In this paper, models of metallic absorbers for electromagnetic waves in the infrared to microwave frequency range are reported and discussed. The Hadley's formalism (1D model) of transmission, reflection and absorption for semi-infinite layers, which allows to design all configurations of unstructured absorber films and dielectrics is generalized. To make the micro-fabrication of the metallic absorbers easier (that means to have layers thick enough), the metallic layers need to be structured (grid for example). We developed a model that allows us to consider the structure of metal as a homogeneous layer, where the diffraction is negligible. This new layer can be used with the previous model. When diffraction effects must be taken into account, we modified an electrical model made by Ulrich. We further developed it for the configuration of a dielectric before the metallic grid. The results showed the importance to take into account all the dimensions of the grid, the dielectric layer parameters and the wavelength to design the best absorber.
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