Lin Tingting, Chen Wuqiang, Du Wenyuan, Zhao Jing
College of Instrumentation and Electrical Engineering, Jilin University, Changchun 130061, China and Key Lab of Geo-Exploration Instrumentation of Ministry of Education, Jilin University, Changchun 130061, China.
Rev Sci Instrum. 2015 Nov;86(11):114702. doi: 10.1063/1.4934969.
To obtain a precise 2D/3D image of fissure or karst water, multi-channel magnetic resonance sounding (MRS) systems using edge-to-edge or overlapping receiving coils are needed. Thus, acquiring a nano-volt signal for a small amount of the aquifer and suppressing the mutual coupling between adjacent coils are two important issues for the design of the signal acquisition module in the system. In the present study, we propose to use a passive low pass filter, consisted of a resistance (R) and capacitance (C), to inhibit the mutual coupling effects of the coils. Four low-noise operational amplifiers LT1028, OPA124, AD745, and OP27 were compared with respect to achieving the lowest system noise. As a result, 3 pieces of LT1028 were chosen and connected in parallel to serve as preamplifier, with a sensitivity of 1.4 nV/√Hz at 2 kHz. Experimental results are presented for 2D MRS groundwater investigations conducted in the suburb of Changchun, China. The inversion result is consistent with the result of drilling log, suggesting that the signal acquisition module is well developed.
