Estimation of Electromagnetic Parameters by Linear Dipole Array in a Borehole

It is important to estimate conductivity and per- mittivity 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 modula- tor 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 ex- periments in granite with the borehole radar. We calculated the array signals, including the granite medium and the antenna characteristics, by Method of Moment. These ex- perimental and theoretical results were analyzed by cross- spectrum 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.