Spatial filtering magnetic metasurface for misalignment robustness enhancement in wireless power transfer applications

Abstract

In this paper, we present the design of spatial filtering magnetic metasurfaces to overcome the efficiency decay arising in misaligned resonant inductive Wireless Power Transfer systems. At first, we describe the analytical framework for the control of currents flowing on a finite-size metasurface, avoiding classical truncation effects on the periphery and opportunely manipulating, at the same time, the spatial magnetic field distribution produced by the closely placed RF driving coil. In order to validate the theoretical approach, we conceive a numerical test case consisting of a WPT system operating at 12 MHz. By performing accurate full-wave simulations, we prove that inducing a uniform current in the metasurface results in a more robust WPT system in terms of misalignment with respect to conventional configurations, also including standard metasurfaces. Therefore, while the use of metasurfaces in WPT systems has been already demonstrated to be beneficial in terms of efficiency enhancement, we confirmed that a proper control of the metasurfaces field filtering response can be advantageous also for the misalignment issue. Notably, the free space wavelength at the operating frequency (12 MHz) is 25 m, whereas the proposed metasurface dimensions are only 0.0024λ × 0.0024λ. Despite the extremely reduced dimensions, the spatial magnetic field distribution produced by the closely placed RF driving coil can be nevertheless opportunely manipulated. Finally, experimental measurements conducted on fabricated prototypes validated the numerical results, demonstrating the effectiveness of the proposed approach. These achievements can be particularly helpful in WPT applications where the position of driving and receiving coils frequently changes, as in consumer devices and biomedical implants.

Arbitrarily Conformal Metasurfaces for Enhanced Wireless Power Transfer Systems

“…By correctly designing such materials, it is possible to obtain specific properties and, consequently, to manipulate the electromagnetic radiation in order to achieve improved system performance. Being extremely popular in countless electromagnetic applications, magnetic metasurfaces were specifically proved as capable to homogenize the magnetic field, leading to a better misalignment robustness in WPT systems [33]. Moreover, other studies have shown the possibility to exploit near-zero permeability in order to realize a shielding slab [34], [35], [36].…”

Analysis of current distribution and termination conditions in 2D metasurfaces

“…The usefulness of a uniform current distribution in the metasurface has been shown in different application fields; still referring to WPT systems (hence to specific dimensions and frequency of operation), in Lazzoni et al (2023) it is demonstrated that the unit-cell current uniformity leads to a significantly more homogenous magnetic field distribution, fundamental to improve the WPT performance in terms of robustness to misalignment.…”

Broadband and precise reconfiguration of megahertz electromagnetic metamaterials for wireless power transfer

“…Taking inspiration from the recent advancements in metamaterials encompassing novel materials [25][26][27], intricate structures [28][29][30][31], and equivalent theories [32,33], there has been a burgeoning research focus on bestowing EMMs with exceptional reconfigurability. At present, one prevalent way to adjust the electromagnetic properties of an EMM unit cell is to introduce external capacitance [34][35][36] (see figure 1(c)). Most research work uses adjustable capacitors [37,38], which can alter their capacitance values by mechanically rotating the rotor to change the relative area with the stator.…”