Tese de Doutorado #290: Roberto Sardenberg

In this work we present 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. Spectral analyses of our data demonstrate that in fact, the impedance of these passive circuits present a frequency-dependent phase angle able to cover the full trigonometric cycle [-π, π]. 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. With this, we guaranteed that external sources couldn’t possibly induce any relevant noise in our measurements. A first-principles theoretical model that assumes the presence of longitudinal undamped waves propagating in the system was devised. With this, 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.