In several works developed about transformers sinusoidal excitation are considered. In others researches evaluate effects on transformers when excited by square waves as power electronics, the studies about effects on core materials or analysis in high voltage, as pulse transformers are made. When analyzing a transformer when an excitation of square wave is applied, some works show effects due its transfer function, while researches about planar coils and transformers built with these types of coils, generally is made on microcircuits, where some analysis about electromagnetic fields are realized, to apply on technology. Considering transformers built with planar coils inner ring coils, basically are found in literature very few works, where important effects are analyzed. Considering the effects of induced electromotive force, we observe similar considerations when analyzing systems with pulsed excitation. However, although these systems show similarities, are not found analysis about systems defined as planar coil inner ring coil. In the analysis presented in some papers resulting of researches, we see the phenomenon of double sine waves in response to an excitation by square wave in primary coil (planar) of the transformer for planar coil with two hundreds of turns, which is uncommon on literature. In this case, these effects are shown as presence of parasitic capacitances. This phenomenon of double sine wave which appears as amplitude modulation occurs only the turn ratio between planar coil and ring coil appears between fifteen and twenty five. This phenomenon is very interesting to several researches areas as power electronics, pulse transformers and others. In the case of this paper, an analysis using other planar coils, with different turn numbers have shown other effects about these responses (with double sine waves), which is a phenomenon that occurs in specific values on terms of the transfer function of the system.
Such analysis is shown in this paper, where these effects open new prospects on researches with planar coils and other areas that uses pulse excitation. In other words, this paper presents an analysis about the results of experiments using planar coils inner ring coils, determining a transformer, where 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 (called direct system) and the inverse (ring coil as primary and planar coil as secondary - called inverted system). In this study a phenomenon not common on 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 several researches on areas as power electronics and pulse transformers.