The finite element method in electromagnetism and methods for reducing radar signature of objects

This master's thesis describes the methodologies used for high-frequency electromagnetic analysis, focusing on the Radar Cross section(RCS), a parameter that gives information on how detectable an object is by radar. Numerous studies are still going on with the aim of reducing this parameter, since the lower it is, the more difficult it will be for a radar to detect the object in question. This problem is of great importance especially in the military sphere, since the Second World War, studies have been started on how to reduce the RCS in order to be detected as late as possible, so as to give the defence little time to respond to attacks. With the discovery of new types of materials over the years, enormous progress has been made in this area, but radars have also become increasingly powerful, so stealth missions are still complicated. The following thesis was conducted in the I2M and IMS laboratories in Bordeaux(FR) and is in collaboration with the Atomic Energy Commission (CEA), which is interested in evaluating the results obtained in the study of RCS of a cylinder, using finite element analysis software. The first part goes on to introduce what the RCS is specifically, how to calculate it and what it is most affected by, going on to investigate what factors can be manipulated to reduce it. The thesis goes on to introduce the theory of electromagnetism, starting with Maxwell's equations, from which the electromagnetic wave equation is derived. From the solution of the equation, it is analysed how a wave is reflected or transmitted by a target. The theoretical part is concluded by describing the cylinder scattering problem using the finite element method. In the second part, various electromagnetic analyses are carried out using finite element analysis software: Ansys Electromagnetics and Comsol Multiphysics. We start by analysing how waves are reflected or transmitted by a simple body such as a plane of infinite extension, and then study more complex objects such as spheres and cylinders. There is then a whole chapter dedicated to comparing the two software mentioned above, so as to understand which one is best suited to the problem of interest concerning the scattering of a cylinder. The main difference between the two softwares is that Comsol allows electromagnetic analysis using 2D or 3D elements, whereas Ansys Electromagnetic only allows the use of 3D elements. Several factors are to be taken into account in the comparison, such as the number of elements , calculation time and the quality of results. After determining which software is more suitable, the thesis goes on to analyze the cylinder coated first with a layer of a dielectric material going to do a sensitivity analysis with respect to layer thickness, and electromagnetic properties, to understand precisely how the RCS is affected by these factors. In the final part, there is an in-depth discussion with applications concerning Radar Absorbing Materials (RAM), which use their ability to absorb and dissipate the energy of the incident wave to reduce the intensity of the wave reflected by the target. In fact covering the cylinder with a layer of RAM material it is possible to significantly decrease RCS,as will be shown in the analysis.