Nanostructured Composite Material for Electromagnetic Interference Shielding Applications

Currently some aerospace application of composite materials is to substitute classical metal based structural element with composite based structural element and most current work deal with the importance of EMI shielding systems. This is particularly important as an example on board the satellite / space vehicle, where several electronic subsystems have to operate with different interference sensitivity close to each other e.g., telecommunication and telemetry subsystems at microwave frequencies, DC supplier subsystems, acquisition data subsystem, navigation subsystem attitude control subsystem and so on. In this paper we propose an advanced concept of composite structure which is simultaneously microwave shielding and microwave absorbing capable. The absorbing properties reduce the reflected electromagnetic field while the shielding properties reduce the transmitted electromagnetic field. Both properties are useful in all the scenarios where the requirements are contemporary to reduce as much as possible the microwave propagation in terms of reducing the traveling spurious microwave interfering signals, and in military applications in terms of radar absorbing and microwave shielding structure too. As far as structures proposed they are based on multilayer system made of nanostrucutred composite materials built using epoxy-resin and carbon nanopowders as carbon nanotube, carbon nanofiber, micrographite. Such materials have been first characterized in terms of electric permittivity in previous works and here are assumed to be ready in order to be properly chosen by optimization algorithms. The design of such multilayer structure is not trivial since they must respect structural mechanics and electrical properties, in this work we focused our research in optimizing microwave absorbing properties only. In particular the design algorithms have multiple tasks since they must determine an optimized multilayer structure based on carbon composite nanostrucutred materials available in the data base as a trade off between overall thickness and microwave reflection and transmission coefficient to be minimized as much as possible. With respect to the current literature the optimization task here is even more difficult since, the microwave absorbing requirements have to be satisfied for several incidence angles and in the entire frequency band considered. The algorithm proposed here for the design of structure is a new evolutionary algorithm in-house built and baptized by us as winning particle optimization. It is a very simple algorithm where at each time epoch of evolution, particle which best fit the objective function, is deputed to pilot the trajectory of the remaining particles within the multidimensional space of solutions. Winning particle optimization is easy to implement and run, in fact, each single particle acts with no any knowledge about other particles with exception of index of the best fitting particle, under this point of view winning particle optimization it's like a primordial non intelligent life form which tries to find the best place to grow and proliferate. Step by step this simple but quite effective method evolves toward the best solution; the iterations are stopped when all particles end to converge in a single point which represents the optimal solution. In the first part of the paper the winning particle optimization algorithm is described, in the second part the electromagnetic model of multilayer absorber is in detail presented, in the third part the winning particle optimization and in-house particle swarm optimization are compared in terms of overall thickness and electromagnetic performances of the optimized multilayer absorber.