| abstract |
Devices for detecting and obtaining information about an event, for example the presence of an organic liquid, which comprise a swellable member which swells upon occurrence of the event and a restraining member which, when the swellable member swells, restricts movement of the swellable member and thus causes the impedance of the device to change. In a preferred embodiment, the device comprises two elongate conductors (2, 4) helically wrapped around a support core (6), and separated and covered by an apertured insulating braid (12); a swellable, conductive polymer member (14) surrounding the braid, and an insulating restraining member (16) surrounding the swellable member (14). Occurrence of an event causes the swellable member (14) to swell through the apertured member (12) and form a conductive bridge between the conductors (2, 4). |