Novel detection system for NMR logging tool

We present a novel detection system for nuclear magnetic resonance (NMR) logging tool with direct connection of receiver to low inductance antenna. The detection system contains receiver and signal acquisition circuit with high signal-to-noise ratio (SNR). The direct balanced connection of receiver to antenna increases SNR of the NMR signal. The first stage of receiver has a balanced input built on ultra low noise wideband operational amplifiers LMH6626. The maximum receiver gain is 105 dB and its frequency bandwidth is from 600 kHz to 1 MHz. The signal acquisition circuit uses Digital Signal Processor (DSP) and Field Programmable Gate Array (FPGA) to obtain the flexible programmable ability and powerful data processing. Its resolution is 14 bit and maximum sampling frequency is 40 MHz. The acquisition algorithm uses digital phase sensitive detection to obtain the amplitude and phase information of NMR signal. Tests show that a range of common NMR experiments can be performed with our system. The CPMG echo train with high SNR is acquired successfully.