Compact Low-Frequency Metamaterial Design for Wireless Power Transfer Efficiency Enhancement

An extremely compact and low-frequency metamaterial design is presented in the following work. A ferrite loaded solenoid with a size on the order of 1/10000 of the wavelength of operation is used as the unit cell of the proposed metamaterial. This unit cell allows for the construction of a 77 unit-cell sample with dimensions of 6 cm × 6 cm × 2 cm and operating at a working frequency of 5.57 MHz. Measurements show that using this metamaterial sample in a wireless power transfer (WPT) system results in an efficiency enhancement of 10% at a working distance of 4.5 cm, which is twice the efficiency of the original system at the same distance. Alternatively, for a target efficiency of 10%, the range of the system can be extended from 4.5 to 8.8 cm by using the proposed metamaterial, a 4.3-cm, or 95%, extension over the original system range. The proposed metamaterial design, characterized by compactness, low frequency of operation, and large efficiency enhancement, is useful in a number of applications, such as biomedical telemetry systems and wireless charging.