Internet of Things (IoT) is a new emerging paradigm which requires billions of wirelessly connected devices that communicate with each other in a complex radio-frequency (RF) environment. Considering the huge number of devices, recharging batteries or replacing them becomes impractical in real life. Therefore, harvesting ambient RF energy for powering IoT devices can be a practical solution to achieve self-charging operation. The antenna for the RF energy harvesting application must work on multiple frequency bands (multiband or wideband) to capture as much power as possible from ambient; it should be compact and small in size so that it can be integrated with IoT devices; and it should be low cost, considering the huge number of devices. This thesis presents a fully printed 3D cube Cantor fractal RF energy harvesting unit, which meets the above-mentioned criteria. The multiband Cantor fractal antenna has been designed and implemented on a package of rectifying circuits using additive manufacturing (combination of 3D inkjet printing of plastic substrate and 2D metallic screen printing of silver paste) for the first time for RF energy harvesting application. The antenna, which is in a Cantor fractal shape, is folded on five faces of a 3D cube where the bottom face accommodates rectifying circuit with matching network. The rectenna (rectifying antenna) harvests RF power from GSM900, GSM1800, and 3G at 2100 MHz frequency. Indoor and outdoor field tests of the RF energy harvester have been conducted in the IMPACT lab and the King Abdullah University of Science and Technology (KAUST) campus territory, and 252.4 mV of maximum output voltage is harvested.

Em trabalhos anteriores realizados em síntese e caracterização cristalográfica, a existência de uma nova fase de estequiometria Ta1-xHfxB (com x variando no intervalo entre 0,05 e 0,4) que cristaliza no protótipo FeB foi descoberta. Este ternário cristaliza num protótipo diferente do protótipo CrB aceito no binário TaB. Na verdade, essa substituição é capaz de gerar uma mudança significativa na estrutura cristalina de TaB, a qual sofre uma distorção e modifica o protótipo CrB para FeB. Além desta mudança estrutural os compostos de composição global Ta1-xHfxB apresentam supercondutividade com temperatura crítica supercondutora acima do binário TaB (Tc ~ 4,0 K). Foi observado que a supercondutividade otimizada na composição Ta0,7Hf0,3B com Tc ~ 6,7 K na qual medidas de calor específico revelam forte assinatura de manifestação multibanda neste novo composto. Motivados por esta descoberta, neste trabalho são investigadas a possiblidade desta transformação estrutural bem como o seu impacto nas propriedades supercondutoras em ligas de composição global Ta1-xZrxB, devido à similaridade eletrônica entre Zr e Hf na tabela periódica. De fato, resultados publicados a respeito da transformação cristalográfica com a substituição de Ta por Zr revelam o mesmo comportamento observado nas ligas produzidas com Hf e este trabalho revela que os compostos Ta1-xZrxB também são supercondutores. A composição com a maior temperatura crítica é Ta0,8Zr0,2Be tem uma temperatura de transição aproximadamente 7,8 K. Entretanto, esse composto tem evidencia de um supercondutor não convencional. Assim, este trabalho revela a existência de supercondutividade não convencional em ligas do sistema ternário Ta-Zr-B revelados por medidas de resistividade, magnetização e caracterização estrutural e microestrutural. / In previous works carried out in synthesis and crystallographic characterization, the existence of a new Ta1-xHfxB stoichiometry phase (with x varying in the interval between 0.05 and 0.4) that crystallizes in the FeB prototype was discovered. This ternary crystallizes in a prototype different from the prototype CrB accepted in the TaB binary. In fact, this substitution is capable of generating a significant change in the crystalline structure of TaB, which undergoes distortion and modifies the CrB prototype for FeB. In addition to this structural change, the compounds of global composition Ta1-xHfxB present superconductivity with critical superconducting temperature above the TaB Tc ~ 4.0 K. It was observed that the superconductivity optimizes at Ta0,7Hf0,3B composition with Tc ~ 6.7 K in which specific heat measurements reveal a strong multiband manifestation signature in this new compound. Based on this finding, this work investigates the possibility of this structural transformation as well as its impact on the superconducting properties of alloys of global composition Ta1-xZrxB, due to the electronic similarity between Zr and Hf in the periodic table. In fact, published results on crystallographic transformation with the substitution of Ta by Zr reveal the same behavior observed in the alloys produced with Hf and this work reveals that the Ta1-xZrxB compounds are also superconducting. The composition with the highest critical temperature is Ta0,8Zr0,2Band has a transition temperature of about 7.8K. However, this compound has evidence of an unconventional superconductor. Thus, this work reveals the existence of unconventional superconductivity in alloys of the Ta-Zr-B ternary system revealed by resistivity, magnetization and structural and microstructural characterization measurements.

O grupo de diboretos isoestruturais ao MgB2 com estrutura representada pelo protótipo AlB2 é considerado candidato à supercondutividade. Contudo, a existência do estado supercondutor é um fenômeno raro nesse grupo de materiais, de fato a grande maioria dos diboretos de metais de transição é caracterizada por um Tc menor que 0,7 K. Nesse grupo, os compostos normais HfB2, VB2, YB2 e ZrB2 exibem assinatura do comportamento paramagnético de Pauli em baixas temperaturas. Nesse trabalho é mostrado que a substituição parcial do metal (Hf e Zr) por V nas amostras M1-xVxB2, gera distorções da rede cristalina, com o surgimento de um estado supercondutor volumétrico. As medidas magnéticas, elétricas e térmicas revelam um Tc máximo atingindo 8,7 e 9,3 K para as respectivas amostras de composição Zr0,96V0,04B2 e Hf0,97V0,03B2, com valores elevados de ? 0Hc2(0) (~16 e ~21 T, respectivamente). Nessas amostras, os resultados a cerca do comportamento do ? 0Hc1 (T), do Cp(T) e da VHall (T), e medidas de ETS (electronic tunneling spectroscopy) em um monocristal, revelam a claras assinaturas da supercondutividade multibanda, tal como é reportado para o MgB2. Ainda, resultados mostram a que a existência do estado supercondutor no ZrB2 parece não ser uma exclusividade da substituição por V, já que é observada também na amostra de Zr0,96Y0,04B2, cujo Tc atinge 6,7 K novamente com assinatura de comportamento multibanda. Também são mostrados os resultados da existência dos comportamentos magnéticos competitivos nas amostras do sistema Zr1-xAlxB2, com um surpreendente ordenamento ferromagnético. Nesse mesmo cenário, também é mostrado que substituição de Nb por Ni é hábil em elevar a temperatura crítica do composto NbB2-? de 3,6 K para 6,0 K. Já em outros boretos, como nos sistemas Th1-xMxB12 (M = Zr, Sc, Y, Ti Hf) em condições especiais de síntese e substituição a fase ThB12 (inexistente no equilíbrio) pode ser estabilizada, onde se observa para amostra Th0,97Zr0,03B12 um Tc próximo a 5,5 K e comportamento supercondutor BCS, porém com um baixo valor do parâmetro k o que abre discussão para uma classe nova de supercondutores do tipo 1,5. / The diborides group isostructural to MgB2 represented by AlB2 prototype structure are considered important candidates for superconductivity. However, the existence of the superconducting state is a rare phenomenon in this group of materials, indeed the majority of transition metal diborides are characterized by a Tc lower than 0.7 K. In this group, the normal compounds HfB2, VB2, YB2, and ZrB2 exhibit signature Pauli paramagnetic behavior at low temperatures. In this work it is shown that the metal partial substitution (Hf and Zr) by V in M1-xVxB2 samples generates distortions of the crystal lattice, with the emergence of a bulk superconducting state. The magnetic, electric and thermal measurements reveal a maximum Tc reaching 8.7 and 9.3 K for the respective samples Zr0.96V0.04B2 and Hf0.97V0.03B2 composition with high values of ? 0Hc2(0) (~ 16 and ~ 21 T, respectively). In these samples, the results about the behavior ? 0Hc1 (T), Cp(T), and VHall (T); and ETS (electronic tunneling spectroscopy) measurements in a single crystal; reveal a clear signatures of multiband superconductivity such as reported to the MgB2. Furthermore, the results show that the existence of the superconducting state ZrB2 appears to be not exclusive by V substitution, it is also observed in the sample Zr0.96Y0.04B2 whose Tc reaches 6.7 K again with signature multiband behavior. Also shown are the results of the existence of competitive magnetic behavior in samples of Zr1-xAlxB2 system, with a surprising ferromagnetic ordering. In this same scenario, it is also shown that substitution of Nb by Ni is able to raise the critical temperature of the NbB2-? compound from 3.6 K to 6.0 K. Since other borides as in Th1- xMxB12 (M = Zr, Sc, Y, Ti Hf) systems, in special conditions of synthesis and substitution the ThB12 phase (non-existent in the equilibrium conditions) can be stabilized, which is observed to Th0.97Zr0.03B12 sample with Tc close to 5.5 K and BCS superconducting behavior, but with a low of the k parameter value opening discussion for a new class of 1.5 type superconductors.

Em trabalhos anteriores realizados em síntese e caracterização cristalográfica, a existência de uma nova fase de estequiometria Ta1-xHfxB (com x variando no intervalo entre 0,05 e 0,4) que cristaliza no protótipo FeB foi descoberta. Este ternário cristaliza num protótipo diferente do protótipo CrB aceito no binário TaB. Na verdade, essa substituição é capaz de gerar uma mudança significativa na estrutura cristalina de TaB, a qual sofre uma distorção e modifica o protótipo CrB para FeB. Além desta mudança estrutural os compostos de composição global Ta1-xHfxB apresentam supercondutividade com temperatura crítica supercondutora acima do binário TaB (Tc ~ 4,0 K). Foi observado que a supercondutividade otimizada na composição Ta0,7Hf0,3B com Tc ~ 6,7 K na qual medidas de calor específico revelam forte assinatura de manifestação multibanda neste novo composto. Motivados por esta descoberta, neste trabalho são investigadas a possiblidade desta transformação estrutural bem como o seu impacto nas propriedades supercondutoras em ligas de composição global Ta1-xZrxB, devido à similaridade eletrônica entre Zr e Hf na tabela periódica. De fato, resultados publicados a respeito da transformação cristalográfica com a substituição de Ta por Zr revelam o mesmo comportamento observado nas ligas produzidas com Hf e este trabalho revela que os compostos Ta1-xZrxB também são supercondutores. A composição com a maior temperatura crítica é Ta0,8Zr0,2Be tem uma temperatura de transição aproximadamente 7,8 K. Entretanto, esse composto tem evidencia de um supercondutor não convencional. Assim, este trabalho revela a existência de supercondutividade não convencional em ligas do sistema ternário Ta-Zr-B revelados por medidas de resistividade, magnetização e caracterização estrutural e microestrutural. / In previous works carried out in synthesis and crystallographic characterization, the existence of a new Ta1-xHfxB stoichiometry phase (with x varying in the interval between 0.05 and 0.4) that crystallizes in the FeB prototype was discovered. This ternary crystallizes in a prototype different from the prototype CrB accepted in the TaB binary. In fact, this substitution is capable of generating a significant change in the crystalline structure of TaB, which undergoes distortion and modifies the CrB prototype for FeB. In addition to this structural change, the compounds of global composition Ta1-xHfxB present superconductivity with critical superconducting temperature above the TaB Tc ~ 4.0 K. It was observed that the superconductivity optimizes at Ta0,7Hf0,3B composition with Tc ~ 6.7 K in which specific heat measurements reveal a strong multiband manifestation signature in this new compound. Based on this finding, this work investigates the possibility of this structural transformation as well as its impact on the superconducting properties of alloys of global composition Ta1-xZrxB, due to the electronic similarity between Zr and Hf in the periodic table. In fact, published results on crystallographic transformation with the substitution of Ta by Zr reveal the same behavior observed in the alloys produced with Hf and this work reveals that the Ta1-xZrxB compounds are also superconducting. The composition with the highest critical temperature is Ta0,8Zr0,2Band has a transition temperature of about 7.8K. However, this compound has evidence of an unconventional superconductor. Thus, this work reveals the existence of unconventional superconductivity in alloys of the Ta-Zr-B ternary system revealed by resistivity, magnetization and structural and microstructural characterization measurements.

O grupo de diboretos isoestruturais ao MgB2 com estrutura representada pelo protótipo AlB2 é considerado candidato à supercondutividade. Contudo, a existência do estado supercondutor é um fenômeno raro nesse grupo de materiais, de fato a grande maioria dos diboretos de metais de transição é caracterizada por um Tc menor que 0,7 K. Nesse grupo, os compostos normais HfB2, VB2, YB2 e ZrB2 exibem assinatura do comportamento paramagnético de Pauli em baixas temperaturas. Nesse trabalho é mostrado que a substituição parcial do metal (Hf e Zr) por V nas amostras M1-xVxB2, gera distorções da rede cristalina, com o surgimento de um estado supercondutor volumétrico. As medidas magnéticas, elétricas e térmicas revelam um Tc máximo atingindo 8,7 e 9,3 K para as respectivas amostras de composição Zr0,96V0,04B2 e Hf0,97V0,03B2, com valores elevados de ? 0Hc2(0) (~16 e ~21 T, respectivamente). Nessas amostras, os resultados a cerca do comportamento do ? 0Hc1 (T), do Cp(T) e da VHall (T), e medidas de ETS (electronic tunneling spectroscopy) em um monocristal, revelam a claras assinaturas da supercondutividade multibanda, tal como é reportado para o MgB2. Ainda, resultados mostram a que a existência do estado supercondutor no ZrB2 parece não ser uma exclusividade da substituição por V, já que é observada também na amostra de Zr0,96Y0,04B2, cujo Tc atinge 6,7 K novamente com assinatura de comportamento multibanda. Também são mostrados os resultados da existência dos comportamentos magnéticos competitivos nas amostras do sistema Zr1-xAlxB2, com um surpreendente ordenamento ferromagnético. Nesse mesmo cenário, também é mostrado que substituição de Nb por Ni é hábil em elevar a temperatura crítica do composto NbB2-? de 3,6 K para 6,0 K. Já em outros boretos, como nos sistemas Th1-xMxB12 (M = Zr, Sc, Y, Ti Hf) em condições especiais de síntese e substituição a fase ThB12 (inexistente no equilíbrio) pode ser estabilizada, onde se observa para amostra Th0,97Zr0,03B12 um Tc próximo a 5,5 K e comportamento supercondutor BCS, porém com um baixo valor do parâmetro k o que abre discussão para uma classe nova de supercondutores do tipo 1,5. / The diborides group isostructural to MgB2 represented by AlB2 prototype structure are considered important candidates for superconductivity. However, the existence of the superconducting state is a rare phenomenon in this group of materials, indeed the majority of transition metal diborides are characterized by a Tc lower than 0.7 K. In this group, the normal compounds HfB2, VB2, YB2, and ZrB2 exhibit signature Pauli paramagnetic behavior at low temperatures. In this work it is shown that the metal partial substitution (Hf and Zr) by V in M1-xVxB2 samples generates distortions of the crystal lattice, with the emergence of a bulk superconducting state. The magnetic, electric and thermal measurements reveal a maximum Tc reaching 8.7 and 9.3 K for the respective samples Zr0.96V0.04B2 and Hf0.97V0.03B2 composition with high values of ? 0Hc2(0) (~ 16 and ~ 21 T, respectively). In these samples, the results about the behavior ? 0Hc1 (T), Cp(T), and VHall (T); and ETS (electronic tunneling spectroscopy) measurements in a single crystal; reveal a clear signatures of multiband superconductivity such as reported to the MgB2. Furthermore, the results show that the existence of the superconducting state ZrB2 appears to be not exclusive by V substitution, it is also observed in the sample Zr0.96Y0.04B2 whose Tc reaches 6.7 K again with signature multiband behavior. Also shown are the results of the existence of competitive magnetic behavior in samples of Zr1-xAlxB2 system, with a surprising ferromagnetic ordering. In this same scenario, it is also shown that substitution of Nb by Ni is able to raise the critical temperature of the NbB2-? compound from 3.6 K to 6.0 K. Since other borides as in Th1- xMxB12 (M = Zr, Sc, Y, Ti Hf) systems, in special conditions of synthesis and substitution the ThB12 phase (non-existent in the equilibrium conditions) can be stabilized, which is observed to Th0.97Zr0.03B12 sample with Tc close to 5.5 K and BCS superconducting behavior, but with a low of the k parameter value opening discussion for a new class of 1.5 type superconductors.

>Magister Scientiae - MSc / The lack of monitoring of non-perennial rivers is a major problem for water resources management, despite their significance in satisfying agricultural, economic and recreational needs. Pools in non-perennial rivers are not monitored, due to their remoteness. Remote sensing offers a promising alternative for the monitoring of changes in water storage in these pools. This study aims to assess the extent to which remotely-sensed datasets can be used to monitor the spatio-temporal changes of water storage of pools along non-perennial rivers in the Western Cape. The objectives of this study are: (1) to determine a suitable image preprocessing and classification technique for detecting and monitoring surface water along nonperennial rivers, and (2) to describe the spatial and temporal changes of water availability of pools along non-perennial rivers, using remotely sensed datasets. The Normalised Difference Water Index (NDWI), Modified NDWI (MNDWI), Normalised Difference Vegetation Index (NDVI), Automated Water Extraction Index for shadowed (AWEIsh) and non-shadowed regions (AWEInsh) and the Multi-Band Water Index (MBWI) classification techniques were investigated in this study, using the Sentinel-2 and Landsat 8 datasets. In-situ measurements were used to validate the satellite-derived datasets, while the use of high resolution aerial photography and Digital-Globe WorldView imagery were further compared to the results. The results suggested that the NDWI is the most suitable classification technique for identifying water in pools along non-perennial rivers throughout the Western Cape. The NDWI applied to the Sentinel-2 Top-of-Atmosphere (TOA) reflectance dataset had the highest overall accuracy of 85%, when compared to the Sentinel-2 Dark Object Subtraction 1 (DOS1) atmospheric correction, Sentinel-2 Sen2Cor atmospheric correction, Landsat 8 TOA reflectance and Landsat 8 DOS1 atmospheric correction datasets. The incorporation of atmospheric correction was shown to eliminate surface water pixels in many of the smaller pools.

As the microwave wireless communication systems growing rapidly, microstrip planar ceramic filters attract many attentions because of the advantages of small size, low cost, easy fabrication, higher performance and easy integration. In this thesis, several kinds of bandpass filters are designed for different operating purposes. First, two kinds of dual-mode bandpass filters are designed for 2.4 GHz wideband with the T-shaped I/O arranging in a straight way for easy integration. Second, the hook-coupling and insert-coupling structures are adopted for series connecting of the stepped-impedance resonator structures, and 2.4/5.2 GHz dual-band filtering properties could be achieved. Third, two open-loop rectangular ring resonators and U-shaped I/O are designed for 2.4/5.2 GHz dual-band bandpass filters with deep transmission zeros. The quarter wavelength stubs and groove structures are used for enhancing deep transmission zeros between two passband and ripples of the second passband, respectively. Fourth, the parallel positioned resonators with phase difference method are used to design the dual-band (1.23/2.4 GHz) and quad-band (1.23/2.4/3.5/5.2 GHz) bandpass filter with asymmetrical bandwidths and transmission zeros. In the thesis, high quality Al2O3 ceramic substrates are used to fabricate different kinds of bandpass filters for pattern minimization and low losses. The electromagnetic simulators, HFSS and IE3D, were used to adjust and optimize the associated parameters. The printing method was used to fabricate the proposed bandpass filters, which did not need using the FeCl3 to etch the Cu plate from the surface of Duroid or the FR4 substrates. The proposed filters are measured by Agilent-N5230A with the SMA connectors welding. Finally, the simulated and measured results of proposed bandpass filters are in good agreement.

This work deals with the principles on which they are based multiband antennas, especially for GSM (900/1800). It then focuses on different ways you can implement these multi-band antennas, mainly deals with structures that can be easily realized using planar technology. These antennas was designed and optimized in electromagnetic simulation software. Selected antenna was practically realized.

Current HF communication systems are confined to transmit in relatively narrow frequency band of a few 100 kHz at the time. The problems with limited bandwidth accumulate in HF-networks with multiple links and such networks are therefore hardly “internet capable” today. Previously, systems using channel aggregation over narrow channels in multiple frequency bands have been proposed to increase the capacity and reliability of the system by exploiting current propagation conditions in a better way. An interesting implementational problem is the design of practical and efficient antennas for concurrent multiband transmission in HF. Constraints like complexity, size and ease of deployment are considered. Some classical wideband aperiodic schemes are compared with switchable multiband solutions that cover a limited number of adjacent bands. Designs, simulations and some early field test results are presented. Finally, implementation aspects and constraints are discussed. / Nuvarande HF-kommunikationssystem är begränsade till att sända i ett relativt smalt frekvensband på några 100 kHz åt gången. Problemen med begränsad bandbredd ökar i HF-nät med flera länkar och sådana nät är därför knappast lämpliga för internet-trafik idag. Tidigare har system som aggregerar flera smala kanaler i flera frekvensband föreslagits för att öka systemets kapacitet och tillförlitlighet genom att utnyttja nuvarande utbredningsförhållanden på ett bättre sätt. Ett intressant implementeringsproblem är utformningen av praktiska och effektiva antenner för samtidig flerbandsöverföring i HF. Begränsningar som komplexitet, storlek och enkel implementering beaktas. Vissa klassiska bredbandiga aperiodiska antenn system jämförs med omkopplingsbara flerbandslösningar som täcker ett begränsat antal angränsande band. Konstruktioner, simuleringar och några tidiga fälttestresultat presenteras. Slutligen diskuteras implementeringsaspekter och begränsningar.

Yes / In this paper, a balanced antenna for mobile handset applications with enhanced bandwidth performance, that covers four bands (GSM1800, GSM1900, UMTS and 2.4-GHz WLAN), is investigated. The antenna is a slot planar dipole with folded structure and a dual-arm on each monopole. A wide bandwidth planar balun is employed to feed the wideband balanced antenna from an unbalanced source. A prototype of the proposed antenna is fabricated and tested. The performance of the antenna is veri¯ed and characterized in terms of return loss, radiation patterns and power gain. The calculated and measured results show good agreement and also con¯rm good wideband characteristics for the proposed antenna with multiband operation.