A sensor is a detector: a circuit behind glass, wired with copper plate, made in a Fabricator. Sensors go into the Surveyor, picket and wayfarer; the Lab, research station, sensor array and point defence array; and the point defence, sensor suite, lattice scanner and deep scanner fittings. A nav computer and each of the torpedoes take one.
Most of a sensor's material cost is copper, through the circuit and the plate.