Solenoidal and planar microcoils for NMR spectroscopy

The extraction of nuclear magnetic resonance (NMR) spectra of samples having smaller and smaller volumes is a real challenge. Reductions of volume are dictated by the difficulties of production of sufficiently large samples or by necessities of miniaturization of the analyzing system. In both cases a careful design of the radiofrequency (RF) coil, ensuring an optimum reception of the NMR signal, is mandatory. We evaluated the usefulness of an electromagnetic simulation software for the design and optimization of these radio-frequency coils, which are more and more used in biology and health research projects. The contribution of different effects (dc, skin and proximity) at the total resistance of the coils were assessed as well as the expected SNR per sample volume unit and the quality factor. Designed for a biological application, these coils have to be as less invasive as possible and they must allow small quantities analysis of metabolites inside capillary tubs or surrounding the microcoil. In order to evaluate detection efficiency and spectral resolution, preliminary experiments have been performed at 85.13 MHz under a static magnetic field of 2 T.