Design and optimization of deep sub-wavelength metamaterials using a hybrid search algorithm

The efficiency of wireless power transfer (WPT) can be enhanced considerably by using a metamaterial with appropriate electromagnetic parameters. For safety and applicability concerns, deep sub-wavelength metamaterials with low operating frequencies and small sizes are required in WPT. This paper proposes a hybrid search method for the optimization design of planar spiral metamaterials which are widely used in WPT systems. Firstly, the sensitivities of the design parameters of planar spiral metamaterials are investigated. Then the high-sensitive parameters are optimized in the general design procedure by using a modified simulated annealing algorithm where a sensitivity and margin based perturbation is adopted to reduce the time consumption. Subsequently, the low-sensitive parameters are modified in the succeeding elaborate design procedure by using the differential evolution algorithm. A case study of a metamaterial with a permeability of -0.5 at 20 MHz is presented. The results show that the hybrid search method can reach the design aim of a small error in acceptable search time.