Magnetoelectric (ME) interactions in matter correspond to the appearance of magnetization by means of an electric field (direct effect) or the appearance of electric polarization by means of a magnetic field (converse effect). The composite laminates which possess large ME coefficient, have attracted much attention in the field of sensors, modulators, switches and phase inverters. In this thesis, we report on the ME performances of the bi- and tri- layered composites. It is shown that their ME couplings can be achieved by combining magnetostrictive and piezoelectric layers. A model based on a driven damped oscillation is established for the piezoelectric/magnetostrictive laminated composite. It is used to simulate the mechanical coupling between the two layers. In addition, we report that the ME coupling can be achieved without magnetic phase but only with eddy current induced Lorentz forces in the metal electrodes of a piezoelectric material induced by ac magnetic field. The models based on the Lorentz effect inducing ME coupling in PZT unimorph bender, polyvinylidene fluoride (PVDF) film and PZT ceramic disc are thus established. The results show the good sensitivity and linear ME response versus dc magnetic field change. Thus, the room temperature magnetic field detection is achievable using the product property between magnetic forces and piezoelectricity. Besides, we report on the electrostrictive performance of cellular polypropylene electret after high-voltage corona poling. We use the Surface Potential test, Thermal Stimulated Depolarization Current experiment and Differential Scanning Calorimetry experiment to analyse its charge storage mechanism. The result show that the electrostrictive coefficient and relative permittivity of the charged samples increase. Last but not least, in order to explain this phenomenon, a mathematic model based on the charged sample has been established.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Mémoire (M.Eng.)--Université du Québec à Chicoutimi, 2001. / Document électronique également accessible en format PDF. CaQCU

Diss.--Mayence, 1992. / Bibliogr. p. 367-384.

Η παρούσα μεταπτυχιακή διπλωματική εργασία πραγματεύεται την εισαγωγή ενός νέου πεδίου πεμπτουσίας, η ενέργεια του οποίου ταυτίζεται με το ενεργειακό απόθεμα της σκοτεινής ενέργειας του σύμπαντος. Η εισαγωγή ενός τέτοιου πεδίου αποτελεί εναλλακτική λύση στην προσπάθεια ερμηνείας της επιταχυνόμενης διαστολής του σύμπαντος που συνδέεται συνήθως με την κοσμολογική σταθερά Λ, των πεδιακών εξισώσεων Άινσταϊν. Παρότι έχουν προταθεί και άλλα μοντέλα πεδίων πεμπτουσίας, το συγκεκριμένο χαρακτηρίζεται από μία ιδιότητα που δεν επιτρέπει την εκτεταμένη παραβίαση της Αρχής της Ισοδυναμίας, που αποτελεί θεμελιώδη παραδοχή στην οποία στηρίζεται η Γενική Θεωρία της Σχετικότητας. Η μάζα των αντίστοιχων σωματιδίων εξαρτάται από την πυκνότητα ύλης σε κάθε περιοχή του σύμπαντος, εξ ου και το όνομα χαμαιλέοντες. Αφορμή για την εισαγωγή ενός τέτοιου πεδίου είναι η επιβεβαίωση της Αρχής της Ισοδυναμίας μέχρι κάποιο συγκεκριμένο όριο, πέραν του οποίου επιτρέπεται η εισαγωγή νέων μοντέλων αλληλεπιδράσεων που δεν έγιναν ακόμα αντιληπτές σε πληθώρα πειραμάτων. Όλα τα προηγούμενα αναφέρονται εν συντομία στο εισαγωγικό πρώτο κεφάλαιο. Στο δεύτερο κεφάλαιο γίνεται μια παρουσίαση της Αρχής της Ισοδυναμίας και του βαθμού παραβίασης της ο οποίος καθορίζει την ένταση της νέας θεμελιώδους δύναμης (fifth-force). Στο τρίτο κεφάλαιο, γίνεται μια ανασκόπηση του καθιερωμένου κοσμολογικού μοντέλου για το σύμπαν, που από παρατηρήσεις χαρακτηρίζεται από ομοιογένεια, ισοτροπία και σχεδόν επίπεδη γεωμετρία (WMAP-7). Με αυτά τα δεδομένα, καθώς και με τα πρόσφατα αποτελέσματα για ένα επιταχυνόμενα διαστελλόμενο σύμπαν προκύπτει η ανάγκη ύπαρξης ενός πεδίου με τα χαρακτηριστικά ενός σκοτεινού υγρού αρνητικής πίεσης και μάζας σε κοσμολογικές κλίμακες, της τάξης της σταθεράς Hubble στο παρόν (m_\phi\sim H_0\sim 10^{-33}eV). Η ανάγκη ύπαρξης ενός τέτοιου πεδίου (πάντα ως εναλλακτική της κοσμολογικής σταθεράς) παντού στο σύμπαν σε συνδυασμό με την μη ανίχνευση του μέχρι στιγμής σε κανένα πείραμα ή παρατήρηση, συνυπάρχουν στο μοντέλο των Khoury-Weltman για τα σωματίδια χαμαιλέοντες που εξετάζεται στο κεφάλαιο τέσσερα. Επειδή η μάζα του πεδίου εξαρτάται από την τοπική πυκνότητα ύλης, στη Γη η χαμαιλεοντική αλληλεπίδραση έχει πολύ μικρή εμβέλεια σε αντίθεση με την εμβέλεια σε κοσμολογικές κλίμακες και δεν γίνεται αντιληπτή. Επιπλέον η συνεισφορά στην αλληλεπίδραση σε ένα σώμα εκτός Γης από όλο τον όγκο της Γης είναι ελάχιστη και περιλαμβάνει μόνο αυτήν που προκαλείται από ένα λεπτό φλοιό στην επιφάνεια, όπου η τοπική πυκνότητα ύλης ελαττώνεται (thin-shell effect). Η νέα δύναμη το δυναμικό της οποίας είναι της μορφής Yukawa, θα είναι ασθενέστερη τουλάχιστον κατά τρεις τάξεις μεγέθους σε σύγκριση με τη βαρύτητας πειράματα στη Γη. Στο τελευταίο κεφάλαιο γίνεται μια παρουσίαση του CAST (Cern Solar Axion Telescope), στο οποίο θα μπορούσαν να ανιχνευτούν τα σωματίδια χαμαιλέοντες, λαμβάνοντας υπόψη την επέκταση του μοντέλου ώστε να περιλαμβάνει και ζεύξη με το ηλεκτρομαγνητικό πεδίο πέραν των πεδίων της ύλης. Οι χαμαιλέοντες που παράγονται από φωτόνια παρουσία ισχυρού μαγνητικού πεδίου στο θερμό πλάσμα του Ήλιου, φτάνουν στη Γη έχοντας ενέργεια της τάξης του 1keV και μπορούν να εισχωρήσουν στο εσωτερικό του μαγνήτη του CAST. Ο ισχυρός μαγνήτης του πειράματος που είναι ιδίου τύπου με αυτούς που απαρτίζουν τον Μεγάλο Αδρονικό Επιταχυντή (LHC), δημιουργεί μαγνητικό πεδίο της τάξης των 9Τ. Στο εσωτερικό του, οι χαμαιλέοντες θα μπορούσαν να επαναμετατραπούν σε φωτόνια και να ταυτοποιηθούν. Επιπλέον, ένα μικρό ποσοστό των χαμαιλεόντων που αφήνουν την επιφάνεια του Ήλιου μπορούν να μετατραπούν πίσω σε φωτόνια εξαιτίας των μαγνητικών πεδίων πάνω από τη φωτόσφαιρα. Αυτά τα φωτόνια θα έχουν φάσμα ενέργειας που κορυφώνεται στην περιοχή των μαλακών ακτίνων-Χ, οπότε θα δίνουν λύση στο πρόβλημα θέρμανσης του ηλιακού στέμματος (solar corona problem). / In the present Thesis, we review the chameleon field model and its discovery potential at CAST (Cern Axion Solar Telescope). The introduction of this new scalar field, of the so called quintessence type, is an alternative way of modeling the ubiquitous dark energy in the Universe, which drives its accelerated expansion. Moreover, the coupling of chameleons to photons enriches their discovery potential by experiments already operating such as CAST. Due to the fact that the mass of the field depends on the local matter density, in a dense environment such as the earth's surface the chameleon particle becomes heavy and undetectable. On the contrary, in cosmological scales the mass of the field is reduced to values related to the present Hubble's constant value (m_\phi\sim H_0\sim 10^{-33}eV) in order to coincide with the dark energy budget. This Thesis is organized in five chapters. The first chapter serves as a quick introduction to the subject of the current Thesis and the reasons for introducing a new field are stated. The second chapter refers to the Principle of Equivalence (E.P), a foundational principle of Einstein's General Relativity. It states that the gravitational mass of a freely falling body is proportional to its inertial mass. The level of verification of the former principle is of crucial importance for the characteristics of a quintessence field. If the E.P is not valid below a certain length scale, then the introduction of a quintessence field also implies the excistence of a new fundamental force in nature (fifth-force). In the third chapter, a small review of the standard cosmological model is made, which in combination with the results for an accelerated universe, leads to the necessity of introducing a new form of energy, dark energy. This form of energy behaves like a dark fluid of negative pressure (repulsive force) that tends to expand spacetime. It is modeled by adding the cosmological constant Λ, in Einstein's field equations or by introducing quintessence fields as the case of this Thesis. As already mentioned, the excistence of a quintessence field yields to violation of the Equivalence Principle. To overcome an extensive violation of the E.P the chameleon model is ``equipped'' by the peculiar property of its mass dependance on the environmental density. A second phenomenon related to the former property and the suppression of the E.P violation, is the ``Thin Shell Effect''. It simply states that the chameleonic profile of a large object is suppresed inside its bulk, and only a thin shell near its surface produces the chameleon force which is exerted on other massive bodies. This effect interprets the weakness and to date not discovered possible fifth-force. The fourth chapter ends up with a discussion on the fifth-force mediated by the chameleon particle. It is estimated that if such force exists, is about 3 orders-of-magnitude weaker than gravity. In the final chapter of this Thesis, the CAST experiment is presented. CAST has been operating for over ten years, searching for axions emitted by the Sun. It is believed that photons can oscillate to chameleons in the presence of a strong magnetic field in the Sun, travel through space and reach the Earth's surface where they can reconvert to photons inside the helioscope's pipe. The spectrum of the chameleons reaching the Earth is peaked at sub-keV region. Furthermore a small part of the chameleons leaving the Sun are converted back to photons over the photosphere due to the magnetic fields present there. These photons have energy lying in the soft X-ray region, hence addressing the solar corona problem.

abstract: Electric utilities are exploring new technologies to cope up with the in-crease in electricity demand and power transfer capabilities of transmission lines. Compact transmission lines and high phase order systems are few of the techniques which enhance the power transfer capability of transmission lines without requiring any additional right-of-way. This research work investigates the impact of compacting high voltage transmission lines and high phase order systems on the surface electric field of composite insulators, a key factor deciding service performance of insulators. The electric field analysis was done using COULOMB 9.0, a 3D software package which uses a numerical analysis technique based on Boundary Element Method (BEM). 3D models of various types of standard transmission towers used for 230 kV, 345 kV and 500 kV level were modeled with different insulators con-figurations and number of circuits. Standard tower configuration models were compacted by reducing the clearance from live parts in steps of 10%. It was found that the standard tower configuration can be compacted to 30% without violating the minimum safety clearance mandated by NESC standards. The study shows that surface electric field on insulators for few of the compact structures exceeded the maximum allowable limit even if corona rings were installed. As a part of this study, a Gaussian process model based optimization pro-gram was developed to find the optimum corona ring dimensions to limit the electric field within stipulated values. The optimization program provides the dimen-sions of corona ring, its placement from the high voltage end for a given dry arc length of insulator and system voltage. JMP, a statistical computer package and AMPL, a computer language widely used form optimization was used for optimi-zation program. The results obtained from optimization program validated the industrial standards. / Dissertation/Thesis / M.S. Electrical Engineering 2012

Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study that including the process in which a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be sufficiently accelerated to up to several hundred MeV within 2-3 solar radii. When the shock propagates through a streamer-like magnetic field, particles are more efficiently accelerated compared to the case with a simple radial magnetic field, mainly due to perpendicular shock geometry and the natural trapping effect of closed magnetic fields. Our results suggest that the coronal magnetic field configuration is an important factor for producing large SEP events. We further show that the coronal magnetic field configuration strongly influences the distribution of energetic particles, leading to different locations of source regions along the shock front where most high-energy particles are concentrated. This work may have strong implications for SEP observations. The upcoming Parker Solar Probe will provide in situ observations for the distribution of energetic particles in the coronal shock region, and test the results of the study.

The objective of this thesis is to create Gaussian 1D filters with rotating kernel theory which enables to program algorithm for noise reduction and beam structure highlighting in a digital picture of the solar corona. A fragment of original picture of solar corona and of pictures filtred by this algorithm is in the enclosure.

A novel insulating cross-arm (ICA) has been developed for new and existing overhead transmission lines of up to 400 kV. The cross-arm consists of four insulating members, end fittings, field grading devices and a nose connection for the attachment of the conductor. The two main structural elements of the assembly have a unique non-cylindrical geometry which gives them improved mechanical characteristics compared to conventional overhead line insulators. The profile for the compression insulator has been designed. After examining six profile variations, it was determined that the lateral orientation which would give the best performance would be with the flat face of the core facing upwards and tilted by 6o. Using the results obtained from performing flashover tests on a conventional 145 kV insulator, the elevation angle for the compression insulator was set to 6o. The dimensions of the compression insulator were calculated based on the assumption that the ICA would be used to uprate an OHL with L3 towers from 275 kV to 400 kV. The optimal insulator profile was determined to be an alternating profile with three different shed sizes, an arcing distance of 3083 mm and a creepage distance of 12470 mm. Electric field grading devices for the ICA were designed. For the LV end, a grading device resembling a ring which follows the general shape of the cross-section of the insulator was designed. For the HV end, an iterative process yielded two designs. First, the ‘butterfly’ grading device was a unibody piece of cast aluminium for all four ICA members. FEA simulations and tests in the laboratory showed that it could effectively control the electric field at voltages of up to 132 kV. The design was patented and the device was used on six cross-arms installed on a live line in Scotland in August 2013. Second, the ‘M-W’ grading device, was a solution made out of four components for managing the field at voltages of up to 400 kV. The device was designed to be easy to install and service, easy and cheap to manufacture and to have minimal visual impact. The compression insulator and the cross-arm assembly were subjected to a multitude of tests adapted from international standards and the Technical Specifications of National Grid. The performed tests aimed to test the electrical characteristics of the cross-arm and the quality of the materials and manufacturing process of the compression insulator. All of the tests were completed successfully except from the corona extinction test for which the appropriate equipment was not available at the time. Two trials were commissioned to examine how the cross-arm performs in a service-like environment. The snow and ice accretion patterns recorded at the mechanical trial site were used for optimising the profile of the compression insulator. The results after a year of continuous monitoring of leakage current and weather conditions at the live trial site showed that there were humidity and visibility thresholds, above 93% for the former and below 400 m for the latter, which increased the average leakage current by 15% on the tension insulators and by 20% on the compression insulators. It was found that when the longitudinal axis of the cross-arm was perpendicular to the weather the leakage current was higher because more of its surface was exposed. The performance of the novel compression insulators was found to be as good as that of the industry standard tension insulators, reaffirming the potency of the design. Finally, on-site observations showed that the ‘butterfly’ grading device could not effectively manage the electric field on the cross-arm at 400 kV, confirming the results of the FEA simulations and testing.

Due to the universal considerable population and economic growth rate, demands for energy have risen significantly over the past decade. This means that the integration of renewable energies in the power grid has escalated as well as requests for reactive power compensation, voltage stability, and mitigation of harmonic filters. Capacitor banks are widely used in the modern electrical transmission system in order to improve power quality and efficiency. In other words, this device aims to be involved in harmonic disturbance elimination, improve the power factor (PF), provide voltage control and stability which leads into more sustainable energy systems. Utilizing high voltage components, such as shunt capacitors in the power grid can introduce new challenges. One of these challenges is known as corona discharge. The aim of the presented master thesis is to study and develop corona discharge suppression models on high voltage capacitor banks which is implemented in collaboration with ABB power grids, Sweden. The main concerns are, effective factors on corona emergence, corona inception voltage levels, and corona suppression methods. Also, this study evaluates the verification of existing suppression. Two various approaches were applied and compared. The aim of the first approach is to evaluate corona discharge by electric field calculations on three various capacitor banks with different voltage levels. The simulation was implemented based on Maxwell’s equations and finite element method (FEM) by utilizing COMSOL Multiphysics software. The second approach is based on streamer inception and propagation. The calculation on this method is fulfilled with the help of MATLAB software. The results of both approaches were found reasonably compatible. It is discovered that corona discharge can appear in different voltage levels on capacitor banks based on various factors, such as the geometry of the bank. Consequently, the suppression method may vary case by case and different proposals were suggested in order to optimize the corona suppression rings. / På grund av den allmänna betydande befolknings- och ekonomiska tillväxttakten har kraven på energi ökat markant under det senaste decenniet. Detta innebär att integrationen av förnybara energier i elnätet har eskalerat samt begäran om reaktiv effektkompensering, spänningsstabilitet och mildring av harmoniska filter. kondensatorbatterier används ofta i det moderna elektriska transmissionssystemet för att förbättra strömkvaliteten och effektiviteten. Med andra ord syftar denna enhet till att vara involverad i eliminering av harmonisk störning, förbättra effektfaktorn (PF), tillhandahålla spänningskontroll och stabilitet som leder till mer hållbara energisystem. Att använda högspänningskomponenter, som shuntkondensatorer i elnätet, kan skapa nya utmaningar. En av dessa utmaningar kallas korona-urladdning. Syftet med den presenterade masteruppsatsen är att studera och utveckla korona-urladdningsmodeller på högspännings-kondensatorbatterier som implementeras i samarbete med ABB Power Grids, Sverige. De viktigaste problemen är effektiva faktorer för korona uppkomst, spänningsnivåer korona och metoder för att underlätta korona. Dessutom utvärderar denna studie verifieringen av befintliga undertryckningsmetoder. Två olika tillvägagångssätt tillämpades och jämfördes. Syftet med det första tillvägagångssättet är att utvärdera korona-urladdning genom elektriska fältberäkningar på tre olika kondensatorbatterier med olika spänningsnivåer. Simuleringen implementerades baserat på Maxwells ekvationer och finita elementmetoden (FEM) genom att använda COMSOL Multiphysics programvara. Det andra tillvägagångssättet är baserat på strömningslinjernas början och utbredning. Beräkningen av denna metod genomförs med hjälp av MATLAB-programvaran. Resultaten från båda metoderna tycktes vara rimligt kompatibla. Det upptäcks att korona-urladdning kan förekomma i olika spänningsnivåer på kondensatorbatterier baserat på olika faktorer, till exempel batteriets geometri. Följaktligen kan undertryckningsmetoden variera från fall till fall och olika förslag föreslogs för att optimera koronaundertryckningsringarna.