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When working in the areas with strong interference and limited sites, such as cities, dams, and mountainous areas, using the conventional transient electromagnetic (TEM) devices is difficult to lay out large transmitter loops for conventional surveys. The small-loop transient electromagnetic method, which has the advantages of lightweight and high efficiency, is a new technology of current researches. First of all, A one-dimensional (1-D) layered model and a three-dimensional (3-D) homogeneous half-space model were established by using numerical simulation method. The research results show that the small-loop TEM devices can not only accurately reflect the anomaly information of deep targets, but also be more sensitive to the detection of shallow targets. By using high-current technology, the signal intensity and detection depth of multi-turn small-loop TEM devices and that of large loop device are the same. Finally, the accuracy and effectiveness of small-loop devices were verified through analysing the results of dam karst investigation. The research work provides a reference for the qualitative analysis of response characteristics and data interpretation of small-loop TEM.

The small loop transient electromagnetic method (TEM) in shallow water has strong adaptability and high resolution and is one of the current research hotspots. In this paper, a shallow-water model of a typical low resistance anomaly is established, which can be obtained through numerical simulation analysis. In the early time, the shallow water layer has large response and the low resistivity abnormal body has small response; In the late time, the shallow water layer has small response induction response and the low resistivity anomaly has larger response, and the response curve shows “double peak” attenuation law; The effects of different thicknesses of shallow water layers on the response of low resistivity abnormal bodies show “single peak”, “double peak”, and “peak wave trough” attenuation laws; However, the effect of different resistivity in shallow water layer on the response of the low resistivity abnormal body only shows the attenuation pattern of “single peak” and “peak wave trough”. Finally, the article takes the highway site selection survey as an example, combined with the high density resistivity method comparison analysis, and verifies the reliability and accuracy of the detection results of the small loop TEM in shallow water. The research work provides a theoretical reference for the qualitative analysis of the response characteristics and data processing interpretation of the small loop TEM in shallow waters.

Corrosion testing of buried metal pipelines is an important measure to ensure the safe operation of pipelines. In order to investigate the transient electromagnetic field named response of buried metal pipelines, a three-dimensional simulation model was established by using multiphysics simulation software named ANSYS Multiphysics to calculate and analyze buried metal pipelines with different corrosion degrees, ie different wall thicknesses, on the receiving coil after the excitation signal is turned off[1]. The induced electromotive force changes, the results show that the larger the wall thickness, that is, the smaller the corrosion degree, the slower the attenuation of the induced electromotive force curve of the receiving coil, the smaller the wall thickness, the faster the attenuation; and the verification was experimented: the transient electromagnetic method can effectively detect the degree of corrosion of metal pipes buried under the ground.