The Reference Conductor node solves for Ampère’s law and imposes the constraint that the voltage is zero, that is,

The Reference Conductor node computes the resistance of the reference conductor Rref as the real part of the ratio between a voltage difference between the signal and a reference conductor of 1 V, and a current of −1 A.

By default, the Electric conductivity σ (SI unit: S/m) for the media is defined From material. Alternatively, select User defined and specify a value or expression.