Simulation and Experimental Study on the Influence of Cables on the Performance of Search Coil Magnetometers

In response to the performance impact of long cable signal transmission between the search coil and the preamplifier circuit, this paper establishes for the first time a circuit equivalent model of Search Coil - Cable - Preamplifier Circuit. Through simulation analysis and experimental verification, the influence of cable length on the frequency distribution of sensor noise is revealed. Theoretical analysis indicates that cable length has limited impact on sensor sensitivity, but significantly increases the noise level in the high-frequency band (>1 kHz). Based on a prototype search coil magnetometer with a target specification of 10～1000 Hz bandwidth and 30 fT·Hz^1/2 (1 kHz) noise, the variation law of noise with cable length is validated. Experimental results show that as the cable length increases from 3 m to 39 m, the noise corner frequency shifts forward from 7.5 kHz to 2 kHz, while the high-frequency noise at 10 kHz increases by a factor of six. The study finds that an increase in cable length has a significant impact on the noise of inductive magnetometers, specifically manifested as a slight improvement in low-frequency noise and a sharp deterioration in high-frequency noise. Although cable length has a notable effect on inductive magnetometers, its influence can be predicted and mitigated through theoretical modeling incorporating cable parameters. This research provides critical parameter basis for the engineering implementation of search coil magnetometers in space exploration scenarios requiring long-cable applications.