A system for transmitting data and/or power across a structural component, comprising: a structural component formed of first and second layers which conform to one another, the first layer comprising a dielectric composite material having first and second surfaces , and the second layer comprising a conductive material contacting the first surface of the first layer , whereby the electrical reactance of the first layer is configured for the propagation of electromagnetic surface waves thereacross; a first transducer on or adjacent the second surface of the first layer of the structural component at a first location, the first transducer being adapted to generate electromagnetic surface waves for carrying data and/or power across the first layer ; and a second transducer on or adjacent the second surface of the first layer of the structural component at a second location spaced from the first location, the second transducer being adapted to receive electromagnetic surface waves from the first layer and to retrieve data and/or power from the received electromagnetic surface waves; whereby the electromagnetic surface waves are transmitted from the first transducer to the second transducer by the first layer of the structural component , and wherein: the dielectric composite material forming the first layer comprises reinforcement elements disposed in a matrix material , and the first layer has a bulk region in which both the reinforcement elements and the matrix material are present and a first skin region comprising a greater proportion of matrix material to reinforcement elements than in the bulk region , the first skin region forming the first surface of the first layer . a structural component formed of first and second layers which conform to one another, the first layer comprising a dielectric composite material having first and second surfaces , and the second layer comprising a conductive material contacting the first surface of the first layer , whereby the electrical reactance of the first layer is configured for the propagation of electromagnetic surface waves thereacross; a first transducer on or adjacent the second surface of the first layer of the structural component at a first location, the first transducer being adapted to generate electromagnetic surface waves for carrying data and/or power across the first layer ; and a second transducer on or adjacent the second surface of the first layer of the structural component at a second location spaced from the first location, the second transducer being adapted to receive electromagnetic surface waves from the first layer and to retrieve data and/or power from the received electromagnetic surface waves; whereby the electromagnetic surface waves are transmitted from the first transducer to the second transducer by the first layer of the structural component , and wherein: the dielectric composite material forming the first layer comprises reinforcement elements disposed in a matrix material , and the first layer has a bulk region in which both the reinforcement elements and the matrix material are present and a first skin region comprising a greater proportion of matrix material to reinforcement elements than in the bulk region , the first skin region forming the first surface of the first layer . <EOS>