Topology optimization design of surface radar absorbing coatings

In this study, a topology optimization method is proposed to design the layout of the radar absorbing coatings (RACs) outside the surface. The radar cross section (RCS) of a structure with RACs is evaluated by the physical optics method. A material interpolation model oriented to the relative permittivity and relative permeability of RACs is established, while the sensitivity of the RCS with respect to the design variables is derived analytically. With the objective of minimizing the RCS at the specified incident angles and the constraint of the material usage, the strategy is implemented based on a gradient-based algorithm and the so-called three-field density method. Additionally, the phenomenon of the RCS increasing in certain regions when RACs are applied is explained in detail. Finally, the effectiveness of the proposed method is demonstrated by two numerical examples.