An increasing need for smaller, higher-power-density devices is driving the development of more advanced topologies for use in power architectures. The challenge, however, is to reduce the size of the passive components in circuit boards (e.g., the inductors), which are typically the most bulky. There are two ways to approach this problem. The first is to redesign the flux in the inductor in order to minimize its size; the second is to optimize the magnetic properties of the constituent magnetic materials, which include permeability, density, resistivity, core loss density, saturation magnetization value, fluidity, sintering temperature, and others. Compared to altering the nature of solid magnetic materials to reduce space constraints, modifying the magnetic composite is preferred. The most popular candidates for use in magnetic composites are magnetic powders and polymer composites. In particular, when metal alloys are chosen as magnetic powders they have high initial permeability, high saturation magnetization values, but low electrical resistivity. Since polymers can serve as insulation materials, mixing metal alloys with polymers will increase electrical resistivity. The most common metal alloy used is nickel-iron (permalloy) and Metglas. Since existing modeling methods are limited in (a) that multiphasic composites cannot be utilized and (b) the volume fraction of magnetic particles must be low, this investigation was designed to utilize FE (finite element) simulation to analyze how magnetic properties change with the distribution of permalloy powder or Metglas flakes in composites. The primary magnetic properties of interest in this study are permeability and core loss density. Furthermore two kinds of magnetic composites were utilized in this investigation: a benzocyclobutene (BCB) matrix-permalloy and a benzocyclobutene (BCB) matrix-permalloy-based amorphous alloy (Metglas 2705M) material. In our FE simulations, a BCB matrix-permalloy composite was utilized in a body-centered cubic model with half-diameter smaller particles serving as padding. The composite was placed in a uniform magnetic field surrounded by a material whose relative permeability was equal to zero in simulation. In comparison to experimental results, our model was able to predict permeability of composites with volume fraction higher than 52%. It must be noted, however, that although our model was able to predict permeability with only 10% off, it was less effective with respect to core loss density findings. The FE model also showed that permeability will increase with an increasing volume fraction of magnetic particles in the composite. To modify the properties of the composite material, the model of the BCB matrix-permalloy-Metglas composite followed model simulations up to the point at which flakes were inserted in BCB matrix-permalloy composite. The thickness of flakes was found to be an important factor in influencing resulting magnetic properties. Specifically, when the thickness of flakes decreased to quarter size at the same volume fraction, the permeability increased by 15%, while core loss density decreased to a quarter of the original value. The analysis described herein of the important relationship between magnetic properties and the composites is expected to aid in the development and design of new magnetic composite materials. / Master of Science / Power converters are essential for a wide variety of electronic applications (e.g., mobile phones, motor drives, etc.). And with the current push toward miniaturization, power converters that are smaller in size and feature higher power density are demanded. The most challenging aspect of reducing overall size while maintaining or, preferably, increasing the power density of a power converter is to reduce the size of the passive components in the circuit boards (e.g., the inductors). To optimize the performance of an inductor, the magnetic properties of the constituent magnetic materials in an inductor must be well designed. In particular, scientists and engineers are focusing on the two most important characteristics of a magnetic material—namely its permeability and core loss density. In order to achieve the objective of high relative permeability and low core loss density, the incorporation of magnetic powders and polymer composites into the fabrication of magnetic materials is being considered. Since this method tends to require a great deal of trial and error to determine optimal fabrication parameters, it can be both time consuming and costly. This study, therefore, was designed to simplify the fabrication process by investigating the effects of altering the parameters of a number of constituent components in a series of composites. Specifically, this investigation targeted the impact of altering the volume percentage, the shape, and the species of each component on the properties of composite materials by simulation, which was useful in predicting the performance of the magnetic materials under scrutiny. The simulation method utilized herein was FE (finite element), which was effective in determining the permeability and core loss density of the magnetic properties of interest in this study.

Since a substantial amount of coal combustion byproducts (CCB) are produced each year, generating value-added product from fly ash, which is a major constituent of these CCBs, has been an important area of research for several decades. Natural magnetite (NM), which is used to maintain dense medium slurry pulp density in coal preparation plants, has a current market value of more than $200 per ton. The use of fly ash derived magnetite (FAM) as an alternative to natural magnetite has potential benefits for dense medium processes, such as lower cost, greater stability at low medium density, more efficient delivery systems. This study developed a suitable processing scheme to extract high-grade (> 96%) magnetite from fly ash generated from burning high sulfur coal, and investigated the suitability of the FAM product for dense medium application in coal preparation plants. A classifying cyclone was utilized in the process flow sheet for the pre-concentration of FAM in its underflow stream, which was enriched to high grade FAM by a single stage wet magnetic separator of low intensity (~1000 gauss). A statistically designed experimental program was utilized to maximize the magnetite grade and recovery achieved from the above mentioned flow sheet. The FAM product particles had a slightly coarser particle size distribution than the NM particles. In addition, the FAM particles were found to have a spherical shape; but about one unit lower specific gravity in comparison to the NM particles. However, the F5 Stability Index of the resulting FAM product was found to be in the desired range of 30 to 40 for its suitable application as a dense medium. The coal cleaning performance obtained from a 0.15 m diameter dense medium cyclone using dense medium prepared from both of FAM and NM, were quite similar. However, the effective separation density (SG50) obtained from the FAM-based dense medium was significantly different from the medium density; this may need further investigation in future. A preliminary economic analysis, conducted for a hypothetical mini-plant having a fly ash handling capacity of 100 ton/hour, indicated the cost of FAM extraction to be nearly $5/ton. The cost assumes that the FAM extraction plant is located at the fly ash producing utility site and does not include the cost of thermal drying that may be required to reduce the moisture content of the FAM filter cake produced at the FAM plant. A preliminary civil engineering study conducted to investigate the effect of FAM extraction on the compressive strength property of the non-magnetic flyash (left behind after FAM extraction) failed to produce a conclusive finding. The specimens prepared using 10% and 30% fly ash replacements indicated that the compressive strength does not change due to FAM extraction. However, the specimens using 20% fly ash replacement indicated that compressive strength does change due to FAM extraction. Hence, a more detailed study is recommended to investigate this discrepancy.

Soft magnetic materials have been widely used in electric motors, routers, and detectors. Tremendous studies have been conducted to report microstructural features corresponding to magnetic performance. The laser-based powder bed fusion (L-PBF) additive manufacturing technique was implemented to bulk-scale fabricate the Finemet nanocrystalline magnetic alloy. This research study aims to reveal the capability of replacing the traditional melt spinning process with decent bulk density and magnetic properties. Nanocrystalline materials originate from optimizing amorphous metallic alloys, resulting in low coercivity and high saturation magnetization by facilitating the formation of nanocrystals. An extremely high cooling rate is the foundational factor for controlling the microstructure. Selective Laser Melting (SLM) offers a layer thickness of 20-100 µm, naturally providing a cooling rate of 105 - 107 K/s. Subsequent melting will impact the microstructure by conducting heat continuously through the melt pools. The relationship between microstructural features and crystalline phase characterization is discussed. Magnetic characterization, in terms of saturation magnetization and coercivity, with various processing parameters, is investigated. / Master of Science / Additive manufacturing of Finemet soft magnetic materials to approach expected microstructure and magnetic properties open up the path of replacing traditional manufacturing techniques. Freedom of complicated near net morphology design and inter-layer microstructural control by manipulating processing parameters offer revolutionary fabrication process comparing to traditional casting and welding. The magnetic performance of soft magnetic materials in real life applications such as electric motor is depending on multiple factors. Thus, the fascinating magnetic properties of soft magnetic materials owing strict requirement of microstructure and crystallite size. Aside from magnetic properties, as-printed bulk density fabricated by SLM would hugely impact the overall mechanical properties and porosity. Thus, processing parameters optimization through experiment and characterization would significantly benefit this study. Afterwards, comparison groups of samples with decent bulk density were taken into characterizations to reveal the crystalline phases, microstructure of metallic phases with respect to the melt pool morphology and then magnetic property of coercivity and saturation magnetization were carefully analyzed.

A stochastic dynamic micromagnetics code using the LLG equation has been developed and applied to study the seed induced magnetic reversal of a cobalt element array. The spin orientation of the seed element is chosen to be antiparallel to the spin orientation of the first element in the array producing a domain wall that is stabilized by the strong crystalline anisotropy and exchange interactions of cobalt. By exposing the element array to an applied magnetic field for a specific time, the domain wall moved along the easy axis and was pinned at a specific position. In this manner, the portions of the element array to be switched could be controlled arbitrarily and information can be stored in the array in terms of the total magnetization of the array. The effects of the magnitude of applied field, the cutting area and the cellsize of the element array were also studied.

No description available.

La machine synchrone à griffes est un dispositif très utilisé comme alternateur dans l’automobile. La fabrication de cette machine, produite en masse, met en œuvre des procédés impactant les caractéristiques des matériaux ferromagnétiques et donc, in fine , les performances de l’alternateur. Ce travail de thèse est donc consacré à étudier l’impact du processus de fabrication d’un stator Slinky (basé sur un enroulement d’une bande de tôle plutôt qu’un empilement) sur les propriétés magnétiques. Pour ce faire, une première partie du travail consiste à quantifier l’impact de chaque procédé mis en œuvre. Le but est de séparer les procédés les plus fortement impactant. Une campagne de caractérisation magnétique, sur des échantillons prélevés avant et après chaque procédé, a été réalisée. Les résultats montrent que le procédé d’enroulement est l’étape la plus destructive à cause des déformations et des contraintes engendrées dans le plan de la tôle à la fois en traction et en compression. L’optimisation de ce procédé nécessite donc d’établir le lien entre les propriétés mécaniques et magnétiques. Nous proposons une nouvelle méthode de caractérisation magnéto-mécanique. Elle permet de réaliser une caractérisation magnétique sous chargement uni axial en traction et en compression. Enfin, nous présentons des résultats montrant l’évolution du comportement magnétique, d’un matériau FeSi NO, en fonction de la déformation et de la contrainte appliquée. / The synchronous claw pole machine represents a widely used device, as an alternator, in the automobile industry. The production of this machine implements a line of several processes which impact the characteristics of ferromagnetic materials and, ultimately, the performance of the alternator. Therefore, this work is devoted to studying the impact of the manufacturing processes of a Slinky stator (based on a rolled sheet metal strip rather than stacked sheets) on the magnetic properties. To reach our goal, a first task consists in quantifying the impact of each manufacturing process. The aim is to separate the most detrimental processes. Thus, a magnetic measurement campaign was carried out on samples withdrawn before and after each process.The results show that the rolling step represents the most detrimental process due to the generated stresses and strains in the plane of the sheet in both modes (tension and compression). Therefore, the optimization of this process requires setting up the link between the mechanical and magnetic properties. Hence, we propose a new method of magneto-mechanical characterization. It enables to carry out magnetic measurements under uniaxial loading (tension and compression). Finally, we present results showing the evolution of the magnetic behavior of a FeSi NO material depending on the applied stress and strain.

The ever-increasing demand for wireless communication has led to an incentive to increase the data rate and reduce the size of communication devices, be it antennas or other components of RF front-ends. The emphasis is primarily on increasing data rate, which leads to the use of higher frequency bands and wider bandwidths in modern communication technology research and innovations. However, increasing frequency in many technology areas cannot necessarily be beneficial because of physical constraints. For example, communication under seawater or other RF harsh environment requires very-low-frequency (VLF) or ultra-low-frequency (ULF) signals to penetrate lossy media that block high-frequency signals. Furthermore, recent advances in neuroscience have demonstrated the potential of VLF and ULF electromagnetic (EM) waves for studying brain function and treating neurological conditions. The main challenge is that most VLF and ULF generators are large and power-hungry, making them impractical to use in many applications. As a result, recent approaches using permanent magnets have started to provide groundbreaking solutions that can revolutionize VLF/ULF communication. This work presents a new method for generating low-frequency EM waves for navigation and communication in challenging environments, such as underwater and underground, as well as magnetic stimulation of brain neurons. The key concept is to disturb the magnetic energy stored around a permanent magnet in a time-variant fashion. The magnetic reluctance of the medium around the permanent magnet is modulated to alter the magnetic flux intensity and direction (disturb the stored energy) in order to achieve this goal. The nonlinear properties of the surrounding magnetic material are a critical phenomenon for efficient and effective modulation. Since the proposed method of generating the EM field is not based on a second-order system (resonant structure), the bandwidth of any modulation schema is not limited to the overall system quality factor. A transmitter is prototyped as a proof of concept, and the generated field is measured. Compared to the rotating magnet, the prototyped transmitter can modulate up to 50% of the permanent magnet's stored energy with much lower power consumption. The magnetic equivalent circuit (MEC) approach is also used to analyze the transmitter. Finally, the transmitter is optimized, and the measurement results show a 7 dB improvement in efficiency compared to the primary structure. As a result of promising performance, we propose that this method be used to improve the performance of transcranial magnetic stimulation (TMS) devices. Furthermore, the comparison simulated results back up the validity of the proposed technique, revealing that focality and penetration depth are improved while utilizing much less power than traditional TMS devices. / Doctor of Philosophy / The growing demand for wireless communication has created an incentive to increase the data rate while decreasing the size of communication devices, whether they are antennas or other radio frequency (RF) components between the antenna and at least one mixing stage of a receiver and/or the power amplifier of the transmitter. The emphasis is primarily on increasing data rate, which leads to the use of higher frequency bands and wider bandwidths in modern communication technology research and innovations. However, increasing frequency in many technology areas may not be beneficial because of physical constraints. For example, communication under seawater or underground requires very-low-frequency (VLF) or ultra-low-frequency (ULF) signals to penetrate lossy media that block high-frequency signals. Furthermore, recent advances in neuroscience have demonstrated the potential of VLF and ULF electromagnetic (EM) waves for studying brain function and treating neurological conditions. The main challenge is that most VLF and ULF generators are large and power-hungry, making them unsuitable for many applications. As a result, recent approaches using permanent magnets have started to provide groundbreaking solutions that can revolutionize VLF/ULF communication. This work presents a new method for generating low-frequency EM waves for navigation and communication in challenging environments, such as underwater and underground, as well as magnetic stimulation of brain neurons. The key idea is to disturb the magnetic energy stored around a permanent magnet in a time-variant fashion. The magnetic reluctance of the medium around the permanent magnet is modulated to change the magnetic flux intensity and direction (disturb the stored energy) in order to achieve this goal. The nonlinear properties of the surrounding magnetic material are a critical factor in achieving efficient and effective modulation. Since the proposed method of generating the EM field does not rely on a second-order system (resonant structure), the bandwidth of any modulation schema is not constrained by the overall system quality factor. As a proof of concept, a transmitter is prototyped, and the generated field is measured. Compared to the rotating magnet, the prototyped transmitter can modulate up to 50% of the permanent magnet's stored energy with much lower power consumption. The magnetic equivalent circuit (MEC) approach is also used to analyze the transmitter. Finally, the transmitter is optimized, and the measurement results show a 7 dB improvement in efficiency compared to the primary structure. As a result of promising performance, we propose that this method be used to improve the performance of transcranial magnetic stimulation (TMS) devices. Furthermore, the comparison simulated results support the validity of the proposed technique, revealing that focality and penetration depth are improved while using much less power than traditional TMS devices.

Most electrical machines available in the market utilise some form of silicon iron (SI) as the core material. Although SI based electrical machine manufacturing methods are well established and simple, SI has significant iron losses specifically in high frequency variable-speed motor drive applications. Two alternative magnetic materials have recently been developed: amorphous magnetic material (AMM) and soft magnetic composite, which can each offer unique characteristics that can be utilised to improve the performance of electric machines. AMM offers extremely low iron losses which makes it a good candidate for high-efficiency and variable-speed motor applications. However, due to handling and cutting limitations, AMM has not been utilised widely in rotating electrical machines. A commercially viable AMM cutting technique was recently developed by the industrial partner of this project. It is thus now practical to cut the AMM ribbon into a machine stator, particularly for axial-field stators which generally require less cutting than radial-field stators. This thesis investigates an innovative motor design based on applying the cut AMM in an axial-field permanent magnet (AFPM) machine for general drive applications. It includes a detailed review of the analytical approach, finite element analysis (FEA), iron loss investigation and prototype performance comparisons. Analytical analysis of the AFPM machine was performed and the key design variables were evaluated to optimise the design parameters based on the use of AMM. The AMM cutting constraints, design and performances trade-offs were also investigated in the design. The research study provides a design procedure to determine the basic physical size and configuration (e.g. combination of the number of slots and poles, slot width and depth, number of winding layers, air gap length, magnet thickness) based on certain basic specifications. In addition, a comprehensive investigation was conducted on the iron loss of various materials to compare these with AMM. Due to the three dimensional (3D) nature of the AFPM structure, the theoretical design was validated using 3D FEA and extensive simulation results are provided. A number of AMM AFPM prototypes were successfully designed and constructed. Due to limited available materials, the prototypes were built using uncoatedAMMribbon which has substantially higher iron loss characteristics. Nevertheless, it is believed that it would still provide a valuable understanding of the real machine characteristics and allow initial design validation. The prototype was tested in a custom-built test rig to validate the analytical and 3D FEA predictions. Overall, a good correspondence between the results and predictions has been achieved. Extensive experiments have been conducted to investigate and demonstrate the characteristics of the AMM prototype machines which are based on fractional-slot concentratedwinding single-sided AFPM machines. This includes comparisons against identical silicon iron and soft magnetic composite prototypes. In addition, the laboratory experimental results also highlighted the significant effect of the open-circuit losses on the overall machine performance. Therefore, the open-circuit loss components which includes bearing, windage, magnet and iron losses were separated based on 3D FEA and experimental results. The above research studies demonstrated the potential and feasibility of cut AMM to produce highly efficient AFPM machines. In addition, the innovative cutting technique also has the potential for mass production of low-cost AMM machines. The research work in this thesis makes a significant contribution to the design of axial-field permanent magnet machines based on AMM. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1375647 / Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2009

abstract: Antennas are required now to be compact and mobile. Traditional horizontally polarized antennas are placed in a quarter wave distance from a ground plane making the antenna system quite bulky. High impedance surfaces are proposed for an antenna ground in close proximity. A new method to achieve a high impedance surface is suggested using a metamaterial comprising an infinite periodic array of conducting loops each of which is loaded with a non-Foster element. The non-Foster element cancels the loop's inductance resulting in a material with high effective permeability. Using this material as a spacer layer, it is possible to achieve a high impedance surface over a broad bandwidth. The proposed structure is different from Sievenpiper's high impedance surface because it has no need for a capacitive layer. As a result, however, it does not suppress the propagation of surface wave modes. The proposed structure is compared to another structure with frequency selective surface loaded with a non-Foster element on a simple spacer layer. In particular, the sensitivity of each structure to component tolerances is considered. The proposed structure shows a high impedance surface over broadband frequency but is much more sensitive than the frequency selective surface structure. / Dissertation/Thesis / M.S. Electrical Engineering 2010

Este trabalho tem como objetivo o projeto, construção e análise do funcionamento de uma máquina elétrica síncrona trifásica com núcleo do rotor produzido a partir da metalurgia do pó e ímãs de neodímio-ferro-boro para aplicação em aerogeradores. Tomando como base a máquina elétrica modelo VTOP da fabricante Grupo Voges, foram realizadas mudanças na forma construtiva dos núcleos do estator e do rotor. O pacote chapas que compõem o núcleo do estator foi montado de maneira que as ranhuras apresentem um ângulo de inclinação de 10º ao longo de toda a extensão da máquina. Para o rotor, foi projetado e construído um núcleo através do processo de metalurgia do pó utilizando como matéria-prima pó de ferro puro. A esse novo núcleo foram acrescentados ímãs de neodímio-ferro-boro. Após a montagem dos componentes, a máquina elétrica foi ensaiada em uma bancada de testes. Paralelamente com a confecção do núcleo foi efetuada a simulação computacional da máquina com três tipos diferentes materiais no núcleo do rotor. Os resultados encontrados indicaram que a metalurgia do pó é uma alternativa viável para produção do núcleo de máquinas elétricas. Entretanto alterações na topologia e na forma de fixação dos ímãs são necessárias para um melhor desempenho. / This work aims at the design, construction and performance analysis of a three-phase synchronous electric machine with a rotor core produced by powder metallurgy and neodymium-iron-boron magnets for application in wind turbines. Based on the electric machine VTOP model of the manufacturer Grupo Voges, changes were carried out in the constructive form of the stator and rotor cores. The bundle of plates that make the role of stator core were mounted with a 10º slope along the entire length of the machine. For the rotor, a core was designed and built by employing powder metallurgy process using pure iron powder as raw material. The neodymium-iron-boron magnets were added to this new core. After assembling the components, the electric machine was tested on a test bench. Simultaneously with the core fabrication, the machine was simulated with three different materials in the rotor core. The results indicated that powder metallurgy is a viable alternative to produce the core of electric machines. However, changes in the topology and shape of the magnets are necessary for better assembly, improving the performance.