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Wireless power transfer (WPT) has recently emerged as a prominent technology to liberate various applications with small devices from limited mobility and design constraints. Among various techniques, magnetic field focusing (MFF) with multiple transmit (Tx) coils have been known as a powerful solution to enhance the efficiency of power transfer to multiple receivers (Rxs) in midrange WPT. However, in such MFF techniques, even unintended Rx may suffer from unwanted power due to leakage, which may disrupt the operations of the devices. Motivated by this issue, in this article, we consider selective magnetic resonance coupling (MRC)-based WPT, which enables WPT systems to better shape power distribution only focusing on the intended Rxs while leakages to the unintended Rx are suppressed. To this end, we first formulate the selectivity requirement of WPT as an optimization problem. Then, we propose a method to obtain the optimal Tx voltage vector for simultaneous MFF and null-steering optimization. Simulation and experimental results validate the theoretical analysis and the proposed method in practical scenarios.

This paper proposes a multiphase resonance-based rectifier (MPRR), capable of delivering power to multiple loads with large difference in their output voltages. This behavior is particularly useful for wireless sensors and actuators, in which the micromachined transducer/actuator needs a high voltage to operate but the interface circuitry requires only a fraction of that voltage. This is achieved by shorting the receiver (Rx) L3C3-tank to increase its loaded quality factor, QRx , over several cycles to accumulate wirelessly transferred energy in the inductor during this period, and then first break the loop in-phase, by connecting the L3C3-tank to the in-phase load ( RL,I ), to transfer energy at low voltage in a half cycle (in-phase charging), and then transfer energy to the quadrature load ( RL,Q ) through a diode in a quarter cycle at high voltage (quadrature charging). By optimizing the number of cycles for in-phase charging, NI , and quadrature charging, NQ , through an iterative design procedure, the MPRR can achieve the highest power delivered to the load under a given set of design constraints. Governing equations in the MPRR operation are derived to identify the key specifications for the design procedure. Using an exemplar set of specifications, the optimized MPRR was able to generate 21.5 and 1.84 V across 100 kΩ and 200 Ω loads, respectively, from a class-D power amplifier operating at 15 V, 6.78 MHz sinusoid input in the industrial-scientific-medical band (ISM-band) at a Tx/Rx coil separation of 1.3 cm with NI = 3 cycles, NQ = 6 cycles, and IQ Ratio = 5.

In this paper, a new LED fluorescent driver compatible with a rapid-start ballast is proposed. Using a compensation circuit composed of passive elements, a new LED fluorescent driver having highly reliable and robust characteristics was developed. This driver can prevent the fire problem that arose in conventional LED fluorescent switching power supplies. The design principle and architecture of the proposed LED driver was explained, and its feasibility was confirmed by simulations and experiments.