Several researches have been developed about resonance in different kinds of transformers. In the other hand, researches about coils are common in literature, using usual ring coils or planar coils. When considering the analysis of induced emf in systems excited by square waves, some papers are found in which the focus are high voltages, or applied to power electronics, or planar coils inner ring coils. However, using the transfer function of the system ona can generate voltages not common when resonance is reached. This result is a sum of responses in each rise and fall of the square wave. That is, in each rise and fall, the system presents a response to step voltage that is added with the posterior variation of the square wave in opposite sign. When the square wave and the response frequencies of the system are equal, the effect of resonance occurs. This occurs due to system capacitances, that increases the output voltage. In some papers are seen the effects of parasitic capacitances, whose effects are shown in oscillatory responses on output, at low frequencies. The case of resonance is shown here in some experiments involving planar and ring coils, where the effects of parasitic capacitances are added to external capacitances that increases the output voltage of the system, generating in some cases, values higher than one hundred times the input, although the turn ratio on coupled circuit does not satisfy this relationship.
Summarily, in this paper, the theoretical and experimental results explain how the Tesla transformer reaches the high voltages, since that it has the same behavior as the analyzed system. 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.