Magnetic circuits and transformers; a first course for power and communication engineers,

"A publication of the Technology Press, Massachusetts Institute of Technology."

Development of a large scale flexible LED display matrix for the screen industry

This project addresses the viability of lightweight, low power consumption, flexible, large format LED screens. The investigation encompasses all aspects of the electrical and mechanical design, individually and as a system, and achieves a successful full scale prototype. The prototype implements novel techniques to achieve large displacement colour aliasing, a purely passive thermal management solution, a rapid deployment system, individual seven bit LED current control with two way display communication, auto-configuration and complete signal redundancy, all of which are in direct response to industry needs.

Asymmetrical magnetization in three-phase core type transformers

The performance of the three-phase core type transformers, under AC/DC double excitation is discussed in this work. It is presented a mathematical model that considers the mutual coupling between phases and the magnetic nonlinearity. The validity of the proposed model is verified by means of the experimental and simulated results.

Optimization of multipulse converters with delta and Y-differential connections

This work presents a study regarding the optimization of multipulse converters. A general expression for the connection (Δ or Y) for both 12 and 18-pulses is obtained and describes the output voltages on the secondary windings, depending on the voltage reference from the primary. These generalized expressions allows choosing different ratios between input and output voltages and as result an optimum operation point for the converter can be calculated. Considering Δ-connected converters the optimum point occurs when the magnetic core of the autotransformer processes 18% and 17% of the output power for 12 and 18-pulses, respectively. For Y-connected converters the optimum point occurs when the kVA rating is 13% and 18% for 12 and 18-pulses, respectively. Based on these results magnetic elements can be calculated and designed leading to a great weight and volume reduction and also to lower costs and losses. Finally an analysis is made to improve the kVA rating of the transformers for 12 and 18 pulses converters. © 2009 IEEE.

Família de retificadores multipulsos com topologias diferenciais de transformadores

Multipulse rectifier topologies based on auto-connections or differential connections, are more and more applied as interface stages between the mains and power converters. These topologies are becoming increasingly attractive not only for robustness, but to mitigate many low order current harmonics in the utility, reducing the total harmonic distortion of the line currents (THDi) and increasing the power factor requirements. Unlike isolated connections (delta-wye, zigzag, etc.), when the differential transformer is employed, most of the energy required by the load is directly conducted through the windings. Thus, only a small fraction of the kVA is processed by the magnetic core. This feature increases the power density of the converter. This paper presents a mathematical model based on phasor diagrams, which results in a single expression able to merge all differential connections (wye and delta), for both step-up and step-down rectifiers for 12 or 18 pulses. The proposed family of converters can be designed for any relationship between the line input voltage and the DC voltage, unlike the conventional phase-shift voltage connections. An immediate application would be the retrofit, i.e. to replace a conventional rectifier with poor quality of the processed energy by the 12 or 18-pulse rectifiers with Wye or Delta-differential connections, keeping the original values for the input and load voltages. The simple and fast design procedure is developed and tested for a prototype rating 6 kW and 400 V on DC load.

Influence of double excitation AC/DC in the reactive power demand of 3-phase transformers

In this work it is discussed the performance of the reactive power demand in three-leg transformer core and three-phase transformer bank, under different conditions of AC/DC double excitation. In order to analyse the influence of double excitation in reactive power theoretically a mathematical model was developed considering the mutual coupling between phases and the magnetic nonlinearity. The validity of the proposed model is verified by means of the experimental and simulated results.

Field-based models for low speed switched reluctance machine designs

Trabalho apresentado na Conferência CPE-POWERENG 2016, 29 junho a 01 de julho 2016, Bydgoszcz, Polónia

Activation in mesolimbic and visuospatial neural circuits elicited by smoking cues: evidence from functional magnetic resonance imaging.

OBJECTIVE: The authors sought to increase understanding of the brain mechanisms involved in cigarette addiction by identifying neural substrates modulated by visual smoking cues in nicotine-deprived smokers. METHOD: Event-related functional magnetic resonance imaging (fMRI) was used to detect brain activation after exposure to smoking-related images in a group of nicotine-deprived smokers and a nonsmoking comparison group. Subjects viewed a pseudo-random sequence of smoking images, neutral nonsmoking images, and rare targets (photographs of animals). Subjects pressed a button whenever a rare target appeared. RESULTS: In smokers, the fMRI signal was greater after exposure to smoking-related images than after exposure to neutral images in mesolimbic dopamine reward circuits known to be activated by addictive drugs (right posterior amygdala, posterior hippocampus, ventral tegmental area, and medial thalamus) as well as in areas related to visuospatial attention (bilateral prefrontal and parietal cortex and right fusiform gyrus). In nonsmokers, no significant differences in fMRI signal following exposure to smoking-related and neutral images were detected. In most regions studied, both subject groups showed greater activation following presentation of rare target images than after exposure to neutral images. CONCLUSIONS: In nicotine-deprived smokers, both reward and attention circuits were activated by exposure to smoking-related images. Smoking cues are processed like rare targets in that they activate attentional regions. These cues are also processed like addictive drugs in that they activate mesolimbic reward regions.

Mice behaviorally selected for high Pavlovian fear memory exhibit fear generalization, HPA-axis alterations and increased basal activity in cortico-limbic circuits

Biological factors underlying individual variability in fearfulness and anxiety have important implications for stress-related psychiatric illness including PTSD and major depression. Using an advanced intercross line (AIL) derived from C57BL/6 and DBA/2J mouse strains and behavioral selection over 3 generations, we established two lines exhibiting High or Low fear behavior after fear conditioning. Across the selection generations, the two lines showed clear differences in training and tests for contextual and conditioned fear. Before fear conditioning training, there were no differences between lines in baseline freezing to a novel context. However, after fear conditioning High line mice demonstrated pronounced freezing in a new context suggestive of poor context discrimination. Fear generalization was not restricted to contextual fear. High fear mice froze to a novel acoustic stimulus while freezing in the Low line did not increase over baseline. Enhanced fear learning and generalization are consistent with transgenic and pharmacological disruption of the hypothalamic-pituitary-adrenal axis (HPA-axis) (Brinks, 2009, Thompson, 2004, Kaouane, 2012). To determine whether there were differences in HPA-axis regulation between the lines, morning urine samples were collected to measure basal corticosterone. Levels of secreted corticosterone in the circadian trough were analyzed by corticosterone ELISA. High fear mice were found to have higher basal corticosterone levels than low line animals. Examination of hormonal stress response components by qPCR revealed increased expression of CRH mRNA and decreased mRNA for MR and CRHR1 in hypothalamus of high fear mice. These alterations may contribute to both the behavioral phenotype and higher basal corticosterone in High fear mice. To determine basal brain activity in vivo in High and Low fear mice we used manganese-enhanced magnetic resonance imaging (MEMRI). Analysis revealed a pattern of basal brain activity made up of amygdala, cortical and hippocampal circuits that was elevated in the High line. Ongoing studies also seek to determine the relative balance of excitatory and inhibitory tone in the amygdala and hippocampus and the neuronal structure of its neurons. While these heterogeneous lines are selected on fear memory expression, HPA-axis alterations and differences in hippocampal activity segregate with the behavioral phenotypes. These differences are detectable in a basal state strongly suggesting these are biological traits underlying the behavioral phenotype (Johnson et al, 2011).

A novel modeling approach for design studies of brushless doubly fed induction generator based on magnetic equivalent circuit

Brushless doubly fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind turbine generator. However, it suffers from lower efficiency and larger dimensions in comparison to DFIG. Hence, optimizing the BDFIG structure is necessary for enhancing its situation commercially. In previous studies, a simple model has been used in BDFIG design procedure that is insufficiently accurate. Furthermore, magnetic saturation and iron loss are not considered because of difficulties in determination of flux density distributions. The aim of this paper is to establish an accurate yet computationally fast model suitable for BDFIG design studies. The proposed approach combines three equivalent circuits including electric, magnetic and thermal models. Utilizing electric equivalent circuit makes it possible to apply static form of magnetic equivalent circuit, because the elapsed time to reach steady-state results in the dynamic form is too long for using in population-based design studies. The operating characteristics, which are necessary for evaluating the objective function and constraints values of the optimization problem, can be calculated using the presented approach considering iron loss, saturation, and geometrical details. The simulation results of a D-180 prototype BDFIG are compared with measured data in order to validate the developed model. © 1986-2012 IEEE.

A nanowire magnetic memory cell based on a periodic magnetic superlattice

We analyse the operation of a semiconductor nanowire-based memory cell. Large changes in the nanowire conductance result when the magnetization of a periodic array of nanoscale magnetic gates, which comprise the other key component of the memory cell, is switched between distinct configurations by an external magnetic field. The resulting conductance change provides the basis for a robust memory effect, which can be implemented in a semiconductor structure compatible with conventional semiconductor integrated circuits.

Electronic states of InAs verfically-assembled quantum disks in magnetic fields and two-electron quantum-disk qubit

We have studied the single-electron and two-electron vertically-assembled quantum disks in an axial magnetic field using the effective mass approximation. The electron interaction is treated accurately by the direct diagonalization of the Hamiltonian matrix. We calculate the six criergy levels of single-electron quantum disks and the two lowest energy levels of two-electron quantum disks in an axial magnetic field. The change of the magnetic field as an effective potential strongly modifies the electronic structures. leading to splittings and crossings between levels The results demonstrate the switching between the around states with the total spins S = 0 and S = 1. The switching results in a qubit allowed to fabricate by current growth techniques.

Metamaterial-enhanced coupling between magnetic dipoles for efficient wireless power transfer

Nonradiative coupling between conductive coils is a candidate mechanism for wireless energy transfer applications. In this paper we propose a power relay system based on a near-field metamaterial superlens and present a thorough theoretical analysis of this system. We use time-harmonic circuit formalism to describe all interactions between two coils attached to external circuits and a slab of anisotropic medium with homogeneous permittivity and permeability. The fields of the coils are found in the point-dipole approximation using Sommerfeld integrals which are reduced to standard special functions in the long-wavelength limit. We show that, even with a realistic magnetic loss tangent of order 0.1, the power transfer efficiency with the slab can be an order of magnitude greater than free-space efficiency when the load resistance exceeds a certain threshold value. We also find that the volume occupied by the metamaterial between the coils can be greatly compressed by employing magnetic permeability with a large anisotropy ratio. © 2011 American Physical Society.

Magnetophoretic circuits for digital control of single particles and cells.

The ability to manipulate small fluid droplets, colloidal particles and single cells with the precision and parallelization of modern-day computer hardware has profound applications for biochemical detection, gene sequencing, chemical synthesis and highly parallel analysis of single cells. Drawing inspiration from general circuit theory and magnetic bubble technology, here we demonstrate a class of integrated circuits for executing sequential and parallel, timed operations on an ensemble of single particles and cells. The integrated circuits are constructed from lithographically defined, overlaid patterns of magnetic film and current lines. The magnetic patterns passively control particles similar to electrical conductors, diodes and capacitors. The current lines actively switch particles between different tracks similar to gated electrical transistors. When combined into arrays and driven by a rotating magnetic field clock, these integrated circuits have general multiplexing properties and enable the precise control of magnetizable objects.

Scaling issues for analogue circuits using Double Gate SOI transistors

This work presents a systematic analysis on the impact of source-drain engineering using gate