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Wireless power transfer (WPT) systems have been widely adopted for full autonomy in various fields due to their convenience. However, changes in the air gap between the Tx and Rx coils significantly affect efficiency. To overcome this challenge, this paper introduces the determination of a compensation capacitor for a distance-variable WPT system that is robust in varying air gap conditions. The proposed method was verified using theoretical analysis, simulation, and experimental measurement. The electrical circuit was modeled using a T-equivalent model in a series–series (SS) topology to calculate power transfer efficiency (PTE). Specifically, compensation capacitors were analyzed at distances of 10, 30, and 50 mm, considering different self-inductance values. These results are compared against varying load resistances to demonstrate the effectiveness of the proposed approach. Additionally, the PTE drop ratio was defined to facilitate comparison. The results show that the PTE drop ratio for the compensation capacitor at the farthest distance was consistently smaller than that for the capacitor at the nearest distance under varying air gaps and load resistances. In this research, the difference in the PTE drop ratio between 10 and 50 mm was measured, demonstrating that determining the capacitor at the farthest distance reduces the PTE drop ratio across a range of operational conditions. [ABSTRACT FROM AUTHOR]

In this article, a microrobot capable of creating propulsion force and receiving electrical energy using a wireless power transfer (WPT) system is proposed. As a source of propulsion and rotation for the microrobot, we use the force and torque of magnetic material in a time-variant magnetic field generated by the transmitting coil of the WPT system, with a specifically designed magnetic material which produced even greater force under the same volume. While microrobot propulsion based on the Lorentz force is closely related to the magnitude of the induced current, because the force of the magnetic material in the proposed design is independent of the induced current, it is more practical for miniaturization of the microrobot. Additionally, the proposed model is able to use the LC resonance frequency, and a magnetic material located in the receiving coil introduces a higher coupling coefficient between the transmitting coil and the receiving coil. These characteristics make the proposed microrobot suitable for powering through a WPT system. The feasibility of the proposed model was initially investigated by theoretical analysis and then verified in simulation and an experiment. In the experiment, the fabricated microrobot $4.5\times 2.0\times2.0$ mm3 in size achieved a power transfer efficiency rate of 4.5% at 103 kHz with a propulsion speed of 7.5 mm/s and rotating motion. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) technvvology can be employed for the wireless charging of unmanned underwater vehicles. However, in an underwater WPT (UWPT) system, the eddy current loss (ECL) caused by the conductivity of seawater must be considered. Designs that do not properly consider the ECL can cause the unpredictable efficiency decrease of the system. In this article, we propose an efficient modeling for the UWPT system using Z-parameters. Utilizing the electromagnetic analysis and two-port network analysis, we can derive an impedance model of coils considering the frequency and the conductivity of seawater. The impedance model can be used to make an equivalent circuit of an UWPT system. The ECL can be predicted accurately by using the proposed equivalent circuit. For validation, an UWPT system was implemented and measured to compare with theoretical calculated results and electromagnetic simulation results. The calculation, simulation, and measurement results were in good agreement. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) technologies are currently growing in popularity because of problems with batteries in portable devices, such as the added weight and the inconvenience of conventional wired charging methods. However, wireless charging systems generate leakage magnetic fields, causing malfunctions in adjacent electronic devices. Technologies to suppress electromagnetic interference (EMI) from portable WPT systems are required to prevent this problem. In this paper, we propose a topology design for a multiresonance reactive shield to suppress the EMI from WPT systems. The proposed shield employs closed loops, which are located peripheral to the WPT coil and resonance matching capacitor. The power efficiency and shielding performance of the proposed method were compared with those of the conventional WPT system coil shielding topologies. The proposed shield exhibited about 27.37 dB more 3rd harmonic EMI suppression than other methods while maintaining higher power transfer efficiency. [ABSTRACT FROM AUTHOR]

The paper proposes a method for locating an electric means of transportation such as electric vehicles that adopts dynamic wireless charging system. The method works with magnetic wireless power transfer systems, based on a ferrite core counting approach. The ferrite core counter system operates by counting all the ferrite cores of the source coils used for guiding the magnetic field in a magnetic wireless power transfer system. The proposed ferrite core counter has a position detection accuracy equivalent to the spacing of the ferrite cores. In addition, this paper proposes a ferrite position identification (FPID) messaging unit to correct ferrite core counter errors. FPID blocks which are successively placed under the source coil are recognized by the ferrite core counter, and their passage is reported as a sort of message in the vehicle. This FPID messaging unit provides the ferrite core counter with a system that can correct errors in the number of ferrite cores counted. The effectiveness of the vehicle positioning system with the ferrite core counter and the FPID messaging unit has been demonstrated through simulation and experiments. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel coil structure, using a ferromagnetic material which concentrates the magnetic field, as the propulsion system of a wireless power transfer (WPT) based micro-robot. This structure uses an incident magnetic field to induce current during wireless power transfer, to generate a Lorentz force. To prevent net cancelation of the Lorentz force in the load coil, ferrite films were applied to one side of the coil segment. The demonstrated simplicity and effectiveness of the proposed micro-robot showed its suitability for applications. Simulation and experimental results confirmed a velocity of 1.02 mm/s with 6 mW power transfer capacity for the 3 mm sized micro-robot. [ABSTRACT FROM AUTHOR]

In this paper, a high-efficiency wireless power transfer (WPT) and force transfer system for a micro-robot is proposed. Two-coil systems are employed to power the micro-robot. The two-coil parts are ac and dc, and each consists of an external source and a load coil inside the micro-robot. In the ac coil part, the external source coil generates a time-varying magnetic field that is received by the ac load coil in the micro-robot as electrical energy. In the dc coil part, the external source coil is used as an electromagnet, which is used to generate propulsion force for the micro-robot. Through the proposed system, both the efficiency of electrical energy transfer and the generation of propulsion force can be significantly improved. The feasibility of the proposed approach was verified through simulation and experimentation results. [ABSTRACT FROM AUTHOR]

In this paper, we propose a microrobot powered by wireless power transfer (WPT) system which can generate propulsion force and torque as well as electrical energy to perform complex missions. The magnetic field and the induced current from the WPT coils can be utilized into the propulsion force and the Lorentz force for implementing rotational movement. The generated propulsion force and the torque are verified by 3-D finite-element simulations and experimental measurements. [ABSTRACT FROM AUTHOR]

Wireless charging of electric vehicles based on wireless power transfer (WPT) has become increasingly popular in recent years. However, a leakage electromagnetic field (EMF) that affects other electronic devices or the human body is inevitably generated from the coils of a WPT system, and requirements regarding the suppression of the leakage EMF are increasing. In this paper, we propose a novel three-phase power line in a WPT system for the reduction of the leakage EMF. The proposed structure employs six power lines to reduce the leakage magnetic flux. This structure is compared with conventional power line structures with respect to induced voltage and magnetic field distribution. We also present analytical solutions of the EMF for the proposed and conventional power line structures. These solutions are then compared with numerical solutions using 3-D finite-element analysis and good agreement is demonstrated. The results of the numerical analysis indicate that the proposed power line can significantly reduce the leakage magnetic field from a WPT system. For verification, the proposed and conventional power lines are implemented and the EMFs are measured. A strong correlation between the numerical and experimental results is exhibited. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a method of wirelessly torque transfer (WTT) and power (WPT) to a drug pump, one of implantable medical devices. By using the magnetic field generated by the WPT system to transfer torque and power to the receiving coil at the same time, applications that previously used power from the battery can be operated without a battery. The proposed method uses a receiving coil with magnetic material as a motor, and can generate torque in a desired direction using the magnetic field from the transmitting coil. The WPT system was analyzed using a topology that generates a constant current for stable torque generation. In addition, a method for detecting the position of the receiving coil without using additional power was proposed. Through simulations and experiments, it was confirmed that WTT and WPT were possible at the same time, and in particular, it was confirmed that WTT was stably possible. [ABSTRACT FROM AUTHOR]

Wireless power transfer systems are increasingly used as a means of charging implantable medical devices. However, the heat or thermal radiation from the wireless power transfer system can be harmful to biological tissue. In this research, we designed and implemented a wireless power transfer system-based implantable medical device with low thermal radiation, achieving 44.5% coil-to-coil efficiency. To suppress thermal radiation from the transmitting coil during charging, we minimized the ESR value of the transmitting coil. To increase power transfer efficiency, a ferrite film was applied on the receiving part. Based on analyses, we fabricated a cardiac monitoring system with dimensions of 17 × 24 × 8 mm3 and implanted it in a rat. We confirmed that the temperature of the wireless charging device increased by only 2 °C during the 70 min charging, which makes it safe enough to use as an implantable medical device charging system. [ABSTRACT FROM AUTHOR]

Implantable medical devices (IMDs) enable patients to monitor their health anytime and receive treatment anywhere. However, due to the limited capacity of a battery, their functionalities are restricted, and the devices may not achieve their intended potential fully. The most promising way to solve this limited capacity problem is wireless power transfer (WPT) technology. In this study, a WPT based implantable electrocardiogram (ECG) monitoring device that continuously records ECG data has been proposed, and its effectiveness is verified through an animal experiment using a rat model. Our proposed device is designed to be of size 24 × 27 × 8 mm, and it is small enough to be implanted in the rat. The device transmits data continuously using a low power Bluetooth Low Energy (BLE) communication technology. To charge the battery wirelessly, transmitting (Tx) and receiving (Rx) antennas were designed and fabricated. The animal experiment results clearly showed that our WPT system enables the device to monitor the ECG of a heart in various conditions continuously, while transmitting all ECG data in real-time. [ABSTRACT FROM AUTHOR]

The wireless power transfer (WPT) method for electric vehicles (EVs) is becoming more popular, and to ensure the interoperability of WPT systems, the Society of Automotive Engineers (SAE) established the J2954 recommended practice (RP). It includes powering frequency, electrical parameters, specifications, testing procedures, and other contents for EV WPT. Specifically, it describes the ranges of self-inductances of the transmitting coil, the receiving coil, and coupling coefficient (k), as well as the impedance matching values of the WPT system. Following the electrical parameters listed in SAE J2954 RP is crucial to ensure the EV wireless charging system is interoperable. This paper introduces a method for adjusting the effective permeability of the ferrite blocks in the standard model, to tune the self-inductance of the coils as well as the coupling coefficient. To guarantee the given values of the self-inductance of the coil and coupling coefficient matched those in the standard, we slightly modified the air-gap between the ferrite tiles in a specific region. Based on this method, it was possible to successfully tune the self-inductance of the transmitting coil and receiving coil as well as the coupling coefficient. The proposed method was verified by simulation and experimental measurements. [ABSTRACT FROM AUTHOR]

An autonomous coil alignment system (ACAS) using fuzzy steering control is proposed for vehicles with dynamic wireless charging. The misalignment between the power receiver coil and power transmitter coil is determined based on the voltage difference between two coils installed on the front-left/front-right of the power receiver coil and is corrected through autonomous steering using fuzzy control. The fuzzy control is chosen over other control methods for implementation in ACAS due to the nonlinear characteristic between voltage difference and lateral misalignment distance, as well as the imprecise and constantly varying voltage readings from sensors. The operational validity and feasibility of the ACAS are verified through simulation, where the vehicle equipped with ACAS is able to align with the power transmitter in the road majority of the time during operation, which also implies achieving better wireless power delivery. [ABSTRACT FROM AUTHOR]