Industrial Applications of Gradient Field NMR

Abstract

Nuclear Magnetic Resonance (NMR) techniques and systems have been developed to provide spatial resolution, measurement localization and selective detection and measurement of solid and liquid materials having specific ranges and combinations of spin-lattice, T1, and spin-spin, T2, relaxation times. Spatial resolution and localization are achieved by use of gradient fields while multi-pulse methods have been developed to obtain T1, T2 selectivity. NMR systems utilizing Sensors based on the use of U-shaped magnets and flat, spiral-wound radiofrequency detection coils have been developed to make remote, spatially localized NMR measurements from a single surface. A schematic diagram of this approach is shown in Figure 1. The size, shape and location of the localized region from which NMR signals are obtained is determined by the magnitude and gradients of the magnetic fields. The localized region can be moved closer to, or farther away from, the sensor by varying the magnetic field strength. The NMR system incorporates an integral microcomputer for control of the data acquisition and signal processing, and includes a radiofrequency transmitter operating at 2 MHz capable of producing pulses of a controlled width and power up to 200 kW peak to insure optimum NMR detection over a specified remote region.