Circuit duality: the gyrator is the electromagnetic analog of the magnetic monopole
The gyrator (Tellegen 1948) is a two-port element relating port voltages and currents via V₁ = R·I₂, V₂ = −R·I₁. This is a duality transformation, converting inductors↔capacitors. The gyrator realizes a fictitious "magnetic current" — the circuit analog of Dirac's magnetic monopole. The field lines show a monopole-like radial B-field from a single magnetic charge.