Electromagnetic Field Leakage Research Articles

A Dual-Band Coil Array With Novel High-Order Circuit Compensation for Shielding Design in EV Wireless Charging System

For the wireless power transfer (WPT) system in electric vehicle (EV) applications, a serious concern lies in the leakage electromagnetic field (EMF) emission. In order to address this issue, this article presents a dual-band coil array (DB-CA) with novel high-order circuit (HOC) compensation. The most attractive feature of DB-CA is that both the first and third harmonics of leakage EMF can be reduced simultaneously, while the system still resonates at the same frequency. A detailed mathematical model is established to intuitively reveal the relevance between impedance design and shielding performance, as well as the constraints to achieve resonance. In addition, the novel HOC compensation is employed to decouple the shielding design at each harmonic. Both simulated and experimental results verify the effectiveness of DB-CA, and a 1-kW WPT prototype operating at 85 kHz is established. By applying DB-CA, the leakage EMF can be reduced by 3.88 dB at 85 kHz and 1.84 dB at 255 kHz, respectively. Meanwhile, the system resonant frequency still locates at 85 kHz, and the achieved zero phase angle condition is independent with load condition. It can provide significant guidance to the design of shielding configurations in EV Wireless Charging System.

A Dual-Sided LCLC Topology for AGV Wireless Charging System With Low Leakage EMF

The leakage electromagnetic field (EMF) generated during the wireless charging for automatic guidance vehicle will affect the regular operation of communication equipment and human safety. To reduce the leakage EMF, a dual-sided LCLC topology is introduced and optimized. The core idea is to construct the currents opposite to that flowing through the power transmission coils on primary and secondary sides, respectively. On this basis, connecting the shielding coils in the reverse current branches can generate the canceling magnetic field opposite to the leakage EMF. Thus, a low leakage magnetic coupler is established via the combination of power transmission coils and shielding coils. To minimize the leakage EMF, the specific parameters of magnetic coupler and dual-sided LCLC topology are optimized, and an experimental prototype is built to verify the shielding effect. The results show that when the output power is 1 kW, the shielding effect reaches 84.70%, and the power transfer efficiency is improved by 0.907%. Moreover, in the case of coil misalignment, there is still over 53.15% shielding effect by using the proposed method.

A Comprehensive Analysis of Metamaterial-Coupled WPT Systems for Low Electromagnetic Field Leakage

In this article, electromagnetic metamaterials with mu-near-zero (MNZ-MM) have been presented to explain the shielding effect in the wireless power transfer systems. First, the optimized design of the metamaterials unit cell has been carried on to achieve the near-zero permeability at the working frequency of 13.56 MHz. The equivalent circuit model of the MNZ-MM unit cell has been derived, which illustrates metamaterials with near-zero permeability have the great electromagnetic field (EMF) shielding effect. Additionally, the self- and mutual inductances associated with the resonance coils and MNZ-MM unit cells are deduced in detail. Moreover, the simplified human head model is established to investigate the magnetic field cancellation by MNZ-MM on the coil side. To evaluate the performance of the proposed MNZ-MM, the magnetic field strengths of the receiving terminal with different shielding materials have been compared in simulation. Finally, a series of experiments in real-environment are implemented to discuss the shielding effect of the MNZ-MM. The measurement results show the MNZ-MM has better performance in the swine brain sample than the ferrite and aluminum plate on the whole. With the proposed MNZ-MM, we demonstrate a maximum reduction of 17.52 dB in the leakage EMF and basically no effect on transfer efficiency.

A Magnetic Field Containment Method for an IPT System with Multiple Transmitting Coils Based on Reflective Properties

Inductive power transfer (IPT) systems with multiple transmitting coils are mainly used in specific scenarios, such as IPT sharing platforms and dynamic wireless charging of electric vehicles, etc. However, it faces problems of electromagnetic field leakage and low efficiency. A new magnetic field containment method based on reflective properties is proposed to solve the above shortcomings. Firstly, the reflective properties and performance figures of the IPT system with a unified passive compensation network are described and derived. Then, an S−LCL topology appropriate for the time−varying coupling IPT system is presented, where the IPT system’s transmitter consists of multiple coils that are compatible with one or more moving receivers and is powered by an inverter. Then, magnetic field focusing, power transfer and overall efficiency are analyzed and simulated. Finally, an experimental prototype is built to validate the feasibility of the proposed system. The experimental results show that the proposed method can increase the power transfer of the coupled transmitting coil and reduce the magnetic field leakage of the standby transmitting coils without complex shielding measures, switch, position detection and communication circuits.

Applications of negative permeability metamaterials for electromagnetic resonance type wireless power transfer systems

With the development of electric drive systems such as unmanned aerial vehicles and electric vehicles, the charging problem of power supply devices has become increasingly prominent. However, the traditional charging method requires physical circuits, which makes it impossible to achieve freedom of the position in actual use. The wireless power transmission technology, which mainly relies on electromagnetic wave to complete energy transmission, is expected to get rid of the restriction of physical space location and solve the problem of charging location, which has great potential in medical treatment, rescue, detection and other fields. However, the low transmission efficiency and short transmission distance caused by electromagnetic field leakage are the two main problems faced by radio energy transmission systems. In general, with the increase of transmission distance, the transmission efficiency will drop sharply. Fortunately, inserting a negative permeability metamaterial with extraordinary electromagnetic characteristics into the transmitting and receiving coils will greatly alleviate this attenuation trend and can also shield electromagnetic radiation to a certain extent. In this paper, some experiments of negative permeability metamaterials used in electromagnetic resonance type wireless power transfer systems are summarized for reference.

Effects of Ferromagnetic Cores in Wireless Power Transfer System for Charging Electric Vehicles

Wireless Power Transfer (WPT) technology for charging Electric Vehicle (EV) batteries is promising technology. System performance improvement and reducing Electromagnetic field (EMF) leakage are the key factors in designing an optimum charger. In this paper, adding ferrite disk to the WPT resonator is intensively studied. Three case studies are proposed, including coils only without ferrite, ferrite disk at the transmitting side only, and ferrite disks are used with the two coils. Finite Element Method (FEM) software is used for designing 3 kW-class, 20 cm transfer distance, 85 kHz charger. The simulation results are recorded and compared with regard to the system coil-to-coil efficiency and the EMF levels above the receiving coil and inside the air-gap. The results show that adding ferrite disks is significantly enhanced the system performance as well as reduced the EMF leakage surrounding the charger.

Electromagnetic Characterization of Thin Films by Using Non-Contacting Waveguides

Surface impedance represents a crucial parameter for the characterization of thin films. Indeed, materials with a sheet impedance varying as a function of their elongation could be used in radio frequency piezoresistive sensors. To estimate this quantity while having the possibility of stretching the sample under test, a waveguide-based non-contact approach is proposed. The absence of contact between the sample under test and the waveguides determines an electromagnetic field leakage, which is prevented by adopting an electromagnetic band gap (EBG) structure. The surface impedance of the sample is retrieved through an inversion procedure exploiting the scattering parameters measured using the proposed setup. The inversion procedure is based on a circuit representation of the waveguide-air-waveguide Section as a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -junction. The reliability of the proposed measurement method has been experimentally assessed using a WR137 waveguide. The proposed method allows to accurately determine the real part of surface impedance (the sheet resistance), while higher uncertainty is achieved in the estimation of the imaginary part.

A critical review on wireless power transfer systems using metamaterials

Recently, wireless power transfer (WPT) has been a topic of interest due to its attractive applications in modern life. Starting from Tesla’s idea about a century ago, WPT has developed tremendously and appeared in many of the most modern electronic devices. However, some WPT systems still have limitations such as short transmission distance, low transfer efficiency, and electromagnetic leakage. Magnetic metamaterial (MM) is a potential candidate that can overcome the above disadvantages of WPT. This paper is intended to present an overview of recent advances and research progress on WPT systems. Three classes of WPT consisting of short-range, mid-range, and long-range, will be analyzed in detail both in terms of fundamentals and applications. Especially, MM configurations can be used to enhance the near-field WPT efficiency and reduce the leakage of electromagnetic field will also be evaluated. This article is expected to provide a comprehensive review of the mechanism and applications as well as the future development of metamaterial-based WPT systems.

An Improved Hybrid Shielding With LC Coil for Wireless Power Transfer System

The leakage electromagnetic field (EMF) from the wireless power transfer system caused by loose coupling is hazardous to the human body and sensitive electronic devices. Studies have shown that the reactive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> coil has good shielding effect in the internal area nearby the coil central axis but poor shielding effect in the external area around the coil boundary. To overcome this, a hybrid shielding structure is proposed, which weakens leakage EMF in the external area by surrounding reactive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> coil with a ring-shaped aluminum plate. Two representative target planes are selected for evaluating the shielding effect. To minimize the average of magnetic flux density on target planes, the position and equivalent inductance of the proposed structure are optimized through ANSYS Maxwell. Experimental results show that, compared with the shielding method using horizontal aluminum plate, the proposed structure has an improvement of 68% shielding effect for target plane at coil alignment, even 88% for individual points, but with a 1.02% drop in efficiency. It also performs well under coil misalignment condition, and the shielding effect is still improved by 50% when the coils are offset by 100 mm.

Hardware RFID Security for Preventing Far-Field Attacks

Radio frequency identification (RFID) is a widely used approach for a short-range contactless data exchange, i.e., employed in billing systems. During the last years, unauthorized access has become an issue, as it has been proven on numerous unpleasant occasions. A typical theft scheme is based on approaching a victim with a card reader. However, a straightforward adaptation of the reader’s antenna elements allows performing the attack from a distance, opening a severe security loophole. Here, we propose and demonstrate hardware-based protection capable of preventing a far-field attack of this kind. Our solution is based on an RFID chip shielding with an opaque metal. The Faraday type of the enclosure has a small aperture, which suppresses electromagnetic field leakage from the device. This property affects both up and down interrogation links, virtually making the far-field attack impossible. Activation of the card is done by holding it in hand–this way, it is made accessible to an authorized readout, which still remains wireless. The physical principle of the operation is placing a high-index dielectric structure next to a subwavelength aperture, making it electromagnetically larger and, as a result, supporting the field leakage. Our experimental prototype, validated by several different users, shows the capability to diminish far-field attacks on ultrahigh frequency (UHF) RFID tags. This hardware security solution can find usage in numerous applications, such as biometric passports, credit cards, and many others, where unauthorized access to sensitive data is highly undesirable.

Design of Compact Magnetic Coupler With Low Leakage EMF for AGV Wireless Power Transfer System

Severe leakage electromagnetic field (EMF) generated by automatic guided vehicle wireless power transfer (WPT) systems is hazardous to the surrounding objects. To reduce the leakage EMF, a novel compact magnetic coupler is proposed in this article. The idea of this work is, first, adopting the compensation inductors of the <i>LCC</i>&#x2013;<i>LCC</i> compensated WPT system as EMF canceling coils, and EMF alleviation can be achieved without any additional components; second, integrating the power transfer coils and the EMF canceling coil into one magnetic coupler to compact the system. An experimental prototype is fabricated to verify the EMF shielding effect of the proposed magnetic coupler. Experimental results show that compared with that of the general magnetic coupler, the EMF of the proposed magnetic coupler is dramatically reduced by 82.24&#x0025; at maximum and by 75.18&#x0025; on average from <i>y</i> &#x003D; 200 to 350&#x00A0;mm. Besides, the transfer efficiency is decreased by 0.32&#x0025; with the same output power. That means the proposed magnetic coupler can effectively alleviate the EMF without a significant negative impact on the transfer efficiency.

Investigation of Electromagnetic Exposure of WPT Coil to Human Body Based on Biological Electromagnetic Safety Assessment

When the wireless power transmission (WPT) system of electric vehicle(EV) is working, the leakage of high frequency electromagnetic field (EMF) to the non-working area will be threaten to human safety. According to SAE J2954 standard, the coupling coils modeling of WPT and car shell modeling are established. WPT's bit-directional guidance technology and deviation correction control strategy are given. According to the harm degree of SAR, power density P, current density J and magnetic induction intensity B to human body when the human model is in different positions of standing, lying and sitting, the comprehensive harm index of electromagnetic radiation Σhurt is creatively proposed to assess the electromagnetic radiation hazard of EV. Field circuit co-simulation helps us to study the bio-electromagnetic safety of WPT in vehicle environment. A human exposure EMF joint test system is designed and made to measure vehicle’s surrounding EMF. Through simulation and experimental verification, WPT coil’s electromagnetic exposure level to the human body inside the EV meets the requirements of ICNIRP, the EMF at the ankle outside the EV exceeds the standard and needs to be protected.

Coil Scaling Law of Wireless Power Transfer Systems for Electromagnetic Field Leakage Evaluation for Electric Vehicles

Coil Scaling Law of Wireless Power Transfer Systems for Electromagnetic Field Leakage Evaluation for Electric Vehicles

Double-Coil Dynamic Shielding Technology for Wireless Power Transmission in Electric Vehicles

During wireless charging, the transmission distance of electric vehicles varies, resulting in different levels of electromagnetic field leakage. An improved active shielding technology, the double-coil dynamic shielding technology, is proposed in this paper for wireless power transfer (WPT) systems with different transmission distances. Modeling, simulation, and experiments are performed for the WPT system with a double-coil dynamic shielding scheme and compared with other cases. The results show that the proposed double-coil dynamic shielding scheme is able to shield approximately 70% of the electromagnetic field leakage for WPT systems at different transmission distances. In addition, it essentially causes no degradation in transmission efficiency (only 3.1%). The effectiveness and feasibility of the proposed scheme are verified.

A Multipole Approach Toward On-Chip Metal Routing for Reduced EM Side-Channel Leakage

With the proliferation of smart interconnected devices, the importance of securing computational data has increased manifold. While computational security layers like cryptographic algorithms protect against software-domain vulnerabilities, they cannot prevent leakage of electromagnetic (EM) fields from its parent device, hence compromising physical layer security. Most proposed methods of reducing EM side-channel leakage involve incorporating complex blocks into the design of an integrated circuit (IC). In this letter, we take an entirely novel stance, by borrowing fundamental concepts from multipole EM field decay and adapting the same for ICs by proposing a multipole routing approach. By building proof-of-concept scaled-up routing in PCBs, we demonstrate that unlike conventional dipole-style routing, metal layers incorporating higher-order multipoles result in a much faster-decaying side-channel leakage. Through detailed measurements, we infer guidelines toward optimizing the order of multipole needed to minimize side-channel leakage, thus enabling convenient implementation of physical layer security.

Coil Scaling Law of Wireless Power Transfer Systems for Electromagnetic Field Leakage Evaluation for Electric Vehicles

Coil Scaling Law of Wireless Power Transfer Systems for Electromagnetic Field Leakage Evaluation for Electric Vehicles

Dual Loop Reactive Shield Application of Wireless Power Transfer System for Leakage Magnetic Field Reduction and Efficiency Enhancement

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 transfer efficiency (PTE) of the WPT system was decreased. Therefore, a shielding method providing high shielding effectiveness (SE) without PTE degradation is necessary. This paper proposes a dual loop reactive shield application for reducing leakage EMF with PTE enhancement. The proposed dual loop reactive shield generates in phase and out of phase magnetic fields simultaneously. The out of phase magnetic field depresses leakage EMF, and the in phase magnetic field increases the PTE. The proposed method is verified for the cases of symmetric and asymmetric WPT systems, including misalignment conditions. The experimental results of the symmetric WPT system showed a 2.1% PTE increase with 55.5% SE in an alignment condition, and a 3.9% PTE increase with 53% SE in a misalignment condition. In addition, the experimental results of the asymmetric WPT system presented a 1.6% PTE increase with 61.3% SE in an alignment condition, and a 2.7% PTE increase with 54.1% SE in a misalignment condition.

Equivalent circuit method for Mu‐Negative‐Magnetic and Mu‐Near‐Zero metamaterials in wireless power transfer system

The application of the metamaterial (MM) in wireless power transfer (WPT) system has received a great deal of attention in improving the transfer efficiency and reducing the leakage of electromagnetic field (EMF) in recent years. However, most of the analytical methods for MM-inspired WPT system are based on microwave technologies, such as negative refraction effect, magnetic dipole coupling model and magneto-inductive wave theory. In this study, the equivalent circuit model of the MM in the WPT system is analysed in detail. Two different types of MMs, Mu-Negative-Magnetic (MNM) and Mu-Near-Zero (MNZ), are constructed to verify this method. In particular, a tuning strategy by changing the distances between the drive (load) loop and internal coils is established to improve the power transfer efficiency for the WPT system with the MNM-MM. In addition, the MNZ-MM is described to cancel EMF leakage in the WPT systems by this method. Moreover, a series of practical experiments are carried out to prove the numerical analysis, which are well consistent with the theoretical solution employed by the Advanced Design System software. Finally, the combination of two types of MMs applied in the WPT system is also discussed.

Optimization on Three-Coil Long-Range and Dimension-Asymmetric Wireless Power Transfer System

With the rapid development and extensive application requirements of wireless power transfer (WPT) technology, the common symmetrical WPT system is growing more mature, but it may still struggle to meet the vast demands. When the WPT system has a long transmission distance and the dimensions of transmitter and receiver coil are asymmetric, the current in the transmitter coil of traditional two-coil symmetrical structure may be excessive. The addition of a relay coil between the transmitter and the receiver coil can effectively reduce the current of transmitter coil, thereby improving system efficiency and reducing electromagnetic field (EMF) leakage. In this article, the parameters of relay coil are optimized by theoretical calculation and multiobjective genetic algorithm. The results show that the optimized three-coil system can reduce the current of transmitter coil by 73.1%, improve the efficiency by 10.7%, and suppress the EMF leakage by 12 dB simultaneously. Finally, the effectiveness of the proposed system is verified by experiments.

Comprehensive Analysis of Side-Placed Metamaterials in Wireless Power Transfer System

In this article, we propose the side-placed negative-permeability metamaterial (NPM) and zero-permeability metamaterial (ZPM) in the wireless power transfer (WPT) system to simultaneously enhance the level of efficiency and meet the electromagnetic field (EMF) safety regulations. A theoretical analysis, simulation, and experiment are conducted to verify the feasibility of the proposed system model. Based on the principle of magneto-inductive waves (MIWs) and the shielding theory, the transmission characteristics of the WPT system without and with two NPM slabs, two ZPM slabs, and the combination of NPM and ZPM slabs are analyzed. The results demonstrate that the ZPM slabs and the combination of NPM and ZPM slabs have a high efficiency improvement when the transfer distance is located under 40 cm and exceeds 40 cm, respectively. Both methods can control the EMF leakage. Moreover, the side-placed metamaterial exhibits tolerance to the misalignment of the coil. Finally, comparative studies on the ZPM slab and aluminum are carried out. The experimental and simulation results show that the ZPM slab performs better than aluminum.