Transformer-coupled NMR probe

Abstract

In this study, we propose an NMR probe circuit that uses a transformer with a ferromagnetic core for impedance matching. The ferromagnetic core provides a strong but confined coupling that result in efficient energy transfer between the sample coil and NMR spectrometer, while not disturbing the B(1) field generated by the sample coil. We built a transformer-coupled NMR probe and found that it offers comparable performance (loss <1 dB) to a conventional capacitor-coupled circuit. Our probe operates over a wide frequency range (500 kHz-5 MHz in this example) without the need for matching adjustments. Such probes could be useful for low-field mobile NMR applications of multi-frequency operation, such as imaging, relaxation, and diffusion measurements, as well as NQR.