http://depot.umc.edu.dz/handle/123456789/5505 2026-04-30T13:06:09Z http://depot.umc.edu.dz/handle/123456789/14825 Contrôle d’attitude d’un microsatellite, analyse multi objectives de la boucle de retour. Benenia, Meriem; Benslama, Malek This thesis deals with the study of attitude control systems and the development of control laws to ensure the stabilization of the attitude system. This was achieved by combining the dynamic systems control theory and applying this principles on the satellite attitude control system. This research was carried out from a theoretical point of view by the design of two control laws to treat the problem in two different ways. To achieve the goal a satellite attitude modeling study is first approached using mathematical relationships governing the rigid bodies rotational motion, several attitude representations have been proposed. The work focused mainly on the sliding mode control, which has the property of robustness against the model uncertainties, and external disturbances. The control concept considered in this thesis was to discuss the different characteristics of the sliding surfaces by adding a new selection criterion. In addition to the study of a PD based controller, with an estimator to compensate the effect of uncertain or unknown parameters of inertia and disturbances. In addition to the theoretical treatment, the thesis contains simulation results for the developed controllers. 2018-10-21T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14808 D´etection automatique CFAR de cibles dans les SAR imageurs. Madjidi, Hicham; Laroussi, Toufik In this PhD Thesis, we address the problem of automatic ship detection acquires from SAR (Synthetic Aperture Radar) images in complex marine environments. Assuming a non-Gaussian sea clutter with no prior knowledge about the presence or not of any clutter edge and/or interfering targets in the sliding reference window, we propose and analyze the detection performances of three CFAR (Constant False Alarm Rate) detectors in homogeneous and heterogeneous Log- normal or Weibull sea clutter. In doing this, we first analyze the QM-CFAR (Quantile Matching-Constant False Alarm Rate) detector in a Weibull background. This detector addresses the problem of fixed-point(s) censoring detector in multiple target situations. Specifically, assuming a non-stationary Weibull clutter with the presence or not of interfering targets, the QM and the MLE (Maximum Likelihood Estimator) are concomitantly used to allow the proposed detector to perform robustly in multiple target situations with a priori unknown Weibull parameters. MC (Monte-Carlo) simulations show that, compared to recent existing CFAR algorithms, the QM-CFAR detector provides robust and accurate estimates of the Weibull distribution parameters and achieves less degradation of the PD (Probability of Detection) in multiple target situations. Then, for the sake of reducing the effect of outliers on the SD (Standard Deviation) based detector, we suggest the use of the MAD (Median Absolute Deviation), as it is a robust and fast alternative to SD. The newly presented MAD-CFAR detector’s detection threshold can be computed straightforwardly; yielding a significant gain in the PD and processing time. Finally, we address the problem of lower and upper automatic censoring of unwanted samples from a rank ordered data of reference cells, i.e., bilateral or dual automatic censoring. To this end, we suggest the use of CFCR (Constant False Censoring Rate) and CFAR detection biparametric thresholds to censor lower and upper outliers. In doing this, we propose a novel estimator AML (Approximate Maximum Likelihood), which generates closed-form expressions of lognormal distribution parameters with no iterations needed. We showed that in a log-normal heterogeneous background, the AML-CFAR ship detector acquires a fair PFA (Probability of False Alarm) regulation, a high detection performance and a fair time cost with regard to the challenging state-of-the-art detectors. 2023-07-04T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14752 Etude d’un capteur chimique à base d’un transducteur à électrodes interdigitées. Dallah, Khalid; Bellel, Azzedine The extreme volatility of volatile organic compounds (COVs) molecules gives them the ability to diffuse far from their source of emission, resulting in direct and indirect impacts on ecosystems and human health. The exposure to high concentrations of certain COVs even for short term may cause serious irreversible effects or disease. The detection and the evaluation of the chemical species activity present in the environment require very efficient and often expensive analysis materials. As an alternative method of analysis, is to design a chemical sensor with equivalent characteristics in terms of reliability, simplicity, speed and selectivity at lower cost. Chemical sensors are often simple and compact devices that transform the chemical signal into an electrical signal that can be easily exploited. Capacitive type sensors have generated considerable interest because they have a low fabrication cost, can operate at room temperature, consume a very small amount of energy and can be easily integrated into the associated electronics circuit. In this work, chemical sensors based on IDCs (interdigital capacitance) and organosilicon films were elaborated and tested for the detection of organic volatile compounds. Aluminum interdigital electrodes have been deposited on glass substrates using microelectronics technique with different geometrical configurations. The sensitive films used as dielectric layers were deposited by PECVD technique from the HMDSO monomer with different pressures. The sensitivity of the sensors in terms of capacity change was assessed for different concentrations of methanol, ethanol and acetone ranging from 100 ppm to 400 ppm. The simulation results showed that the IDC structural based sensors can be successfully designed by COMSOL Multiphysics software using the finite element method. The observed results on the variation of the capacity of the structure show that an increase in the width and the number of fingers induces a significant increase in the value of the capacity. On the other hand, the thickness of the sensitive layer must be taken into account because it greatly affects the total capacity of the structure. The simulation work revealed the optimal design of the IDC structure for specific applications such as chemical sensors. Four types of sensors were manufactured with sensitive layers deposited with different pressure of the monomer to assess its impact on the sensitivity and affinity of the sensor. Then, four other capacitive sensors based on interdigitated structures were manufactured with different spacing between electrodes to evaluate the effect of the gap on the sensor’s detection properties. The variation in monomer pressure during plasma discharge produces layers with different detection properties which have been correlated with the results of characterizations by FTIR, contact angle and AFM. The results of COV detections were interpreted by the growth of a nanoporous structure with a large specific surface area associated with a highly hydrophobic surface behavior. The sensor manufactured with a low gap (36 µm) and high monomer pressure (50 Pa) has the best detection characteristics with a sensitivity of about 0.32, 0.24 and 0.20 pF/ppm towards methanol, ethanol and acetone, respectively. All the developed sensors show a good affinity to methanol vapors due to their small molecular sizes and high values of the dielectric constant. The performance of the sensors studied in terms of sensitivity values and detection limit obtained from measurements at different analyte concentrations indicates that these sensors have good response characteristics compared with those reported in the literature and a potential application for the detection of volatile organic molecules. 2023-07-09T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14729 Etude théorique d’un capteur optique à cristaux photoniques à base d’un résonateur en anneau en forme de U. Alioueche, Ahmed; Benmerkhi, Ahlem This work is a proposal for a new structure of voltage sensor based on photonic crystals; it is composed of U-shaped photonic crystal ring resonator placed between two waveguides. The sensors structures have been changed in order to improve important sensor parameters such as quality factor and transmission. A large quality factor induces a good light confinement in semiconductor defect, making the photon more sensitive to voltage variation. The studied device offers nearly 100% transmission efficiency and a quality factor about 24064. The electro-optical materials properties are ideally suited for narrow-channel optical communication systems and sensing applications. The values of about 622.22 nm / RIU, 1.12 nm / V and 2.24 nm per kV / mm have been obtained for refractive index sensitivity (Sn), the voltage sensitivity (SV) and the electric field sensitivity (SE), respectively. The results of the simulation presented in this thesis are carried out and analyzed by the two methods PWE and FDTD, using the Rsoft software. The simulation results presented in this thesis are carried out and analyzed by the two methods plane wave expansion (PWE) and finite-difference time-domain (FDTD) using the Rsoft software. 2023-05-04T00:00:00Z