Influence of Excitation Signal Type and Period Selection on Detection Capability of TEM System

Abstract

The type and period of excitation signal are the important technical indexes of TEM system detection, which have an important influence on the detection accuracy and detection depth of the system. In this paper, by simulating the magnetic field distribution characteristics and magnetic focusing effects of transmitting coils with different excitation signals at the same depth, the differences of excitation signal types are analyzed and studied. Then, the echo effect diagram of receiving coils and the change curve of magnetic flux at the equivalent depth are simulated under different periods to determine the minimum period of excitation signal by comparative analysis. The simulation results show that the focusing and propagation depth of the magnetic field energy generated by the excitation signal are better when the rectangular pulse is selected and its period is determined to be 500 ms. Experimental tests under different thickness of steel plate show that the induced voltage on the receiving coil is different with different thickness. The thicker the ferromagnetic material is, the smaller the peak value of echo signal is. Moreover, in the case of no ferromagnetic material model, the induced voltage of the receiving coil is the maximum. This provides a theoretical basis for evaluating the corrosion of buried metal pipes by transient electromagnetic detection system.