Effectiveness of current electromagnetic shielding techniques in composite aircraft has been called into question several times before and is a subject of interest and research in the aerospace industry. We present an analytical approach to understand the issues in detail. It was found using first order approximations that a panel with Aluminum expanded metallic foil (ExMF) along with carbon fiber plies used on composite aircraft provides fair albeit lower electromagnetic shielding from source frequencies of a few KHz until well into MHz range when compared to an aluminum panel used on metallic aircraft.
This was primarily attributed to relatively large skin depth value at low frequencies which was due to: a) low electrical conductivity of aluminum ExMF when compared to bulk aluminum; b) low electrical conductivity of resin impregnated carbon fiber layers and; c) very thin layer of aluminum ExMF used.
It was also found that as source frequency goes higher (between 800 MHz to 18 GHz range), fields penetrate through the aluminum ExMF and although they may get attenuated by the CFRP plies however, shielding effectiveness at higher frequencies still remains lower for composite aircraft when compared to metallic aircraft.
