Research on towed TEM on off-centre self-compensation technology for urban underground space detection

Abstract

Abstract Transient electromagnetic (TEM) is a geophysical method that can obtain the electrical information of underground media. It will provide strong technical support for the safe development and operation of urban underground space. However, the coupling effect of the transmitting current on the receiving loop leads to the shallow blind area of TEM. Especially, the coupling effect is more serious when the multi-turn and small-size coil structure is required because of the limitation of urban buildings and ground facilities. To solve these problems, this paper proposes a towed TEM technology based on off-centre self-compensation with the small size structure. The new technology adopts the idea of non-coplanar eccentricity structure to design a self-compensation system, which can eliminate the coupling effect. In this paper, the distribution of primary field in receiving coil is studied, and the key structural parameters of transmitting coil and receiving coil is obtained by theoretical model. The experimental results show that the towed TEM system based on the new technology can directly obtain pure secondary field signal. Compared with other TEM structures, it has higher tolerance for physical size error and higher practicability. The towed TEM technology proposed in this paper will provide a theoretical basis for the realization of blind area free, high-speed and accurate scanning measurement of urban underground space.