Department of Electronics and Electrical Egineering

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Acoustic Charge Transport in Organic Semiconductors using Surface Acoustic Wave Devices
(2024) Mishra, Himakshi
A surface acoustic wave (SAW) is a periodic deformation of the surface of an elastic material propagating at the surface primarily as a linear wave front. Despite the fact that their existence had already been established by Lord Rayleigh in 1885, it wasn't until 1965, through the development of the interdigital transducer (IDT), that they were first utilised for various applications. It is now feasible to stimulate and detect SAWs on a piezoelectric surface in an effective manner. It is established that SAW devices have a very broad range of applications in several fields. Professional radar and communications systems extensively use SAW delay lines, band pass filters, resonators, oscillators, and matched filters. SAW can also be employed as a pressure, humidity, and temperature sensor for chemical sensing and analysis purposes. SAW has very low velocity and narrow wavelengths, reducing size and weight and hence, can be mass manufactured. When a semiconductor comes into interaction with SAW, the acoustic deformations induced by SAW have a significant impact on the semiconductor's energy bands and, consequently, its electrical characteristics. SAW-induced band edge modulation leads to the spatial separation of charge carriers of a semiconductor. Furthermore, the energy and momentum carried by SAW are transmitted to charge carriers resulting in a dragging force on them. This phenomenon is known as the acoustoelectric effect, and the transport caused by this effect is termed acoustic charge transport (ACT). The process of ACT has been demonstrated by several researchers in inorganic semiconductors either by injecting carriers through an input bias or optically generating carriers. Organic semiconductors are increasingly being used as the active layer in a wide variety of innovative technologies due to their solution-processability, lightweight, and flexibility. In contrast to inorganic semiconductors, organic materials form a polycrystalline layer, and their charge transport is mostly limited by grain boundaries. Numerous studies have been done, throughout the past few years, to investigate the factors affecting and contributing to the charge transport of organic semiconductors. However, the interaction of an acoustic wave with these materials has not been reported yet. The primary objective of the thesis is to observe the charge transport of ambipolar electrons and holes in organic semiconductor films by means of acoustic waves and to investigate potential acousto-optic applications that may result from this interaction.
Adaptive compensation based actuator fault tolerant control of nonlinear uncertain systems with emphasis on transient performance improvement
(2018) Chakravarty, Arghya
Growing demands of reinforced reliability, survivability, safety and stringent performance requirements in complex critical systems have led to the inception of a new control paradigm, widely known as Fault Tolerant Control (FTC). Systems equipped with an FTC module are, in general, presumed to be resilient to uncertain eventualities of faults and failures. Ever since its outset, FTC has been well recognized as a promising research domain and extensive contributions have been reported so far; however largely in the context of linear dynamical systems. Given the fact that almost all physical systems existing in nature exhibit an inherent nonlinear behavior; FTC schemes for linear systems may not be fruitful when the operating regime is desired to large and precise fault tolerant control performance also becomes a critical design attribute. In addition to actuator faults/failures, the presence of unknown parametric uncertainties, modeling imperfections and external disturbances combined with structural limitations in such systems pose numerous challenges to the problem of an effective active FTC design. Therefore, this thesis resorts to an fault estimation based FTC (FE/FTC) architecture and attempts to propose some new adaptive FTC methodologies for nonlinear uncertain dynamical systems assuming the occurrence of unanticipated actuator failures. The emphasis of the design algorithms is laid on achieving an improvement in start up and post failure transients without yielding to any decrement in input performance (quantified in terms of total variation and energy of input signal). Therefore in this thesis, such ambitious objectives are attained through an amalgamation of robust control ideas with the inherent online learning capabilities of adaptive control. The proposed control laws exhibit promising fault tolerant performance, affirm all theoretical propositions and qualifies well for applicability to practical systems.
Adaptive controller design for nonlinear uncertain systems using multiple model based two level adaptation technique
(2018) Pandey, Vinay Kumar
Adaptive control technique is a popular and successful control strategy for controlling nonlinear uncertain systems. However, using adaptive control schemes in parametrically uncertain environments often leads to poor transient response and sluggish steady state response. Use of multiple estimation models has been found to be promising in addressing these issues. This thesis proposes an adaptive control method for nonlinear uncertain systems using multiple model based two level adaptation (MMTLA). At the first level, multiple models are used and a single model at the second level is proposed by combining these first level models for controlling different classes of nonlinear uncertain systems. The proposed control method is applied to nonlinear single-input single-output (SISO) systems with linear and nonlinear parameterizations, nonlinear multiple-input multiple-output (MIMO) coupled systems and nonlinear MIMO model following control systems. For all the considered systems, state transformation and feedback linearization method have been used to algebraically transform nonlinear system dynamics to linear ones. The unknown system parameters are assumed to be bounded within a set of compact parameter space. Multiple estimation models are distributed evenly in this region of uncertainty and their unknown parameters are tuned. The tuning laws for estimator parameters have been obtained using Lyapunov stability criterion. Stability analysis using Lyapunov's criterion has been carried out to assess the close loop stability and tracking error convergence of the overall system. The transient and steady state performances using the proposed scheme are evaluated by performing both simulation and experimental studies, which confirm superior performance of the proposed control technique over some existing adaptive control methods. The commonly known problems with adaptive control systems like oscillatory transient response, poor parameter convergence and sluggish response are found to be improved considerably by using the proposed multiple model based two level adaptation approach.
Adaptive Network based Fuzzy Inference System (ANFIS) as a Tool for System Identification with Special Emphasis on Training Data Minimization
(2009) Buragohain, Mrinal
Nearly two decades back nonlinear system identification consisted of several ad-hoc approaches which were restricted to a very limited class of systems. However, with the advent of the various soft computing methodologies like neural networks, the fuzzy logic and the genetic algorithm combined with modern structure optimization techniques, a wider class of systems can be handled at present. Complex systems may be of diverse characteristics and nature. These systems may be linear or nonlinear, continuous or discrete, time varying or time invariant, static or dynamic, short term or long term, central or distributed, predictable or unpredictable, ill or well defined. System outputs may be measurable or unmeasurable. Models of real systems are of fundamental importance in virtually all disciplines and hence there is a strong demand for advanced modeling, identification and controlling schemes. This is because models help in system analysis which in turn help to get a better understanding of the system for predicting or simulating a systemDs behavior. Also, system models facilitate application and validation of advanced techniques for controller design. Development of new processes and analysis of the existing ones along with their optimization, supervision, fault detection, and component diagnosis are all based on the models of the systems. As most of the real world systems are nonlinear in nature, an endeavor is made for modeling a nonlinear system in the present work. A linear system is considered to be a special case of the nonlinear system. The challenges involved in modeling, identification and control of a nonlinear system are too many and attempt has been made to tackle them by applying various soft computing methodologies. In most of the conventional soft computing methods the system modelling results are dependent on the number of training data used. It has been found that the modeling results improve as the number of training data increases. But in many complex systems the number of available training data are less and the generation of new data is also not cost effective. In such a scenario the system has to be modelled with the available data. The proposed modeling scheme hasD The results obtained by applying the proposed technique are comparable and in some cases superior to those obtained by using the conventional neuro-fuzzy model. D Comparable or superior results are obtained with this proposed model even though the number of data pairs used for system modeling here are less as compared to that used in the conventional methods. D It resulted in reduction of the number of computations involved. As the experiments were performed by using reduced number of specifically chosen data, the number of computations required to be performed also came down. been devised keeping such a possibility in mind. The results obtained by applying this proposed model are compared with the results obtained by using various statistical and genetic algorithm based fuzzy models and finally the relative merits and demerits involved with the respective models are discussed. The work embodied in the present thesis is concerned with optimal design of the conventionally existing soft computing based system models. The statistics based Full factorial design (FFD) and the V-fold cross validation technique are applied to...
Adaptive second order sliding mode control strategies for uncertain systems
(2013) Mandal, Sanjoy
The main objective of this thesis is to develop robust sliding mode control strategies for uncertain systems. More specifically, the aim of this thesis is to develop sliding mode control schemes which are successful in controlling systems affected by both matched and mismatched types of uncertainty. One major drawback suffered by conventional sliding mode controllers is the presence of high frequency oscillations in the control input known as chattering. Because of the discontinuous control action in sliding mode controllers, chattering becomes an inherent undesired phenomenon. Apart from chattering, another disadvantage faced by conventional sliding mode controllers is their design prerequisite of advance knowledge about the upper bound of the system uncertainty. This thesis is an attempt to provide solution for these two main limitations of conventional first order sliding mode controllers. The central focus of this thesis is to improve upon the existing sliding mode control techniques with the prime objective of chattering mitigation. An adaptive gain tuning mechanism which can estimate the uncertainty adaptively is proposed in this thesis. Hence prior knowledge about the upper bound of system uncertainty is no longer a necessary requirement in the proposed adaptive sliding mode controller. The basic idea of the proposed adaptive sliding mode controller is that the discontinuous sign function is made to act on the time derivative of the control input and the actual control signal obtained after integration is continuous and hence chattering is removed. The adaptive gain tuning strategy ensures that the controller gain is not overestimated. Based upon the core idea of adaptive sliding mode, various classes of sliding mode controllers are proposed in this thesis. In order to ensure smooth control action throughout the entire operating range, this thesis proposes an adaptive integral sliding mode controller. The integral sliding mode (ISM) algorithm eliminates the reaching phase. Therefore, invariance towards matched disturbances can be ensured from the very beginning by using this method. The proposed adaptive sliding mode control methodology is used to control nonlinear multiple input multiple output (MIMO) systems which are highly cross-coupled. The proposed con.
Addressing pitch Mismatch for Children's Automatic Speech Recognition
(2011) Ghai, Shweta
This thesis addresses the acoustic mismatch due to pitch differences between the adults' and the children's speech for children's automatic speech recognition (ASR) on adult's speech trained models. The motivation for the work is obtained through the study done on exploring various acoustic sources of mismatch: pitch, speaking rate, formant frequencies and glottal flow parameters (open quotient, return quotient and speed quotient) for children's ASR on adults' speech trained models. The effect of variations in each of these acoustic correlates across speech signals is studied on Mel frequency cepstral coefficient (MFCC) features and ASR models. Following that, their relative significance is explored for children's speech recognition on the adults speech trained models in a consistent setup. It is found that apart from the formant frequencies, the pitch is the other major source of acoustic mismatch between the adults' and the children's speech. The increase in the pitch of the signals is found to significantly increase the dynamic range and in turn the variances of the higher order coefficients of MFCC (C0DC12) features. Motivated by that, the pitch-robustness of perceptual linear prediction cepstral coefficient (PLPCC) and perceptual minimum variance distortionless response (PMVDR) cepstral coefficient features is studied to explore their efficacy for children's ASR on adults' speech trained models in comparison to MFCC features. It is found that MFCC features outperform PLPCC features while with suitable optimization of model order PMVDR features are more pitchrobust than MFCC features. However, the children's ASR performance obtained with MFCC features after explicit pitch normalization of children's speech is found to be comparable to that obtained with PMVDR features after optimization of its model order for children's speech. Following the observations, a pitch normalization algorithm is proposed which modifies the Mel filterbank during MFCC test feature extraction based on the average pitch of the test signal for children's ASR on adults' speech trained models. Also, a Mel cepstral truncation based method is proposed for reducing the pitch mismatch be-tween the training and the test data. The proposed algorithm automatically selects the appropriate length of the base MFCC features for each test signal without prior knowledge about the speaker of the test utterance. Significant improvements are obtained in the children's speech recognition performances using the proposed algorithms on the adults' speech trained models. Using the proposed adaptive MFCC feature truncation algorithm significant improvements are found in the children's and adults' ASR performances on children's speech trained models as well. The improvements obtained in the ASR performances with the proposed algorithms are also found to be additive to those obtained with the existing speaker normalization and model adaptation techniques viz., VTLN, MLLR and CMLLR. Keywords: Children's speech recognition, acoustic mismatch, pitch, speaking rate, glottal flow parameters, MFCC, PLPCC, PMVDR, Mel filterbank, cepstral truncation...
Advanced Spatial Modulation Schemes: Performance Analysis and Applications
(2020) Bhowal, Anirban
Spatial Modulation (SM) and its advanced versions are investigated for various applications in this thesis. Performance analysis of advanced spatial modulation (ASM) are carried out in terms of bit error rate (BER) and outage probability (OP). The ASMs considered are enhanced spatial modulation (ESM), spatial media based modulation (SMBM), optical ESM (OESM), optical generalized spatial modulation (OGSM), optical improved quadrature spatial modulation (OIQSM), transmit laser selection (TLS) combined with optical SM (TLS-OSM), hybrid SM (HSM) and transmit source selection (TSS) combined with HSM (TSS-HSM). Firstly, SM along with physical layer network coding (PLNC) is proposed for full-duplex wireless radio frequency (RF) communication. Closed form expressions of OP of such systems are provided in this thesis. Cascaded _ − μ channel model is considered for such communication. It is observed that such systems can achieve signal-to-noise ratio (SNR) gain of 8 dB over PLNC scheme. Secondly, ESM and SMBM are proposed for body area network (BAN) communication especially for sporting activities such as running and cycling. Performance analysis is carried out for both single input-single-output (SISO) system as well as multiple-input-multiple-output (MIMO) system employing the above mentioned ASM schemes in terms of BER and OP. Lognormal-4 (LN-4) channel is considered for BAN communication. It is observed that SMBM outperforms SM and ESM schemes. Another observation is that cycling has better BER and OP than running due to less body shadowing effects. Thirdly, optical SM (OSM) along with PLNC is proposed for full-duplex free-space optical (FSO) cooperative system. Bounds of OP are calculated for such systems. Further, in order to achieve higher spectral efficiencies in FSO communication, ASM techniques such as OESM, OGSM and OIQSM are proposed. BER, cost and power consumption analysis of the above mentioned ASM techniques are provided in the thesis. Gamma-Gamma (G-G) channel model with pointing error is considered for FSO communication. It is observed that OESM, OGSM, OIQSM and TLS-OSM gives better BER than the conventional OSM. Fourthly, SISO one-way and two-way relay based underwater optical wireless communication (UOWC) is proposed and performance analysis is carried out in terms of OP. OIQSM and TLS-OSM are proposed for UOWC cooperative communication. Performance analysis of such schemes are carried out in terms of OP and average symbol error probability (ASEP). Lognormal channel is assumed for UOWC. It is observed that OIQSM and TLS-OSM also outperform OSM for UOWC. Lastly, HSM and TSS are proposed for hybrid FSO/RF cellular communication. In this cellular system, base station (BS) to access points (APs) are assumed to be connected with FSO links and AP to mobile users are connected using RF links. FSO links are modelled as G-G channel whereas RF links are modelled as Rayleigh fading channel. Performance analysis is carried out in terms of OP. It is observed that TSS-HSM outperforms HSM and TSS based hybrid FSO/RF systems
(An) Intelligent Electric Vehicle Charging Infrastructure
(2022) Sah, Bikash
Electric vehicle charging infrastructure is the foundation for ensuring wider acceptance of electric vehicles (EVs). Governments and organisations worldwide are working on policies for deeper penetration of EVs in the transportation sector. The infrastructure comprises various stakeholder who communicates with each other. The communication ensures an optimal operation of each entity in the infrastructure, meeting the requirements of all the stakeholders. Although the present electricity infrastructure is able to support the charging of EVs, there are challenges of integrating bidirectional power flow between EVs and electric grid, developing appropriate communication infrastructure and support systems, motivating users to perform coordinated charging, and options to utilise EVs for ancillary services. Apart from the challenges in the electric grid, the requirement of fast charge with constrained battery degradation is another major challenge to persuade user acceptance. Henceforth, the work presented in the thesis proposes controllers, algorithms, estimation procedures, and techniques to develop an intelligent infrastructure that can perform coordinated charging with the least disturbances in the electric grid and meet the requirement of fast charge with constrained degradation at the user end.
Analog/RF circuit optimization using adjoint network sensitivity analysis and metaheuristics
(2018) Joshi, Deepak
The design methodology for analog and RF circuit sizing has evolved from “pen and paper” approach to an optimization-based scheme via simulation-based approach. In general, analog circuit designers derive design equations for circuit design (optimization) and solve them for a given set of specifications. Nowadays, automated problem solving is becoming more and more efficient and applicable due to the advent of computational intelligence approaches. Various numerical methods have been presented to study circuit performance. With the advent of new optimization-based methodologies, development of efficient circuit sizing approach has become essential for analog design process-flow. The performance evaluation of analog circuits, which undergoes a complicated design process, empowers circuit simulators to iteratively modify design variables through the use of optimization techniques. Analog circuit sizing problem is represented in the format of a standard numerical optimization problem. Although such analytical representation of analog circuit sizing problem varies with the type of applied optimization technique, a few equation-based optimization techniques have been proposed for single and multi-objective optimization of analog circuits in this thesis. The first technique is based on sensitivity analysis applied with the classical optimization approach. The sensitivity of a response with respect to the circuit’s parameters is determined by applying adjoint network sensitivity analysis (ANSA). The second technique is proposed using a hybrid of evolutionary algorithms (HPSO) for circuit sizing and, third proposed technique is, a multi-objective optimization (MHPSO) using metaheuristics is proposed for analog circuit optimization. An extended version (MHPSO-CD) for improved archive maintenance (using crowding distance), is also proposed. These methods are verified by optimizing test circuits, namely two-stage operational amplifier, an operational transconductance amplifier, low noise amplifier and standard multiobjective benchmarks.
Analysis and Automatic Detection of Aspirated Fricative and Aspirated Nasals
(2022) Rabha, Saswati
Unlike aspiration in stops, aspiration in non-stop consonants is quite rare. Most of the languages that have aspirated non-stop consonants are low-resource languages. Hence, data-driven, quantitative, and statistical analysis of their aspiration phenomena is fairly limited. From the literature review, it has been observed that there is still a need to explore a novel framework that will utilize the advantages of both linguistic and signal- processing knowledge-based approaches for acoustic-phonetic analysis and automatic classi cation of aspirated fricatives and aspirated nasals. To address these issues, we study two phonemes,/s/ and /sh/ in a North-eastern language of India of Tibeto-Burman origin - Rabha, where contrast exists between aspirated and unaspirated counterparts. Also, for the study of aspirated nasals (/m/- /mh/, /n/-/nh/ and /N/-/Nh), we choose the Angami language, another North-eastern language of India of Tibeto-Burman origin. Both languages are low-resourced and are characterized by these unique sounds.
Analysis and Design of Matched Feeds for Offset Parabolic Reflector Antennas using Analytical and Numerical Techniques
(2016) Jana, Rajib
This research deals with the analysis and design of few novel matched feed structures for offset parabolic reflector antenna systems. An effective hybrid numerical technique is developed to evaluate the performance of a complete system of feed and reflector which reduces computation time and memory requirement at the same time maintain appropriate level of accuracy. The hybrid technique is formed by using the combination of mode matching (MM) and 2-D finite element method (FEM) for interior field analysis of horn; method of moment (MoM) solution for Kirchoff Huygen’s equation using Rao, Wilton and Gilsson (RWG) basis functions for open ended waveguide problem; physical optics (PO) to evaluate the far field radiation pattern of the reflector. The performance of this technique is compared with simulated results of HFSS and close match is obtained. Further, particle swarm optimization (PSO) technique and analytical or computed semi-analytical far field pattern of feed aperture using the available analytical or 2-D FEM based solution of Helmholtz equation respectively, are incorporated for conjugate matching to estimate the mode coefficients and relative phases in the matched feed design. In this thesis, the detail of conjugate matching and matched feed design is investigated and also, few novel matched feed configurations are introduced. The proposed matched feed structures reported in this thesis have the ability to achieve the wide bandwidth for both return loss and conjugate matching.
Analysis and Evaluation of Electromagnetic Losses in Induction Machines and their Impact on Motor Design and Performance
(2022) Kumar, Rajendra
In this thesis, various electromagnetic losses, viz. core losses and stray losses of an induction machine have been studied and characterized for their fast and accurate representation in the iterative motor design process. To accomplish this, the first part of the work uses the measurement results of various medium power three-phase induction motors ranging from 1kW to 375kW output power. The factors affecting the stray losses and the magnetic circuit parameters of a motor are then investigated for all these motors to develop various empirical correlations of stray loss.
Analysis and simulation of piezoelectric vibration energy harvesters having uniform stress profile
(2023) Kundu, Sushanta
The objective of the presented work is to improve the electrical power output by modifying the geometry of the piezoelectric vibration energy harvester (PVEH). The key contributions of the thesis are, modification of the thickness profile of conventional cantilever-based bimorph PVEH to achieve uniform stress along the beam length. In this regard, two thickness-tapered geometries are proposed: PVEH-1, which consists of a thickness-tapered substrate sandwiched between two uniform thickness piezoelectric layers, and PVEH-2, which consists of a bimorph cantilever with a substrate of uniform thickness sandwiched between two thickness-tapered piezoelectric layers. In diaphragm-based PVEH, radial cuts are introduced to reshape it in identical slices (sectors) of 32.7o each resulting in improved harvested power. Further, a broadband energy harvester is designed using several slices of different central angles.
Analysis of Printed Monopole Antennas
(2016) Bhattacharjee, Somen
Printed monopole antenna (PMA) is one of the most suitable antenna for achieving large bandwidth and omnidirectional radiation pattern. In the last one decade, several printed monopole antenna configurations have been proposed and such antennas have been designed using different simulation softwares (HFSS, IE3D, CST Microwave Studio etc) for various wireless communication applications such as wireless LAN, WiFi, UWB etc. However, very few theoretical works are reported for the analysis of printed monopole antennas. Our present work is devoted to development of analytical framework for investigation of printed monopole antennas. Full wave analysis using Mixed Potential Integral Equation is performed along with the derivation of spatial domain potential (scalar and vector) Green’s function for horizontal electric dipole lying on an ungrounded dielectric layer. The input impedance and return loss of printed monopole antenna is calculated and validated by simulation (HFSS) and available experimental results. Approximate analysis of printed monopole antenna is also done to calculate input impedance using transmission line theory. In this, substrate is considered as a transmission line section terminated with free space characteristic impedance. The intrinsic impedance of the medium (substrate) depends on the thickness and the dielectric constant of the medium. Spectral domain Green’s function for the field components is also derived in order to calculate the radiation pattern and gain of rectangular and circular printed monopole antenna and the theoretical results are validated by simulation (HFSS) and available experimental results. Next, the performance of printed monopole antenna with a magneto-dielectric cover and uniaxial substrate is investigated both in theory as well as in simulation (HFSS). Finally, appropriate circuit representation of printed monopole antenna is presented for different geometries of antenna and the ground plane, which are further verified by simulation (HFSS) and available experimental results.
Analysis of Speech and Music Content for Movie Genre Classification
(2023) Bhattacherjee, Mrinmoy
Movies are a popular mode of entertainment around the world. The consistent rise in the production and consumption of movies demands more efficient automatic movie content analysis applications. Movie Genre Classification (MGC) is vital for underage censorship, search, retrieval, and targeted publicity. Current trends in MGC literature indicate a focus on short trailers instead of full movies and a multimodal approach. The audio modality is generally used only as an auxiliary channel. However, due to its rich genre-specific information, the audio signal deserves a dedicated study in the current context. Hence, this thesis aims to perform only audio-specific MGC. The thesis has four principal contributions. First, spectral peak tracking-based magnitude spectrum features are proposed for isolated speech and music classification. Second, the underexplored phase component of the audio signals is utilized for discriminating speech and music. The third contribution involves using harmonic-percussive sourceseparated features and classifiers in the multi-task learning framework for identifying speech overlapped with music. Finally, the above proposals are employed for the MGC task. The spectral peak trackingbased method performs better than the other proposals and the baselines. Specific combinations of all the proposed and baseline features provide the overall best performance, even in the cross-dataset scenario. The thesis work can be extended in the future by analyzing the individual constituents of speech and music for a more nuanced representation of movie genres.
Analysis, design and modeling of approximate adders for error-resilient applications
(2018) Dutt, Sunil
Over the decades, Complementary Metal-Oxide-Semiconductor (CMOS) technology scaling has been the fundamental driver for computing. However, we are now in a phase where CMOS technology scaling is becoming less effective in improving the system capability. The consequence is that we must either accept that the computing systems are good enough or look for alternate avenues to advance them without significant technology progress. Recent studies show that there are several promising alternate avenues that jointly can improve the system capability equivalent to 2 − 3 decades of Moore’s law. Approximate computing is one of them and has attracted a lot of attention of researchers. It should be noted that the concept of approximate computing trade-offs computation quality for computation efforts.In recent years, several approximate adders have been proposed in the literature. The key design approach behind these approximate adders is to truncate the carry-chain. The two most commonly used approaches to truncate the carry-chain are: (i) Approximate Full Adder (AFA); and (ii) Equal Segment Adder (ESA). In the first approach, an N-bit adder is segmented into two sub-adders: (i) Accurate sub-adder that includes the higher order k bits; and (ii) Approximate sub-adder that includes the remaining lower order (N − k) bits. For accurate sub-adder, Full Adders (FAs) are used, whereas for approximate subadder, AFAs are used. In the second approach, an N-bit adder is segmented into several smaller disjoint or overlapping equally sized accurate sub-adders. The Carry-in (Cin) of all sub-adders is considered as 0. Consequently, all sub-adders become independent and operate in parallel. This thesis is divided into three parts in which analysis, designing, analytical modeling, optimization and applications of AFAs and ESAs are presented.
Analytical and simulation modeling of the terahertz photoconductive antennas
(2018) Prajapati, Jitendra
This research deals with the various aspects of the modeling of the Photoconductive Antennas (PCAs). The PCAs are used to radiate the Terahertz (THz) waves. This research work presents the simulation and the theoretical modeling of the PCAs. The simulation studies have been performed using Technology Computer Aided Design (TCAD). For this purpose, Sentaurus from Synopsys has been used. The simulation based modeling of the current pulse in a PCA has been done taking into account the underlying semiconductor device physics as well as the carrier transport dependencies on the different parameters such as the applied electric field, the defect concentrations, and their energy levels.An improved equivalent electrical circuit model of the PCA working as the THz source has been proposed incorporating the basic semiconductor physics. In this work, a novel approach has been adopted to develop an equation for estimating the capacitance of the PCA. The presented circuit model is capable in predicting the effect of the different physical parameters on the performance of the PCA. The proposed model has been validated by simulation studies and available experimental results. Furthermore, a novel equivalent electrical circuit model of the PCA working as the THz receiver is also proposed. To compute the values of the circuit parameters, the same computation strategies have been adopted as proposed in the PCA source modeling.This thesis also examines extensively the effect of the radiated near-zone fields on the PCA performance, an issue which was not adequately addressed in the earlier literature. Moreover, this thesis proposes a novel method for improving the radiated power from a PCA through the use of an external magnetic field. Furthermore, the analytical formulation of the radiated fields relating different PCA parameters is another topic which literature does not address adequately and in this thesis an attempt has been made to bridge this gap with the help of an improved semiconductor carrier dynamics.
Application of Reduced Switch Single DC Source based Cascaded H-bridge Multilevel Inverter for Power Quality Improvement
(2022) Chakrabarty, Ramyani
Distribution static compensator (DSTATCOM) is a shunt connected custom power device which is widely used for load compensation and improvement of power quality. The conventional MLIs used for DSTATCOM implementation pose some drawbacks like large component count, multiple DC-link capacitors and capacitor voltage balancing issues which complicate its design and control. To overcome these issues, a 7-level reduced switch single DC source based cascaded H-bridge multilevel inverter (RSDCHBMLI) topology is presented in this thesis. RSDCHBMLI utilizes lesser number of switches, single DC source and has no requirement of additional diodes or capacitors. As the number of switches in this topology is reduced, a single carrier level shifted pulse width modulation (SC-LS-PWM) technique is developed which is implemented in low-cost controller. The RSDCHBMLI operation is implemented and analyzed in both open-loop and closed loop using state-feedback control (SFB). SFB controller combined with SC-LS-PWM results in constant switching frequency operation of the inverter. The 7-level RSDCHBMLI is implemented as a DSTATCOM connected to weak distribution system. Both SFB current control and finite-control-set model- predictive-control (FCS-MPC) is implemented for load compensation, and it is observed that FCS-MPC gives better dynamic response. It also develops a current based DC-bus voltage controller whose gains can be easily computed and gives better performance than conventional controllers. Detailed case studies for DSTATCOM operation under various conditions of loads and source voltages are also presented.
Approaches for robust text-dependent speaker verification under degraded conditions
(2019) Bhukya, Ramesh Kumar
The objective of this thesis work is to develop a robust text-dependent speaker verification (TDSV) system by using robust techniques for achieving better system performance under clean and degraded speech conditions. To achieve this, three different directions are explored for a TDSV task. The existing TDSV system employs energy based end point detection, mel frequency cepstral coefficients (MFCCs) as features and dynamic time warping (DTW) for template matching. The same is treated as baseline system in this work. The performance of the baseline system affected depending on operating conditions in practice. The work attempts to improve the performance by providing robustness at different levels.In practice, the speech signal is affected by the acoustic degradation present in the recording environment. This results in poor performance at different stages. One way is to first enhance the speech signal and then perform TDSV. The first novel contribution proposes combined temporal and spectral speech enhancement for enhancing speech regions embedded in background noise. The efficacy of the proposed framework is demonstrated by comparing the performance with the baseline system.The spectral or cepstral based features, mainly MFCCs are used in the baseline system. In the next exploration, the goal is to develop new features. A new approach for feature extraction based on modified empirical mode decomposition (MEMD) is attempted. The Hilbert spectrum (HS) based features are extracted from the intrinsic mode functions (IMFs) of MEMD and used as features for TDSV.
Architecture and Power Balancing Strategies of Multifrequency Microgrid
(2023) Dey, Rajdip
A new type of microgrid called multifrequency microgrid (MFMG) is investigated in this thesis. It is formed based on the superposition theorem, orthogonal power flow theory, and frequency selectivity criteria. It is a unique system where different frequency voltages and currents are present on the multifrequency (MF) bus and different frequency powers maintain orthogonality and transmit simultaneously through the MF bus without mixing. Frequency selectivity criteria states that the consumers can choose any available frequency power from the MF bus based on their requirements. This research work focuses on the basic architecture, converters, and control strategies of MFMG.

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