Dans le cadre du traitement statistique du signal, la plupart des algorithmes couramment utilisés reposent sur l'utilisation de la matrice de covariance des signaux étudiés. En pratique, ce sont les versions adaptatives de ces traitements, obtenues en estimant la matrice de covariance à l'aide d'échantillons du signal, qui sont utilisés. Ces algorithmes présentent un inconvénient : ils peuvent nécessiter un nombre d'échantillons important pour obtenir de bons résultats. Lorsque la matrice de covariance possède une structure rang faible, le signal peut alors être décomposé en deux sous-espaces orthogonaux. Les projecteurs orthogonaux sur chacun de ces sous espaces peuvent alors être construits, permettant de développer des méthodes dites rang faible. Les versions adaptatives de ces méthodes atteignent des performances équivalentes à celles des traitements classiques tout en réduisant significativement le nombre d'échantillons nécessaire. Par ailleurs, l'accroissement de la taille des données ne fait que renforcer l'intérêt de ce type de méthode. Cependant, cet accroissement s'accompagne souvent d'un accroissement du nombre de dimensions du système. Deux types d'approches peuvent être envisagées pour traiter ces données : les méthodes vectorielles et les méthodes tensorielles. Les méthodes vectorielles consistent à mettre les données sous forme de vecteurs pour ensuite appliquer les traitements classiques. Cependant, lors de la mise sous forme de vecteur, la structure des données est perdue ce qui peut entraîner une dégradation des performances et/ou un manque de robustesse. Les méthodes tensorielles permettent d'éviter cet écueil. Dans ce cas, la structure est préservée en mettant les données sous forme de tenseurs, qui peuvent ensuite être traités à l'aide de l'algèbre multilinéaire. Ces méthodes sont plus complexes à utiliser puisqu'elles nécessitent d'adapter les algorithmes classiques à ce nouveau contexte. En particulier, l'extension des méthodes rang faible au cas tensoriel nécessite l'utilisation d'une décomposition tensorielle orthogonale. Le but de cette thèse est de proposer et d'étudier des algorithmes rang faible pour des modèles tensoriels. Les contributions de cette thèse se concentrent autour de trois axes. Un premier aspect concerne le calcul des performances théoriques d'un algorithme MUSIC tensoriel basé sur la Higher Order Singular Value Decomposition (HOSVD) et appliqué à un modèle de sources polarisées. La deuxième partie concerne le développement de filtres rang faible et de détecteurs rang faible dans un contexte tensoriel. Ce travail s'appuie sur une nouvelle définition de tenseur rang faible et sur une nouvelle décomposition tensorielle associée : l'Alternative Unfolding HOSVD (AU-HOSVD). La dernière partie de ce travail illustre l'intérêt de l'approche tensorielle basée sur l'AU-HOSVD, en appliquant ces algorithmes à configuration radar particulière: le Traitement Spatio-Temporel Adaptatif ou Space-Time Adaptive Process (STAP). / Most of statistical signal processing algorithms, are based on the use of signal covariance matrix. In practical cases this matrix is unknown and is estimated from samples. The adaptive versions of the algorithms can then be applied, replacing the actual covariance matrix by its estimate. These algorithms present a major drawback: they require a large number of samples in order to obtain good results. If the covariance matrix is low-rank structured, its eigenbasis may be separated in two orthogonal subspaces. Thanks to the LR approximation, orthogonal projectors onto theses subspaces may be used instead of the noise CM in processes, leading to low-rank algorithms. The adaptive versions of these algorithms achieve similar performance to classic classic ones with less samples. Furthermore, the current increase in the size of the data strengthens the relevance of this type of method. However, this increase may often be associated with an increase of the dimension of the system, leading to multidimensional samples. Such multidimensional data may be processed by two approaches: the vectorial one and the tensorial one. The vectorial approach consists in unfolding the data into vectors and applying the traditional algorithms. These operations are not lossless since they involve a loss of structure. Several issues may arise from this loss: decrease of performance and/or lack of robustness. The tensorial approach relies on multilinear algebra, which provides a good framework to exploit these data and preserve their structure information. In this context, data are represented as multidimensional arrays called tensor. Nevertheless, generalizing vectorial-based algorithms to the multilinear algebra framework is not a trivial task. In particular, the extension of low-rank algorithm to tensor context implies to choose a tensor decomposition in order to estimate the signal and noise subspaces. The purpose of this thesis is to derive and study tensor low-rank algorithms. This work is divided into three parts. The first part deals with the derivation of theoretical performance of a tensor MUSIC algorithm based on Higher Order Singular Value Decomposition (HOSVD) and its application to a polarized source model. The second part concerns the derivation of tensor low-rank filters and detectors in a general low-rank tensor context. This work is based on a new definition of tensor rank and a new orthogonal tensor decomposition : the Alternative Unfolding HOSVD (AU-HOSVD). In the last part, these algorithms are applied to a particular radar configuration : the Space-Time Adaptive Process (STAP). This application illustrates the interest of tensor approach and algorithms based on AU-HOSVD.

This work extends the technology of amorphous silicon (a-Si) thin film transistors (TFTs) from traditional switching applications to on-pixel signal amplification for large area digital imaging and in particular, is aimed towards enabling emerging low noise, high resolution and high frame rate medical diagnostic imaging modalities such as digital tomosynthesis. A two transistor (2T) pixel amplifier circuit based on a novel charge-gate thin film transistor (TFT) device architecture is introduced to shrink the TFT based pixel readout circuit size and complexity and thus, improve the imaging array resolution and reliability of the TFT fabrication process. The high resolution pixel amplifier results in improved electrical performance such as on-pixel amplification gain, input referred noise and faster readouts. In this research, a charge-gated TFT that operates as both a switched amplifier and driver is used to replace two transistors (the addressing switch and the amplifier transistor) of previously reported three transistor (3T) APS pixel circuits.. In addition to enabling smaller pixels, the proposed 2T pixel amplifier results in better signal-to-noise (SNR) by removing the large flicker noise source associated with the switched TFT and increased pixel transconductance gain since the large ON-state resistance of the switched TFT is removed from the source of the amplifier TFT. Alternate configurations of 2T APS architectures based on source or drain switched TFTs are also investigated, compared, and contrasted to the gate switched architecture using charge-gated TFT. A new driving scheme based on multiple row resetting is introduced which combined with the on-pixel gain of the APS, offers considerable improvements in imaging frame rates beyond those feasible for PPS based pixels. The novel developed 2T APS architectures is implemented in single pixel test structures and in 88 pixel test arrays with a pixel pitch of 100 µm. The devices were fabricated using an in-house developed top-gate TFT fabrication process. Measured characteristics of the test devices confirm the performance expectations of the 2T architecture design. Based on parameters extracted from fabricated TFTs, the input referred noise is calculated, and the instability in pixel transconductance gain over prolonged operation tine is projected for different imaging frame rates. 2T APS test arrays were packaged and integrated with an amorphous selenium (a-Se) direct x-ray detector, and the x-ray response of the a-Se detector integrated with the novel readout circuit was evaluated. The special features of the APS such as non-destructive readout and voltage programmable on-pixel gain control are verified. The research presented in this thesis extends amorphous silicon pixel amplifier technology into the area of high density pixel arrays such as large area medical X-ray imagers for digital mammography tomosynthesis. It underscores novel device and circuit design as an effective method of overcoming the inherent shortcomings of the a-Si material . Although the developed device and circuit ideas were implemented and tested using a-Si TFTs, the scope of the device and circuit designs is not limited to amorphous silicon technology and has the potential to be applied to more mainstream technologies, for example, in CMOS active pixel sensor (APS) based digital cameras.

This work extends the technology of amorphous silicon (a-Si) thin film transistors (TFTs) from traditional switching applications to on-pixel signal amplification for large area digital imaging and in particular, is aimed towards enabling emerging low noise, high resolution and high frame rate medical diagnostic imaging modalities such as digital tomosynthesis. A two transistor (2T) pixel amplifier circuit based on a novel charge-gate thin film transistor (TFT) device architecture is introduced to shrink the TFT based pixel readout circuit size and complexity and thus, improve the imaging array resolution and reliability of the TFT fabrication process. The high resolution pixel amplifier results in improved electrical performance such as on-pixel amplification gain, input referred noise and faster readouts. In this research, a charge-gated TFT that operates as both a switched amplifier and driver is used to replace two transistors (the addressing switch and the amplifier transistor) of previously reported three transistor (3T) APS pixel circuits.. In addition to enabling smaller pixels, the proposed 2T pixel amplifier results in better signal-to-noise (SNR) by removing the large flicker noise source associated with the switched TFT and increased pixel transconductance gain since the large ON-state resistance of the switched TFT is removed from the source of the amplifier TFT. Alternate configurations of 2T APS architectures based on source or drain switched TFTs are also investigated, compared, and contrasted to the gate switched architecture using charge-gated TFT. A new driving scheme based on multiple row resetting is introduced which combined with the on-pixel gain of the APS, offers considerable improvements in imaging frame rates beyond those feasible for PPS based pixels. The novel developed 2T APS architectures is implemented in single pixel test structures and in 88 pixel test arrays with a pixel pitch of 100 µm. The devices were fabricated using an in-house developed top-gate TFT fabrication process. Measured characteristics of the test devices confirm the performance expectations of the 2T architecture design. Based on parameters extracted from fabricated TFTs, the input referred noise is calculated, and the instability in pixel transconductance gain over prolonged operation tine is projected for different imaging frame rates. 2T APS test arrays were packaged and integrated with an amorphous selenium (a-Se) direct x-ray detector, and the x-ray response of the a-Se detector integrated with the novel readout circuit was evaluated. The special features of the APS such as non-destructive readout and voltage programmable on-pixel gain control are verified. The research presented in this thesis extends amorphous silicon pixel amplifier technology into the area of high density pixel arrays such as large area medical X-ray imagers for digital mammography tomosynthesis. It underscores novel device and circuit design as an effective method of overcoming the inherent shortcomings of the a-Si material . Although the developed device and circuit ideas were implemented and tested using a-Si TFTs, the scope of the device and circuit designs is not limited to amorphous silicon technology and has the potential to be applied to more mainstream technologies, for example, in CMOS active pixel sensor (APS) based digital cameras.

L'évolution des réseaux électriques d'une transmission de puissance unidirectionnelle classique vers un réseau diversifié avec, une grande variété de consommateurs et producteurs d'électricité, requiert le développement des technologies de mesure et de communication avancés et/ou nouvelles. Dans le cadre du projet SOGRID, une méthode innovante de mesure de courant a été développée pour enrichir la gamme existante des capteurs de courant et pour faciliter l’installation dans le réseau électrique. En effet, le capteur innovant développé ici est non seulement non-intrusif, mais peut également être déporté du câble.Dans les réseaux électriques, l'obstacle principal pour une mesure précise du courant est la nature triphasée de transmission de puissance. Un capteur de courant qui doit être utilisé dans le réseau électrique doit donc fournir une sélectivité géométrique entre les différentes phases. Les solutions commerciales existantes sont dites non-intrusives, mais nécessitent tout de même de venir entourer le conducteur d'intérêt pour mesurer le champ le long d'un chemin fermé. Ces solutions comprennent des bobines de Rogowski et les mesures en boucle fermée avec des capteurs de champs comme les magnétorésistances, les capteurs à effet Hall ou les fluxgates. Toutefois, un placement autour du conducteur limite la miniaturisation requise par le développement des réseaux intelligents : des capteurs miniatures peuvent être intégrés avec d'autres unités de mesure et de transmission de données pour permettre le suivi et le contrôle des réseaux intelligents modernes avec une maille plus dense.Afin de rependre à ces exigences, et pour améliorer la sélectivité géométrique des conducteurs, une méthode de mesure de courant basée sur la décomposition du champ en harmoniques spatiales a été développée dans cette thèse.Cette décomposition est basée sur le développement du champ magnétique à l'intérieur d'une région défini avec une série de fonctions périodiques angulaires, une loi d’évolution radiale particulière et des coefficients de développement correspondants, de sorte que la somme des ordres (théoriquement infini) de développement reconstruit le champ avec précision. Si ce développement est effectué pour une région sans sources, qui est donc entouré des sources de champ, il est défini comme une décomposition interne, qui utilise des fonctions croissantes du rayon, à partir du centre de décomposition en direction de la source de champ. Le procédé de mesure de courant est basé sur la détermination des coefficients de développement pour les différents ordres, dans lequel les ordres supérieurs présentent une dépendance réduite aux sources de perturbation (plus éloignes du conducteur d’intérêt). La relation entre ces coefficients et le courant d'intérêt est linéaire et défini par des facteurs de transfert.Afin d'exploiter la sélectivité géométrique accrue des ordres supérieurs, il est nécessaire d'effectuer un nombre suffisant de mesures du champ magnétique sur la limite d'une région appropriée afin de déduire les coefficients de développement à partir de la résolution d'un problème inverse. La taille et le positionnement de ce réseau de capteurs jouent des rôles essentiels dans la détectabilité des contributions d'ordre supérieur. Des prototypes appropriés pour une décomposition en 2D (pour les conducteurs rectilignes) et en 3D (pour les conducteurs avec des chemins arbitraires) ont été conçus, mis en œuvre et ensuite testés en laboratoire au cours de cette thèse.D'autres développements se concentrent sur la détermination des facteurs de transfert caractéristiques. En effet, tandis que ceux-ci peuvent être facilement déterminés si un courant contrôlé connu est introduit dans le conducteur, une méthode qui permet de les retrouver dans des conditions d'opération réelles doit être développée pour des applications industrielles. Afin de répondre à ce besoin, une méthode de calibration appropriée est aussi présentée dans cette thèse. / The evolution of electrical grids from conventional unidirectional power transmission to diverse networks with a large variety of electricity consumers and producers requires the development of advanced and/or novel measurement and communication technologies, in order to create smart grids. As a part of the SOGRID project, an innovative current measurement method was developed to supplement the existing range of current sensors and to facilitate the installation, since the sensor is not only non-intrusive but can also be located at a distance from the cable.The primary obstacle for precise current measurement in power grids is the three-phase nature of power transmission. A current sensor that is to be employed in the electrical grid must therefore provide geometrical selectivity between the individual phases. Existing commercial current sensors are non-intrusive but require placement around the conductor of interest, e.g. to measure the field along a closed path. Solutions include Rogowski coils, magnetoresistors, Hall effect or fluxgate sensors as well as magneto-optical solutions. However, a placement around the conductor limits the miniaturization required by smart grid development: miniature sensors can be integrated with other measurement and data transmission units, thus enabling the densely meshed monitoring and control of modern smart grids. In order to avoid these restrictions and to improve geometrical selectivity, a current measurement method based on the decomposition of the field into spatial harmonics has been developed in this thesis. The measurement principle allows for the fabrication of innovative current sensors that can be installed besides the conductor.The decomposition of the magnetic field into spatial harmonics is based on the development of the magnetic field within a defined area/volume in a series of products of periodic functions, a radial dependence and corresponding development coefficients, so that the sum of the (in theory infinite number of) development orders reconstructs the field accurately. If this development is performed for a source-free region besides the source of the field, it is defined as an internal decomposition, which uses functions that increase from the center of decomposition toward the field source. The current measurement process is based on the determination of the development coefficients for the various orders, wherein higher orders exhibit a reduced dependence on perturbing sources (as long as the field measurements are performed closer to the conductor of interest than to the perturbing conductor). The relation between these coefficients and the current of interest is linear and defined by transfer factors.In order to exploit the increased geometrical selectivity of higher orders, it is necessary to perform a sufficient number of magnetic field measurements on the boundary of a suitable area/volume in order to derive the development coefficients from the solution of an inverse problem. The size and positioning of this sensor array also plays a vital role in the detectability of higher order contributions to the field. Suitable 2D (for straight conductors) and 3D (for arbitrary conductor paths) prototypes were designed, implemented and subsequently tested in the laboratory during this thesis.Further developments focus on determining the characteristic transfer factors. While these can be easily determined if a known controlled current is induced in the conductor, a method that allows for their determination under real operating conditions must be developed for industrial applications. A suitable calibration method is presented in this thesis.

Multiphase flow denotes the simultaneous flow of two or more physically distinct and immiscible substances and it can be widely found in several engineering applications, for instance, power generation, chemical engineering and crude oil extraction and processing. In many of those applications, multiphase flows determine safety and efficiency aspects of processes and plants where they occur. Therefore, the measurement and imaging of multiphase flows has received much attention in recent years, largely driven by a need of many industry branches to accurately quantify, predict and control the flow of multiphase mixtures. Moreover, multiphase flow measurements also form the basis in which models and simulations can be developed and validated. In this work, the use of electrical impedance techniques for multiphase flow measurement has been investigated. Three different impedance sensor systems to quantify and monitor multiphase flows have been developed, implemented and metrologically evaluated. The first one is a complex permittivity needle probe which can detect the phases of a multiphase flow at its probe tip by simultaneous measurement of the electrical conductivity and permittivity at up to 20 kHz repetition rate. Two-dimensional images of the phase distribution in pipe cross section can be obtained by the newly developed capacitance wire-mesh sensor. The sensor is able to discriminate fluids with different relative permittivity (dielectric constant) values in a multiphase flow and achieves frame frequencies of up to 10 000 frames per second. The third sensor introduced in this thesis is a planar array sensor which can be employed to visualize fluid distributions along the surface of objects and near-wall flows. The planar sensor can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. It can be operated by a conductivity-based as well as permittivity-based electronics at imaging speeds of up to 10 000 frames/s. All three sensor modalities have been employed in different flow applications which are discussed in this thesis. The main contribution of this research work to the field of multiphase flow measurement technology is therefore the development, characterization and application of new sensors based on electrical impedance measurement. All sensors present high-speed capability and two of them allow for imaging phase fraction distributions. The sensors are furthermore very robust and can thus easily be employed in a number of multiphase flow applications in research and industry.

<p> </p> <p>Gas sensors have many applications. Volatile organic compound (VOC) sensors are used for monitoring air quality in homes and office spaces, as well as monitoring manufacturing environments where a wide variety of VOCs can be produced. These gases can include formaldehyde, which can be toxic to humans at concentrations as low as 1 ppm. Other applications for gas sensors include flammable refrigerant detection. With the move towards developing more environmentally friendly appliances, many companies have started to use refrigerants such as R600a (isobutane) and R32 (difluoromethane), which have a much lower global warming potential (GWP) than their predecessors, such as R134a and R410a. While this move is beneficial for the environment, steps to ensure their safe usage have not been widely implemented to date. Therefore, sensors to detect VOCs at or below exposure limits, as well as flammable refrigerants at or below lower flammability limits (LFL), should be developed to ensure undue hazards are identified and mitigated. </p>

Searching with the key word “measuring instrument of traditional Chinese medical massage” in CNK, 62 academic literature papers can be found. According to statistics, research of “measuring instrument of traditional Chinese medical massage” are carried out in 5 directions, including normalized operation, high-tech based teaching and training, perception analysis of massage manipulation force, the structural design of robot, and the design of measuring instrument. As the manipulation of traditional Chinese medical massage is a multi-field medical effect, without the supporting of measurement of high-tech based multi-field sensor of massage actions, the quantification, normalized and standardized operation, scientific and modern teaching, microcosmic, precise and quantified perception, robotized and intellectualized actuation implementation, and design of measuring instrument are hard to realize. Meanwhile, the online diagnosis and treatment service model of traditional Chinese medical massage based on “internet plus” depends on the establishment of digital database of massage manipulation, which is based on the creation of high-tech sensor system of traditional Chinese medical massage measurement. Thus, the measuring sensor of the traditional Chinese medical massage manipulation is an unavoidable key scientific problem for scientific, normalized, and internet-enabled traditional Chinese medical massage. Flexible fiber grating sensor array will be a research direction for implementing multi-field measurement of traditional Chinese medical massage manipulation.

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[pt] O problema de estimação de direção (DoA) de chegada é um importante tópico de pesquisa em áreas como radar, sonar, sismologia, vigilância eletrônica e comunicações sem fio. Este trabalho teve como principal resultado o desenvolvimento de um novo algoritmo que combina o método da máxima verossimilhança (ML) estocástica com o algoritmo ganancioso de busca ortogonal (OMP), comumente empregado em recuperação esparsa com Sensoriamento Compressivo (CS). Muito embora técnicas ML sejam consideradas ótimas em termos de erro médio quadrático, atingindo o limitante inferior de Cramér-Rao (CRLB), o menor limitante inferior para a variância do estimador, estas técnicas demandam de modo significante, às vezes inexequível, os recursos computacionais. Por outro lado, a partir de uma variante esparsa da equação de aquisição de dados, o problema de encontrar a solução mais esparsa possível de sistemas de equações subdeterminados com o algoritmo OMP tem sido empregado de modo satisfatório para encontrar as estimativas de direção, porém com muitas oportunidades de melhoria em casos com cenários sujeitos a condições severas. Por exemplo, cenários com acoplamento eletromagnético (EM), baixa razão sinal-ruído (SNR) e um número limitado de amostras temporais disponíveis. O estimador de direção proposto, baseado em coarranjo diferença, denominado OMP com Máxima Verossimilhança Baseado em Lista (LBML-OMP), apresentou uma melhora significativa no processo de estimação em comparação com técnicas tradicionais e modernas, tais como: OMP, Técnica de Limiar Iterativa (IHT) e Classificação de Múltiplos Sinais Espacialmente Suavizados (SS-MUSIC). A técnica proposta utiliza uma lista de candidatos gerada a partir da solução do algoritmo OMP original e decide pelo melhor a partir de uma busca limitada utilizando o estimador ML estocástico, o que justifica seu uso em cenários práticos. Para a amostragem dos sinais no ambiente, arranjos lineares não-uniformes clássicos e modernos foram empregados, tais como Arranjos Aninhados de Segunda Ordem (NAQ2), Arranjos Aninhados de Segunda Ordem Aperfeiçoados (SNAQ2), Arranjos de Redundância Mínima (MRA) e Arranjos Coprimos (CPA). Além disso, a estimação foi realizada considerando-se o efeito do acoplamento EM e ruído. Ainda, um novo modelo para estimação de direção em coarranjo diferença foi desenvolvido. Este modelo considera o número de amostras temporais finitas (não-assintótico) e mostrou melhora significativa quando do seu emprego no processo de estimação de direção de todos os algoritmos considerados, não apenas o LBML-OMP, evidenciando fontes secundárias de erro no modelo original estabelecido. De forma a complementar o trabalho, um algoritmo de atenuação de ruído chamado OMP aleatorizado (RandOMP) foi utilizado para aumentar a precisão da estimação em cenários com condições de ruído severas. Neste sentido, as contribuições deste trabalho estão relacionadas principalmente ao desenvolvimento de um novo algoritmo e um novo modelo de transformação em coarranjo diferença de modo a melhorar as estimativas de direção das fontes com arranjos lineares não-uniformes. Além disso, enfatiza-se o emprego de diferentes geometrias para as simulações, tornando-se evidente o impacto da posição dos sensores nas curvas de raiz quadrada do erro médio quadrático (RMSE). / [en] The Direction of Arrival (DoA) estimation or Direction Finding (DF) is a relevant topic for research in areas such as radar, sonar, seismology, electronic surveillance, and wireless communications. This thesis devises a new algorithm that combines a stochastic Maximum Likelihood (ML) method with the widely-known Orthogonal Matching Pursuit (OMP) greedy algorithm, commonly used in sparse recovery with Compressive Sensing (CS). Even though ML techniques are known to be optimal in the mean-squared error sense, achieving the Cramér-Rao Lower Bound (CRLB), the tighter lower bound on estimator variance, they demand a significant, sometimes infeasible, amount of computational resources. On the other hand, departing from a sparsified variant of the data acquisition equation, the problem of finding the sparsest solution of underdetermined systems of equations with OMP has been employed successfully to find the DoA estimates, but with many opportunities for improvement in cases of challenging scenarios. For instance, scenarios with electromagnetic (EM) coupling, low signal-to-noise ratio (SNR), and a limited number of available snapshots (time samples). The proposed difference coarray DoA estimator termed List-Based Maximum Likelihood OMP (LBML-OMP) has shown substantial improvements over traditional and modern techniques, such as OMP, Iterative Hard Thresholding (IHT), and Spatial Smoothing Multiple Signal Classification (SS-MUSIC). It uses a list of candidates generated from the OMP solution and decides for the best based on a limited search using the stochastic ML rule. Thus, it does not perform a grid search with the ML estimator, and this justifies its use in practical scenarios. For the sensing of space-time field, classic and modern non-uniform linear arrays are employed, such as 2-nd Order Nested Array (NAQ2), 2-nd Order Super Nested Array (SNAQ2), Minimum Redundancy Array (MRA), Minimum Hole Array (MHA), and Coprime Array (CPA). Additionally, the estimation is performed under the assumption of EM coupling and noise as disturbing side effects. Furthermore, a new model for difference coarray DoA estimation is developed. It accounts for the finite number of snapshots and has shown to increase the estimation accuracy for all the algorithms, not only LBML-OMP, evidencing secondary sources of error for the difference coarray transformation. To complement the work, a denoising algorithm called Randomized OMP (RandOMP) was applied to successfully increase the estimation accuracy for difference coarray estimators in scenarios with severe noisy conditions. The contributions of this work relate mainly to the development of a new algorithm and a new difference coarray transformation to improve the DoA estimation accuracy with non-uniform linear arrays. Also, it should be noticed the employment of different geometries for the numerical experiments, making evident the impact of the array sensors positions in the root mean square error (RMSE) curves.

Resistances in two-dimensional matrices can be measured by addressing individual sensors one by one using two multiplexers. Thereby, it is assumed that the injected measurement current flows only through the target sensor. Nevertheless, if no special precautions are taken, a part of the injected current may flow through other sensors and this can significantly affect the measurement accuracy. This so-called cross-talk effect is therefore crucial for the measurement of two-dimensional sensor matrices. One possible solution to overcome this problem is to use the short-circuiting method, which sets the same potentials on both sides of the non-target sensors and avoids thereby the cross-talk currents leading to an improvement of measurement accuracy. The short-circuiting method is widely used because it requires no addition of further components, like diodes or MOSFETS, into the matrix. Nowadays, most of the short-circuiting methods are designed for the measurement of purely resistive (e.g., the zero potential circuit driving by DC signals) or capacitive sensor matrices. Thereby, capacitive matrix measurement methods are mainly designed to realize a high scanning speed and do not focus on reducing measurement deviations as they are more conceived for touch screens. In this thesis, the development of accurate measurement methods is focused, to reduce the cross-talk effects in two-dimensional impedimetric sensor matrices, where both the real part and imaginary part of the impedance need to be accurately measured. A multi-row excitation strategy using AC signals having different frequencies is proposed to avoid DC deviations due to the non-ideal behavior of electronic components and to enable simultaneous impedance measurement of all sensors. First, a novel method is proposed, to enable a multiplexer-free simultaneous measurement of resistive sensors in the two-dimensional matrix. This method is named the AC - Zero Potential Circuit (AC-ZPC Type 0), and it is extended for the measurement of impedimetric sensors. Then, based on analytical investigations, two advanced methods are proposed to realize higher measurement accuracy. The first advanced method (AC-ZPC Type 1) corrects the deviations caused by the row interface impedance by introducing a column with reference elements and dispenses with the measurement of the row side excitation signals. The second advanced method (AC-ZPC Type 2) extends the basic AC-ZPC method further. It uses a voltage follower on the row input side to reduce the row interface impedance and introduces a row and a column with reference elements. This method reduces the deviations related to the non-ideal features of the column side amplifier circuits, including their input/output impedance, open-loop gain factor, leakage current, and load impedance. The evaluation of the three proposed methods is carried out first by simulations and then on a specially developed experimental platform. In the simulations, the measurement deviations achieved by the proposed methods are less than 0.005% for the impedimetric targets composed of parallel RC pairs in the range from 2 kΩ||362 pF to 100 kΩ ||$ 7 pF. The feasibility of these proposed methods has been validated by the experimental investigations. Thereby, the AC-ZPC Type 2 method has shown better accuracy than the AC-ZPC Type 1 method. For purely resistive targets in the range from 2 kΩ to 100 kΩ, the averaged absolute deviation of 0.087% is achieved by the AC-ZPC Type 2 method, which is 20% less than the DC-ZPC methods.:1 Introduction 2 Theoretical background 3 Measurement methods for 2D sensor matrices 4 Novel methods for impedimetric sensor matrices 5 Performance in reducing cross-talk effects 6 Practical validation of the proposed methods 7 Conclusion and outlook References Appendix A Operational amplifier model Appendix B Calculation of the resistive and capacitive parts of a time constant unit Appendix C Supplements to performance investigation / Widerstände in zweidimensionalen Matrizen können gemessen werden, indem einzelne Sensoren mit zwei Multiplexern angesprochen werden. Dabei wird davon ausgegangen, dass der eingespeiste Messstrom nur durch den Zielsensor fließt. Ohne besondere Vorkehrungen kann jedoch ein Teil des eingespeisten Stroms durch andere Sensoren fließen, was die Messgenauigkeit erheblich beeinträchtigen kann. Dieser so genannte Übersprechungseffekt ist daher für die Messung von zweidimensionalen Sensormatrizen von entscheidender Bedeutung. Eine mögliche Lösung zur Überwindung dieses Problems ist die Kurzschlussmethode, bei der auf beiden Seiten der nicht zu messenden Sensoren die gleichen Potenziale angelegt werden und dadurch die Übersprechungsströme vermieden werden, was zu einer Verbesserung der Messgenauigkeit führt. Die Kurzschlussmethode ist weit verbreitet, da sie keine weiteren Komponenten, z.B. Dioden oder MOSFETS, in der Matrix erfordert. Heutzutage sind die meisten Kurzschlussverfahren für die Messung von rein resistiven (z.B. die Nullpotenzialschaltung, die durch Gleichstromsignale angetrieben wird) oder kapazitiven Sensormatrizen ausgelegt. Dabei sind kapazitive Matrixmessverfahren hauptsächlich auf eine hohe Messgeschwindigkeit ausgelegt und konzentrieren sich nicht auf die Reduzierung von Messabweichungen, da sie eher für Touchscreens konzipiert sind. In dieser Dissertation ist die Entwicklung präziser Messmethoden das Ziel, um die Übersprechungseffekte in zweidimensionalen impedimetrischen Sensormatrizen zu reduzieren, bei denen sowohl der Realteil als auch der Imaginärteil der Impedanz genau gemessen werden müssen. Es wird eine mehrreihige Erregungsstrategie unter Verwendung von Wechselstromsignalen mit unterschiedlichen Frequenzen vorgeschlagen, um Gleichstromabweichungen aufgrund des nicht idealen Verhaltens elektronischer Komponenten zu vermeiden und die gleichzeitige Impedanzmessung aller Sensoren zu ermöglichen. Zunächst wird eine neue Methode vorgeschlagen, die eine multiplexerfreie gleichzeitige Messung von Widerstandssensoren in einer zweidimensionalen Matrix ermöglicht. Diese Methode wird als AC-Nullpotenzialschaltung (AC-ZPC Typ 0) bezeichnet und für die Messung von impedimetrischen Sensoren erweitert. Anschließend werden auf der Grundlage analytischer Untersuchungen zwei fortschrittliche Methoden vorgeschlagen, um eine höhere Messgenauigkeit zu erzielen. Die erste fortschrittliche Methode (AC-ZPC Typ 1) korrigiert die durch die Impedanz der Reihenschnittstelle verursachten Abweichungen durch die Einführung einer Spalte mit Referenzelementen und verzichtet auf die Messung der reihenseitigen Anregungssignale. Die zweite fortgeschrittene Methode (AC-ZPC Typ 2) erweitert die grundlegende AC-ZPC Methode weiter. Sie verwendet einen Spannungsfolger auf der Reiheneingangsseite, um die Reihenschnittstellenimpedanz zu verringern, und führt eine Reihe und eine Spalte mit Referenzelementen ein. Diese Methode reduziert die Abweichungen, die mit den nicht idealen Eigenschaften der spaltenseitigen Verstärkerschaltungen zusammenhängen, einschließlich ihrer Eingangs-/Ausgangsimpedanz, des Open-Loop-Verstärkungsfaktors, des Leckstroms und der Lastimpedanz. Die Bewertung der drei vorgeschlagenen Methoden erfolgt zunächst durch Simulationen und dann auf einer speziell entwickelten Versuchsplattform. In den Simulationen liegen die mit den vorgeschlagenen Methoden erzielten Messabweichungen bei weniger als 0,005% für die aus parallelen RC-Paaren bestehenden impedimetrischen Ziele im Bereich von 2 kΩ||362 pF bis 100 kΩ ||$ 7 pF. Die Durchführbarkeit der vorgeschlagenen Methoden wurde durch die experimentellen Untersuchungen bestätigt. Dabei hat die AC-ZPC Typ 2 Methode eine bessere Genauigkeit als die AC-ZPC Typ 1 Methode gezeigt. Für rein resistive Ziele im Bereich von 2 kΩ bis 100 kΩ wird mit der AC-ZPC Typ 2-Methode eine gemittelte absolute Abweichung von 0.087% erreicht, was 20% weniger ist als bei den DC-ZPC-Methoden.:1 Introduction 2 Theoretical background 3 Measurement methods for 2D sensor matrices 4 Novel methods for impedimetric sensor matrices 5 Performance in reducing cross-talk effects 6 Practical validation of the proposed methods 7 Conclusion and outlook References Appendix A Operational amplifier model Appendix B Calculation of the resistive and capacitive parts of a time constant unit Appendix C Supplements to performance investigation