The Influence of a Nonconstant Magnetic-Field Gradient on PFG NMR Diffusion Experiments. A Brownian-Dynamics Computer Simulation Study
✍ Scribed by Björn Håkansson; Bengt Jönsson; Per Linse; Olle Söderman
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 237 KB
- Volume
- 124
- Category
- Article
- ISSN
- 1090-7807
No coin nor oath required. For personal study only.
✦ Synopsis
The influence of a nonconstant magnetic-field gradient on the the magnetic-field gradient over the active sample volume performance of pulsed-field-gradient NMR diffusion experiments (the active sample volume is taken to be the volume enclosed was investigated by performing Brownian-dynamics simulations by the RF coil) may vary in design due to factors such as for two different coil designs using two different active sample available space, required direction of the gradient (i.e., z, x, volumes for each coil. The active sample volumes were chosen in or y), and desired strength of the gradient. The anti-Helmorder to represent different degrees of deviation from a perfectly holtz coil (15, 16) (also called the Maxwell pair) and the constant magnetic-field gradient. The results show that one can quadrupole coil (17-19) are two common coil configurations actually tolerate a rather large deviation from a perfectly constant used today. There are also other types of configurations remagnetic-field gradient and still obtain accurate values of the selfported in the literature (20-22). The quadrupole coil has diffusion coefficients. The dependence of D (the observation time) some definite advantages over other configurations. It gives and the dependence of D (the self-diffusion coefficient) while keeping D and D constant, respectively, were also investigated for field-gradient uniformity over large sample volumes and has three of the active sample volumes. The simulations show that the lower inductance. The latter property is important for better effects due to a nonconstant field gradient depend only slightly performance in high-gradient PFG experiments, since it on the values of D and D. In conclusion, the Brownian-dynamics allows for rapid rise and fall times of the gradient pulses.
computer simulations procedure is a quantitative way of investi-However, the quadrupole coil is not a suitable choice gating the performance characteristics of a gradient coil of a cerwhen using superconducting magnets. The reasons for this tain design before it is built. ᭧ 1997 Academic Press fact is that the direction of the main field is such that the gradient coil must be placed perpendicular to the main field, which is impractical. Therefore the anti-Helmholtz coil is a