A novel high-gradient permanent magnet for the profiling of planar films and coatings.

The design and construction of a low-cost, permanent magnet is described. The magnet is intended for applications which require a large static gradient, such as those for which stray field imaging or fringe field diffusometry are conventionally employed. The magnet has been designed using the scalar potential method. Particular features of the magnet include a field profile such that ||B || is constant in the horizontal plane and such that B is horizontal at the midpoint between the poles. There is a vertical, and therefore orthogonal, strong gradient, G, in ||B ||. The ratio G/ ||B || is constant within a large volume and so allows measurements at a range of gradient strengths. It is this ratio which governs the shape of the pole-pieces. The constructed magnet has a typical operating field of 0.8 T, gives a gradient of 20 Tm-1, and has a useable interpole access of 20 mm. Field plot data show values consistent with the theory. In particular ||B || has a curvature of less than +/-5 microm over a 5 x 5 mm area at the target field. The magnet is most suitable for the one-dimensional profiling of thin planar samples. As an example of the magnet's use, a profile of a sandwich structure made of several polymer layers is shown. In addition, a set of one-dimensional profiles of an alkyd coating, recorded during solvent loss and cross-linking, is presented. This example demonstrates quantitative T2 measurements at a resolution of 6.5 microm across a 70-microm-thick film.     

混合型波荡器的3维优化

 以波荡器辐射波和共振电子能及混合型波荡器的解析计算为基础，通过3维磁场的有限元计算，在欧洲光源横向优化基础上，给出了同步辐射和自由电子激光用混合型波荡器纵向优化参数，进而给出了用于DUV FEL混合型波荡器的设计计算参数。加侧位和顶部永磁块后，峰值磁场分别提高到0.722T和0.773T，辅助以1μm量级分辨率的磁间隙调节机械系统，磁场分辨率好于10^-4T量级。     

A unilateral NMR magnet for sub-structure analysis in the built environment: the Surface GARField

A new, portable NMR magnet with a tailored magnetic field profile and a complementary radio frequency sensor have been designed and constructed for the purpose of probing in situ the sub-surface porosity of cement based materials in the built environment. The magnet is a one sided device akin to a large NMR-MOUSE with the additional design specification of planes of constant field strength /B0/ parallel to the surface. There is a strong gradient G in the field strength perpendicular to these planes. As with earlier GARField magnets, the ratio G//:B0/ is a system constant although the method of achieving this condition is substantially different. The new magnet as constructed is able to detect signals 50mm (1H NMR at 3.2 MHz) away from the surface of the magnet and can profile the surface layers of large samples to a depth of 35-40 mm by moving the magnet, and hence the resonant plane of the polarising field, relative to the sample surface. The matching radio frequency excitation/detector coil has been designed to complement the static magnetic field such that the polarising B0 and sensing B1 fields are, in principal, everywhere orthogonal. Preliminary spatially resolved measurements are presented of cement based materials, including two-dimensional T1-T2 relaxation correlation spectra.     

Multidimensional imaging using combined stray field and pulsed gradients

The paper describes an advance in stray field imaging (STRAFI) whereby images of planar samples can be obtained in the stray field of a superconducting magnet without the need for sample rotation. This is achieved by using the static stray magnetic field gradient in combination with pulsed orthogonal gradients. Results of both two- and three-dimensional implementations of the experiment are presented and discussed. An extension to diffusion-weighted imaging is introduced. The technique is expected to prove particularly useful in experiments where high resolution is required in only one direction while lower resolution is acceptable in the orthogonal directions, such as in studies of the drying and curing of paints and varnishes. Arising from the work, a new method for accurately calibrating the radiofrequency pulse width in stray field is found.     

L波段三维ESR成像系统的研制（Ⅱ）——L波段三维ESR成像系统

叙述了一个L波段（1.05 GHz）用于ESR和ESR成像的装置，用这套自制装置实现了3D ESR成像. 该装置由L波段ESR谱仪、三组梯度场线圈及控制单元和PC机数据采集系统组成. 样品腔是一个3-环2-缝再进入式谐振腔，可放入直径为20 mm、 长30 mm的H₂O样品，空谐振腔的频率是1.05 GHz. 微波振荡频率用自动频率控制（AFC）的方法自动锁在有载腔的频率上. 梯度场线圈沿X-，Y-和Z-轴产生线性梯度场，在中心40 mm球形范围内梯度场强度为2 mT/cm. 依照Lauterbur's方法进行3D ESR 图像重建. 用该系统检测了样品中TEMPO氮氧自由基的3D空间分布. 得到了TEMPO的2D、3D ESR图像、用像素灰度表示的自旋密度分布图及3D ESR-CT图像.     

纯永磁波荡器磁场计算的三维修正

 用归一化量对纯永磁波荡器的磁场进行三维计算分析,讨论了一般情况下有限磁极宽度的三维修正以及对好场区的影响,给出了磁极宽度对通常二维近似的修正曲线以及在不同磁极宽度下相对场强的横向变化曲线。     

Two-dimensional imaging with a single-sided NMR probe

A new low field unilateral NMR sensor equipped with a two-dimensional gradient coil system was built. A new NMR-MOUSE concept using a simple bar magnet instead of the classical U-shaped geometry was used to produce magnetic field profiles comparatively homogeneous in extended lateral planes defining a suitable field of view for 2D spatial localization. Slice selection along the depth direction is obtained by means of the highly constant static magnetic field gradient produced by this magnet geometry. Implementing a two-dimensional phase-encoding imaging method 2D cross sections of objects were obtained with high spatial resolution. By retuning the probe it was possible to change the depth of the selected slice obtaining a 3D imaging method. The details of the construction of the new device are presented together with imaging tests to show the quality of space encoding.     

Dipole magnet of the injection system for the SALO recirculator

A design of a dipole magnet was developed for the injection system of the SALO recirculator. The constructed prototype magnet has a C-shaped structure with rectangular sections. The pole section is 100 × 100 mm; the aperture is 25 mm. Field distributions in the magnet at a gap induction of 0.05 and 0.2 T were measured. The effective length of the magnet and multipole components of the magnetic field were calculated.     

L波段三维ESR成像系统的研制(Ⅳ)--系统组成与各部分性能指标

报道了自行研制的L波段三维电子自旋共振成像（3D-ESRI）系统的整机结构及各部分性能指标. 该系统主要由L波段ESR谱仪、三维梯度磁场装置、数据处理及图像重建软件组成. 系统的微波频率为1.05 GHz;最大微波功率500 mW. 采用3-环2-缝再进入式谐振腔,无载Q值>1 000;最大测量体积为φ 20 mm, 高30 mm柱状水溶液样品. 接收系统采用100 kHz锁相放大电路,最大增益可达1×10⁶;时间常数0.02 ms～1 s;磁场调制幅度>0.5 mT. 最大梯度磁场2 mT/cm;三维梯度线性度均优于5 ％;稳定度可达10^-5;主磁场可在1.6～96 mT范围内任意点选择扫场起始点;在0.2～16 mT范围选择磁场扫描宽度. 数据系统为12位A/D实现数据采集,三路8位D/A控制梯度磁场. 采用滤波反投影法实现图像重建, 成像功能包括：二维、三维自旋浓度成像;等浓度线2D图像显示;3D立体和断层图像显示等. 对水溶液和固体模型样品进行ESR成像的结果表明：本系统可以开展较大体积生物样品的ESRI研究.     

A unilateral magnet with an extended constant magnetic field gradient

Unilateral magnetic resonance (UMR) has become, in different research areas, a powerful tool to interrogate samples of arbitrary size. Numerous designs have been suggested in the literature to produce the desired magnetic field distributions, including designs which feature constant magnetic field gradients suitable for diffusion and profiling experiments. This work presents a new approach which features extended constant magnetic field gradients with a three magnet array. Constant gradients of more than 3cm extent can be achieved in a very simple, compact and safe design. Diffusion measurements from different positions over the magnet are presented in addition to practical applications for reservoir core plug characterization. The idea of a solenoid as a probe for specific measurements in UMR is introduced. Simple profiling experiments are also presented.     

3D imaging with a single-sided sensor: an open tomograph

An open tomograph to image volume regions near the surface of large objects is described. The central achievement in getting such a tomograph to work is the design of a fast two-dimensional pure phase encoding imaging method to produce a cross-sectional image in the presence of highly inhomogeneous fields. The method takes advantage of the multi-echo acquisition in a Carr-Purcell-Meiboom-Gill (CPMG)-like sequence to significantly reduce the experimental time to obtain a 2D image or to spatially resolve relaxation times across the sensitive volume in a single imaging experiment. Depending on T(2) the imaging time can be reduced by a factor of up to two orders of magnitude compared to the one needed by the single-echo imaging technique. The complete echo train decay has been also used to produce T(2) contrast in the images and to spatially resolve the T(2) distribution of an inhomogeneous object, showing that variations of structural properties like the cross-link density of rubber samples can be distinguished by this method. The sequence has been implemented on a single-sided sensor equipped with an optimized magnet geometry and a suitable gradient coil system that provides two perpendicular pulsed gradient fields. The static magnetic field defines flat planes of constant frequency parallel to the surface of the scanner that can be selected by retuning the probe frequency to achieve slice selection into the object. Combining the slice selection obtained under the presence of the static gradient of the open magnet with the two perpendicular pulsed gradient fields, 3D spatial resolution is obtained.     

Single sided imaging sensor

A portable single sided sensor to render depth profiles of MR signal non-invasively is presented. The device utilizes a tailored permanent magnet array producing flat sensitive volumes up to 40 mm from the mobile inspection head. Automated slice selection is performed using a set of switched capacitors in the tuning and receiver circuits. A single channel spectrometer drives the multi-slice acquisition. The RF coil and magnet array geometries have been tailored to house gradient sets to further extend the image rendering capabilities for in-plane spatial resolution (2D and 3D MRI). The probe has been tested acquiring moisture profiles in concrete and porous rocks and measuring diffusion parameters on a phantom sample.     

In vivo imaging of the human brain at 1.5 T with 0.6-mm isotropic resolution

We present high-resolution in vivo anatomical scans with 3D whole-brain coverage and an isotropic resolution of 0.6 mm, obtained at a clinical field of 1.5 T. The data are acquired in 10 independent scans over two sessions using a 3D magnetization-prepared, gradient echo sequence, modified to output phase images in addition to magnitude images. The independent scans are coregistered to correct for head motion, prior to performing complex averaging. The resolution of the final, averaged image, is found to be equal to the nominal one.     

Ultracompact NMR: <Superscript>1</Superscript>H Spectroscopy in a Subkilogram Magnet

We demonstrate the first subkilogram permanent magnet and microcoil probe combination capable of ¹H nuclear magnetic resonance spectroscopy with subparts-per-million resolution. The 1 T magnet with a weight of 685 g utilizes steel pole faces and flux return paths to provide a sufficiently homogeneous magnetic field in a robust, easy-to-use device nearly immune to environmental influences. The microcoil probe provides a signal-to-noise ratio of 61 in a single data acquisition from 21 nanoliters of water. The line width achieved, 0.24 ppm, can be explained by the measured field variations across the sample volume. The device does not have shim coils, temperature insulation and control, or adequate radio frequency shielding, so simple improvements in these areas will lead to further increases in performance. When combined with commercially available miniaturized electronics, the magnet and the probe described here will form the first handheld device capable of ¹H spectroscopy. Authors' address: Andrew F. McDowell, ABQMR Inc., 2301 Yale Boulevard SE, suite C-2, Albuquerque, New Mexico 87106, USA     

Multi-objective optimization of gradient coil for benchtop magnetic resonance imaging system with high-resolution

Significant high magnetic gradient field strength is essential to obtaining high-resolution images in a benchtop mag- netic resonance imaging （BT-MRI） system with permanent magnet. Extending minimum wire spacing and maximum wire width of gradient coils is one of the key solutions to minimize the maximum current density so as to reduce the local heating and generate higher magnetic field gradient strength. However, maximum current density is hard to optimize together with field linearity, stored magnetic energy, and power dissipation by the traditional target field method. In this paper, a new multi-objective method is proposed to optimize the maximum current density, field linearity, stored magnetic energy, and power dissipation in MRI gradient coils. The simulation and experimental results show that the minimum wire spacings are improved by 159% and 62% for the transverse and longitudinal gradient coil respectively. The maximum wire width increases from 0.5 mm to 1.5 mm. Maximum gradient field strengths of 157 mT/m and 405 mT/m for transverse and lon- gitudinal coil are achieved, respectively. The experimental results in BT-MRI instrument demonstrate that the MRI images with in-plane resolution of 50 ~tm can be obtained by using the designed coils.     

辅助永磁体磁化方式对单畴GdBCO超导块材捕获磁场分布及其磁悬浮力的影响

通过对方形永磁体和方形辅助永磁体在液氮温度下对GdBCO超导体磁化后超导磁悬浮力的测量, 研究了两种组态中方形辅助永磁体对超导体的磁化方式对单畴GdBCO超导块材磁场分布及其磁悬浮力的影响. 结果发现, 方形辅助永磁体的下表面和超导体上表面保持在同一个水平面上, 磁化进程中方形辅助永磁体在GdBCO超导体上表面水平面内沿直径方向的位置x从–15 mm增加到+15 mm时, 超导磁悬浮力大小与超导体的磁化方式有着密切关系(以Z=0.1 mm为例): 1) 当方形辅助永磁体N极垂直向上且场冷后去掉辅助永磁体时, 超导体最大磁悬浮力先从16.7 N增大到23.1 N, 再减小到16.6 N; 2) 当方形辅助永磁体N极垂直向下且场冷后去掉辅助永磁体时, 超导体最大磁悬浮力先从17.7 N减小到7 N, 再增加到17.6 N; 3) 两种组态中最大磁悬浮力不相等, 而且与零场冷下的最大磁悬浮力(17.1 N)也不同. 这些结果说明: 只有通过科学合理地设计超导体和永磁体的组合方式, 才能获得较高的磁场强度, 有效地提高超导体的磁悬浮力特性, 该结果对促进超导体的应用具有重要的指导意义. 关键词： 单畴GdBCO 永磁体 捕获磁场 磁悬浮力     

A simple, small and low cost permanent magnet design to produce homogeneous magnetic fields

A new portable, pocket-size NMR probe based on a novel permanent magnet arrangement is presented. It is based on a Halbach-type magnet design which mimics the field of a spherical dipole by using cylindrical bar and ring magnets. The magnet system is made up of only three individual magnets, and most field calculations and optimisations can be performed analytically. A prototype system has been built using a set of small, off the shelf commercially available permanent magnets. Proton linewidths of 50 ppm FWHM could be achieved at a field strength of 1T. Calculations show that with custom-sized permanent magnets, linewidths of less than 1 ppm can be achieved over sample volumes of up to 1 mm3, which would in theory enable chemical shift resolved proton spectroscopy on mass-limited samples. But even with the achieved linewidth of 50 ppm, this can be a useful portable sensor for small amounts of liquid samples with restricted molecular mobility, like gels, polymers or high viscosity liquids.     

Multi-dimensional magnetic resonance imaging in a stray magnetic field

Stray field imaging has been extensively utilized in the last 10 years to perform very high resolution imaging of samples in a single dimension using the massive field gradient present in the fringe of a superconducting magnet. By spinning the sample around the magic-angle, the stray field gradient is successively reoriented along three orthogonal directions in the sample reference frame, allowing the acquisition of a full three-dimensional Fourier image, thereby providing the possibility to perform multi-dimensional very high-resolution imaging with standard nuclear magnetic resonance spectroscopy equipment. Here, we show multi-dimensional images demonstrating the feasibility of this technique.     

EPR Spectroscopy Using Magnetic Field Gradient Modulated by a Triangular Wave

Magnetic field gradient modulation is one of the techniques to obtain an electron paramagnetic resonance (EPR) spectrum in a selected region of the sample. In this study, the magnetic field gradient modulation using a triangular wave was performed to overcome a problem during the sine wave modulation. Plastic materials were used for the bobbins and cases of the electromagnet to reduce the eddy current loss and drive the gradient coils in three-dimensional directions at a frequency of over 160 Hz. While the EPR signal splitting in a nonselected region, which is a problem in spectral analysis, was observed during the simulation and the actual measurement with the sine wave gradient modulation, the EPR signal broadening without splitting was observed in those with the triangular wave modulation. Thus, it is postulated that the triangular wave is more suitable than the sine one for the field gradient modulation. The spatial resolution was determined to be about 4 or 2 mm at the field gradient of 1 or 2 mT/cm, respectively. The separation of the EPR spectra of two types of radicals was also made by the triangular wave gradient modulation. Authors' address: Hidekatsu Yokoyama, Department of Pharmaceutical Sciences, International University of Health and Welfare, 2600-1, Kitakanemaru, Ohtawara 324-8501, Japan     

基于金刚石色心自旋磁共振效应的微位移测量方法

基于压电陶瓷精密微位移系统的扫描探测技术是目前精密测量仪器进行微纳区域/结构性能测试的核心系统,但压电陶瓷材料存在迟滞、非线性问题,限制了对微位移分辨能力的提升.本文以金刚石氮空位色心为敏感单元,利用电子自旋效应对磁场强度的高分辨敏感机理,结合永磁体周围不同位置对应的磁场强度变化关系,提出了一种基于金刚石氮空位色心电子自旋敏感机理的微位移检测方法.通过建立电子自旋效应与微位移的关联模型,搭建了相应的微位移测量系统.经实验验证,该系统对微位移测试的灵敏度为16.67 V/mm,检测分辨率达到60 nm,实现了对微位移的高分辨率测量.并通过理论分析,该系统的微位移测量分辨率可进一步提升至亚纳米级水平,为新型微位移测量技术提供了发展方向和研究思路.