Evidence for undamped waves on ohmic materials
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Universidade Federal de Minas Gerais
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Tese de doutorado
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Membros da banca
Gilberto Medeiros Ribeiro
Leonardo Cristiano Campos
Guilherme Penello Temporão
Luiz Roberto Evangelista
Leonardo Cristiano Campos
Guilherme Penello Temporão
Luiz Roberto Evangelista
Resumo
We present in this work a yet unexploited property of the Maxwell equations
when applied to conductors. It was found that the real part impedance of passive circuits
can achieve negative values. We have performed calculations which forecast this so far
unobserved part of the impedance spectrum of conducting materials. A series of
experiments which confirms our predictions was also conducted. The impedance of
single spires and also of some coils of specific geometry were measured in the MHz
frequency range. Metallic and carbon wires were used in constructing these spires and
coils. Spectral analyses of our data demonstrate that in fact, the impedance of these
passive circuits presents a frequency-dependent phase angle able to cover the full
trigonometric cycle [-π, π].
Besides direct impedance readings, additional experiments were performed in
order to check our data against possible systematic errors. We have constructed and
enclosed our circuits within several kinds of electromagnetic shields, all of them
presenting wall thickness several times larger than the skin dept of the radiation in the
frequency range of measurement. With this, we guaranteed that external sources could
not possibly induce any relevant noise in our measurements. The negative real part
impedance effects were also present on these shielded experiments. In addition to that, it
was confirmed on an oscilloscope screen that the voltage and current on a passive
circuit may, in fact, present a phase difference of π.
A first-principles theoretical model that assumes the presence of longitudinal
undamped waves propagating in the system was devised. An expression for the
impedance of circuits possessing theses waves was then obtained. This way we were
able to make numerical calculations and predict the negative real part impedance
effects. Experimental evidence for the existence of these longitudinal waves was also
obtained. On these footings we have pointed out a special propagation mode of the
electromagnetic field as the cause of the unusual observed spectral response. A
discussion on the validity of impedance data and causality issues is also presented.
Abstract
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Equações de Maxwell
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Maxwell equations, Ohmic materials
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