Applying Stray Inductance Model to Study Turn-off Current in Multi-Turn Loop of Shallow Transient Electromagnetic Systems

The multi-turn, small loop is usually used as the transmitting loop for shallow transient electromagnetic (TEM) surveying. As an inductive load of the current inverter of the TEM system, it finds that there are serious oscillations at early part of the turn-off current. However, the existed
RLC
equivalent model of the loop alone fails to explain this phenomenon. In this paper, a novel current inverter for shallow TEM survey is designed and analyzed. The passive constant voltage clamping technology is used to achieve fast linear turn-off current. Furthermore, a novel stray inductance model of the current inverter is first proposed and utilized to analyze the serious oscillations of turn-off current. Based on this model, the turn-off current of the current inverter is simulated, and the simulated results agree well with the measured results of the experiment, which verifies that the proposed stray inductive model is effective and reasonable. According to the TEM principle, the high-frequency oscillations of the early part turn-off current will badly influence the shallow transient electromagnetic response. In order to suppress the oscillations of the turn-off current, two effective suppressing methods are proposed and analyzed. It will effectively enhance the electromagnetic data interpretation quality for shallow TEM survey.