Observer-Based Quadrature Signal Generator for UPQC in a Single-Phase Distribution System

This paper presents a control algorithm for generation of reference voltage and current based on Observerbased QSG (Quadrature Signal Generator) for UPQC (Unified Power Quality Conditioner) in a Single-Phase Distribution System. The proposed UPQC is a combination of DSTATCOM and DVR used for load and source compensation such as voltage sag and swell, voltage and current harmonics etc. The proposed control algorithm is capable of generating reference signals from the distorted voltages and currents. In this paper, an improved OQSGbased PLL (Phase-Locked Loop) is utilized over OQSG to enable and operate with increased bandwidths that will improve the dynamic response, tracking accuracy and faster detection of reference signal under all varying load and grid conditions. The control algorithm is tested and evaluated using MATLAB / Simulink

Evaluation of quadrature signal generation methods with reduced computational resources for grid synchronization of single-phase power converters through phase-locked loops

Low-cost single-phase grid connected converters require synchronization with the grid voltage to obtain a better response and protection under diverse conditions, such as frequency perturbations and distortion. Phase-locked loops (PLLs) have been used in this scenario. This paper describes a set of quadrature signal generators for single-phase PLLs; compares the performances by means of simulation tests considering diverse operation conditions of the electrical grid; proposes strategies to reduce the computational burden, considering fixed-point digital implementations; and provides both descriptive and quantitative comparisons of the required mathematical operations and memory units for implementation of the analyzed single-phase PLLs.This work has been supported by the Spanish Ministry of Science and Innovation under Project RTI2018-095138-B-C31 PEGIA—Power Electronics for the Grid and Industry Applications

Rolling contact fatigue failures in silicon nitride and their detection

The project investigates the feasibility of using sensor-based detection and processing systems to provide a reliable means of monitoring rolling contact fatigue (RCF) wear failures of silicon nitride in hybrid bearings. To fulfil this investigation, a decision was made early in the project to perform a series of hybrid rolling wear tests using a twin disc machine modified for use on hybrid bearing elements.The initial part of the thesis reviews the current understanding of the general wear mechanisms and RCF with a specific focus to determine the appropriate methods for their detection in hybrid bearings. The study focusses on vibration, electrostatic and acoustic emission (AE) techniques and reviews their associated sensing technologies currently deployed with a view of adapting them for use in hybrids. To provide a basis for the adaptation, an understanding of the current sensor data enhancement and feature extraction methods is presented based on a literature review.The second part describes the test equipment, its modifications and instrumentation required to capture and process the vibration, electrostatic and AE signals generated in hybrid elements. These were identified in an initial feasibility test performed on a standard twin disc machine. After a detailed description of the resulting equipment, the thesis describes the calibration tests aimed to provide base data for the development of the signal processing methods.The development of the signal processing techniques is described in detail for each of the sensor types. Time synchronous averaging (TSA) technique is used to identify the location of the signal sources along the surfaces of the specimens and the signals are enhanced by additional filtering techniques.The next part of the thesis describes the main hybrid rolling wear tests; it details the selection of the run parameters and the samples seeded with surface cracks to cover a variety of situations, the method of execution of each test run, and the techniques to analyse the results.The research establishes that two RCF fault types are produced in the silicon nitride rolling element reflecting essentially different mechanisms in their distinct and separate development; i) cracks, progressing into depth and denoted in this study as C-/Ring crack Complex (CRC) and ii) Flaking, progressing primarily on the surface by spalls. Additionally and not reported in the literature, an advanced stage of the CRC fault type composed of multiple and extensive c-cracks is interpreted as the result of induced sliding in these runs. In general, having reached an advanced stage, both CRC and Flaking faults produce significant wear in the steel counterface through abrasion, plastic deformation or 3-body abrasion in at least three possible ways, all of which are described in details

Treatise on Hearing: The Temporal Auditory Imaging Theory Inspired by Optics and Communication

A new theory of mammalian hearing is presented, which accounts for the auditory image in the midbrain (inferior colliculus) of objects in the acoustical environment of the listener. It is shown that the ear is a temporal imaging system that comprises three transformations of the envelope functions: cochlear group-delay dispersion, cochlear time lensing, and neural group-delay dispersion. These elements are analogous to the optical transformations in vision of diffraction between the object and the eye, spatial lensing by the lens, and second diffraction between the lens and the retina. Unlike the eye, it is established that the human auditory system is naturally defocused, so that coherent stimuli do not react to the defocus, whereas completely incoherent stimuli are impacted by it and may be blurred by design. It is argued that the auditory system can use this differential focusing to enhance or degrade the images of real-world acoustical objects that are partially coherent. The theory is founded on coherence and temporal imaging theories that were adopted from optics. In addition to the imaging transformations, the corresponding inverse-domain modulation transfer functions are derived and interpreted with consideration to the nonuniform neural sampling operation of the auditory nerve. These ideas are used to rigorously initiate the concepts of sharpness and blur in auditory imaging, auditory aberrations, and auditory depth of field. In parallel, ideas from communication theory are used to show that the organ of Corti functions as a multichannel phase-locked loop (PLL) that constitutes the point of entry for auditory phase locking and hence conserves the signal coherence. It provides an anchor for a dual coherent and noncoherent auditory detection in the auditory brain that culminates in auditory accommodation. Implications on hearing impairments are discussed as well.Comment: 603 pages, 131 figures, 13 tables, 1570 reference

Scanning micro interferometer with tunable diffraction grating for low noise parallel operation

Large area high throughput metrology plays an important role in several technologies like MEMS. In current metrology systems the parallel operation of multiple metrology probes in a tool has been hindered by their bulky sizes. This study approaches this problem by developing a metrology technique based on miniaturized scanning grating interferometers (μSGIs). Miniaturization of the interferometer is realized by novel micromachined tunable gratings fabricated using SOI substrates. These stress free flat gratings show sufficient motion (~500nm), bandwidth (~50 kHz) and low damping ratio (~0.05). Optical setups have been developed for testing the performance of μSGIs and preliminary results show 6.6 μm lateral resolution and sub-angstrom vertical resolution. To achieve high resolution and to reduce the effect of ambient vibrations, the study has developed a novel control algorithm, implemented on FPGA. It has shown significant reduction of vibration noise in 6.5 kHz bandwidth achieving 6x10-5 nmrms/√Hz noise resolution. Modifications of this control scheme enable long range displacement measurements, parallel operation and scanning samples for their dynamic profile. To analyze and simulate similar optical metrology system with active micro-components, separate tools are developed for mechanical, control and optical sub-systems. The results of these programs enable better design optimization for different applications.Ph.D.Committee Chair: Degertekin, Levent; Committee Co-Chair: Kurfess, Thomas; Committee Member: Adibi, Ali; Committee Member: Danyluk, Steven; Committee Member: Hesketh, Pete

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

Optical Properties of TMDC Monolayers and Their Heterostructures

Recently, the 2D semiconductors represented by transition-metal dichalcogenides (TMDCs) received strong attention owing to a number of important features. These include the large exciton binding energies relevant for room-temperature applications, the valley pseudo-spin degree of freedom and polarization sensitivity, and the overall strong light-matter interactions at the monolayer limit which motivate their use for optoelectronics. Furthermore, van-der-Waals stacking of different 2D crystals results in out-of-plane heterostructures, which can, in addition to the inherited properties of the individual layered constituents, even exhibit tailored properties caused by the strong influence of the environment and hybridization of atomic orbitals. Accordingly, a mixture of unique and novel properties can arise. Ultimately, in contrast to conventional semiconductor heterostructure growth, there is no direct need for lattice matching or a fixed orientation during assembly. Nonetheless, the relative orientation between different or similar 2D lattices may indeed be important for the composed stack’s features. Thus, the vast number of possible combinations of 2D-materials with each other, as well as with substrates and with conventional semiconductors or molecular materials, offer huge opportunities for engineering and tailoring the material stack properties to meet the demand of a specific application. To do that effectively and systematically, several questions need to be addressed, to the answering of which the following studies contribute with important insights focusing on the optical properties of semiconductor monolayers and van-der-Waals stacks. In this work, four central chapters discuss excitonic signatures in different TMDC 2D structures, shedding light on the role of the environment and stacking configuration, as well as on the quasi-particle energy-momentum dispersion, valley polarization as well as light-matter interactions. Firstly, the influence of the surroundings on the fundamental properties of 2D-semiconductor monolayers, such as the energetics, the exciton–phonon coupling, exciton–exciton annihilation and exciton diffusion, is addressed based on time-integrated and time-resolved photoluminescence spectroscopy. Thereby, the important role of hexagonal BN as substrate or capping layer and as encapsulant is discussed. Following that, a better understanding of high-symmetry alignments for bilayers is gained employing epitaxially grown tungsten-disulfide samples with two distinct and deterministically obtained configurations. While formerly only the symmetry of the stack itself was considered, the study presented here shows that also the symmetry of the surrounding has to be considered as it can lift the degeneracy between the layers. Thereby, the out-of-plane symmetry break renders homobilayers in fact heterojunctions. Moreover, the aspect of spin–valley and spin–layer locking has been discussed for the natural and artificial bilayer type, with eyes towards valleytronic applications. In contrast to high-symmetry stacks, investigations on arbitrarily stacked heterostructures are at the starting point for explorations on the impact of moiré patterns and interlayer hybridization. Here, a preliminary study on a tungsten-based heterostructure exhibits pronounced spectral features attributed to such interlayer effects, besides the occurrence of conventional intra- and interlayer excitons. Next, regarding linewidth improved encapsulated monolayers, a unique access to the excitonic energy–momentum dispersion is demonstrated with the help of angle-resolved spectrospopy. The analysis of Fourier-space-resolved emission and reflection spectra hereby facilitate the ongoing discussion of dispersion relations in 2D semiconductors. The so far unrivalled optical measurements show novel experimental evidence of meV strong excitonic dispersion within the light cone in support of theories discussed in the literature. Furthermore, Fourier-space spectroscopy delivers a tool to identify the radiative patterns of bright and partially dark excitonic states and provided evidence for the phonon-sidebands in agreement with the prediction in the literature. Finally, improvements of the light–matter interactions and of the emission behavior towards optoelectronic applications are crucial, taking further into account challenges in the integration of van-der-Waals materials in established silicon-, III/V semiconductors- or fiber-based technology. Therefore, a nanostructured photonic substrate landscape for lateral confinement of optical fields and vertical enhancement of coupling of light into and out of 2D-materials is investigated as a prototype structure for possible nanophotonic applications

Index to 1985 NASA Tech Briefs, volume 10, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1985 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Analysis and implementation of algorithms for embedded self-mixing displacement sensors design

L'interaction entre un faisceau laser émis avec une partie de la lumière réfléchi depuis une cible qui rentre dans la cavité active du laser, est à l'origine du phénomène de rétro-injection optique ou self-mixing. L'utilisation de ces franges interférométriques non conventionnelles, semble attractive du au faible nombre des composant optiques et son caractère auto-aligné. Dans cette thèse nous approchons leur développement en tant qu'implémentation embarqué rentable pour la mesure du déplacement. A cette fin, nous avons exploré des méthodes du traitement du signal pour la détection des franges et la reconstruction du mouvement de la cible, en évitant l'usage de composant externes. Premièrement, nous avons identifié quelques incompatibilités dans des algorithmes précédentes établis dans notre centre de recherche, puis nous avons avancé des solutions. Fondé sur la théorie d'interpolation, an algorithme simplifié mais démontré convenable en temps-réel à été proposé pour la reconstruction du déplacement. En s'appuyant sur l'élaboration d'un signal analytique, il à été proposé une version amélioré pour le calcul de phase. Celle-ci nous à permit de fournir un algorithme pour la détection de franges, robuste aux variations d'amplitude, sans tenir compte du régime de rétro-injection, impliquant une convenable utilisation pour une variété d'applications. ABSTRACT: The interaction between an emitted laser beam and a small portion of backscattered light from a pointed target that re-enters the laser's cavity, is at the origin of optical feedback phenomenon or self-mixing. Exploiting these unconventional interferometric fringes for non-contact sensors is attractive due to its minimal optical part-count and self-aligned nature. In this thesis we approach its development as a cost-eective embedded implementation for displacement measurement. To this end we explored signal processing methods for fringe detection and target's movement reconstruction, avoiding the usage of external components. We first identified some incompatibilities in prior algorithms from our research center, and then proposed further solutions. Based on interpolation theory, a simplified but proved real-time algorithm resulted for displacement reconstruction. Relying on analytical signal elaboration, an improved approach for phase calculation allowed us to provide a fringe detection algorithm robust to amplitude variations, disregarding the feedback regime and thus, allowing a seemly usage over an increased variety of applications

Prognostic-based Life Extension Methodology with Application to Power Generation Systems

Practicable life extension of engineering systems would be a remarkable application of prognostics. This research proposes a framework for prognostic-base life extension. This research investigates the use of prognostic data to mobilize the potential residual life. The obstacles in performing life extension include: lack of knowledge, lack of tools, lack of data, and lack of time. This research primarily considers using the acoustic emission (AE) technology for quick-response diagnostic. To be specific, an important feature of AE data was statistically modeled to provide quick, robust and intuitive diagnostic capability. The proposed model was successful to detect the out of control situation when the data of faulty bearing was applied. This research also highlights the importance of self-healing materials. One main component of the proposed life extension framework is the trend analysis module. This module analyzes the pattern of the time-ordered degradation measures. The trend analysis is helpful not only for early fault detection but also to track the improvement in the degradation rate. This research considered trend analysis methods for the prognostic parameters, degradation waveform and multivariate data. In this respect, graphical methods was found appropriate for trend detection of signal features. Hilbert Huang Transform was applied to analyze the trends in waveforms. For multivariate data, it was realized that PCA is able to indicate the trends in the data if accompanied by proper data processing. In addition, two algorithms are introduced to address non-monotonic trends. It seems, both algorithms have the potential to treat the non-monotonicity in degradation data. Although considerable research has been devoted to developing prognostics algorithms, rather less attention has been paid to post-prognostic issues such as maintenance decision making. A multi-objective optimization model is presented for a power generation unit. This model proves the ability of prognostic models to balance between power generation and life extension. In this research, the confronting objective functions were defined as maximizing profit and maximizing service life. The decision variables include the shaft speed and duration of maintenance actions. The results of the optimization models showed clearly that maximizing the service life requires lower shaft speed and longer maintenance time