We propose a fast maximum efficiency tracking, which instantly optimizes all. TX coils' currents using runtime-extracted mutual inductances, for simultaneously activated multiple TXs whose output levels are different each other. For fast control, we propose a theory to runtime extract all the mutual inductances between multiple TXs and an RX. Here, one prerequisite of extracting the values of mutual inductances is to acquire its relative ratios between the mutual inductances. It is proposed that the relative ratio can be obtained by reflected resistances and coil currents of each TX, which are ac quantities but can easily be measured using dc input property of LCC inverter. Using the ratio information in conjunction with RX dc output, the exact values of mutual inductances can be extracted. The aim of the proposed method is to enable fast (no iteration) maximum efficiency tracking for multiple TXs, which entails the optimization of the relative ratios among TX currents, as well as the RX load optimization. A 200-W RX moves at 10 km/h, and the controller can track the optimum target TX currents in response to time-varying magnetic couplings.

A receiver that can adjust the output voltage of coil is proposed to simultaneously charge as many receivers of different couplings as possible. One large coil of traditional receiver is split into two small coils while total coil volume is kept constant. The receiver has three output modes: half voltage, same voltage, and boosted voltage. Firstly, the boosted mode can produce the RX coil voltage that is ~60% higher than the traditional receiver with identical coil volume. It is useful for low-coupling and low-TX-output condition. Secondly, the half-voltage mode protects the semiconductor devices from overvoltage by outputting half of the traditional receiver with identical volume. It is necessary for high-coupling and high-TX-output condition with otherwise high voltage stress. Finally, same-voltage mode produces the same coil voltage as with traditional receiver. By the mode selection, relatively constant RX coil voltage can be maintained at both high coupling and low coupling conditions. This enables a single TX to charge both the strongly-coupled RX and the weakly-coupled RX simultaneously. In the experiment, the proposed 30 W receiver can operate across 1.9~7.5 cm whereas the conventional receiver is restricted to 3.5~5.5 cm.

In spread-spectrum electromagnetic interference (EMI) suppression, transmitter ( TX ) frequency is continuously modulated with fast speed. Conventional receiver (RX) autotuning methods cannot be used because of their slow response speed. Another limitation of conventional autotuning is their low efficiency if the incoming TX frequency is deviated far from RX nominal frequency (i.e., boundary of tunable range), even if the RX is reconfigured to tuned resonance. To solve the issues, the proposed PWM-tuning RX achieves constantly high efficiency even at the boundary of frequency tuning range. The proposed topology boosts the reflected resistance, thereby increasing the TX -to- RX efficiency compared to traditional variable tunings. We also propose an RX feedback loop which can track the fast-varying TX frequency and tune the RX capacitor accordingly. The step-response of proposed loop is fast (0.1 ms) in order to be suitable for spread-spectrum EMI suppression. The tuning mosfet achieves soft switching both at turn- on and turn- off . A simple grounded gate driving can be used. The measurement results show that the proposed ATR can improve the overall power transfer efficiency (PTE) by 7%–12% point for spread-spectrum ranging from 108 to 137 kHz, enabling 19.9 dB EMI suppression.

This article presents a new application field of a giant magneto-impedance (GMI) sensor. It shows valuable findings for the GMI sensor on the possibility of a new receiving element in magnetic field communication. The proposed GMI sensors serve as antennas and mixers in receiver systems. They have the advantage of being easily implemented and in terms of mass production and manufacturing processes due to the manufacture base on a printed circuit board (PCB). Their smaller size, lower cost, and higher sensitivity have more advantages than conventional magnetic sensors, such as the magneto-inductive, anisotropic magneto-resistive, and giant magneto-resistive sensors. Two types of PCB-based GMI sensors are proposed. The first type of GMI sensor is directly wound around the solenoid-shaped pickup coil onto an alumina insulation tube inserted with an amorphous microwire. The second type of GMI sensor has a patterned pickup coil that does not require the winding of the coil, similar to the patterned pickup coil of a micro electro-mechanical system-based GMI sensor. This GMI sensor provides a new geometry that can be easily manufactured with two PCB substrates. The proposed GMI sensors achieve the equivalent magnetic noise spectral density to the high-sensitivity characteristics of the pT/ $\surd $ Hz level. The equivalent magnetic noise spectral density of 1.5 pT/ $\surd $ Hz at 20.03 MHz is obtained for the first type of GMI sensor, and 3 pT/ $\surd $ Hz at 3.03 MHz is achieved the second type. The analyzed results of the bandwidth and the channel capacity for the two types of GMI sensors are acceptable. This first analysis confirms the possibility of the implementation of GMI sensors in magnetic field communication. The results of this experiment confirm the high performance of the proposed GMI sensors and their applicability in magnetic field communication. The detailed experimental results of the proposed GMI sensors are presented and discussed.

A resonant current-mode receiver is studied to charge low-voltage batteries wirelessly for supplying medical implantable systems. To increase efficiency, the root-mean-square (RMS) current in the LC tank of the receiver (RX) is reduced by using a voltage-boosted current-mode (VBCM) receiver. This receiver combines the conventional current-mode receiver with a switched-capacitor converter to boost the voltage instantaneously at the switching node ( $V_X$ ) of coil. Owing to the suggested technique, the receiver directly charges a low-voltage battery while maintaining a small RMS current without using a complex voltage regulator. The receiver achieves an efficiency as high as 84.7% with a 1.1 V battery while operating at the resonant frequency ( $f_{reso}$ ) of 6.78 MHz. The power delivered to the output ( $P_{o}$ ) is in the range from 1.5 mW to 50 mW. The VBCM receiver was fabricated by 180 nm CMOS technology with a total active area of $\rm0.22 mm^2$