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Cross-borehole electromagnetic probing in the VHF band has been used successfully for locating underground tunnels and other subsurface structures, even when these are deeply buried and devoid of highcontrast reflecting materials. Full scale studies of available and developmental field techniques can be expensive and difficult, and analytical models are insufficient in complexity for adequate description of real-world problems. Laboratory scale models offer a valuable alternative approach for investigating such subsurface exploration techniques, although they, too, have limitations related to the impossibility of perfectly scaling all relevant parameters, duplicating the intricacy of a real-world host medium, etc. This study utilized a circular metal tank lined with microwave absorbing material and filled with a relatively inexpensive low-loss ceramic powder medium. Simulated boreholes, targets, scaled dipole antennas and baluns were constructed, and instrumentation operating in the 2–4 GHz band was assembled and automated. The result is a scale model measurement technique that has proven useful for tunnel detection investigations and that is neither unduly expensive nor difficult to implement. |
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