Design method for broadband free-space electromagnetic cloak based on isotropic material for size reduction and enhanced invisibility

A design method is proposed that not only improves the invisibility of but also minimizes the size of a two-dimensional (2D) free-space electromagnetic cloak based on the quasi-conformal mapping (QCM) technique. The refractive index profile of the cloak based on the QCM is optimally scaled to minimize performance deterioration due to the imperfect isotropy of the cloak medium. Moreover, the method can be applied to compensate for the performance degradation due to size reduction. Based on the proposed method, as much as a 78.3% reduction in size is demonstrated. Enhancement of invisibility is evidenced by a 71% reduction in the normalized scattering cross section (SCS) at 10 GHz. Performance enhancement and miniaturization are achieved simultaneously with the extremely simple proposed method, making it one of the most practical cloaks reported thus far. Finally, experimental results over a broad bandwidth as well as for a wide range of incident angles are provided for cloaks fabricated using a 3D printer, which validate the effectiveness of the proposed method of cloak design.