The Wire Was Already a Capacitor
The Wire Was Already a Capacitor
A capacitor, on a schematic, is a discrete thing: two plates, a gap, a symbol. But capacitive coupling names a device with none of that. A gimmick loop is just two strands of wire, closely spaced, usually twisted together for convenience — no plates, no dielectric chosen on purpose, no part number. And it works: a few picofarads of real coupling, enough to pass a signal from one node to another, exactly like the deliberate component would.
Nothing was built. Two conductors got close to each other, and an electric field did what an electric field does between any two conductors that are close to each other. The capacitor symbol in a schematic doesn't create capacitance — it's the engineered, quantified, deliberately-placed case of a relationship that exists by default between any two wires, any two traces, any two anything with a potential difference and a small separation. The named component is capacitance on purpose. The gimmick loop is capacitance that was going to happen anyway, pressed into service instead of fought.
This is also why parasitic coupling isn't a separate phenomenon needing a separate explanation. Two PCB traces running side by side, an amplifier's output near its own input, a signal wire near a ground line — none of these were designed to couple. They couple anyway, for the identical reason the twisted pair does, at whatever picofarad value their geometry happens to produce. A designer who wants isolation has to actively spend distance, ground planes, and shielding to push an accidental coupling down toward zero. A designer who wants coupling can, if the layout is generous enough, skip the component altogether and simply let two wires be near each other on purpose.
There is no line in the physics between "capacitor" and "two nearby conductors." There's only a line, drawn by an engineer, between the couplings that were requested and the couplings that showed up uninvited.
This piece is part of the wider power electronics index, though it marks a related-but-distinct edge of it: parasitic capacitance and gimmick coupling rather than switching topology.