However, there is no sense to use such a coil as a LC resonant circuit coil. It is only necessary that the coil impedance modulus | Z | remained high enough. If the coil is used as an RF choke, this fact does not really matter. With increasing frequency, the losses increase and the active part of the impedance can exceed the reactive one, while the Q-factor of the coil tends to zero (vector 3 in the diagram). The Q factor of a coil can be defined as the ratio of the reactive to the active part of its impedance or, after simplification, as the ratio of the real to the imaginary part of the complex magnetic permeability of ferrite.Īt relatively low frequencies, the Q factor is very high. At relatively low frequencies, the losses in the ferrite are small and the relative magnetic permeability is close to the initial permeability of the ferrite (vector 2 in the diagram). The vector diagram shown below can help to visualize the behavior of a ferrite core coil at different frequencies. We take the value of inductance L from here (formula ), and the relative magnetic permeability μ r from the expression above (all measurements are in SI units): To calculate the impedance of such a coil, we will make the appropriate substitutions in the impedance formula. Since the losses in the ferrite are an order of magnitude higher than the conductor losses, the last can be ignored. Torus sizes can be set manually or selected from a standard range. The data are approximated for working frequency using the cubic spline approximation method. The complex magnetic permeability data of some common ferrite materials are automatically inserted from the adapted official Fair Rite tables in csv format. You can find it in datasheets and put manually in the corresponding input fields in the Coil64 program. Many manufacturers publish graphs and tables of the complex magnetic permeability of ferrite versus frequency. And the imaginary part of μ'' takes into account the losses in the ferrite. In this case, the real part of this value μ' corresponds to the usual concept of magnetic permeability, which takes into account how many times the magnetic flux density in ferrite increases. To do this, the relative magnetic permeability of ferrite is presented as a complex value: Since the magnetic permeability of ferrite and its losses essentially depend on the frequency, this occasion must be taken into account when calculating the inductance of such coils at radio frequencies. At the same time, with appearance of new high-frequency ferrites, radio amateurs are increasingly using ferrite toroid cores to make the LC resonant filters. The use of ferrite cores can significantly reduce the dimensions of the inductive elements. Inductance, Q-factor and self-capacitance of a ferrite toroid coil at radio frequencies Multilayer air core inductor on a rectangular form.Self-capacitance of single-layer inductor.Features of calculation of power supply chokes.