On the electromagnetic detection of the thickness of a coal or lignite seam with slate backing

The use of two small current loops for probing the thickness of a two-layer earth structure is discussed. The thickness and the conductivity contrast can be found by zeroing the secondary magnetic field on the axis of the receiving loop. The inversion from the measured data to the layer thickness proves that our procedure is simple. The whole method can be incorporated into an automated mining machine for sensing a coal or lignite seam with a slate backing.