Magnetic resonance wireless power transfer for laptop computer with a ground plane

It is well known that the power transfer efficiency (PTE) of a two-coil wireless power transfer (WPT) system is maximized at critical coupling under fixed system parameters. However, the two-coil WPT system is critical-coupled with a relatively short distance between the coils. To overcome the problem, a multicoil WPT system has been studied. In this paper, we review the impedance characteristics of the critical-coupled two-coil WPT system and reveal that the conventional three-coil WPT system cannot have the same impedance characteristics as critical coupling. Based on the impedance matching conditions with critical coupling of the two-coil WPT system, we propose a design method of a three-coil WPT system in which the free resonant frequencies of all resonators are changed. The proposed design method is successfully implemented at the operating frequency of 6.78 MHz. The experimental results are in good agreement with the simulated PTEs and show that by changing the free resonant frequencies, a higher PTE can be effectively achieved in comparison to the conventional two-coil and thee-coil WPT systems.

At present, wireless power transfer systems based on magnetic resonance, parity-time symmetry, and fractional order have received more and more attention, especially in wireless charging applications of mobile phones, electric vehicles, and other products. However, the consequent electromagnetic radiation safety issues are becoming increasingly prominent. Therefore, this paper compares and studies the magnetic field distribution of magnetic resonance, parity-time symmetric and fractional-order wireless power transfer systems, and uses ANSYS simulation software to simulate and comparative analyze. The simulation results show that under the condition of equal output power, the magnetic field distribution of the parity-time symmetric wireless power transfer system is more concentrated when the coupling coefficient is small, while the magnetic field distribution of the magnetic resonance wireless power transfer system is more concentrated when the coupling coefficient is large, but it is significantly smaller than that of the fractional-order wireless power transfer system. In addition, the safety range of the parity-time symmetric wireless power transfer system is significantly larger than that of the magnetic resonance and the fractional-order wireless power transfer system at different output power. Remarkably, the magnetic field distribution of fractional-order wireless power transfer system will also change with different order, which implies that the safety range of the fractional-order wireless power transfer system can be designed according to the requirements to achieve the ideal safety range.

A highly efficient wireless power transfer (WPT) system is required in many applications to replace the conventional wired system. The high temperature superconducting (HTS) wires are examined in a WPT system to increase the power-transfer efficiency (PTE) as compared with the conventional copper/Litz conductor. The HTS conductors are naturally can produce higher amount of magnetic field with high induced voltage to the receiving coil. Moreover, the WPT systems are prone to misalignment, which can cause sudden variation in the induced voltage and lead to rapid damage of the resonant capacitors connected in the circuit. Hence, the protection or elimination of resonant capacitor is required to increase the longevity of WPT system, but both the adoptions will operate the system in nonresonance mode. The absence of resonance phenomena in the WPT system will drastically reduce the PTE and correspondingly the future commercialization. This paper proposes an open bifilar spiral coils based self-resonant WPT method without using resonant capacitors at both the sides. The mathematical modeling and circuit simulation of the proposed system is performed by designing the transmitter coil using HTS wire and the receiver with copper coil. The three-dimensional modeling and finite element simulation of the proposed system is performed to analyze the current density at different coupling distances between the coil. Furthermore, the experimental results show the PTE of 49.8% under critical coupling with the resonant frequency of 25 kHz.

Wireless power transfer (WPT) systems have attracted considerable attention in relation to providing a reliable and convenient power supply. Among the challenges in this area are maintaining the performance of the WPT system with the presence of a human body and minimizing the induced physical quantities in the human body. This study proposes a magnetic resonant coupling WPT (MRC-WPT) system that utilizes a resonator with a grounded loop to mitigate its interaction with a human body and achieve a high-efficiency power transfer at a short range. Our proposed system is based on a grounded loop to reduce the leakage of the electric field, resulting in less interaction with the human body. As a result, a transmission efficiency higher than 70% is achieved at a transmission distance of approximately 25 cm. Under the maximum-efficiency conditions of the WPT system, the use of a resonator with a grounded loop reduces the induced electric field, the peak spatial-average specific absorption rate (psSAR), and the whole-body averaged SAR by 43.6%, 69.7%, and 65.6%, respectively. The maximum permissible input power values for the proposed WPT systems are 40 and 33.5 kW, as prescribed in the International Commission of Non-Ionizing Radiation Protection (ICNIRP) guidelines to comply with the limits for local and whole-body average SAR.

Simultaneous power distribution to multiple loads using a single source in the wireless power transfer (WPT) system is a challenging issue due to cross-coupling between the load coils, which reduces the power transfer efficiency. In a resonant WPT system, when two or more coils operated under over coupled condition, the original operating resonant frequency gets bifurcated, and thereby reduction in the power transfer efficiency. Different techniques are investigated in the literature to mitigate the frequency bifurcation phenomena in the resonant WPT system. However, the utilization of frequency bifurcation approach for the simultaneous power transfer to multiple loads is not addressed. This paper proposes a simultaneous power transfer approach using frequency bifurcation for the multiple load system designed with different operating frequency. Mathematical, simulation, and experimental studies performed for dual, triple, and four coil WPT systems with multiple loads. In addition, an automatic power flow control method is implemented to estimate the load current from the source, which helps to select a new set of load coils to be charged. The experimental results confirm the proposed power transfer, helps to attain higher power transfer efficiency of 39.34%, 49.31%, 68.22% and cross interference of -31.2 dBV, -36.2 dBV, -41.2 dBV for dual, triple, and four coil WPT system, respectively.

<sec>Magnetic resonance wireless power transfer (WPT) has gradually become a popular research topic of near-field regulation in recent years, with wide applications in the fields of mobile phones, implantable medical devices, electric vehicles, and many other fields. However, several challenges remain to be addressed: near-field coupling, which induces multiple frequency splits and prevents the system from maintaining a fixed operating frequency; coupled arrays, which are susceptible to structural errors and parameter perturbations; current research, which primarily focuses on single-load transmission and has resulted in undeveloped multi-load transmission systems; the direction of transmission, which is difficult to control flexibly. In recent years, photonic artificial microstructures have provided a flexible platform for studying topological physics, arousing significant research interest in their fundamental topological characteristics. The most prominent features of topological structures are their nonzero topological invariant and the robust edge states determined by the bulk-edge correspondence: these features can overcome disturbances caused by defects and disorders. Moreover, by modulating the wave function distribution of topological states, energy can be precisely localized, enabling directional WPT. Therefore, implementing topological modes in WPT systems are of significant scientific importance.</sec><sec>This review summarizes recent researches on topological models for robust WPT, which are divided into three main parts. The first part introduces one-dimensional periodic topological structures, focusing primarily on the significant improvements in transmission efficiency and robustness achieved by utilizing topological edge states in the Su-Schrieffer-Heeger (SSH) model for WPT. Moreover, a composite chain formed by two SSH chains is constructed to realize a higher-order parity-time (PT) symmetric topological model. This approach solves the frequency splitting caused by coupled edge states and exhibits lower power losses in standby mode. The second part discusses several types of aperiodic one-dimensional topological chains. By introducing topological defect states at the interface between two different dimer chains, robust multi-load WPT is achieved. Furthermore, based on the integration of artificial intelligence algorithms, the SSH-like topological model enables more efficient and robust WPT than traditional SSH model. The asymmetric edge states in quasi-periodic Harper chain provide a solution for directional transmission in WPT applications. By introducing nonlinear circuits, this model enables active control of the transfer direction. The third part presents the application of high-order topological corner states in multi-load robust WPT, demonstrating the selective excitation of both symmetric and asymmetric corner modes.</sec><sec>Finally, the application prospects of topological modes in WPT systems are discussed. With the development of new physics, the integration of non-Hermitian physics and topological physics holds great promise for achieving simultaneous energy-information transfer, and is expected to achieve compatible WPT, wireless communication, and wireless sensing within a single system. Such a fusion technology will provide breakthroughs in efficiency, robustness, and multifunctionality for next-generation wireless systems.</sec>

A Wireless Power Transfer (WPT) system, known for its contactless power delivery, is extensively used for power supply in spacecraft applications. Achieving efficient and stable power transfer necessitates the integration of DC/DC converters on both the primary and secondary sides of WPT systems for power conversion and control. Traditional efficiency optimization methods primarily focus on impedance matching within the wireless power resonance network, often neglecting the overall efficiency optimization of multi-stage DC-DC and WPT systems. This oversight results in suboptimal overall system efficiency despite optimal efficiency in the wireless transmission segment. Additionally, the time-varying nature of mutual inductance and load parameters during power transmission in WPT systems presents challenges for maximum efficiency tracking and power control. This paper introduces a multi-level coordinated control efficiency optimization method for WPT systems utilizing the particle swarm optimization (PSO) algorithm. This method takes into account the transmission losses across all power conversion units within the WPT system, establishing a mathematical model for the joint optimization of overall system transmission efficiency and power. The PSO algorithm is then employed to solve this optimization model using estimated mutual inductance and load values. By adjusting the DC/DC converters on both sides, the method ensures optimal overall system efficiency and consistent power transmission. Experimental results indicate that under varying load and mutual inductance conditions, a Series–Series (SS) compensated WPT system using this method achieves a 200 W power output with maximum efficiency tracking, a power output error of 0.63%, and an average transmission efficiency of 86.2%. This demonstrates superior power transmission stability and higher efficiency compared to traditional impedance matching methods.

This study reports, for the first time, the use of coupled‐line‐based impedance matching in wireless power transfer (WPT) system. The transmitter and receiver of the WPT system are realised by microstrip feed line and symmetric coupled line at the top plane. The ground plane is realised with triangular‐shaped defect along with the excitation slot mounted by an external capacitor. The defect in the ground plane and the external capacitor regulate the resonant frequency and also enable miniaturisation of the WPT system. The design is augmented with a systematic analytical approach for impedance matching and a simplified design procedure for the WPT system. A novel equivalent circuit model consisting of parallel LC network and coupled lines is also developed for the evaluation of the proposed WPT system design technique. A prototype of the system operating at 300 MHz developed on Rogers RO4350B substrate achieves a peak efficiency of 80% at a transmission distance of 17 mm. An excellent agreement between the measured and the electromagnetic simulated results is a testament of the robustness of the proposed design technique. Furthermore, evaluation of the commonly used WPT‐related figure of merit shows significant enhancement when compared to the existing state of the art.

The wireless power transfer (WPT) system based on parity-time (PT) symmetry has the advantages of robustness, stable, and efficient power transmission. However, the region of PT symmetry is limited, which cannot satisfy some practical requirements. Multiple transmitting coils have been shown to improve the misalignment tolerance of WPT systems. Towards this end, a parity-time-symmetric-based WPT (PT-based WPT) system with double-transmitting coil is presented in this article. First, an approximate equivalent circuit model of this PT-based WPT system was developed. Second, compared with the conventional single transmitting coil PT-based WPT system, the proposed system expands the PT symmetry region and provides higher output power and transmission efficiency. Furthermore, the mutual inductance between two transmitting coils can be designed to meet the requirements of different scenarios, which improves the freedom of system design. Finally, a 30 W prototype is designed to evaluate the proposed WPT system. Experimental results show that the critical coupling coefficient is reduced by about 12.5% at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> = 0.51, which implies a longer transmission distance. Moreover, the maximum output voltage fluctuation in the strongly coupled region is only 3.5%, while the transfer efficiency is approximately constant, which implies stable and efficient power transfer.

In previous researches, an operator-based sliding mode control design to achieve high power transfer efficiency of a wireless power transfer (WPT) system via magnetic resonance coupling were shown. However, it is difficult to reduce the steady-state error by using SMC-based tracking controller. In this paper, an operator-based integral sliding mode control method is adopted to reduce the steady-state error in the WPT system. Moreover, high power efficiency should be achieved in the WPT system by using an impedance matching control. The effectiveness of the proposed method is verified by simulation results.

In this study, an advanced wireless power transfer (WPT) system of two coils with the artificial magnetic conductors (AMC) is explored through simulations and experiments. The AMC structure is added on the transmitter coil, and the multiple resonant modes on the surface of the AMC can be energized. On the other hand, the AMC structure act as a magnetic field shield, which leads to the magnetic field above AMC structure is localized. Therefore, the localized resonant magnetic field enhance the transmission coefficient of the WPT system. The results show that the WPT transmission coefficient is increased from 16% to 35% in the experiment at 26.2 MHz resonant frequency when transmission distance is 3 cm. The experimental results agree with the simulation results. Additionally, AMC has the advantages of low-cost and can easily be installed on the WPT system.

The use of resonant magneto-inductive links is an efficient technique to transfer power over midranges in the field of wireless power transfer (WPT). Power transfer efficiency (PTE) and power delivered to the load (PDL) are two important indicators of power transmission for a WPT system. A predetermined amount of PDL need be generated at maximum PTE for practical application in a WPT system; thus, the authors focus on maximising PTE and a predetermined amount of PDL for transfer in this study. First, load-matching conditions are presented for maximum PTE transfer though circuit theory-based analyses. Then, a new tuning method is proposed to transfer a predetermined amount of PDL which can be controlled by source-matching distance at maximum PTE. The relations between the loss of a load-matching resonator and the PTE (or PDL) of a correspondingly unmatched system are derived though analyses as well. Finally, the calculated results of the design examples are verified through electromagnetic simulations and experimental measurements.

The power transfer efficiency of magnetic-resonance coupled wireless power transfer (WPT) systems is sensitive to the alignment of coils. In this paper, a novel multi-coil WPT system is proposed to enhance power transfer efficiency. It can overcome the misalignment problem and maintain high power transfer efficiency. The proposed coil loop structure can provide a strong magnetic resonance coupling between the Tx and Rx coils. There are four induvial resonators applied in the system and it demonstrates that at least a pair of coupled resonators in several misaligned conditions could realize high power transfer efficiency over a misaligned distance. The experimental results show that the proposed multi-loop WPT system can achieve 90.2% peak efficiency when the coils are well aligned. Mean-while, this WPT system maintains over 70% efficiency over a misalignment distance from 0 to 55 mm, which is about 66% of the length of the Rx board. The proposed WPT system could be used either in implant devices for biomedical healthcare and treatment or for electric vehicles charging systems.

Dual-band coil modules facilitate efficient access to distinct-band, high-power, or rapid-charging wireless power transfer (WPT) systems. However, they do not function efficiently when the frequency ratio between two operating frequencies is large. To overcome this problem, we propose enhanced dual-band coil modules that adopt repeaters in the WPT system. We present a circuit-based analysis of repeaters in various dual-band coil modules compared with those in a single-band WPT system. The analytical results provide a design methodology applicable to diverse types of dual-band coil modules with a repeater in the WPT system. Our experimental results are consistent with the circuit-based analysis: coil power transfer efficiencies of 55% at 200 kHz and 74% at 6.78 MHz were obtained concurrently in the dual-band WPT system with a dual-band repeater. This paper reduced the application constraint of dual-band coil modules and facilitated the realization and application of multiband WPT systems.

This work develops a reconfigurable coil array that compensates for the misalignment between coils in magnetic resonance coupled wireless power transfer (WPT) systems. By tuning the magnitude of the currents induced in the coil array with the variable capacitors that load them, the effect of reconfiguring the size and/or shape of the coil can be achieved. Therefore, the near field can be steered in a certain direction to overcome the notorious misalignment problem in WPT systems. For experimental demonstration, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 1$ </tex-math></inline-formula> array is designed and fabricated for a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$60\times 60$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> coil. For a vertical distance between Tx and Rx coils of 10 mm, which is 16.7% of the largest coil dimension, the transfer efficiency maintains more than 40% and up to 141.6% misalignment. This is more than an 81% increase over the conventional coil. For a vertical distance of 30 mm or 50%, the minimum transfer efficiency is 37.1% up to 100% misalignment, which is almost 5.5 times that of the conventional counterpart. The results suggest that the demonstrated technology successfully overcomes the notorious misalignment problem in both short-range and midrange WPT systems and even in asymmetric systems where the reconfigurable coil array technique is applied only on the Rx.