceptual design, to a final electronic circuit - is discussed. The design is also built, measured in the laboratory and taken for initial field trails. The following aspects are considered: • Pulse generation by means of an original circuit based on power MOSFETs. • Routing of the transmitted- and received signal between transmitter, receiver and antenna. This is done using a novel, active quasi circulator topology. • Methods of increasing isolation (actively and passively) between transmitter and receiver. • Interfacing with a specific receiver, antenna and data acquisition system.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2001. / Over the last decade, as the mining industry of South Africa is moving to ever deeper mines, the borehole radar is becoming an increasingly important field of research. In December 2000, Burger completed his thesis on Electromagnetic Modelling of a Borehole Radar Environment with the FDTD Method. The goal of this thesis is to extend the research presented in Burger's thesis, considering how more advanced modelling techniques can be applied to the FDTD analysis of the borehole radar environment. Some of these techniques include implementation of dispersive and conductive material models, and developing Uniaxial Perfectly Matched Layer boundary conditions for matching these model. Simulations were run to measure the performance of these boundary condition for matching dispersive and conductive materials. The thesis also includes the implementation of a parallel version of the FDTD algorithm using the Message Passing Interface library. Finally several realistic borehole models where simulated to test the accuracy of the code and to show how the code can be used to model real world problems.