Synthesis of arbitrary frequency domain transmitting pulses applicable to pulsed NMR instruments

Abstract

The synthesis of specialized excitation waveforms for pulsed NMR spin systems is an integral part of many present-day NMR experiments. Methods in use include various types of constant amplitude rectangular rf pulse trains with controlled interpulse delay times, modulating amplitudes of the envelopes of a chain of rectangular pulses, special long pulse rectangular pulses, and recently, single sideband spectral selections for NMR imaging. This paper describes, in quantitative fashion with experimental results, analysis and implementation of a method to generate pulsed NMR excitation waveforms using AM and FM techniques which yield individual pulses with controllable frequency spectral distributions. Examples given are of simplified cases, but the extension to complex frequency distribution requirements is clear.