True Cause for Multi-Layer Inductive Coils’ Sensitivity to Ambient Relative Humidity

For analyzing the properties of humidity-effect on the measurement of the inductance of multi-layer coils, a formula that establishes an approximate relationship between the coil’s inherent capacitance and interlayer parasitic capacitance has been derived. Such a derivation using the inductor’s equivalent circuit to include humidity effects clarifies the characterization of inductance, after more than half a century of neglect in the literature.