Coupling Coils Research Articles

Reduction of eddy current losses in inductive transmission systems with ferrite sheets

BackgroundImprovements in eddy current suppression are necessary to meet the demand for increasing miniaturization of inductively driven transmission systems in industrial and biomedical applications. The high magnetic permeability and the simultaneously low electrical conductivity of ferrite materials make them ideal candidates for shielding metallic surfaces. For systems like cochlear implants the transmission of data as well as energy over an inductive link is conducted within a well-defined parameter set. For these systems, the shielding can be of particular importance if the properties of the link can be preserved.ResultsIn this work, we investigate the effect of single and double-layered substrates consisting of ferrite and/or copper on the inductance and coupling of planar spiral coils. The examined link systems represent realistic configurations for active implantable systems such as cochlear implants. Experimental measurements are complemented with analytical calculations and finite element simulations, which are in good agreement for all measured parameters. The results are then used to study the transfer efficiency of an inductive link in a series–parallel resonant topology as a function of substrate size, the number of coil turns and coil separation.ConclusionsWe find that ferrite sheets can be used to shield the system from unwanted metallic surfaces and to retain the inductive link parameters of the unperturbed system, particularly its transfer efficiency. The required size of the ferrite plates is comparable to the size of the coils, which makes the setup suitable for practical implementations. Since the sizes and geometries chosen for the studied inductive links are comparable to those of cochlear implants, our conclusions apply in particular to these systems.

Miniaturized Resonant Power Conversion for Implanted Medical Devices

The design of a millimetre-sized power converter is proposed which is based on coil coupling that could be integrated into the neural or cardiac implantable medical device (IMD) to provide isolated power or energy transmission by harvesting it from external transmitter device. A special step-up case of transformer coupling to a millimetre-sized receiver coil by a comparatively larger transmitter coil is examined. This paper is expected to increase research efforts to develop the battery-less IMD’s with reduced size, low power, high efficiency, and improved reliability and feasibility. Based on our work, we believe that the inductive coupling link with low loss ferrite material is the suitable method to be used to power the batteryless devices. The converter produces the targeted output power of more than 400 $\mu \text{W}$ with 1 mm3 size of the coil at 2 MHz.

Experimental analysis of self-frequency tracking control strategy for inductive power transfer system

Inductive power transfer (IPT) systems are capable to transfer an electrical power from a power source (transmitter) into electronic devices (receiver) via an air gap. Since the power transmission is based on the induced voltage concept of two inductive resonance coupling coils, the frequency of the driver circuit may dynamically drift away from the designed circuit. Hence, in order to rectify the aforementioned problem, phased lock loop (PLL) circuit is proposed to ensure the frequency of the IPT system that is maintained to operate at its operating frequency which is 1 MHz in this work. The analysis of the IPT system with self-frequency tracking control strategy performance is validated through the experimental works. The experimental results revealed that the efficiency of self-frequency tracking is equal to 92% and the efficiency without tracking is 87% at 10 mm of air gap distance for 0.8 coupling coefficient.

Improvements and Performance of the Fermilab Solenoid Test Facility

The Solenoid Test Facility at Fermilab was built using a large vacuum vessel for testing of conduction-cooled superconducting solenoid magnets, and was first used to determine the performance of the MICE Coupling Coil [1, 2]. The facility was modified recently to enable testing of solenoid magnets for the Mu2e experiment, which operate at much higher current than the Coupling Coil. One pair of low current conduction-cooled copper and NbTi leads was replaced with two pairs of 10 kA HTS leads cooled by heat exchange with liquid nitrogen and liquid helium. The new design, with additional control and monitoring capability, also provides helium cooling of the superconducting magnet leads by conduction. A high current power supply with energy extraction was added, and several improvements to the quench protection and characterization system were made. Here we present details of these changes and report on performance results from a test of the Mu2e prototype Transport Solenoid (TS) module. Progress on additional improvements in preparation for production TS module testing will be presented.

An Inductive-Coupling Blocker Rejection Technique for Miniature RFID Tag

Miniaturization is a promising trend for future RF identification (RFID) in many applications such as the Internet of Things (IoT) and implantable devices. For a small-sized RFID tag using near-field communication, the reader is required to emit a large amount of RF power in order to power up the tag while simultaneously picking up a weak backscattering communication signal. This results in a very small signal-to-blocker ratio (SBR), making the demodulation very difficult for the reader-side receiver (RSR). In this paper, we propose a novel blocker rejection technique based on inductive coupling. Several coupling coils and transmission lines are designed and optimized on the same printed circuit board (PCB) with the main power transmitting (Tx) coil of the reader, which leads to a much higher SBR. As a demonstration vehicle, a $200 \mu{\text {m}} \times 200 \mu{\text {m}}$ RFID tag with an on-chip antenna is fabricated using 65-nm CMOS technology with a harvested power of 12 $\mu $ W, an operating frequency of 2 GHz, and a backscattering data rate of 625 kb/s. Measured result shows the proposed block rejection technique improves the SBR by 44 dB.

The Parallel Transmission of Power and Data With the Shared Channel for an Inductive Power Transfer System

A shared physical communications channel is designed and implemented in this paper for inductive (contactless) power transfer (IPT) applications, wherein data are transferred without interfering power transfer, and, thus, maintained the efficiency of the IPT system. The channel is made of coupling coils, which are used to control the system and to transfer data bidirectionally at the rate of 19.2 Kb/s. To make the system work in two relatively independent modes, the wave trappers (passive bandpass and band-reject filters) are added into the system, and an integrated mathematical model is established based on separate models of data and power transfer. The proposed method was tested on a laboratory scale prototype, and was proved to be reliable for the parallel transmission of power and data. Therefore, the proposed method can be used to improve performance of the IPT system by precise control due to communication between the primary side and the pickup side.

Coil Design and Efficiency Analysis for Dynamic Wireless Charging System for Electric Vehicles

Wireless charging electric vehicles (EV) is the development trend of EV. However, the battery taken by EVs has the disadvantages of big volume, long time to recharge, and limited driving distance. In this paper, an innovative dynamic wireless charging system based on magnetic coupled resonant power transmission is presented. The transmitting coil of this charging system can selectively turn ON/OFF for charging vehicles while driving. The structures of the transmitting coil and receiving coil are researched and improved. In addition, the dispersed coupling structure named grouped periodic series spiral coupler is proposed, and its characteristics are described. A simulation of coupling coefficients at different $D$ values is carried out. A prototype is built to experiment on the dynamic wireless charging process of EV. Meanwhile, the coil coupling and variation of transmission efficiency are analyzed. The comparison of the experiment indicated that the EV can obtain a stable charging process under 25 mm transmission distance using the improved receiving coil with $R$ : $H$ : $D=4:5:13$ . Moreover, the dynamic charging process is relatively stable without an obvious fluctuation while passing the interval between two transmitting coils, and the transmission efficiency is promoted by 50%.

Parameter Design for a 6.78-MHz Wireless Power Transfer System Based on Analytical Derivation of Class E Current-Driven Rectifier

Magnetic resonance coupling working at megahertz (MHz) is widely considered as a promising technology for the mid-range transfer of a medium amount of power. It is known that the soft-switching-based Class E rectifiers are suitable for high-frequency rectification, and thus potentially improve the overall efficiency of MHz wireless power transfer (WPT) systems. This paper reports new results on optimized parameter design of a MHz WPT system based on the analytical derivation of a Class E current-driven rectifier. The input impedance of the Class E rectifier is accurately derived, for the first time, considering the on-resistance of the diode and the equivalent series resistance of the filter inductor. This derived input impedance is then used to develop and guide design procedures that determine the optimal parameters of the rectifier, coupling coils, and a Class E PA in an example 6.78-MHz WPT system. Furthermore, the efficiencies of these three components and the overall WPT system are also analytically derived for design and evaluation purposes. In the final experiments, the analytical results are found to well match the experimental results. With loosely coupled coils (mutual inductance coefficient $k$ =0.1327), the experimental 6.78-MHz WPT system can achieve 84% efficiency at a power level of 20 Watts.

Non-Contact Measurement of Electrolyte Solution With a Passive Coil Placed in Inductive Coupling System

A non-contact electrolyte solution measurement system is developed based on inductive coupling coils fabricated on printed circuit boards (PCBs). The basic sensing system is made up of a readout coil and the electrolyte solution under test. A passive coil is composed by a coil printed on the PCB substrate, and a capacitance element to make an $LC$ resonator. When it is placed in the basic sensing system, the measurement performance is enhanced because of the strong coupling around its resonant frequency. Sodium chloride solution with 0%–5% massed fraction concentration in a plastic container is adopted as the target to be detected. Impedance spectrums are experimentally analyzed for the cases of that the passive coil is placed in front and at the back of the target solutions, respectively. The results indicate that, when the target is located at the same distance, a measurement system with a passive coil performs a higher sensitivity to solution concentration than that without one. Furthermore, when the target solution is located beyond the sensing range of the basic sensing system, the solution concentration can also be effectively measured with the aid of a passive coil. Such an enhancement effect of the passive coil can efficiently promote the performances of non-contact measurement systems for low conductivity targets, such as electrolyte solutions or biological tissues. This is especially true when the passive coil is fabricated on a flexible circuit substrate, since the flexible coil can be attached to the non-planar surface of the target to ensure a stronger magnetic coupling.

Design and operation of the RFX-mod plasma shape control system

The aim of executing Single Null discharges in RFX-mod operating as a Tokamak led to the design and implementation of a plasma shape feedback control system. A fully model-based approach was followed which allowed dealing with critical issues such as the presence of a conducting shell, the strong coupling of the poloidal field coils and the voltage limits of the power supplies. A Linear Quadratic regulator and a Kalman state estimator were designed and implemented in the real time MARTe framework together with an algorithm for the real-time plasma boundary reconstruction. The problem of a number of sensors along the poloidal direction adequate only for circular discharges was also successfully tackled. The development of the system and its performances in terms of tracking and disturbance rejection capability are presented in the paper.

Improving the Mass-Limited Performance of Routine NMR Probes using Coupled Coils

We report a method to convert, on demand, a general use dual-broadband probe to a high performance mass-limited probe for both high band and low band nuclei. This technology uses magnetic coupling of inductors to achieve this capability. The method offers a cost effective way of increasing the performance of routine NMR probes without having to change probes or increase the overall foot print of the spectrometer.

Experimental implementation of array-compressed parallel transmission at 7 tesla.

To implement and validate a hardware-based array-compressed parallel transmission (acpTx) system. In array-compressed parallel transmission, a small number of transmit channels drive a larger number of transmit coils, which are connected via an array compression network that implements optimized coil-to-channel combinations. A two channel-to-eight coil array compression network was developed using power splitters, attenuators and phase shifters, and a simulation was performed to investigate the effects of coil coupling on power dissipation in a simplified network. An eight coil transmit array was constructed using induced current elimination decoupling, and the coil and network were validated in benchtop measurements, B1+ mapping scans, and an accelerated spiral excitation experiment. The developed attenuators came within 0.08 dB of the desired attenuations, and reflection coefficients were -22 dB or better. The simulation demonstrated that up to 3× more power was dissipated in the network when coils were poorly isolated (-9.6 dB), versus well-isolated (-31 dB). Compared to split circularly-polarized coil combinations, the additional degrees of freedom provided by the array compression network led to 54% lower squared excitation error in the spiral experiment. Array-compressed parallel transmission was successfully implemented in a hardware system. Further work is needed to develop remote network tuning and to minimize network power dissipation. Magn Reson Med 75:2545-2552, 2016. © 2016 Wiley Periodicals, Inc.

Efficient Wireless Powering of Biomedical Sensor Systems for Multichannel Brain Implants

This paper describes the complete mathematical optimization process of an inductive powering system suitable for the application within implanted biomedical systems. The optimization objectives are thereby size, energy efficiency, and tissue absorption. Within the first step, the influence of the operational frequency on the given quantities is computed by means of finite element simulations, yielding a compromise of power transfer efficiency of the wireless link and acceptable tissue heating in terms of the specific absorption rate. All simulations account for the layered structure of the human head, modeling the dielectric properties with Cole-Cole dispersion effects. In the second step, the relevant coupling and loss effects of the transmission coils are modeled as a function of the geometrical design parameters, enabling a noniterative and comprehensible mathematical derivation of the optimum coil geometry given an external size constraint. Further investigations of the optimum link design also consider high-permeability structures being applied to the primary coil, enhancing the efficiency by means of an increased mutual inductance. Thereby, a final link efficiency of 80% at a coil separation distance of 5 mm and 20% at 20 mm using a 10-mm planar receiving coil can be achieved, contributing to a higher integration density of multichannel brain implanted sensors. Moreover, the given procedure does not only give insight into the optimization of the coil design, but also provides a minimized set of mathematical expressions for designing a highly efficient primary side coil driver and for selecting the components of the secondary side impedance matching. All mathematical models and descriptions have been verified by simulation and concluding measurements.

Performance and analysis of wireless power charging system from room temperature to HTS magnet via strong resonance coupling method

The technology of supplying the electric power by wireless power transfer (WPT) is expected for the next generation power feeding system since it can supply the power to portable devices without any connectors through large air gap. As such a technology based on strongly coupled electromagnetic resonators is possible to deliver the large power and recharge them seamlessly; it has been considered as a noble option to wireless power charging system in the various power applications. Recently, various HTS wires have now been manufactured for demonstrations of transmission cables, motors, MAGLEV, and other electrical power components. However, since the HTS magnets have a lower index n value intrinsically, they are required to be charged from external power system through leads or internal power system. The portable area is limited as well as the cryogen system is bulkier. Thus, we proposed a novel design of wireless power charging system for superconducting HTS magnet (WPC4SM) based on resonance coupling method. As the novel system makes possible a wireless power charging using copper resonance coupled coils, it enables to portable charging conveniently in the superconducting applications. This paper presented the conceptual design and operating characteristics of WPC4SM using different shapes' copper resonance coil. The proposed system consists of four components; RF generator of 370 kHz, copper resonance coupling coils, impedance matching (IM) subsystem and HTS magnet including rectifier system.

Modeling Endovascular MRI Coil Coupling With Transmit RF Excitation.

To model inductive coupling of endovascular coils with transmit RF excitation for selecting coils for MRI-guided interventions. Independent and computationally efficient FEM models are developed for the endovascular coil, cable, transmit excitation, and imaging domain. Electromagnetic and circuit solvers are coupled to simulate net B1 + fields and induced currents and voltages. Our models are validated using the Bloch-Siegert B1 + mapping sequence for a series-tuned multimode coil, capable of tracking, wireless visualization, and high-resolution endovascular imaging. Validation shows good agreement at 24-, 28-, and 34-μT background RF excitation within experimental limitations. Quantitative coil performance metrics agree with simulation. A parametric study demonstrates tradeoff in coil performance metrics when varying number of coil turns. Tracking, imaging, and wireless marker multimode coil features and their integration is demonstrated in a pig study. Developed models for the multimode coil were successfully validated. Modeling for geometric optimization and coil selection serves as a precursor to time consuming and expensive experiments. Specific applications demonstrated include parametric optimization, coil selection for a cardiac intervention, and an animal imaging experiment. Our modular, adaptable, and computationally efficient modeling approach enables rapid comparison, selection, and optimization of inductively coupled coils for MRI-guided interventions.

Origin of frequency difference between damped and sustained modes in vibrating wire sensors

Vibrating wire sensors can operate in two modes, damped mode and sustained mode. In practice, the resonant frequency measured in sustained mode is higher than the one measured in damped mode. In this paper, the theoretical analysis indicates that average magnetic force and coil coupling are responsible for the frequency difference. This prediction is experimentally confirmed by measuring the resonant frequencies for different values of the two parameters. It is shown how to correct measurements in order to obtain the same results for the two modes.

A Novel RFID-Based Sensing Method for Low-Cost Bolt Loosening Monitoring.

In coal mines, bolt loosening in the cage guide is affected by the harsh environmental factors and cage hoist vibration, leading to significant threats to work safety. It is crucial, to this effect, to successfully detect the status of multipoint bolts of guide structures. This paper proposes a system to monitor bolt status in harsh environments established based on the RFID technique. A proof-of-concept model was demonstrated consisting of a bolt gearing system, passive UHF RFID tags, a reader, and monitoring software. A tinfoil metal film is fixed on the retaining plate and an RFID tag bonded to a large gear, with the bolt to be detected fixed in the center of a smaller gear. The radio-frequency signal cannot be received by the reader if the tag is completely obscured by the tinfoil, and if the bolt is loose, the tag’s antenna is exposed when the gear revolves. A radio-frequency signal that carries corresponding bolt’s information is transmitted by the RFID tag to the RFID reader due to coil coupling, identifying loose bolt location and reporting them in the software. Confirmatory test results revealed that the system indeed successfully detects bolt loosening and comparative test results (based on a reed switch multipoint bolt loosening monitor system) provided valuable information regarding the strengths and weaknesses of the proposed system.

Detecting Malposition of Coil Couple for Transcutaneous Energy Transmission.

Transcutaneous energy transmission technology based on coil coupling is widely required for various wireless powering implanted devices in human body. However, the coupling performance is commonly affected by malposition between coils in practice. It is difficult for users to know the actual position of the implanted receiver coil (RC) and how to realign the transmitter coil (TC) outside the body. This article proposes a detecting method of coil-coupling malposition based on a sensing board with coil array fitted on the TC. In this article, the sensing system and the data processing algorithm separating the sensing coil (SC) signals induced by TC and RC currents, respectively, are introduced. Then, an analytical model formulating the induction effect between the RC and SCs is given. Inverse computation algorithms of the malposition based on the processed sensing data and the induction effect model are presented at last. The proposed method is validated by experiments simulating malposition both in distance and concentricity on an actual coil couple. The results show that the sensing system can provide accurate parameterized guide for users to adjust the installation of the TC for good energy transmission performance.

Capability Assessment of the Equilibrium Field System in KTX**supported by the Ministry of Science and Technology of China (No. 2011GB106000)

Radial equilibrium of the KTX plasma column is maintained by the vertical field which is produced by the equilibrium field coils. The equilibrium is also affected by the eddy current, which is generated by the coupling of copper shell, plasma and poloidal field coils. An equivalent circuit model is developed to analyze the dynamic performance of equilibrium field coils, without auxiliary power input to equilibrium field coils and passive conductors. Considering the coupling of poloidal field coils, copper shell and plasma, the evolution of spatial distribution of the eddy current density on the copper shell is estimated by finite element to analyze the effect of shell to balance. The simulation results show that the copper shell and equilibrium field coils can provide enough vertical field to balance 1 MA plasma current in phase 1 of a KTX discharge. Auxiliary power supply on the EQ coils is necessary to control the horizontal displacement of KTX due to the finite resistance effect of the shell.

A General Design Method of Primary Compensation Network for Dynamic WPT System Maintaining Stable Transmission Power

Dynamic wireless power transmission (DWPT) is considered as a solution to the problems encountered in the development of electrical vehicle (EV), such as range anxiety resulted from battery bottleneck and the difficulty of convenient charging. However, the requirement of DWPT, maintaining almost constant transmission power with constant voltage load in effective movement process, is quite different from Stationary WPT. The power fluctuation is easily brought by the coupling coils over large misalignment in movement. A general design method of primary compensation network from the perspective of DWPT is presented in this paper. Under the premise of ensuring high transmission efficiency and soft switching, a novel T-type compensation network for DWPT is proposed, which maintains a stable output characteristic over a wide misalignment, companied with an inherent current limiting ability under no-load operation. A WPT prototype with a fixed frequency operation based on the T-type compensation network is built. The output power is kept almost stable even though magnetic coupling coefficient varies twice showing the effectiveness of the design method.