Metamaterial-enhanced coupling seen as non-Foster impedance matching

Abstract

Electrically small antennas (ESA) are characterized by high-Q impedances presenting high reactance and low radiation resistance. Since in most wireless power transmission (WPT) applications, such as inductive power transmission (IPT), to use a full-size antenna is neither practical or desired, the system overall efficiency is usually very poor due to the drivers large reactance. In the last decade, various works have demonstrated that a class of artificial material called metamaterials (MTMs) can synthesize munegative (MNG) media capable of evanescent-wave focusing which largely enhances the coupling between ESA. In the present work, MTM-enhanced coupling in IPT systems is examined. Adopting a lumped element approach to describe the general MTM-enhanced IPT system, it is evidenced that MNG media can be interpreted as a negative inductance (a non-Foster reactance) from a circuital point of view. This paper also presents an approach based on energy density to calculate the module of the MNG slab equivalent inductor.