Asymmetric Coil Research Articles

Magnetic-Field Analysis of the Asymmetric Quadrupole for the FFAG Accelerator

We proposed a quadrupole magnet with an asymmetric coil for a nonscaling fixed-field alternatinggradient (NS-FFAG) accelerator. The proposed magnet has a nonlinear magnetic field with the same geometric characteristics as a conventional quadrupole. This nonlinear magnetic field was confirmed to afford beam stability in a ring-type accelerator. In this paper, a magnetic-field analysis using POISSON SUPERFISH to evaluate the generation of the desired nonlinear magnetic field in the 2D geometry of the asymmetric quadrupole magnet for an electron ring is reported. In addition, the magnetic field of the asymmetric quadrupole is compared with that of a conventional quadrupole in an NS-FFAG accelerator.

Asymmetric Coil Structures for Highly Efficient Wireless Power Transfer Systems

A transmitter coil (TX-coil) as well as a receiver coil (RX-coil) has been designed at 6.78 MHz for magnetic resonant wireless power transfer systems not only to have high efficiency at medium distances, which is comparable to the coil dimensions, but also to provide stable efficiency over the position variation of the RX-coil. For mobile devices, the coils should be compact and have low profile and asymmetric, meaning that TX- and RX-coils have different dimensions. In this paper, TX-coil is designed by adding a small coil in series to achieve high quality factor (Q-factor) as well as relatively uniform magnetic field distribution. On the other hand, the scaling factor is introduced for wire width to design RX-coil with higher Q-factor. As a result, the proposed asymmetric coils reveal improved efficiency and degree of freedom in terms of position variation. This has been verified by measuring the system performance, including a power amplifier, full-wave rectifier, regulator, and load. The proposed TX-coil has size of $200 \times 200 \times 1$ mm3, while the size of the RX-coil is $100\times 100\times0.4$ mm3. The power transfer efficiency is 96% and 39% at the transmission distances of 50 and 300 mm, respectively.

The FapF Amyloid Secretion Transporter Possesses an Atypical Asymmetric Coiled Coil

Gram-negative bacteria possess specialized biogenesis machineries that facilitate the export of amyloid subunits, the fibers of which are key components of their biofilm matrix. The secretion of bacterial functional amyloid requires a specialized outer-membrane protein channel through which unfolded amyloid substrates are translocated. We previously reported the crystal structure of the membrane-spanning domain of the amyloid subunit transporter FapF from Pseudomonas. However, the structure of the periplasmic domain, which is essential for amyloid transport, is yet to be determined. Here, we present the crystal structure of the N-terminal periplasmic domain at 1.8-Å resolution. This domain forms a novel asymmetric trimeric coiled coil that possesses a single buried tyrosine residue as well as an extensive hydrogen-bonding network within a glutamine layer. This new structural insight allows us to understand this newly described functional amyloid secretion system in greater detail.

Design Considerations for Enhanced Coupling Coefficient and Misalignment tolerance Using Asymmetrical Circular Coils for WPT System

In case of misalignment, variation in the coupling coefficient between transmitting and receiving coils employed for wireless power transfer is obvious. During the design process of coil system, assurance of least affected coupling coefficient during misalignment is an important issue and can be addressed through appropriate coil structure. Asymmetrical circular spiral coils with unequal outer diameter and fixed self-inductance exhibits better tolerance to misalignment with the limitation of smaller averaged coupling coefficient. The present paper considers the analytical model of asymmetrical circular spiral coils to investigate the dependency of the coil system dimensions on mutual inductance and coupling coefficient with equal outer diameter. Based on the observations from analytical expressions, simulations are performed through finite element method approach using ANSYS MAXWELL. Outcome of the investigations has been used for the design consideration of coil system, which is less sensitive to the misalignment. Based on the proposed design considerations, experimental setup is developed and tested for the case study of E-Rickshaw with 400 mm outer diameter and 120-mm air gap.

Development of a Short Model of the Superconducting Separation Dipoles D2 for the High Luminosity Upgrade of LHC

The luminosity upgrade of the Large Hadron Collider requires that the new separation/recombination dipoles D2 deliver a field integral of 35 Tm. A design has been developed of a twin dipole generating a magnetic field as high as 4.5 T in apertures of 105-mm and 7.78-m magnetic length. The magnetic field direction is identical in both apertures causing not negligible magnetic cross talk, which could be highly detrimental for the field quality. In order to minimize the cross talk effects a design based on asymmetric coils has been developed in the past years. Recently, the design has achieved a level of maturity allowing the starting of a second phase of development involving the construction of a short model preliminary to prototyping activities. The short model (1.6-m long) has been designed in all aspects and it is presently under construction in industry. The contribution is focused on the design of the short model with emphasis on the mechanical aspects, which includes a novel approach to the integration of coils in the mechanical structure through the use of Al-alloy sleeves.

Electromagnetic Design Study of a 20-T Cos-Theta 2-in-1 Dipole Magnet for High-Energy Accelerators

High-field superconducting magnets are the key components of the high-energy particle accelerators. The Institute of High Energy Physics, Beijing, China, has been working on the related R&D since 2014. In parallel with the baseline R&D roadmap with common coil configuration, preliminary electromagnetic design of a 20-T 2-in-1 dipole magnet with cos-theta configuration has been carried out as an option for the model magnet R&D in future. Totally six layers of coils are required for each aperture of this dipole with the high temperature superconductor for the inner two layers and the low temperature superconductor for the outer four layers. Graded coil design is selected to increase the efficiency of the conductor utilization. For each aperture, the clear bore diameter is 50 mm. Asymmetric coil configuration has been adopted to obtain a good geometrical field quality. After optimization, the field uniformity of 10 -4 within 2/3 of the aperture is achieved. The coil ends of the dipole magnet have also been designed and optimized. The detailed magnetic analysis and the main characteristics of this magnet are presented.

Design of transverse head gradient coils using a layer-sharing scheme

In this paper, a new design for transverse asymmetric head gradient coils is proposed for Magnetic Resonance Imaging (MRI). Unlike the conventional coil designs where the x and y coils are placed onto separate radial layers, the new design has windings for both the x and y coils in each transverse coil layer. The coil performance using the new design was compared with the conventional coils with the same dimensions and constraints. The results showed that the new design can improve coil performance in terms of a lower inductance, lower resistance and a higher figure of merit.

An improved asymmetric gradient coil design for high-resolution MRI head imaging

For head magnetic resonance imaging, local gradient coils are often used to achieve high solution images. To accommodate the human head and shoulder, the head gradient coils are usually designed in an asymmetric configuration, allowing the region-of-uniformity (ROU) close to the coil’s patient end. However, the asymmetric configuration leads to technical difficulties in maintaining a high gradient performance for the insertable head coil with very limited space. In this work, we present a practical design configuration of an asymmetric insertable gradient head coil offering an improved performance. In the proposed design, at the patient end, the primary and secondary coils are connected using an additional radial surface, thus allowing the coil conductors distributed on the flange to ensure an improvement in the coil performance. At the service end, the primary and shielding coils are not connected, to permit access to shim trays, cooling system piping, cabling, and so on. The new designs are compared with conventional coil configurations and the simulation results show that, with a similar field quality in the ROU, the proposed coil pattern has improved construction characteristics (open service end, well-distributed wire pattern) and offers a better coil performance (lower inductance, higher efficiency, etc) than conventional head coil configurations.

An Asymmetric Birdcage Coil for Small-animal MR Imaging at 7T.

The birdcage (BC) coil is currently being utilized for uniform radiofrequency (RF) transmit/receive (Tx/Rx) or Tx-only configuration in many magnetic resonance (MR) imaging applications, but insufficient magnetic flux (|B1|) density and their non-uniform distribution still exists in high-field (HF) environments. We demonstrate that the asymmetric birdcage (ABC) transmit/receive (Tx/Rx) volume coil, which is a modified standard birdcage (SBC) coil with the end ring split into two halves, is suitable for improving the |B1| sensitivity in 7T small-animal MR imaging. Cylindrical SBC and ABC coils with 35 mm diameter were constructed and bench tested for mouse body MR imaging at 300 MHz using a 7T scanner. To assess the ABC coil performance, computational electromagnetic (EM) simulation and 7T MR experiment were performed by using a cylindrical phantom and in vivo mouse body and quantitatively compared with the SBC coil in terms of |B1| distribution, RF transmit (|B1+|) field, and signal-to-noise ratio (SNR). The bench measurements of the two BC coils are similar, yielding a quality value (Q-value) of 74.42 for the SBC coil and 77.06 for the ABC coil. The computational calculation results clearly show that the proposed ABC coil offers superior |B1| field and |B1+| field sensitivity in the central axial slice compared with the SBC coil. There was also high SNR and uniformly distributed flip angle (FA) under the loaded condition of mouse body in the 7T experiment. Although ABC geometry allows a further increase in the |B1| field and |B1+| field sensitivity in only the central axial slice, the geometrical modification of the SBC coil can make a high performance RF coil feasible in the central axial slice and also make target imaging possible in the diagonal direction.

Asymmetric gradient coil design for use in a short, open bore magnetic resonance imaging scanner

A conventional cylindrical whole-body MRI scanner has a long bore that may cause claustrophobia for some patients in addition to being inconvenient for healthcare workers accessing the patient. A short-bore scanner usually offers a small sized imaging area, which is impractical for imaging some body parts, such as the torso. This work proposes a novel asymmetric gradient coil design that offers a full-sized imaging area close to one end of the coil. In the new design, the primary and shielding coils are connected at one end whilst separated at the other, allowing the installation of the cooling system and shim trays. The proposed coils have a larger wire gap, higher efficiency, lower inductance, less resistance and a higher figure of merit than the non-connected coils. This half-connected coil structure not only improves the coils’ electromagnetic performance, but also slightly attenuates acoustic radiation at most frequencies when compared to a non-connected gradient coil. It is also quieter in some frequency bands than a conventional symmetric gradient coil.

High slew-rate head-only gradient for improving distortion in echo planar imaging: Preliminary experience.

To investigate the effects on echo planar imaging (EPI) distortion of using high gradient slew rates (SR) of up to 700 T/m/s for in vivo human brain imaging, with a dedicated, head-only gradient coil. Simulation studies were first performed to determine the expected echo spacing and distortion reduction in EPI. A head gradient of 42-cm inner diameter and with asymmetric transverse coils was then installed in a whole-body, conventional 3T magnetic resonance imaging (MRI) system. Human subject imaging was performed on five subjects to determine the effects of EPI on echo spacing and signal dropout at various gradient slew rates. The feasibility of whole-brain imaging at 1.5 mm-isotropic spatial resolution was demonstrated with gradient-echo and spin-echo diffusion-weighted EPI. As compared to a whole-body gradient coil, the EPI echo spacing in the head-only gradient coil was reduced by 48%. Simulation and in vivo results, respectively, showed up to 25-26% and 19% improvement in signal dropout. Whole-brain imaging with EPI at 1.5 mm spatial resolution provided good whole-brain coverage, spatial linearity, and low spatial distortion effects. Our results of human brain imaging with EPI using the compact head gradient coil at slew rates higher than in conventional whole-body MR systems demonstrate substantially improved image distortion, and point to a potential for benefits to non-EPI pulse sequences. J. Magn. Reson. Imaging 2016;44:653-664.

Peripheral nerve stimulation characteristics of an asymmetric head‐only gradient coil compatible with a high‐channel‐count receiver array

To characterize peripheral nerve stimulation (PNS) of an asymmetric head-only gradient coil that is compatible with a commercial high-channel-count receive-only array. Two prototypes of an asymmetric head-only gradient coil set with a 42-cm inner diameter were constructed for brain imaging at 3T with maximum performance specifications of up to 85 mT/m and 708 T/m/s. Tests were performed in 24 volunteers to measure PNS thresholds with the transverse (x = left-right; y = anterior-posterior [A/P]) gradient coils of both prototypes. Fourteen of these 24 volunteers were also tested for the z-gradient PNS in the second prototype and were scanned with high-slew-rate echo planar imaging (EPI) immediately after the PNS tests. For both prototypes, the y-gradient PNS threshold was markedly higher than the x-gradient threshold. The z-gradient threshold was intermediate between those for the x- and y-coils. Of the 24 volunteers, only two experienced y-gradient PNS at 80 mT/m and 500 T/m/s. All volunteers underwent the EPI scan without PNS when the readout direction was set to A/P. Measured PNS characteristics of asymmetric head-only gradient coil prototypes indicate that such coils, especially in the A/P direction, can be used for fast EPI readout in high-performance neuroimaging scans with substantially reduced PNS concerns compared with conventional whole body gradient coils. Magn Reson Med 76:1939-1950, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

A Method for Reducing Secondary Field Effects in Asymmetric MRI Gradient Coil Design.

This research introduces an original method for the design of MRI gradient coils that reduces secondary field effects created by eddy current coupling. The method is able to deal with asymmetric coils and provides a new way to ensure a reduction in the magnitude of the eddy current induced fields. New constraints are introduced at the surface of passive objects to bind the normal field component below a given value. This value is determined by first treating the passive surface as an active surface, and then, calculating the ideal stream function on that surface to produce the desired secondary field. Two coils were designed, one to image the knee and the other to image the head and neck. The secondary field was analyzed using linear regression and was found to improve the secondary field from 10.41 to 0.498 mT/m and from 7.84 to 0.286 mT/m in the examples used. The power loss in the passive structure also decreased to below 1% of the original value using the new method. The method shows the ability to constrain the field to values below the minimum seen under the traditional approaches. This will allow the design of asymmetric systems with highly linear, reduced magnitude of secondary fields and may lead to better image quality.

Some Particularities of EC Crack Detection in Aluminum using an Asymmetrical GMR-Coil Configuration

This paper presents experimental results related to an asymmetrical coil - GMR configuration for the detection of surface cracks using eddy currents. The system is evaluated for three different excitation frequencies and the relationship between the extracted parameter (DV) from the GMR output voltage and the crack's dimension is validated. The analysis of the presence of the intermediate peak in the output voltage of the GMR sensor is performed. The stability of the excitation current source is presented and it is demonstrated that the presence of the intermediate peak does not have a significant influence on the relationship of DV with the depth of the crack.

Asymmetric Coil Sets for Wireless Stationary EV Chargers With Large Lateral Tolerance by Dominant Field Analysis

Asymmetric coil sets for wireless stationary electric vehicle (EV) chargers, which has significantly larger lateral tolerance than previous ones, is proposed. The pick-up coil set is much smaller than the power supply coil set, thereby allowing large lateral and longitudinal displacements as well as robustness to air-gap displacement. Electromagnetic field (EMF) is reasonably reduced by arranging magnetic poles along the EV's moving direction so that alternating magnetic flux through adjacent poles cancels each other. A dominant field analysis useful for complex vector magnetic flux simulation is newly proposed, which is applicable to any resonating coils of an inductive power transfer system (IPTS). Furthermore, a hysteresis loss model is suggested, which appropriately reflects the partial core saturation on a system analysis. A prototype IPTS including the proposed coil sets were designed and successfully verified by experiments. In the quick charging mode, maximum output power of 15 kW, large lateral displacement of 40 cm, longitudinal displacement of 20 cm, air gap of 15 cm were achieved, and low EMF of 6.1 μT at 20 kHz was achieved in the normal charging mode of 5 kW.

Algebraic method to synthesize specified modal currents in ladder resonators: Application to noncircular birdcage coils.

Detectors such as birdcage coils often consist of networks of coupled resonant circuits that must produce specified magnetic field distributions. In many cases, such as quadrature asymmetric insert body coils, calculating the capacitance values required to achieve specified currents and frequencies simultaneously is a challenging task that previously had only approximate or computationally inefficient solutions. A general algebraic method was developed that is applicable to linear networks having planar representations such as birdcage coils, transverse electromagnetic (TEM) coils, and numerous variants of ladder networks. Unlike previous iterative or approximate methods, the algebraic method is computationally efficient and determines current distribution and resonant frequency using a single matrix inversion. The method was demonstrated by specifying irregular current distributions on a highly elliptical birdcage coil at 3 Tesla. Measurements of the modal frequency spectrum and transmit field distribution of the two specified modes agrees with the theory. Accuracy is limited in practice only by how accurately the matrix of self and mutual inductances of the network is known. The algebraic method overcomes the inability of the existing inductance equalization method to account for all elements of the inductance matrix and the inability to accommodate modal currents that are not (co)sinusoidal.

Study on the Transmission Efficiency of Wireless Charging System using Asymmetrical Flat Spiral Coil

This paper represents the research finding of wireless electric power transmission using same or different outer diameter flat spiral coil. The coupling factor, transmission power and transmission efficiency of asymmetrical coil which has same inner diameter but different turn numbers was compared with symmetrical coil which has same inner diameter and same turn numbers. In the application of wireless electric power transmission for electric assisted bicycles, small size diameter coil (less than ø10 cm) is more suitable than large size diameter coil (larger than ø50 cm), therefore, a small size coil is used. In the results, an electric power transmission by using asymmetrical coil was found the same as that of symmetrical coil. However, the distance for power transmission by asymmetrical coil was found smaller than symmetrical coil. When a secondary battery was connected with wireless power transmission as a load, the apparent resistance of secondary battery had influence on charging rate. This resistance change was used for battery charging apparatus instead of feedback control.

Long range inductive power transfer system

We report upon a recently developed long range inductive power transfer system (IPT) designed to power remote sensors with mW level power consumption at distances up to 7 m. In this paper an inductive link is established between a large planar (1 × 1 m) transmit coil (Tx) and a small planer (170 × 170 mm) receiver coil (Rx), demonstrating the viability of highly asymmetrical coil configurations that real-world applications such as sensor networks impose. High Q factor Tx and Rx coils required for viable power transfer efficiencies over such distances are measured using a resonant method. The applicability of the Class-E amplifier in very low magnetic coupling scenarios and at the high frequencies of operation required for high Q operation is demonstrated by its usage as the Tx coil driver.

Bilaterale 23Na-MR-Bildgebung der Mamma und Quantifizierung der Natriumkonzentration

A novel setup for 23Na MRI, which allows bilateral imaging of the breast, is presented. For this purpose a figure-eight receive-only 23Na surface coil was developed. For our experiments on three samples with NaCl solutions of different sodium concentrations and two female subjects we used an asymmetric birdcage coil in transmit mode and the developed surface coil for receiving the signal at 3T. Imaging of the samples showed the applicability of the employed normalization method for measuring the distribution of sodium concentration. In a sample of concentration [Na+]=51mM we achieved SNR=70 at a nominal isotropic resolution of 2,5mm (TR=66ms, TE=0,6ms, TA=20min). Furthermore we showed that by means of this setup it is possible to quantify the sodium concentration in breast tissue (TSC) of a female subject with an accuracy of 23% (TR=150ms, TE=0,5ms, TA=45min).

Potentialities of an Electro-Optic Crystal Fed by Nuclear Magnetic Resonant Coil for Remote and Low-Invasive Magnetic Field Characterization

In this paper, we demonstrate the use of a LiTaO3 crystal associated with a typical nuclear magnetic resonant loop coil to perform an optically remote radio frequency magnetic-field characterization. The whole transduction scheme is theoretically and experimentally studied. The measurement dynamics reaches 60 dB. The minimum detectable magnetic field is lower than 1 nT, which corresponds to an induced inner crystal electric field as low as 30 mV/m. To evaluate the spatial potentialities of the sensor, a 1-D mapping of the field along an asymmetric butterfly-shaped loop coil is performed. The result is in good agreement with finite-difference time-domain simulations and demonstrates the vectorial behavior of the sensor device.