Magnetic Excitation Response Optimization Technique for Detecting Metal Targets in Middle-Shallow Strata

Abstract

Specific to the full-range detection demand for the magnetic anomaly targets such as metal in shallow strata, transportation pipelines, and mined-out regions during the geophysical survey, based on the transient electromagnetic method, using the Gauss inverse Laplace transform, a magnetic excitation model for metal targets in medium-shallow strata is proposed. By using the adjustment of the electrical parameters such as frequency, amplitude, and phase of the excitation current, a spatial multimode magnetic excitation field is formed, an array magnetic excitation detection device is developed, and a distribution model for the array magnetic excitation field is established. The hardware-in-the-loop simulation results show that the frequency and amplitude of the excitation signal are directly proportional to the spectral amplitude and the induced amplitude of the secondary field of the signal, where the signal has the most spectral components when selecting a frequency of 25 Hz. The duty cycle of the excitation signal is of nonlinear correlation to the magnitude of the signal frequency spectrum. When the duty cycle is 50%, the signal spectral components are the least and concentrated in the part with lower frequency, and when the duty cycle is lower or higher than 50%, the spectral components increase and spread to the middle and high frequencies. The indoor test results indicate that changing the excitation signal parameters can also increase the detection range and depth to a certain extent without changing the sensor parameters. It can also reduce the detection blind area to a certain extent. Therefore, the conclusion of this article can solve the problem of large detection blind areas in transient electromagnetic detection, and the application field can also be extended from deep mineral detection to new areas, such as medium and shallow unexploded bombs, metal pipelines, and goafs.