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.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/74946 |
| Date | 06 February 2017 |
| Creators | Sun, Weizhen |
| Contributors | Electrical and Computer Engineering, Lu, Guo Quan, Ngo, Khai D., Li, Qiang |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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