System Immunity in HIRF/Lightning Environment and Interconnecting Cable Characterization Based on Functionality Mode

The advances in electronics and software since two decades have increased the use of digital technology in modern aircraft. Because digital electronics are powered with low level energy and are made of miniatured components, they are very sensitive to electromagnetic energy. It takes a single glitch to change the entire information. Therefore, insuring the proper protection of critical systems against Electromagnetic energy is a must during early design phase of the modern aircraft.

All the onboard systems that govern aircraft functions are interconnected by hundreds of meters of wires and bundles. Moreover, the immunity of any signal on board aircraft is for at least 50% guaranteed by the cable shielding effectiveness and the shield termination. Wiring acts like an antenna: it can either radiate or collect energy. If not protected, it may pick up any electromagnetic noise in the surrounding; consequently, unwanted energy can modulate signals and cause system malfunction. The criteria for choosing cables are governed by the functionality mode of the system (common mode or differential mode) and their Common Mode Rejection Ratio, and the signal immunity.