NMR Coils Research Articles

An inductively coupled, series-tuned NMR probe

A matching circuit for NMR coils for in vivo experiments is described. This circuit uses an inductive coupling of the NMR coil to the transmitter-receiver. This arrangement produces a nearly perfectly balanced NMR coil with respect to the sample and thus reduces the electric losses in the sample and also the radiative and resistive losses in the ground loops. Moreover, a series capacitor is inserted in the middle of the coil which further reduces the electric losses in the sample. Both inductive coupling and series tuning reduce the frequency shift of the coil resonance frequency upon the introduction of the sample or due to the movements of the animal under studies.

NMR coils with segments in parallel to achieve higher frequencies or larger sample volumes

The question of using multisegment coils, connected in parallel, for NMR is investigated. It is shown theoretically and experimentally that such coils offer significant improvements over equivalent single coils in several ways: (1) For a given size, they are usable at much higher frequencies; (2) for a given Larmor frequency, they can be made larger to contain more sample; and (3) the axial component of the rf electric field can be reduced for certain coil geometries.

Remote (inside-out) NMR. III. Detection of nuclear magnetic resonance in a remotely produced region of homogeneous magnetic field

Recent discovery of a method of producing a region of homogeneous magnetic field remotely, combined with the recent detection of NMR in samples external to the nuclear magnetic resonance coil, led to this report of the detection of NMR from a remotely produced toroidal region external to the coil. Using a modified 4-in. laboratory electromagnet, a toroidal region of homogeneous radial magnetic field 28 cm in diameter with a field strength of 117.5 G was produced. Proton NMR signals were detected from a variety of coaxially located NMR coils of 15-, 18-, 20-, and 24-cm diameter. The data suggest an inverse fifth-power dependence of signalto-noise ratio on r a , the ratio of sample-to-coil radii. Correction for sample volume dependence on R results in an inverse square dependence of S/N on R when a is fixed.

Experimental studies of solitons in superfluid 3He-A

Magnetic textures have been created and studied in the A phase of superfluid 3He at several pressures, in magnetic fields from 15 to 20 mT, by intense rf magnetic pulses which invert the magnetization of the fluid. To create this new state we find that the initial large pulse must tip the magnetization by at least 140‡. In this state the fluid evolves from a condition where the NMR frequency shift Ω-γH 0is smaller than that in the unperturbed superfluid by a factor of 0.54, over a time scale of tens of seconds to a condition where the frequency shift is 0.70 times the unperturbed value. We have studied the fluid's linear response to small-angle sampling pulses as well as the nonlinear response to large-angle pulses. By using two independent NMR coils we have seen this new state move through the fluid; we find that a lower limit on its propagation velocity is around one-half the spin wave velocity. All of our results are generally consistent with the model of solitons in the order parameter proposed by Maki and co-workers.

A simple technique for encapsulating NMR coils in Teflon PTFE

A simple technique used in this laboratory for encapsulation of NMR coils in polytetrafluoroethylene (Teflon PTFE) is described. The process has wide applicability for simple systems in which PTFE encapsulation is advantageous.