Near-field Wireless Power Transfer Research Articles

On the Limitations of the Coupled Mode Theory and Parity-Time Symmetry for Near-Field Wireless Power Transfer Research

On the Limitations of the Coupled Mode Theory and Parity-Time Symmetry for Near-Field Wireless Power Transfer Research

Survey of near-field wireless communication and power transfer for biomedical implants

Survey of near-field wireless communication and power transfer for biomedical implants

Null-Free Wireless Power Transfer System Based on a Coil Array to Compensate for 2-D Misalignment

In this study, a coil array technology is proposed to compensate for 2-D misalignment between coils, regardless of its direction, in a wireless power transfer (WPT) system at 6.78 MHz. The primary coil is printed on one side of the substrate, while the assistant coil is printed on the other side in a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 2 array configuration. Depending on the degree of misalignment, the coil pair with the best alignment can be switched on. Thus, high efficiency can be maintained without increasing the size of the coils. Experimental results for a 47 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 47 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^2$</tex-math> </inline-formula> -sized coil system demonstrate null-free operation that maintains transfer efficiency of more than 80% with diagonal misalignment of up to 98% relative to the largest coil dimension. Regardless of the direction of the misalignment, its efficiency is 80% or higher with up to 72% misalignment, and 50.5% or higher with extremely high misalignment (up to 120%). The results indicate that the proposed coil array technology successfully addresses the notorious misalignment issue in a near-field WPT system, regardless of the direction of the misalignment, without increasing the coil size. Furthermore, the results for an asymmetric system in which the coil array technology is adopted only on the Tx side reveal the feasibility of the proposed method for practical applications.

Experimental verification of magnetic near-field channeling using a helical-shaped wire medium lens

We experimentally verify that a magnetic uniaxial wire medium lens consisting of a racemic array of helical-shaped metallic wires may enable channeling the normal component of the magnetic field of near-field sources with resolution well below the diffraction limit over a broad bandwidth. It is experimentally demonstrated that the helical-shaped wire medium lens can be regarded as the magnetic counterpart of the usual wire medium lenses formed by straight metallic wires. The experimental results are validated with full-wave numerical simulations. We envision that the proposed metamaterial lens may have potential applications in magnetic resonance imaging, near-field wireless power transfer, and sensing.

Remaining Opportunities in Capacitive Power Transfer Based on Duality With Inductive Power Transfer

Wireless power transfer (WPT) has proven to be an effective solution for electric vehicle charging. As two mainstream near-field WPT technologies, inductive and capacitive power transfer (IPT and CPT) have many similarities. This paper aims to explore the remaining opportunities in CPT systems, not yet reported in existing literature, based on duality with the mature IPT technology. First, a generic modeling method based on two-port network theory is proposed, which contributes to unified modeling and analysis for both inductive and capacitive couplings. Then, power transfer mechanism of IPT and CPT couplers is compared, and unified transfer efficiency is derived, promoting CPT theory developments. Last, the duality between existing IPT and CPT circuits is demonstrated in two aspects: compensation circuit configuration and resonant relationship. 14 CPT topologies are derived based on duality with the existing 7 mainstream IPT circuits, of which 11 circuits do not exist in literature, offering future opportunities in CPT. Detailed comparison and evaluation of the derived 14 CPT circuits are conducted, and high-performance circuits are recommended. As a demonstration, a case study of a 2.1kW 3MHz CPT system is implemented in hardware based on the newly proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SS</i> topology. This example system achieves a peak efficiency of 93.19% with the predicted circuit properties of load-independent constant-voltage (CV) output and zero-phase-angle (ZPA) property.

Integration of Wireless Power Transfer Technology With Hierarchical Multiwalled Carbon Nanotubes-Polydimethylsiloxane Piezo-Responsive Pressure Sensor for Remote Force Measurement

Integrating sensory devices with wireless power transfer technology for remote sensing (RS) requires the implementation of complex electronic circuitry and communication protocols. To overcome this challenge and remotely monitor mechanical force, we directly integrated piezo-responsive porous multiwalled carbon nanotubes (MWCNTs)/polydimethylsiloxane (PDMS) nanocomposites with a near-field wireless power transfer system. The wireless system transfers power bidirectionally between the transmitter and the sensing receiver at the resonant frequency of 13.56 MHz. The detection principle is based on the mechanical force-induced impedance changes in the receiver circuit. The modulated impedance signal is detected wirelessly at the transmitter circuit via a full-bridge rectifier and a smoothing capacitor. Furthermore, we demonstrate the wireless monitoring of finger bending and applied force using our flexible and disposable sensor without using any energy storage devices. The results suggest a response and recovery time of 400 ± 50 ms, strain sensitivity of 24.73, and pressure sensitivity of 0.98. Our approach adds a new path for disposable haptic-based sensory applications that do not require complex communication protocols in medical, robotics, and other fields.

A Multi-Domain Model for Variable Gap Iron-Cored Wireless Power Transmission System

Wireless power transfer (WPT) devices represent one of the most efficient and increasingly used technologies for the transfer of data and power in the near-field range. This work analyzes and describes a new type of device: a ferrite-cored, variable gap, high-frequency power and data transfer system. The classic theoretical models existing in the literature for near-field communication (NFC) and WPT devices have foreseen a lumped-parameters characterization based on the representation of an equivalent circuit model (ECM). The strict interdependence between the different physical domains has clearly increased the difficulty in predicting the behavior of the device, due to the unwanted continuous and chaotic variation of the parameters. The proposed paper aims to provide a general and reliable multi-physics model based on the co-simulation of a Spice®-based ECM analysis and the ESRF Radia®-based 3D finite volume methodology (3DFVM), placing particular emphasis on the intrinsic sensitivity with respect to variables that cannot be directly controlled, such as the variation of the air gap between the coupled coils interfaces. Furthermore, this work outlines a detailed and effective experimental methodology for the estimation of static and dynamic electro-magnetic parameters and the validation of the numerical models in both the time and frequency domain, through the analysis of a real coupled WPT device.

Design Considerations of Capacitive Power Transfer Systems

Capacitive power transfer (CPT) is a near-field wireless power transfer (WPT) technology that has attracted attention in different charging applications. By utilizing electric fields, CPT gives charging systems advantages in terms of cost, weight, flexibility, and mobility. This paper surveys a number of empirical published works in a period between 2015 and 2023. Additionally, it discusses theoretical and practical design considerations of a CPT system to understand and improve the technology and its applications. The paper studies the one- and two-port measuring approaches using vector network analyzers to determine the coupling parameters and compares the measurements to the simulated values using COMSOL Multiphysics ©. The two-port approach gives more accurate results than the one-port approach. The paper designs and tests a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {13.56 \text {M} \text {Hz} }$ </tex-math></inline-formula> CPT system using the two-port measurement results. The system transfers <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {100 \text {W}}$ </tex-math></inline-formula> at 87.4% efficiency and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {30 mm }$ </tex-math></inline-formula> separation distance. Lastly, the paper discusses the design limitations and challenges of the CPT systems, aiming to emphasize the design obstacles that can drive the advancement of the CPT systems for wireless charging applications.

Recent Trends and Challenges in Near-Field Wireless Power Transfer Systems

Recent Trends and Challenges in Near-Field Wireless Power Transfer Systems

Near-Field Wireless Power Transfer Technology for Unmanned Aerial Vehicles: A Systematical Review

Unmanned aerial vehicles (UAVs) technology has seen a significant boost over the past ten years and has been widely adopted in entertainment, rescue, intelligent transportation, no-touch delivery, environmental monitoring, and other real-world applications. However, the ranging limitation due to the shortage of battery energy capacity remains a major issue hindering further development of UAVs. Wireless power transfer (WPT) technology is a new technology of great potentials in improving the endurance of UAVs. The integration of WPT into UAV not only activates the recharging of UAVs batteries but also enables UAVs to recharge other devices. Moreover, wireless charging technology allows the device to be fully enclosed and suitable for harsh weather conditions. In this article, we present a comprehensive review in regard to the state-of-the-art of near-field WPT technologies for UAV charging, including technologies characteristics, design issues, as well as multiple case studies. A comparative analysis of existing technologies is also presented, associated with key future research discussions of WPT for UAVs.

A Planar Switching Integrated Quadrant Coil Antenna to Form Widespread Switched Polarized H-Field for Misalignment Resilient WPT System

This article presents a planar switching integrated quadrant coil antenna to mitigate lateral and angular misalignment problems in near-field wireless power transfer (WPT) applications. To allow a completely free receiver movement, both the misalignment problems are concurrently addressed by forming widespread distributions of switched polarized H-field in the receiver region. To achieve this, current circulations through the four quadrant coils composing the proposed antenna are judiciously controlled to form three orthogonal H-field components. For lateral misalignment mitigation, the widespread field distributions are obtained by using a field-forming approach for optimizing the antenna parameters. To produce the switched polarized H-field for angular misalignment mitigation, time-switching of the orthogonal H-field components is performed. This switching operation is realized by three double pole double throw (DPDT) switches interconnecting the coils and integrated within the design for a cost-effective planar antenna solution. The fabricated prototype is measured and the experimental results are corroborated with the analysis. The results demonstrate the potential of the proposed antenna to simultaneously mitigate both the misalignment problems for medium-range WPT of small devices, such as medical implants, wireless endoscopy capsules, and wearable devices, which are allowed to freely rotate and displace.

Experimental Study of Effectiveness of Metasurface for Efficiency and Misalignment Enhancement of Near-Field WPT System

Unlikely for a far-field wireless power transfer (WPT) system, designing a metasurface is critical for a near-field WPT system. First, a robust near-field WPT system using open-loop spiral resonators and a metasurface are designed, and then, the effectiveness of the metasurface is investigated in improving the power transfer efficiency (PTE) and misalignment effects. Furthermore, a study of planar and angular misalignments is also executed experimentally to prove the WPT system immunity. The proposed WPT system offers a PTE of 30% when the Rx shifts by the lateral length of the Rx that means the Rx does not remain in front of the Tx. Moreover, the efficiency is almost unchanged due to the angular misalignment.

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.

Development and Prospect of Wireless Power Transfer Technology Used to Power Unmanned Aerial Vehicle

Recently, unmanned aerial vehicles (UAV) have been widely used in the military and civil fields. However, the battery power is a key factor that restricts the operation range of the UAV. Using wireless power transfer (WPT) technology to power UAVs can improve the endurance of UAVs and enhance their maneuverability and flexibility. In this paper, the WPT technology is divided into three types: near-field WPT technology, far-field WPT technology and solar-powered UAV. The developments, challenges and prospects of these three types of WPT technologies used to power UAVs are summarized. For each type of WPT technology, the basic working principles are first introduced. The development of each type of WPT technology, as well as the challenges and application prospects in UAV charging, is introduced. The related works consist of academic and industry research, ranging from prototypes to commercial systems. Finally, three types of WPT technology used in UAV charging are compared and discussed, and the advantages and disadvantages of each type of WPT technology are shown. The related research showed that using WPT technology to power the UAV is a promising way to enhance the endurance of the UAV.

A Power-Efficient Resonant Current Mode Receiver With Wide Input Range Over Breakdown Voltages Using Automated Maximum Efficiency Control

This article proposes a series-<i>LC</i> resonant current mode receiver (RCM R_X) for wirelessly powered battery chargers. With a series-<i>LC</i> scheme, the RCM R_X can operate at higher resonant voltages than transistor breakdown voltages, enabling robust near-field wireless power transfer. In the series-<i>LC</i> RCM R_X, a dual automated maximum efficiency control (AMEC) and a passive zero-current detector (ZCD) adaptively adjust operation states, ensuring nonresidual energy in the R_X <i>LC</i> tank at the end of the charging mode. Moreover, the passive ZCD operation algorithm increases the power delivered to the load or battery by minimizing the idle period between charging and resonant modes. The 180-nm standard CMOS chip, which used only 1.8-V transistors, can operate with 6.84&#x00D7; higher resonant voltage up to 12.32 V than the transistor breakdown voltage, 1.8 V, while receiving an input power up to 169 mW, enabling a wide input range over variable coil distances. The proposed system achieves the measured power conversion efficiency up to 84.9&#x0025; at the input power of 16.8 mW.

Safety Analysis of Medical Implants in the Human Head Exposed to a Wireless Power Transfer System

The interactions of medical implants in the human body with electromagnetic fields from newly introduced high-field technologies such as near-field wireless power transfer (WPT) are of great concern. In this study, the effects of implants on the specific absorption rate (SAR) in a head model were computationally evaluated in the immediate vicinity of a WPT system operating at 6.78 MHz with a transferred power of 50 W. The SAR in the head model located 30 mm above the WPT system was evaluated with a skull plate, bone plates (different shapes), miniplate, fixtures, and a deep brain stimulator. The results indicated that even small implants had notable effects on the SAR distribution and corresponding local peak and mass-averaged SAR values. Apart from the size and shape of the implant, the crucial factor influencing the SAR was the implant’s position with respect to the WPT system. Therefore, various position configurations were simulated for the WPT system to determine the worst case scenario for each specific implant. Although the local peak SAR value was increased by a factor of 600 in the worst-case scenario (for the skull plate), the SAR <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{\text{1}g}$</tex-math></inline-formula> and SAR <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{\text{10}g}$</tex-math></inline-formula> were only increased by factors of seven and four, respectively. Compliance with international safety limits was studied, followed by computing the maximum allowable transmit power (MATP). It was found that, without the implant, the MATP satisfying SAR <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{\text{1}g}$</tex-math></inline-formula> was 43 W for the designed WPT system, and was reduced to 6.9 W in the presence of the skull plate.

Comparison Techniques for Optimization Switching Frequency In Energy Encryption Of Wireless Power Transfer System

This paper reviews the techniques for optimization switching frequency used in Wireless power transfer (WPT). WPT is one of the most useful ways to transfer power. Based on distances power transfer, the WPT system can be divided into three categories, namely, near, medium, and far fields. Inductive coupling and capacitive coupling contactless techniques are used in the near-field WPT. Magnetic resonant coupling technique is used in the medium-field WPT. Electromagnetic radiation is used in the far-field WPT. From the comparison in this paper, a model and design algorithm to optimize switching frequency for energy encryption of medium field wireless power transfer system are purposed. The maximum value of the performance are suitable to compute the optimal circuit parameter by algorithm itself.

Near-Field Wireless Power Transfer for 6G Internet of Everything Mobile Networks: Opportunities and Challenges

Radiating wireless power transfer (WPT) brings forth the possibility to cost-efficiently charge wireless devices without requiring a wiring infrastructure. As such, it is expected to play a key role in the deployment of limited-battery communicating devices, as part of the 6G-enabled Internet of Everything (IoE) vision. To date, radiating WPT technologies are mainly studied and designed assuming that the devices are located in the far-field region of the power radiating antenna, resulting in relatively low energy transfer efficiency. However, with the transition of 6G systems to mmWave frequencies combined with the use of large-scale antennas, future WPT devices are likely to operate in the radiating near-field (Fresnel) region. In this article, we provide an overview of the opportunities and challenges that arise from radiating near-field WPT. In particular, we discuss the possibility to realize beam focusing in near-field radiating conditions, and highlight its possible implications for WPT in future IoE networks. Furthermore, we overview some of the design challenges and research directions that arise from this emerging paradigm, including its simultaneous operation with wireless communications, radiating waveform considerations, hardware aspects, and operation with typical antenna architectures.

Constant output characteristics and design methodology of double side LC compensated capacitive power transfer

Capacitive power transfer (CPT) has been verified to be capable of transferring a power level as high as inductive power transfer (IPT) recently, and has its own merits. It is a well complement of IPT in near-field wireless power transfer (WPT). This paper gives a newly designed method of realizing both constant output voltage (COV) and constant output current (COC) modes of double side LC compensated CPT. Firstly, through analysis of basic circuit characteristics, the conditions for both of the two modes are deduced theoretically. Especially, one merit of the method is that the conditions indicate a very clear relationship between the compensation components forming resonant tanks. Another merit is that the couple capacitors also participate in resonant tanks. Different from the COV mode, the COC mode can theoretically reach zero phase angle condition simultaneously. Based on these conditions, the parameter design methodology is proposed. Besides, an efficient model of double side LC compensated CPT is built, and the optimum load is calculated theoretically to guide the design course. Finally, the results of both simulations and experiments demonstrate high consistency with the theoretical analysis.

A 403 MHz Wireless Power Transfer System With Tuned Split-Ring Loops for Implantable Medical Devices

A near-field wireless power transfer (WPT) system for implantable medical devices, such as pacemakers, is proposed. Operating at 403 MHz within the medical implants communication service (MICS) band, the WPT link constitutes a primary loop to be based outside the body as a transmitter and an implantable loop with a single-turn as a receiver. Simulation and experimental results show that the proposed link offers good power transfer efficiency (PTE) performance. The maximum measured PTE of the proposed link is 57.9&#x0025; at a transfer distance of 6 mm through 1 mm of air and 5 mm of body tissue. The maximum input power that can be supplied to stay within specific absorption rate safety guidelines is 159 mW. A rectifying circuit is designed to convert 403 MHz RF signals to dc for a 1.5 <inline-formula> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> load with a measured conversion efficiency of 73.2&#x0025;. The measured end-to-end PTE of the proposed WPT system is 42.4&#x0025;.