The near-surface non-ferromagnetic targets survey with electromagnetic induction technology

Urban development often leads to minor changes in near-surface structures and the presence of metal objects on or below the ground, causing metal contamination. These objects can be ferromagnetic or non-ferromagnetic. Geophysical electromagnetic induction (EMI) technology is used to locate them. Magnetic surveys identify ferromagnetic targets, which are widely used around the world, while electromagnetic induction surveys detect non-ferromagnetic metal objects, which are under development. A comprehensive Geophysical EMI scan can reveal both types of metal contamination. In July 2023, we investigated potential non-ferromagnetic metal contamination through physical simulations in a park in Pudong New Area, Shanghai. Three sets of aluminum tubes, each 1 meter long with a wall thickness of approximately 1 cm and diameters of 18 cm, 32 cm, and 40 cm, were placed on a 10-meter-wide by 20-meter-long area. A frequency domain electromagnetic (FDEM) induced conductivity meter with external GPS was used in continuous survey mode, with survey lines spaced 25 cm apart and survey points approximately 10 cm. The meter was positioned about 1 meter above ground and operated at 10 operation frequencies, providing in-phase and quadrature readings in ppm, as well as apparent conductivity and magnetic susceptibility for each frequency. The all resulting images clearly show the three non-ferromagnetic targets, demonstrating that frequency domain electromagnetic induced technology effectively images non-ferromagnetic materials.