Strongly Coupled Magnetic Resonance Research Articles

Compact Broadband Planar Resonator With a Viaed Double Spiral for Robust Wireless Power Transfer

A common problem for most strongly coupled magnetic resonance (SCMR) wireless power transfer (WPT) systems is the dramatic efficiency drops by surrounding high-dielectric objects, e.g., people, caused by the narrow bandwidth of the systems due to a high quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> ). In this paper, a compact broadband planar double-spiral resonator with a via is proposed to obtain a robust SCMR system with a stable efficiency where interference from high-dielectric surrounding objects is mitigated. The increased bandwidth is obtained without compromising power transfer efficiency by introducing coupling enhancement to the structure while <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> is reduced. The bandwidth of the system is increased by over 15% compared to a conventional system with single-sided resonators, and the efficiency is comparable. In this paper, it is found that the location of the via affects both the efficiency and bandwidth of the SCMR system. Meanwhile, this paper reports an experiment with human hand phantom and a simulation study with multi-layered tissue model, both of which mimic a real human-involved environment, and successfully demonstrate the stability and high efficiency of power transfer of the proposed broadband resonators in a WPT system. Moreover, the proposed structure is tested to be less sensitive to misalignment between the transmitter and the receiver, and the proposed method is compared to the systems proposed for similar human-involved environments. This proposed viaed double-spiral resonator is a promising candidate for a robust WPT system for human-involved environments.

A Study of Wearable Wireless Power Transfer Systems on the Human Body

A study is performed to evaluate the performance of wearable Wireless Power Transfer (WPT) systems on various parts of the human body. Specifically, the effects of the human body on the Power Transfer Efficiency (PTE) of a Conformal Strongly Coupled Magnetic Resonance (CSCMR) WPT system is systematically examined. Two CSCMR systems are designed to operate at the 27.12 MHz Industrial, Scientific, and Medical (ISM) band, one on a 1.5 mm thick FR-4 substrate and one on a 1.5 mm thick ferrite sheet. Simulations and measurements of these two configurations are performed for 26 different placement locations on the human body. Considering our measured data on these 26 locations, it is found that when a CSCMR WPT system with a traditional substrate, such as FR-4, is placed directly on the skin of the human body, its PTE decreases on average by 7.2%. However, when the same system uses a ferromagnetic substrate instead of FR-4, its PTE decreases on average by only 1.6%. Additionally, a study of the Specific Absorption Rate (SAR) for the different placement locations is performed.

A brief feasibility study of wireless power transfer using strongly coupled magnetic resonance (SCMR) on cochlear implant at 11.7 MHz

A brief feasibility study of wireless power transfer using strongly coupled magnetic resonance (SCMR) on cochlear implant at 11.7 MHz

Miniaturization of SCMR Systems Using Multilayer Resonators

Multilayer elements are used to miniaturize the size of highly efficient wireless power transfer systems based on the Strongly Coupled Magnetic Resonance (SCMR). Specifically, inspired by miniaturization techniques used in antennas, multilayer resonators in conformal SCMR systems (instead of single-layer resonators traditionally used) are tightly stacked to significantly shrink the size of CSCMR systems. An analytical methodology is developed, based on Kirchhoff's law and Maxwell's mutual inductance formula using elliptic integrals, which can predict the system's resonance. Excellent agreement is shown between analytical, simulated and measured results. Based on our results the proposed multilayer CSCMR systems can operate at significantly lower frequencies than traditional CSCMR systems, while maintaining significantly smaller size as well as providing significantly higher efficiency and transmission range than traditional CSCMR systems.

A Wideband Strongly Coupled Magnetic Resonance Wireless Power Transfer System and Its Circuit Analysis

Conventional strongly coupled magnetic resonance (SCMR) wireless power transfer (WPT) systems have high quality factor ( $Q$ ), leading to limited system bandwidths. In practical applications, especially in human-involved environments, the resonant frequency of SCMR resonators will shift due to the effect of highly dielectric human body. In this letter, a wideband four-coil SCMR WPT system is proposed by improving the coupling between the tx/rx coil and their corresponding resonators. The bandwidth is increased by over 100% compared to a conventional system without sacrificing the efficiency much. The wideband feature is demonstrated by both simulation and measurement. It is analyzed physically and by using an equivalent circuit analysis.

Cylindrical Misalignment Insensitive Wireless Power Transfer Systems

The widely used wireless power transfer method known as inductive coupling, suffers from dramatic efficiency drops; even over short distances. Strongly coupled magnetic resonance (SCMR) was introduced recently, and can achieve high efficiency at larger distances when compared to inductive coupling. However, standard SCMR systems are highly sensitive to the alignment between the transmitter and receiver, which is an issue that has limited their application in practical wireless powering systems. This paper proposes a new SCMR-based topology that can maintain a constant high efficiency through 360° of misalignment. Specifically, a cylindrical geometry is proposed for the SCMR transmitter instead of using planar loops. Two types of materials are used: copper wire and flexible PCB, and their performances are compared and studied. This new system is able to achieve efficiency above 40% for the entire 360° misalignment without null points, and for the majority of angles the efficiencies stay at 70%. In addition, this new system is wearable and can be used as a portable wireless powering device.

Misalignment Sensitivity of Strongly Coupled Wireless Power Transfer Systems

A traditional strongly coupled magnetic resonance (SCMR) system is highly sensitive to the alignment between the transmitter and receiver elements, which is an issue that has limited their applicability in practical wireless power transfer systems. This paper proposes, for the first time, a novel set of SCMR-based topologies that are less sensitive to misalignment while providing large wireless powering efficiencies. Specifically, instead of using planar coils for the transmitter and the receiver, we connect two orthogonal coils together into a 3-D model to provide misalignment insensitivity. Three SCMR systems (standard SCMR, conformal SCMR, and hybrid SCMR systems) are studied and compared to the proposed 3-D SCMR system in terms of angular azimuth, angular elevation, and lateral misalignment. Also, the ranges of these SCMR systems are compared. It is shown that the proposed misalignment system achieves above 40% efficiency for the entire range of 360° of angular misalignment. Also, our results show that the proposed misalignment system provides longer range.

Multiband and Broadband Wireless Power Transfer Systems Using the Conformal Strongly Coupled Magnetic Resonance Method

Novel multiband and broadband wireless power transfer (WPT) systems based on conformal strongly coupled magnetic resonance (CSCMR) are presented in this paper. An analytical model for CSCMR systems is developed in order to study their performance. Optimal multiband and broadband CSCMR systems are designed and their performance is validated using simulations and measurements. A broadband CSCMR system, which exhibits seven times broader bandwidth than conventional SCMR and CSCMR systems operating at the same frequency, is designed and prototyped.

Combined Conformal Strongly-Coupled Magnetic Resonance for Efficient Wireless Power Transfer

This paper proposes a hybrid circuit between a conformal strongly-coupled magnetic resonance (CSCMR) and a strongly-coupled magnetic resonance (SCMR), for better wireless power transmission (WPT). This combination promises to enhance the flexibility of the proposed four-loop WPT system. The maximum efficiency at various distances is achieved by combining coupling-matching between the source and transmitting coils along with the coupling factor between the transmitting and receiving coils. Furthermore, the distance between transmitting and receiving coils is investigated along with the distance relationship between the source loop and transmission coil, in order to achieve the maximum efficiency of the proposed hybrid WPT system. The results indicate that the proposed approach can be effectively employed at distances comparatively smaller than the maximum distance without frequency matching. The achievable efficiency can be as high as 84% for the whole working range of the transmitter. In addition, the proposed hybrid system allows more spatial freedom compared to existing chargers.

Wireless Power Transfer (WPT) using Strongly Coupled Magnetic Resonance (SCMR) At 5.8 GHz for Biosensors Applications: A Feasibility Study by Electromagnetic (EM) Simulations

Wireless Power Transfer (WPT) using Strongly Coupled Magnetic Resonance (SCMR) At 5.8 GHz for Biosensors Applications: A Feasibility Study by Electromagnetic (EM) Simulations

Low frequency (LF) RFID sensors and selective transient feature extraction for corrosion characterisation

In this paper, Low Frequency (LF) RFID sensing system is used to characterise marine atmospheric corrosion on steel samples. Considering the conductivity and permeability variation in the corrosion layer, optimisation of sensing sensitivity and communication distance of commercial RFID tags placed on both coated and uncoated samples (exposure duration between 1 and 12 months) for impedance matching and appropriate operation frequencies are analysed. To balance the communication distance between RFID reader and tag and to match the impedance variation of RFID tags on metallic samples, a concept of wireless power transfer (WPT) through strongly coupled magnetic resonance (SCMR) method at RFID is applied. Static and transient features are extracted and selected to characterise corrosion. To enhance the sensing sensitivity to corrosion characterisation, further experimental studies have been carried out using ferrite sheets. The proposed LF RFID sensing system has been validated using commercial RFID tags with different feature extractions and selection of features for corrosion characterisation.

A Critical Review of Wireless Power Transfer via Strongly Coupled Magnetic Resonances

Strongly coupled magnetic resonance (SCMR), proposed by researchers at MIT in 2007, attracted the world’s attention by virtue of its mid-range, non-radiative and high-efficiency power transfer. In this paper, current developments and research progress in the SCMR area are presented. Advantages of SCMR are analyzed by comparing it with the other wireless power transfer (WPT) technologies, and different analytic principles of SCMR are elaborated in depth and further compared. The hot research spots, including system architectures, frequency splitting phenomena, impedance matching and optimization designs are classified and elaborated. Finally, current research directions and development trends of SCMR are discussed.

Spiral resonators for optimally efficient strongly coupled magnetic resonant systems

The wireless efficiency of the strongly coupled magnetic resonance (SCMR) method greatly depends on the Q-factors of the TX and RX resonators, which in turn are strongly dependent on the geometrical parameters of the resonators. This paper analytically derives the equations that can be used to design optimal spiral resonators for SCMR systems. In addition, our analysis illustrates that under certain conditions globally maximum efficiency can be achieved.

Wireless Power Transfer in Concrete via Strongly Coupled Magnetic Resonance

The wireless efficiency of the strongly coupled magnetic resonance (SCMR) method is studied here for non-homogenous interfaces. Specifically, SCMR's wireless power transfer from a source in air to a sensor embedded in concrete is analyzed. The concrete material properties are modeled for various humidity levels using the extended Debye model. The performance of SCMR is examined for both plain and reinforced concrete. Finally, rectification of the RF power is performed and the DC power delivered to the embedded sensor's battery is calculated.

Experimental demonstration of the equivalence of inductive and strongly coupled magnetic resonance wireless power transfer

In this work, we show experimentally that wireless power transfer (WPT) using strongly coupled magnetic resonance (SCMR) and traditional induction are equivalent. We demonstrate that for a given coil separation, and to within 4%, strongly coupled magnetic resonance and traditional induction produce the same theoretical efficiency of wireless power transfer versus distance. Moreover, we show that the difference between traditional induction and strongly coupled magnetic resonance is in the implementation of the impedance matching network where strongly coupled magnetic resonance uses the mini-loop impedance match. The mini-loop impedance mach provides a low-loss, high-ratio impedance transformation that makes it desirable for longer distance wireless power transfer, where large impedance transformations are needed to maximize power transfer.

Optimal Design Parameters for Wireless Power Transfer by Resonance Magnetic

The wireless power transfer (WPT) efficiency of systems based on strongly coupled magnetic resonance (SCMR) depends on the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor of the system elements, which is a function of the geometrical parameters. This letter analytically derives the equations that can be used to design optimal loop and helical elements for SCMR systems. Also, for loops and helices, a global maximum condition is derived in order to design SCMR systems with maximal efficiency.