A METHOD FOR IMPROVING MODULATION IN NMR USING HARMONIC-ANALYSIS

Modulated pulses designed for NMR often suffer from imperfections aris ing from the pulse-shape modulator. This produces a nonideal magnetiza tion distribution which may lead to the failure of the experiment. Thi s paper describes how to perform quantitative analysis of the imperfec tions of the RF modulator by harmonic analysis of the output wave form , using the NMR spectrometer itself. From these measurements, an analy tical form of the transfer function is obtained. The wave form which c ompensates for the distortion is then calculated by an iterative proce ss. To demonstrate the performance of the method, it was applied to re presentative pulse shapes. The comparison of the experimental frequenc y profiles, obtained with and without correction, with the simulated p rofiles illustrates the reliability of the method. (C) 1996 Academic P ress, Inc.