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The subject of this thesis is the development of parametric methods for the calibration of array shape errors. Two physical scenarios are considered, the online calibration (self-calibration) using far-field sources and the offline calibration using near-field sources. The maximum likelihood (ML) estimators are employed to estimate the errors. However, the well-known computational complexity in objective function optimization for the ML estimators demands effective and efficient optimization algorithms. A novel space-alternating generalized expectation-maximization (SAGE)-based algorithm is developed to optimize the objective function of the conditional maximum likelihood (CML) estimator for the far-field online calibration. Through data augmentation, joint direction of arrival (DOA) estimation and array calibration can be carried out by a computationally simple search procedure. Numerical experiments show that the proposed method outperforms the existing method for closely located signal sources and is robust to large shape errors. In addition, the accuracy of the proposed procedure attains the Cram´er-Rao bound (CRB). A global optimization algorithm, particle swarm optimization (PSO) is employed to optimize the objective function of the unconditional maximum likelihood (UML) estimator for the farfield online calibration and the near-field offline calibration. A new technique, decaying diagonal loading (DDL) is proposed to enhance the performance of PSO at high signal-to-noise ratio (SNR) by dynamically lowering it, based on the counter-intuitive observation that the global optimum of the UML objective function is more prominent at lower SNR. Numerical simulations demonstrate that the UML estimator optimized by PSO with DDL is optimally accurate, robust to large shape errors, and free of the initialization problem. In addition, the DDL technique is applicable to a wide range of array processing problems where the UML estimator is employed and can be coupled with different global optimization algorithms.

The mutual coupling in phased array is a well-known phenomenon. It affects the active element pattern of the array as the phase of the individual element is altered. In an array that has many elements, the effect is identical for all the elements that are nearer to the center of the antenna, thus allowing a more predictable scan performance with respect to the phase of the elements. However, in a small array that has only three elements, the active element pattern for the elements at the end can be significantly different from the center element and this affects the predictability of operations such as direction finding. The thesis investigates two ways that can potentially reduce or at least control the mutual coupling in small arrays. The first method simply adds a dummy element with a special load condition to each end of the array to make the edge element "feel" as if there are more elements next to it. The second method uses a passive feedback circuit to both monitor and correct the magnitude and phase of the mutual coupling at the input of each array element. A hybrid ring is attached to each of the elements to monitor the amount of interference received by that element. Simulation results for the dummy element method shows that some reduction in phase error can be achieved if the spacing and length of the element are selected properly. The compensation network approach relies on an efficient two-port array element. The research has focused on the design of a two-port printed circuit dipole that could be used in such an array. The dipole was designed, simulated, and fabricated. Future research will use this element in a compensation network. / Republic of Singapore Navy author.

Técnicas de aquisição paralelas e hardware dedicados vem sendo desenvolvidos desde a década de 1980 para reduzir o tempo de aquisição de imagens via ressonância magnética (IRM). Uma bobina do tipo phased array é um dispositivo do tipo receptor, que usa múltiplas bobinas (canais) cada qual com seu próprio circuito de detecção para adquirir simultaneamente os sinais que formam uma imagem ou espectro via IRM. Exemplos de técnica de imagem paralela que usa bobinas tipo phased array são Sensitivy Enconding (SENSE) e GeneRalized Autocalibrating Partial Parallel Acquisition (GRAPPA). Sampled array é o nome de um método proposto neste trabalho em que cada canal de uma bobina multicanal é responsável por adquirir de forma independente o sinal da sua amostra de modo que cada sinal de amostra é endereçado ao seu canal específico. Neste trabalho, descrevemos o desenvolvimento de uma bobina phased array de quatro canais para anatomia de cabeça de rato usando circuito impresso flexível para operar em um sistema de IRM pré-clínico de 2T com objetivo de validar o método de construção e uso de circuito flexível como bobina de recepção. Também desenvolvemos uma bobina de quatro canais para realizar simultaneamente a imagem de quatro sementes na mesma varredura para validar o método Sampled Array com objetivo de melhorar a qualidade da imagem e simultaneamente acelerar experimentos de múltiplas amostras. Os resultados mostram que a bobina de circuito impresso phased array, em comparação com uma bobina de enrolamento de fio regular, forneceu uma boa relação sinal / ruído (RSR) e possui geometria mais adequada à anatomia por ser flexível. Além disso, o processo de fabricação da bobina seja facilitado desde que toda a bobina é construída como um protótipo de circuito impresso. Os bons resultados da bobina sampled array mostraram o método como promissor para imageamento de múltiplas amostras com aumento de RSR e diminuição de tempo de experimentos em relação ao uso de bobinas de canal único. / Parallel techniques and dedicated hardware has been developed since the 1980s to reduce acquisition time on Magnetic Resonance Imaging (MRI) scanners. A phased array is a receiver only mode device concept, which uses multiple channels (coils) with their own detection circuits to simultaneously acquire MRI or localized spectroscopic signals. An example of parallel imaging technique that uses phased array coils is Sensitivy Enconding (SENSE). Sampled array is the name proposed in this work for a method in which each channel of a multichannel coil is responsible to acquire independently the signal from its sample so that each sample signal is addressed to its specific channel. In this work, we describe the development of a four-channel phased array coil for rat head anatomy using flexible printed circuit board (PCB), to operate on a 2T pre-clinical MRI scanner to validate the construction method and usage of flexible PCB as a receiver coil. We also developed a four-channel sample array coil to simultaneously perform the imaging of four seeds at the same scan, to validate the proposed method to improve image quality at the same time accelerating multiple seed imaging for agriculture studies. The results show that phased array PCB coil as compared to a regular wire winding coil provide good signal-to-noise ratio (SNR) imaging with more adequate geometry to the anatomy by being flexible. In addition, the coil manufacturing process is facilitated since the entire coil is constructed as a PCB prototype. The sample array imaging showed as a promising method for multiple sample increasing SNR and time to do experiments.

Thesis (M.S.)--Ohio State University, 2006. / Includes bibliographical references (leaves 98-90). Available online via OhioLINK's ETD Center

Phased array surface coils offer high SNR over a large field of view. Phased array volume coils have high SNR at the surface and centre of the volume. Most array coil designs typically employ a combination of geometrical and additional techniques, such as isolating preamplifiers for element-to-element decoupling. The development of array coils for small animal MRI is of increasing interest. However isolation preamplifiers are expensive and not ubiquitous at the field strengths typically employed for small animal work (4.7T, 9.4T, etc). In addition, isolating preamps complicates the designs of coils for transmit SENSE since they do not decouple during transmitting. Therefore, this thesis reexamines a "tried and true" method for decoupling coil elements. In this work five different coils for mouse imaging at 200MHz are presented: a 16 leg trombone design quadrature birdcage coil and four geometrically decoupled volume phased array coils. The first mouse array coil is a two saddle quadrature coil with a circularly polarized field. The second coil is a four channel transmit/receive volume array coil that is decoupled purely geometrically, without the need for other forms of decoupling. The third array coil is a modified 'open' configuration to facilitate the loading of animals. The fourth coil presented is a 'tunable' decoupling coil, where the geometric decoupling between elements is 'tunable', in order to compensate for different loading conditions of the coil. Tunable decoupling between elements was achieved using two mechanisms, a decoupling paddle for isolation of top to bottom elements, with a variable overlap mechanism for decoupling diagonal elements. Bench measurements demonstrate good decoupling (better than -20dB) of the coil elements and 'tunability' of both mechanisms. Phantom images from all coils are presented.

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This paper presents a novel active-alignment technique to fabricate one-dimensional optical fiber array. The advantages of this technique are providing simple structure on silicon- based optoelctronic device and individually adjusting relative position error of fiber array and laser diode array. The way to adjust fiber displacement is applying electric force to pull the adhesive which used to fix fibers and microholders. Then the adhesive has adhesive force with fiber surface that bring fiber moving away from its original position. The method has to consider some issues including choosing the adhesive viscosity, controlling adhesive volume in the microholder, confirming adjusting precision of fiber displacement, compensating the fiber Offset after curing. So we can obtain the minimum adjusting precision 0.5£gm and control the fiber traveling distance at ¡Ó0.4£gm. The way to improve those issues of adjusting the fiber array to achieve the best coupling position is described in this paper.

Abstract For the requirements of high-speed signal transmission has been increasing in the optical communication system ,so the fiber array in the communication system has a lot of advantages which can not be replaced. But the loss of coupling efficiency is a difficult problem as the distance of communication is getting longer and longer. The packaging quality of the fiber array module. In order to increase the transmission and the coupling efficiency, we produce the high precision to reach the goal. This paper use adhesive bonding technology to packageing of the fiber array module. But the adhesive had shrinkage and strength two problem. This paper presents a novel height and strength control strategy is constructed to fabricate one-dimensional optical fiber array. For the height,a active-alignment technique is used and shrinkage control and pick adhesive parameter can improve accuracy to displacement distance is below 1£gm in the work tempeture.For the strength of the adhesion¡Aa way to use different kind temperature in the work can add adhesion's strength. After work use to replace temperature in order to add strength. All the improvements of the above packading technologies are proposed to raise or keep the performance of the fiber array module.So,the error between theories and experiments can be minimized.Meanwhile,a high stability and repeatability of the packaging can be achieved due to the automation of the positioning force sensing,andinspection.

Using analytical formula to estimate a complex problem of cavity based on a transmission line approach is called the ETL (Equivalent Transmission Line) method . Operating frequency of dominant mode of standard case is several hundreds of megahertz that is lower than frequency of CPU, higher-order mode must be considered . Several papers always discuss a single aperture that does not correspond to practical array of apertures of case .Array of apertures can be estimated using analytical formula and higher-order mode can be considered in this paper .Usually array of apertures is not placed at the center of metallic plate, we can modify the analytical formula to get ETL of shifted array of apertures. To consider industrial design and esthetics, many possible shape of array of apertures are discussed by adapting to the ETL method .The problem of how to improve the shielding effectiveness of array of apertures is treated in the latter half of this thesis. The FDTD (Finite-Difference Time Domain) method is a full-wave analytical algorithm and is not efficient for analyzing cavity. Advantage of ETL is that it is faster than full-wave analytical algorithm .However, traditional ETL can not get accurate level of shielding effectiveness without higher-order modes. Thus improved ways are introduced in the paper to simulate practical array of apertures to reach the result of good agreement and short computing time.