http://depot.umc.edu.dz/handle/123456789/5505 Sat, 17 Oct 2026 20:58:08 GMT 2026-10-17T20:58:08Z http://depot.umc.edu.dz/handle/123456789/14859 La modélisation de nouvelles structures dans le domaine du guidage et du filtrage des ondes acoustiques. Amrani, Hamza; Grine, Farouk Acoustic metamaterials represent an exciting frontier in the control of waves and vibrations. The precise control of acoustic waves is fundamental for key technological applications, ranging from sound insulation to ultrasonic detection. In this work, the design, modeling, and analysis of novel two-dimensional phononic crystal (PnC) structures that integrate the architecture of auxetic materials are addressed. The objective is double: to create new structures capable of generating and controlling wide and tunable phononic bandgaps (PBGs), and to control the direction of energy flow and the propagation of acoustic waves. The study relies on the Finite Element Method (FEM) and the rigorous application of the Floquet-Bloch theory for the calculation of dispersion relations. We introduce and analyze two specific auxetic architectures derived from star-shaped honeycomb structure: the concave circular-headed structure and the Arabesque structure. A parametric study is performed on the geometric variables to optimize structural and vibrational performances. The results obtained not only confirm the auxetic behavior of these designs but demonstrate their excellent ability to open robust complete PBGs. By exploiting Iso Frequency Contours (EFCs), we have modeled the phenomenon of self-collimation. This mechanism proves that these PCs can naturally focus and guide vibrational energy along precise trajectories, offering a promising trajectory for the unconventional manipulation of waves. This project opens concrete prospects for the development of high-precision acoustic insulation and filtering devices. Thu, 18 Dec 2025 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14859 2025-12-18T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14858 Contributions to fractional-order fault-tolerant control of nonlinear systems. Daoudi, Islam; Chemachema, Mohamed The primary aim of this thesis is to develop adaptive control strategies tailored for specific categories of uncertain single-input single-output (SISO) and interconnected multi-input multi-output (MIMO) fractional-order nonlinear systems. The investigation includes the analysis of the effect of saturation on the control inputs along with the external disturbances on the dynamics of systems. In all the proposed methodologies, neural networks or fuzzy logic systems serve as universal approximators to estimate the unknown nonlinear dynamics of the systems. The architectures of the proposed controllers address the well-known challenges associated with complexity explosion while circumventing the conventional back-stepping technique thanks to the introduction of a new fractional systems transformation into the controllable Bronovsky form. By using the implicit function theorem and the strictly positive real (SPR) property, output feedback approaches become feasible. Compared to similar approaches, the proposed adaptive neural/fuzzy controllers exhibit minimal online learning parameters. Furthermore, the integration of the Eventtriggered mechanism optimizes resource utilization by updating control actions only when necessary, thereby reducing computational burden and communication overhead. Additionally, stability analysis of all control loops is conducted using the Lyapunov method, and simulation results are provided for each scheme to demonstrate its efficacy. Mon, 22 Dec 2025 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14858 2025-12-22T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14857 Conception d’un coupleur optique Chergui, Imane; Labbani, Amel The primary objective of this thesis is to develop models and optimize the performance of optical switches and power splitters based on directional couplers. These devices are essential components in optical telecommunication systems, as they enable the switching and splitting of optical signals into multiple paths. A key advantage of directional couplers over conventional switches and power splitters is their significantly lower radiation losses, which enhance system efficiency. To analyze the optical properties and evaluate the performance of these devices, simulations were conducted using RsoftCAD software, employing the FiniteDifference Time-Domain (FDTD) method and the Plane Wave Expansion (PWE) method. The coupler consists of two linear waveguides separated by a row of silicon columns. Various technologies have been proposed to enhance the performance of photonic crystal-based directional couplers (DCs) and minimize the coupling length between the two waveguides. The proposed directional coupler replaces the central row of silicon rods with core/shell (C/S) particles, which are created by perforating the silicon rods to introduce air holes. The internal and external radii of the silicon rods in the central row of the C/S structure are denoted as rin and rout, respectively. The modified directional coupler reduces the coupling length (Lc) to 5a, where a is the lattice constant. Simulation results show that increasing the inner radius rin enhances the coupling coefficient while reducing the coupling length (Lc). The first devices designed using the new directional coupler architecture are 2×2, 3×3, and 4×4 optical switches based on photonic crystals. The basic structure consists of rows of silicon (Si) rods arranged in an air medium on a hexagonal lattice. The influence of varying the inner and outer rods, as well as modifications to the permittivity or refractive index of the core and shell, on the coupling length and output power was also studied. Simulation results demonstrate that the three proposed switches exhibit high normalized transmission, negligible reflection, fast delay times, and low crosstalk (measured in dB). The areas of the 2×2, 3×3, and 4×4 optical switches are 185.35 μm², 273.53 μm², and 356.53 μm², respectively.The modified directional coupler reduces the coupling length (Lc) to 5a, where a is the lattice constant. Simulation results show that increasing the inner radius rinenhances the coupling coefficient while reducing the coupling length (Lc). The first devices designed using the new directional coupler architecture are 2×2, 3×3, and 4×4 optical switches based on photonic crystals. The basic structure consists of rows of silicon (Si) rods arranged in an air medium on a hexagonal lattice. The influence of varying the inner and outer rods, as well as modifications to the permittivity or refractive index of the core and shell, on the coupling length and output power was also studied. Simulation results demonstrate that the three proposed switches exhibit high normalized transmission, negligible reflection, fast delay times, and low crosstalk (measured in dB). The areas of the 2×2, 3×3, and 4×4 optical switches are 185.35 μm², 273.53 μm², and 356.53 μm², respectively. Moreover, the proposed switches are compact and can be integrated into optical telecommunication systems. The second set of devices in this thesis focuses on the design and modeling of 1×2 and 1×4 Y-junction power splitters, based on the new directional coupler architecture. These devices split the signal into two or four paths with minimal radiation losses, particularly in curved regions. An ideal power splitter uniformly divides the optical signal injected at its input into multiple outputs without any radiation loss. To minimize radiation losses while maximizing total transmission, an optimization technique was proposed that involved modifying the inner radii of the (C/S) structure. The optical properties of the optimized splitters are significantly improved, achieving total transmission of up to 99% of the incident light. The sizes of the proposed 1×2 and 1×4 Y-junction dividers are 177.63 μm² and 449.45 μm², respectively. These devices are highly compact and deliver excellent splitting performance, making them particularly suitable for applications in optical telecommunications and photonic integrated circuits. Thu, 27 Nov 2025 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14857 2025-11-27T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14851 Contribution à la modélisation d’un diviseur de puissance a base des cristaux photoniques Moumeni, Imène; Labbani, Amel Photonic crystals are periodic dielectric structures, at the wavelength scale, and with high index contrast. In such a medium, the propagation of light exhibits properties, if not exotic, at least surprising. These structures exhibit a unique optical property which is the photonic band gap (PBG) in which no electromagnetic mode can propagate. This BPG is very interesting for several applications in the field of optical telecommunication such as the splitter. Ideally, the splitter should divide the input power equally between the output channels without reflection losses and should be of compact size. In this work, a contribution was made to design power splitters in Y-junctions 1×2, 1×4, and 1×8 based on photonic crystals. These devices play a crucial role in optical telecommunications systems. To improve the performance of these splitters, optimization techniques were proposed. Advanced optimization methods were implemented, such as increasing the radius of the holes in curved areas and adding ring slots. These modifications help minimize losses induced by the bends and junctions of the structures. Our power splitters achieve near perfect transmission (≈ 100%), a relatively wide bandwidth (≈ 3.5%), and remarkable compactness. Compared to our results, previous works have shown lower transmissions (ranging from 86% to 99%) and narrower bandwidths, generally between 1.5% and 3%. Thus, our devices exhibit a transmission improvement of +5% to +15%, and a bandwidth increase of +17% to +133% compared to published works. The power splitters were simulated using RSoftCAD software, employing the Finite-Difference Time-Domain (FDTD) method and the Plane Wave Expansion (PWE) method. A modified T-shaped duplexer, with an area of 272.214 μm², was also proposed. This compact device can be used in integrated optics for applications in FTTH networks. Mon, 13 Oct 2025 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14851 2025-10-13T00:00:00Z