Analysis of homonuclear RF gradient NMR spectroscopy

A formalism for describing the spin dynamics of radio frequency (RF) gradient experiments is introduced. It has the advantage over the most straight-forward applications of product operator methods of cleanly separating the steps of coherence transformation and gradient evolution which become confused in many RF gradient methods. The analysis is used to explore the dynamics of RF gradient homonuclear multiple quantum filtering experiments. Experimental results of these new sequences are included.     

低场核磁共振短死时间射频线圈与射频开关的设计

本文以核磁共振（NMR）射频线圈振铃信号产生原理为对象进行分析研究,提出了一种适用于低场环境下由环状间隙腔线圈与螺线管线圈构成的收发分离式短死时间射频线圈设计方案,采用优化调谐匹配网络提高发射效率;根据射频线圈方案需求设计了快速切换的射频开关及驱动．在此基础上依据仿真结果制作了短死时间射频线圈,并应用于自主研制的低场9.51 MHz便携式NMR谱仪系统,进行NMR实验,结果显示可将收发切换时间缩短至10 μs以内,验证了该设计方案的可行性．     

Magic Angle Spinning NMR Spectroscopy with Composite RF Pulses

Using numerical optimization procedures it is shown that it is possible to design composite 180 degrees RF pulses for MAS NMR spectroscopy by explicitly taking into account the variation of the resonance offset of each crystallite during the application of the RF pulses. When using composite RF pulses in experiments such as TOSS, where the delays between the RF pulses have to be critically adjusted, an optimization of these delays can lead to the desired performance characteristics.     

Error-tolerant RF litz coils for NMR/MRI.

A new class of NMR RF volume coils is being developed that permits improved tuning range, B(1) homogeneity, tuning stability, and sensitivity compared to birdcages over a wide range of practical conditions, especially for microscopy and wraparound flexible applications. They are denoted litz coils, as their flux transparency and current distribution is obtained from woven foil patterns with insulated crossovers. Contrary to the design criteria of phased arrays, the parallel routes in litz coils use high coupling coefficients to achieve optimal current distribution, which is highly independent of tuning, balancing, and matching adjustments and is compatible with multiple capacitive segmentation. Magnetic filling factors, loaded Q, and inhomogeneity measurements and calculations are presented for a variety of litz coils with frequency-diameter products from 7 to 20 MHz-m and are compared to similar birdcages.     

Solid phase synthesis of azapeptides using an automatic synthesizer

Peptides containing azaglycine located terminally or within the backbone have been prepared in the solid phase by means of an automatic synthesizer.     

Characterization of sedimentary rocks with a single-sided NMR instrument

Single-sided nuclear magnetic resonance (NMR) instruments are now becoming very popular due to their interesting capability of ex situ measurements and useful applications in material testing. Measurements performed on such devices, however, are very critical due to the presence of inhomogeneous radio-frequency and magnetic fields. The presence of a very large static magnetic field gradient near the magnet surface could be usefully applied to exploit diffusion properties of materials. These features were investigated by combining the measurements with application of diffusion editing sequences. A significant improvement was obtained, allowing more information on the contribution of the separate fluids and possible considerations on petrophysical properties of the porous media investigated. In fact, the diffusion-relaxation distribution functions obtained allowed complete separation of the terms related to the fluids investigated. The experimental data demonstrate the feasible application of methods based on diffusion editing sequences, even in the presence of a very large magnetic field gradient, typically associated with a single-sided NMR device.     

Fiber-optic color synthesizer

Full-color synthesis was achieved, for what we believe is the first time, utilizing a novel 3x1 hard polymer-clad fiber coupler along with red, green, and blue (RGB) LED primaries. By using RGB LEDs that are coupled to three input ports, the device rendered full color from the output port with a circular emitting pixel of 135 microm in diameter with an extended color gamut. The proposed fiber-optic color synthesizer can provide a compact waveguide solution for the beam scanning display and the tunable pure white source for LED backlighting.     

低场脉冲NMR中静磁场不均匀性的射频场补偿

在低场脉冲核磁共振实验中为了增大射频激励的带宽,通常采用的方法是提高射频激励磁场的场强. 针对共振区域中静磁场的不均匀性,本文提出了根据共振区域中的静磁场分布设计射频线圈以提高射频激励带宽,并用目标场方法实现了这一构想.      

Highly homogeneous circularly polarized RF field for whole body NMR imaging

Conditions for generation of polarized RF fields in cylindrical symmetry by high order coils are presented. Whole body NMR transmitters utilizing this principle would require a current control on a certain number of loops. In the present design this is obtained by feeding each loop by an appropriate linear combination of two in quadrature waves. The development has been experimentally tested by three scaled down experimental prototypes operated at 500 kHz and a good agreement has been found.