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O Grupo de Pesquisa em Eletromagnetismo
(GEMA), iniciado em agosto de 2009, desenvolve pesquisas em
várias linhas, buscando desenvolver metodologias teóricas e aplicações
tecnológicas dos campos eletromagnéticos. Como parte fundamental dos
objetivos do GEMA, a produção intelectual é uma necessidade. No momento, trabalhos estão sendo
desenvolvidos, e a produção específica do mesmo, referenciada aos
resultados de seus projetos, será inserida aqui. Em princípio, as
produções individuais de seus pesquisadores podem ser vistas nos Lattes de
cada um, no link
Integrantes
no menu ao lado.
Atualmente, as pesquisas desenvolvidas desde a criação do GEMA tiveram
como publicações, as citadas a seguir:
Projeto: Estudo sobre Efeitos
Eletromagnéticos em Transformadores com Núcleo de Ar Alimentados com
Tensão Pulsada
 Costa, E. M. M.,
A Basic
Analysis About Induced EMF of Planar Coils to Ring Coils,
Progress
In Electromagnetics Research B  PIER B, Vol. 17,
pp. 85100, 2009.
Resumo:
This paper presents a basic analysis about the results of experiments
using planar coils inner to ring coils, when planar coil is applied to a
square wave voltage. In this study an uncommon phenomenon occurs in the
ring coil, which is analyzed.
 Costa, E. M. M.,
Responses in
Transformers Built With Planar Coils Inner Ring Coils Excited by Square
Waves,
Progress
In Electromagnetics Research B  PIER B, Vol. 18,
pp. 4358, 2009.
Resumo:
This paper presents an analysis about the results of experiments using
planar coils inner ring coils to determine a transformer. The excitation
of this system was a square wave voltage, where experiments were realized
in two ways: considering planar coil as primary and observing responses on
secondary being ring coil (direct system) and the inverse (ring coil as
primary and planar coil as secondaryinverted system). In this study, a
phenomenon not common in literature on system response is analyzed,
showing effects of changes on transfer function in both cases when varying
turn numbers of each coil and several variations on responses due to
changes on resistances, parasitic capacitances, self and mutual
inductances of the coils. The uncommon phenomenon appears as modulated
response on specific turn ratio. The obtained results can be used to
researches in areas as power electronics and pulse transformers.
 Costa, E. M. M.,
Resonance
Between Planar Coils vs Ring Coils Excited by Square
Waves,
Progress
In Electromagnetics Research B  PIER B, Vol. 18,
pp. 5981, 2009.
Resumo:
This paper presents a basic analysis about experiment results using planar
coils inner ring coils, defining a transformer, when this system is
excited by square wave voltage. In this study phenomena of response to
step voltage due to parasitic capacitances is analyzed, and a sum of
responses when the input square wave frequency increases is given too.
These phenomena are uncommon in literature, which can be applied to
several areas of researches in electrical engineering, pulse transformers
and power electronics.
Costa, E. M. M.,
Resonance on
Transformers Excited by Square Waves and Explanation of the High Voltage
on Tesla Transformer,
Progress
In Electromagnetics Research B  PIER B, Vol. 18,
pp. 205224, 2009.
Resumo:
This paper presents an analysis about resonance on coupled systems when
excited by square waves, generated through experiments using planar and
ring coils. Because of the phenomenon described by its transfer function,
a sum of responses appear when the square wave frequency increases, which
causes a resonance response with high voltage, in several cases, greater
than common turn ratio of the transformer. With parallel capacitances
inserted on output, the resonance frequency reduction and change of gain
is observed. Due to this effect, explanation of how output of Tesla
transformer presents high voltage which is shown, and strategies to reach
the maximal value on output are proposed.
Costa, E. M. M.,
Parasitic Capacitances on Planar Coils,
Journal of Electromagnetic Waves and Applications
 JEMWA, Vol. 23,
no. 17/18, pp. 23392350, 2009.
Resumo:
In this paper is proposed a formalism to calculate parasitic
capacitances on planar coils. This
analysis is based on experimental results through RL circuits where the
inductor are coils built in a plastic disc with
fixed diameter, having the turns disposed elliptically over
this disc. The proposed formulation approaches the ellipsis of the
turns to circles, and an empirical formula to describe electric
potential is obtained, which is used to
calculate effective electrical flux and
determine the equation that describe the values
of parasitic capacitances on these coils. In this
procedure, small errors are verified when comparing to obtained
experimental results..

Costa, E. M. M.,
Planar
Transformers Excited by Square Waves,
Progress
In Electromagnetics Research  PIER 100,
pp. 5568, 2010.
Resumo:
In this paper is presented an analysis of
found results of experiments developed with
transformers built with planar coils, when they
are excited by square waves, in comparison with transformers
built with planar coils inner ring coils. The transformer was built
joining two planar coils one over the other. In this kind of
transformer, similar responses as analysis of
transformers built with planar coil inner ring
coil is found, as well the results of resonance. Because
the low selfinductances and parasitic capacitances obtained in
these configurations,
although the coils resistance are low, what generates
low exponential drops on responses, the resonance is found in
higher frequencies, but satisfying conditions of
sum of responses in resonance.
.

Costa, E. M. M.,
Resonance on Coils Excited by Square Waves: Explaining Tesla Transformer,
IEEE Transactions on Magnetics,
v. 46, p. 11861192, 2010.
Resumo:
In this paper effects of induced emf on coils excited by square
waves are shown, as well as how these influence resonance phenomena. The
work was based on experimental results, using planar coils and inner ring
coils. A priori, the resonance is presented as effects of parasitic
capacitances on coils, which through inclusion of external capacitances,
is established that the phenomenon of high voltage on output is the sum of
responses of the induced emf added with response to step voltage on
rise and fall of the square wave. Consequently, the found results
explicate the phenomenon of high energy (or high voltage) in the output of
Tesla transformer.
.

Costa, E. M. M.,
Effects of Induced Electromotive Force (EMF) in Transformers Built with Planar Coils.,
Revista IEEE América Latina,
v. 9, no. 5, Setembro de 2011.
Resumo:
In this paper are presented some effects observed on induced
electromotive force (emf) in transformers built with planar coils.
Several experiments were realized crossing the planar coils with
different turn number, exciting primary with square wave and observing
responses on secondary. The results obtained are analyzed through
transfer function of the transformer, showing important results about
systems excited with square waves, which can be used in several
researches as pulse transformers.

Costa, E. M. M.,
Resonance Analysis of Induced EMF on Coils,
InTech Open Access Publisher, University Campus, STeP Ri, Croatia  Capítulo de livro (Eletromotive Force and Measurement in Several Systems  ISBN: 9789533077284) Novembro de 2011.
Resumo:
(Introduction of Chapter Proposal)In all analysis of resonance at RLC
circuits, the concept of equality in the inductive reactance and
capacitive reactance generates the maximum energy transfer. In the same
way, this concept is applied to transformers, due to parasitic
capacitances present inter turns (Costa, 2009). Such concept determines
explanation of several phenomena of the induced EMF on coils, showing
through differential equations and others formalisms of how happens
this phenomenon (Costa, 2009a). However, phenomena as secondary energy
at Tesla Transformer (that is a pulse transformer (Lord, 1971), where
the input energy is a square wave) present some problems that are not
fully comprehensible, as the high energy in secondary coil apparently
greater then input energy, which was explained in (Costa, 2009b; Costa,
2010) as the sum of responses of the induced EMF at secondary coil. By
other side, when analysing these same transformers with input energy as
sinusoidal excitation, the induced EMF at resonance appears in the same
way, but with smaller gain. Several analysis of coils, considering
planar coils and ring coils, forming special transformers has been
analysed, exciting one (primary) and verifying the other (secondary),
in a experimental way, to find new expectations in this area. When
exciting primary coil in these transformers, built with planar coil
versus ring coil (having the planar coil or the ring coil as primary,
and the other as the secondary) or planar coil versus planar coil, the
effect of induced EMF at secondary coil presents some common
characteristic previously yields studied in circuit theory (as
resonance due the RLC characteristic of the transformer). However, with
the experimental analysis of the induced EMF in these transformers,
when exciting primary coil with square wave and sinusoidal wave,
although are found resonance frequencies in medium frequencies (above 3
MHz) depending of the configuration (number of turns in each coil, and
type of coil – planar or ring), gain variations are seen. Also, on
resonance frequencies, other phenomena are seen, as high voltage gain
in the transformer, even if the primary coil of the transformer
presents less turns than the secondary, which contradicts ideal
transformer theory. These cases are analysed here, showing these
phenomena, and checking the problem in some mathematical analysis. The
induced EMF from primary coil to secondary coil at transformers in the
resonance has shown several properties that generates new perspectives
in electromagnetic theory, as formalisms to develop new type of
transformers, others explanations about resonance theory, analysis of
energy transfer through resonance on coils, generation of high energy
from low power sources, analysis about parasitic capacitances and
others characteristics at coils and transformers, and others. This
chapter treats of these analysis, checking some experimental results,
and mathematical formalisms that explain some properties and phenomena
that occurs at secondary coil when the resonance frequency is reached
in the coupled circuit (transformer), due to induced EMF generated by
the excitation of the primary coil with square wave or sinusoidal wave.
.
.

Caldas, A. A. S. e Costa, E. M. M.,
Análise da Indução Eletromagnética em Transformadores Planos e em Anéis na Ressonância.,
Seminário Nacional de Controle e Automação  VII SNCA,
Novembro de 2011.
Resumo:
Este trabalho apresenta resultados de observações dos efeitos da força
eletromotriz senoidal induzida em transformadores com núcleo de ar
formados por bobinas planas e anelares. Nos experimentos do trabalho
foram utilizadas bobinas planas e em anel, alternando primário e
secundário, e variando a frequência a fim de se observar picos de
ressonância, onde esses transformadores apresentaram altos ganhos de
tensão no secundário, onde verificouse um aumento expressivo no ganho
desses transformadores com base na relação de ganho por número de
espiras.

Caldas, A. A. S. e Costa, E. M. M.,
Efeitos da Ressonância em Bobinas Excitadas com Ondas Senoidais,
V Jornada de Iniciação Científica da UNIVASF,
20/21 de Outubro, 2010.
Premiado como 2o. melhor trabalho apresentado em Painel.

JÚNIOR, V. P. B.,
Análise de Efeitos de Indução Eletromagnética em Transformadores Planos
e Anelares,
Trabalho de Conclusão de Curso, Julho, 2012.
