A load-enhanced methodology has been proposed to enable the in situ detection, localization, and characterization of damage in metallic plate-like structures using Lamb waves. A baseline-free load-differential method using the delay-and-sum imaging algorithm is proposed for defect detection and localization. The term “load-differential” refers to the comparison of recorded ultrasonic signals at various levels of stress. Defect characterization is achieved by incorporating expected scattering information of guided waves interacting with defects into the minimum variance imaging algorithm, and a method for estimating such scattering patterns from the measurements of a sparse transducer array is developed. The estimation method includes signal preprocessing, extracting initial scattering values from baseline subtraction results, and obtaining the complete scattering matrix by applying radial basis function interpolation. The factors that cause estimation errors, such as the shape parameter used to form the basis function and the filling distance used in the interpolation, are discussed. The estimated scattering patterns from sparse array measurements agree reasonably well with laser wavefield data and are further used in the load-enhanced method. The results from fatigue tests show that the load-enhanced method is capable of detecting cracks, providing reasonable estimates of their localizations and orientations, and discriminating them from drilled holes, disbonds, and fastener tightness variations.

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.

Le diagnostic de l'occlusion dentaire reste actuellement un défi majeur pour les chirurgiens-dentistes. Des outils dédiés existent, comme le papier à articuler et le T-Scan®, mais sont limités pour diverses raisons. L'objectif de cette thèse est alors de développer un nouvel outil sous forme de matrice de capteurs de pression sur substrat flexible alliant les avantages des outils nommés précédemment, à savoir un produit électronique, informatisé et de faible épaisseur pour ne pas être intrusif. Nous avons choisi une technologie piézorésistive et l'utilisation de jauges de contrainte en silicium microcristallin. Ce matériau est déposé à basse température (< 200°C) directement sur substrat Kapton® par PECVD (Plasma Enhanced Chemical Vapor Deposition) dans une perspective de faible coût. Ces jauges ont d'abord été caractérisées mécaniquement et électriquement lors de tests de courbure. Les facteurs de jauge longitudinaux et transversaux du silicium microcristallin ont été étudiés afin de maîtriser son comportement sous déformation. Les dispositifs restent fonctionnels jusqu'à des contraintes de 0,6 %, à partir de laquelle des dégradations apparaissent. Ces valeurs de contraintes permettent d'atteindre des rayons de courbure de l'ordre du millimètre pour des substrats de 25 µm d'épaisseur. Deux types de matrices ont ensuite été développées : une première de 800 jauges pour l'étude de la surface occlusale d'une dent puis une seconde de 6400 jauges pour l'étude d'une moitié de mâchoire. Dans les deux cas, des corrélations intéressantes entre le papier à articuler et nos réponses électriques ont été observées lors de caractérisations en conditions « semi-réelles » à l'aide d'un articulateur dentaire. Ces deux prototypes ont ainsi permis une preuve de concept fonctionnelle de l'objectif visé en utilisant des jauges en silicium microcristallin. / Dental occlusion diagnosis is still a major challenge for dentists. A couple of tools are dedicated to occlusal analysis, such as articulating papers and the T-Scan® system, but they are limited for various reasons. That's why, the goal of this thesis is to develop a novel system consisting in pressure sensor arrays on flexible substrates combining the positive aspects of both previously cited tools: an electronic and computerized system, on a very thin non-invasive flexible substrate. We chose a piezoresistive technology based on microcrystalline silicon strain gauges and 25-µm- or 50-µm-thick Kapton® substrates. Microcrystalline silicon is deposited directly on plastic at low temperature (< 200°C) using PECVD technique (Plasma Enhanced Chemical Vapor Deposition) in a cost-effective solution perspective. Strain gauges have firstly been characterized using bending tests. Longitudinal and transversal gauge factors have been studied in order to understand the behavior of our deposited materials under bending. Those gauges remained functional until strains up to 0.6 % and degradations appeared for higher values. These values correspond to bending radius on the order of 1 mm for 25-µm-thick substrates. Then, those gauges have been integrated in arrays with two different designs: one was an 800-element array to study the occlusal surface of one tooth, and the second was a 6400-element array to study the occlusal surface of a hemiarcade. Those prototypes have showed interesting correlations between articulating paper marks and our electrical responses during characterizations using a dental articulator to simulate a human jaw. Thus, we have developed in this work a proof-of-concept of a flexible strain sensor using microcrystalline silicon dedicated to dental occlusion diagnosis.

This work deals with the further development of a method for Direction of Arrival (DOA) estimation based on the Discrete Fourier Transform (DFT) of the sensor array output. In the existing DFT-based algorithm, relatively high SNR is considered, and it is assumed that a large number of sensors are available. In this study an overview of some of the most commonly used DOA estimation techniques will be presented. Then the performance of the DFT method will be analyzed and compared with the performance of existing techniques. Two main objectives will be studied, firstly the reduction of the number of sensors and secondly the performance of the DFT based technique in the presence of noise. Experimental simulations will be presented to illustrate that in absence of noise, the proposed method is very fast and using just one snapshot is sufficient to accurately estimate DOAs. Also, in presence of noise, the method is still relatively fast and using a small number of snapshots, it can accurately estimate DOAs. The above mentioned properties are the result of taking an average of the peaks of the DFTs, X_n (k), obtained from a sequence of N_s snapshots. With N_s sufficiently large, the average over N_s snapshots approaches expected value. Also, the conditions that should be satisfied to avoid overlapping of main-lobes, and thus loosing the DOA of some signals, in the DFT spectrum are examined. This study further analyzes the performance of the proposed method as well as two other commonly used algorithms, MUSIC and conventional beamformer. An extensive simulation was conducted and different features of the spatial DFT technique, such as accuracy, resolution, sensitivity to noise, effect of multiple snapshots and the number of sensors were evaluated and compared with those of existing techniques. The simulations indicate that in most aspects the proposed spatial DFT algorithm outperforms the other techniques. / Graduate

In recent years (Of late year)microelectronic technology significantly affected in the field of sensor technology, especially in the field of electrochemical sensors. This thesis deals with design and construction of thick-film voltammetric sensors array. The reason for proposal of voltammetric sensors array is to increase of speed, increase the accuracy and extension possibilities measurement compared with common systems.By reason of increase of sensitivity of these sensors it is efficient use the potentiostat chip for measurement output signal. Created sensors must fulfill the specified parameters and also requirements of thick-film technology. Next step is design the basic blocks of electronic circuit used to evaluate the measured values.

In der vorliegenden Arbeit wird die Entwicklung eines auf mikromechanischen Sensorstrukturen basierenden Schwingungsmesssystems dargestellt. Die Besonderheit besteht im frequenzselektiven Wirkprinzip. Der Sensor siebt an seiner Resonanzstelle aus einem breitbandigen Anregungssignal ein schmales Band heraus und unterdrückt die anderen Frequenzbereiche. Auf diese Weise werden ohne Fourier-Transformation direkt spektrale Informationen gewonnen. Weiterhin sind die Resonanzfrequenz und damit der Messbereich mittels elektrostatischer Kräfte in einem weiten Bereich abstimmbar.

Conductive polymer composite sensors have shown great potential in identifying gaseous analytes. To more thoroughly understand the physical and chemical mechanism of this type of sensors, a model was developed by combining two sub-models: a conductivity model and a thermodynamic model, which gives a relationship between the vapor concentration of analyte(s) and the change of the sensor signals. In this work, 64 chemiresistors representing eight different carbon concentrations (8–60 vol.% carbon) were constructed by depositing thin films of a carbon black–polyisobutylene composite onto concentric spiral platinum electrodes on a silicon chip. The responses of the sensors were measured in dry air and at various vapor pressures of toluene and trichloroethylene. Three parameters in the conductivity model were determined by fitting the experimental data. It was shown that by applying this model, the sensor responses can be predicted if the vapor pressure is known; furthermore the vapor concentration can be estimated based on the sensor responses. This model will guide the improvement of the design and fabrication of conductive polymer composite sensors for detecting and identifying organic vapors. A novel method was developed to optimize the selection of polymeric materials to be used within a chemiresistor array for anticipated samples without performing preliminary experiments. It is based on the theoretical predicted responses of chemiresistors and the criterion of minimizing the mean square error (MSE) of the chemiresistor array. After the number of chemiresistors to be used in an array and the anticipated sample chemistry are determined, the MSE values of all combinations of the candidate chemiresistors are calculated. The combination which has the minimum MSE value is the best choice. This can become computationally intensive for selection of polymers for large arrays from candidates in a large database. The number of combinations can be reduced by using the branch and bound method to save computation time. This method is suitable for samples at low concentrations where thermodynamic multi-component interactions are linear. To help users apply this polymer selection method for the sensors, a website including 10 solvents and 10 polymers was developed. Users can specify a target sample and obtain the best set of polymers for a sensor array to detect the sample. The activities of trichloroethylene and toluene in polyisobutylene were measured at very low concentrations. The activities for toluene are consistent with published values at higher concentrations. The values for trichloroethylene are a new contribution to the literature.

Yes / The issue of asset tracking in dense environments where the performance of the global positioning system (GPS) becomes unavailable or unreliable is addressed. The proposed solution uses a low-profile array of antenna elements (sensors) mounted on a finite conducting ground. A compact-size sensor array of six electrically small dual-band omnidirectional spiral antenna elements was designed as a front end of a tracker to operate in the 402 and 837 MHz spectrum bands. For the lower band, a three-element superposition method is applied to support estimation of the angle of arrival (AOA), whereas all six sensors are employed for the higher band. A low complexity and accurate AOA determination algorithm is proposed, the projection vector (PV), and this is combined with the array mentioned. Orthogonal frequency division multiplexing (OFDM) is integrated with the PV technique to increase the estimation resolution. The system was found to be suitable for installation on the roof of vehicles to localize the position of assets. The proposed system was tested for the tracking of nonstationary sources, and then two scenarios were investigated using propagation modeling software: outdoor to outdoor and outdoor to indoor. The results confirm that the proposed tracking system works efficiently with a single snapshot. / European Union Horizon 2020 Research and Innovation Program; 10.13039/501100009928 - Higher Committee for Education Development (HCED), Iraq

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