High dielectric constant materials have tremendous impact on miniaturization of devices that are used in various applications like wireless communication systems, microelectronics, global positioning systems, etc. To store electric charge in a very small space necessarily needs a capacitor with very high dielectric constant. Thus, these materials are very important in fabricating capacitors, or metal oxide semiconductor filed effect transistor (MOSFET). Among the existing commercially available devices, silicon-based microelectronic devices are commonly used based on the moderately stable dielectric constants of silicon with low losses and minimal temperature and frequency dependence. However, now-a-days, the perovskite based transition metal oxides have drawn attention that have the ability to fulfill all the requirements for being a good dielectric material in all the industrial applications. In this thesis we have studied a few selected perovskite based transition metal oxide systems in terms of their dielectric and magnetic behaviour. In Chapter 1, we have have given brief introductions about the some application of dielectric materials and the origin of dielectric and magnetic properties in the materials. We have also discussed about the polarisation in the dielectric materials to understand it’s frequency dependence and also to formalise different relaxation behaviour with the help of physical and mathematical explanation. In Chapter 2, we describe the various methodologies adopted in this thesis. In Chapter 3, we have studied the dielectric behaviour of Nd2NiMnO6, a rare earth based double perovskite ferromagnetic insulator. We successfully synthesised and characterised the compounds, settled the valency issues with the help of temperature dependent XAS of the transition metal atom in contrast to the existing controversy available in literature. We have found that this material shows relaxor kind behaviour with a colossal dielectric constant value. We have studied in details the origin of the colossal dielectric constant and the relaxation behaviour along with the a.c and d.c. transport properties. We have shown the origin of the ferromagnetism (TC ∼ 200 K) with a low temperature antiferromagnetic ordering (TN ∼ 55 K) with the help of detailed studies of temperature dependent d.c., a.c. magnetism and their XMCD. We have also investigated the isothermal variation of magnetodielectric and magnetoresistance behaviour as a function of magnetic field and their origin. In Chapter 4,we study the effect of cation anti-site disorder on the magnetic, dielectric and transport properties of another rare earth based ferromagnetic double perovskite insulator La2NiMnO6 by controlling different extent of anti-site disordered. We have confirmed the valency of the transition metal cations using XAS technique and followed by shown, different types of magnetic interaction between the transition metal cations using d.c magnetic, quantitative XMCD analysis and the origin of large dielectric response, a.c. transport & dielectric relaxation using temperature variation dielectric measurement as an experimental evidence in contrast of our previous speculation published in literature. We further have studied, the coupling between the magnetic and electric spin through isothermal magnetodielectric measurement. In Chapter 5, we have successfully synthesised and characterised a solid solution of YMnxIn1−xO3 series via different mol % of In doping in the multiferroic YMnO3 system. YMnO3 is a well known multiferroic material studied rigorously during past few decades. We have seen, YMnO3 which has a antiferromagnetic ordering temperature of ∼ 75 K suppressed with increasing the dopant concentration In. We have figured out the effect of In doping in the suppression of multiferroic phase and extended it to the dielectric properties. We have found that, the temperature dependence of dielectric constant shows an anomaly at the magnetic ordering temperature and studied magnetodielectric coupling. We have also investigated the temperature variation of dielectric relaxation and a.c. transport behaviour as a function of composition. In Chapter 6, we have identified the phase seperation and proposed a phase diagram as function of Gd doping in the Ho2−xGdxCuTiO6 double perovskite, where two end member, namely Ho2CuTiO6 and Gd2CuTiO6 are found to be in two different crystallographic phase as, hexagonal (P63cm) and orthorhombic (Pnmm), respectively. We have characterised the valency of the transition metal cations using XAS.We have seen very less temperature and frequency dependence of dielectric constant in hexagonal phase in compare to the orthorhombic phase and tried to figuring out from experimental analysis by performing temperature dependence dielectric const measurement. We also have shown the effect of doping in the origin of dielectric relaxation, a.c transport and magnetic behaviour of this system. In Chapter 7, we have synthesised and characterised successfully two different rare earth based layered perovskite La3Cu2VO9 and La4Cu3MoO12 compounds are of centrosymmetric space group. We have figured it of the valency of the different atoms present in the compound using XAS. We also do have observed the good temperature stability of dielectric constant of these materials and explored origin of mechanism in the dielectric relaxation, a.c. transport property by performing the temperature dependance dielectric measurement. The magnetic structure also have shown with the help of d.d. magnetic measurements. In Appendix A, we have seen the very stable dielectric constant constant from very low to above room temperature of the 2D nano PbS. The frequency stability of dielectric constant is also remarkable in compare to bulk PbS values available in literature. We have explored the origin of the conductivity and relaxation mechanism performing dielectric constant measurement. In conclusion, we investigate, in this thesis, dielectric properties of different transition metal oxides system and the mechanism of dielectric relaxation, a.c, d.c transport and their origin of magnetic response.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-11-11T17:33:21Z No. of bitstreams: 0 / Made available in DSpace on 2016-11-11T17:33:21Z (GMT). No. of bitstreams: 0 / O desenvolvimento de sistemas laser com pulsos ultracurtos trouxe a possibilidade de usinagem de estruturas muito pequenas em praticamente qualquer tipo de material. Neste trabalho foi dada continuidade a estudos já iniciados no Centro de Lasers e Aplicações (CLA) com os materiais dielétricos, introduzindo a largura temporal dos pulsos laser como mais uma variável e utilizando os conhecimentos adquiridos para a determinação de limiares de ablação e parâmetros de incubação em alguns metais como: aço AISI 1045, aço inoxidável VI138, cobre eletrolítico e molibdênio. A ausência de calor no processo de ablação dos metais torna-se muito difícil, pois a criação de uma camada de íons é muito prejudicada pela mobilidade eletrônica ao seu redor. Assim a ablação de metais com pulsos ultracurtos, tem como principal mecanismo a explosão de fase associada a outros processos que também contribuem na ablação, porém em menor escala, como a explosão coulombiana e a fusão ultrarrápida. Além disso, propriedades como a constante de acoplamento elétron-fônon e a condutividade térmica assumem um papel importante e devem ser levadas em conta na investigação do processo de ablação dos metais. Este trabalho possibilitou a obtenção de parâmetros de operação nos quais o calor transferido para a rede é minimizado, possibilitando a microusinagem de precisão e alterações controladas na morfologia da superfície de diversos metais. Os resultados propiciaram assim condições para novos desenvolvimentos e aplicações práticas de usinagem com pulsos ultracurtos. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

This diploma thesis deals with the fundamental properties of epoxide mixtures, as determining of these fundamental properties of epoxide mixtures could in the case of favorable results lead to diminishing the amount of defects in epoxide-embedded instrument transformers. As the influence of effects in the manufacturing process of transformers causing poor quality is very extensit, the biggest emphasis is laid capitally on the influence of the epoxide casting mixture composition. The thesis describes the manufacture technology including used methodics and materials. The compositions of epoxide resins and the mechanisms of their curing. Also, the definitions of fundamental properties of dielectric materials and the description of diagnostic methods used to relative permitivity, dissipation factor and inner resistivity are included. suitable casts of acquired samples were set and dried out within the experimental part, followed by measurement of fundamental electrical properties in temperature and frequency relations. Hereafter a comparison of individual samples and the evaluation of their electrical properties will be carried out.

Le sujet de cette thèse concerne les applications hautes températures, où les moteurs doivent être capables de fonctionner à 400°C pendant 2 heures, selon la norme en vigueur. Il convient dans ce type d’applications de disposer de matériaux assez stables pour que leurs propriétés isolantes restent inchangées, ce qui est le cas du fil émaillé PolyImide (PI). Ce fil émaillé pose néanmoins des problèmes économiques et de fournisseurs, d’où la nécessité de trouver d’autres alternatives. Ce travail de thèse a eu pour but de mettre au point et valider des techniques d’analyses (ATG / ATM / ATR-FTIR / DRS) adaptées au fil émaillé, et ce jusqu’à 400°C. Le PEI présente des propriétés insuffisantes pour ce type d’application car il se dégrade avant 350°C et perd ses propriétés d’isolation électrique. Le PAI est un matériau qui ne se dégrade que peu avant 400°C, et présente des caractéristiques électriques (propriétés diélectriques et de conduction) déjà plus proche du PolyImide. Nous avons pu établir la comparaison de deux PAI dont l’un est conventionnel et l’autre est un nanocomposite à base d’alumine. Ce dernier PAI est plus stable en température mais ne semble pas avoir de propriétés électriques très supérieures. Pour confronter les résultats expérimentaux obtenus dans des conditions particulières aux conditions réelles d’utilisation, des moteurs avec ces fils émaillés ont été fabriqués. Les moteurs équipés des fils PEI/PAI (fil standard) et PAI sont défaillants après 40 minutes au lieu de 2h, contrairement aux moteurs équipés de fil PI. La dégradation du PEI et le fluage du PAI, caractérisé au-delà de sa Tg (280°C), peuvent être la cause des dysfonctionnements de ces moteurs / This work is related to the high temperature application where motors have to withstand severe conditions - 400°C during 2 hours - according to the standard. Electrical insulation becomes a serious challenge for such application where materials have to remain stable, which is the case of PolyImide enameled wire. Other alternatives have to be found because this is a very expensive material with a small number of suppliers. The thermal, structural, mechanical and electrical properties of these systems have been investigated in-situ until 400°C by thermogravimetric analysis, ATR-FTIR microscopy, thermomechanical analysis, dielectric spectroscopy and DC voltage experiments. Dielectric spectroscopy has indicated a loss of insulating properties during the thermal cycle especially for PEI-containing enamels that degrades before 350°C. PAI enameled wires degrade just before 400°C, and electrical properties (dielectric properties and conductivity) are closer to PI‘s in this temperature range. A comparison between a conventional PAI and a PAI filled with nanoparticules of aluminium oxide has been made. The nanocomposite is thermally more stable but does not show better electrical behavior. To correlate all these results to the real test conditions (combined thermal, electrical and mechanical stresses), electrical motors have been fabricated using the enameled wires said before. They all breakdown after 40 minutes running, except motors made with PI enameled wires. The degradation of PEI ad the creeping of PAI up to its Tg (280°C) can explain the breakdown of these motors

No description available.

This master’s thesis is focused on the study of chemical and physical properties of dielectric materials with main focus on epoxy resins. It includes possible processes that can influence the properties of epoxy resins, both processes that improve polymer properties and processes that cause material degradation. Next part of the thesis is a description of diagnostic methods suitable for measurement of basic electrical quantities of material and design of a suitable method for measuring properties of epoxy resins with different additives, influencing the samples by solar radiation. At the end, the work includes an experiment dedicated to the degradation of epoxy resins with various additives by solar radiation and the evaluation of the experiment.

This master‘s thesis deals with measurement of liquid dielectric materials (insulators). Above all, it is the different kinds of clean and drinking water, but also transformer oils. There was done theoretical information retrieval about the given topic in this project and on the basis of theory there were realized the relevant measurements of selected properties of liquid dielectric, such as permittivity, capacitance, loss number, conductivity, but also temperature dependence of these parameters. The measurements were realized with the help of product manufactured at the faculty FEKT VUT and with the help of measuring system AGILENT 16452A. The measured results were evaluated, graphically processed and compared.

Η ανίχνευση με τη χρήση μικροκυμάτων παίζει πολύ σημαντικό ρόλο στην τεχνολογική εξέλιξη του κόσμου τα τελευταία 50 χρόνια. Από τα ραντάρ μέχρι τη Μικροκυματική Ραδιομετρία, η ανίχνευση με τη χρήση μικροκυμάτων έχει χρησιμοποιηθεί για έναν αυξανόμενο αριθμό εφαρμογών σε διάφορα επιστημονικά πεδία, μεταξύ των οποίων η χαρτογράφηση του εδάφους, ο καθορισμός της υγρασίας του εδάφους, η θερμογραφία και η ανίχνευση του καρκίνου του μαστού. Έτσι, οι μικροκυματικοί αισθητήρες, διαθέτοντας την ικανότητα να διαπερνούν πολλά είδη μέσων (πχ. σύννεφα, βιολογικοί ιστοί), έχουν μια σημαντική θέση ανάμεσα σε άλλες τεχνικές μέτρησης. Η Μικροκυματική Ραδιομετρία αποτελεί ένα σημαντικό τομέα της επιστημονικής έρευνας και εφαρμογής της ανίχνευσης με τη χρήση μικροκυμάτων, καθώς αποτελεί μια παθητική μέθοδο ανίχνευσης της φυσικά εκπεμπόμενης χαοτικής θερμικής ακτινοβολίας από κάθε σώμα που βρίσκεται σε θερμοκρασία άνω του απόλυτου μηδενός (-273 Κελσίου). Ένα μικροκυματικό ραδιόμετρο είναι η συσκευή που χρησιμοποιείται για τη διεξαγωγή ραδιομετρικών μετρήσεων. Η ραδιομετρία έχει αποτελέσει ένα σημαντικό τομέα έρευνας όχι μόνο για την αξιολόγηση της ατμόσφαιρας και της επιφάνειας της γης, αλλά και για την περαιτέρω διερεύνηση των παθητικών μετρήσεων, με σημαντικές εφαρμογές ειδικά στον τομέα της βιοϊατρικής. Στα πλαίσια της παρούσας Διδακτορικής Διατριβής μελετήθηκε σε θεωρητικό και πειραματικό επίπεδο η βελτιστοποίηση των ιδιοτήτων ανίχνευσης ενός Τρισδιάστατου Συστήματος Παθητικής Μικροκυματικής Ραδιομετρικής Απεικόνισης για διαγνωστικές εφαρμογές εγκεφάλου. Η καινοτομία της προτεινόμενης μεθόδου έγκειται στη χρήση μιας αγώγιμης ελλειψοειδούς κοιλότητας που δρα σαν μορφοποιητής δέσμης, ώστε να επιτευχθεί μέγιστη συγκέντρωση και εστίαση της ακτινοβολίας που εκπέμπει το φυσικό σώμα ενδιαφέροντος, σε συνδυασμό με ευαίσθητους ραδιομετρικούς δέκτες και ομοιοκατευθυντικές κεραίες λήψης στο φάσμα συχνοτήτων 1 – 4 GHz. Η μέτρηση πραγματοποιείται με την τοποθέτηση του ανθρώπινου εγκεφάλου στην περιοχή της πρώτης εστίας και τη λήψη της ακτινοβολίας που συγκλίνει, μέσω ανάκλασης στα τοιχώματα του ελλειψοειδούς, στη δεύτερη εστία. Εκεί είναι τοποθετημένη η κεραία λήψης που συνδέεται στον ευαίσθητο ραδιομετρικό δέκτη. VI Με σκοπό τη βελτίωση των ιδιοτήτων εστίασης του συστήματος, πραγματοποιήθηκε η μοντελοποίησή του και ακολούθησε εκτενής ηλεκτρομαγνητική μελέτη για την ανάλυση της επίδρασης διατάξεων προσαρμογής από κατάλληλα υλικά στο εσωτερικό της ελλειψοειδούς κοιλότητας. Τα αποτελέσματα δείχνουν πως με τη σωστή επιλογή των υλικών και των ιδιοτήτων τους, είναι δυνατό να επιτευχθεί σημαντική βελτίωση του βάθους ανίχνευσης του κατωφλίου ανίχνευσης θερμοκρασίας και της χωρικής διακριτικής ικανότητας του συστήματος. Τα πειράματα με ομοιώματα που πραγματοποιήθηκαν, επαληθεύουν τις βασικές αρχές λειτουργίας του συστήματος καθώς επίσης και την ευεργετική επίδραση των διατάξεων προσαρμογής στις ιδιότητες εστίασής του, που μελετήθηκαν θεωρητικά στο πρώτο στάδιο της έρευνας,. Τέλος, οι πειραματικές διαδικασίες, που σχεδιάστηκαν με βάση πιθανές κλινικές εφαρμογές του συστήματος, δείχνουν ότι έχει βασικά χαρακτηριστικά και ιδιότητες ώστε να αποτελέσει στο μέλλον κλινικό, διαγνωστικό εργαλείο. / Microwave sensing has played an increasingly significant role in the world’s technological advances over the past 50 years. From radar to radiometry, microwave sensing has been used for a large number of applications, including ground mapping, soil moisture determination, thermography, and breast cancer detection. With the ability to safely penetrate many kinds of media (e.g., clouds or biological specimens), microwave sensors find a significant place among other modalities of measurement. Microwave radiometry is an important scientific research and application area of microwave sensing because it provides a passive sensing technique for detecting naturally emitted chaotic thermal radiation by any material object being above the absolute zero temperature (-273 Celsius). A microwave radiometer is the device used to conduct radiometric measurements. While radiometry has been a significant research field for atmospheric and earth surface evaluations, it lends itself to further exploration of passive measurements, with significant applications especially in the biomedical field. In the framework of the present PhD Thesis, a theoretical and experimental optimization study of the sensing capabilities of a Three Dimensional Passive Microwave Radiometry Imaging System for brain diagnostic applications was performed. The novelty of the proposed methodology consists in the use of a conductive ellipsoidal cavity acting as a beamformer to achieve maximum peak of radiation pattern in order to measure the intensity of the microwave energy, radiated by the medium of interest, by using sensitive microwave radiometers and relevant non – contacting antennas within the range of 1 – 4 GHz. The measurement is realized by placing the human brain in the region of the first focus and collecting the radiation converged at the second focus by a receiving antenna connected to the sensitive radiometer. Towards the improvement of the system’s focusing properties, extended electromagnetic analysis was performed in order to validate the impact of matching configurations made from appropriate materials, located inside the ellipsoidal cavity. The results show that with the appropriate choice of materials and careful assessment of their properties, it is possible to significantly improve the system’s detection depth, temperature detection level and spatial sensitivity. VIII The experimental procedures that were performed verify the proof of concept and confirm the beneficial impact of matching configurations on the system’s focusing properties, which was theoretically studied in the first part of the research. Finally, the experimental set used in the study, related to possible clinical applications, produced promising results regarding the potential perspective of the system to serve as a future clinical diagnostic tool.

<p>There are no commercially available wearable shoe in-sole sensors that are capable of measuring and distinguishing between shear and compression forces. Companies have already developed shoe sensors that simply measure pressure and make general inferences on the collected data with elaborate software [2, 3, 4, 5]. Researchers have also attempted making sensors that are capable of measuring shear forces, but they are not well suited for biomedical applications [61, 62, 63, 64]. This work focuses on the development of a novel wearable sensor system that is capable of identifying and measuring shear and compression forces through the use of capacitive sensing. Custom hardware and software tools such as materials test systems and capacitive measurement systems were developed during this work. Numerous sensor prototypes were developed, characterized, and optimized during the scope of this project. Upon analysis of the data, the best capacitive measurement system developed in this work utilized the CAV444 IC chip, whereas the use of the Arduino-derived measurement system required data filtering using median and Butterworth zero phase low pass filters. The highest dielectric constant reported from optimization experiments yielded 9.7034 (+/- 0.0801 STD) through the use of 60.2% by weight calcium copper titanate and ReoFlex-60 silicone. The experiments suggest certain sensors developed in this work feasibly measure and distinguish between shear and compressional forces. Applications for such technology focus on improving quality of life in areas such as managing diabetic ulcer formation, preventing injuries, optimizing performance for athletes and military personnel, and augmenting the scope of motion capture in biomechanical studies.</p>