低场脉冲NMR横向弛豫信号的反演分析

从第一类积分方程的反演求解入手,推导出了适合低场脉冲核磁共振横向弛豫信号多指数反演的一种解谱算法.对解谱的具体过程进行了详细论述,并对不同信噪比、不同布点方式下的解谱结果进行了对比与分析.本算法对推广低场脉冲核磁共振分析测量技术的应用具有重要的参考价值.     

实验低场脉冲核磁共振仪数据接收与处理

低场脉冲核磁共振系统接收到的信号信噪比低，解谱结果对系统噪声敏感。针对我们自行研制的实验低场脉冲核磁共振仪，以小波分析等现代信号处理理论为基础，提出了一些数据接收与处理的方法，在有效抑制噪声的基础上准确提取回波信号峰值。通过多指数反演解谱算法获得磁共振信号的正谱分布，从而进行样品的定量分析。     

永磁低场核磁共振分析仪原理和应用

近年来随着核磁共振技术不断进步,国内许多公司和科研机构成功研制出永磁低场磁共振分析仪,本文以NM120-Analyst型核磁共振分析仪作为这类仪器的代表,简单介绍永磁低场磁共振分析仪的结构原理,再分类讨论永磁低场磁共振分析仪在相关领域的基本应用。实践证明,该类仪器已分别在医学磁共振成像设备教学和培训、食品研究、石油勘探、新能源开发等领域中得到广泛应用。     

核磁共振基础(三) 三、核磁共振波谱仪概况

1.核磁共振仪器的分类(1)按射频场施加的方式分类根据核磁共振实验中射频场施加的方式,可以把核磁共振仪分为两种。一种是连续波核磁共振仪,它是把射频场连续不断地加到样品上,得到频率谱(或者称波谱)。另一种是脉冲核磁共振波谱仪,它是把射频场以窄脉冲的方式加到样品上,得到时间谱,或者称自由感应衰减信号(FID)。以观察自旋回波方式工作     

基于小波变换的低场脉冲核磁共振系统高斯白噪声估计

介绍了以小波分析理论为基础，结合小波阈值去噪算法找到一种有效的噪声分离方法。采用该方法从实际低场脉冲核磁共振系统噪声信号中分离出高斯白噪声并对其进行了参数估计。该方法还可以用于其它信号处理领域高斯白噪声的估计。     

利用实时优化技术快速确定低场核磁共振系统的脉冲宽度

为了快速确定低场核磁共振系统的90度脉冲宽度,提出了一种实时优化方法。该方法主要包括90°脉冲宽度保守估计方法和实时确定下一个待测数据点方法,首先利用90°脉冲宽度保守估计方法估计出一个小于实际90°脉冲宽度的方法,然后根据估计的保守90°脉冲宽度确定下一个待测脉冲宽度的安全范围,并利用实施优化的思路确定下一个待测数据点,最后通过迭代测试和计算确定90°脉冲宽度。实验结果和仿真结果表明,该方法快速有效、脉冲宽度确定结果可靠性高。     

多溶剂峰压制核磁共振技术用于固相萃取研究效果评价

基于可变角多种溶剂峰选择,结合脉冲梯度场技术和多频率选择激发的整形脉冲,在对WET脉冲序列进行分析的基础上,针对含有低浓度化学毒剂的环境样品,建立多溶剂峰压制核磁共振方法,并成功地用于强离子干扰水样中固相萃取研究的效果评价,该技术与预饱和技术相比较,具有压制效率高、灵敏度好、基线平整的优点。     

高场NMR谱仪的应用和进展简介

高场核磁共振谱仪具有高灵敏度和高分辨率等优点,能在接近生理条件下,测定生物大分子的溶液结构。本文介绍了高场核磁共振谱仪在结构生物学中的一些应用,以及核磁共振谱仪的一些进展。     

高场NMR谱仪的应用和进展简单

高场核磁共振谱仪具有高灵敏度和高分辨率等优点，能在接近生理条件下，测定生物大分子的溶液结构，本文介绍了高场核磁共振谱仪在结构生物学中的一些应用，以及核磁共振谱仪的一些进展 。     

基于DDS的脉冲核磁共振频率源设计

针对脉冲核磁共振技术对频率源的高精度要求,采用DDS技术设计了一种脉冲核磁共振频率源。选择AD9850作为DDS芯片,给出了AD9850与AT89S52的硬件接口电路以及软件控制程序。实验验证表明,频率源工作稳定可靠,能够满足设计要求。     

Nuclear magnetic resonance apparatus for pulsed high magnetic fields

A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.     

Novel method for determination of flow velocities with pulsed nuclear magnetic resonance

A method for the determination of flow velocities with pulsed nuclear magnetic resonance is presented, based on a sequence of inhomogeneous 180 degrees pulses and a gradient in the stationary magnetic field. Results are shown for a capillary containing water with flow velocities in the range of 0.5 to 5 mm/s.     

瞬态脉冲磁场频谱分析

当线圈中通过上升沿为纳秒级的脉冲电流时,在脉冲电流的激励下,线圈中产生感应脉冲磁场,该磁场以介质磁化的方式向外传播,从而产生激磁波。利用傅里叶积分对脉冲磁场进行频谱分析,讨论了脉冲磁场大小随所选择频率上限之间的关系。     

铁磁性构件缺陷的脉冲涡流检测传感机理研究

铁磁性构件的脉冲涡流检测法是一种融合了漏磁检测与涡流检测的新的复合磁传感检测法。建立了脉冲涡流复合传感有限元仿真模型,仿真分析了铁磁性构件电导率、磁导率和导入直流电流激励大小对脉冲涡流响应信号的影响规律。实验结果表明:随着导入直流电流激励增加,铁磁性构件表面缺陷漏磁场和电流密度引起扰动磁场的复合场对脉冲涡流响应信号的影响更显著,而铁磁构件亚表面埋藏缺陷随着缺陷深度的增大而增大,缺陷漏磁及电流扰动磁场的复合场对脉冲涡流响应信号的影响变小,涡流响应信号占主导地位,为脉冲涡流传感器设计奠定理论基础。     

脉冲漏磁检测的三维场特征分析及缺陷分类识别

漏磁检测方法广泛应用于石油、运输及化工等行业中金属的缺陷检测.介绍了漏磁检测原理,采用有限元法建立了三维缺陷脉冲漏磁检测模型,分析了缺陷脉冲漏磁场B_x、B_y和B_z分量的特点.结果表明,与传统漏磁检测系统提取缺陷漏磁场水平分量B_x和法向分量B_z进行缺陷识别相比较,三维缺陷脉冲漏磁场分量的提取将提供更多有关缺陷尺寸、位置等信息,尤其是当外加磁场方向与缺陷主平面近似平行时.最后给出了实验验证,实验结果与仿真分析有较好的一致性,这说明有限元仿真分析对实际脉冲漏磁检测系统的设计有重要的指导意义.     

感应式磁声成像脉冲磁场的测量方法

阐述了利用电磁感应法测量脉冲磁场的磁感应强度,首先测量放置在标准的已知正弦波磁场里的探测线圈的线圈常数,再用这种已知线圈常数的探测线圈进行脉冲磁场的测量。介绍了微型磁场探测线圈的绕制和固定方法,设计了脉冲磁场的实际测量装置,给出了线圈平面的调整方法,利用该装置实际测量了感应式磁声成像系统中的脉冲磁场,并对测量结果进行了误差分析。     

Using magnetic hysteresis for testing electroconductive objects in pulsed magnetic fields

The distributions of the electric voltage U(t) that is read from an induction magnetic head as it scans a discrete magnetic medium with residual magnetic field records that were obtained under the action of a pulsed magnetic field with different-polarity surges on a magnetic medium with a tested object are given. The onset of ordered distributions of the residual magnetic fields on the magnetic medium due to the sequential action on it by pulses of the magnetic field is called the hysteresis interference of a pulsed magnetic field (HI). The scheme of an experimental device for studying propagations of pulsed magnetic fields and methods of testing objects made of electroconductive and magnetic materials, which increase the accuracy of the determination of their specific conductivity σ, permeability μ, distribution uniformity of σ and μ, thickness, and parameters of continuous defects in them, are described.     

A pulse-periodic gyroresonant plasma accelerator

A plasma electron accelerator based on the gyromagnetic autoresonance effect is described. Electrons of the initially cold internal-injection plasma (a classical ECR discharge) are accelerated in the magnetic field of a magnetic mirror trap under a one-stage effect of the resonant microwave field and an additional pulsed magnetic field. The synchronism in maintaining the resonance conditions is ensured by a smooth increase in the pulsed magnetic field in the course of a microwave pulse. At the moderate values of the input microwave power (up to 2.5 kW) and the steady-state and pulsed magnetic fields (each up to 1 kG), it is possible to obtain stable relativistic plasma bunches, in which the energy of the electron components is a few hundred keV. The measured X-ray bremsstrahlung spectra have features characteristic of the energy distribution of photons, and the high-energy tails are recorded in the region of 600–800 keV. The dependences of the bremsstrahlung characteristics on the experimental conditions—the value of the steady-state magnetic field and the amplitude of the pulsed magnetic field—are investigated. The experimental data are in good agreement in the quantitative sense with the results of the computer simulation and with the earlier studies.     

Acoustic ringing effects in pulsed nuclear magnetic resonance probes

The troublesome spurious ringing phenomenon found in pulsed nuclear magnetic resonance probes is explained in terms of the electromagnetic generation and detection of ultrasonic waves. A few techniques for eliminating this problem are discussed.     

Magnetostriction varieties and stress relief caused by pulsed magnetic field

Magnetostriction is investigated to evaluate the stress relief caused by pulsed magnetic field treatment, because this physical property is closely associated with residual stress. Magnetostriction of different stressed samples is measured in this paper. The stress variations caused by pulsed magnetic treatment are also compared. It is found that magnetostriction variations are closely associated with stress changes. Thermodynamic potential is used to find the relationship between them. Based on several assumptions, we find that the product of magnetostriction amplitude and stress magnitude is nearly a constant during magnetic field treatment, which is valuable for stress relief evaluation and optimizing processing parameters. This conclusion is testified by stress measurements, and the calculated values are in accordance with the experiment results.