Estimation of Electromagnetic Parameters by Linear Dipole Array in a Borehole

It is important to estimate conductivity and permittivity of formation around a borehole. Arrival time and amplitude of the direct wave in single-hole borehole radar is related to the electromagnetic parameters. In this paper, we propose a liner array of dipole antenna elements in a borehole for a receiver. We introduced an optical modulator to transfer the received array signals to optical signals near the antenna elements. We made the liner array type borehole radar with the five antenna elements. We did experiments in granite with the borehole radar. We calculated the array signals, including the granite medium and the antenna characteristics, by Method of Moment. These experimental and theoretical results were analyzed by crossspectrum analysis to calculate the relative amplitude and the group delay among the array elements. We compared experimental data with theory calculation to estimate the electromagnetic parameters.