Characterization and reduction of background noise for the detection of plastic anti-personnel landmine in mineralized soil

Abstract

If the continuous-wave electromagnetic induction (EMI) method is used to detect plastic anti-personnel (PAP) landmines in strongly mineralized soil, background noise may interfere with and further submerge the weak secondary field generated by the landmine. To analyze quantitatively the characteristics of this noise, a semi-space homogenous medium model was developed based on a cylindrical coordinate system. The results of simulation show that, in the signal of the background noise generated by the mineralized soil, the real component dominates whereas the imaginary component is insensitive to changes in the electromagnetic properties and sensor height. A noise reduction method based on the quadrature electromagnetic method is proposed. Assuming a spherical model for the ferromagnetic components of the PAP landmine, an optimal excitation frequency of the primary field was determined. By considering the phase shift in the sensor and signal processing circuit, a method was developed to determine a sensor pre-correction. In addition, an experimental platform was built that included a PCB-based double-D EMI sensor, a data acquisition card, and a three-dimensional scanning slideway. Experimental tests with a PAP landmine buried in clay, laterite, and magnetite produced results that corroborated the above theoretical analysis. The quadrature electromagnetic method is still able to detect secondary fields with high signal-to-noise ratio generated by the PAP landmine buried 15 cm deep in the magnetite.