Multiarray Transmitting Technique of Multiturn Small-Loop TEM for High-Performance Measurement

The transient electromagnetic method (TEM) employing multiturn small-loop transmit coils offers an effective approach for high-resolution geological prospecting, where rapid and stable current turn-off characteristics are critical. However, the presence of substantial parasitic parameters in multiturn small-loop transmitting systems results in prolonged current turn-off duration and severe oscillations during the turn-off transient, drastically degrading the detection performance. To mitigate these limitations, this article presents a comprehensive analysis of the dynamic current characteristics in multiturn small-loop transmitting circuits. Based on this analysis, we propose a high-performance multiarray transmitting technique that replaces traditional single-coil systems with an optimized array configuration. Simulations demonstrate that the proposed approach achieves a substantial reduction in turn-off time while effectively suppressing early stage oscillations. Furthermore, we design and implement a prototype array transmitting system with a magnetic moment of 400 A $\cdot $ m2. Comparative experiments show that, at an equivalent magnetic moment, the multiarray system reduces the turn-off time by 62% (from 63 to $24~\mu $ s) and decreases the oscillation ratio by 62.7% (from 109.6% to 46.9%), significantly outperforming conventional systems. The proposed method effectively enhances the performance of TEM transmitting systems.