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.

This letter introduces a novel transparent single-layer frequency-selective surface (FSS) design on conventional window glass, which aimed at achieving signal selectivity for 5G millimeter-wave communication (n257; 26.5–29.5 GHz). The unit cell of the FSS layer features a structure formed by square loops and spirals, using small-width metal lines (200 and 250 μm). Additionally, a new approach is presented to enhance the transmission characteristics of the FSS layer by integrating a transparent dielectric slab while maintaining good optical transparency (>60%) in the visible light spectrum. The measurement results validate both the theoretical predictions and the design procedure, confirming the feasibility and transparency for signal filtering on window glass at millimeter waves. These findings hold promising potential for optimizing 5G wireless communication systems and simplifying signal filtering applications.

In this paper, we propose a method to reduce the leakage magnetic field from wireless power transfer (WPT) systems with series–series compensation topology by adjusting the phase difference between the transmitter (TX) coil current and the receiver (RX) coil current without additional shielding coils or materials. A WPT system employing the proposed method adjusts the phase difference between the TX coil current and RX coil current by tuning a resonant capacitor of the RX coil. The conditions for minimizing the leakage magnetic field are derived, and the range of the resonant capacitor of RX, considering power transfer efficiency and the leakage magnetic field, is proposed. Through simulations and experiments, it is verified that the proposed method can reduce the leakage magnetic field level without any additional materials. For that reason, the proposed method can be suitable for size-limited, weight-limited or cost-limited WPT systems.

This letter details the design of a compact pattern reconfigurable antenna that is based on the analysis of a tunable gap-incorporated band-stop frequency selective surface (FSS) unit cell. By changing the state of the RF PIN diode, the proposed FSS unit cell can demonstrate either a dipole-resonance mode or a circulating-current mode, thus allowing it to behave as a reflective or transparent structure, respectively, around the same frequency. A simple pattern reconfigurable antenna with reduced active switching elements for omnidirectional and directional beam-steering that is created by utilizing the proposed FSS unit cell can fulfill the desired function while avoiding the complexities involved in employing large FSS arrays. A prototype of the proposed antenna is fabricated and measured, and it shows a return loss |S11| < –10 dB from 1.7 – 1.8 GHz along with a peak gain of 6.8 dBi. Ultimately, this proposed antenna is expected to be applicable in various wireless communication systems.

This article analyzes the characteristics of the harmonic components in wireless power transfer (WPT) systems depending on load in the LCC -S topology. In a WPT system, the equivalent load can be changed depending on the charging state. Depending on the equivalent load, the operation of the rectifier can be divided into two modes. The first is continuous conduction mode (CCM), and the second is discontinuous conduction mode (DCM). The harmonic characteristics in CCM and DCM operation were each analyzed. The electromagnetic field (EMF) level is the largest when the output power was the largest. However, the electromagnetic interference (EMI) level is largest when the magnitude of the load was at the boundary between CCM and DCM. In practical WPT systems, a dc–dc converter is used for output voltage regulation, and by using the converter, the equivalent load can be changeable. A design method to suppress the leakage magnetic field is proposed in terms of EMF and EMI. Through simulation and experiment, we verified when EMF and EMI levels have the largest value. Also, the effect of suppressing the leakage magnetic field was verified by changing the value of the equivalent load.

The power transfer efficiency of a wireless power transfer is degraded by mismatch between LC resonant frequency and TX switching frequency. One of the drawbacks of conventional resonance tuning methods is that only increment of capacitor is allowed. Even if some conventional tunings allow both increment and reduction of capacitance, they fail zero-voltage switching (ZVS) at the increment of capacitance, which practically limits their tuning range. To solve the issue, we propose an automatic tuning resonant capacitor (ATRC), which can both increase and decrease the resonant capacitor. The tuning mosfet s achieve zero-voltage turn- on (ZVS) both at the capacitor-reduction mode and the capacitor-increment mode. These two (decrement/increment both are possible, and ZVS for both modes) are the advantages compared to conventional autotuning methods. Additionally, low dv/dt turn- off is achieved at capacitor-increasing mode in proposed method. Hence, the delivered power and overall efficiency is improved. The proposed method is suitable for any LC network to solve the detuning problem. A 200 W prototype is fabricated and tested experimentally. The measurement results show that the proposed ATRC can improve the overall PTE by 25%–63% point when the operating frequency is detuned ranging 75–125 kHz for 100 kHz nominal LC resonant frequency.