Low-field NMR micro coils based on printed circuit board technology

Radiofrequency coil is one of the most important components for a nuclear magnetic resonance (NMR) instrument. In this article, some planar micro coils with an inner diameter of 2 mm and number of turns that varied from 1 to 11 were investigated based on the printed circuit board (PCB) technology. The electrical characterization of micro coils show that self-resonant frequencies are larger than 200 MHz. Then, an NMR measurement platform with a static magnetic field of 0.66 T was constructed and the signal to noise ratio (SNR) values of the NMR were analyzed. It was found that the SNR is optimal when the turn number of the micro coils is six and the excitation time of a 90° pulse is 0.8 ms. Finally, we used the micro coil with six turns to study the transverse relaxation rate of copper sulfate pentahydrate aqueous solution with different concentrations. It was found that the transverse relaxation rate is proportional to the solution concentration. Results from the micro coil were verified by measurements using a Bruker Minispec MQ60.