An Inexpensive Earth Field NMR Spectrometer with Improved Shimming.

A simple, cost-effective, do-it-yourself earth field nuclear magnetic resonance spectrometer with shimming is demonstrated. A spectrometer for understanding magnetic resonance physics in an academic environment is presented here along with its coil and system component design. This system was designed with inexpensive and readily available electronic components costing less than US $130. The three signal chains in the system include the polarizer along with the polarization coil, transmitter driver with transceiver coil, and receiver circuit serving as a low-noise amplifier. A microcontroller acting as the signal generator and processor controls the entire system. Switching between the transmitter and the receiver is via a relay circuit. In experiments, the free induction decay obtained from the water sample lasted 2 s with an amplitude of 5 a.u. at 1512 Hz. The line width decreased by 13 Hz after active shimming compared to 3 Hz with passive shimming. The spin echo results of the commercially available Terranova-MRI system with and without sample were used as a benchmark for the low-cost earth field nuclear magnetic resonance spectrometer. The entire system had to be fine-tuned to visualize the free induction decay because the 1.2 kHz and 50 Hz noise was predominant before tuning. Future work will involve the incorporation of gradients and time-shared pulse sequence design.