Abstract

The predominant means to detect nuclear magnetic resonance (NMR) is to monitor the voltage induced in a radiofrequency coil by the precessing magnetization. To address the sensitivity of NMR for mass-​limited samples it is worthwhile to miniaturize this detector coil. Although making smaller coils seems a trivial step, the challenges in the design of microcoil probeheads are to get the highest possible sensitivity while maintaining high-​resolution and keeping the versatility to apply all known NMR experiments. This means that the coils have to be optimized for a given sample geometry, circuit losses should be avoided, susceptibility broadening due to probe materials has to be minimized and finally the B₁-fields generated by the RF-coils should be homogeneous over the sample area. This contribution compares three designs that have been miniaturized for NMR detection; solenoid coils, flat helical coils and the novel stripline and microslot designs. So far most emphasis in microcoil research was in liquid-​state NMR. This contribution gives an overview of the state-​of-​the-​art of microcoil solid-​state NMR by reviewing literature data and showing the latest results in the development of static and microMAS solenoid-​based probeheads. Besides their mass-​sensitivity microcoils can generate tremendously high RF-fields which is very useful in various solid-​state NMR experiments. The benefits of the stripline geometry for studying thin films are shown. This geometry also proves to be a superior solution for microfluidic NMR implementations in terms of sensitivity and resolution.