On the self-resonant frequency reduction of closed- and open-bifilar coils

In this work we present the electrical characterization of closed- and open-bifilar solenoid coils by comparing their self-capacitance, self-inductance, and self-resonant frequency (SRF). The analysis is done by relating these parameters with those of a conventional solenoid coil with same dimensions and number of turns. It is shown that bifilar coils have a greater self-capacitance and lower SRF when compared with the respective conventional coil and that this relation can be expressed only in terms of the number of turns of the coils. Therefore, these components have a potential use in applications that need to avoid the use of a real capacitor and need to operate in a smaller resonant frequency, such as in wireless power transfer systems, for example. In a similar way, the self-inductances of closed- and open-bifilar coils are also compared with those of conventional coils with the same dimensions. It is also shown that the SRF of closed- and open-bifilar coils are approximately the same for practical values of the quality factor and that their impedance behaves as series and parallel RLC circuits. Practical experiments are conducted validating the developed theory.