Improvement of the Uniformity of the RF Field Generated by the Helical Surface Coil of a Nuclear-Quadrupole-Resonance Spectrometer

A simple and rather efficient method is proposed for improving the uniformity of the RF field generated by a surface helical coil with nonlinearly distributed turns. An optimal law of the distribution of the turns of a helical coil is suggested. The results of a computer simulation of the field produced by this coil are presented and compared with the data for a conventionally used coil in the form of a linear spiral. The coils were tested during detection of nuclear quadrupole resonance signals on ¹⁴N nuclei in a (CH₂)₆N₄polycrystal and demonstrated the efficiency of the technique proposed for improving the field uniformity.