Inductive wireless power transfer (WPT) systems require compensating capacitors to operate efficiently. However, these capacitors can introduce additional costs, weight, and losses, particularly at MHz-range operating frequencies. To mitigate these issues, self-resonant coils can be used by exploiting the parasitic capacitances inherent in double-layer printed circuit boards (PCBs). In this work, a double-layer coil for a self-resonant series WPT system is developed for operation at the AirFuel standard frequency of 6.78 MHz. Unlike conventional design methods adopted for self-resonant coils, mainly based on analytical formulations, the proposed approach employs Finite Element Method simulations that couple electro-quasistatic and magneto-quasistatic formulations. This approach enables accurate evaluation of the self-resonant frequency (SRF) as well as the current distribution along the PCB layers, revealing significant non-uniformity. Building on this insight, copper trace length is reduced to save material while maintaining performance in terms of operating frequency. Both the full-trace and reduced-trace coils are fabricated and tested, showing good agreement with simulations. Notably, the proposed reduction in the copper trace affects the SRF by only 3% compared with the full-trace design.

More mobile devices such as mobile phones and robots are wirelessly charged for convenience, simplicity, and safety, and it would be desirable to achieve three-dimensional (3D) wireless charging with high spatial freedom and long range. This paper proposes a 3D wireless charging cube with three orthogonal coils and supporting magnetic cores to enhance the magnetic flux outside the cube. The proposed system is simulated by Ansoft Maxwell and implemented by a downsized prototype. Both simulation and experimental results show that the magnetic cores can strengthen the magnitude of B-field outside the cube. The final prototype demonstrates that the power transfer distance outside the cube for getting the same induced electromotive force in the receiver coil is extended approximately by 50 mm using magnetic cores with a permeability of 2800. It is found that the magnitude of B-field outside the cube can be increased by increasing the width and the permeability of the magnetic cores. The measured results show that when the permeability of the magnetic cores is fixed, the induced electromotive force in the receiver coil at a point 300 mm away from the center of the cube is increased by about 2V when the width of the magnetic cores is increased from 50 to 100 mm. The increase in the induced electromotive force at an extended point implies a greater potential of wireless power transfer capability to the power pickup.

The objective of the presented work is to take advantage of the precision capabilities of tailor-fiber-placement (TFP) embroidery processes in order to qualify carbon-fiber parts as viable antennas for wireless power transfer applications in multifunctional carbon-fiber-reinforced plastic (CFRP) composites. The solution comes first from a literature study of electrical, high-frequency, and textile engineering concepts. This review built familiarity with the technological challenges and state-of-the-art of the presented technology. Next step was iterative experimentation of machine capabilities for the production of carbon-fiber antennas. Finally, antenna prototypes were produced and their physical and electrical characteristics were evaluated through several test methods. The results showed that TFP embroidery machines were capable of producing quality, carbon antennas. Induction values of the antennas from 0.5 to 3.5 ‘H were achieved. Signal transfer efficiencies from carbon-antenna transmitters to an aftermarket receiver show promise in commercial application.

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.

In this work, a shorting control (SC) scheme is integrated into a complementary metal-oxide-semiconductor (CMOS) synchronous rectifier for the output voltage regulation of a wireless power supply. The rectifier is designed to operate in a parallel tuned pickup with a 500 mW output power capability for biomedical implants. Without any additional components, the proposed SC method enables the power pickup to operate with high efficiency under variable coupling conditions while maintaining the required load power to keep the output voltage constant. Desired operating conditions are achieved with increased power transfer capability at weak magnetic coupling conditions and higher power efficiency at strong coupling. A novel derivation describes the change in efficiency with SC duty ratio. Experimental validation is completed with an original custom CMOS integrated rectifier with embedded SC. It is demonstrated that the proposed SC method can increase the overall secondary pickup power transfer efficiency by 14% as the magnetic coupling increases to the stronger end.

This paper proposes a Voltage-controlled Variable Capacitor Structure (VVCS) to adjust the frequency of an autonomous push–pull converter. Unlike traditional switch mode capacitors or inductors where active switches are used, the equivalent capacitance of the VVCS varies with the on/off periods of a diode controlled by a DC voltage. The frequency of the autonomous push–pull converter can be controlled by this DC voltage when the VVCS is used as a variable resonant capacitor. As no active switching is involved in the VVCS, the circuit operates more smoothly than its switch mode counterpart so as to provide a simple way to adjust the operating frequency of the autonomous push–pull converter for high frequency and low electro magnetic interference operations. Mathematical model is developed for the relationship between the equivalent capacitance of the VVCS and the DC control voltage, and is verified by experimental results at more than 900 kHz with an approximately 12 W inductive power transfer system.

In light of the increased interest in e-mobility, comfortable, and safe charging systems, such as inductive charging systems, are gaining importance. Several standardization bodies develop guidelines and specifications for inductive power transfer systems in order to ensure a good interoperability between different coil architectures from the various car manufacturers, wireless power transfer suppliers, and infrastructure companies. A combination of a bipolar magnetic coil design on the primary side with a secondary solenoidal coil promises a good magnetic coupling and a high-transmitted power with small dimensions at the same time. In order to get a profound knowledge of the influence and behavior of the main variables on the coil system, a detailed parameter study is conducted in this paper. Based on these findings, a solenoid was designed for a specific case of application. Further, this design is optimized. The dimensions of the system could be reduced by 50% with a constant coupling factor at the same time. Besides the reduction of the dimensions and subsequently the costs of the systems, the stray field could be reduced significantly.

The design of magnetic couplers for inductive power transfer has probably become the major challenge for those who wish to enter this promising research field. The number of variables that determine physical dimensions of a coupler is typically too high to allow analytical (exact) solutions in practical time when realistic magnetic materials are to be included. Thus, this paper suggests and describes a series of algorithms based on the finite element method (FEM) able to convert basic inputs (target inductances, primary current, frequency, and mechanical restrictions) into a geometric solution that satisfies user-defined targets for uncompensated power, open-circuit voltage, and short-circuit current. Advantages of these algorithms when compared with other existing design methods are: simplicity in terms of structure at the same time that require minimum user intervention to complete a full design; do not rely in expensive finite element solvers; user does not require previous background in FEM formulation. Experimental results show that the proposed design method based on two-dimensional FEM has errors of <8% when compared with three-dimensional FEM and can perform iterations in seconds. It is expected that the proposed routines encourage and provide design insights for practitioners, enthusiasts, and non-specialized engineers.

This study presents a method of determining the magnetic coupling coefficient of inductive power transfer (IPT) systems under real-time operating conditions by measuring the open-circuit voltage and short-circuit current of coupled coils. Besides the theoretical analysis, the proposed method is verified by finite elements simulation and practical evaluation. Both simulation and experimental results have demonstrated that the proposed method can determine the coupling coefficient of both closely and loosely coupled coils with high-quality factors. The method can be used for online monitoring of the coupling condition and real-time power flow controller design of IPT systems.

This paper is dedicated to the extensive review of state-of-the-art contactless energy transfer (CET) systems that are gaining increasing interest in the automatic machinery industries. We first introduce the circuit equivalent networks considered in the literature, and discuss the main operating principles. Possible circuital resonant solutions are also discussed together with the required compensating networks. Then we focus on the problem of transferring, at the maximum efficiency, high-power levels (of the order of 1 kW or higher), showing that highly coupled inductive links are needed, requiring to refrain from the resonance condition. These systems are usually referred to as CET systems, since the link distances are negligible with respect to the coils dimensions. The operating frequencies are of the order of tens to hundreds of kilohertz. The fundamental figures of merit are analytically defined and used to measure the actual limitations involved in this class of systems, including aspects related to realization feasibility with respect to voltages and currents limitations. Finally, state-of-the-art CET works are surveyed, and realistic applications for different operating frequencies are considered and critically compared.