Coil Resistance Research Articles

Feasibility Study of the Impregnation of a No-Insulation HTS Coil Using Solder

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using solder. NI coils are widely studied and used in many situations. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. Epoxy impregnation is a common method to protect the HTS field from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability. However, traditional epoxy resins are electrical insulating materials which might cause the turn-to-turn contact resistance of NI coils to increase. Therefore, we proposed a new kind of impregnation method using the electrically conductive material, solder. Two coils were fabricated and tested for comparison. One is the NI coil without impregnation and the other is the NI coil impregnated with solder. The charge-discharge and sudden-discharge tests were performed in liquid nitrogen at 77 K. The experimental results were studied with equivalent circuit analyses. The results of this paper could provide useful data for the application of solder impregnated NI HTS coils.

Electromagnetic Microactuators using Non-spiral Planar Microcoils for Robotic Applications

Electromagnetic microactuators offer several advantages for robotic applications such as relatively large stroke and low input voltage requirements. Micro coils are significant components for electromagnetic microactuators for generating force required for micro robots. Non-spiral planar microcoils of square and circular geometries are analyzed here considering the fabrication easiness and low power consumption of non-spiral planar coils. Microfabrication of non-spiral planar coil is simpler and requires a single mask process only. Comparison between non-spiral coils and conventional spiral coils are also discussed. Series resistance of non-spiral coil is found out to be lesser than that of spiral coils though magnetic field is slightly lesser for non-spiral coils. The fabrication advantages and low power dissipation of non-spiral structures make them a strong alternative for conventional spiral planar microcoils. Comparison of different planar microcoils shows that the circular non-spiral coil gives better performance than other coil geometries considered here for robotic applications. Circular coil is found to provide a uniform field with lesser parasitic resistance. Electromagnetic microactuator using non-spiral planar circular and square microcoils are also analyzed to compare the performance between the two coil types. The results show that the force generated using non-spiral circular microcoil in the microactuator is adequate for microrobotic applications with an added advantage of uniform magnetic field provided by the circular coils.

Three-dimensional Simulation and Prediction of Solenoid Valve Failure Mechanism Based on Finite Element Model

The solenoid valve is a kind of basic automation component applied widely. It’s significant to analyze and predict its degradation failure mechanism to improve the reliability of solenoid valve and do research on prolonging life. In this paper, a three-dimensional finite element analysis model of solenoid valve is established based on ANSYS Workbench software. A sequential coupling method used to calculate temperature filed and mechanical stress field of solenoid valve is put forward. The simulation result shows the sequential coupling method can calculate and analyze temperature and stress distribution of solenoid valve accurately, which has been verified through the accelerated life test. Kalman filtering algorithm is introduced to the data processing, which can effectively reduce measuring deviation and restore more accurate data information. Based on different driving current, a kind of failure mechanism which can easily cause the degradation of coils is obtained and an optimization design scheme of electro-insulating rubbers is also proposed. The high temperature generated by driving current and the thermal stress resulting from thermal expansion can easily cause the degradation of coil wires, which will decline the electrical resistance of coils and result in the eventual failure of solenoid valve. The method of finite element analysis can be applied to fault diagnosis and prognostic of various solenoid valves and improve the reliability of solenoid valve’s health management.

Design and Construction of a Mini Hydro Turbine Model

This research is aimed at design and construction of a mini hydro turbine generator that can be made available at the consumer level, so as to improve the generation and availability of power at lower rate without pollution to the environment so as to help boost power generation, quality of power to its power consumers in developing countries. Pelton’s wheel design was used for the turbine research. Water stored in a tank or reservoir at a three meter height contains potential energy, this water is allowed to fall on the turbine wheel which drives the turbine. The potential and kinetic energy available in the water is converted to mechanical energy by rotating the runner connected to the turbine blade. The runner is connected to the rotor part of the alternator (containing the permanent magnet) and the stator (containing the windings) which is kept at permissible air gap to the rotor for effective induction. The voltage is tapped out from the stator as a single phase output, which is used to power household utilities and other machineries which need power supply. The result obtained was gotten from the various tests carried out on this research the tests includes water flow rate test, stator coil resistance test, output voltage test, power quality test and rotational speed test. The output power result shows that domestic power could be generated at individual residential level this will help improve and stabilize the power in the national grid.

Basic Characterization of Magnetocoated Wire Fabricated Using Spray Method

Recently, there has been an increase in the demand for high-efficiency miniature electronic equipment such as personal computers. Therefore, using high drive frequencies and reducing copper loss have become important in meeting the demand. In this paper, we propose the use of magnetocoated wires (MCWs) for coil windings fabricated using the spray method. MCW coils reduce the resistance due to the proximity effect because a magnetic layer leads a magnetic field. As a result, the resistances of the copper wire (COW) and MCW coils at the frequency $f = 2.5$ MHz are 668 and 447 $\text{m}\Omega $ , respectively, which show a reduction of 33% from resistance of COW to MCW. The resistances of the MCW coils at the frequency $f = 20$ kHz and the current $I = 8$ A decreased by 10% compared with the resistances of the COW. The temperature increment of the MCW coils decreased by 5 °C compared with that of COW. This was because MCWs decrease the ac resistance of coils. The magnetic saturation was examined in detail using the finite-element method from the measured value of complex permeability. From the calculated magnetic field and measured magnetization curve, we show the absence of magnetic saturation in coils of nine turns.

Design of PCB search coils for AC magnetic flux density measurement

This paper presents single-layer, double-layer and ten-layer planar square search coils designed for AC magnetic flux density amplitude measurement up to 1 T in the low frequency range in a 10 mm air gap. The printed-circuit-board (PCB) method was used for producing the search coils. Special attention is given to a full characterization of the PCB search coils including a comparison between the detailed analytical design method and the finite integration technique method (FIT) on the one hand, and experimental results on the other. The results show very good agreement in the resistance, inductance and search coil constant values (the area turns) and also in the frequency dependence of the search coil constant.

Simulation, design, and test of an elliptical surface coil for magnetic resonance imaging and spectroscopy

AbstractThe simplest design of surface coils for magnetic resonance imaging (MRI) applications is circular and square loops, both producing a magnetic field perpendicular to the coil plane in the central region‐of‐interest (ROI), with an amplitude that decreases along the coil axis. However, a surface coil constituted by a loop with different geometry could be necessary when particular field‐of‐views (FOVs) are desired, especially for performing imaging in an elongated region. This can be achieved by using an elliptical loop, which can guarantee a wide longitudinal FOV and a good penetration in deep sample regions. This work proposes the application of a method for elliptical coil Signal‐to‐Noise Ratio (SNR) estimation previously developed for circular and square loop design, in which coil inductance and resistance are analytically calculated and the magnetic field pattern is estimated using the magnetostatic approach, while the sample‐induced resistance is calculated with the vector potential calculation method. In the second part of the paper, we propose the simulation and the design of a transmit/receive elliptical coil for MRI in mice with a 3T clinical scanner. We also evaluated the coil performance in a preliminary magnetic resonance spectroscopy (MRS) study in phantom.

A Design Method for Making an LCC Compensation Two-Coil Wireless Power Transfer System More Energy Efficient Than an SS Counterpart

A new design approach is presented in this paper to show that under certain conditions, in a two-coil wireless power transfer system, the double-sided inductor-capacitor-capacitor (LCC) compensated wireless power transfer (LCC-WPT) system can be more energy efficient than the series-series (SS) compensated wireless power transfer (SS-WPT) system for the same load power, with special attention being paid to the effect that the parasitic coil and capacitor resistances have on the system efficiency. To make a fair comparison between the SS and LCC WPT systems, the direct current (DC) link voltage was adjusted to set equal load power for the two systems whilst using identical transmit and receive coils, coil-to-coil distance and load resistance. The system performance in terms of the system efficiency, the voltage stresses on the components, and the losses in the power devices were analysed for a practical system, comparing the LCC-WPT system and the SS-WPT system with respect to the load resistance. The effect of coil misalignment on the transferred power and efficiency for the two systems was compared. The theoretical proof and the conditions for meeting the objective are derived and practically verified in a two-coil WPT practical prototype, showing good agreement between analysis and experiments.

Q-factors of CVD monolayer graphene and graphite inductors

A carbon-based inductor may serve as an important passive component in a carbon-based radio-frequency (RF) integrated circuit (IC). In this work, chemical vapor deposition (CVD) synthesized monolayer graphene and graphite inductors are fabricated and their Q-factors are investigated. We find that the large series resistance of signal path (including coil resistance and contact resistance) in monolayer graphene inductors causes negative Q-factors at the whole frequency range in measurement. Comparatively, some of the graphite inductors have all of their Q-factors above zero, due to their small signal path resistance. We also note that some other graphite inductors have negative Q-factor values at low frequency regions, but positive Q-factor values at high frequency regions. With an equivalent circuit model, we confirm that the negative Q-factors of some graphite inductors at low frequency regions are related to their relatively large contact resistances, and we are able to eliminate these negative Q-factors by improving the graphite-metal contact. Furthermore, the peak Q-factor (Qp) can be enhanced by lowering down the resistance of graphite coil. For an optimized 3/4-turn graphite inductor, the measured maximum Q-factor (Qm) can reach 2.36 and the peak Q-factor is theoretically predicted by the equivalent circuit to be as high as 6.46 at a high resonant frequency, which is beyond the testing frequency range. This research indicates that CVD synthesized graphite thin film is more suitable than graphene for fabricating inductors in carbon-based RF IC in the future.

Spiral Gradient Coil Design for Use in Cylindrical MRI Systems

In magnetic resonance imaging, the stream function based method is commonly used in the design of gradient coils. However, this method can be prone to errors associated with the discretization of continuous current density and wire connections. In this paper, we propose a novel gradient coil design scheme that works directly in the wire space, avoiding the system errors that may appear in the stream function approaches. Specifically, the gradient coil pattern is described with dedicated spiral functions adjusted to allow the coil to produce the required field gradients in the imaging area, minimal stray field, and other engineering terms. The performance of a designed spiral gradient coil was compared with its stream-function counterpart. The numerical evaluation shows that when compared with the conventional solution, the inductance and resistance was reduced by 20.9 and 10.5%, respectively. The overall coil performance (evaluated by the figure of merit (FoM)) was improved up to 26.5% for the x -gradient coil design; for the z-gradient coil design, the inductance and resistance were reduced by 15.1 and 6.7% respectively, and the FoM was increased by 17.7%. In addition, by directly controlling the wire distributions, the spiral gradient coil design was much sparser than conventional coils.

Liquid metal spiral coil enabled soft electromagnetic actuator

Soft robot is a kind of machine form with flexible deformation capability. Making flexible actuators has recently become a hot research topic in the field. In this study, we demonstrated the facile fabrication of a soft electromagnetic actuator using liquid metal coil of Ga-In alloys, and designed several illustrative mechanical devices, such as jellyfish like robot, soft fishtail and flexible manipulator. Measurements of the liquid metal coil’s electrical properties confirmed that the liquid metal coil was mechanically stable under 48% uniaxial strains. Furthermore, the resistance of the liquid metal coil is stable under 60° bending deformation. Tests on the liquid metal coil’s driving properties confirmed that the liquid metal coil (55 mm×55 mm×1 mm) could reach the maximum displacement amplitude of 21.5 mm with the current of 0.48 A. It was shown that the electromagnetic interaction between the magnet and the liquid metal coil enables the coil as a highly efficient actuator. The mechanisms lying behind were interpreted and future applications of such system were discussed.

Investigation of electrical characteristics of no-insulation coil wound with surface-processed HTS tape

This paper deals with the electrical characteristics of no-insulation coil wound with surface-processed HTS tape. The bypassing current path through turn-to-turn contacts within a coil is formed in the no-insulation coil, and this bypassing current path determines two characteristics: 1) self-protection and 2) charge-discharge delay. The amplitude of bypassing current is determined by contact resistance between the turn-to-turn contacts of the no-insulation coil. The surface roughness of the HTS tape is one of the parameters to change the contact resistance. The HTS tapes were processed to roughen by bead blast and abrasive paper, and the no-insulation coil is fabricated using processed HTS tape. We have studied the charge-discharge delay and self-protecting characteristic of each no-insulation coil by 1) sudden discharge tests and 2) overcurrent tests. The FEM simulations of contact resistance of no-insulation coil were carried out. The contact surface resistance of a case processed by abrasive paper has almost three times larger than that of reference no-insulation coil, and a case processed by bead blast presents almost same contact surface resistance with reference no-insulation coil.

A method to assess the loss of a dipole antenna for ultra-high-field MRI.

To describe a new bench measurement based on quality (Q) factors to estimate the coil noise relative to the sample noise of dipole antennas at 7 T. Placing a dipole antenna close to a highly conductive sample surrogate (HCSS) greatly reduces radiation loss, and using QHCSS gives a more accurate estimate of coil resistance than Qunloaded . Instead of using the ratio of unloaded and sample-loaded Q factors, the ratio of HCSS-loaded and sample-loaded Q factors should be used at ultra-high fields. A series of simulations were carried out to analyze the power budget of sample-loaded or HCSS-loaded dipole antennas. Two prototype dipole antennas were also constructed for bench measurements to validate the simulations. Simulations showed that radiation loss was suppressed when the dipole antenna was HCSS-loaded, and coil loss was largely the same as when the dipole was loaded by the sample. Bench measurements also showed good alignment with simulations. Using the ratio QHCSS /Qloaded gives a good estimate of the coil loss for dipole antennas at 7 T, and provides a convenient bench measurement to predict the body noise dominance of dipole antenna designs. The new approach also applies to conventional surface loop coils at ultra-high fields. Magn Reson Med 79:1773-1780, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Network-based energy supply optimal system in the condition where both heating and cooling are required simultaneously in a swing season

ABSTRACTRecent building control models have adopted advanced algorithms to replace conventional controllers to improve the performance of plant or system levels. However, most models used to optimize fuel use or fan speed have several disadvantages to respond to, accurately and promptly, zone-scaled level. This paper proposes network-based controllers utilizing Artificial Neural Network (ANN) in space cooling and heating through the simultaneous control of the amount of supply air and its temperature. Two controllers are developed to evaluate the optimum of supply air conditions for a swing season that requires both moderate heating and cooling and they are compared to conventional thermostat on/off model by using the total control errors and energy consumption for operating damper and resistance coil. The result describes the advantage of the ANN simultaneous control that control errors reduce by 61.5% and energy consumption decreases by 3.5% in comparison with on/off controller. The ANN controller effectively optimizes the supply air conditions to reduce control errors and energy consumption, as they relate to human comfort and energy savings in a swing season.

Improvement in Stability and Operating Characteristics of HTS Coil Using MIT Material

This paper proposes a new method of achieving electrical stability and controllability of a high-temperature superconductor (HTS) coil. The proposed method applied a material with a metal-insulator transition (MIT) property to the turn-to-turn resistance of an HTS coil. As a result, the turn-to-turn resistance remained at the insulator level in the normal state, thus removing delay during charging and discharging. During transient state, the turn-to-turn resistance dropped to the metal level, and current bypass occurs similar to that in a noinsulation coil, thus preventing the coil from burning out. The validity of the MIT characteristic and the proposed method were verified through experiments.

Numerical Investigation of Metal Insulation Technique on Turn-to-Turn Contact Resistance of REBCO Pancake Coils

No-insulation (NI) REBCO pancake coils show high thermal stability, however the charging delay is an issue. Hence, to improve the charging delay, it was proposed that a stainless steel (SUS) tape was cowound between turns, called “metal-as-insulation” or “metal-insulation (MI),” to increase the turn-to-turn contact resistivity. The MI technique could make the turn-to-turn contact resistivity approximately 50 times large compared to a conventional NI REBCO pancake coil. This paper reports a bypass current behavior on the cross section of MI REBCO pancake coil using two-dimensional finite element method. The influence of the SUS tape thickness, the MI material, and the number of SUS tapes on the turn-to-turn contact resistivity is investigated. As the result, it is clarified that the turn-to-turn contact resistivity strongly depends on the surface condition and number of SUS tapes.

Numerical Optimization of the Tube-Cored Induction Magnetometer Weight Under Specific Noise Constraints

The aim of this paper is to achieve the minimum weight for the induction magnetometer (IM) with specific noise constraints. First, a tube magnetic core was used to decrease the weight and achieve a similar magnetic concentrating performance as the rod one. The parameters, including the coil resistance, the inductance, the apparent permeability with different coil-to-core length ratios, and the noise equivalent magnetic induction, were evaluated theoretically. A chopping pre-amplifier circuit was used to suppress the $1/f$ noise in low frequencies. Finally, the optimization problem proposed from the practical applications was solved using the penalty function method (interior point method). To verify the theoretical analysis, the optimal IM was manufactured and tested. The experimental results showed 3.1 pT/ $\surd $ Hz at 1 Hz, noise floor 22 fT/ $\surd $ Hz, and total weight 0.52 kg, which were well coincided with the theoretical calculation. Moreover, the relationships among the noise constraints and the coil weight were also discussed.

Maximization of the extracted power in resonant electromagnetic vibration harvesters applications employing bridge rectifiers

The capability of a resonant electromagnetic vibration harvester to provide power to a load, in given vibration conditions, is usually quantified by considering the power POPT that can be transferred to the harvester optimal impedance. In this paper it is explained that, in presence of a bridge rectifier between the harvester and the DC load, it is instead necessary to consider the power PSUBOPT, that is the power that can be transferred by the harvester to its optimal resistive load. PSUBOPT≤POPT and represents a more accurate estimate of the upper bound of the average power Ptot that can be actually transferred to the load in case a bridge rectifier is placed between the harvester and the DC load. In particular, in this paper it is shown that a bridge rectifier is able to roughly emulate a resistance and hence Ptot<PSUBOPT≤POPT. By means of a suitable theoretical analysis, it is also demonstrated why and how the power that can be transferred to the load by the harvester strongly depends on the value of the DC voltage V0 at the output of the bridge rectifier. Moreover, a closed form estimate of the optimal value V0* of V0 is also provided. Experimental results are also reported and discussed in order to validate the theoretical findings. In particular, a resonant electromagnetic vibration harvester prototype has been used. The values of its main parameters are: resonance frequency 16.2Hz, max output power 0.25mW (at a vibration amplitude equal to 1g), optimal DC voltage 1.2V, coil resistance=5720.4Ω, coil inductance=0.56H.

New Insight of Maximum Transferred Power by Matching Capacitance of a Wireless Power Transfer System

Most research on wireless power transfer (WPT) has been focused on how to achieve a high-efficiency power transfer. Our study found that under the impedance matching for achieving maximum WPT efficiency, the power transferred to the load cannot reach the maximum when a WPT system is supplied by an AC voltage source with constant amplitude. However, the load power or the voltage across the load is essential for a low-power electric device such as the implanted medical device where the transfer efficiency is not the priority to be considered. The paper presents a method for achieving maximum power on the load by matching capacitance in a WPT system with given two-coupled-coils. Three sets of matching capacitances for extreme load power were deduced based on the circuit model considering the coil's resistance, and all these three matching make the WPT system operate at the resonant state. Two sets can make the system achieve the global maximum of load power. One set can make the system achieve the local maximum of load power and reach the power transfer efficiency next to 1. Experimental results verified the theoretical calculations. The results can contribute to the compensation design of a practical WPT system for transferring the maximum power to the load.

A high-Q resonance-mode measurement of EIS capacitive sensor by elimination of series resistance

An EIS capacitive sensor is a semiconductor-based potentiometric sensor, which is sensitive to the ion concentration or pH value of the solution in contact with the sensing surface. To detect a small change in the ion concentration or pH, a small capacitance change must be detected. Recently, a resonance-mode measurement was proposed, in which an inductor was connected to the EIS capacitive sensor and the resonant frequency was correlated with the pH value. In this study, the Q factor of the resonant circuit was enhanced by canceling the internal resistance of the reference electrode and the internal resistance of the inductor coil with the help of a bypass capacitor and a negative impedance converter, respectively. 1% variation of the signal in the developed system corresponded to a pH change of 3.93 mpH, which was about 1/12 of the conventional method, suggesting a better performance in detection of a small pH change.