Lightweight electromagnetic shields using optimized polyaniline composites in the microwave band

A genetic algorithm (GA) was used to optimize a multilayer electromagnetic shield of polyaniline (PANI)-polyurethane (PU) conducting composites in the microwave band. First, the electronic properties of freestanding films with different mass fractions of polyaniline were studied. A very low percolation threshold (0.2%) was found, with a maximum of conductivity of 10(4) S/m. Second, the electromagnetic shielding effectiveness of the films were investigated in the X and Ku bands (8.2-18 GHz), showing an attenuation increase of 1-40 dB with the mass fraction of polyaniline in the blends. Then, the electromagnetic shielding properties of multi-layered PAni-PU composites were investigated in order to obtain an attenuation superior to 40 or 80 dB, depending on the application. To improve the performances of the electromagnetic shields, three-layered PAni-PU composites were made, using an optimization method. The intrinsic physical parameters of the composites were used as a database for the optimization calculation. The optimization results showed that materials with a thickness of <500 mu m could answer many industrial or military shielding applications. As the electronic properties can be tuned easily with the mass fraction of polyaniline in the blends, conducting multi-layered composite materials can be made following the results of the optimization. Their electromagnetic shielding effectiveness was measured, showing good agreement between the measurements and modeling. These results demonstrated that the genetic algorithm allows us to conceive lightweight and high performance electromagnetic shields using intrinsically conducting polymers. The mass per unit of surface of the shield was <200 g/m(2), giving potential applications in the aeronautics domain. Copyright (C) 2007 John Wiley & Sons, Ltd.