Input impedance of an insulated dipole in a borehole for underground radiation of electromagnetic waves

Abstract

An insulated short dipole antenna is needed for the subsurface underground radar useful for the remote sensing of underground targets such as underground tunnel in the depth more than 30 meters. Input impedance of such an antenna may be obtained by using the transmission line model having coaxial crosssectional layers of the insulating acetal tube, the muddy water, and the water-saturated granite on the aluminum tube. calculated input impedance based on the lossy transmission line is compared with the measured input impedance in the frequency band of 10MHz to 80MHz. The calculated input impedance does not coincide with the measured values but their trends are similar. A commercial numerical program based on the finite element method is used to compute the input impedance but its values are far off those of either the measured or the lossy transmission line model.