Numerical Calculation of Frequency Characteristic of Induction Coils

Induction coils are widely used in electromagnetic non-destructive testing and measurement of alternating magnetic fields. It is important to acquire the frequency characteristics of induction coils for parameter optimization. In this paper, a numerical method is proposed to estimate the frequency characteristics of an air core induction coil, with which the inductance (L), self-capacitance (Cs) and AC resistance (Rac) of a coil are calculated. Then the impedance of the coil versus frequency curve is derived based on an equivalent circuit model including correction of the resonance quality factor and skin effect of AC current. The curves obtained with the method of two coils are compared with experimental results, which validate the numerical method. This method is a useful and inexpensive tool for coil's parameters optimization and choosing proper operating frequency range for eddy current testing probes.