Other features

The circular arrangement of the coils significantly improves the signal-to-noise ratio, up to 50%, which considerably increases the detection depth. The 5 time gates and the decoupling of the receiver coils significantly improve detection and resolution. The dimensioning and geometric arrangement of the inner receiver coils combined with an early measurement also contribute to the improved performance and increase the resolution of small objects near the surface. The dimensions and arrangement of the external receiver coils are adapted to the detection of larger and more deeply buried targets. The geometric dimensioning of the system ensures a significant increase in productivity due to the large scanning area covered.ApplicationOne of the basic requirements when using electromagnetic methods for detecting 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 resistivity of 10-7 Ωm respectively. This corresponds to a difference of 7 orders of magnitude compared to the most conductive soils/rocks. The same applies to the magnetic permeability (magnetite μr =5, iron μr =120). This extremely high contrast with regard to electrical conductivity and magnetic permeability compared to naturally occurring soils/rocks forms the basic requirement for detection using electromagnetic methods. This measurement method belongs to the family of transient electromagnetic methods (TEM), which operate in 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 in a horizontal transmitter coil. The constant transmitter current is switched on or off as abruptly as possible and causes the constant primary magnetic field to collapse, which almost has 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 conducting substrate according to Maxwell's equations. This current system decays due to ohmic losses, which in turn produce a secondary magnetic field, which also decays with time. The time-dependent changes in the magnetic field components induce a decay voltage (transient) that will be measured in the receiving coils (here the change in the vertical magnetic component with time).