Analysis of multilayer radio frequency microcoils for nuclear magnetic resonance spectroscopy

Although its strength lies in its ability to determine chemical structure completely, nuclear magnetic resonance (NMR) spectroscopy is relatively insensitive compared to other analytical techniques. As a result, significant research has been directed at improving the overall sensitivity of NMR spectroscopy by optimizing radio-frequency (RF) coil design. To investigate volume- and mass-limited samples, RF microcoils have been examined extensively. These solenoidal wire coils take advantage of reduced coil diameter to improve the signal-to-noise ratio (SNR) of microcoils for constrained samples. To study the properties of a multilayer configuration, both theoretical and experimental solutions for conductor thicknesses above the skin depth at the frequency of operation. Experimental data for thicker conductors displays a reduction in SNR with increased layers, supporting the theoretical development. As indicated by analytical theory and as partially confirmed by experimentation, SNR improvements for multilayer microcoils may be realized only when the conductor thickness is on the order of the skin depth. However, the utilization and availability of skin-depth conductors in the fabrication of current microcoil designs are not trivial matters. To take advantage of the SNR benefits of a multilayer microcoil geometry, we suggest a new configuration called the scroll coil. This novel geometry offers additional flexibility in fabrication that may be of great benefit in high-resolution NMR spectroscopy, especially at very small coil dimensions.