Small-sized Coils Research Articles

Multichannel pulse high-current driver of magnetic actuator

Magnetic linear actuators have a wide range of applications. Their main advantage is the ease with which they can be controlled by regulating the current. However, high electrical power is required for obtaining a large continuous force, acceleration, and stroke from a device with small dimensions. In this study, we developed a comprehensive open-source system consisting of simple movable iron magnetic actuators, a four-channel controller, and dedicated software. The graphical user interface facilitates the designing of the sequence of piston strokes, including the start time, duration of movement, and force for each stroke separately. The controller generates a high current of pulses, which allows achieving a high force, acceleration, and stroke from small-sized coils while maintaining a relatively safe voltage. The system was originally designed as a reagent syringe driver to control the rapid mixing process used for studying the kinetics of enzymatic reactions. However, this driver may also be applied in various other scientific as well as nonscientific applications.

A Cross-Shape Coil Structure for Use in Wireless Power Applications

This paper presents a novel coil structure employing two parallel-connected subunit rectangular coils. The structure is based on the fact that the rectangular coils are less sensitive to misalignment along its longer side. Therefore, two identical subunit rectangular coils are vertically-oriented to one another and connected in parallel to form a cross-shape coil. The cross-shape coils have the advantage of better misalignment tolerance as compared to circular and square coils with similar footprints at the cost of an increased wire usage. Electromagnetic simulations and experiments on various small-sized coils are performed to verify the advantages of the proposed coil structure. Based on the simulation and measurement results, cross-shape coils exhibit not only better tolerance to misalignment, but also smaller self-inductance values resulting in larger coupling coefficients as compared to square and circular coils. A large cross-shape coil pair consisting of 100 × 70 cm subunit rectangles are fabricated with copper tubes and utilized in a frequency-tuned wireless power transfer system. When coils are separated by 17 cm, a near constant efficiency of more than 89% up to 15 cm misalignment along x- or y-directions and 13 cm along diagonal direction is obtained in the frequency-tuned system.

Analysis of a Small Charging System for Wearable Devices Based on Magnetic Coupling Resonance

近几年，越来越多的可穿戴设备走进人们的生活。但对大多数可穿戴设备而言，电池续航时间短，充电困难已经成为用户普遍反映的问题，磁耦合谐振无线能量传输技术能够为可穿戴设备提供方便，安全的能量供应。由于可穿戴设备体积小，因此设计一种小尺寸的无线充电系统十分必要。本文通过对谐振线圈进行仿真分析，得到了影响线圈谐振频率的关键设计参数。在此基础上设计出了小小匹配的谐振系统和新型的大小匹配的谐振系统，并且系统中小谐振线圈的体积仅为0.675cm3，能够满足可穿戴设备的体积需求。对两谐振系统的传输效率进行实验分析，结果表明大小匹配的谐振系统具有更好的能量传输性能，在可穿戴设备领域具有良好的应用前景。 As more and more wearable devices come into people’s lives, the short duration of the battery and charging difficulties of wearable devices need more focus. Magnetic coupling resonance wireless energy transmission technology can provide convenient and safe energy supply for wearable devices. Wearable devices are small in size, and it is necessary to design a small size wireless charging system. In this paper, the relationship between coil parameters and resonant frequency are modeled by simulation, and the key parameters are obtained. On the basis of simulation, two systems are designed, one consists of two same small size coils, the other consists of a big size coil and a small size coil, and the volume of the small size coil is only 0.675cm3, it can meet the requirements of wearable devices. In addition, the transmission efficiency of the two systems is analyzed, and the results show that this new system has high transmission performance and a good application prospect in the field of wearable devices.

An Investigation on Eddy Current Pulsed Thermography to Detect Surface Cracks on the Tungsten Carbide Matrix of Polycrystalline Diamond Compact Bit

Polycrystalline diamond compact (PDC) bits are commonly used drill bits in the petroleum drilling industry. Cracks often occur on the surface of a bit, which may result in the unexpected suspension of the drilling operation, or even accidents. Therefore, the detection of surface cracks on PDC bits is of great importance to ensure continuous drilling operation and to prevent accidents. However, it is extremely difficult to detect such cracks by visual inspection or other traditional nondestructive testing (NDT) techniques due to the small size of cracks and the irregular geometry of bits. As one emerging NDT technique, eddy current pulsed thermography (ECPT) can instantly detect surface cracks on metal parts with irregular geometry. In this study, the feasibility of ECPT of detecting surface cracks on the tungsten carbide matrix of PDC bits was investigated. A successive scanning detection mode is proposed to detect surface cracks by using ECPT with a low power heating excitation unit and small-size coils. The influence of excitation duration on the detection result was also investigated. In addition, principal component analysis (PCA) was employed to process the acquired IR image sequences to improve detection sensitivity. Finally, the whole shape of a crack was restored with processed images containing varied cracks segments. Based on the experimental results, we conclude that the surface cracks on the tungsten carbide matrix of PDC bit can be detected effectively and conveniently by ECPT in scanning mode with the aid of PCA.

Characteristic comparison of different resonators to extend transfer distance in superconducting wireless power transfer for electric vehicle using high temperature superconducting resonance coil

AbstractThis paper presents the feasibility of technical fusion between wireless power transfer (WPT) based on resonance coupling system and superconducting technology to improve the transfer efficiency and spread the electromagnetic field widely in spite of small size coils. Until now, the various copper wires have generally been adopted in WPT system. From this reason, the transfer efficiency is limited since the copper wire keeps low Q intrinsically. On the other hand, as superconducting wires keep larger current density and higher Q value, the superconducting resonance coil can be expected as a reasonable option to deliver large transfer power as well as improve the transfer ratio since it exchanges energy at a much higher rate and keeps stronger magnetic fields out. In this study, we examined the transmission ratio using HTS and cooper wires in the antenna (Tx) or/and receiver (Rx) within input power of 500 W under various performances; copper Tx to copper Rx, HTS Tx to copper Rx, copper Tx to HTS Rx...

Proposal and Performance Evaluation of a Magneto-Striction Type Torque Sensor Consisting of Small-Sized Coils Connected in Series

We propose a sensor consisting of small-sized coils connected in series and a detection method for the sensor based on the iteration of the periodic time difference. The evaluation results are also presented and show the effectiveness of the proposed system. The target performance of the sensor is as follows: (i) a detection range from 0 to ±100 Nm, (ii) a hysteresis error of less than 1%, (iii) an angular-dependent noise of less than 2%, and (iv) a sensor drift of less than 2%. From the evaluation results, it is clear that these performance targets, as well as a sufficient response time, are realized.

Magnetic Induction Communications for Wireless Underground Sensor Networks

The main difference between the wireless underground sensor networks (WUSNs) and the terrestrial wireless sensor networks is the signal propagation medium. The underground is a challenging environment for wireless communications since the propagation medium is no longer air but soil, rock and water. The well established wireless signal propagation techniques using electromagnetic (EM) waves do not work well in this environment due to three problems: high path loss, dynamic channel condition and large antenna size. New techniques using magnetic induction (MI) create constant channel condition and can accomplish the communication with small size coils. In this paper, detailed analysis on the path loss and the bandwidth of the MI system in underground soil medium is provided. Based on the channel analysis, the MI waveguide technique for communication is developed in order to reduce the high path loss of the traditional EM wave system and the ordinary MI system. The performance of the EM wave system, the ordinary MI system and our improved MI waveguide system are quantitatively compared. The results reveal that the transmission range of the MI waveguide system is dramatically increased.

An Iterative Periodic Time Difference Detection Method for High Sensitivity Eddy Current Sensor

In this paper, a new non-contacting strain sensing method applying an iterative periodic time difference detection to eddy current sensor is proposed. The iterative periodic time difference detection means that the time difference between zero cross points of sensing coil voltage is accumulated repetitively. Proposed method is characterized as a simple sensor which consists of very small size coils, oscillator circuits, and a microprocessor. Previously, the periodic time difference caused by inductance changes has been detected by a synchronous amplifier, especially a lock-in amplifier. The new method proposed in this paper will be equivalent to the synchronous detection technique, in which the lock-in amplifier is needless. The accumulation can be held by repetitive drive of the oscillator circuit which consists of sensing coil connected to a capacitor in series or parallel. In the experiment, a torque test unit is used, and torque which causes up to 0.2% torsional strain in test pieces is applied. For test pieces, aluminum alloys and a stainless steel with a nonmagnetic characteristic are selected. From experimental results, a linear relation between sensor output and applied torque is observed. And it is shown that the proposed method is effective.

漏れ磁界低減超電導磁石配置における起磁力増加時の特性

Vehicles of superconducting maglev system are suspended and driven by superconducting (SC) coils, which have strong magnetic field, and their passenger cabin must be shielded from leakage flux by the SC coils. In order to reduce the leakage flux, we have studied an improved configuration of SC coils, which has small size coils on its end. This configuration can reduce the environmental magnetic field, so that it can strengthen the magnetomotive force of SC coils. This paper describes the characteristics of levitation, guidance and propulsion performance at strengthening the magnetomotive force on the improved configuration of SC coils.