Topology optimization for the layout design of radar absorbing coatings in cavities

Radar cross section (RCS) reduction for cavities is essential in flight vehicle design. As a conventional method to reduce the RCS, coating radar absorbing materials has been widely employed in engineering. Nevertheless, radar absorbing coatings (RAC) will additionally increase the structural weight. In this paper, a topology optimization approach is introduced for the layout design of RAC on the inner cavity walls. The objective of this problem is to minimize the mean value of RCS under the prescribed incident angles. A SIMP-like model is employed to represent the relative impedance of areas of intermediate density. The design variable is iteratively updated during the optimization process using a gradient-based algorithm. The RCS of the cavity is computed by the iterative physical optics method, which is utilized for the subsequent analytical gradient derivation. The validity of the proposed method is demonstrated by optimizing the RAC layout of two different shaped cavities. In both numerical examples, when optimizing the RCS in both planes with a weight of 1:1 and a volume fraction of 50%, the highest RCS loss rate in both horizontal and pitch planes is 18.02% and the lowest is only 6.89%. The optimization results indicate that the proposed method can be employed as a design procedure to consider both weight cost and cavity RCS reduction when coating the absorbing materials, instead of the classical experience-based RAC distributions.