激励信号类型及周期对线圈聚焦和检测深度的影响

激励信号类型与周期选取是影响瞬变电磁法(TEM)系统检测能力的重要因素。利用时域有限元积分方法对不同激励信号进行仿真，通过发射线圈磁场分布特性与同等深度处磁聚焦效果的对比、分析，确定激励信号类型；根据探测深度与灵敏度依赖于激励信号周期的特性，确定激励信号的最小周期。以此周期为下限，在不同周期下进行仿真，得到接收线圈回波信号变化图与同等深度处的磁通量变化曲线图，对比分析，最终确定周期为500 ms的矩形脉冲作为激励信号较为合适，更有利于磁场能量聚焦与传播的深度。最后对不同厚度的钢板进行仿真，分析回波信号与钢板厚度的关系，为实际瞬变电磁探测系统设计提供理论依据。

Influence of excitation signal type and the cycle on the coil focusing and the detection depth

The excitation signal type and cycle selection are important factors affecting Transient Electromagnetic Method(TEM) system detection ability. Using the time-domain finite element integration method to simulate different excitation signals, through the contrast and analysis of the transmitter coil magnetic field distribution characteristics and magnetic focusing effect in the same depth, the excitation signal types can be determined. For the detection depth and sensitivity depending on the excitation signal cycle, the minimum period of the excitation signal is determined. Taking the minimum period as the lower limit, the simulation is carried out in different cycles, and the receiving coil of the echo effect diagram and the magnetic flux change curves of equivalent depth are obtained. Comparison and analysis are conducted to determine the appropriate cycle. The conclusion is that the rectangular pulse with 500 ms is more suitable as excitation signal, and is helpful to magnetic field energy focusing and the depth of propagation. Finally, the steel plates with different thicknesses are simulated, and the relationships between the echo signal and the thickness of steel plate are analyzed. This work can provide a theoretical basis for the practical transient electromagnetic detection system.