Dissertations / Theses on the topic 'Phase-frequency response'

This thesis concerns partial discharge (PD) diagnostics withvariable frequency of applied voltage in the frequency range 1mHz - 400 Hz. The exploration of a new type of spectroscopythat combines partial discharge analysis and dielectricresponse is demonstrated. A question addressed is if and howthe PD activity varies with the frequency of the appliedvoltage. The nature of an existing frequency dependence couldbe useful in the classification of different defects and tojudge the degree of progressive ageing. A Variable-Frequency Phase Resolved Partial DischargeAnalysis (VF-PRPDA) technique is developed for the appliedvoltage frequency range 1 mHz - 400 Hz. The VF-PRPDA techniqueis combined with a system for high voltage dielectricspectroscopy that allows simultaneous measurements. TheVF-PRPDA technique is used for studying the frequencydependence of PD. The PD activity is for example measured byintegrated measures like total charge per cycle and totalnumber of discharges per cycle. Statistical measures like mean,standard deviation, skewness, kurtosis etc. are applied tomeasure the frequency dependence of the phasedistributions. High voltage dielectric spectroscopy is supplemented withharmonic analysis for studying non-linear dielectric responsecurrents. The VF-PRPDA technique is demonstrated on defined objectslike point-plane gaps and artificial voids, but also on aninsulated stator bar and a paper insulated cable. Surfacedischarges on insulating surfaces are studied in an environmentwith a controlled relative humidity and temperature. Theadsorption of moisture on the insulating surface alters thesurface conductivity of the surface and the frequencydependence of the PD activity. The influence of temperature upon the PD activity is studiedfor a oil paper insulated cable. The results of the measurements show that the partialdischarge activity in general is frequency dependent over thefrequency range 1 mHz - 400 Hz. The reasons behind thefrequency dependence are linked to surface- and bulk-conducting mechanisms, frequency dependent field distributionsand statistical effects of the supply of start electrons. An algorithm is developed that relates the phase resolved PDcurrent measured with the PRPDA technique to the non-linearcurrent measured with dielectric spectroscopy. The algorithm isexperimentally verified by simultaneous measurements of PRPDAand dielectric spectroscopy on defined objects. The resultsexplain the contribution of PD to the apparent capacitance andloss. Moreover, the harmonics of the fundamental currentcomponent yield information about, for example, polaritydependent discharge sources. Keywords:diagnostic methods, partial discharges, phaseresolved, variable frequency, dielectric spectroscopy,dielectric response, harmonics, insulation
QC 20100527

The hardware validation of a novel average-value model (AVM) for the simulation of a synchronous-generator/controlled rectifier system is presented herein. The generator is characterized using genetic algorithm techniques to fit standstill frequency response (SSFR) measurements to q and d-axis equivalent circuits representing the generator in the rotor reference frame. The generator parameters form the basis of a detailed model of the system, from which algebraic functions defining the parametric AVM are derived. The average-value model is compared to the physical system for a variety of loading and operating conditions including step load change, change in delay angle, and external closed-loop control, validating the model accuracy for steady-state and transient operation.

В роботі проведено аналіз методів вимірювання амплітудно-частотної характеристики чотириполюсників. Розроблено схему електричну структурну вимірювача. Запропоновано канал комунікації з комп’ютером через порт. Управління роботою вимірювача здійснюється мікроконтролером. Розроблено схему електричну принципову та проведено розрахунки її каскадів. Технічні характеристики вимірювача: Діапазон робочих частот 0…50 МГц; Діапазон частот, обмежений чистотою спектру сигналу 0…33 МГц; Діапазон вимірюваного рівня сигналу в логарифмічному масштабі 0…-83дБ; Мінімальний крок переналаштування 1 Гц; Відношення сигнал/шум 105 дБ. Параметри вимірювача відповідають заявленим в технічному завданні.
The analysis of methods of measurement of amplitude-frequency characteristic of fourpoles is carried out in the work. The scheme of the electric structural meter is developed. A communication channel with a computer through the port is offered. The meter is controlled by a microcontroller. The electric circuit diagram is developed and calculations of its cascades are carried out. Technical characteristics of the meter: Operating frequency range 0… 50 MHz; Frequency range limited by the purity of the signal spectrum 0… 33 MHz; The range of the measured signal level on a logarithmic scale 0… -83dB; Minimum reconfiguration step 1 Hz; The signal-to-noise ratio is 105 dB. The parameters of the meter correspond to those stated in the technical task.
Вступ 8 1 Основна частина 9 1.1 Аналіз технічного завдання 9 1.2 Проектування схемотехнічне 10 1.3 Розробка і розрахунок структурної схеми 10 1.4 Розрахунок схеми електричної принципов 11 1.5 Проектування програмне 37 1.6 Розробка алгоритму роботи мікроконтролера 37 1.7 Вибір і обґрунтування елементної бази 40 1.8 Розробка компоновки і конструкції друкованого вузла 42 2 Безпека життєдіяльності, основи охорони праці 44 2.1 Моделі безпеки життєдіяльності 44 2.2 Джерела електромагнітного випромінювання 46 Висновки 51 Список використаних джерел 52 Додатки 53

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.
Includes bibliographical references (leaves 39-40).
Phase reversals and phase plateaus have been found in studies that measure motion of the basilar membrane (BM) at the base of the cochlea in response to high-level sounds above the characteristic frequency (CF). In contrast, such patterns have not been found in responses of auditory-nerve fibers (ANF) from the base of the cochlea, primarily because these ANFs do not have synchronized responses to high-frequency tones. We sought counterparts to the BM responses in auditory nerve fibers (ANF) by using a new method that extracts phase information from beat-producing multi-tone stimuli. The method can determine the relative phases of ANF responses to high-frequency tones by measuring the phases of low-frequency beats and from these beats, reconstructing the relative phases of the original tone response. We also used amplitude modulated (AM) tones at high sound levels. The data collected suggest that the new beat-producing phase-analysis method is effective at tip and tail regions of the ANF tuning curves. However, this method has low success in measurements at frequencies above CF due to low signal-to-noise ratios and large distortion products in the ANF responses. AM tones, however, were more successful and showed significant evidence of a phase plateau at high levels and at frequencies well above the fiber's CF.
(cont.) Thus this plateau response appears to be present in ANF firings as well as BM motion. ANF responses to multi-tone stimuli presented above CF and at moderate level resulted in an anomalous negative group delay. Presuming that the multi-tone method yields a valid picture of the original high frequency phase responses we speculate that the anomaly is produced by complex interactions among two or more response components at the above-CF region of the ANF tuning curve.
by Holden Cheng.
S.M.

This thesis deals with the dynamic properties of electric pressure transducers. These are properties that are reflected in the measurement of rapid, time-dependent processes. They could be described in two ways. Either by using amplitude and phase frequency response characteristics, or just one particular value. Natural frequency, cutoff frequency or time constant. These parameters indicate the extreme values for the use of measuring devices in the measurement of time-dependent processes. In this work will be described procedures for determining these parameters.

У роботі досліджена актуальна задача проектування двосмугових фільтрів на діелектричних резонаторах з вищими типами коливань, що полягає в розробці математичних моделей та нових конструкцій, що забезпечують необхідні електричні параметри за мінімальної кількості елементів зв’язку. Запропоновано використання вищого робочого типу коливання ДР з більш високою добротністю разом із нижчим для побудови двосмугового фільтра; спосіб побудови двосмугових фільтрів на прямокутних ДР, який відрізняється тим, що за рахунок використання видовжених форм ДР з робочими коливаннями TE11δ та TE12δ дозволяє забезпечити приблизно однакові коефіцієнти зв’язку в обох робочих смугах пропускання; спрощений спосіб розрахунку коефіцієнтів зв’язку ДР на основі напруженості магнітного поля; отримано нові аналітичні вирази для розрахунку коефіцієнта взаємного зв'язку між резонаторами; розроблені математичні моделі двосмугових багаторезонаторних фільтрів на «дипольному» та «квадрупольному» типах коливань прямокутних ДР; запропоновано нові конструкції двосмугових багаторезонаторних фільтрів, які відрізняються тим, що мають мінімальну кількість елементів зв'язку.

A resonantly-coupled ��-Stirling (RCAS) cooler was designed and constructed. Tests on air and helium were performed with constant driving displacement over a range of frequencies. The effects of changing driving amplitude and charged pressure were studied. The use of stainless steel bellows in place of pistons eliminated the problem of piston seals and relaxed the construction tolerances. The fatigue life of the bellow is, however, a problem. The experimental optimization based on Taguchi methods was performed on regenerator mass, regenerator wire diameter, vibrating mass, and damping coefficient. Driven by a voice coil actuator, the characteristic phase shift of the Stirling cycle cooler was demonstrated where the hot-end displacement led the cold-end displacement. The 90�� phase shift was selected as the natural frequency. The pressure-volume diagrams for each working space were plotted and the indicated powers were determined. The compression powers in the hot and cold-ends show maximum values near the natural frequency. The mechanisms are different. At the hot-end where the displacement was kept constant, operation near the natural frequency gave a maximum pressure ratio and also maximized the compression power. The phase shifts in the cold-end were, however, relatively constant. The maximum pressure ratio and amplitude gave the maximum expansion power near the natural frequency. The expansion powers in the cold-end as indicators of cooling potential were approximately 2-4 watts for the air case, and 3-7 watts for the helium case. In both air and helium tests, the value of the parasitic losses reached 12 watts. The temperature difference developed across the regenerator is considered an indication of the cooling capacity. Good correlations were found between the indicated cooling capacity in the expansion space and the temperature difference. For a given size of cooler, the use of helium offered higher cooling capacity due to smaller pressure drop loss and smaller amplitude ratio. Higher cooling performance was also attained from helium at elevated pressures.
Graduation date: 1998

碩士
國立臺灣大學
電信工程學研究所
96
Nowadays, direct-conversion radio frequency (RF) receivers become more appealing. However, orthogonal frequency division multiplexing (OFDM) systems with direct-conversion RF receivers are very sensitive to non-idealities at the front-end of receiver, such as I/Q imbalance, carrier frequency offset (CFO), and phase noise (PHN). These non-idealities at the receiver result in inter-carrier interference (ICI). Accurate estimates of the non-idealities and channel response are required in OFDM systems. In this thesis, the effects of I/Q imbalance, CFO, and PHN on OFDM systems are studied, and the estimation of these parameters is considered. To solve the problems, we propose a time domain method for joint estimation of I/Q imbalance, CFO, and PHN as well as channel response. The proposed method requires only one OFDM training block as a preamble to accomplish joint estimation. Moreover, we do not put any restrictions on the preamble signal and thus the proposed method can be adopted in any communication systems with a preamble. It is shown by simulation results that our proposed method performs well for any channels as long as their order is not longer than cyclic prefix (CP).

碩士
國立中正大學
通訊工程研究所
96
Orthogonal Frequency Division Multiplexing (OFDM) systems play an important role in physical layer of modern WLAN.Direct-conversion RF receiver is low-cost and low-power-consuming, but it introduces IQ imbalance.Phase noise is common when imperfect oscillators are used at the transmitter and receiver.The channel frequency response varies as time proceeds or as the location of transmitter and receiver change.In this thesis, we consider recovering the WLAN OFDM signals in the presence of these imperfect conditions.We propose two methods, one is the least-square (LS) equalization, and the other is least-mean-square (LMS) equalization.From computer simulation results, we conclude that the LMS equalization outperforms,in terms of bit error rates, the LS equalization.

We develop a theory of vectorial wave coupling in cubic photorefractive crystals placed in an alternating ac-field to enhance the nonlinear response. First we analytically and numerically investigate the dependences of the first Fourier harmonics of the space-charge field, induced in an AC-biased sillenite crystal by a light-interference pattern, on the light contrast m. The data obtained was used to extend the vectorial beam-coupling theory on the whole contrast region. In particular, we proved in the general case that despite of essential differences between thediffusion and AC nonlocal responses the later keeps the light interference fringes straight during the interaction. This fundamental feature allows, under certain restrictions, to reduce the nonlinear problem of vectorial coupling to the known linear problem of vectorial Bragg diffraction from a spatially uniform grating, which admits an exact solution. As a result, the nonlinear vectorial problem can be effectively solved for a number of practically important cases.The developed theory was applied to describe the transformation of a momentary phase changes of one of the input beams into the output intensity modulation (so-called grating translation technique). In contrast to the previous studies, we take into account the change of the space-charge field amplitude across the crystal (the coupling effects). The theory developed is employed to optimize the conditions for the linear signal detection under polarization filtering for the transverse and longitudinal optical configurations. We also analyze the possibility of the linear detection without polarization filtering.Illumination of AC-biased photorefractive BTO crystals with a coherent light beam results in development of strong nonlinear scattering. We investigate the angular and polarization characteristics of the scattered light for the diagonal optical configuration and different polarization states of the pump.

The main goal of this thesis is to develop practical digital controller architectures for multi-phase dc-dc converters utilized in low power (up to few hundred watts) and cost-sensitive applications. The proposed controllers are suitable for on-chip integration while being capable of providing advanced features, such as dynamic efficiency optimization, inductor current estimation, converter component identification, as well as combined dynamic current sharing and fast transient response. The first part of this thesis addresses challenges related to the practical implementation of digital controllers for low-power multi-phase dc-dc converters. As a possible solution, a multi-use high-frequency digital PWM controller IC that can regulate up to four switching converters (either interleaved or standalone) is presented. Due to its configurability, low current consumption (90.25 μA/MHz per phase), fault-tolerant work, and ability to operate at high switching frequencies (programmable, up to 10 MHz), the IC is suitable to control various dc-dc converters. The applications range from dc-dc converters used in miniature battery-powered electronic devices consuming a fraction of watt to multi-phase dedicated supplies for communication systems, consuming hundreds of watts. A controller for multi-phase converters with unequal current sharing is introduced and an efficiency optimization method based on logarithmic current sharing is proposed in the second part. By forcing converters to operate at their peak efficiencies and dynamically adjusting the number of active converter phases based on the output load current, a significant improvement in efficiency over the full range of operation is obtained (up to 25%). The stability and inductor current transition problems related to this mode of operation are also resolved. At last, two reconfigurable digital controller architectures with multi-parameter estimation are introduced. Both controllers eliminate the need for external analog current/temperature sensing circuits by accurately estimating phase inductor currents and identifying critical phase parameters such as equivalent resistances, inductances and output capacitance. A sensorless non-linear, average current-mode controller is introduced to provide fast transient response (under 5 μs), small voltage deviation and dynamic current sharing with multi-phase converters. To equalize the thermal stress of phase components, a conduction loss-based current sharing scheme is proposed and implemented.

In this thesis, multidimensional signal processing techniques to mitigate disturbances in synthetic aperture systems such as radio telescopes are investigated. Here, two computationally efficient three-dimensional (3D) spatio-temporal (ST) finite impulse response (FIR) cone filter bank structures are proposed. Furthermore, a strategy is proposed to design 3D ST FIR frustum filter banks, having double-frustum-shaped passbands oriented along the temporal axis, derived from appropriate 3D ST FIR cone filter banks. Both types of cone and frustum filter banks are almost alias free and provide near-perfect reconstruction. In the proposed cone and frustum filter banks, both temporal and spatial filtering operations can be carried out at a significantly lower rate compared to previously reported 3D ST FIR cone filter banks implying lower power consumption. Furthermore, the proposed cone and frustum filter banks require a significantly lower computational complexity than previously reported 3D ST FIR cone and frustum filter banks. Importantly, this is achieved without deteriorating the improvement in signal-to-interference-plus-noise ratio. A theoretical analysis of brightness distribution (BD) errors caused by parameter perturbations and mismatches among the transfer functions of receivers employed in synthetic aperture systems is presented. First, the BD errors caused by perturbations in the transfer functions of low noise amplifiers (LNAs) and anti-aliasing filters (AAFs) are considered, and the characteristics of the additive BD error and its effects on synthesized BDs are thoroughly analyzed. Second, the conditions that should be satisfied by the transfer functions of digital beamformers to eliminate the BD errors caused by their phase responses are examined. The sufficient condition to eliminate the BD errors is that the transfer functions are matched, and, interestingly, the phase responses are not necessary to be linear. Furthermore, the BD errors caused by typical tolerances of passive L and C elements used to implement the AAFs and those caused by the random variations of gain from LNA to LNA are quantified through numerical simulations. The simulations indicate that substantial BD errors are observed at frequencies that are close to the passband edge of the AAFs.
Graduate

The current research work aims at the development of Biomedical Neuroengineering tools (Biotechnologies) for the in-depth functional study, rapid diagnosis, continuous monitoring and well-timed management of acute and chronic brain disorders, of individuals that are subjected to or suffer from any kind of systemic hypoxaemia or more localized brain hypoxia; as well as the functional assessment and continuous control of adaptability during the training of “altinauts” and generally of individuals that practice activities and function within environments of increased visual-cognitive-motor response demands (a type of brain “stress test”). For this purpose, we subject the entire visuocognitive system, from the elementary sensory to the most complex cognitive level, to an experimental test of categorical discrimination of complex visuocognitive stimuli, following ultra-rapid visual stimulation that leads to a motor response upon categorization of targets (images of animals elicit productive responses) and to its suppression upon categorization of nontargets (images of nonanimals elicit inhibitory responses). The oscillatory electro-physiological responses that are concurrently recorded at the occipital-temporal-parietal brain areas are analyzed in the time-domain (<20Hz) and in the joint time-frequency domain broadband (1-60Hz) with the Continuous Wavelet Transform that optimizes the multiresolution analysis of the high frequency (≥20Hz) γ-band oscillatory activity. This visuocognitive categorization test takes place in normoxaemic as well as hypoxaemic conditions (monitored reduction in the blood oxygen saturation from ≥97% to around 80% under conditions of hypobaric hypoxia within a hypobaric chamber), in order to assess electrophysiological markers that can detect and capture in the most sensitive and dynamic way even so transient, short-living and rather mild changes in brain function. The statistical parametric analysis of the time-frequency maps and the generalized, statistically safer, method of analysis of variance have established as the most sensitive and reliable the following markers: the major deflections of the evoked potentials, the phase-coherence factor of the oscillations across single-trials and the elicited energy of the evoked/phase-locked and the induced/total oscillatory activity. These electrophysiological markers in conjunction with psychometric tests allow for the investigation of the stages/levels of the decline as well as of the compensatory reserves in the visual-perceptive and cognitive-mental brain functions in order to determine the functional sensitivity thresholds of different brain functions to hypoxia. They open up the way for the functional characterization, the diagnosis and monitoring of brain insults or other acute and chronic pathological brain conditions.
Η παρούσα ερευνητική εργασία στοχεύει στην ανάπτυξη εργαλείων Βιοϊατρικής Νευρομηχανικής (Βιοτεχνολογίες) για την σε βάθος λειτουργική μελέτη, ταχεία διάγνωση, συνεχή παρακολούθηση και έγκαιρη αντιμετώπιση οξέων και χρόνιων εγκεφαλικών διαταραχών, ατόμων που υπόκεινται σε ή πάσχουν από οιαδήποτε μορφή συστηματικής υποξαιμίας ή πιο εντοπισμένης εγκεφαλικής υποξίας, καθώς και για την λειτουργική αξιολόγηση και το συνεχή έλεγχο της προσαρμοστικότητας κατά την εξάσκηση των «υψιβατών», και γενικότερα ατόμων που ασκούν δραστηριότητες και λειτουργούν μέσα σε περιβάλλοντα αυξημένων οπτικο-γνωστικο-κινητικών απαιτήσεων (ένα είδος «στρες τεστ» για τον εγκέφαλο). Για το σκοπό αυτό υποβάλλουμε ολόκληρο το οπτικογνωστικό σύστημα, από το στοιχειώδες αισθητηριακό έως το πιο πολύπλοκο νοητικό επίπεδο, σε μια πειραματική δοκιμασία κατηγορικής διάκρισης σύνθετων οπτικογνωστικών ερεθισμάτων, μετά από υπερταχεία οπτική διέγερση που οδηγεί στην έκλυση κινητικής απάντησης κατά την κατηγοριοποίηση στόχων (εικόνες «ζώων» εκλύουν παραγωγικές αποκρίσεις) και στην καταστολή της κατά την κατηγοριοποίηση μη-στόχων (εικόνες «μη-ζώων» εκλύουν ανασταλτικές αποκρίσεις). Οι ταλαντωτικές ηλεκτροφυσιολογικές αποκρίσεις που συγχρόνως καταγράφονται στις ινιακές-κροταφικές-βρεγματικές περιοχές του εγκεφάλου αναλύονται στο πεδίο του χρόνου (<20Hz) και στο συζευγμένο χρονοφασματικό πεδίο ευρυζωνικά (1-60Hz) με το συνεχή μετασχηματισμό του κυματίου που βελτιστοποιεί την πολυφασματική ανάλυση της υψίσυχνης (≥20Hz) γ-ταλαντωτικής δραστηριότητας. Αυτή η δοκιμασία οπτικογνωστικής κατηγοριοποίησης λαμβάνει χώρα τόσο σε νορμοξαιμικές όσο και υποξαιμικές συνθήκες (ελεγχόμενη μείωση στον κορεσμό του αίματος σε οξυγόνο από ≥97% γύρω στο 80% για 15 λεπτά κάτω από συνθήκες υποβαρικής υποξίας μέσα σε υποβαρικό θάλαμο), προκειμένου να ελέγξουμε ηλεκτροφυσιολογικούς δείκτες που μπορούν να ανιχνεύσουν και να συλλάβουν με τον πιο ευαίσθητο και δυναμικό τρόπο ακόμη και τόσο βραχύβιες και σχετικά ήπιες μεταβολές της εγκεφαλικής λειτουργίας. Η στατιστική παραμετρική ανάλυση των χρονοφασματικών χαρτών και η γενικευμένη, στατιστικά πιο ασφαλής, μέθοδος ανάλυσης των διακυμάνσεων ανέδειξαν ως πλέον ευαίσθητους και αξιόπιστους τους ακόλουθους δείκτες: τις κύριες αιχμές των προκλητών δυναμικών, τον παράγοντα φασικής συνάφειας των ταλαντώσεων μεταξύ των μοναδιαίων καταγραφών και την εκλυόμενη ενέργεια των προκλητών/φασικά-κλειδωμένων και επαγόμενων/ολικών ταλαντώσεων. Οι ηλεκτροφυσιολογικοί αυτοί δείκτες σε συνδυασμό με ψυχομετρικές δοκιμασίες επιτρέπουν τη διερεύνηση των σταδίων/επιπέδων κάμψης καθώς και των αποθεμάτων αντιρρόπησης των οπτικο-αντιληπτικών και γνωστικών-νοητικών λειτουργιών του εγκεφάλου για τον καθορισμό των λειτουργικών ουδών ευαισθησίας διάφορων εγκεφαλικών λειτουργιών στην υποξία. Ανοίγουν μάλιστα το δρόμο. για το λειτουργικό χαρακτηρισμό, τη διάγνωση και την παρακολούθηση εγκεφαλικών προσβολών ή άλλων οξέων και χρόνιων παθολογικών καταστάσεων του εγκεφάλου.