Thomson-cgr

Alain Marilier

Patrick LeRoux

Size variation of samples subjected to NMR examinations entails the need for calibration of the radiofrequency excitation which gives rise to the resonance phenomenon measured during experiments. Determination of the most suitable value of the radio-frequency excitation amplitude is carried out by scanning the range of potential amplitudes, starting from one end of the range. During the scanning operation, the variation in excitation amplitude varies in a geometrical progression with the order number of the experimentation. It is shown that, by adopting this procedure, determination of the calibrated amplitude is achieved more rapidly while maintaining constant accuracy of determination.

Method for calibrating a radiofrequency excitation in NMR experimentation

Calibration of radiofrequency excitation involves application of two successive pulses of identical waveform and amplitude. The excitations are applied in series of excitations of variable amplitude from one excitation to the next in order to determine the calibrated value of the excitation pulses to be employed by transition of the amplitude of the received signal through a minimum value. It is demonstrated that this procedure prevents the calibration from being impaired by inhomogeneities of the orienting field of the apparatus. Spatial and spectral inhomogeneities of the excitation are also eliminated by applying throughout the calibration a selection gradient to the body under examination. Defects are eliminated by frequency filtering of the detected signal.

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Bourg La Reine, France

Alain Marilier