The topic of my thesis is electromagnetic concealment. In this work I present a cloaking device, which can hide a scatterer object exposed to monochromatic electromagnetic radiation. If the operation frequency is in the visible spectrum, the cloaked object will become invisible for the human eye. My thesis presents the numerical simulation of the cloaking device designed with transformation optics. Furthermore, I present the design of a cloaking device constructed with composite materials, which operates in the range of infrared light. In the first chapter the basics of concealment are explained. I describe what concealment means actually and what kind of material parameters are needed to realise the effect. In the second chapter the numerical implementation of the method is presented. With the developed procedure I can simulate the electromagnetic cloaking of the device designed with transformation optics. Applying the numerical algorithm I analyse the properties and the efficiency of the cloaking device under various excitation conditions (plane wave illumination, electromagnetic field of finite dimensional excitations). In the third part of my thesis a metaheuristic numerical optimization method, the Differential Evolution is introduced, which is applied to engineer the metamaterials of the invisibility cloak. The chapters fourth and fifth analyse the applicability of isotropic and anisotropic two-phase metal-dielectric composites to create electromagnetic concealment. The material parameters of the composites are described by mixing rules based on the Effective Medium Theory. The geometry and the composition of the composite are calculated with the Differential Evolution based optimization. At the end of these chapters I evaluate the results of the optimization, and I discuss the efficiency of the cloaking. In the sixth part I conclude the results and the achievement of this work.