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Dissertations / Theses on the topic 'Frequency'
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1
Saarinen, Linn. "The Frequency of the Frequency : On Hydropower and Grid Frequency Control." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-308441.
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Variations in the electricity consumption and production connected to the power system have to be balanced by active control. Hydropower is the most important balancing resource in the Nordic system, and will become even more important as the share of variable renewable energy sources increases. This thesis concerns balancing of active power, especially the real-time balancing called frequency control. The thesis starts in a description of the situation today, setting up models for the behaviour of hydropower units and the power system relevant to frequency control, and comparing the models with experiments on several hydropower units and on the response of the Nordic grid. It is found that backlash in the regulating mechanisms in hydropower units have a strong impact on the quality of the delivered frequency control. Then, an analysis of what can be done right now to improve frequency control and decrease its costs is made, discussing governor tuning, filters and strategies for allocation of frequency control reserves. The results show that grid frequency quality could be improved considerably by retuning of hydropower governors. However, clear technical requirements and incentives for good frequency control performance are needed. The last part of the thesis concerns the impact from increased electricity production from variable renewable energy sources. The induced balancing need in terms of energy storage volume and balancing power is quantified, and it is found that with large shares of wind power in the system, the energy storage need over the intra-week time horizon is drastically increased. Reduced system inertia due to higher shares of inverter connected production is identified as a problem for the frequency control of the system. A new, linear synthetic inertia concept is suggested to replace the lost inertia and damping. It is shown that continuously active, linear synthetic inertia can improve the frequency quality in normal operation and decrease wear and tear of hydropower units delivering frequency control.
2
Walker, Scott A. Luna Lauro. "Frequency mapping for the operational frequency manager." Monterey, Calif. : Naval Postgraduate School, 2008. http://bosun.nps.edu/uhtbin/hyperion-image.exe/08Mar%5FWalker%5FScott.pdf.
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Thesis (M.S. in Information Technology Management)--Naval Postgraduate School, March 2008.<br>Thesis Advisor(s): Bordetsky, Alex ; Bourakov, Eugene. "March 2008." Description based on title screen as viewed on May 1, 2008. Includes bibliographical references (p. 119). Also available in print.
3
Luna, Lauro. "Frequency mapping for the operational frequency manager." Thesis, Monterey, California. Naval Postgraduate School, 2008. http://hdl.handle.net/10945/4231.
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The Department of Defense (DOD) has placed great emphasis on the networking and connectivity of forces over the last several years. Programs include the Global Information Grid (GIG), Force Net, and Net Centric Warfare to name a few. These programs emphasize and stress the warfighter's need to stay connected to their appropriate operational command and control structure during operations. The value of this connectivity is crucial to both the individual warfighter and the command structure as a force multiplier in modern warfare. One solution to this problem of connectivity is giving our operating forces the tools and knowledge of existing network infrastructure that details the information regarding the location, frequency and power out of existing nodes and spectrum analysis. The knowledge and ability of a trained Frequency Manager will allow our forces to use the full electromagnetic spectrum to maintain connectivity with their command structure. The goal of this research is to provide a systematic approach to detecting existing network and telecommunication frequencies and mapping their positions. This information can then used by a Frequency Manager for planning operational test exercises and for operational forces that may operate in an area that is frequency saturated. In these situations and with the knowledge of existing frequencies these forces will be better able to manage, configure, and exploit existing network communications. The experimental study will encompass the collection, data processing, modeling and mapping of existing networks and their electromagnetic effects in both a rural and urban environment using the TNT 802.16 OFDM test bed in the San Francisco Bay area and Camp Roberts.
4
Wong, S. W. "Frequency hopping data transmission at high frequency." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317262.
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5
Mai, Cuong. "Frequency Estimation Using Time-Frequency Based Methods." ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/571.
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Any periodic signal can be decomposed into a sum of oscillating functions. Traditionally, cosine and sine segments have been used to represent a single period of the periodic signal (Fourier Series). In more general cases, each of these functions can be represented by a set of spectral parameters such as its amplitude, frequency, phase, and the variability of its instantaneous spectral components. The accuracy of these parameters depends on several processing variables such as resolution, noise level, and bias of the algorithm used. This thesis presents some background of existing frequency estimation techniques and proposes a new technique for estimating the instantaneous frequency of signals using short sinusoid-like basis functions. Furthermore, it also shows that the proposed algorithm can be implemented in a popular embedded DSPmicroprocessor for practical use. This algorithm can also be implemented using more complex features on more resourceful processing processors in order to improve estimation accuracy
6
Ceylan, Oktay. "Resolving frequency ambiguities in step : frequency compressive receivers." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA374376.
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Thesis (M.S. in Systems Engineering) Naval Postgraduate School, December 1999.<br>"December 1999". Thesis advisor(s): D. Curtis Schleher. Includes bibliographical references (p. 129-130). Also available online.
7
Shenouda, Hany H. "An agile frequency synthesizer for frequency hopping radio." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0016/MQ49683.pdf.
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8
Rohani-Mehdiabadi, Bijan. "Frequency discriminator detection in frequency-selective fading environments." Thesis, Curtin University, 1998. http://hdl.handle.net/20.500.11937/451.
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In recent years, millions of customers all over the world have been subscribing to mobile telephony services which are based on modern digital transmission. At the high transmission bit rates that these systems use, the mobile radio channel exhibits frequency-selective fading characteristics. Under such conditions, the received signal could experience significant intersymbol interference (ISI) from severe distortion to the waveform of the received baseband signal. Therefore, such techniques as adaptive waveform equalisation or adaptive maximum likelihood sequence estimation (MLSE) are used in modern digital mobile radio telephone systems to combat this undesirable ISI. These adaptive schemes have almost always been used in conjunction with coherent demodulation in the receivers.This study examines the application of noncoherent demodulation, in the form of frequency discriminator detection, as an alternative to coherent demodulation. The GSM (Global System for Mobile Communications) standard has been used as the basis for this investigation. It has been shown analytically that in the presence of frequency-selective fading, a propagation environment common to the GSM system, the use of frequency discriminator detection gives rise to nonlinear ISI in the demodulated signal. It has also been shown that frequency-selective fading could cause large unwanted "spikes" to appear in the demodulated signal, thus leading to a severe degradation in the bit-error-rate (BER) performance. Consequently, several waveform distortion cancellation schemes for combatting the nonlinear ISI have been formulated. The BER performances of these proposed schemes, under various propagation conditions, have been studied by computer simulation.Furthermore, it has been observed that the undesirable "spikes", that occur in the demodulated signal due to frequency-selective fading, could be suppressed by the use of inverse-limiting in conjunction with frequency discriminator detection. As a result, an effective adaptive detection scheme has been formulated, based on modelling the combination of the GMSK modulator, the mobile channel, the frequency discriminator, and any transmit and receive fitters, as a finite-state machine. The transmitted data is then detected using an MLSE. The BER performance of this proposed adaptive detection scheme has been extensively investigated by computer simulation. This has been carried out assuming various propagation conditions, including the two-ray fading channel model with equal path powers and relative delays of up to four bit periods, the maximum relative delay considered in the GSM system. Also, the effectiveness of the proposed adaptive detection scheme in combatting IS] has been investigated by computer simulation based on the six-ray GSM empirical propagation models for typical urban (TU), hilly terrain (HT) and rural area (RA) environments. The computer simulated results confirm that the voice grade performance required for the GSM system could be achieved by the proposed adaptive detection scheme in all the recommended GSM propagation models considered. Furthermore, the BER performance of the receiver remains unaffected by a carrier frequency offset of up to 2 kHz.
9
Rohani-Mehdiabadi, Bijan. "Frequency discriminator detection in frequency-selective fading environments." Curtin University of Technology, School of Electrical and Computer Engineering, 1998. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=12148.
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In recent years, millions of customers all over the world have been subscribing to mobile telephony services which are based on modern digital transmission. At the high transmission bit rates that these systems use, the mobile radio channel exhibits frequency-selective fading characteristics. Under such conditions, the received signal could experience significant intersymbol interference (ISI) from severe distortion to the waveform of the received baseband signal. Therefore, such techniques as adaptive waveform equalisation or adaptive maximum likelihood sequence estimation (MLSE) are used in modern digital mobile radio telephone systems to combat this undesirable ISI. These adaptive schemes have almost always been used in conjunction with coherent demodulation in the receivers.This study examines the application of noncoherent demodulation, in the form of frequency discriminator detection, as an alternative to coherent demodulation. The GSM (Global System for Mobile Communications) standard has been used as the basis for this investigation. It has been shown analytically that in the presence of frequency-selective fading, a propagation environment common to the GSM system, the use of frequency discriminator detection gives rise to nonlinear ISI in the demodulated signal. It has also been shown that frequency-selective fading could cause large unwanted "spikes" to appear in the demodulated signal, thus leading to a severe degradation in the bit-error-rate (BER) performance. Consequently, several waveform distortion cancellation schemes for combatting the nonlinear ISI have been formulated. The BER performances of these proposed schemes, under various propagation conditions, have been studied by computer simulation.Furthermore, it has been observed that the undesirable "spikes", that occur in the demodulated signal due to frequency-selective fading, could be ++<br>suppressed by the use of inverse-limiting in conjunction with frequency discriminator detection. As a result, an effective adaptive detection scheme has been formulated, based on modelling the combination of the GMSK modulator, the mobile channel, the frequency discriminator, and any transmit and receive fitters, as a finite-state machine. The transmitted data is then detected using an MLSE. The BER performance of this proposed adaptive detection scheme has been extensively investigated by computer simulation. This has been carried out assuming various propagation conditions, including the two-ray fading channel model with equal path powers and relative delays of up to four bit periods, the maximum relative delay considered in the GSM system. Also, the effectiveness of the proposed adaptive detection scheme in combatting IS] has been investigated by computer simulation based on the six-ray GSM empirical propagation models for typical urban (TU), hilly terrain (HT) and rural area (RA) environments. The computer simulated results confirm that the voice grade performance required for the GSM system could be achieved by the proposed adaptive detection scheme in all the recommended GSM propagation models considered. Furthermore, the BER performance of the receiver remains unaffected by a carrier frequency offset of up to 2 kHz.
10
Borda, Fortuny C. "New frequency reconfigurable antennas for wide frequency range tuning." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1544686/.
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Frequency reconfigurable antennas are becoming a compelling solution for the increasing demand of higher antenna capabilities, since they can operate at tunable narrow frequency bands while rejecting the undesirable signals from other bands. The aim of this project is to develop new designs for frequency reconfigurable antennas that can work across a wide frequency range (from 1 GHz up to 6 GHz) while maintaining stable radiation pattern and polarisation as required by the industry sponsors. A Vivaldi antenna is considered as the basis for a frequency reconfigurable design as it maintains the radiation characteristics in its operating band. Dual-band, tri-band and quad-band switched reconfigurable designs are proposed and analysed. These antennas are electronically-tuned using RF switches which adjust the impedance to reconfigure the operating band of the antenna. A prototype is tested in an anechoic chamber obtaining good performance. However, as the switches lead to several challenges, such as the effect of bias lines and the excessive insertion losses, a new approach is taken. State-of-the-art technologies are studied and fluid antennas are introduced. Current developments show that liquid antennas can have radiation efficiencies up to 90 % and conductivities close to copper, which makes them a good candidate to fulfil the requirements of this project. A hybrid Vivaldi antenna with an ionised water switch is proposed and a prototype tested. By introducing ionised water into a specific point of the feed line the operating frequency of the antenna is adjusted. The replacement of RF switches for electronically-controlled fluids brings high flexibility, suppression of the bias lines impact, dynamic adjustment and continuous frequency tuning compared to conventional antenna systems.
11
Challakere, Nagaravind. "Carrier Frequency Offset Estimation for Orthogonal Frequency Division Multiplexing." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1423.
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This thesis presents a novel method to solve the problem of estimating the carrier frequency set in an Orthogonal Frequency Division Multiplexing (OFDM) system. The approach is based on the minimization of the probability of symbol error. Hence, this approach is called the Minimum Symbol Error Rate (MSER) approach. An existing approach based on Maximum Likelihood (ML) is chosen to benchmark the performance of the MSER-based algorithm. The MSER approach is computationally intensive. The thesis evaluates the approximations that can be made to the MSER-based objective function to make the computation tractable. A modified gradient function based on the MSER objective is developed which provides better performance characteristics than the ML-based estimator. The estimates produced by the MSER approach exhibit lower Mean Squared Error compared to the ML benchmark. The performance of MSER-based estimator is simulated with Quaternary Phase Shift Keying (QPSK) symbols, but the algorithm presented is applicable to all complex symbol constellations.
12
Abdoush, Yazan <1989>. "Time-Frequency Signal Analysis and Adaptive Instantaneous Frequency Estimation." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amsdottorato.unibo.it/9079/1/Thesis.pdf.
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Most of the human-made and physical signals have nonstationary spectra that evolve rapidly with time. To study and characterize such signals, the classic time-domain and frequency-domain representations are inadequate, since they do not provide joint time and frequency information; meaning that, they are signal representations in which the time and frequency variables are mutually exclusive. Time-frequency (TF) signal analysis (TFSA) concerns the processing of signals with time-varying spectral content. It allows for the construction of a signal representation in which the time and frequency variables are not averaged with respect to each other, but rather present together. This doctoral thesis has two main points of focus: TFSA based on a linear TF transform with progressive frequency-dependent resolution in the TF domain, known in the literature as the S-transform (ST), and designing adaptive methods for instantaneous frequency (IF) estimation, which is a fundamental concept in TFSA with numerous practical applications. The main original contributions are: 1- Modifications in the existing discrete definitions for implementing and inverting the ST to ensure exact invertibility and eliminate artifacts in the synthesized signal. 2- Derivation of an algorithm for least-squares signal synthesis form a modified discrete ST. 3- Formulation of a computationally efficient, fully discrete, and exactly invertible ST with a controllable TF sampling scheme, providing frequency resolution that can be varied and made as high as required. 4- Accuracy analysis of IF estimation based on a family of linear TF transforms that use Gaussian observation windows to localize the Fourier oscillatory kernel with arbitrarily defined standard deviations, and derivation of closed-form easily interpreted expressions for the bias and the variance of the estimation error. 5- Design of adaptive methods for IF estimation based on linear and quadratic TF representations.
13
Cooperrider, Jason R. "Interactions between word frequency and neighborhood frequency in lexical access." Connect to resource, 2007. http://hdl.handle.net/1811/28449.
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Thesis (Honors)--Ohio State University, 2007.<br>Title from first page of PDF file. Document formatted into pages: contains 25 p. Includes bibliographical references (p. 15). Available online via Ohio State University's Knowledge Bank.
14
Murji, Rizwan Deen M. Jamal. "Low-power CMOS radio frequency integrated circuits for frequency synthesis /." *McMaster only, 2005.
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15
Holman, Kevin W. "Distribution of an ultrastable frequency reference using optical frequency combs." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/cr/colorado/fullcit?p3190346.
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Žitkevičius, Evaras. "Analysis of medical images in frequency and space-frequency domains." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2007. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2007~D_20071204_102356-91944.
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Images of CT and MRI are grayscale images and usually they are analyzed by radiologists on display either on transparency screen. Then objects in images are recognized by their properties like average luminosity of the region, localization, shape, dimensions, etc. The process of visual recognition is affected by many factors. The totality of factors determines uncertainties of diagnostics. More and more often there are used software utilities in the analysis of images which help to lower the uncertainties and speed up the analysis time. The aim of the work is investigation of medical image processing and analysis using frequency and joint space-frequency domains and developing of algorithms suitable for segmentation of regions of diseases.<br>Žmogaus galvos KT bei MR vaizdus analizuoja apmokyti diagnostikos specialistai – radiologai. Vaizdai, kuriuos turi analizuoti radiologas, yra pilkieji vaizdai, pateikiami monitoriuje arba skaidrėse. Juose tiriami objektai yra atpažįstami pagal tam tikrų vaizdo sričių pilkumo lygį, išsidėstymą, formą, dydį ir kitus požymius. Atpažinimo procesui turi įtakos eilė veiksnių, kurių visuma lemia diagnostines neapibrėžtis. Jų sumažinimui bei diagnostikos paspartinimui vis plačiau taikoma pagalbinė kompiuterinė programinė įranga, kuri, be to, suteikia daug papildomų trimačio vizualizavimo ir skaičiavimo galimybių. Šio darbo tikslas yra ištirti medicininių vaizdų analizės ir apdorojimo galimybes, taikant dažninius ir erdvinius dažninius spektrus, bei sudaryti algoritmus, skirtus ligų sričių ar kitų specifinių vaizdo sričių segmentavimui.
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Khumsat, Phanumas. "Transition frequency integration : technique for high frequency continuous-time filters." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398200.
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Veerakitti, Paesol. "High Frequency VCO and Frequency Divider in VLSI 90nm Technology." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1278426944.
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Moghaddar, Ali. "Time-frequency representation of frequency-dispersive waveguide and cavity scatterers /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487859879939625.
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Heuschel, Eugene R. "Time-frequency, bi-frequency detector analysis of noise technology radar." Thesis, Monterey, California. Naval Postgraduate School, 2006. http://hdl.handle.net/10945/2636.
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Enemy integrated air defense systems (IADS) using low probability of intercept (LPI) emitters can cause significant problems for suppression of enemy air defense (SEAD) techniques. New threat emitter configurations using low-power random noise modulation have a significant processing gain unavailable to non-cooperative intercept receivers. Consequently, the detection of these emitters can not be accomplished with conventional intercept receiver detection methods. This thesis examines the use of time-frequency, bi-frequency signal detection techniques to identify the parameters of the four types of continuous waveform noise radar recently reported. These include: (a) random noise, (b) noise plus frequency modulation continuous wave (FMCW), (c) noise FMCW plus sine and (d) random binary phase modulation. Quadrature mirror filtering for wavelet decomposition is used to investigate the four types of noise signals in order to extract the signal parameters. The FFT accumulation method for estimating the spectral correlation density function is also used to examine the cyclostationary bi-frequency properties of the waveforms. In addition, the periodic autocorrelation function and periodic ambiguity function are studied to determine the waveform properties in the delay- Doppler offset domain. Results show that non-cooperative intercept receivers can increase their processing gain using these types of signal processing techniques providing a more efficient response time to the threat.
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Koski, Antti E. "Rapid frequency estimation." Worcester, Mass. : Worcester Polytechnic Institute, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-032806-165036/.
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Thesis (M.S.)--Worcester Polytechnic Institute.<br>Keywords: DSS; ECM; SVD; Singular Value Decomposition; rapid frequency estimation; frequency estimation. Includes bibliographical references (leaves 174-177).
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Karim, Omair. "Electronic frequency controller." Thesis, Blekinge Tekniska Högskola, Institutionen för tillämpad signalbehandling, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-690.
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The project was performed with universal electronics which is based in Karachi Pakistan at PRD Lab. Due to the energy crises the industry is switching to alternative power generators. The main issue with the maintenance of the generator is the constant failure of the controller which has to be imported ,the purpose of this project is to make a cheap efficient Electronic Frequency Controller (EFC) that can be used in almost all kinds of generators. The work was tested on Multisim and then soldered together. To make it functional the frequency generation was converted to voltage which was connected to the controller. The controller was joined with the actuator and the actuator opens the amount of fuel needed to run the generator so that there is a smooth constant voltage. If we have high frequency from the input like a heavy machinery is operational then the actuator will widen its opening and when the frequency is low the actuator will open appropriately. The presentation was a successful one but due to time deadline few minor adjustment could be made to make it more effective as discussed later.
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Torres, Wade Patrick. "Generalized frequency modulation." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8697.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.<br>Includes bibliographical references (p. 127-128).<br>In frequency modulation (FM) systems, a continuous-time information signal is modulated onto a sinusoidal carrier wave by using the information signal to modulate the frequency of the carrier wave. In this thesis, a more general type of modulation is developed, of which FM is a special case, that we refer to as rate modulation. A rate modulation system consists of a dynamical system whose rate of evolution is varied in proportion to an information signal. The rate-modulated carrier wave is a scalar function of the state variables of the modulator. The thesis is focused on three aspects of rate modulation and demodulation systems. First, explicit expressions are derived for the power density spectrum of the rate modulated carrier wave for sinusoidal modulation. Second, a systematic procedure is derived for constructing demodulators. This procedure requires that the dynamical system used in the modulator has a known exponentially convergent observer. Assuming such an observer is known, a systematic procedure for constructing demodulators is given that depends on the underlying dynamical system in a simple manner. Finally, the quasi-moment neglect closure technique is used to approximate the signal-to-noise ratio when the carrier wave is corrupted by additive white-noise.<br>by Wade P. Torres.<br>Ph.D.
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Minns, Alan Ronald. "Low frequency variability." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624871.
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Geldenhuys, N. D. "Microwave frequency discriminators." Thesis, Stellenbosch : Stellenbosch University, 2001. http://hdl.handle.net/10019.1/52337.
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Thesis (MScEng)--University of Stellenbosch, 2001.<br>ENGLISH ABSTRACT: The topic of microwave frequency discriminators is introduced.
Various applications and implementation techniques of these devices
are given and discussed. This thesis may serve as reference
foundation for future research on this topic.
Discriminators are developed at both S- and X-band, with high
linearity and good sensitivity. The systems used to implement these
devices are developed as well. The S-band discriminator is used in
a direct FM demodulation system, which works well.<br>AFRIKAANSE OPSOMMING: Hierdie is 'n inleiding tot die onderwerp van mikrogolf frekwensie
diskrimineerders. Verskeie toepassings en implementeringstegnieke
van hierdie toestelle word genoem en bespreek. Hierdie tesis kan
dien as verwysings-raamwerk vir toekomstige navorsing oor hierdie
onderwerp.
Diskrimineerders is ontwikkel by beide S- en X-band, met 'n goeie
lineariteit en sensitiwiteit. Die stelsels wat gebruik word om hulle
te implementeer, is ook ontwikkel. Die S-band diskrimineerder is
gebruik in 'n direkte FM demodulasie sisteem en werk goed.
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Coates, Mark J. "Time frequency modelling." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/272036.
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Ganesan, Adarsh. "Phononic frequency combs." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274878.
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Optical frequency combs have resulted in significant advances in optical frequency metrology and found wide application to precise physical measurements and molecular fingerprinting. A direct analogue of frequency combs in the phononic or acoustic domain has not been reported to date. This thesis describes a series of results to provide the first clear evidence for the generation of phononic frequency combs in the domain of micromechanical resonators. These results are supported by a theoretical framework which was originally developed to predict the existence of such features of combs in physical systems described by Fermi-Pasta-Ulam dynamics. The phononic frequency combs is mediated by nonlinear coupling between a primary driven mode and one or more parametrically excited internal modes. We provide experimental evidence for the formation of such phononic frequency combs in systems comprising of 2 or more coupled modes, with results qualitatively consistent with previous numerical studies based on Fermi-Pasta-Ulam dynamics. Additionally, externally pumped comb processes are also reported. Through systematic experiments at different drive frequencies and amplitudes, we portray the well-connected processes of phononic frequency comb formation and define attributes to control their concomitant features. Further, the interplay between these new nonlinear resonances and the well-established Duffing phenomenon is also discussed. While the experimental verification of the existence of phononic frequency combs is of scientific interest, several potential engineering applications exist including the unique capability to track resonant frequency of a micromechanical resonator without the requirement for an external feedback loop to sustain oscillations at the resonant frequency. The initial experimental results also demonstrate that good short-term frequency stability may be obtained for such micromechanical resonators operated under ambient conditions.
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Gaucher, Yann. "Odd-Frequency Pairing." Thesis, Uppsala universitet, Materialteori, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-401811.
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Mazzer, Eva <1996>. "HIGH FREQUENCY TRADING." Master's Degree Thesis, Università Ca' Foscari Venezia, 2021. http://hdl.handle.net/10579/19441.
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This paper is going to discuss the role of High Frequency Trading (HTF) in financial market and
whether it helps the economy or if it is obstructing other agents in the market. HFT is a subset of
the algorithmic trading (‘AT’) distinguished by the speed at which it processes and determines
plays in the market. This is due to the sophisticated technology components that are reducing the
latency, the time occurring between when the order is placed and when it is executed. The
analysis starts from current knowledge of HFT and why its introduction was so revolutionary in the
way trading is done today, changing its perception over time. HFT is not just algorithms that help
execute orders, but brains that think on their own, making decisions in milliseconds backed by
machine learning based on proprietary strategies programmed by a firm. Characterizing the HFT
strategies could give an insight into the motives for trading, which could impact market quality,
also providing evidence on intraday return predictability. The regulatory and real effects on the
market, taking into consideration the so-called flash-crash, particularly the one that occurred on
May 6, 2010, will be discussed further in this paper. Ultimately, after the analysis of pros and cons
are evaluated, this paper will conclude with the implications surrounding HFT and fairness in the
market – which is the main crux of this paper. Human beings are supposed to know what it is right
and what it is wrong but trying to put a border between the two of them is not definitively clear
with regards to HFT. Using this assumption, a study will be conducted to see if the assumption
holds true and whether fairness in the market is adversely affected by HFT.
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Marian, Adela Ye Jun. "Direct frequency comb spectroscopy for optical frequency metrology and coherent interactions." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/dissertations/fullcit/3186934.
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Cai, Kun, and 蔡琨. "Bayesian carrier frequency offset estimation in orthogonal frequency division multiplexing systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841367.
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Li, Jie. "High frequency power transformer modelling for frequency response analysis (FRA) diagnosis." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538489.
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Transformer fault diagnosis through Frequency Response Analysis (FRA) has been receiving a great deal of attention in recent years. As a comparative technique, FRA has good capability and sensitivity in detecting mechanical faults that are difficult to identify by conventional condition assessment techniques. Power transformers are among the most expensive equipment owned by electric utilities, and it is not reasonable to produce deformation on actual transformers and carry out measurement sensitivity studies. On the other hand, simulation models, which can accurately reproduce transformer high frequency behaviours, are flexible tools for performing FRA deformation type sensitivity studies for deriving FRA interpretation rules. The main objective of this thesis is to develop appropriate simulation models for use in FRA diagnosis and to improve the interpretation of FRA responses through simulation studies. The transformer models developed at the University of Manchester (then UMIST) were by far the best representation of state-of-art modelling techniques; the inductance and the capacitance of the basic model unit were calculated using winding geometry and material properties, the frequency dependent conductive and dielectric losses were also included. In addition, mutual capacitive and inductive couplings between units were carefully considered to ensure the accuracy of the model. However, there is still some room for improvement on these models and during this PhD research, major contributions are made on as. follows: firstly take core effect into consideration to reproduce valid FRA characteristic representation in the low frequencies, secondly status of network terminal nodes are uniformed represented by externally connecting an impedance so that during FRA deformation sensitivity study, it is flexible to change the terminal condition, thirdly reconfigure the network node and unit relationship so that tap winding connection are precisely represented as the design, finally convert the single-phase model to a three-phase model and by developing a reduced matrix model, keep the simulation accuracy intact for a three-phase transformer up to 2 MHz, at the same time reduce computational time significantly. In detail, this PhD thesis describes the following three parts of my research: Firstly a transformer model incorporating a magnetic core based on the Principle of Duality is established to interpret low frequency characteristics of FRA responses (from 10Hz to up to 1 kHz). This model includes leakage inductances and capacitances of windings and can explain FRA low frequency differences caused by asymmetry of magnetic paths in three-limb and five-limb core transformers. Secondly, FRA characteristics were studied systematically using a component-system approach through building models for single windings, a one-phase winding set and finally the three-phase transformer. In this way the effects of winding structure, inductive and capacitive coupling among windings, among phases and terminal connection effect on FRA characteristics were studied. FinaUya complete three-phase transformer reduced matrix model is built, that can flexibly represent winding terminal connection and precisely describe tap positions. Using this modelling strategy, transmission power transformers at 2751132 kVand 275/33 kV voltage levels are simulated and numerous deformation sensitivity studies are performed, in order to gain better understanding on their FRA characteristics and to identify FRA features of different winding deformation types on these transformers. The research indicates that the overall approach used to develop these simulation models has helped in improving interpretation of FRA responses. The transformer modelling techniques being developed, with further refinement, can be a useful tool for FRA diagnosis and benefit the test engineers from the industry.
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Feng, Mabel Y. "Frequency translation method for low frequency variable gain amplification and filtering." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41642.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.<br>Includes bibliographical references (leaves 75-78).<br>This thesis discusses an innovative solution to an industry challenge. A frequency translation method is designed to shift low frequency signals to intermediate frequencies in order to utilize higher-frequency components. This solution, appropriate for applications involving 1-10MHz signals, can provide continuously variable gain and filtering at little cost in dynamic performance. The working system converts the low frequency signals up to the 70MHz band to achieve up to 28dB attenuation and 60-86MHz variable filtering. A Single Side Band system has a Signal-to-Noise Ratio (SNR) of 71dB with a 73dB SNR Analog-to-Digital Converter (ADC), 44 dB Output Third-Order Intercept Point (OIP3), and a Noise Figure (NF) of 14dB. Ultrasound and other applications in the 1-10MHz range benefit greatly from this upconversion scheme.<br>by Mabel Y. Feng.<br>M.Eng.
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Gul, Malik Muhammad Usman. "Timing and frequency synchronization for orthogonal frequency division multiple-access systems." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52328.
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Reliable timing and frequency synchronization is a major requirement in orthogonal frequency division multiple-access (OFDMA) systems as synchronization errors can result in inter-symbol-interference (ISI) and inter-carrier-interference (ICI) in the received signal, which severely degrade system performance. Thus, the objective of the proposed research is to develop, analyze, and prototype timing and frequency synchronization techniques for downlink (DL) and uplink (UL) OFDMA transmissions. For synchronization in DL OFDMA transmissions, we have developed conditions to select appropriate Zadoff-Chu sequences as training symbols that allow timing synchronization in the presence of large carrier frequency offsets (CFO). Using the proposed training block, we have designed training signal detection, timing synchronization, and integer CFO estimation algorithms. We have further proposed the training signal design for frequency synchronization in DL coordinated multi-point (COMP) transmissions, in which a user has to synchronize to multiple base-stations at the same time. In this respect, a frequency synchronization algorithm for DL COMP receiver has been designed using the proposed training signal along with its hardware implementation to analyze real-time performance. For frequency synchronization in UL OFDMA transmissions, we have proposed a null sub-carrier-based CFO estimation algorithm, and carried out its identifiability and acquisition range analysis. The proposed algorithm supports both sub-band and generalized sub-carrier allocations. We have also designed a CFO estimation and compensation algorithm for UL single-carrier frequency division multiple-access (SC-FDMA) transmissions. The proposed algorithm is based on parallel factor analysis and supports interleaved sub-carrier allocation. In addition, it guarantees the identifiability of CFO estimation and allows the system to operate on full load. Detailed simulations results have been provided along with discussions on computational requirements, which reveal that the proposed algorithms provide significant improvements in performance and efficiency compared to state of the art schemes in the literature.
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Elayouty, Amira Sherif Mohamed. "Time and frequency domain statistical methods for high-frequency time series." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8061/.
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Advances in sensor technology enable environmental monitoring programmes to record and store measurements at high-temporal resolution over long time periods. These large volumes of high-frequency data promote an increasingly comprehensive picture of many environmental processes that would not have been accessible in the past with monthly, fortnightly or even daily sampling. However, benefiting from these increasing amounts of high-frequency data presents various challenges in terms of data processing and statistical modeling using standard methods and software tools. These challenges are attributed to the large volumes of data, the persistent and long memory serial correlation in the data, the signal to noise ratio, and the complex and time-varying dynamics and inter-relationships between the different drivers of the process at different timescales. This thesis aims at using and developing a variety of statistical methods in both the time and frequency domains to effectively explore and analyze high-frequency time series data as well as to reduce their dimensionality, with specific application to a 3 year hydrological time series. Firstly, the thesis investigates the statistical challenges of exploring, modeling and analyzing these large volumes of high-frequency time series. Thereafter, it uses and develops more advanced statistical techniques to: (i) better visualize and identify the different modes of variability and common patterns in such data, and (ii) provide a more adequate dimension reduction representation to the data, which takes into account the persistent serial dependence structure and non-stationarity in the series. Throughout the thesis, a 15-minute resolution time series of excess partial pressure of carbon dioxide (EpCO2) obtained for a small catchment in the River Dee in Scotland has been used as an illustrative data set. Understanding the bio-geochemical and hydrological drivers of EpCO 2 is very important to the assessment of the global carbon budget. Specifically, Chapters 1 and 2 present a range of advanced statistical approaches in both the time and frequency domains, including wavelet analysis and additive models, to visualize and explore temporal variations and relationships between variables for the River Dee data across the different timescales to investigate the statistical challenges posed by such data. In Chapter 3, a functional data analysis approach is employed to identify the common daily patterns of EpCO2 by means of functional principal component analysis and functional cluster analysis. The techniques used in this chapter assume independent functional data. However, in numerous applications, functional observations are serially correlated over time, e.g. where each curve represents a segment of the whole time interval. In this situation, ignoring the temporal dependence may result in an inappropriate dimension reduction of the data and inefficient inference procedures. Subsequently, the dynamic functional principal components, recently developed by Hor mann et al. (2014), are considered in Chapter 4 to account for the temporal correlation using a frequency domain approach. A specific contribution of this thesis is the extension of the methodology of dynamic functional principal components to temporally dependent functional data estimated using any type of basis functions, not only orthogonal basis functions. Based on the scores of the proposed general version of dynamic functional principal components, a novel clustering approach is proposed and used to cluster the daily curves of EpCO2 taking into account the dependence structure in the data. The dynamic functional principal components depend in their construction on the assumption of second-order stationarity, which is not a realistic assumption in most environmental applications. Therefore, in Chapter 5, a second specific contribution of this thesis is the development of a time-varying dynamic functional principal components which allows the components to vary smoothly over time. The performance of these smooth dynamic functional principal components is evaluated empirically using the EpCO2 data and using a simulation study. The simulation study compares the performance of smooth and original dynamic functional principal components under both stationary and non-stationary conditions. The smooth dynamic functional principal components have shown considerable improvement in representing non-stationary dependent functional data in smaller dimensions. Using a bootstrap inference procedure, the smooth dynamic functional principal components have been subsequently employed to investigate whether or not the spectral density and covariance structure of the functional time series under study change over time. To account for the possible changes in the covariance structure, a clustering approach based on the proposed smooth dynamic functional principal components is suggested and the results of application are discussed. Finally, Chapter 6 provides a summary of the work presented within this thesis, discusses the limitations and implications and proposes areas for future research.
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Ismael, Alexander. "Comparison of fast frequency reserve strategies for Nordic grid frequency stability." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-411503.
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How long would modern society cope with a power outage, what would happen to vital systems that we today take for granted in modern society. The Nordic electricity grid is facing a major shift where electricity production from non-renewable sources are to be replaced increasingly by renewable sources. By increasing the penetration of wind and solar power the electric power system might be exposed to disturbances due to decreasing inertia as a result of the electricity transition. Currently the electric power system has different reserves to use to maintain frequency stability but there are other reserves that could help further in the fight for the balance between electricity production and consumption. This project examines whether the new reserve service, fast frequency reserve (FFR), can help the existing frequency containment reserve for disturbed (FCR-D) operation. Therefore, two experiments were conducted using the simulation tool ARISTO, addressing relevant issues involving frequency stability. Motivation for the hypothesis was to investigate if FFR could reduce the frequency transients and improve frequency variations by developing various setups and cases when inertia was retained and when the system inertia was reduced at different stages. The results of the experiments showed that the global minimum frequency, nadir, had increased for all test cases compared to the reference case when using FFR, this proved that the FFR in fact help reducing frequency transients. The results showed furthermore that when the FFR had a duration time of 30 seconds compared to only 5 seconds, the frequency variations could be improved for certain setups for experiment 2.
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Abdulhamed, Bilal Khudhur Abdulhammed. "Digital Instantaneous Frequency Measurement Receiver for Fine Frequency and High Sensitivity." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1559548084463134.
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Cai, Kun. "Bayesian carrier frequency offset estimation in orthogonal frequency division multiplexing systems." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42841367.
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Pei, Zhengyang. "Load Frequency Control Design for Improving Frequency Quality of Power Systems." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21979.
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Load frequency control (LFC) has been widely recognized as a feasible tool in power system frequency regulation. With the rapidly increasing scale of power grids and proportion of renewables in power systems, the frequency control has been potentially impaired because this occurrence may raise more power fluctuations and diminish power system inertia. In light of this, there is a necessity to accommodate the current frequency control methods to the emerging integrated power systems. Against this background, this thesis addresses the frequency control problems from two aspects: one of ameliorating the performance of load frequency control immediately after frequency excursions, and the other of mitigating the power fluctuations in wind energy penetrated power systems. On the one hand, the traditional frequency control can be enhanced by tuning appropriate parameters through optimization tools. Meanwhile, by scheduling proper power dispatch for each generator unit, which refers to optimal power dispatch, the system also sees improvement. Specifically, with the commercialization of power industries, the optimal power dispatch is related to operating economy in electricity markets, where frequency ancillary services are provided. Therefore, the frequency ancillary service, as well as the economic factor is considered to comprehensively compose the reformed load frequency control design. In consideration of this, to start with, an optimal power dispatch scheme (OPDS) method is presented. This method incorporates power dispatch within load frequency control through the proposed optimization framework. Sequentially, an optimal frequency ancillary service strategy (OFASS) considering the operational costs is developed in frequency control ancillary services (FCAS) markets. In these markets, power industries tender for carrying out the ancillary services of load frequency control, and part of them are elected based on the cost and performance. As a part of the OFASS, the OPDS is used to propound the optimal scheme based on the determinate generating units to pursue a balance between minimizing the cost and facilitate the frequency control through reconstructing a comprehensive objective function. Genetic algorithm (GA) is utilized as the optimization tool. Simulations based on the singlearea control system and two-area system are carried out to verify the efficacy of this work in MATLAB Simulink. On the other hand, as an indispensable renewable resource, wind energy calls for further attention, of which the noticeable integration in power grids aggravates the power fluctuations in wind plants’ side due to its intractable characteristic, provoking the issue of power system frequency stability compared with the conventional power resources. Therefore, this thesis presents a novel control method to help manage the scarcely predictable and intensively fluctuating wind power to maintain the frequency quality. In this thesis, a discrete control is initially developed to curtail the undesirable wind power, which is caused by the wind speed rising in a short time, under the context of growing wind energy penetration. The potential overproduction of wind power is evaluated and categorized into three types by a classification mechanism, which monitors the instant change of wind speeds and assesses the offloading scheme. Specifically, the wind turbines are coordinated through using the pitch control in accordance with the given scheme. Meanwhile, a battery energy storage system (BESS) is equipped to compensate the fluctuating active power through storing and releasing the energy, contributing to frequency regulation. Consequentially, the discrete control and the BESS are incorporated into the BESS cooperating with the discrete control (BCDC) method to ameliorate the frequency quality in integrating wind power. Finally, Monte Carlo (MC) method is used to simulate the variable wind speed samples while validating the feasibility and performance of the work in MATLAB Simulink and DIgSILENT PowerFactory.
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Jones, Graeme Stephen. "Instantaneous frequency, time-frequency distributions and the analysis of multicomponent signals." Thesis, Queensland University of Technology, 1992.
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Hill, Martin T. "New techniques for measurement and tracking of phase and frequency." Thesis, Curtin University, 1997. http://hdl.handle.net/20.500.11937/1923.
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This thesis presents and analyses new techniques to measure and track the phase and frequency of high frequency narrow bandwidth signals. In particular, these techniques are all digital in nature or can be implemented in digital integrated circuit technology.Presented first is a frequency measurement technique which involves sampling at regular intervals a binary quantized narrow band signal. The binary quantized samples are digitally processed to obtain the instantaneous frequency of the signal.It is shown that small phase movements in the signal can be detected even though the sampling occurs at a rate much lower than the signal frequency; that there are no frequency offsets in the frequency measurement technique; that the phase error in the technique is small and bounded provided the signal frequency is maintained within derived limits. Other properties of the technique are also derived.The frequency measurement technique is experimentally demonstrated in a number of typical applications.Secondly, a new phase tracking system is presented, which has similarities to conventional phase locked loops. However, unlike phase locked loops, the new system incorporates a local reference source which effectively stabilizes the phase estimate of the signal input being tracked.It is shown that the new system has the following advantages: Precise centre frequency, controllable lock range, and elimination or reduction of the effects of imperfections like voltage controlled oscillator phase noise. General behaviour in noise of the new phase tracking system is derived.An implementation of the new system is presented which employs the frequency measurement technique described above. This implementation is characterized by very precise centre frequency, high phase noise suppression, and can be built almost entirely in digital integrated circuit technology. The new system is experimentally demonstrated in some typical applications.The techniques presented in this thesis provide improvements of several orders of magnitude in the ability of systems implemented in digital integrated circuit technology to: Measure and control phase and frequency of narrow band signals; Implement high performance phase tracking systems.
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Geladakis, Dimitrios N. "Comparison of the step frequency radar with the conventional constant frequency radars." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA328272.
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Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, December 1996.<br>"December 1996." Thesis advisor(s): Gurnam S. Gill. Includes bibliographical references (p. 45). Also available online.
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Xu, Yiwen. "Frequency analysis of low-frequency field fluctuations detected by the Cluster satellites." Thesis, KTH, Rymd- och plasmafysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91547.
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Elias, Bartholomew. "Cross-modal facilitation of spatial frequency discriminations through auditory frequency cue presentations." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/28611.
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Ledingham, Jamie Andrew. "The estimation of flood frequency curves by mapping from rainfall frequency curves." Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1320.
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Recent large flooding events have reinforced the need for prudent flood risk management. The July 2007 floods in Yorkshire and the Midlands and the November 2009 floods in the Lake District have highlighted the current vulnerability of key infrastructure and the built environment in the UK to flooding. This existing flood risk is coupled with concerns over the potential impacts of future climate change on flood regimes. Therefore, there is a need to develop tools and methodologies to assess the potential impact of likely climate change on flood risk. The link between large rainfall and flow events is first examined, as well as an assessment of the seasonality of these events. This reveals a distinct east-west split in the seasonal concentration of flooding. This work provides a basis for the development of a statistical modelling technique which estimates a catchment flood record on an event basis. The model uses estimates of the flood generating storm and the antecedent conditions to estimate a flow magnitude. The modelled flood record is then transformed into a flood frequency curve using an appropriate statistical method. Extensive testing of the model has assessed its robustness to the length of flood record used in fitting and its sensitivity to the input climate data. Several case studies using the UKCP weather generator show how the method works as well as providing an indication of how future climate changes may affect the flood frequency curve. The frequency curve mapping method developed here performs best on catchments whose flood regime is driven by rainfall. The use of a simple antecedent rainfall accounting method has been shown to perform as well as a quasi-physical soil moisture estimation method. The research undertaken offers several possibilities to develop understanding of flood frequency curves in catchments with short gauged records. This new methodology has the potential for further development and can be used to explore a wide range of future scenarios.
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Ziai, Mohamad Ali. "Electrically thin and platform insensitive ultra high frequency radio frequency identification tags." Thesis, University of Kent, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.594196.
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The objective of this research is to design passive UHF RFID tags that are insensitive to the platform they are applied to. The tag antennas developed in this work will exhibit good read range in harsh electromagnetic environments, such as metallic objects, liquid containers and human skin, while balancing the tag unit cost and form factor with perfonnance. In the early part of this thesis a brief introduction to RFID, the essential antenna parameters, the physics of RFID and the environmental effects on tag antennas sets the background necessary for understanding the procedure used when designing and measuring tag performance. As part of this fundamental research process, a tag design methodology is developed and evaluated by designing a global tag, before proceeding to design passive tags specific for unfriendly electromagnetic environments. In later part of the thesis, passive platform tolerant tags will be designed to identify electromagnetically unfriendly objects in different real working environments. The first design will identify large EM unfriendly objects. The requirement for this tag is ruggedness and long read range on any object, while keeping the tag profile as low as possible. The second tag will be designed to identify curved metallic objects such as gas cylinder. This tag will be designed on a tou-gh flexible substrate to conformal on curved objects. This main objective of this design is to identify metallic cylinder from all direction in the plane of the tag antenna. The third tag will be an ultra-thin design for identification of objects where low profile and low cost platform tolerant tagging is required. Ultra low profile platform tolerant tag design is also one of the main objectives of this work, which will be achieved in this design. The last tag in this work will ~ designed to identify humans in secure environments, where temporary access to facilities or sites is paramount. This non-transferable tag will be designed to be mountable directly onto the skin surface in the form of a transfer patch in much the same way that a temporary tattoo could be applied. - Since passive tags have ·to be designed for massive production at low cost and high reliability, all the designs in this work will aim at uncomplicated planar structures with high efficiency and high manufacturing tolerance on low cost commonly available substrates .
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Bozic, Milos. "Suppression techniques of unwanted spurious frequency components in direct digital frequency synthesis." Thesis, University of Bradford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385596.
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MARTINEZ, DIANA MARGARITA GARCIA. "VOLTAGE STABILITY ASSESSMENT CONSIDERING PRIMARY FREQUENCY CONTROL AND FREQUENCY-DEPENDENT LINE PARAMETERS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25603@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>PROGRAMA DE EXCELENCIA ACADEMICA<br>A crescente demanda de energia elétrica faz com que a complexidade dos
sistemas elétricos de potência seja cada vez maior, associado às limitações na
expansão do sistema de transmissão, resulta na operação dos sistemas elétricos
mais próximos de seus limites, tornando-os vulneráveis a problemas de
estabilidade de tensão. Nesse contexto, faz-se necessário o desenvolvimento de
ferramentas computacionais capazes de representar os sistemas elétricos mais
adequadamente, melhorando assim as condições de análise. Neste trabalho são
apresentadas três modelagens do fluxo de carga mais completas que a modelagem
clássica, a saber: a modelagem de múltiplas barras swing, a modelagem com
regulação primária e a modelagem com parâmetros da rede de transmissão
variáveis com a frequência. Uma vez utilizadas na solução do problema do fluxo
de carga estas modelagens são estendidas para a realização do cálculo dos índices
de estabilidade de tensão das barras de carga, barras de tensão controlada e barras
swing. Testes numéricos com um sistema-teste de 6 barras são apresentados para a
verificação da aplicabilidade e adequação dos modelos analisados.<br>The growing demand for electricity increases the complexity of electric
power systems which, when combined with limitations in the expansion of
transmission systems, results in the operation of electrical systems closer to their
limits, making them vulnerable to voltage stability problems. In this context, there
is a gap in the market for the development of computational tools that can
represent the electrical systems more appropriately, thereby improving the
conditions of analysis. The present study formulates three non-classical load flow
representations: multiple swing buses, primary frequency control, and frequency
dependent transmission network parameters. Once used in the load flow problem
solving, these models are also extended to allow the calculation of voltage
stability indices of load buses, controlled voltage buses and swing buses.
Numerical tests with a 6-bus test system are presented to verify the applicability
and adequacy of the proposed models.
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Delichatsios, Stefanie Alkistis. "Multi-dimensional ultra-high frequency passive radio frequency identification tag antenna designs." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37050.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.<br>Includes bibliographical references (leaves 77-79).<br>In this thesis, we present the design, simulation, and empirical evaluation of two novel multi-dimensional ultra-high frequency (UHF) passive radio frequency identification (RFID) tag antennas, the Albano-Dipole antenna and the Albano-Patch antenna, that provide omnidirectional communication capabilities. The performance of a passive UHF RFID tag is highly dependent upon the tag's antenna design, the tag's placement on an item, the materials in the item, and the item's surrounding environment. The majority of existing commercial tag antennas are two-dimensional making the tags a) orientation-sensitive, working well in some directions and not at all in others, and b) susceptible to communication interference from the contents of the tagged object. The Albano antenna designs are three-dimensional, affording the tags to be minimally affected by object material while maintaining near omnidirectional performance. The Albano antenna designs provide significantly improved orientation insensitivity compared with existing widely deployed commercial tag antenna designs.<br>by Stefanie Alkistis Delichatsios.<br>M.Eng.
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Jung, Chang won, Ming-jer Lee, Sunan Liu, G. P. Li, and Flaviis Franco De. "RECONFIGURABLE PATCH ANTENNA FOR FREQUENCY DIVERSITY WITH HIGH FREQUENCY RATIO (1.6:1)." International Foundation for Telemetering, 2005. http://hdl.handle.net/10150/605028.
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ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada<br>Reconfigurable patch antenna integrated with RF mircoelectromechanical system (MEMS) switches is presented in this paper. The proposed antenna radiates circularly polarized wave at selectable dual frequencies (4.7 GHz and 7.5GHz) of high frequency ratio (1.6:1). The switches are incorporated into the diagonally-fed square patch for controlling the operation frequency, and a rectangular stub attached to the edge of the patch acts as the perturbation to produce the circular polarization. Gain of proposed antenna is 5 - 6dBi, and axial ratio satisfies 3dB criterion at both operating frequencies. The switches are monolithically integrated on quartz substrate. The antenna can be used in applications requiring frequency diversity of remarkable high frequency ratio.