Wireless power transfer (WPT) provides a convenient method of delivering energy to multiple devices. With the increasing use of WPT, safety concerns inevitably create the need for a reliable control mechanism. Previous approaches in advanced WPT or metamaterial-enhanced WPT, however, have the limitation that neither the intensity nor the shape of the field-localizing area can be dynamically controlled. To address this limitation, we introduce the novel concept of a hotspot or power-focused region using field-localizing WPT. Using the proposed method, we provide experimental evidence demonstrating that the location, shape, and intensity of the hotspot can be manipulated as desired. The hotspot effectively enhances power delivery to the intended device while reducing leakage to unwanted areas. To dynamically reconfigure the hotspots, we propose an active metasurface with multi-functionality due to its frequency switching and tuning capability. The dynamic reconfiguring capability provides a wide range of versatile practical applications, overcoming the limitations associated with passive metamaterials. Because the location, shape, and intensity of hotspots can readily be controlled, the proposed method is not limited to WPT applications. It can also be used for a broad range of applications that require precise control of power delivery.

In this article, we investigated the efficiency of a magnetic resonant wireless power transfer (MR-WPT) in conducting medium and found out an optimal frequency for designing the system. In conducting environment, the eddy current loss is generated by the high-frequency alternating currents in the coils. It is manifested by increased radiation resistance of resonator coil leads to decrease the quality factor (Q-factor), which reduces the wireless power transfer (WPT) efficiency in conducting medium. The Q-factor of the resonator coil strongly depending on the conductivity, frequency, and thickness of conducting block. Two MR-WPT systems operating at 10.0 MHz and 20.0 MHz are implemented to study the effect of conducting medium on efficiency. The achieved results indicated that the 20.0 MHz system has higher efficiency at a conductivity smaller than 6.0 S/m. However, at the larger conductivity, the 10.0 MHz system is more efficient. The results provide a method to determine the optimal frequency of a WPT system operating in the conducting medium with various conductivities and thickness blocks. This method can be used to design MR-WPT systems in numerous situations, such as autonomous underwater vehicles and medical implants.

In this letter, we propose a magneto-inductive wave (MIW) metamaterial cavity for enhanced mid-range wireless power transfer (WPT) applications. Cavity operation is achieved by controlling the propagation of MIWs at lower megahertz frequencies. The cavity is realized by omitting a cell and thereby breaking the periodicity of the closely coupled metamaterial slabs. The cavity in the proposed metamaterial effectively confines the MIWs into a subwavelength region. Consequently, it localizes the magnetic field in the WPT region and provides enhanced power transmission. When the proposed MIW metamaterial cavity is used, the measured efficiency improves significantly from 8.7 to 54.9%.

To meet both safety and efficiency demands of future wireless power transfer (WPT) systems, field leakage to the nearby environment should be controlled below a certain level. Therefore, field localization is one of the key issues in advanced WPT systems. Recently, metamaterials have shown great potential for enhanced control of electromagnetic propagation in various environments. In this work, we investigate a locally modified metamaterial to create a two-dimensional (2D) cavity for field localization at a sub-wavelength scale. We also show that the field localization in the cavity can be explained using Fano-type interference. We believe that this is one of the first works demonstrating that Fano-type interference can be applied for resonance-coupled mid-range WPT. Using the proposed approach, we achieve a localized WPT in a region that is eight times smaller than that of a transmit coil. At a distance of 0.6 meters, the measured efficiency is 56.5%, which represents a six-fold and two-fold enhancement compared to free space and uniform metamaterial slabs, respectively.