Analysis on performance of magnetic induction-based through-the-earth wireless initiation system using close wound small diameter coils

In order to realize safe and portable TTE wireless initiation in the mining areas, a scheme based on magnetic induction (MI) of TTE wireless initiation with small diameter coils at the ground transmitter is proposed, and the equivalent coupled circuit analysis model of the transmitting coils on the ground and the receiving coils underground is established. Based on the established coupled circuit analysis model, the voltage expression of underground receiving terminal load is derived. In the expression, the mutual inductance coefficient between the transmitting coils on the ground and the receiving coils underground represents the coupling strength between the transmitting and receiving coils. Since the relative position relationship between the transmitting coils on the ground and the receiving coils underground is not parallel or coaxial, the traditional mutual inductance formula based on parallel and coaxial coils is no longer applicable. Therefore, the general expression of mutual inductance coefficient between single-turn circular coils with general positional relationship considering eddy current effect is derived from magnetic vector position. The simulation results of mutual inductance coefficient show that there is a blasting blind zone when the transmitting coils on the ground are placed horizontally, so it can be determined that the transmitting coils on the ground should be placed vertically. According to the load voltage formula, the influences of the radius and turns of the transmitting coils, the frequency of the transmitting signal and the vertical penetration depth on the load voltage and horizontal coverage distance of the underground receiving terminal of the TTE initiation system are simulated and analyzed. The simulation results show that, the horizontal coverage distance of the TTE wireless initiation system with transmission coils used vertical mode can reach 200 m ～ 300 m. With the increase of the depth of penetration, the horizontal coverage distance of the system gradually decreases. However, the horizontal coverage distance of the TTE wireless initiation system can be improved by appropriately increasing the radius and turns of the transmission coils and reducing the signal frequency to meet the requirements of TTE wireless initiation in mining application scenarios of different scale mining areas.