Monday, March 17, 2008
Probe Coil Geometry
The NMR sample sits inside a coil within the NMR probe. The coil is part of a tuned circuit which delivers radio frequency (RF) pulses to the sample and detects the RF signals from the sample. The RF fields delivered by and detected from the coil must be perpendicular to the static magnetic field, Bo. The most efficient way to do this is with a horizontal solenoid coil. Such coils are commonly used in NMR probes for solids. The probe must be removed from the magnet when samples are changed. A less efficient, but more convenient, Helmholtz coil is commonly used for liquids samples. Like horizontal solenoid coils, vertical Helmholtz coils deliver and detect RF fields perpendicular to Bo, but due to their geometry they allow samples to be inserted and ejected form the probe with a pneumatic system. The probe need not be removed from the magnet to change samples.