Not available / text

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

<p>The focus of this dissertation is on the dynamics of electromagnetic systems for energy harvesting and filtering applications. The inclusion of magnets into systems generates nonlinearity due to the nature of electromagnetic interactions. In this work, magnetic nonlinearity manifests in tip interactions for cantilever beams, coupling effects for electromagnetic transduction, and bistable potential wells for a two beam system. These electromagnetic interactions are used to add non-contact coupling effects for the creation of bistable oscillators or arrays of coupled beams for energy filtering.</p><p>Nonlinearity at the tip of cantilever beams acts to change the dynamic and static behavior of the system. In this dissertation, these interactions are analyzed both with and without the nonlinear tip interactions. A linear analysis of the system without the tip interaction first provides insight into the shifting frequencies of the first four natural oscillation modes when considering a rigid body tip mass with rotational inertia and a center of mass that is offset from the tip of the beam. Then, the characterization of the nonlinearities in the beam stiffness and magnetic interaction provide insight into the static and dynamic behavior of the beam. The analytical and numerical investigations, using Rayleigh-Ritz methods and an assumed static deflection, are shown to be consistent with experimental tests. These methods provide a framework for theoretically establishing nonlinear static modes and small-amplitude linear modes that are consistent with physical behavior.</p><p>In electromagnetic coupling, the role of nonlinearity can have a detrimental or beneficial effect on energy harvesting. This work includes an investigation of the response of an energy harvester that uses electromagnetic induction to convert ambient vibration into electrical energy. The system's response behavior with linear coupling or a physically motivated form of nonlinear coupling is compared with single and multi-frequency base excitation. This analysis is performed with combined theoretical and numerical studies.</p><p>The ability of magnets to add nonlinearity to a system allows for the expansion of the phenomenological behavior of said system and potential advantages and disadvantages for energy harvesting. This work studies a two beam system made up of carbon fiber cantilever beams and attached magnetic tip masses with a focus on energy harvesting potential. Numerical and experimental investigations reveal an array of phenomena from static bifurcations, chaotic oscillations, and sub-harmonic orbits. These features are used to highlight the harvesting prospects for a similarly coupled system.</p><p>Beyond nonlinearity, the non-contacting coupling effects of magnets allow for the hypothetical creation of energy filtering systems. In this work, the band structure of a two dimensional lattice of oscillating beams with magnetic tip masses is explored. The focus of the wave propagation analysis is primarily on regions in the band structure where propagation does not occur for the infinite construction of the system. These band gaps are created in this system of 2 x 2 repeating unit cells by periodically varying the mass properties and, for certain configurations, the frequency band gaps manifest in different size and band location. Uncertainty in these regions is analyzed using potential variations associated with specific physical parameters in order to elucidate their influence on the band gap regions. Boundary effects and damping are also investigated for a finite-dimensional array, revealing an erosion of band gaps that could limit the expected functionality.</p> / Dissertation

Electromagnetic microactuators with permanent magnets have many potential applications such as micro-energy scavengers, microswitches, micromirrors and microfluidics. However, many electromagnetic microactuator designs utilize either external permanent magnet or external coil, which do not allow tight integration to other MEMS components and further miniaturization. Furthermore, all of the available permanent magnet microfabrication technologies have some drawbacks and improvements are required. Thus the integrated monolithic electromagnetic microactuator is investigated in this project. The three main components of the electromagnetic actuator have been investigated separately. A novel microfabrication technology called ???Template printing???for the fabrication of polymer bonded permanent magnet has been investigated and developed. It is based on ???Screen printing??? which has its drawbacks on alignment accuracy and poor line definition. This is eliminated in ???Template printing??? by photolithography of the photoresist template. The shape and location of the permanent magnet is defined by the template. A new approach based on the filling of dry magnetic powder and vacuum impregnation has been developed to form the polymer bonded permanent magnet. This allows the use of short pot-life matrix material and the elimination of homogenous mixing. A monolithic electromagnetic microactuator has been fabricated successfully. It consists of a 2-layer planar copper microcoil, surface micromachined polyimide beam and Strontium ferrite/EPOFIX permanent magnet (diameter of 460 ??m and 30 ??m thickness). Large deflection in excess of 100 ??m at 35 mA driving current and magnetic force of 0.39 ??N/mA have been achieved. It compares favourably with other much larger electromagnetic actuators that have been reported. ???Template printing??? has the potential of being a low temperature batch process for the microfabrication of thick polymer bonded permanent magnets with high magnetic properties and low residual stress. The fabrication consistency and the quality of template printed magnet can be improved in future studies.

Thesis (M. Phil.)--University of Hong Kong, 1991.

Made available in DSpace on 2014-10-09T12:54:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:59Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:54:14Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:14Z (GMT). No. of bitstreams: 1 12437.pdf: 4743815 bytes, checksum: 224eec9c107091a47a85eb64ff2540c5 (MD5) / Dissertacao (Mestrado) / IPEN/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Single-Molecule Magnets (SMMs) are discrete molecules that exhibit slow relaxation of magnetization. Unlike conventional magnets that rely on the long range magnetic ordering in the form of domains, these molecules act as magnets independently, that is without the influence of neighbouring molecules. SMMs have intrigued physicists and chemists alike for over twenty years with their potential future applications in data storage quantum computing, and with this communal interest there has been significant collaboration between the two fields of research. SMMs have brought forth an opportunity for coordination chemists to muster their creativity and synthetic expertise in the rational design and development of these magnetic materials. From these new and fascinating compounds, both experimental and theoretical physicists have sought to develop and refine our understanding of the aspects of these molecular magnets in order to improve their performance at higher temperatures. In this work, new topologies for lanthanide complexes are explored using a novel Schiff base ligand. The magnetic properties of dinuclear, tetranuclear and octanuclear lanthanide complexes are discussed and correlated to their structural properties. The rational design of tetrazine-based Schiff base ligands for magnetic studies is also discussed in hopes of developing high performance SMMs.

Made available in DSpace on 2014-10-09T12:54:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:59Z (GMT). No. of bitstreams: 0 / Ímãs sinterizados foram produzidos utilizando o pó obtido pelo processo de Hidrogenação, Desproporção, Dessorção e Recombinação (Processo HDDR). O processo HDDR na produção de ímãs sinterizados foi adotado visando uma redução no tempo de moagem e investigar seu efeito nas propriedades magnéticas e na microestrutura. As ligas utilizadas nesse trabalho apresentaram a seguinte composição: Pr14FebalCoxB6Nb0,1 (x= 0; 4; 8; 10; 12; 16) e Pr20,5Fe72,5B5Cu2,0 (utilizada como aditivo de sinterização). O pó HDDR foi utilizado para produzir ímãs sinterizados com uma mistura dessas ligas (liga principal + aditivo), nas seguintes proporções: 80 % em peso da liga principal e 20% em peso do aditivo de sinterização (Pr20,5Fe72,5B5Cu2,0). O processo de decrepitação por hidrogênio (Processo HD) na produção de ímãs também foi utilizado nesse trabalho para efeito de comparação (tempos de moagem: 20, 15, 10 e 5 horas). A temperatura e o tempo de sinterização foram mantidos constantes para todos os ímãs (1050 º C por 60 minutos). O ímã sinterizado produzido pelo processo HD apresentou melhor remanência (1220 mT).Esse ímã foi fabricado com a liga Pr14Fe75,9B6Co4Nb0,1 utilizando um tempo de 20 horas de moagem. A melhor coercividade intrínseca foi obtida com a liga Pr14Fe75,9B6Co4Nb0,1 em ambos os processos, de 1020 mT para o processo D (5 horas de moagem) e de 1190 mT para o processo HD (20 horas de moagem). As microestruturas dos ímãs permanentes foram analisadas por microscopia eletrônica de varredura (MEV) e por dispersão de energia de raios-X (EDS). / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:54:14Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:14Z (GMT). No. of bitstreams: 1 12437.pdf: 4743815 bytes, checksum: 224eec9c107091a47a85eb64ff2540c5 (MD5) / Dissertacao (Mestrado) / IPEN/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP