By using quasi-optical tools, it is possible to approximate microwave radiation to Gaussian beams, which enables the study of its propagation and coupling to different components. Hence, their usefulness for wireless power transfer and rapid system design. In this paper, a system composed of two reflectors is analyzed both theoretically and by discussing two cases where quasi-optical tools were applied. The near- and far-field regimes were considered and corresponding frequencies of operation, beam radius, and radius of curvature were computed.

Near-field communication (NFC) readers, ubiquitously embedded in smartphones and other infrastructures can wirelessly deliver mW-level power to NFC tags. Our previous work NFC-wireless identification and sensing platform (WISP) proves that the generated NFC signal from an NFC enabled phone can power a tag (NFC-WISP) with display and sensing capabilities in addition to identification. However, accurately aligning and placing the NFC tag's antenna to ensure the high power delivery efficiency and communication performance is very challenging for the users. In addition, the performance of the NFC tag is not only range and alignment sensitive but also is a function of its run-time load impedance. This makes the execution of power-hungry tasks on an NFC tag (like the NFC-WISP) very challenging. Therefore, we explore a low-cost tag antenna design to achieve higher power delivered to the load (PDL) by utilizing two different antenna configurations (2-coil/3-coil). The two types of antenna configurations can be used to dynamically adapt to the requirements of varied range, alignment and load impedance in real-time, therefore, we achieve continuous high PDL and reliable communication. With the proposed method, we can, for example, turn a semi-passive NFC-WISP into a passive display tag in which an embedded 2.7″ E-ink screen can be updated robustly by a tapped NFC reader (e.g. an NFC-enable cell-phone) over a 3 seconds and within 1.5cm range.

Power repeaters are used to extend the power transfer range or enhance the power transfer capability of Inductive Power Transfer (IPT) systems, but how to tune the power repeaters to improve the system power transfer performance remains an unsolved problem. In this paper, studies of the effect of the tuning capacitance of the power repeater of an IPT system on the power transfer capability are presented. A theoretical model is established to analyze the output power of the system with the primary coil and secondary coil tuned at a nominal resonant frequency, and a passive power repeater placed in between. By analyzing the relationship between the tuning capacitance of the power repeater and the output power, a critical tuning capacitance which sets up the boundary between enhancing and reducing the output power is determined, and the optimal tuning capacitances corresponding to the maximum and minimum output power are also obtained. A practical IPT system with a passive power repeater placed at 40, 80, and 104 mm from the primary coil is built. It has shown that the practically measured critical capacitance and the optimal tuning capacitance for maximum power transfer are in good agreement with the analytical results.

This work presents a novel efficient and compact size coupled resonator system for wireless power transfer (WPT) based on compact half-ring resonators defected ground structure (HRRs-DGS). The proposed design is capable of supplying low power electronic devices. The suggested system is based on coupled resonators of DGS. An HRR-DGS band-stop filter is designed and proposed, and when two HRRs-DGS are coupled back-to-back, it transfers to a band-pass filter leading to a compact and highly efficient WPT system working at 3.4 GHz. The measured efficiency of the proposed coupled HRRs-DGS system is around 94% at a transmission distance of 12 mm which is filled with foam for stable measurements. The proposed design is suitable for charging electronic devices such as wireless sensor nodes at 3.4 GHz. Simulation and experimental results have shown acceptable agreement.