Mag-E4E: Trade Efficiency for Energy in Magnetic MIMO Wireless Power Transfer System

Magnetic resonant coupling (MRC) wireless power transfer (WPT) is a convenient and potential power supply solution for smart devices. The scheduling problem in the multiple-input multiple-output (MIMO) scenarios is essential to concentrate energy at the receiver (RX) side. Meanwhile, strong TX-RX coupling could ensure better power transfer efficiency (PTE), but may cause lower power delivered to load (PDL) when transmitter voltages are bounded. In this paper, we propose the frequency adjustment based PDL maximization scheme for MIMO MRC-WPT systems. We formulate such joint optimization problem and decouple it into two sub-problems, i.e., high-level frequency adjustment and low-level voltage adaptation. We solve these two sub-problems with gradient descent based and alternating direction method of multipliers (ADMM) based algorithms, respectively. We further design an energy-voltage transform matrix algebra based estimation mechanism to reduce context measurement overhead. We prototype the proposed system, and conduct extensive experiments to evaluate its performance. As compared with the PTE maximization solutions, our system trades smaller efficiency for larger energy, i.e., 361% PDL improvement with respect to 26% PTE losses when TX-RX distance is 10cm.