Other features

The circular arrangement of the coils significantly improves the signal-to-noise ratio by up to 50%, substantially increasing the detection depth. The 5 time ports and the decoupling of the receiving coils significantly improve detection and resolution. The dimensioning and geometric placement of the inner receiving coils, combined with early measurement, also contribute to improved performance and increase the resolution of small objects near the surface. The dimensions and placement of the external receiving coils are adapted for the detection of larger and more deeply buried targets. The geometric dimensioning of the system ensures a significant increase in productivity thanks to the large scan area covered. Application: One of the basic requirements when using electromagnetic methods to detect metal anomalies is a high contrast in the electrical parameters of the objects to be detected compared to the natural conductivity of the subsurface. Iron has an extremely high conductivity of 10⁷ S/m and an electrical resistance of 10⁻⁷ Ωm. This corresponds to a difference of 7 orders of magnitude compared to the best conductive soils/rocks. The same applies to magnetic permeability (magnetite μr = 5, iron μr = 120). This extremely high contrast regarding electrical conductivity and magnetic permeability relative to naturally occurring soils/rocks forms the basic requirement for detection when using electromagnetic methods. This measurement method belongs to the family of transient electromagnetic methods (TEM), which operate within the time range. A source field is used that induces current systems in the subsurface, the propagation of which depends on the conductivity distribution in the subsurface. In the case of inductive transmitter coupling, a constant direct current flows into a horizontal transmitter coil. The constant transmitter current is switched off or on as abruptly as possible, causing the constant primary magnetic field to collapse, which has almost the geometry of a vertical magnetic dipole (VMD). At the same time, the time-dependent primary magnetic field generates a current system according to Ampere's law and Faraday's law of induction. Depending on the substrate, it propagates both vertically and laterally (diffusion) as time passes and induces eddy currents in the conductive substrate in accordance with Maxwell's equations. This flow system decreases due to ohmic losses, which in turn produce a secondary magnetic field that also decreases over time. The time-dependent changes in the magnetic field components induce a voltage decay (transient) that will be measured in the receiving coils (here, the change in the vertical magnetic component over time).