Parasitic Coupling
Electrostatic charges accumulate between adjacent wraps of wire in a wound coil to form an unintended capacitive path. This inter-turn capacitance modifies the electrical characteristics of the inductor at high operating frequencies. The effect is modeled as a capacitor in parallel with the coil inductance.
Resonant Limit
Impedance peaks occur when the parasitic capacitive reactance equals the inductive reactance of the coil. This point represents the maximum usable frequency of the sensor. Beyond this threshold, the coil behaves as a capacitor rather than an inductor.
Winding Geometry
Physical separation of the wire turns determines the magnitude of the parasitic capacitance within the winding structure. Multi-layer windings increase the capacitive coupling due to the proximity of wires with different electrical potentials. Special winding patterns, such as the basket-weave or sectionalized methods, are used to increase the distance between turns and reduce this effect.
Coil designers select wire insulation thickness and winding layout to control the parasitic capacitance.
Frequency Drift
Temperature changes cause the wire insulation and coil geometry to expand or contract, which alters the parasitic capacitive value. This variation shifts the resonant frequency of the sensor over time. Calibration routines must compensate for this temperature-induced shift to maintain accuracy.
