Abstract: A system for sensing disruption to a signal propagating along a guiding medium for guiding electromagnetic surface waves, the system comprising: a guiding medium for guiding electromagnetic surface waves; a transmitter arranged to transmit electromagnetic surface waves along the guiding medium; a receiver arranged to receive electromagnetic surface waves transmitted along the guiding medium and to measure changes to a signal transmitted via the guiding medium in order to sense disruption to said signals based on said measured changes.

Abstract: A system for detecting electromagnetic surface waves scattered from a guiding medium, the system comprising: a guiding medium for guiding electromagnetic surface waves; a transmitter arranged to cause electromagnetic surface waves to be transmitted along the guiding medium; at least one transducer arranged to receive electromagnetic waves scattered from said guiding medium as a result of disruption to a surface wave passing over the guiding medium; and a sensor coupled to the transducer and arranged to detect said received electromagnetic waves.