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The wireless power transfer (WPT) system generates a high density leakage electromagnetic field (EMF) during its operation. Exposure to leakage EMF has adverse effects on human health. In order to reduce the leakage EMF, a shielding method can be applied to the WPT system. The shielding methods in previous studies reduced leakage EMF, but the power...
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... means that PTE decrease can be prevented by preserving the quality factor of the WPT coil, and furthermore the PTE can be enhanced if the quality factor of the WPT can be increased. Figure 2 shows the concept of the proposed dual loop reactive shield. The proposed TS and RS coils have an inner and outer loop, respectively, and the inner and outer loops are connected to each other. ...
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... PTE of the previous reactive shield was 75.3%, and this is a 7.3% PTE decrease. Figure 20 shows the simulation and experimental results of the SE for the symmetric WPT system in the alignment condition. The average SE of the dependent active shield was 49.1%, and that of the previous reactive shield was 51.8%. ...
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... experimentally measured load power of the case w/o shield and the proposed shielding method was identically 207 W. The load power of active and previous reactive shield was 201 W and 206 W, respectively. Figure 22 shows the simulation and experimental results of the PTE for the symmetric WPT system in the misalignment condition. In the case of w/o shields, the PTE was 77%. ...
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... PTE of the previous reactive shield was 64.7%, and this result is a 12.3% PTE decrease compared with the case w/o shield. Figure 23 shows the simulation and experimental results of SE for the symmetric WPT system in the misalignment condition. The SE of all shielding methods decreased in the misalignment condition. ...
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... EXPERIMENTAL SETUP FIGURE 24. Experimental setup of asymmetric WPT system Figure 24 shows the experimental setup of the asymmetric WPT system. The setup of the asymmetric WPT system is identical to that of the symmetric WPT system except for the coils. ...
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... load power of all experimental subjects is similarly about 200W as in the case of the symmetric WPT system. Figure 26 are the coil geometry and the fabricated TX and RX coils of the proposed shielding method for the asymmetrical WPT system. The radius of the TX coil in the asymmetrical WPT system is larger than that of the RX coil. ...
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... diameter of the ferrite and aluminum plate applied to the RX coil is identically 300 mm. Figure 27(a) shows the MPs of the aligned asymmetric WPT system. Each measurement point in MP1 and MP2 has 200, 250, and 300 mm distance from the TX coil, respectively. ...
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... and MP4 are identical to the case of the symmetric WPT system. Figure 27(b) shows the MPs of the misaligned asymmetric WPT system. The misalignment condition in the asymmetric WPT system is that the RX coil has 100 mm lateral displacement for the TX coil. Figure 29 shows the simulation and experimental results of PTE for the asymmetric WPT system in the alignment condition. ...
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... misalignment condition in the asymmetric WPT system is that the RX coil has 100 mm lateral displacement for the TX coil. Figure 29 shows the simulation and experimental results of PTE for the asymmetric WPT system in the alignment condition. In the case of w/o shield, the PTE was 81.1%. ...
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... 31 shows the simulation and experimental results of the transferred power to load for the asymmetric WPT system in misalignment condition. The experimentally measured load power of the case w/o shield and the proposed shielding method was respectively 204 W and 207 W. The load power of the active and previous reactive shield was 204 W and 201 W. Figure 32 shows the simulation and experimental results of PTE for the symmetric WPT system in the misalignment condition. In the case of the w/o shield, the PTE was 78.8%. ...
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Citations
... Among the methods for reducing magnetic leakage from planar coils, the most actively researched is the reactive shield (SH) method [25][26][27]. Park et al. [25] proposed a method to reduce magnetic leakage in a WPT system using a planar coil for mobile applications. In Kim et al.'s study [27], power transfer efficiency was increased, and the leakage magnetic field was reduced using a dual-loop reactive shield. ...
... Park et al. [25] proposed a method to reduce magnetic leakage in a WPT system using a planar coil for mobile applications. In Kim et al.'s study [27], power transfer efficiency was increased, and the leakage magnetic field was reduced using a dual-loop reactive shield. Furthermore, Wei and Wu [28] studied similar content using the frequency split phenomenon. ...
... In (8), ω n2 is the resonant frequency of the RX side. Meanwhile, the resonant circuit on the SH side is adjusted with a capacitor (C SH ), as shown in Figure 4. Studies have found that for the magnetic field generated in the SH coil to have an opposite phase of the magnetic field generated in the TX coil, the resonant frequency of the SH coil (ω SH ) must be set lower than that of the system operating frequency (ω o ) [25][26][27]. In essence, the resonant of the SH coil must be in the inductive region, as shown in Figure 5a,b. ...
This paper proposes a reactive shield structure to reduce the leakage magnetic field of a wireless power transfer (WPT) system with a dipole coil structure. The reactive shield resonates at a frequency lower than that of the WPT system and operates in an inductive region where the reactance is positive. Therefore, the magnetic field generated by the shield coil is 180° different in phase from that generated by the transmitting coil, resulting in an effective reduction in the leakage magnetic field. The methodology for designing the reactive shield for the dipole coil structure is mathematically analyzed, and the current and magnetic field phases are compared. Its effectiveness has been validated through simulations and experiments. Specifically, the proposed method is validated through a 50 W class WPT experiment, which showed that the proposed shielding structure achieves efficiency reductions ranging from 0.3% to 1.5% and has a leakage magnetic field reduction effect of up to 67% compared to the comparison groups.
... However, aluminum or magnetic electromagnetic shielding will significantly reduce the self-inductance and mutual inductance. J Kim et.al proposed a novel reactive shielding method having shielding effectiveness (SE) and power transfer effectiveness (PTE) [125]. He et.al proposed a dualband-coil array with novel high-order circuit compensation [126]. ...
This article provides a comprehensive overview of on-board wireless motors based on WPT system. Based on the mathematical models of common wireless motors, the coupling strength of on-board wireless motors is divided, and their characteristics and advantages are comprehensively summarized and classified. In order to provide power to the three-phase wireless motors, the rotary transformer is used to replace the common coupling coil in the WPT system. This paper conducts electromagnetic model on the rotary transformer, as well as a comprehensive summary of structures and materials of the rotary transformer. The resonant compensation topology of WPT system is crucial. Comparing the transmission characteristics and advantages and disadvantages of various compensation topologies is beneficial for selecting appropriate compensation topologies in different application scenarios. For the control strategy of WPT system, this paper mainly focuses on the issues of output power and transmission efficiency. Finally, the research difficulties and directions of on-board wireless motors are proposed, such as electromagnetic interference and resonance, and this technology is extended to other fields, including wireless charging, robotics, etc.
... Regarding this category of screens, several studies have been conducted [68][69][70][71][72][73][74]. Table 1 compares the most recent work on this screen type for the WPT system. ...
... This indicates that the proposed technology effectively reduces EMF leakage without significantly impacting the transmission efficiency of the WPT system in EVs. J.Kim et al. [74] The authors proposed a dual loop reactive shield application to reduce leakage electromagnetic field (EMF) while enhancing power transfer efficiency (PTE) in WPT systems. The proposed dual-loop reactive shield generates in-phase and out-ofphase magnetic fields simultaneously. ...
Electromagnetic compatibility (EMC) is crucial when designing and operating wireless power transfer (WPT) systems for charging Electric Vehicles (EVs). WPT technology allows the transmission of electrical energy from a power source to a device without requiring physical contact. However, it can generate electromagnetic interference (EMI) that could disturb nearby electronic devices or harm people nearby. Shielding techniques are commonly employed to mitigate EMI in WPT systems. However, implementing effective shielding techniques can be complex, involving trade-offs between effectiveness, cost, and shielding weight. In this article, different types of existing shielding techniques for wireless charging systems of EVs are compared. The main concepts regarding the functioning of electromagnetic shields and the theory of the functioning of WPT systems have been also briefly introduced.
... Active-shielding method can eliminate the magnetic field at some specific positions. But extra active-shielding coils and excitation are required as well as accurate magnetic (or current amplitude and phase of transmitting coil) tracking and control strategy [22], [27]. Passive shielding is easy to operate, while only the magnetic in the direction of power transmission channel is suppressed [12], [28]. ...
Electromagnetic field is used as medium for wireless power transfer to realize noncontact power transmission, which is hoped to be concentrated in the power transmission channel as much as possible to improve performance and reduce the impact on surrounding environment. A magnetic coupling mechanism (MCM) with omnidirectional magnetic shielding (ODMS) is designed in this article. Ferrite shielding layers are added at the back of power channel to guide more for power transmission and restraint leakage. The reverse-wound magnetic shielding coil and forward-wound power transmitting coil are connected in reverse series to form a bidirectional antiparallel coil, which eliminates the complex control and additional excitation source, and restrict magnetic in the side areas of power channel. Active and passive shielding methods are comprehensively used to improve the magnetic field distribution in the power transmission channel and reduce magnetic in the full space around MCM. The optimal design method of ODMS MCM is summarized, and the experiments are carried out. The results are consistent with the theoretical and simulation analysis. The proposed ODMS MCM can effectively limit magnetic leakage in all directions and improve transmission power and efficiency.
... Additionally, since drones used in inspections swim in narrow and obstacle-filled places, the wireless coupler must be small, lightweight, and highly durable. Inductive WPT has attracted attention due to its high efficiency in lossy underwater environments [6]- [12]. A previous research has achieved an efficiency of over 90% [10]- [12]. ...
... Inductive WPT has attracted attention due to its high efficiency in lossy underwater environments [6]- [12]. A previous research has achieved an efficiency of over 90% [10]- [12]. However, due to the use of wound coils and magnetic cores, the inductive coupler is heavy and shock sensitive, making it challenging to mount on small underwater drones for inspection. ...
The misalignment of a coupler is a significant issue for capacitive wireless power transfer (WPT). This paper presents a capacitive WPT system specifically designed for underwater drones operating in flowing freshwater environments. The primary design features include a capacitive coupler with an opposite relative position between feeding and receiving points on the coupler electrode, two phase compensation circuits, and a load-independent inverter. A stable and energy-efficient power transmission is achieved by maintaining a 90° phase difference on the coupler electrode in dielectrics with a large unloaded quality factor (Q factor), such as in freshwater. Although a 622-mm coupler electrode is required at 13.56 MHz, the phase compensation circuits can reduce to 250 mm as one example, which is mountable to small underwater drones. Furthermore, the electricity waste is automatically reduced using the constant-current (CC) output inverter in the event of misalignment where efficiency drops occur. Finally, their functions are simulated and demonstrated at various receiver positions and transfer distances in tap water.
... The performance of these systems are evaluated by some factors like, the amount of transmitted power, the compensation circuits used, the amount of the air gap between the transmitter and receiver, the system efficiency for each study, and the program used if any. (Kim and Ahn 2021;Park et al. 2017) ...
Wireless Power Transfer (WPT) is a technology of transmitting electric, magnetic, optical, or microwave power without the use of physical connections. This technology is used to charge electric vehicles and other applications. It has several advantages over conductive charging method in terms of automation, safety in harsh environments, as well as reliability during environmental disasters. However, this technology faces challenges such as complex design, high cost, and sensitivity to misalignment and safety conditions for people. These challenges are associated with receiver and transmitter coils. This paper provides an overview of transmitter coil types, magnetic materials used, types of shields to provide safety for people, various pads structures, as well as the types of methods used to charge electric vehicles and electronic compensation circuits. This paper will be a reference for researchers and those interested in wireless power transfer to check these factors.
... Using additional cancelling coils carrying opposite-phase currents is a prevalent method. The cancelling coil currents can be actively fed [63] or generated by an induced voltage [64][65][66][67]. Resonant reactive shielding uses series LC resonant cancelling coils to cancel the field with the induced voltage [64][65][66][67]. ...
... The cancelling coil currents can be actively fed [63] or generated by an induced voltage [64][65][66][67]. Resonant reactive shielding uses series LC resonant cancelling coils to cancel the field with the induced voltage [64][65][66][67]. However, in practice, the current amplitude cannot be adequately controlled. ...
Wireless charging is already taking hold with abundant commercial products that operate at around a hundred kHz. Currently, high frequency (HF, 30 MHz) and very high frequency (VHF, 30-300 MHz) wireless power transfer (WPT) stand out because of better passive components, faster transient response, better combination with communications, and higher receiver input voltages. However, current WPT systems are not fully scalable for different applications with different power levels and transfer distances in the wireless power world. The thesis investigates scalable architectures for HF and VHF WPT, which can scale the power level and transfer distance while maintaining the efficiency with an application range from watts for biomedical and consumer electronics to tens of watts for robots and drones, breaking the trade-offs among devices, power, frequency, and transfer distance. The vision is to provide energy anytime and everywhere for electronic devices in the wireless power world. To fully utilize the fast switching speed of Gallium nitride (GaN) at HF-VHF, an ultrafast and isolated gate driver is investigated with variable frequencies, variable duty cycles, and arbitrarily long on- and off- times. It can be scaled for different active devices with the ultimate speed of below 270 ps rise and fall times. To mitigate the EMI (electromagnetic interference) and EMC (electromagnetic compatibility) problems at HF-VHF, a magnetic field cancellation method is presented for the encircled circuits inside WPT coils to make miniaturized devices operate properly under strong magnetic fields. The fundamental magnetic field for the encircled circuits can be reduced to 1 % compared to that without cancellation. To design robust and resilient WPT systems, a classic circuit topology CMCD is brought back to the renaissance, which can work as both inverter and rectifier. It can absorb parasitics and be modeled as a purely second-order system, which does not require multi-resonant tuning in the higher-order ZVS resonant converters. The straightforward design reveals the advantages of a wide load range and small input current ripple at the same time. With CMCD as a building block, the vision of a wireless power world can be possible. A single CMCD inverter coupled with a CMCD rectifier, i.e. a singleton system, fulfills the low power and short transfer distance applications. A segmented CMCD inverter coupled with a segmented CMCD rectifier, i.e. a segmentation system, fulfills the high power and long transfer distance applications. The segmented CMCD power converters aggregate the magnetic flux and corresponding power together from each identical and synchronous module by electrically connecting the resonance, which also physically increases the coil size at HF-VHF and extends the transfer distance and power level but maintains the efficiency of the optimized singleton system. In the end, the thesis concludes the contributions and illustrates the future directions of HF and VHF power conversion and transmission.
... Shielding of low frequency magnetic field using metal screens (enclosure, sheets, wire meshes) has been important for many decades and is now even more indispensable with the burgeoning number of RF transmitters and sensitive devices of all types [1][2][3][4][5][6]. Frequently, a screen has to contain apertures or slots for ventilation or cabling purposes. ...
An analytical formulation for magnetic field penetration through a circular aperture in a thin perfect electric conductor (PEC) screen with finite-thickness is developed. Especially, we propose an analytical formula for the magnetic coupling between two circular loops separated by the screen and placed coaxially with the aperture. The formula is verified by finite element simulations and experimental data. The thickness effect is explained by the cut off attenuation of TE01 mode in the aperture. The influences of loop-screen-loop distance and loop radius on the coupling intensity are also investigated.
