In this paper is presented a basic analysis about experiment results using planar coils inner ring coils that defines a transformer, when this system is excited by square wave voltage. In this study several phenomena on the system response to step voltage due to parasitic capacitances is analyzed, and a sum of responses when the input square wave frequency increases is also given. These phenomena are uncommon in literature, which can be applied to several areas of researches in electrical engineering, as pulse transformers and power electronics. Resonance studies has been developed in several aspects of the electrical engineering. Some works are found in literature about coupled circuits (transformers), and on square waves, works are more related to power electronics. Some researches are about resonance effects about circuit impedances, where circuit excitation is based on square wave. Also, some of these researches are applied to planar coils in several contexts, as impedances, mutual inductance and self inductances, stray capacitances, and others. However, most researches found in literature about planar coils are in microcircuits, and, on the other hand, researches about resonance are usually formalized in sinusoidal low frequencies on common transformers or, in some cases, in microcircuits as microstrip disks, etc. When analyzing transformers, analysis about inductors is basic, where parasitic capacitances eﬀect are visible, and the analysis about electromagnetic fields is realized for several cases to find relationships between the phenomena and technological applications. Since coils present their capacitive and inductive effects, some responses to step voltage have characteristics of second order, or higher order, with sine waves.
By other side, when a coupled inductance circuit with air core is excited by a square wave, the response to each step in the rise or fall is always equal, but with inverted signal (the response follows the inverse direction of the rise or fall of square wave by the Faraday’s law, repeatedly on each reversal of the input signal) a variation of stored energy in the form of magnetic fields (inductor) as sine wave is presented. Such an effect, a priori, is imperceptible in most cases, specially when inductor is considered ideal (without resistance or capacitance). However, the phenomena which appear with increasing input square wave frequency which excites primary coil will be seen only as the impedance relationship, or effects of active filters. But considering using planar coils as primary of an air core transformer inner to ring coils, ring coil as its secondary, and using time division of oscilloscope in order of nanoseconds, we find as a response to secondary an output voltage which appears as sum of responses of each rise and fall of the input square wave, that comes from stored energy on inductors. In this case, the response in the secondary circuit presents voltages higher than input peak signal, while the turns ratio is not satisfied, in accordance to circuit theory. These phenomena is shown in this paper.