Unusual NMR experiments using home-made and open-resource systems

An open-design NMR spectrometer is described. Its role is to complement the state-of-art commercial NMR systems, to support one to explore new frontiers in NMR spectroscopy. The design policy is to leave all the digital jobs required for an NMR spectrometer to a single field-programmable gate-array (FPGA) chip. Since the hardware modules built inside the FPGA are called "core" modules, and since their source codes are "open" to public, the spectrometer was named as the OPENCORE NMR spectrometer[1-3].

The spectrometer is equipped with three equivalent transmitter channels, each of which is capable of modulating amplitude, phase, and frequency of radio-frequency signals. In our laboratory, we operate all our solid-state NMR systems using the OPENCORE NMR spectrometers.

In addition to performing established sequences, we put our effort on developing NMR methodologies to expand the applicability of NMR spectroscopy. Examples include NMR elemental analysis[4], dynamic receiver-gain modulation[5], covariance spectroscopy extended to heteronuclear spin systems[6], double-nutation irradiation[7], in-situ 7Li NMR of batteries[8], continuous-wave NMR, X-band frequency up-conversion for ESR, and so on. The OPENCORE NMR spectrometer can also serve for MRI experiments with an optional field-gradient waveform generator. Since the spectrometer happens to be compact, one can carry it outside the laboratory. NMR experiments have been demonstrated in a classroom and at home using a permanent magnet for educational and hobby purposes.

Even though the price for the parts is low, it would be fair to mention the non-financial cost. That is, one is required to have some knowledge and skill in electronics, and perhaps, patience, to build a spectrometer and make it operational. Hopefully, the OPENCORE NMR project could inspire those who are trying to start something new. Indeed, we have begun to explore the possibility of applying opto-electro-mechanics[9] to NMR.

[1] K. Takeda, Rev. Sci. Instrum. 78 (2007) 033103.
[2] K. Takeda, J. Magn. Reson. 192 (2008) 218.
[3] K. Takeda, Annual Reports on NMR Spectroscopy 74 (2011) 355.
[4] K. Takeda, N. Ichijo, Y. Noda, K. Takegoshi, J. Magn. Reson. 224 (2012) 48.
[5] K. Takeda, K. Takegoshi, J. Magn. Reson. 208 (2011) 305.
[6] K. Takeda, Y. Kusakabe, Y. Noda, M. Fukuchi, K. Takegoshi, Phys. Chem. Chem. Phys. 14 (2012) 9715.
[7] K. Takeda, A. Wakisaka, K. Takegoshi, J. Chem. Phys. 141 (2014) 224202.
[8] J. Arai, Y. Okada, T. Sugiyama, M. Izuka, K. Gotoh, K. Takeda, J. Electrochem. Soc. 162 (2015) A952.
[9] T. Bagci, A. Simonsen, S. Schmid, L.G. Villanueva, E. Zeuthen, J. Appel, J.M. Taylor, A. Sørensen, K. Usami, A. Schliesser, E.S. Polzik, Nature 507 (2014) 81.