Analysis of multilayer radio frequency microcoils for nuclear magnetic resonance spectroscopy

Although its strength lies in its ability to determine chemical structure c ompletely, nuclear magnetic resonance (NMR) spectroscopy is relatively inse nsitive compared to other analytical techniques. As a result, significant r esearch has been directed at improving the overall sensitivity of NMR spect roscopy by optimizing radio-frequency (RF) coil design. To investigate volu me- and mass-limited samples, RF microcoils have been examined extensively. These solenoidal wire coils take advantage of reduced coil diameter to imp rove the signal-to-noise ratio (SNR) of microcoils for constrained samples. To study the properties of a multilayer configuration, both theoretical an d experimental solutions for conductor thicknesses above the skin depth at the frequency of operation. Experimental data for thicker conductors displa ys a reduction in SNR with increased layers, supporting the theoretical dev elopment. As indicated by analytical theory and as partially confirmed by e xperimentation, SNR improvements for multilayer microcoils may be realized only when the conductor thickness is on the order of the skin depth. Howeve r, the utilization and availability of skin-depth conductors in the fabrica tion of current microcoil designs are not trivial matters. To take advantag e 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.