Ridge-type 1.3£gm InGaAsP diode lasers with a planar waveguide structure have been successfully demonstrated. After ridge etching, a SiO2 thin film was sputtered onto the sample as the surface passivation layer, following by the coating of Benzocyclobutene (BCB) polymer surface planarization. Before metalization, the thin polymer and SiO2 layers above the ridge were removed by dry etching and wet etching techniques. The fabrication was completed by evaporating contact metals to the samples. The cavity length of the measured laser diode is 1mm, and the threshold current of the planar laser and the ridge laser are both 32mA. The total resistance and threshold voltage of the planar device are 6.5£[ and 1.3 V. The differential quantum efficiency as large as 85% is obtained. In addition, a conventional ridge-type laser is fabricated for comparison. The total resistance and threshold voltage of conventional ridge-type device are 14£[ and 2.1V. The differential quantum efficiency is 78%.

The Planar Array of Superheated Spheres (PASS) has been put forward as a possible neutrino and dark matter detector. This work has concentrated on the characteristics of a 100x100 array of spheres, of indium or tin. The superheated-supercooled hysteresis curves, for magnetic fields ranging from the earth's to 16 mT, have been measured in a pumped ⁴He cryostat using an RF-SQUID readout system. Individual superconducting to normal grain flips were recorded with the indium sample due to exposure to 60 keV gammas. The effect of gravity on the shape and structure of the spheres was tested by remelting arrays in a microgravity environment. The hysteresis curves obtained for these arrays showed a decreased transition width, i.e. the temperature difference from where all the spheres are superconducting to where they are all normal. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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Este trabalho trata sobre o desenvolvimento de sensores magnéticos tipo fluxgate baseados em tecnologia planar. O material utilizado como núcleo é baseado em trabalhos anteriores que determinaram os melhores parâmetros de eletrodeposição de ligas de NiFe para esta aplicação. Foram criados dispositivos funcionais mostrando a usabilidade do material. Também foram propostos 4 novos leiautes com o propósito de melhorar características como sensibilidade, preço, consumo de potência e resolução se comparados com sensores similares atuais. Inicialmente somente dispositivos em escala de milímetros foram criados utilizando placas de circuito impresso como substrato e um processo litográfico baseado em toner de impressora a laser. Este processo é muito simples e permite uma rápida ida do desenho ao protótipo em escala macro sem necessitar de equipamentos especiais. Note que ao contrário de macrofluxgates convencionais, estes dispositivos pode ser diretamente escalonados. Estes protótipos fornecerão os dados necessários para a construção de micro sensores otimizados. Para calcular a intensidade do campo magnético ao qual o núcleo está submetido foram feitas simulações de elementos finitos. A pequenas distâncias do plano, menores que a separação entre as espiras e onde o núcleo ferromagnético se situa, o campo é muito influenciado pela periodicidade da bobina, dando origem a um campo com oscilações periódicas de grande amplitude. Os efeitos desta alta inomogeneidade não é bem conhecido. Utilizando as curvas de histerese medida para os filmes de NiFe foram obtidas as curvas de resposta simulada para um fluxgate. A sensibilidade e a região linear em função do campo de excitação também foram simuladas. Enquanto que a sensibilidade tem um máximo para campos pouco mais intensos que o de saturação do material, decrescendo posteriormente, a região linear apresenta um pico para campos excitatórios baixos. O primeiro foi confirmado pelos resultados experimentais que também mostraram evidências do segundo. Os quatro leiautes são basicamente dois tipos com uma versão dupla cada um. Isto é, empilhando duas camadas de bobinas idênticas consegue-se multiplicar por raiz de dois o campo de excitação utilizando a mesma potência e dobrar o número de bobinas coletoras. Os leiautes propostos mostraram melhor sensibilidade, até oito vezes maior, se comparados com uma referência tirada da literatura. Também o ruído foi menor nas versões de dupla camada. O melhor apresentou um ruído menor que 1/3 da referência, ambos com potências de 1 Wrms. Mas todos leiautes propostos tiveram menor região linear. Todas estas características também foram estudadas em função da potência aplicada que está diretamente ligada a amplitude do campo de excitação. / This work present the development of fluxgate magnetic field sensors based on planar technology. The material for the core of the device is based on early works that determined the best NiFe electrodeposition parameters for this application. Functional devices were created proving the usability of the alloy. Also 4 new layouts were proposed in order to build more sensitivity, cheaper, less power consumption and better resolution sensors. Firstly, only macro scale devices were created using printed circuit board as substrate and a laser printer toner based lithography. This process is very simple and allows a fast way from sketch to macro scale prototypes with no need of special equipments. Unlike the conventional macrofluxgates, these devices can be directly scalonable. This prototypes characterization data will be used to produce optimized microsensors. Some finite element simulations computed the magnetic field produced by a square planar coil to predict the intensity that the core is immersed on. At small distances from the coil\'s plane, smaller than the separation between wires, where the core stands, the field is very influenced by the periodicity of the coil giving rise to periodic profiles. The effects of this high inhomogeneity is not well known. Using the measured hysteresis curve from the NiFe films, the simulated response of a fluxgate sensor was obtained. The simulated sensitivity and linear range as a function of the excitation field amplitude showed some unexpected results. While the sensitivity has a maximum with excitation fields just above the core saturation values decreasing later on, the linear range shows a high peak in low field region. The first were confirmed by the experimental data that also showed strong evidences of the existence of the second one. The 4 new layouts are basically 2 with a double version each. That is, stacking two identical coil layers in order to multiply by 1.41 the excitation field using the same power, double the number of pick-up coils and minimize the undesired perpendicular magnetic field produce by planar coils. The new layout prototypes had better sensitivity, up to eight times higher, related to the reference one taken from literature. Also the noise measured was smaller in the double layers version. The best one presented more then three times less noise than the reference for a power of Wrms. But all of them presented smaller linear range. All this sensors characteristics where also studied as a function of the applied power, that is directly related to the excitation field.

Este trabalho trata sobre o desenvolvimento de sensores magnéticos tipo fluxgate baseados em tecnologia planar. O material utilizado como núcleo é baseado em trabalhos anteriores que determinaram os melhores parâmetros de eletrodeposição de ligas de NiFe para esta aplicação. Foram criados dispositivos funcionais mostrando a usabilidade do material. Também foram propostos 4 novos leiautes com o propósito de melhorar características como sensibilidade, preço, consumo de potência e resolução se comparados com sensores similares atuais. Inicialmente somente dispositivos em escala de milímetros foram criados utilizando placas de circuito impresso como substrato e um processo litográfico baseado em toner de impressora a laser. Este processo é muito simples e permite uma rápida ida do desenho ao protótipo em escala macro sem necessitar de equipamentos especiais. Note que ao contrário de macrofluxgates convencionais, estes dispositivos pode ser diretamente escalonados. Estes protótipos fornecerão os dados necessários para a construção de micro sensores otimizados. Para calcular a intensidade do campo magnético ao qual o núcleo está submetido foram feitas simulações de elementos finitos. A pequenas distâncias do plano, menores que a separação entre as espiras e onde o núcleo ferromagnético se situa, o campo é muito influenciado pela periodicidade da bobina, dando origem a um campo com oscilações periódicas de grande amplitude. Os efeitos desta alta inomogeneidade não é bem conhecido. Utilizando as curvas de histerese medida para os filmes de NiFe foram obtidas as curvas de resposta simulada para um fluxgate. A sensibilidade e a região linear em função do campo de excitação também foram simuladas. Enquanto que a sensibilidade tem um máximo para campos pouco mais intensos que o de saturação do material, decrescendo posteriormente, a região linear apresenta um pico para campos excitatórios baixos. O primeiro foi confirmado pelos resultados experimentais que também mostraram evidências do segundo. Os quatro leiautes são basicamente dois tipos com uma versão dupla cada um. Isto é, empilhando duas camadas de bobinas idênticas consegue-se multiplicar por raiz de dois o campo de excitação utilizando a mesma potência e dobrar o número de bobinas coletoras. Os leiautes propostos mostraram melhor sensibilidade, até oito vezes maior, se comparados com uma referência tirada da literatura. Também o ruído foi menor nas versões de dupla camada. O melhor apresentou um ruído menor que 1/3 da referência, ambos com potências de 1 Wrms. Mas todos leiautes propostos tiveram menor região linear. Todas estas características também foram estudadas em função da potência aplicada que está diretamente ligada a amplitude do campo de excitação. / This work present the development of fluxgate magnetic field sensors based on planar technology. The material for the core of the device is based on early works that determined the best NiFe electrodeposition parameters for this application. Functional devices were created proving the usability of the alloy. Also 4 new layouts were proposed in order to build more sensitivity, cheaper, less power consumption and better resolution sensors. Firstly, only macro scale devices were created using printed circuit board as substrate and a laser printer toner based lithography. This process is very simple and allows a fast way from sketch to macro scale prototypes with no need of special equipments. Unlike the conventional macrofluxgates, these devices can be directly scalonable. This prototypes characterization data will be used to produce optimized microsensors. Some finite element simulations computed the magnetic field produced by a square planar coil to predict the intensity that the core is immersed on. At small distances from the coil\'s plane, smaller than the separation between wires, where the core stands, the field is very influenced by the periodicity of the coil giving rise to periodic profiles. The effects of this high inhomogeneity is not well known. Using the measured hysteresis curve from the NiFe films, the simulated response of a fluxgate sensor was obtained. The simulated sensitivity and linear range as a function of the excitation field amplitude showed some unexpected results. While the sensitivity has a maximum with excitation fields just above the core saturation values decreasing later on, the linear range shows a high peak in low field region. The first were confirmed by the experimental data that also showed strong evidences of the existence of the second one. The 4 new layouts are basically 2 with a double version each. That is, stacking two identical coil layers in order to multiply by 1.41 the excitation field using the same power, double the number of pick-up coils and minimize the undesired perpendicular magnetic field produce by planar coils. The new layout prototypes had better sensitivity, up to eight times higher, related to the reference one taken from literature. Also the noise measured was smaller in the double layers version. The best one presented more then three times less noise than the reference for a power of Wrms. But all of them presented smaller linear range. All this sensors characteristics where also studied as a function of the applied power, that is directly related to the excitation field.

No description available.

No description available.

No description available.

Electrical capacitance tomography (ECT) is a low cost and fast imaging technique able to obtain cross sectional images of dielectric permittivity distribution. ECT has been successfully used in industrial process tomography mainly for 2D imaging. One of the key challenges in 3D ECT imaging is a large scale forward problem arising with a large number of elements in the meshed ECT sensor model. Notably a complete sensor model will provide the most appropriate solution to the forward problem. A complete sensor model requires modelling a shielded area behind electrodes, which leads to increase in density of the finite element mesh. In this thesis, an approximation error model (AEM) has been applied to the ECT modelling for the first time. In addition to 3D AEM modelling and to further evaluate the effectiveness of the proposed AEM algorithm, it was implemented to compensate for uncertainty in electrode size and mesh density in 2D ECT. The results achieved using AEM are promising. In terms of application area, this thesis focuses on fundamental development for possible use of ECT in non-destructive evaluation (NDE) application. In more traditional industrial process application the object is surrounded by a number of electrodes on its boundary. In NDE applications a planar array ECT and volumetric imaging is needed. This thesis presents a 3D planar array ECT sensor using a 3D reconstruction algorithm. The results are validated with a number of experimental tests. 3D planar array ECT imaging was further extended to image both dielectric and metallic samples. To quantify the limitations of planar array ECT, a 3D ECT sensor and 3D ECT software have been implemented and used to evaluate the performance of the 3D ECT imaging with missing sides, with planar array ECT being the most extreme case of missing sides. The underlying inverse problem was analysed using singular value decomposition of the sensitivity matrix for the first time. This thesis introduces the use of a resolution matrix to analyse the performance of a 3D ECT reconstruction algorithm. These analysis methods, which enabled an in depth analysis of imaging performance with missing sides, are able to quantify the performance of planar array ECT.

Consider a region Ω in the plane and a point z0 in Ω. If a particle which travels randomly, by Brownian motion, is released from z0, then it will eventually cross the boundary of Ω somewhere. We define the harmonic measure distribution function, or h-function hΩ, in the following way. For each r > 0, let hΩ(r) be the probability that the point on the boundary where the particle first exits the region is at a distance at most r from z0. We would like to know, given a function f, whether there is some region Ω such that f is the h-function of that region. We investigate this question using convergence properties of domains and of h-functions. We show that any well behaved sequence of regions must have a convergent subsequence. This, together with previous results, implies that any function f that can be written as the limit of the h-functions hΩn of a sufficiently well behaved sequence{Ωn}ofregionsis the h-function of some region. We also make some progress towards finding sequences {Ωn} of regions whose h-functions converge to some predetermined function f, and which are sufficiently well behaved for our results to apply. Thus, we make some progress towards showing that certain functions f are in fact the h- function of some region.