The small multiturn overlapping coil is always used in mine transient electromagnetic exploration. For the effect of turn-off, the first field dominates total field during the off-time of transmitting current and early after off-time. This may cause unresponsive for shallow low resistance anomaly. So we suggest that use cross coil for first field eliminating: Analyzes the distribution of first field inside and outside the transmitting coil during the off-time; Deduces the analytic expression of magnetic flow for first field inside the receiving coil; Worked out the coefficient of position for receiving coil is 0.93 when the magnetic flow for first field inside the receiving coil is 0. According to laboratory experiment for low resistance model and site detecting for tunnel filled with water, we verify the availability of cross coil for first field eliminating and low resistance anomaly detecting. It provides technical support to mine transient electromagnetic exploration.
mine transient electromagnetic, antenna, first field eliminating, transmit-receive crossing coil.
The project is supported by National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2016ZX05045-002-0003 and 2016ZX05045004-007).
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