A radar coal thickness sensor

A radar coal thickness sensor is being developed by the Bureau of Mines to measure both the dielectric constant and thickness of a coal seam as part of a sensor array supporting a computer-assisted coal mining machine. The noncontacting stepped-CW radar sensor measures the complex reflection of coefficient of the coal-shale interface to resolve the coal thickness to sub-wavelength accuracies. The technique uses a monostatic antenna configuration. Transfer function errors are identified by using spatial modulation created by antenna motion. Synthetic range gating is used for clutter rejection. Finally, polarimetric scattering matrix techniques are used to calculate the dielectric constant and thickness of the multilayered coal/shale media. Data taken both in the laboratory and in an underground mine, in the 0.6-1.4 GHz range, with a network analyzer and dipole antenna, have validated the technique. Accurate in situ measurements were made of a coal seam 6 in (15.2 cm) thick with a dielectric constant of 4. The coal thickness was confirmed by physical measurement. An independent measurement of the coal dielectric constant confirmed the accuracy of the noncontacting dielectric measurement technique