Coaxial Coils Research Articles

Design and experimental investigation of a bi-directional valveless electromagnetic micro-pump

In this paper, a design of a novel electromagnetic micro-actuator prototype is presented. This prototype is fabricated using conventional elements for a novel working principle as bi-directional valveless micro-pump for biomedical applications. The proposed micro-pump includes two unfixed permanent magnets placed in opposite polarities in a cylindrical channel. The channel is placed between two fixed coaxial coils as external electromagnets. The electromagnetic actuating depends on moving both unfixed permanent magnets vertically via the interaction of their magnetic fields and that resulting from coils. The actuation of magnets is produced with a periodic movement and consists mainly of three main modes. By selecting a suitable coil’s driving currents, the actuation can be controlled either to change fluid flow direction or the actuation speed. An experimental test shows the high performance of the proposed micro-pump, a flow rate of 37 ml/mn and maximum back pressure of 1.98 kPa are attained.

Compact pseudoanalytic formulations of coaxial coil antennas in a cylindrically multilayered medium for well‐logging applications

In this study, the authors present a set of compact and no-overflow formulations to calculate the response of logging tools with coaxial coil antennas in a concentric cylindrically multilayered formation. It can be applied to fast forward computation and the inverse problem for electromagnetic well-logging. The tool mandrel can be cylindrically multilayered, and the electrical parameters of each layer are arbitrary. In contrast with previous formulations, they adopt the novel reflection and transmission coefficients in the authors' formulations so that the notorious overflow problem for numerical computation can be obviated. Numerical results in comparison with those from other approaches have demonstrated the validity and stability of their new formulations.

Micro-Power Antenna With Adjustable Q-Factor and Radiation Distribution

This paper has designed a micro-power antenna architecture in which a component-based flexible ferromagnetic core is integrated into a coaxial diameter-distributed coil with twisted loop antenna (DDC-TLA). A stereo-crossed distributed winding method is introduced to reduce the paradise capacitance in the DDC-TLA. The magnetic-core components are made of the mixture of Fe/Citrate nanoparticle composite and polydimethylsiloxane solution, they are filled in a flexible rubber substrate to achieve adjustable permeability and wearable flexibility. Based on the above architecture, an optimized algorithm is proposed to reduce power loss while determining the preferable structure of the DDC-TLA and the suitable ingredients of the magnetic core. Finally, simulations and experiments are conducted to confirm its performance in terms of higher quality factor, lower heat loss, and better signal waveform.

Levitation of a Soft Magnetic Sphere in a Field of Superconducting Coils Simulating an Axially Magnetic Torus

The ponderomotive forces affecting a soft magnetic sphere in a field of superconducting coaxial coils geometrically simulating a torus are investigated. To determine the forces, we used a mathematical model for the fields produced by an axially magnetized torus. The model includes calculating the polarization of the sphere with the averaging of the surface magnetic charges in two hemispheres and determining the forces affecting the effective magnetic charges of the hemispheres located in their centers of gravity. Thus, the model was reduced to a one-dimensional one. The calculations take into account the magnetic saturation of the sphere. The correctness of the dipole approximation of the calculation of the forces is shown. A correlation between the coordinates of the center of the sphere and the characteristic coordinates of the torus field was established. The areas of the stable equilibrium of the sphere are calculated. The applicability of the model is determined. The results of the calculations are compared with the experimental data.

Simulation and Analysis of Three-Dimensional Electromagnetism, Heat Transfer, and Gas Flow for Flow-Levitation System

Magnetic levitation systems are influenced by an intense demand to gain greater feature sizes of metal nanoparticles and to increase the production efficiency for the flow-levitation (FL) method. This paper presents a systematic stability and temperature analysis of the process during the induction heating based on ANSYS. The comprehensive model was a liquid aluminum droplet levitated electromagnetically in an axisymmetric magnetic field induced by different sets of coaxial circular coils. First, we developed an optimized coil with a double helix structure to compare the force applied to the sample, electric field distribution, and temperature distribution in the eddy current field with an initial coil structure. The optimized coil has a more stable and efficient induction heating process for the FL method. We also utilized the optimized coil geometry to predict the maximum parameters of the electromagnetic induction system used to fabricate Al nanoparticles. The results from this approach shows that the turns = 2 + 3, D = 24 mm, I = ∼350 A, d = 1∼2 mm, with an equilibrium coefficient k of 0.30, are the maximum and optimal settings in the frequency of 400 kHz induction heating process.

Design and construction of a quadruple-resonance MAS NMR probe for investigation of extensively deuterated biomolecules

Extensive deuteration is frequently used in solid-state NMR studies of biomolecules because it dramatically reduces both homonuclear (1H-1H) and heteronuclear (1H-13C and 1H-15N) dipolar interactions. This approach greatly improves resolution, enables low-power rf decoupling, and facilitates 1H-detected experiments even in rigid solids at moderate MAS rates. However, the resolution enhancement is obtained at some cost due the reduced abundance of protons available for polarization transfer. Although deuterium is a useful spin-1 NMR nucleus, in typical experiments the deuterons are not directly utilized because the available probes are usually triple-tuned to 1H,13C and 15N. Here we describe a 1H/13C/2H/15N MAS ssNMR probe designed for solid-state NMR of extensively deuterated biomolecules. The probe utilizes coaxial coils, with a modified Alderman-Grant resonator for the 1H channel, and a multiply resonant solenoid for 13C/2H/15N. A coaxial tuning-tube design is used for all four channels in order to efficiently utilize the constrained physical space available inside the magnet bore. Isolation among the channels is likewise achieved using short, adjustable transmission line elements. We present benchmarks illustrating the tuning of each channel and isolation among them and the magnetic field profiles at each frequency of interest. Finally, representative NMR data are shown demonstrating the performance of both the detection and decoupling circuits.

Design of an ICPT system for battery charging applied to underwater docking systems

High power consumption limits the endurance of autonomous underwater vehicles (AUVs). It’s necessary to build a docking station to recover and recharge AUVs underwater. Inductive coupling is a commonly used method for contactless power transmission, which demonstrates superiorities in an underwater environment. In this study, a pair of coaxial and coreless coil structure is proposed for battery charging of the AUV. The performance of an inductive contactless power transfer (ICPT) system in SP topology is analyzed considering the loss of eddy-current in sea water, switching elements and diode-bridge. An appropriate frequency is selected to realize a maximum system efficiency. In the laboratory experiment, the selected topology demonstrates stable properties and realizes a maximum charging power of approximately 300W. The efficiency of the ICPT system varies from 75% to 91% with a total efficiency of 63–77% during the entire charging period.

A Conduction-Cooled Superconducting Magnet System - Design, Fabrication and Thermal Tests

A conduction-cooled superconducting magnet system with an operating current of 105.5 A was designed, fabricated and tested for material processing applications. The magnet consists of two coaxial NbTi solenoid coils with an identical vertical height of 300 mm and is installed in a high-vacuumed cryostat. A two-stage GM cryocooler with a cooling power of 1.5 W at 4.2 K in the second stage is used to cool the system from room temperature to 4.2 K. In this paper, the detailed design, fabrication, thermal analysis and tests of the system are presented.

Magnetic field homogeneity of a conical coaxial coil pair.

An analytical study of the magnetic field created by a double-conical conducting sheet is presented. The analysis is based on the expansion of the magnetic field in terms of Legendre polynomials. It is demonstrated analytically that the angle of the conical surface that produces a nearly homogeneous magnetic field coincides with that of a pair of loops that fulfills the Helmholtz condition. From the results obtained, we propose an electric circuit formed by pairs of isolated conducting loops tightly wound around a pair of conical surfaces, calculating numerically the magnetic field produced by this system and its heterogeneity. An experimental setup of the proposed circuit was constructed and its magnetic field was measured. The results were compared with those obtained by numerical calculation, finding a good agreement. The numerical results demonstrate a significant improvement in homogeneity in the field of the proposed pair of conical coils compared with that achieved with a simple pair of Helmholtz loops or with a double solenoid. Moreover, a new design of a double pair of conical coils based on Braunbek's four loops is also proposed to achieve greater homogeneity. Regarding homogeneity, the rating of the analyzed configurations from best to worst is as follows: (1) double pair of conical coils, (2) pair of conical coils, (3) Braunbek's four loops, (4) Helmholtz pair, and (5) solenoid pair.

Field and inductance calculations for coaxial circular coils with magnetic cores of finite length and constant permeability

A circular coil equipped with magnetic core of finite length and constant permeability is difficult to analyse by traditional analytical methods in consequence of the complicated boundary conditions. The difficulties can be overcome by using the truncated region eigenfunction expansion method, and with the aid of a special source function K ( z ) introduced in the work, this method can be simplified remarkably and concise expressions of the inductance of coils with magnetic cores are obtained. In addition, the calculations can be extended readily to a pair of coaxial coils with magnetic cores of finite length and different permeability. The eigenvalues and inversions of matrices are implemented numerically in the solving process, while most of calculations are accomplished by analytic integrations and matrix algebra, by which the deduced expressions are quite suitable for numerical evaluations. The proposed method is verified by the numerical results compared with those of finite-element method simulations, from which it is confirmed that the proposed method is much faster and more memory efficient.

Reduction of Effect of Concomitant Gradients in Low Magnetic Field MRI via Optimization of Gradient Magnetic System

The effect of concomitant magnetic fields emerging in conjunction with encoding gradients, which is important in the process of the magnetic resonance imaging in low fields, has been considered. The manifestations of concomitant magnetic fields in a concrete gradient system, namely in the system of two coaxial gradient coils, have been thoroughly analyzed. It has been suggested to improve the gradient system via optimization of the interspace between coils on the basis of the standard criterion of the minimum of root-mean-square deviation of the encoding field dependence from a linear one. It has been shown that the optimal interspace is not the Maxwell condition.

Operations on the pancreas using robotic complex - single centre experience

We present measurements of the penetration depth λ(T) in YBa2(Cu1-xNix)3O7(x=.04,..06) and pure YBa2Cu3O7 films obtained from the T dependence of the mutual inductance of two coaxial coils on opposite sides of the films. λ(0) increases by a factor of 5 with 4% Ni and a factor of 10 with 6% Ni. The data are well fitted by the function λ(T)=λ(0)/(1-T2/Tc2)1/2 over the entire temperature range from 7K to Tc, implying at low temperatures λ(T)≈λ(0)(1+αT2/Tc2) with a coefficient α that is independent of nickel concentration.

Design of an electromagnetic prismatic joint with variable stiffness

PurposeThis paper aims to propose an electromagnetic prismatic joint with variable stiffness. The joint can absorb the sudden shocks and improve the natural dynamics of robotics. The ability of regulating the output stiffness can also be used for force control in industrial applications.Design/methodology/approachUnlike some existing designs of variable stiffness joints (VSJs) in which the stiffness regulation is implemented using the stiffness adjustment motor and mechanisms, the main structure of the electromagnetic VSJ is a permanent magnet (PM) arranged inside coaxial cylinder coils. The adjustment of input current can cause the change of magnetic force between the PM and the cylinder coils, and thus leads to the variation of output stiffness.FindingsAccording to the theoretical model, the output stiffness of the electromagnetic VSJ is linearly proportional to the input current. The experiments further indicate that the current-controlled stiffness can make the stiffness variation response of this VSJ more rapid for practical applications. Due to the large damping introduced by the copper-based self-lubrication bearings, the VSJ shows good properties in motion positioning and trajectory tracking.Originality/valueIn summary, the electromagnetic VSJ is compact in size and light in weight. It is possible to realize the online adaptability to work conditions with dynamic load by using this VSJ.

Magnetic dipole in a nonuniform magnetic field

The magnetic moment of a permanent magnet is determined from forces acting on the magnet in nonuniform magnetic fields produced by two coaxial current-carrying coils. Therefore, the measurements are performed under well controllable and reproducible conditions. With a data-acquisition system, the experiments can be done in a reasonably short time. The magnetic moment of the magnet is in good agreement with values obtained by other experimental techniques. The experiment is well suited for undergraduate laboratories.

Calculation of mutual inductance and magnetic force between two thick coaxial Bitter coils of rectangular cross section

The mutual inductance and magnetic force between coaxial Bitter coils with rectangular cross section were recently calculated by some authors using semi-analytical expressions based on two integrations (Ren et al.) and by using the Bessel function approach (Conway). In this study, these important electrical quantities are calculated using the analytical and semi-analytical expressions based on elliptical integrals of the first and second kinds, Heuman's Lambda function, and two simple integrals with their kernel functions continuous on the whole integration interval. Simple Gaussian numerical integration is used. This method can be applied to calculate the mutual inductance and magnetic force between two thin Bitter disk coils (pancakes) as well as between two Bitter coils, where one has a rectangular cross section and the other is a thin disk (pancake). The calculations of the mutual inductances and magnetic forces are validated by comparison with values already published in the literature. The presented approach has advantages of high accuracy and low computational time.

Experimental study on the detection of rabbit intracranial hemorrhage using four coil structures based on magnetic induction phase shift.

Intracranial hemorrhage (ICH) is the bleeding induced by parenchyma vascular rupture. In this paper, four novel coils (a contralateral hemisphere cancellation coil, a coaxial coil, a double-end exciting coil, and a Helmholtz coil) were developed to detect the volume change of ICH with the magnetic induction phase shift (MIPS) technique. Both numerical studies on an ICH model and animal experiments on rabbits' hemorrhage model were performed with four coils. Twenty rabbits were measured for each coil. The animal results were consistent with the simulation and the theoretical analysis for each coil. The MIPS first declined and then increased with increasing injection volume, indicating the existence of a turning point. The MRI images showed that the average CSF decreased in the heads of five rabbits after blood injection was approximately equal to the average injection volume corresponding to the turning point of all animals. Thus, we concluded that when the MIPS turning point occurs, the CSF is already exhausted and the compensatory stage has ended. The results show that the MIPS technique has the potential to detect ICH growth and MIPS changes with increasing blood in a regular way. The turning point is expected to provide an early warning for ICH growth.

Mutual inductance and magnetic force calculations for coaxial bitter disk coils (Pancakes)

Recently Y. Ren and J.T. Conway calculated the mutual inductance and the magnetic force between an ordinary coil and a bitter coil or between two bitter coils. The bitter coil is the coil with inverse radial current density. In this study, the authors calculate the mutual inductance and the magnetic force between two disk coils (pancakes) with inverse radial current density. This coil configuration with proposed current density seems to be similar to bitter coils. Both calculations give the semi-analytical expressions either for mutual inductance or for the magnetic force. Also they derived the self-inductance for the disk coil with radial current density which is obtained in closed form. The results of this method are compared by those obtained by the modified filament method for the presented configuration.

Analysis of inductance calculation of coaxial circular filamentary coils, thin‐wall solenoids, and disk coils using inverse hyperbolic functions

This study presents a method using inverse hyperbolic functions to calculate the mutual and self-inductance inductance of coaxial circular filamentary coils, thin-wall solenoids, disk coils, and coils with rectangular cross-section in air. A generalised expression is given for any combination of these coils, which only requires numerical integration with one variable. Singularities are fully analysed and methods to resolve the singularities are presented in this study. When calculating the self-inductance of a disk coil or a thin-wall solenoid, the proposed method involves an improper integral, and the accuracy of the proposed method is limited unless a quadrature rule applicable to improper integrals is applied. For other situations, results by the proposed method were compared with those in the literature, and they were in excellent agreement.

Automated paleomagnetic and rock magnetic data acquisition with an in-line horizontal “2G” system

Today's paleomagnetic and magnetic proxy studies involve processing of large sample collections while simultaneously demanding high quality data and high reproducibility. Here we describe a fully automated interface based on a commercial horizontal pass-through “2G” DC-SQUID magnetometer. This system is operational at the universities of Bremen (Germany) and Utrecht (Netherlands) since 1998 and 2006, respectively, while a system is currently being built at NGU Trondheim (Norway). The magnetometers are equipped with “in-line” alternating field (AF) demagnetization, a direct-current bias field coil along the coaxial AF demagnetization coil for the acquisition of anhysteretic remanent magnetization (ARM) and a long pulse-field coil for the acquisition of isothermal remanent magnetization (IRM). Samples are contained in dedicated low magnetization perspex holders that are manipulated by a pneumatic pick-and-place-unit. Upon desire samples can be measured in several positions considerably enhancing data quality in particular for magnetically weak samples. In the Bremen system, the peak of the IRM pulse fields is actively measured which reduces the discrepancy between the set field and the field that is actually applied. Techniques for quantifying and removing gyroremanent overprints and for measuring the viscosity of IRM further extend the range of applications of the system. Typically c. 300 paleomagnetic samples can be AF demagnetized per week (15 levels) in the three-position protocol. The versatility of the system is illustrated by several examples of paleomagnetic and rock magnetic data processing.

The improvement of high power impulse magnetron sputtering performance by an external unbalanced magnetic field

High power impulse magnetron sputtering (HIPIMS) is an emerging technique that improves the ionization rate of magnetron-sputtered materials. However, HIPIMS often demands further improvement in the ionization rate in some applications. In this study, we applied an unbalanced magnetic field to enhance the HIPIMS discharge, using a conventional magnetron and a coaxial electro-solenoid coil. Vanadium target discharge currents and substrate ion currents were recorded using a digitizing oscilloscope at different coil currents. The elemental composition and temporal and spatial distributions of argon and vanadium atoms and ions in the high vacuum plasma were measured by optical emission spectroscopy. The results showed that the substrate ion current increased gradually with the coil current over the range 0–6 A, and that a high-density plasma beam was formed between the substrate and target. We explained this effect as the confinement of energetic electrons by the external magnetic field. Total ion production was also increased. Finally, we observed that the line intensities of Ar0, Ar1+, V0, and V1+ increased gradually to varying degrees under the external magnetic field.