A technique to measure the high frequency electrical impedance across mechanical joints in structures made from conducting materials

Modern aircraft designs are becoming more and more reliant upon the use of advanced composite materials. At present, it is the carbon fibre composites (CFC) that have made the major impact. The use of CFC has resulted in a significant modification to the strategy adopted to protect the avionics contained within the airframe against the various electromagnetic (EM) threats encountered by the aircraft. The general strategy is based upon a three tier topology; (1) EM screening afforded by the airframe, (2) EM screening fitted to internal cable looms, and (3) protection contained within the equipment cases. The combination of 1-3 gives rise to a protection strategy and the effectiveness of stage 1 is determined by the electrical properties of the airframe. It is of great importance to the aircraft manufacturer to be able to quantify this in order to be able to continue to implement the optimum protection strategy. Therefore, a program of work was begun to develop a technique that could be successfully used to measure the bulk electrical conductivity of mechanical joints in conductive structures