Single-coil Configuration Research Articles

Multi-Objective Optimization Design and Performance Comparison of Magnetorheological Torsional Vibration Absorbers of Different Configurations.

The purpose of this study is to provide a convenient optimization design method for magnetorheological torsional vibration absorbers (MR-TVA) suitable for automotive engines, which is a damper matching design method that takes into account the needs of the engine operating conditions. In this study, three kinds of MR-TVA with certain characteristics and applicability are proposed: axial single-coil configuration, axial multi-coil configuration and circumferential configuration. The magnetic circuit model, damping torque model and response time model of MR-TVA are established. Then, under the constraints of weight, size and inertia ratio, according to different torsional vibration conditions, the MR-TVA mass, damping torque and response time are multi-objective optimized in two directions. The optimal configurations of the three configurations are obtained from the intersection of the two optimal solutions, and the performance of the optimized MR-TVA is compared and analyzed. The results show that the axial multi-coil structure has large damping torque and the shortest response time (140 ms), which is suitable for complex working conditions. The damping torque of the axial single coil structure is generally large (207.05 N.m), which is suitable for heavy load conditions. The circumferential structure has a minimum mass (11.03 kg) and is suitable for light load conditions.

Analysis of the Early Quench Development in JT-60SA Toroidal Field Coils Tested in the Cold Test Facility

The toroidal field system of the JT-60SA tokamak is composed of 18 NbTi superconducting coils. Each TF coil is composed of six cable-in-conduit conductor lengths, wound in double-pancakes, and carrying a nominal current of 25.7 kA. These coils are being tested in the single-coil configuration at the so-called cold test facility (CEA/IRFU, Saclay, France). The test program includes for all coils a quench test at nominal current obtained by a progressive increase of the operating temperature at helium inlet up to quench (around 7.5 K). Thanks to the accuracy of the voltage measurements, it has been possible to follow the very early development of the quench at the scale of a few millimeters normal length. The paper presents the evolution of the resistive voltages measured on eight coils before the safety discharge is triggered. In addition, this early quench development over one conductor length was also simulated using the THEA code with relevant boundary conditions. Two different quenches, which occurred on two different coils, were analyzed, one starting on a central pancake (peak magnetic field) and the other starting on a side pancake (warmer conductor due to heat transfer from the casing). The simulations show good agreement with experiments, stressing particularly three phases in the quench development clearly identified in the measured resistive voltages of all coils.

Simultaneous bilateral‐knee MR imaging

To demonstrate and evaluate the scan time and quantitative accuracy of simultaneous bilateral-knee imaging compared with single-knee acquisitions. Hardware modifications and safety testing was performed to enable MR imaging with two 16-channel flexible coil arrays. Noise covariance and sensitivity-encoding g-factor maps for the dual-coil-array configuration were computed to evaluate coil cross-talk and noise amplification. Ten healthy volunteers were imaged on a 3T MRI scanner with both dual-coil-array bilateral-knee and single-coil-array single-knee configurations. Two experienced musculoskeletal radiologists compared the relative image quality between blinded image pairs acquired with each configuration. Differences in T2 relaxation time measurements between dual-coil-array and single-coil-array acquisitions were compared with the standard repeatability of single-coil-array measurements using a Bland-Altman analysis. The mean g-factors for the dual-coil-array configuration were low for accelerations up to 6 in the right-left direction, and minimal cross-talk was observed between the two coil arrays. Image quality ratings of various joint tissues showed no difference in 89% (95% confidence interval: 85-93%) of rated image pairs, with only small differences ("slightly better" or "slightly worse") in image quality observed. The T2 relaxation time measurements between the dual-coil-array configuration and the single-coil configuration showed similar limits of agreement and concordance correlation coefficients (limits of agreement: -0.93 to 1.99 ms; CCC: 0.97 (95% confidence interval: 0.96-0.98)), to the repeatability of single-coil-array measurements (limits of agreement: -2.07 to 1.96 ms; CCC: 0.97 (95% confidence interval: 0.95-0.98)). A bilateral coil-array setup can image both knees simultaneously in similar scan times as conventional unilateral knee scans, with comparable image quality and quantitative accuracy. This has the potential to improve the value of MRI knee evaluations. Magn Reson Med 80:529-537, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Magnetically actuated transport of ferrofluid droplets over micro-coil array on a digital microfluidic platform

Magnetic manipulation of liquid droplets in microfluidic environment offers a promising tool for sample handling in lab-on-chip devices. Biofunctionalized ferrofluid droplets can effectively carry a measured volume of analytes or reagents on a flat microfluidic platform, executing key tasks of a micrototal analysis system (μ-TAS). However, achieving precise control using on-chip miniaturized magnetic coils is challenging and requires delicate combination of operating parameters, e.g., magnetizing current and timing of switching, fluid viscosity, droplet size, etc. Here we present a numerical analysis of magnetic manipulation of an immiscible, microliter-scale ferrofluid droplet over a thin aqueous film on a solid substrate using embedded micro-electromagnet coils. The numerical model is first validated against the experimentally observed droplet trajectory in a simple, single-coil configuration. Subsequently, two-dimensional manipulation of the ferrofluid droplets on the liquid film is predicted numerically when the magnetic field is produced by a sequentially switched array of square spiral microelectromagnets. By adjusting the operating parameters, we show that the droplet can be moved in predefined meandering path over an active substrate area. The transport is broadly classified into viscosity- and inertia-influenced regimes. Transport time of the droplet for the viscous regime is expressed in terms of a generalized group-variable involving the operating parameters. The study is important for selecting the design bases for a magnetically manipulated sample handling system for digital microfluidic platforms.

Design, Assembly, and Test of the CERN 2-m Long 11 T Dipole in Single Coil Configuration

The upgrade of the LHC collimation system includes additional collimators in the LHC lattice. The longitudinal space for the collimators can be obtained by replacing some LHC main dipoles with shorter but stronger dipoles compatible with the LHC lattice and the existing powering circuits, cryogenics, and beam vacuum. A joint development programme aiming at building a 5.5 m long two-in-one aperture Nb 3 Sn dipole prototype suitable for installation in the LHC is being conducted by FNAL and CERN. As part of the first phase of the programme, 1 m and 2 m long single aperture models are being built and tested. Later on, the collared coils from these models will be assembled and tested in a two-in-one aperture configuration in both laboratories. A 2 m long practice model made of a single coil wound with Nb 3 Sn cable, MBHSM101, was developed and constructed at CERN. It has been completed, and tested at both 4.3 K and 1.9 K. This practice model features collared coils based on removable pole concept, S2-glass cable insulation braided over a mica layer, and coil end spacers made of sintered stainless steel with springy legs. The paper describes the main features of this practice model, the main manufacturing steps and the results of the cold tests.

A practical method for 2D multiple‐animal MRI

To investigate practical methods for achieving routine simultaneous 2D MRI of multiple animals in large-bore experimental scanners. Three four-element array geometries were compared against a standard single-coil configuration in terms of image quality, ease of use, and data efficiency using a four-channel, 4.7 T small animal imaging system. A linear arrangement of volume resonators permits unobstructed animal preparation and use of an imaging protocol that is almost identical to the single-coil configuration without requiring any image correction or other additional postprocessing. Resulting in vivo images were visually indistinguishable from those acquired through the single-coil configuration. The efficiency of animal studies employing 2D MRI techniques can be substantially improved by using a linear array of commercially available resonators.

Feasibility of multiple‐mouse dynamic contrast‐enhanced MRI

Dynamic contrast-enhanced (DCE-) MRI is often used to evaluate the response to experimental antiangiogenic therapies in small animal models of cancer. Unfortunately, DCE-MRI studies often require a substantial investment of both time and money to achieve the desired level of statistical significance. Multiple-mouse MRI has previously been used to improve imaging efficiency, but its feasibility for DCE-MRI has not been investigated. The purpose of this work was to determine if multiple-mouse DCE-MRI is feasible when using gadolinium-based contrast agents with a low molecular weight. A population of tumor-bearing mice was scanned using two four-element arrays and a single-coil configuration on a 4.7T, 40 cm bore Bruker Biospec MRI scanner. Pharmacokinetic parameters were calculated and compared to determine if a significant difference between methodologies existed. With both four-animal imaging configurations, animal throughput accelerations of just less than three were achieved and quantitative data were not significantly different than from single-animal acquisitions.

Numerical simulation of the equilibrium and transport of a centrifugally confined plasma

A centrifugally confined plasma utilizes centrifugal forces from supersonic plasma rotation to augment the conventional magnetic confinement of fusion plasmas. Appropriately used, plasma pressure can be contained along the magnetic field lines, allowing for “open” configurations, introducing flexibility in design. The axisymmetric equilibrium of one such system, a single coil configuration, is investigated numerically. Plasma “detachment” is shown at Mach numbers ranging from 3 to 4. It is also shown how flow shear heats the plasma by viscous dissipation. Profiles relaxed with respect to plasma transport are shown.

Very high resolution measurement of the penetration depth of superconductors by a novel single-coil inductance technique

We describe a novel single-coil mutual inductance technique for measuring the magnetic penetration depth λ of superconductors at 2–4 MHz as a function of temperature in the 4–100 K range. We combine a single-coil configuration with a high-stability marginal oscillator; this enables us to measure the absolute value of λ on both bulk samples and thin films with very high resolution (δλ=10 pm) and a precision of 30 nm. As example of application, we report measurements on NbTi bulk samples and Nb films. This contactless technique is suited for probing the superconducting properties of samples over large surfaces.

The surface-coil NMR receiver in the presence of homogeneous B 1 excitation

The signal intensity and inherent spatial localization in a single-pulse steady-state experiment using a circular surface receiver coil in the presence of a homogeneous rf excitation magnetic field ( B 1) is examined theoretically by computer simulation assuming zero interaction between the transmission-coil and the surface-coil radiofrequency circuits. The theoretical analysis is verified by NMR experiments employing appropriate “phantom” samples with the surface coil orthogonal to the transmitter coil to minimize interaction between the two. Under slow pulse repetition conditions the signal intensity of the homogeneous B 1 transmission-surface-coil reception experiment is essentially the same as that obtained in the single-coil configuration surface-coil experiment and is independent of the orientation of the homogeneous B 1 with respect to the surface coil. A significant consequence of this result is that the optimum performance of multiple-pulse sequences which require specific flip angles over the whole sample should be attained while retaining the spatially restrictive sensitivity profile of the surface coil. The homogeneous B 1 transmission-surface-coil reception sensitive volume penetrates deeper into the sample than the surface-coil single-coil configuration sensitive volume, and therefore may be a more appropriate shape for in vivo NMR spectroscopy. The homogeneous B 1 transmission actually induces more xy magnetization than surface-coil transmission does, but differences in signal phase from different regions of the sample result in an incoherent addition when the signal from all parts of the sample are summed together. In imaging experiments, each volume element of the sample is uniquely characterized by its Larmor frequency and phase, thus, signal reduction due to phase differences is absent.