A New Method and Circuit of Ringing Suppression for Low-field NMR Instruments

Abstract

Accelerating the release of the antenna residual energy to weaken the antenna ringing signal is beneficial to shorten the echo time (TE) of low-field nuclear magnetic resonance (NMR) instruments, thus improving the measurement resolution and signal-to-noise ratio (SNR) of fast relaxation components. The antenna Q value has an opposite effect on the energy emission efficiency and discharge speed. For this reason, we first designed a new Q-switch circuit, which can greatly shorten the energy discharge time while ensuring the transmission efficiency. On this basis, an optimized pulse sequence was applied to overcome the defect that traditional phase alternated pair stacking (PAPs) cannot eliminate 90° pulse ringing, and the SNR was further improved by the method of phase cycling. Finally, the new Q-switch circuit was tested on a 2 MHz core analyzer, the Q value of the antenna was reduced to about 1/5 of the transmit period, and the antenna recovery time was reduced from 280.0 μs to 18.2 μs. Moreover, with the new Q-switch circuit and optimized pulse sequence, the T2 signal of the fast relaxation component can be effectively obtained when TE=60 μs.

Keywords

• low-field nuclear magnetic resonance (low-field nmr)
• q-switch
• ring
• signal-to-noise ratio (snr)
• pulse sequence