Post graduate dissertations (Theses) of Electrical and Electronic Engineering (EEE) http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/56 2026-05-06T13:33:25Z 2026-05-06T13:33:25Z Asif Hossain Bhuiyan, Md. http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7315 2026-05-04T04:01:35Z 2025-05-19T00:00:00Z

Polarization insensitive electrically reconfigurable metasurface for metalensing at near infrared wavelength Choudhury, Dr. Sajid Muhaimin; Asif Hossain Bhuiyan, Md.; 0422062304; 623.8/ASI/2025 The conventional fiber communication band at 1.55 µm is approaching its capacity limit due to the growing demand for high-speed and large-volume data transmission. In re- sponse, the 2 µm waveband is emerging as a promising candidate for next-generation communication systems, offering higher capacity and lower transmission loss. In align- ment with this technological shift, we present an optically engineered metasurface tai- lored for this waveband, suitable for applications such as fiber coupling and lensing. The proposed device exhibits polarization insensitivity and dynamic tunability between its transmissive (ON) and reflective (OFF) states. To enable this tunability, we incorpo- rate a novel phase change material, In3SbTe2 (IST), which features fast, reversible, and non-volatile transitions between its metallic and insulating phases. Electrical control is achieved by integrating indium tin oxide (ITO) as a micro-heating element, which modulates the optical properties of IST, thereby enhancing the device’s applicability in point-of-care systems. Utilizing the Finite-Difference-Time-Domain (FDTD) method, we demonstrate a modulation depth of 90%, a high focusing efficiency of 76%, and an ON-OFF switching ratio of 26 dB. The use of multiple thin IST layers ensures uni- form and energy-efficient switching, with a low energy requirement of 232.98 nJ/µm2. With its outstanding performance at the 2 µm communication band and dynamic mul- tifunctional capabilities, the proposed metasurface stands poised to transform future telecommunication technologies and broader optical systems.

2025-05-19T00:00:00Z Das, Sagar Kumar http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7308 2026-03-14T07:11:27Z 2025-05-28T00:00:00Z

Design and implementation of microwave plasma reactor for the production of silicon-nano-particle from locally available quartzite Chowdhury, Dr. Nadim; Das, Sagar Kumar; 0422062110; 623.813/DAS/2025 Plasma nanotechnology plays a crucial role in the large-scale synthesis of nanoparticles, which are widely used in various modern technological applications. Conventional microwave-based plasma reactors typically incorporate components such as circula- tor and directional couplers to protect the magnetron from reflected microwave power. However, these components significantly increase the overall system cost and complex- ity. In this study, a cost-effective alternative design for a microwave plasma reactor was proposed and analyzed using finite element simulations. The design replaces the conventional circulator with a three-decibel (3dB) waveguide bridge, which passively redirects reflected microwave energy away from the magnetron, thereby mitigating the risk of damage. During the design process, particular emphasis was given on mini- mizing microwave reflections on the magnetron side. This was achieved by optimiz- ing for a low reflection coefficient and a low Voltage Standing Wave Ratio (VSWR), ensuring minimal power loss and enhanced operational stability. An operational mi- crowave plasm reactor was successfully fabricated using locally sourced and affordable components. The functionality of the system was demonstrated by synthesizing fumed silica nanoparticles, which were subsequently characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). However, sili- con nanoparticles production from quartz is also possible using the plasma reactor. But due to some complexity this work has been suggested as future prospect for further study and analysis. This alternative reactor design provides a practical and economical solution for microwave plasma generation, eliminating the need for expensive compo- nents while maintaining effective performance. It holds promising potential for a wide range of applications, including nanoparticle synthesis, chemical processing, biomass conversion, and waste treatment.

2025-05-28T00:00:00Z Saha, Sudipta http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7235 2026-01-06T04:22:03Z 2025-04-15T00:00:00Z

Beryllium sulfide monolayer as a biosensor for early lung disease detection Kawsar Alam, Dr. Md.; Saha, Sudipta; 0423062317; 623.81/SAH/2025 Considerable attention has been directed towards the prognosis of lung diseases primarily due to their high prevalence. Despite advancements in detection technologies, current methods such as computed tomography, chest radiographs, bold proteomic patterns, nuclear magnetic resonance, and positron emission tomography still face limitations in detecting diseases related to the lungs. Consequently, there is a need for swift, non-invasive and economically feasible detection methods. Our study explores the interaction between BeS monolayer and breathe biomarkers related to lung disease utilizing the density functional theory (DFT) method. Through comprehensive DFT analysis, including electronic properties analysis, charge transfer evaluations, work function, optical properties assessment and recovery times, the feasibility and efficiency of BeS as a VOC (volatile organic compound) detection are investigated. Findings reveal significant changes in bandgap upon VOC adsorption, with notable alteration in work function for selective compounds. Optical property analyses demonstrate the potential for selective detection of biomarkers within specific wavelength ranges. Moreover, the study evaluates the impact of electric fields and strain on VOC-2D BeS interaction. Furthermore, the desorption of these VOCs from the BeS surface can be achieved through a heating process or under the illumination of UV light. This feature enables the reusability of the 2D material for biosensing applications. These findings highlight the potential of the BeS monolayer as a promising material for the sensitive and selective detection of breath biomarkers related to lung disease.

2025-04-15T00:00:00Z Shahruk Hossain http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7223 2025-12-09T06:59:44Z 2025-04-15T00:00:00Z

Multi-speaker end-to-end text to speech synthesis for low resource languages Ariful Haque, Dr. Mohammad; Shahruk Hossain; 1018062228; 623.99/SHA/2025 This thesis presents a high-quality, end-to-end multi-speaker text-to-speech (TTS) system for Bangla - a language spoken by millions yet lacking in open-source, high- quality speech resources. TTS systems have broad applications, including virtual assistants, audiobooks, dubbing, and accessibility tools. Despite Bangla’s large speaker base, its representation in modern open-source speech synthesis remains limited. Motivated by this gap, and the lack of accessible tooling for building contemporary TTS systems in Bangla, this work presents a curated speech dataset, tentatively named Bani, compiled from publicly available corpora and community- driven projects. To address this, a curated dataset - tentatively named Bani - was compiled from public and community-driven sources. A key contribution is a remastering pipeline using deep learning-based denoising and enhancement, substantially improving audio quality for TTS training. Bani served as the foundation for training single-speaker and multi-speaker TTS models. The architecture is based on the Variational Inference with Adversarial Learning for end-to-end TTS (VITS) model, with two core modifications intro- duced in this work: explicit duration modeling and integration of a pretrained speaker embedding model jointly trained with the system. These changes aimed to improve convergence, speaker similarity, and synthesized speech naturalness. Evaluation combined objective metrics - Mel-Cepstral Distortion (MCD), tran- scription error rates, and speaker similarity - with subjective Mean Opinion Score (MOS) tests from native Bangla speakers (1=poor, 5=excellent). The modi- fied multi-speaker model achieved a MOS of 3.64 ± 0.48, surpassing the baseline (3.46 ± 0.50) and single-speaker (3.10 ± 0.61) models. Objective scores showed a 10% drop in MCD and 9.5% boost in speaker similarity. A commercial Google Bangla TTS system scored 4.12 ± 0.33. These results show that both audio re- mastering and architectural changes significantly enhance perceived and measured synthesis quality, while explicit duration modeling improves training efficiency without sacrificing fidelity.

2025-04-15T00:00:00Z