Abstract
Metamaterials (MTMs) with extraordinary electromagnetic properties are recently applied to wireless power transfer (WPT) systems to improve power transmission efficiency. Although theoretical progress has been made on MTMs in low frequency near field, in the operation frequency of most WPT systems (usually MHz), the design of MTMs still utilizes the model used in high-frequency applications. Therefore, a practical model of MTMs in low MHz band is proposed in this work. The resonance frequency and quality factor are used to describe the characteristics of an MTM slab. The near field WPT systems with MTMs are then modeled as electric circuits, the system efficiency is explicitly deduced, and optimization algorithms are employed to optimize the MTM resonance frequency and maximize the system efficiency. The proposed practical model is validated via a prototype wireless power transfer system operating at 6.78 MHz. Experiments show that the proposed MTM model has good accuracy for low MHz WPT systems compared with the high-frequency model. The proposed practical model of MTMs provides an accurate way to analyze the performance of MTM at low MHz frequencies and greatly benefits the future exploitation of MTM-based low-frequency near field applications.
Highlights
Metamaterials (MTMs) are novel artificial media consisting of a large number of microscopic unit cells and exhibiting negative permeability and/or negative permittivity on some frequencies [1,2,3,4,5,6].Since the first experimental demonstration of a negative index of refraction [7], numerous academic achievements on MTMs have been reported including transforming optics [8], invisibility cloaks [9], and novel MTM-based antennas [10]
MTMs have been introduced to low-frequency near field applications such as wireless power transfer (WPT) and magnetic resonance imaging (MRI) [11,12,13,14,15,16,17,18,19,20]
Unlike those in high-frequency electromagnetics, the electric and magnetic fields are almost decoupled in the near field, and the near field can be manipulated by single-negative MTMs [21]
Summary
Since the first experimental demonstration of a negative index of refraction [7], numerous academic achievements on MTMs have been reported including transforming optics [8], invisibility cloaks [9], and novel MTM-based antennas [10] These researches focus on high-frequency electromagnetics or optics. MTMs have been introduced to low-frequency near field applications such as wireless power transfer (WPT) and magnetic resonance imaging (MRI) [11,12,13,14,15,16,17,18,19,20]. Theoretical analysis and simulations have shown that the power transfer
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