Resonant Coils Research Articles

Efficiency Enhancement in a Multi-coil Wireless Power Transfer System

Wireless power transfer technology via magnetic resonance coupling now has significant interest in industry and research with many applications. This paper proposes a linear multiple transmitter coil array (5 coils) for wireless power transfer for added gain and hence higher transfer efficiency in comparison to a single transmitter coil. The frequency splitting effect as a result of the coupling between the resonant transmitter coils due to their close proximity is shown to reduce the transfer efficiency to a receiver. The effect of the array spacing on splitting effect suppression is verified. It is shown that the splitting effect is sup-pressed as the distance between the coils is increased leading to a higher received signal and hence higher efficiency. Proposed horizontal displacement of the middle transmitter coils (2nd and 4th coils) in the coil array is shown to suppress frequency splitting. To further suppress the splitting effect due to the magnetic coupling between the transmitter coils, a multiple transmitter array is proposed with different coil turns. Thus it is shown that designing the multiple coil array with mixed number of coil turns (the 2nd and 4th coils are designed to have different number of turns as compared to the other three coils) causes uniform coupling among the coils reducing and eventually eliminating the splitting effect. Also to increase the efficiency at the receiver coil, displaced stacked coils are introduced on top of the coil array. The pro-posed stacked coil array is demonstrated to improve the transfer efficiency. Using the techniques, the proposed linear array structure achieves a transfer efficiency of 36.9% for a receiver coil at the boresight of the array at a transfer distance of 40 cm.

Design and Development of Wireless power transfer system for Intracranial pressure monitoring devices

Wireless power transfer was today used for many applications regarding high power and low power transmission. Biomedical applications are lower power applications where WPT occurs between the power coils, one of which will be implanted in the body whereas other will be outside the body as Transmitting coil. Here the paper refers to the Wireless power transfer system to Intracranial Pressure monitoring devices. The proposed system operates at 180 KHz frequency for both Magnetic resonant coil design and WPT system analysis. The Mixed Resonance scheme at receiving side will be used as compensation topology for compatibility in Power delivered to load. Analysis and comparison for different coil structures are also verified for best suitable configuration for efficient power transfer.

스마트폰 무선전력전송 효율의 균일화를 위한 3차원 자기 공진 코일 및 벅 컨버터 설계

스마트폰 무선전력전송 효율의 균일화를 위한 3차원 자기 공진 코일 및 벅 컨버터 설계

Spring Displacement Sensor Composed of LC Resonance Circuit

This paper was prepared to assert that coil springs could be useful as displacement sensors as well as mechanical parts. We have investigated the displacement dependence on the inductance of a coil spring and resonance frequency of a simple LC circuit in which a coil spring took a part as an inductor. The changing ratio of inductance to displacement was 6.6 %/㎜. Inductance and/or inductance change of a coil spring was explained with FEM simulation. The changing ratio of the output voltage, which was obtained with the LC circuit, to displacement was estimated to be 6.23 %/㎜.

Enhancing the Stability of Medium Range and Misalignment Wireless Power Transfer System by Negative Magnetic Metamaterials.

The misalignment of the resonant coils in wireless power transfer (WPT) systems causes a sharp decrease in transfer efficiency. This paper presents a method which improves the misalignment tolerance of WPT systems. Based on electromagnetic simulations, the structural unit parameters of the electromagnetic material were extracted, and an experimental prototype of a four-coil WPT system was built. The influence of electromagnetic metamaterials on the WPT system under the conditions of lateral misalignment and angular offset was investigated. Experiments showed that the transfer efficiency of the system could be maintained above 45% when the transfer distance of the WPT system with electromagnetic metamaterials was 1 m and the resonant coils were shifted laterally within one coil diameter. Furthermore, the system transfer efficiency could be stabilized by more than 40% within an angle variation range of 70 degrees. Under the same conditions, the transfer efficiency of a system without electromagnetic metamaterials was as low as 30% when lateral migration occurred, and less than 25% when the angle changed. This comparison shows that the stability of the WPT system loaded with electromagnetic metamaterials was significantly enhanced.

Dual channel EPR excitation coil array for Overhauser-enhanced MRI

This article describes the development of a two-channel surface coil array for Overhauser-enhanced magnetic resonance imaging (OMRI) with the aim of extending the visualization area. The surface coil array consists of two independent surface coil resonators and PIN-diode switches. We utilized the PIN-diode switch to decouple the surface coils. OMRI measurement using a surface coil array was sequentially performed by switching the channels. To evaluate the effectiveness of the surface coil array, we demonstrated OMRI measurements using a phantom filled with nitroxide solution. In addition, in vivo OMRI imaging with a mouse was performed to demonstrate the applicability of our surface coil array to in vivo measurements. As a result, the visualization area obtained with our surface coil array was extended approximately 2-fold compared to the conventional single surface coil. Furthermore, we showed that in vivo imaging with the surface coil array was possible. These results indicate that the surface coil array could enhance the applicability of OMRI imaging.

A Real-Time-Link-Adaptive Operation Scheme for Maximum Energy Storage Efficiency in Resonant CM Wireless Power Receivers

The development, analysis, and experimental validation of an energy storage algorithmic scheme for performance optimization of resonant inductive power receivers are presented. Motivated by the crucial role of efficient energy storage in the next generation of brain-implantable devices, we introduce an energy management strategy in the design of wireless powering links, in which, the key performance measure is the energy stored during a limited time interval rather than the average energy delivered to the load. The presented strategy is proven analytically to yield the theoretically-maximum energy storage efficiency over a pre-determined period of time. Additionally, thanks to the algorithm's closed-form solution, the optimization can be done in real time, offering the potential for a solution that is adaptive to any variations in physical (e.g., coil separation, Rx rotation, etc.) and/or electrical (e.g., Q-factor, media conductivity, etc.) properties of the link, conditional to a low-power circuit implementation for its evaluation. The efficacy and precision of the solution obtained from the presented analytical model is confirmed with CAD-based simulation results, and later validated using experimental measurements. Our experimental results for two links with different characteristics (resonance frequency, coils size and separation, etc.) show a 52.5% and 67.5% improvement in overall energy storage efficiency compared to the standard CM receiver design in which resonance-to-charging switching is performed when the receiver's LC tank energy accumulation starts to saturate. This is while the presented method does not require any calibration and is designed to be employed by any generic current-mode receiver.

A Design Technique for Optimizing Resonant Coils and the Energy Transfer of Inductive Links

Power transfer efficiency (PTE) is a key performance parameter in development work on resonant inductive power transfer (IPT) systems. Geometrically optimizing the transmitter (Tx) and receiver (Rx) coil pair is a way of improving the IPT system's efficiency. In this article, a new figure-of-merit (FoM) is proposed to find an optimum coil geometry which maximizes the PTE. The employed FoM parameter, called the “strong coupling factor” (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">scf</sub> ), is defined such that its value indicates how strongly the Tx and Rx coils are linked together. Considering the IPT application and its physical size constraints, a proper selection method for identifying the numerical value of P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">scf</sub> is essential for optimal coil geometry design. This article presents an iterative algorithm to assist in the selection of the most favorable P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">scf</sub> value which provides maximized PTE for the designed optimum coil geometry. Design examples of two nominal IPT systems at frequencies of 415 and 0.1 MHz are used to investigate the design algorithm. Theoretical calculations show the optimum geometry designed for the IPT system operating at 415 MHz, with coupling coefficient (K) of 0.2, can achieve maximum PTE of 85.70%. Measurements presented from a practical Tx/Rx coil pair in the IPT link operating at 0.1 MHz, with K = 0.05, show a PTE of 83.10% against a calculated PTE of 84.11% validating the design process.

All-optical modulation in Black Phosphorus functionalized microfibre coil resonator

All-optical modulation is experimentally demonstrated in a microfibre coil resonator (MCR) functionalized with black phosphorus (BP) nanosheets (BP-MCR). The BP nanosheets is deposited onto microfibre and then microfibre is wrapped on a PMMA rod covered with UV-curable low refractive index polycarbonate (PC) resin. The BP-MCR modulation properties are regulated based on BP absorption, photo-thermal and optical Kerr effects. The resonance wavelength and extinction ratio responsivity to incident pump power can attain ∼0.033 nm mW−1 and ∼0.180 dBm mW−1, while the averaged rising/falling response time is ∼9.58/8.53 ms. The device could find applications as all-optical modulator, optical switch or tunable optical filter.

High-Field Pulsed ENDOR with Intra-cavity Radiofrequency Coil

This study compares the performance of two coil configurations for W-band pulsed ENDOR using a setup with both a radiofrequency ‘hairpin’ coil internal to a microwave non-radiative resonator and Helmholtz-like coils external to the resonator. Evaluation of the different coil performances is achieved via the ENDOR study of two model systems. The efficiencies of the coil configurations are first investigated numerically, showing that a higher radiofrequency current-to-magnetic field conversion factor can be achieved with the intra-cavity coil, with a similar radiofrequency magnetic field uniformity. This result is then confirmed by the broadband ENDOR spectra acquired with the two coil arrangements. A gain in the signal-to-noise ratio enabled by the internal coil of about a factor 10 was observed. In some cases, the high conversion factor of the intra-cavity coil led to a saturation of the ENDOR transitions. The possibility to implement a similar intra-cavity radiofrequency coil configuration in higher field spectrometers is finally discussed.

Protection Strategy for Wireless Charging Electrical Vehicles

Wireless charging has become increasingly popular for electric vehicles (EVs) in recent years. However, possible device damage may happen because of the sharp variations of inverter output current and the ZVS angle due to the alignment variation between resonant coils especially while charging. To design a protection strategy, the characters of the inverter output current and phase angle are analyzed when the wireless charging EV leaves. The protection strategy is composed of the insufficient angle protection, overcurrent protection, and the excessive angle protection. A detection circuit is designed to measure the variation of inverter output current and phase angle. A wireless charging EV prototype is established to validate the proposed methods. The experimental results show that the designed detection circuit and protection strategy can catch the abnormal working state of the system when the wireless charged EV leaves and take measures immediately to protect the main circuit of the system from device damages.

Three-Dimensional Magnetic Resonant Coil System with Double Transmitter Coil for Enhancement of Wireless Charging Efficiency and Charging Flexibility

Three-Dimensional Magnetic Resonant Coil System with Double Transmitter Coil for Enhancement of Wireless Charging Efficiency and Charging Flexibility

An S-CLC Compensated Load-Independent Inductive Power Relay System With Constant Voltage Outputs

This article proposes an S-CLC compensation network to achieve a relay system to power multiple gate drivers of series modules. There are three major contributions. First, it achieves the constant voltage (CV) and load-independent property, meaning the induced voltage on each receiver is immune to load variations. Second, the S-CLC circuit topology is compact to be constructed, and an integrated coil structure is proposed to limit the system size. Third, the efficiency of the power relay system is analyzed, including parasitic resistances of resonant components and coils, which reveal the load regulation phenomenon in practical applications. In order to validate the proposed topology, the parameter design methodology to achieve the highest efficiency is proposed, and a single-input-four-output prototype is implemented. The coil size is 180 mm × 175 mm, the transfer distance between receivers is 50 mm, and the switching frequency is 200 kHz. When the input dc voltage is 18 V, the induced voltage of each receiver is around 15 V, and the voltage difference between receivers is within 2 V. When the load resistances vary in a wide range from 15 to 100 Ω, the output voltage regulation rate is within 17.01%. The maximum power of the receiver can reach 13.53 W, and the maximum efficiency can reach 89.79%, showing that the proposed system can be used in practical applications. Besides, the prototype is exploited to power gate drivers with a total power consumption of 2.75 W, further verifying the practical application value.

Research on Magnetic Coupled Resonant Wireless Charging Technology Applied To Intelligent Patrol Robots

Magnetic coupled resonance wireless charging technology can realize high power and high efficiency energy transmission at medium distance, which is highly suitable for wireless charging of patrol robots. In this paper, a magnetic-coupled resonant wireless charging system applied in the patrol robot is designed and researched. The working principle of magnetic coupled resonant wireless charging technology is firstly introduced. Then, based on the theory of equivalent circuit modeling, the transmission efficiency and load power of the system are deduced. Moreover, the coil resonance frequency is calculated, and the coil field is analyzed by using Maxwell electromagnetic field software. Finally, the simulation software of Simplorer and Maxwell is used to verify the feasibility and efficiency of wireless charging technology.

Maximum Efficiency Point Tracking Scheme for Loosely Coupled Multiple-Receiver Wireless Power Charging System With Mutual Inductance Tracking

This article presents a maximum efficiency point tracking (MEPT) scheme for a multiple receivers and loosely coupled wireless power charging (WPC) system with a mutual inductance tracking method. In general, the WPC system should satisfy the requirements of constant output voltage and the highest possible efficiency according to sensitive variation of charging environments. To this end, a state-of-the-art MEPT scheme has been studied in this work. Additionally, one of the advantages of the loosely coupled WPC system is the ability to charge multiple devices simultaneously. However, most studies have focused on a single-input and single-output (SISO) system. In this article, we propose a MEPT scheme for a multiple receiver WPC system and a mutual inductance tracking method. The proposed control scheme determines the current of the transmitter based on the mutual inductance between the transmitter and receivers. For validation, the proposed single-input multiple-output (SIMO) WPC system was implemented at 1 MHz using loosely coupled series-series resonant coils and the proposed mutual inductance tracking method. The results verified the performance of the proposed MEPT scheme in a SIMO system regardless of changing charging environments.

On the Design of Planar Arrays of Nonresonant Coils for Tunable Wireless Power Transfer Applications

In this article, we introduce a novel array-based system for inductive wireless power transfer (WPT) applications and a procedure for its design, which can be interpreted as a generalization of the traditional three-coil systems where the intermediate passive resonant coil (i.e., the transmitter) is replaced with an array of nonresonant concentric loops. We demonstrate that the new WPT array system provides flexibility with respect to the characteristic parameters of the inductive link (i.e., efficiency and gain), thus allowing for their optimal tradeoff depending on the specific WPT application: this is achieved by controlling the current amplitude flowing in each element of the array through the addition of an appropriately selected reactive load. Furthermore, we demonstrate that it is possible to obtain, with the WPT array, focused magnetic field distributions, leading to a potential reduction in the receiver dimensions. Such configuration can be made effectively equivalent to a traditional three-coil system in terms of physical dimensions and performance, through the addition of an appropriate reactance to each loop of the array. To demonstrate the validity and usefulness of the proposed system and design procedure, we first performed extensive numerical simulations of a traditional three-coil system and compared its performance with different array configurations. We then fabricated and experimentally characterized several prototypes, observing an excellent agreement between the measurements and simulations. The innovative features of the proposed design can be extremely useful in many WPT applications requiring a fine optimization in efficiency, gain, and field distribution.

Resonance-filtering combo system for continuous wireless charging range coverage

AbstractDistribution of wireless power charging field uniformly on a large area pad is critical for power receivers, particularly for wearable devices, wherein small form factor coils are involved. Since the receiver coil size is quite limited in these types of applications, the device is very sensitive to the amount of field it could retain and hence, it needs special placement or snapping mechanism to fix it at an optimum location for reliable wireless charging. In order to overcome this limitation for the end-user, a dual-mode multi-coil power transceiver system is proposed; utilizing resonance filtering to increase the amount of total power delivered with the rather uniform spatial distribution. Two concentric coils; center one driven by 6.78-MHz high-frequency driver (A4WP) and the outer larger one with a 200-KHz low-frequency driver (Qi) with resonant blocker could transfer up to 50 mW standards compliant flat power to a 13-mm radius 30-turns wearable receiver coil everywhere across an 8-cm radius charging pad area without any alignment requirement or snapping. Two different feedback topologies corresponding to each of the H-Bridge power drivers were also presented as an automatic series resonance coil drive frequency lock mechanism, extracting peak powers for each system individually from a standard 5 V-1A USB wall charger.

Multi-mode metamaterial-inspired resonator for near-field wireless power transfer

The modern development of wireless power transfer (WPT) technologies brings various products that improve the lives of users. It has become an urgent demand to simultaneously charge multiple mobile devices operating under different WPT standards on a charging platform regardless of their position and orientation with respect to each other. Recent advances in metasurfaces make it possible to control the near electromagnetic fields with much more degrees of freedom in comparison to conventional resonators. Here, we develop a compact multi-mode metamaterial-inspired resonator formed as an array of sub-wavelength parallel strip conductors. This resonator aims to replace conventional flat coil resonators and offers multiple modes with different profiles of electromagnetic field distribution for various near-field WPT applications. The first three eigenmodes are numerically and experimentally studied, and their potential applications for design of multi-mode WPT systems capable of charging multiple receivers simultaneously are discussed.

A Design Method for Magnetically Coupled Resonant Coils Considering Transmission Objectives and Dimension Constraints

This paper proposes a coil design method for the magnetically coupled resonant wireless power transfer (MCR-WPT) system. Based on the Biot–Savart law, the magnetic flux density at the observation point was derived, and the magnetic flux of the observation plane generated by the exciting coil was deduced to build the calculation model of power transfer efficiency (PTE) and power delivered to the load (PDL). The PTE and PDL curves via coil parameters could be fitted in minutes using numerical calculation. The coil was designed according to transmission objectives and dimension constraints. In addition, the calculated PTE and PDL were compared with those from finite element analysis to verify the credibility of the method. Finally, the actual curves of PTE and PDL were achieved, which showed a strong positive correlation with the corresponding curves from the calculation model. The relative average deviations of PDL curves were less than 6.11%. Meanwhile, coils designed with the numerical calculation could realize 309.80 W and 88.51%, which achieved the objectives under the constraints. The results demonstrate that the proposed method can realize a rapid and accurate coil design under constraints. It can also be applied to other coil structures or circuit topologies with strong universality.

Versatile cryogen-free cryostat for the electromagnetic characterization of superconducting radiofrequency coils

The use of high temperature superconducting (HTS) radio frequency (RF) coils in Magnetic Resonance Imaging (MRI) greatly improves the signal-to-noise ratio (SNR) in many biomedical applications and particularly in micro-MRI. However, a detailed understanding of the electrical behavior of HTS coils is important in order to optimize their performance through MR experiments. This paper presents a simple and versatile cryogen-free cryostat designed to characterize the RF properties of HTS coils prior to their use in MRI. The cryostat can be used at temperatures from 50 K to 300 K, with a control precision of approximately 3 mK at 70 K, and can measure the RF electrical power transmitted to an HTS coil over a range from 1 μW to 10 W. The quality factor and resonance frequency of the tested HTS coil are determined as a function of the temperature and the power it dissipates. This cryostat also permits the dynamic adjustment of the coil resonance frequency via temperature control. Finally, this study demonstrates that the HTS coil takes less than 12 μs to transit from the superconducting to the dissipative state, which is compatible with MRI requirements.