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The demand for biomedical devices that can collect high-fidelity data from patients in various environments, inside and outside medical clinics, and can provide high-precision diagnosis and long-term monitoring, is high in the healthcare industry. Among different sensing technologies, this study specifically focuses on providing a review of inductive sensing-based devices used in healthcare. Although the concept of inductive sensing has been used in other fields aside from healthcare, we believe that there is a high potential for a wide range of use of this sensing method across various biomedical devices due to the low cost, flexibility in the sensor design, mature fabrication technologies, and high sensitivity. This review first summarizes the mechanisms of inductive sensing-based devices and design considerations. Then, three main groups of applications that are used in healthcare and rely mainly on inductive sensing for their diagnosis and treatments are presented, including motion tracking and continuous monitoring systems, bio-signal detection systems, and imaging biological tissues. We conclude with a summary of the current status of inductive sensing devices used in healthcare, highlighting the promising capabilities and barriers to overcome.

In this paper, we present a 6.78 MHz Pulsed Wireless Power Transfer (PWPT) system specifically designed for powering the electronics placed on a suction roll of a paper mill machinery, thus enabling rotating equipment monitoring. The system utilizes a pair of different resonant coils to maintain a stable coupling coefficient for a fraction of the roll rotation period while guaranteeing compactness and ease of installation. Designed using both Commercial-off-the-Shelf (COTS) and custom components, the developed WPT system achieves a DC-DC efficiency of 62% in the specific working conditions. The transferred power is used to supply an Internet-of-Things (IoT) node that continuously measures and transmits data about the operation status. A fully operational system for battery and angular position monitoring has been developed and tested in a laboratory environment. This research presents a comprehensive analysis of the system and explores the interaction of different coils to maintain a stable coupling coefficient in dynamic applications. The same approach can be employed for rotating machinery with similar geometrical constraints or more general dynamic applications characterized by periodic movements and limited space for the coupling system.

Parallel transmission (pTX) techniques are required to tackle a number of challenges, e.g., the inhomogeneous distribution of the transmit field and elevated specific absorption rate (SAR), in ultra-high field (UHF) MR imaging. Additionally, they offer multiple degrees of freedom to create temporally- and spatially-tailored transverse magnetization. Given the increasing availability of MRI systems at 7 T and above, it is anticipated that interest in pTX applications will grow accordingly. One of the key components in MR systems capable of pTX is the design of the transmit array, as this has a major impact on performance in terms of power requirements, SAR and RF pulse design. While several reviews on pTX pulse design and the clinical applicability of UHF exist, there is currently no systematic review of pTX transmit/transceiver coils and their associated performance. In this article, we analyze transmit array concepts to determine the strengths and weaknesses of different types of design. We systematically review the different types of individual antennas employed for UHF, their combination into pTX arrays, and methods to decouple the individual elements. We also reiterate figures-of-merit (FoMs) frequently employed to describe the performance of pTX arrays and summarize published array designs in terms of these FoMs. [ABSTRACT FROM AUTHOR]

Simultaneously operating MR-PET systems have the potential to provide synergetic multi-parametric information, and, as such, interest surrounding their use and development is increasing. However, despite the potential advantages offered by fully combined MR-PET systems, implementing this hybrid integration is technically laborious, and any factors degrading the quality of either modality must be circumvented to ensure optimal performance. In order to attain the best possible quality from both systems, most full MR-PET integrations tend to place the shielded PET system inside the MRI system, close to the target volume of the subject. The radiofrequency (RF) coil used in MRI systems is a key factor in determining the quality of the MR images, and, in simultaneous acquisition, it is generally positioned inside the PET system and PET imaging region, potentially resulting in attenuation and artefacts in the PET images. Therefore, when designing hybrid MR-PET systems, it is imperative that consideration be given to the RF coils inside the PET system. In this review, we present current state-of-the-art RF coil designs used for hybrid MR-PET experiments and discuss various design strategies for constructing PET transparent RF coils. [ABSTRACT FROM AUTHOR]

Single-wire power transmission (SWPT) is a power transmission method that uses only one wire to realize long-distance transmission of power. For deep insight, the theory of electromagnetic surface waves in this article is applied to reveal the principle of a long-distance large-scale SWPT system. Maxwell's equations under two different media in this system are established, based on them and the boundary conditions on the interface of the media, the propagation law of electromagnetic field energy in the SWPT system is analyzed. A simulation model is built by high frequency simulator structure (HFSS). The distribution law of the Poynting vector in different situations is studied to verify the correctness of the theoretical analysis. Moreover, long-distance transmission experiments are carried in the campus. It is shown that the transmission power can reach 300 W or 135 W when the transmission distance is 100 m or 200 m, respectively. [ABSTRACT FROM AUTHOR]

The electromagnetic levitation (EML) system serves as a key subsystem in maglev trains for the purpose of levitation. It is highly dynamic, open-loop unstable, and safety-critical. The expense of establishing an accurate model out of the Maglev train, in addition to the varying operating conditions, results in an imperfectly known model in engineering practice. Thus high-performance levitation control, w.r.t. an imperfectly known model, is of considerable practical interest. Motivated by such an observation, this article investigates real-time levitation performance optimization of the EML system, with an imperfectly known model. The EML system is first modeled and an equivalent demonstration benchmark is developed. Then, the structure for levitation performance optimization is presented on top of the coprime factorization technique. Furthermore, the real-time levitation performance optimization algorithm is developed, utilizing only the input and output data. In the end, the proposed methods are validated on the benchmark. [ABSTRACT FROM AUTHOR]

In this article, an iterative optimization algorithm is proposed to design biplanar coils, which is used for dynamic magnetoencephalography to compensate for residual fields in the magnetic shielding room. The effects of magnetic shielding layers and plane’s side length on the uniformity are both considered for designing coils. The iterative calculation is used to minimize the side length of the coil plane. The biplanar coils with 1.3-m side length are designed, which consist of three homogeneous-field coils ($B_{x}, B_{y},\; { \rm and }\; B_{z}\; { \rm coils }$) and five gradient-field coils ($dB_{x}/dy, dB_{x}/dz, dB_{y}/dy, dB_{y}/dz,\; { \rm and }\; dB_{z}/dz\; { \rm coils }$). The coil system can produce homogeneous and gradient fields within 1% error over the volume of 40 cm × 40 cm × 40 cm. Through active magnetic shielding, the central field inside the magnetic room is reduced from 7.56 to 0.17 nT, and standard deviation from the mean value in the target area falls from 1.366 to 0.177 nT. The dynamic auditory stimulation experiment proves that the biplanar coil system will improve the quality of the evoked signals. [ABSTRACT FROM AUTHOR]

Magnetic compensation coils are often used to improve the effectiveness of a magnetically shielded room (MSR), but a distortion of the field is caused by the shielding layer consisting of high-permeability material, which leads to a reduction in compensation capacity. To solve this problem, a new method is presented in this article based on a target-field method, an image method, and particle swarm optimization. By this way, a magnetic compensation system composed of biplanar coils is designed and fabricated to compensate the background field for a wearable magnetoencephalography device inside the MSR, and the coupling effect between the magnetic shielding material and the compensation field is effectively avoided. Experimental data show that these compensation coils produce uniform fields and field gradients with the inhomogeneity of less than 3.8%, consistent with the simulation results. In addition, this system realizes a real-time compensation to the residual field and field gradient in the MSR. [ABSTRACT FROM AUTHOR]

In this article, a switching frequency-modulation-based inductive power transfer system that provides wireless charging of the scooters by magnetic in-band communication is newly proposed. Although the transmitter (Tx) and receiver (Rx) coils are misaligned, the scooters can be freely charged in the charging station by the proposed frequency modulation method without additional power converters in the Tx and Rx sides. In order to implement frequency modulation control, the Rx side can transmit the required information to the Tx side through the magnetic coupling between Tx and Rx coils, i.e., magnetic in-band communication, in the suggested approach. By virtue of the proposed magnetic in-band communication method, the switching frequency can be modulated so that the load power for charging the battery in the Rx side is appropriately controlled, considering the battery charging profile. Contrary to the Qi standard technology using both amplitude shift keying (ASK) and frequency shift keying, the proposed magnetic communication protocol is optimally and simply designed for targeting scooter wireless charging applications. Because the proposed communication method is based on only ASK technique for unidirectional information delivery, the coil misalignment sensitivity and the complexity of the communication process can be reduced, which guarantees the robust frequency modulation control for load power regulation. A 100 W power level prototype for the charging station and the scooters was fabricated and verified by simulations and experiments. The 97.3% of the coil-to-coil efficiency and 90.6% of the dc-to-dc efficiency were obtained at a nominal operating point of k = knom and PL = 100.8 W. As a result, the battery having 44.0–53.0 V and 13 Ah in the Rx side was charged under a wide range of battery charging conditions and coil misalignments. [ABSTRACT FROM AUTHOR]

When a recloser detects fault currents in electric power distribution lines, it breaks the line and then restores the line after several fault tests. To check whether fault remains, the recloser performs CO operations (opening the contacts after reclosing them for a while). In this operation, the fault currents flow into the line, potentially causing damage to equipment connected to the line. Therefore, reducing the current-carrying time during the fault test is desirable, but this reduction is difficult because of the slow actuation mechanism of reclosers. In this article, a novel actuation mechanism combining a permanent magnetic actuator (PMA) and a solenoid actuator (SA) is proposed. During the CO operations for the fault tests, the proposed mechanism can rapidly break the closed contacts by hitting the moving contact with the SA. To increase the energy efficiency of the actuation mechanism, a distinctive PMA driving method is also proposed; it weakens the strong holding force of the PMA using assistive magneto-motive force (MMF). The structure and configuration of the proposed mechanism are explained. The performance of the mechanism and the effectiveness of the driving method are studied through cosimulations. Finally, a prototype is developed, and its practicality is verified through experiments. [ABSTRACT FROM AUTHOR]

In this article, a 2.5m five-stage inductive power transfer (IPT) system based on domino cylindrical solenoid coupler (CSC) compensated, respectively, in layers is proposed. The system is considered to be used as 220 kV post insulators application, transferring power for sensors and measuring instruments of smart grids. The distributed series compensation method is applied to double-layer CSC. Compared with the two types of parallel schemes, this method can significantly reduce the current of the main circuit. Compared with the concentrated series compensation method, this method can effectively reduce the resistance caused by the stray capacitance. The interaction between the post insulator and the magnetic coupling structure is analyzed. The circuit model of the system with constant voltage output characteristics is analyzed. A prototype with a maximum efficiency of 66.7% is built. When the power is transferred to a larger value of 77.8W, the efficiency can still reach 62%. Comparing with previous works, the wireless distance is extended while the efficiency is improved. [ABSTRACT FROM AUTHOR]

For an inductive power transfer (IPT) system, mobility is one of the most attractive features, but coupling variations can dramatically affect the system's output. In this article, a reconfigurable rectifier-based detuned series-series (SS) compensated IPT system is proposed to tolerate an extensive coupling range and improve the system efficiency simultaneously. The reconfigurable rectifier, which can operate in a full-bridge rectifier mode or a half-bridge rectifier mode, is used to alter the equivalent ac load from one value to the other so the expected coupling range of the detuned SS topology can be extended. At the same time, the system efficiency is also partly improved because the ac load is changed to get closer to the optimal load of the IPT system. First, a detuned SS IPT system with the reconfigurable rectifier is presented and followed by the analysis of the working modes. Then, a detailed parameter design process and switching control of the reconfigurable rectifier are introduced. Finally, a 400-W prototype was constructed to verify the validity of the proposed method. The experimental results demonstrate that the output power fluctuation of the proposed IPT system is less than 17.5% and the lowest efficiency can be improved from 68.6% to 87.5% with the coupling coefficient varying from 0.1 to 0.4. The proposed method can implement significant antimisalignment and efficiency improvement simultaneously, and it is regarded as a potential solution for low-power IPT applications with high spatial mobility. [ABSTRACT FROM AUTHOR]

Metal object detection (MOD) is crucial for the safe operation of ground-assembled wireless electric vehicle charging (WEVC) systems. Electromagnetic sensing by passive coils is a reliable MOD method for high-power applications, such as WEVC. Previous designs of sensing coils are mainly targeted at the systems with unpolarized coils (e.g., circular coils). However, they are not suitable for those with DD-coil-coupling engaged due to the fundamentally different field pattern. To fix this problem, in this article, a field-oriented design of sensing coils is proposed, which mainly aims at blind-zone elimination while maintaining high sensitivity and cost-effectiveness. The blind zone arising from axial symmetry of the field is removed by size-modulated C-shape coil units. And removing the central blind spot relies on an extra patch coil by utilizing the characteristic of parallel magnetic flux generated by DD coils. Tested by 13 positions (central blind spot excluded) where MOs might exist using a 3-kW WEVC prototype, the optimized sensing coils completely remove the axial blind zones when 50 mV is set as the threshold voltage. Moreover, for the central blind spot, the proposed patch coil can stably identify MO intrusion no matter if the prototype operates in light-load or heavy-load conditions. [ABSTRACT FROM AUTHOR]

Unwanted cross-couplings greatly hinder the development of double-receiver wireless power transfer (WPT) systems. Whenever the air gap changes or misalignment occurs, cross couplings disrupt the system stability. This article investigates a magnetic coupler for a double-receiver WPT system, which dramatically suppresses the unwanted cross-couplings. Two types of undesirable couplings are significantly reduced by using orthometric DD coils and Q-shaped coils. First, the unwanted couplings between receivers can be eliminated, validated by the measured coupling coefficient kAB = 0.003. Therefore, two receivers can work independently. Second, the unwanted couplings among the source coil and receivers can be eliminated (k1A = 0.003 and k1B = 0.003), resulting in load-independent constant voltage output. Compensation networks can also be designed straightforwardly. In addition, the inverter can achieve zero phase angle, alleviating volt-ampere rating and increasing efficiency. Thanks to the presented structure, this coupler design process is efficient because the decoupling is from the shape rather than turns. Also, it can be easily generalizable to other output voltage or power levels since turns can be changed to meet different charging demands. Validated by a laboratory prototype, experimental results successfully show remarkable agreement with the theoretical analysis, ensuring 72 V load-independent constant output voltages. It also realizes a 90.16% maximum measured overall dc–dc power transfer efficiency with 12 cm air gaps when delivering 518.4 W to two 20 Ω loads. [ABSTRACT FROM AUTHOR]

It is well known that loads of inductive power transfer systems are often energy storage devices. The major benefit of an LCC–LCC compensation topology is that without the additional compensation elements and control methods, the load-independent constant current (CC) and constant voltage (CV) outputs, required by energy storage load, can be achieved at different resonant frequencies. However, the misalignment between two coils at the transmitting and receiving sides is inevitable and can lead to the variation of the resonant frequency in CC or CV output. Therefore, a unique design approach to the LCC–LCC compensation topology is proposed in this article. With the presented method, the resonant frequency, at which load-independent output characteristics can be also implemented, is constant and unaffected by the coupling coefficient, whether in CC mode or CV mode. Furthermore, the transmission gain, which is only impacted by the coupling coefficient, can be conveniently modified by the conventional phase shift control in two modes. Finally, a 120-W prototype is designed to verify the validity of the theoretical analysis. The output current and output voltage fluctuate by only 2.4% and 1.0% in the coupling coefficient range from 0.23 to 0.3 and the large load range, according to experimental results. [ABSTRACT FROM AUTHOR]

Components and circuits encircled by wireless power transfer coils allow miniaturization but require field cancellation for components and circuits that are sensitive to the magnetic field. Very high frequency operation reduces the volume and number of components, which makes encirclement within WPT coils easier. A field cancellation method is investigated to minimize the magnetic field for the encircled circuits in WPT coils using a two-coil structure toward the best cancellation performance, practical construction, and minimum cost. The WPT and canceling coils are driven together by a single current-mode class D power converter with opposite-phase currents to optimize the field cancellation within the coils. Using this cancellation method, the magnetic field for the encircled circuits was reduced by 99% in hardware compared to that without cancellation. [ABSTRACT FROM AUTHOR]

For double-sided LCC compensation topology, it is not easy to maintain the output current and output voltage constant over the variation of coupling coefficient and load. Consequently, in this article, a unique design approach is presented. With the presented method, whether during a constant current output procedure or constant voltage output procedure, the resonant frequency maintains constant and cannot be affected by the coupling coefficient and load condition. In addition, the transmission gain is kept constant in different misalignment by the phase shift modulation. Zero voltage switching with the minimum reactive current can be implemented by the switch-controlled capacitor (SCC) regardless of the coupling coefficient and owing to the constant phasor of the current flowing the SCC, the control system of SCC is greatly simplified. Finally, a 60 W prototype is designed to verify the validity of the theoretical analysis. From the results of the experiment, when the coupling coefficient range is between 0.13 and 0.2, the fluctuation factors of output current and output voltage are only 0.5% and 1.0%, respectively. [ABSTRACT FROM AUTHOR]

With the increased requirements of dynamic wireless charging scenarios, the industry puts forward higher technical specifications for system efficiency. However, the traditional millisecond level response time cannot meet the requirements of dynamic maximum efficiency tracking (MET) system for real-time control. Therefore, this article proposes a wireless power transfer system based on harmonic-informatization, which simplifies the circuit through the harmonic and bandstop filter, so that the mutual inductance can be extracted by harmonic, and then MET can be implemented in real time. Compared with the traditional fundamental system, the harmonic-informatization system has the advantages of no iteration, no communication, and simple calculation. Because the operation of MET under harmonic is simple, the experimental system in this article successfully achieves the microsecond level response time. At the same time, the experiment shows that the system efficiency and power change little after adding the filter, which is due to the low equivalent reactance of the filter under the fundamental. [ABSTRACT FROM AUTHOR]

Encoders and resolvers are the most common position sensors in controlling electrical machines. However, due to their ability to work under harsh conditions, resolvers are more preferred. In linear position detection, the transversal edge effects and the longitudinal end-effects adversely affect the accuracy of conventional linear resolvers. On the contrary, due to the cylindrical symmetry of tubular machines, they are not subject to the edge effects. With this idea, this article presents a novel linear VR resolver with a tubular structure to achieve higher accuracy than the existing linear resolvers. A magnetic equivalent circuit model is then developed to prove the correct performance of the proposed resolver. It is discussed that the proposed resolver is tolerant of mechanical eccentricities. Different configurations are studied, and finite-element analysis is conducted to analyze the resolver's outputs considering longitudinal end-effects and under mechanical eccentricities. The results show the proposed configuration has a robust performance under eccentricities while its accuracy sharply deteriorates due to the longitudinal end effect. Therefore, an effective method is proposed for compensating the longitudinal end effect. Finally, the compensated resolver is experimentally built and tested to verify the success of the developed sensor. [ABSTRACT FROM AUTHOR]

This article introduces a method for efficient and robust free-positioning wireless power transfer (WPT) in a large area, which can be applied to many use cases, including wireless charging of industrial robots, drones, and electric scooters. In these large areas of WPT applications, multiple transmitters (Txs) are placed in a pad-like area, and the Tx coils are optimally excited to enable robust and efficient power transfer to movable receivers within the charging area. The proposed configuration enables almost continuous magnetic flux path from a set of Tx coil(s) to another set of Tx coil(s) through the receiver coil ferrite core. Therefore, efficient power transfer is ensured throughout the whole Tx coverage area. The article introduces a novel method to detect the position and orientation of the receiver only from the Tx-side measurements. The proposed solution is experimentally verified in a laboratory prototype, and the experimental results show dc-to-dc efficiency of 91% with only 1% variation in most of the Rx positions. [ABSTRACT FROM AUTHOR]

In this article, we propose the calculation method of ac copper losses of air-cored axial flux permanent magnet (AFPM) electrical machine with flat wires fed by pulsewidth modulation (PWM) inverters. The ac copper loss due to armature currents in air-cored electrical machines is significant when these machines are driven by PWM inverters. Besides, the exposure of windings to the inhomogeneous alternating rotor magnetic field causes ac copper loss. Analytical formulas are efficient tools to evaluate these losses but few pieces of literature have reported the derivation in such machines. To address this issue, the formulas of aforementioned ac copper losses are derived based on Maxwell's equations and Poynting theorem. As for end windings, the ac copper loss caused by armature current is calculated analytically, while the rotor-induced ac copper loss is calculated by aid of static three-dimensional finite-element analysis (FEA). The interaction of load current and rotor-induced eddy current is also studied. A 12-slot-16-pole air-cored AFPM machine is analyzed with the proposed method, and the analysis is validated by time-transient FEA simulations and prototype experiments. The influence of modulation ratio on ac copper loss due to armature current of the AFPM machine is also discussed. [ABSTRACT FROM AUTHOR]

A demand-customized selective wireless power transfer system is proposed in this article. Multiple receivers can be recognized based on their positions and the magnetic field in the powering area can be controlled and regulated accordingly. For authorized receivers, the system can simultaneously deliver power to meet different output requirements for different electrical appliances, while for unauthorized ones, they can be shut down independently for energy security, even when they are also in the powering area. Compared to the traditional calculation models for multi-input multi-output systems, the proposed current control algorithm uses a piecewise optimization procedure to simplify the iteration and improve control flexibility. Hybrid-frequency pacing is adopted as the control strategy to further reduce the output fluctuation and raise the system efficiency. An experimental prototype with a 3 × 3 transmitter matrix is established. The system can successfully power two receivers with the same sizes for four different power requirement scenarios, which validates the selectivity and the controllability of the proposed system. [ABSTRACT FROM AUTHOR]

For the brushless doubly fed reluctance machine (BDFRM), a composite rotor featuring salient pole reluctance and short-circuited coils (SCC) is applied to efficiently improve the cross-coupling capability and magnetic field modulation effects, where the SCCs induce symmetrical multiphase current and then establish the corresponding additional magnetizing magnetomotive force to modulate the source one. This article investigates the modulation behavior and evaluates the modulation capability of the composite modulator from the perspective of the magnetic field conversion mechanism. The modulated airgap harmonic phase-shift phenomenon in space caused by the SCC modulator is first observed, resulting in the reduction on the effective magnetic field conversion factors in the BDFRM with conventional symmetrical composite rotor. The phase-shift mechanism is revealed for the first time, then an asymmetrical composite modulator configuration is proposed to eliminate the phase shift so as to enhance the rotor cross-coupling capability and improve torque performance. A BDFRM prototype with the asymmetrical composite modulator is designed and manufactured for experimentation. Theoretical predictions are verified by two-dimensional finite-element analysis together with experiments. [ABSTRACT FROM AUTHOR]

In this article, an improved pulse density modulation (PDM) control for secondary side controlled wireless power transfer (WPT) system is proposed. The LCC-S network is selected for the compensation of the reactive power in the system. In the secondary side, an active rectifier with improved PDM control is used to regulate the output voltage. The output voltage regulation is achieved by changing the pulse density of the rectifier switches. By using the proposed PDM pattern, the input pulse sequence of the active rectifier can be distributed more homogenously compared to the conventional PDM control. Therefore, the output current ripple of the primary side inverter and the output voltage ripple of the active rectifier are reduced. The light load efficiency is also improved compared to conventional PDM control. The soft switching conditions are achieved for inverter and active rectifier switches. The experimental prototype with 150 mm air gap is built to validate the performance of the proposed system. The overall efficiency of the system with the proposed PDM is improved by 1.7% and 9.9% compared to the conventional irregular and regular PDM control, respectively. The output voltage ripple of the active rectifier and the output current ripple of the primary inverter are also reduced at light load conditions with the proposed PDM. [ABSTRACT FROM AUTHOR]

Thanks to the absence of rotor windings and permanent magnets, switched reluctance motors have a small weight construction. The integration of a modular power converter in a switched reluctance motor leads to a highly compact and fault-tolerant motor drive with small weight and high power density. In this article, a polygon-retrofitted integration topology is proposed for switched reluctance motors. Both the switched reluctance motor and the power converter are cooled with one shared cooling circuit. The power converter is designed and implemented using silicon carbide technology for its low losses and small thermal resistance. The proposed integration topology is extensively studied using multiphysics modeling and experimental measurements on a fully integrated rotating setup. A highly compact and power dense drive of 3.1 kW/L is obtained. [ABSTRACT FROM AUTHOR]

Losses created by skin and proximity effects can be significant in medium to high-speed ac machine designs. These have been extensively studied for form wound coil machines, but regarding randomly-placed round-wire windings, bundle-level proximity losses have been either neglected, computed via finite element (FE) simulations or estimated analytically by methods that require to know the location of each strand within the slot. This article presents a practical, yet accurate method to estimate bundle-level proximity losses in random-wound ac machines without having to specify the location of each individual conductor. The method consists on approximating the turn size and the arrangement of the conductors within the slot from the overall dimensions of the slot and the winding via simple expressions. This procedure is successfully validated via FE simulations and by constructing and experimentally testing two Interior Permanent Magnet Synchronous Machine prototypes with different winding characteristics. [ABSTRACT FROM AUTHOR]

In this article, a novel radial–axial (RA) flux switching permanent magnet generator (FSPMG) is introduced. In contrast to other RA flux machines, a major advantage of this generator is its implementation only by the use of conventional nonoriented electrical steel sheets, even though the flux linkage of the novel RA-FSPMG has a 3-D path. Besides that, it benefits from the flux concentration strategy and a passive rotor. A concrete foundation of the novel RA-FSPMG is provided, in which, the 3D-Flux path is described, working principles are discussed, and power-sizing equation is derived. No-load characteristics and the full-load performance of an optimized RA-FSPMG are investigated in contrast to an optimized double stator radial FSPMG and an optimized double stator axial FSPMG with similar volume, number of permanent magnets (PMs), and electrical loading. The results show the competitiveness of the novel RA-FSPMG, in particular, in the output power and the required copper mass. Furthermore, the PM demagnetization possibility and the rotor axial pull force of the optimized RA-FSPMG are investigated, in detail. All discussions are supported by the 3-D finite element analysis and experimental results. [ABSTRACT FROM AUTHOR]

The availability of accurate and cost-effective solutions for the real-time monitoring of overhead covered conductors (CC) is now becoming an important tool for the reliability and condition assessments of this class of electrical lines. This is even more crucial due to the possibly large number of conductors and the wide geographical spread of the electrical network. This letter proposes a smart and compact detector for partial discharge (PD) based monitoring, matching the above needs and offering a flexible and cost-effective solution with some important features, including a non-invasive sensing, a field energy harvesting function, and a low-power working operation. The detector has been designed and implemented, proving its effectiveness on real cases involving PD-affected 10 kV CC lines. [ABSTRACT FROM AUTHOR]

Accurate knowledge of the natural frequencies and shapes of corresponding standing waves are essential for gaining deeper insight into the nature of response of coils to impulse excitations. Most of the previous analytical studies on coils assumed shape of standing waves as sinusoidal but numerical circuit analysis and measurements suggest otherwise. Hence, this paper revisits the classical standing wave phenomenon in coils to ascertain reasons for this discrepancy and thereafter extends it by analytically deriving the exact mode shape of standing waves for both neutral open/short conditions. For this, the coil is modeled as a distributed network of elemental inductances and capacitances while spatial variation of mutual inductance between turns is described by an exponential function. Initially, an elegant derivation of the governing partial differential equation for surge distribution is presented which is then analytically solved, perhaps for the first time, by the variable-separable method to find the complete solution (sum of time and spatial terms). Hyperbolic terms in spatial part of solution have always been neglected but are included here, thus, yielding the exact mode shapes. Voltage standing waves gotten from analytical solution are plotted and compared with simulation results on a 100-section ladder network. The same is measured on a large-sized single layer coil. So, it emerges that, even in single layer coils, shape of standing waves deviates considerably from being sinusoidal and this deviation depends on spatial variation of mutual inductance, capacitive coupling, and order of standing waves. [ABSTRACT FROM AUTHOR]

Saturated core fault current limiters are effective means to limit short-circuit currents in high voltage power systems. To solve its problems of a low rate of utilization and large loss, this study proposes a multifunctional saturated-core fault current limiter (MFFCL) with a hybrid excitation system. The MFFCL can limit the short-circuit current and control power flow to reduce losses. The composition and topological structure of the MFFCL are provided, an equivalent electromagnetic circuit model of the MFFCL is then established, and its working mechanisms of limiting current and regulating power flow are analyzed. Following this, a finite-element simulation model of the MFFCL is built to investigate its electromagnetic characteristics and verify its performance in terms of limiting current. The power flow regulation function of the MFFCL was verified through the field-circuit coupling method. Finally, a laboratory-scale prototype of the MFFCL and a test platform was designed to test it. The results of the experiments verified the correctness and feasibility of the proposed structure. It can adequately control power flow in its normal state, and can limit the short-circuit current to 60% of the original in case of a fault. [ABSTRACT FROM AUTHOR]

This article proposes a modular stacked multiport wireless energy interconnection (WEI) system with a virtual ac bus for multisource and multiload wireless power transfer (WPT) applications, which has the following advantages. 1) It can serve as an interface for WPT among multiple sources and loads. 2) Bipolar coils are adopted to eliminate the undesired cross-coupling among multiple coils, which simplifies the complexity of system modeling and power flow control. 3) The relay coil with constant current characteristics is introduced as a virtual ac bus, from which the derived multicoil structure provides the bidirectional channel for power transfer between any two ports. 4) System applicability and scalability are greatly enhanced due to the modularization of coils, power converters, and compensation circuits. For power flow control, the hybrid phase-shifted control method matched with the WEI system is applied, in which the power flow direction is determined by the external phase-shifted angles between ports, whereas the power values are regulated by the internal phase-shifted angles. Furthermore, the peak value of the current of the virtual ac bus, as an intermediate control variable, is controlled to be constant; thus, distributed control can be further realized. Finally, a four-port experimental prototype was built and experiments were carried out under different operating conditions. The efficiency curves and loss distribution, as well as the tolerance analysis of coil misalignments, are given. From the experimental results, the effectiveness of the proposed system architecture and its power flow control strategy is verified. [ABSTRACT FROM AUTHOR]

Conventional high-power wireless power transfer (WPT) systems that are required to deliver power over a wide operating range suffer from issues like hard switching, poor current sharing, and unwanted cross-coupling issues. This article proposes a new resonant inductor integrated-transformer-based multi-inverter to improve the WPT power rating without compromising performance. Viable modulation schemes of the proposed system are analyzed, and a hybrid modulation scheme is proposed for wide-range power regulation. To further investigate the feasibility of the proposed system, the power transfer capacity, current sharing among multiple inverters, and the soft switching regions are studied. A 14-kW LCC–LCC WPT experimental system with three parallel inverters is built, which achieves 93.5% efficiency, demonstrating the high performance of the proposed system. This article is accompanied by a video demonstrating these experiments. [ABSTRACT FROM AUTHOR]

An ideal transformer-like (IT-like) magnetic coupling wireless power transfer system is proposed in this article, which can achieve a large constant power and efficiency output over a wide transfer range. First, the general circuit model is presented along with the analysis of fundamental and harmonic current characteristics. Then, the IT-like operation mechanism with a fixed desired secondary-primary current amplitude ratio independent of mutual inductance is proposed, based on which the transfer range capable of both power and efficiency is greatly improved. The corresponding parameter criteria and implementation methods, including the zero-phase-angle mode and the zero-voltage-switching mode are derived and verified in a practical prototype. The experimental results show that the proposed system can take the output power, transfer efficiency, transfer range, and current characteristic into account at the same time, with strong position robustness and high tolerance to variable couplings. [ABSTRACT FROM AUTHOR]

This article presents a systematic frequency-sweeping based method for fast and accurate determination of mutual coupling coefficient in a series–series wireless power transfer system. The novel contributions involve a sensitivity analysis to evaluate the robustness of the proposed method and an evaluation of several adaptive frequency step functions to minimize detection time with an accuracy of less than 1% error. It is found that the proposed method is the most sensitive when the frequency is swept from the lower frequency boundary in a weakly-coupled system. Several adaptive frequency step functions are evaluated and compared. A power factor reference and an adaptive frequency step function are designed in a systematic way to achieve the dual purposes of minimum detection time and high accuracy. The experimental results obtained from the hardware setups show that the mutual coupling coefficients under a range of conditions can be estimated within 7 ms and with errors typically less than 1.0%. [ABSTRACT FROM AUTHOR]

In automated storage and retrieval systems (ASRS), adopting wireless power transfer (WPT) technology is an available way to avoid the drawbacks of the contact power supply system for multiple stackers. When stackers are dropping goods, it is meaningful to recycle the power generated by the motors and feedback to the other stackers or the ground power supply for improving the overall efficiency of ASRS. This article proposes a bidirectional WPT (BD-WPT) system for multiple receivers. Based on the values of transmission power and the power flow directions of receivers, a general model of the BD-WPT system is established with identifying the system operation modes and their boundaries. To achieve flexible switching among different operation modes and adapt the required transmission power with maximum efficiency point tracking (MEPT), a control strategy of the BD-WPT system is proposed. In the 2-kW experimental prototype built, the power demands can be met in real time, and the power fed back by the stackers can be supplied to other loads or recycled by the ground power supply with good dynamic performance. Compared with the system without MEPT, the efficiency of the proposed system is improved by 26.7% at most, and the maximum efficiency achieves 96.4%. [ABSTRACT FROM AUTHOR]

Hole-edge crack in bolted joints is one of the most critical damages that seriously affect aircraft structural safety. In this article, a novel pentagonal eddy current (EC) sensing array film is proposed to quantify the hole-edge crack parameters. The proposed new sensing film may identify the hole-edge crack angle, depth, and length with fewer layers and eliminate the blind area problem of crack monitoring for the existing sensors at some angles. Finite-element simulation is employed to study the EC distribution around the bolt hole and the interaction between the EC and the crack, which can be used to determine the configuration of the EC array. Both the simulation and the experimental test are conducted to verify the feasibility and effectiveness of the proposed sensing film for quantifying the hole-edge crack angle, depth, and length. [ABSTRACT FROM AUTHOR]

To monitor 3-D position and orientation of a small device having planar receiver (Rx) coil, a switched multicoil transmitter (Tx) antenna is proposed by adopting time-divisional approach. The existing multifrequency methods require eight or more input ports to feed the coils with multifrequency signals for localization. In contrast, the proposed Tx antenna is driven by a single frequency source and uses only three input ports for reduced complexity. Moreover, the multiple coils of the proposed antenna are optimally grouped to form nonuniform magnetic-field distribution using three switches (SWs) in such a manner that better localization accuracy is achieved as compared to the multifrequency design. Rigorous analysis and simulations are performed to investigate the performance of the proposed design and localization approach. To validate the claim, experimental study results proved the potential of the proposed antenna employed for tracking a planar Rx in applications like medical robots, navigation of people with limited vision, virtual reality, etc. [ABSTRACT FROM AUTHOR]

For the International Thermonuclear Experimental Reactor magnets, a significant fraction of the Nb3Sn conductors will be operating at a low field (B < 4 T), such as the outer turns of the central solenoid modules and toroidal field winding packs, while so far, the Ic(B,T, Ɛ) parameterization has been derived from measurements carried out at higher fields (B ≥ 7 T). It may not be accurate enough to adopt this parameterization for the extrapolation of the conductors’ operating performance in terms of critical current (Ic) and current sharing (Tcs). The critical current characteristic can be effectively extended to the lower field region by means of a relation between the magnetization and critical current. The parameterization of the derived critical current scaling law Jc(B) is processed for the field range of the magnetization measurement (0 < B ≤ 9 T) and the critical current measurements (7 ≤ B < 12 T) in order to cover the full range up to 12 T. [ABSTRACT FROM AUTHOR]

This article proposes a low-profile coplanar magnetic coupling resonance wireless power transfer system, which can be expanded segment by segment to power more receivers over a long distance with load-independent constant current output. Due to the low structural profile, it can easily conform to the environment such as desktops, floors, and walls, occupying a small space. By placing low-profile ferrite plates on or under the junctions of adjacent coplanar coils, the main coupling coefficients of the adjacent coils are significantly enhanced, and therefore, the power transmission efficiency (PTE) of the system is greatly improved. With the fixed operating frequency, load-independent current characteristics, simple structure, coplanarity with the environment, good scalability, and high PTE, the system can be easily utilized in various medium and long-range multiload WPT applications. The article describes its principle in detail and clarifies the influence of losses on system performance such as output current characteristics, PTE, and the maximum number of the charging segments. The experimental platform with two and three receivers was established to verify the theory, and the measurement results are in good agreement with the theoretical analysis. The maximum measured PTE reached 93.8% and 93.6% for two and three receivers, respectively. [ABSTRACT FROM AUTHOR]

Utilizing coil inductor of electromagnetic vibration energy harvester (EVEH) to form single stage ac–dc boost converter can make the self-powered milli-power system more compact. However, large output current harmonics of EVEH significantly degraded the output power in such system. This article proposes a new approach of adopting hysteresis current control to realize maximum power point tracking (MPPT) and reduce current harmonics in inductor-less converter by using auxiliary coils. The output characteristics and correlations between multiple coils are firstly studied to verify the feasibility of using auxiliary coil to represent the output of main coil. The optimal winding strategy for main coil and auxiliary coils is revealed for no degradation on maximum output power of main coil. Based upon these, a completely self-powered multicoil EVEH system is designed with auxiliary coils as reference for MPPT controller and as auxiliary power supply in cold-start. Experiments show that the designed prototype can obtain 9.54 mW output power at acceleration of 3 m/s2, with the overall efficiency of 77.6%. To charge a 10 mF supercapacitor from zero to 5 V, an average output power of 7.27 mW can be obtained with an average charging efficiency of 62.4%. In addition, the start-up method adopting auxiliary coil allows the system to cold-start when the output voltage is lower as 0.5 V. The proposed approach has been demonstrated to achieve high overall efficiency in milli-power self-powered EVEH system and also has significant advantages in cost and volume compared with using external devices to obtain reference. [ABSTRACT FROM AUTHOR]

Although the wireless charging system (WCS) achieves flexible power transmission, high system operating performance needs strong anti-misalignment capability and excellent charging controllability. Hence, this article proposes a mistuned WCS that features dual transmission channels using half-bridge inverters, magnetic flux controlled inductors (MFCIs), magnetic couplers with hybrid coils (HMCs), and the series–series compensation. Then, high misalignment tolerance and high-efficient constant power (CP) charging are achieved. First, the interrelation among the mutual inductance, adjustable inductance, load resistance, charging power, and system efficiency is analyzed based on the optimally designed system structure. Second, the circuit structure and working principle of the MFCI are illustrated. Third, the anti-misalignment capability of the optimized HMC is verified by analyzing its coupling characteristics. Then, the relative spatial position between the two HMCs is determined to ensure the negligible cross-coupling influence. In addition, the closed-loop controller's working principle and design method is analyzed to achieve high-efficient and high-controllable CP charging within a wide range of misalignment distance and load resistance. Finally, the experimental results validate the feasibility of the proposed WCS. For CP charging of 150 W, x- and y-direction misalignment ranges reach ±95% and ±47%, and system efficiency exceeds 90%, superior to the commonly used anti-misalignment methods. [ABSTRACT FROM AUTHOR]

The use of multiple transmitters (Txs) has been an attractive solution for enabling free-positioning wireless power transfer (WPT) in a large area. One of the key challenges in such multi-Tx WPT systems is the cross-coupling between Tx coils. This letter proposes a compact self-decoupled Tx coil solution for multi-Tx WPT systems. The measured cross-coupling between Tx coils has been reduced by 95% compared with conventional coil designs. In addition, an integration method for a compensation inductor with the main Tx coil is proposed. Therefore, the coil design proposed in this letter facilitates creation of fully modular and scalable Tx coils for multi-Tx WPT systems. The proposed designs are experimentally verified in a laboratory prototype. [ABSTRACT FROM AUTHOR]

H∞ control can guarantee the performance of a nominal ICPT system. However, the dynamic performance may suffer degradation when the parameter deviates from its nominal value. Thus, to enhance the overall dynamic performance of the ICPT system under parameter perturbations, an H∞ control method with a selected weighting function considering parameter perturbations is proposed in this article. First, a generalized state-space model is established to analyze the influence of parameter perturbations on the open-loop system in detail. After that, an uncertain model is established via frequency-domain analysis, generating a numerical solution of a weighting function used to describe the parameter perturbations. Then, the generalized plant with uncertainty is obtained and transferred into a standard H∞ optimal problem via small gain theory. Based on the proposed controller, the dynamic performance and robustness of the closed-loop system are analyzed and verified theoretically. Finally, simulation and experimental results further verify that the proposed H∞ control method can make the closed-loop system obtain good dynamic performance and strong robustness against parameter perturbations. The settling time is less than 6.8 ms without any overshoot when the system suffers parameter perturbations. Besides, the controller can maintain good dynamic performance in the startup and reference tracking experiments. [ABSTRACT FROM AUTHOR]

The presented experimental method enables the study of the dynamics of a domain wall (DW) moving in bistable microwire in a region of rapidly changing magnetic field. DW velocity versus DW position dependence is obtained in this experiment. Measurements were carried out on Fe77.5Si15B7.5 microwire with strong unidirectional effect in DW propagation. The propagating DW is forced to change its parameters in a very short time, which results in the velocity increasing above its equilibrium value after the DW passes the region of rapid increase in magnetic field. In order to interpret the observed experimental behavior, a simple theoretical model was proposed. Comparison of experimental and model dependences produced a high value of DW inertial mass, indicating that the DW area was much larger than the cross-sectional area of the microwire. Another interesting conclusion was that a DW with stronger damping (shorter wall) does not have a lower value of inertial mass. [ABSTRACT FROM AUTHOR]

This article presents a novel displacement detection method with sensing coils weakly coupled with a conventional eight-pole active magnetic bearing. To improve integration, the sensing coils are completely wound on the magnetic poles of the active magnetic bearing. The proposed method is different from others since each sensing coil is wound around two teeth of an active magnetic bearing, reducing the mutual inductance coefficient between sensing and excitation coils. Thus, the influence of excitation coils on displacement detection can be reduced. A core multiplexing and frequency discrimination method is proposed to detect displacements along ${x}$ - and ${y}$ -directions, simultaneously. Experiment results show that sensitivity along the ${x}$ - and ${y}$ -axes are 8.98 and 5.61 mV/ $\mu \text{m}$ , respectively, showing the feasibility of displacement detection without being affected by displacement variation of the orthogonal axis. Finally, the displacement detected by sensing coils is used for close loop control in an active magnetic bearing system at 2500 rpm, validating the feasibility of sensing coils in active magnetic bearing control. [ABSTRACT FROM AUTHOR]

In this study, a novel design of multiperiod bipolar inductive absolute angle sensor is proposed. The sensor structure is composed of stator and rotor. An inner and outer fan-shaped bipolar pattern is designed and fabricated on the rotor. The receiving coils and signal processing circuits are on the stator. When alternating current is applied to the excitation coil, the eddy current is generated in the rotor. The induced voltage of two adjacent receiving coils is in the form of cosine, when the rotor rotates above the receiving coil. There are two groups of receiving coils in the sensor. One group is composed of eight loops, corresponding to the 45° fan-shaped pattern at the outer edge, and the other group is composed of two loops, corresponding to the 180° fan-shaped (semicircular) pattern at the center. The coil with more loops provides high measurement accuracy and the coil with a small number of loops provides the identification of the number of cycles. The results show that the measurement error is 0.04° and the resolution is better than 0.005° in the range of 0°–360°. Through the multiperiod bipolar pattern proposed in this article, a high accuracy absolute position measurement can be realized. [ABSTRACT FROM AUTHOR]

This article presents a decentralized formation control strategy for electromagnetic formation flight (EMFF). A primary control challenge of EMFF is the coupling that occurs between the electromagnetic fields generated by all satellites. Alternating magnetic field forces (AMFF) are used to address these coupling challenges. Each satellite’s electromagnetic actuation system is driven by a sum of amplitude-modulated sinusoids, where the amplitudes are optimally designed to prescribe the average intersatellite force between each satellite pair while minimizing control effort. The communication structure is a connected undirected graph, where each satellite relies on relative-position and relative-velocity feedback of neighboring satellites. The controller is designed based on an average dynamic model, which is used to provide necessary and sufficient conditions for formation control. [ABSTRACT FROM AUTHOR]

Electric Vehicles are increasingly common, with inductive chargepads being considered a convenient and efficient means of charging electric vehicles. However, drivers are typically poor at aligning the vehicle to the necessary accuracy for efficient inductive charging, making the automated alignment of the two charging plates desirable. In parallel to the electrification of the vehicular fleet, automated parking systems that make use of surround-view camera systems are becoming increasingly popular. In this work, we propose a system based on the surround-view camera architecture to detect, localize, and automatically align the vehicle with the inductive chargepad. The visual design of the chargepads is not standardized and not necessarily known beforehand. Therefore, a system that relies on offline training will fail in some situations. Thus, we propose a self-supervised online learning method that leverages the driver’s actions when manually aligning the vehicle with the chargepad and combine it with weak supervision from semantic segmentation and depth to learn a classifier to auto-annotate the chargepad in the video for further training. In this way, when faced with a previously unseen chargepad, the driver needs only manually align the vehicle a single time. As the chargepad is flat on the ground, it is not easy to detect it from a distance. Thus, we propose using a Visual SLAM pipeline to learn landmarks relative to the chargepad to enable alignment from a greater range. We demonstrate the working system on an automated vehicle as illustrated in the video https://youtu.be/%5fcLCmkW4UYo. To encourage further research, we will share a chargepad dataset used in this work (an initial version of the dataset is shared https://drive.google.com/drive/folders/1KeLFIqOnhU2CGsD0vbiN9UqKmBSyHERd here). [ABSTRACT FROM AUTHOR]

Wireless Power Transfer (WPT) is a promising technology applied in the intelligent transportation infrastructure. This technology can charge electric vehicles dynamically through resonant inductive coupling. The application of WPT is of significance to vehicle-road collaboration. This paper focused on the impact of pavement infrastructure material magnetization on resonant inductive coupling. Here, the experimental analysis was conducted with a Series-Series topological WPT system. Six kinds of pavement materials, including AC-5, AC-13, SMA-5, SMA-13, OGFC-13, and Portland Cement Concrete, were employed as the transfer medium in the shape of rutting plate specimens. The active power and efficiency were recorded by monitoring the voltages and currents on both primary and secondary sides. The experimental analysis revealed the pavement materials changed the active power and efficiency by inductance enhancement and coupling reduction in resonant inductive coupling whose formulae were modified by two influencing factors: the inductance enhancement factor and coupling reduction factor. The influencing factors were varied by pavement materials’ magnetization properties. The influencing factors are useful for adjusting the WPT system’s component parameters to offset the magnetization impact. Moreover, water immersing was considered an environmental impact in the experiments, showing a reduction in the active power and efficiency. The waterproof between pavement layers is also necessary. [ABSTRACT FROM AUTHOR]

A high-density symmetrical transformer based on through-silicon via (TSV) is proposed in this article. The primary winding and secondary winding have strong symmetry, and the inductance mismatch is less than 0.1%, so the transformer structure is suitable for differential circuit. Compared with transformers in other literatures, the proposed transformer has advantages in area and efficiency, which is reflected in that the on-chip area is greatly reduced by 58% to 89%, and the coupling coefficient can reach more than 0.92. [ABSTRACT FROM AUTHOR]