Wireless power transfer (WPT) has been widely used in IoT applications, such as mobile device charging, biomedical implants communication, and RFID field. Maximizing the power transfer efficiency (PTE) becomes one of the most crucial problems for designing the WPT systems. Magnetic induction (MI) beamforming has been proposed recently to maximize the PTE for the near field MIMO WPT systems. However, conventional magnetic beamforming in WPT systems usually requires accurate magnetic channel estimation, both amplitude and phase control of the charging source, which can not be achieved in an extreme environment. In this paper, we propose a novel magnetic induction beamforming scheme in MIMO WPT system using a reconfigurable metasurface. Instead of controlling the source currents or voltages, the reconfigurable metasurface can achieve near field beamforming only by varying the capacitor and resistance in specific coil array units. The beamforming is modeled as a discrete optimization problem and solved by using the Simulate Anneal (SA) method. Through the analytical and COMSOL simulation results, our proposed beamforming scheme can achieve approximately two times PTE of the conventional beamforming method in a 40 cm charging distance.
A Wirelessly Rechargeable AA Battery Using Electrodynamic Wireless Power Transmission
We report the design, fabrication, and characterization of a prototype that meets the form, fit, and function of a household 1.5 V AA battery, but which can be wirelessly recharged without removal from the host device. The prototype system comprises a low-frequency electrodynamic wireless power transmission (EWPT) receiver, a lithium polymer energy storage cell, and a power management circuit (PMC), all contained within a 3D-printed package. The EWPT receiver and overall system are experimentally characterized using a 238 Hz sinusoidal magnetic charging field and either a 1000 µF electrolytic capacitor or a lithium polymer (LiPo) cell as the storage cell. The system demonstrates a minimal operating field as low as 50 µTrms (similar in magnitude to Earth’s magnetic field). At this minimum charging field, the prototype transfers a maximum dc current of 50 µA to the capacitor, corresponding to a power delivery of 118 µW. The power effectiveness of the power management system is approximately 49%; with power effectiveness defined as the ratio between actual output power and the maximum possible power the EWPT receiver can transfer to a pure resistive load at a given field strength.
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