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

Abstract

In this work we present the electrical characterization of closed-and openbifilar 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.

Capacitor‐less induction heating system with self‐resonant bifilar coil

“…The mathematical formulations for inductance and capacitance are carried out for both conventional and bifilar coil. The bifilar coil virtual capacitance is N 2 /4 times greater than the conventional self‐capacitance for the same value of coil inductance 14 . The thermal model of IH load is performed in COMSOL environment in which the magnetic flux density, eddy current, and temperature distribution are studied.…”

“…The total capacitance of the coil is the sum of self‐capacitance (C ad and C bc ) and mutual‐capacitance (C ab and C dc ). Since the geometry of the coils remain symmetric, C ad = C bc and C ab = C dc 14 . Ignoring the capacitance of the nonadjusting turns, the self‐capacitance of the coil is given by …”

“…de Miranda and Pichorim 14 developed the steady‐state analysis for both bifilar coil and conventional coil. The relationship between the inductance and capacitance for the conventional coil and bifilar coil is well established.…”

“…Self‐resonating coil is used in wireless power transfer applications, 13 , 14 and its selection depends on the applications, dimensions, frequency, among others. The capacitance of the coil has either series or parallel resonance effect based on the arrangement.…”

“…The proposed system will reduce the quantity of resonating element, which will reduce the overall system size. The closed bifilar coil has parallel resonance when it is operated at self‐resonant frequency (SRF) and series resonance, if it is operated at a frequency higher than SRF 14 . On the other hand, the open bifilar coil has series resonance at SRF and parallel resonance at a frequency higher than SRF 13 .…”