There is elucidated a device (10) comprising first and second magnetic cores (30, 40; 30a, 30b, 30c, 40a, 40b, 40c) forming a magnetic circuit. The circuit includes a first set of electrical windings (300, 310) for magnetically coupling a first electrical signal through the device (10) via a first magnetic path (350) in the circuit. The circuit includes a second set of electrical windings (400, 410) for magnetically coupling a second electrical signal through the device (10) via a second magnetic path (450) in the circuit. The paths (350, 450) are partially spatially intersecting. The sets of windings (300, 310, 400, 410) are configured so that: (a) the first set of windings (300, 310) is sensitive to magnetic flux in the first magnetic path (350), and insensitive to magnetic flux in the second magnetic path (450); and (b) the second set of windings (400, 410) is sensitive to magnetic flux in the second magnetic path (450), and insensitive to magnetic flux in the first magnetic path (350). The first and second cores (30, 40; 30a, 30b, 30c, 40a, 40b, 40c) enable relative motion (50) there between whilst coupling the signals through the circuit. The device (10) is beneficially employed in a medical system (800).