A system for transmitting data and/or power across a structural component, comprising: a structural component formed of first and second layers (3, 6) which conform to one another, the first layer comprising a dielectric composite material having first and second surfaces (3a, 3b), 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 (7, 7a, 7b) on or adjacent the second surface of the first layer of the structural component at a first location, the first transducer (7, 7a, 7b) being adapted to generate electromagnetic surface waves for carrying data and/or power across the first layer; and a second transducer (8, 8a, 8b, 8c) 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 (8, 8a, 8b, 8c) 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 (7, 7a, 7b) to the second transducer (8, 8a, 8b, 8c) 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 (3, 6) which conform to one another, the first layer comprising a dielectric composite material having first and second surfaces (3a, 3b), 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 (7, 7a, 7b) on or adjacent the second surface of the first layer of the structural component at a first location, the first transducer (7, 7a, 7b) being adapted to generate electromagnetic surface waves for carrying data and/or power across the first layer; and a second transducer (8, 8a, 8b, 8c) 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 (8, 8a, 8b, 8c) 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 (7, 7a, 7b) to the second transducer (8, 8a, 8b, 8c) 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.