Numerical and Experimental Study on Design Optimization of Hybrid Metamaterial Slab for Wireless Power Transmission

Wireless power transmission (WPT) technique has advanced rapidly in the past two decades. For wireless power transmission distances from 40 to 200 mm, the resonance coupling WPT (R-WPT) technique has surpassed its original inductive coupling counterpart in terms of transmission efficiency. Nevertheless, the power transfer efficiency of a R-WPT system is still lower than that of a wired power transfer system. To increase the power transfer efficiency of a R-WPT system, metamaterial (MM) slabs are inserted between the transmitter and receiver. Moreover, it has recently been validated that a hybrid MM (HMM) slab with different resonance frequency unit cells behaves better than a homogeneous MM slab with identical resonance frequency unit cells in a R-WPT application. However, in the existing HMM slab designs for WPT applications, a trial and error approach, is commonly used to decide the physical and circuit parameters of the HMM slab due to the overwhelmingly high computational cost of numerical simulations using three-dimensional (3-D) finite element method. To overcome the deficiencies of the existing designing methodology and to fully automate the design process, a design-of-experiment (DOE) assisted sequential refinement methodology is proposed by introducing an adaptive surrogate model with tabu search method, for design optimizations of HMM slabs in R-WPT applications. Compared with the existing refinement searching procedures, the salient feature of the proposed one is its bi-directional characteristics, which can refine the searches in the promising sub spaces by intensifying sampling points; and use coarse searches or even discarding the exploitations in the worst sub spaces using some adaptive upper and lower limits of the decision parameters. To validate the feasibility and show the advantages of the proposed methodology, detailed numerical and experimental studies on a case study of a four-coil WPT system working at 13.88 MHz are conducted, and the results have shown that the HMM slab optimized by using the proposed methodology does have better performance in WPT applications when compared to its homogenous counterparts.