Low-noise and compact detection system using RF MEMS switch for solid-state NMR spectroscopy at cryogenic temperature: Proof-of-concept experiment

In nuclear magnetic resonance (NMR) spectroscopy, the signal from nuclear spins is extremely weak, and thus, it has been desired to improve the signal-to-noise ratio (SNR). In this study, we designed a compact low-noise probe and peripheral detection system optimized for low-temperature solid-state NMR spectroscopy. We confirmed the operation of a Tx/Rx switch composed of radio frequency microelectromechanical system (RF MEMS) switches and a preamplifier using high electron mobility transistors (HEMTs), which can operate even at 20 K and under a high magnetic field of ∼10 T. In our compactly designed NMR system, we succeeded in sufficiently reducing both thermal noise and external noise. As a result, the 195Pt- and 27Al-NMR measurements for Pt and Al solid powder samples were performed at 12 T and down to 20 K, showing that the SNR was improved by 40%-50% compared with the conventional system. These experiments also provide information on the low temperature properties and operational characteristics of integrated RF electronic devices, such as the RF MEMS switch, the HEMT, and their combined circuit system.