A novel technique to compute impedance of an arbitrarily oriented coil antenna for well logging applications

In a typical well logging application, a hole - about 15 to 30 cm in diameter - is drilled through the earth formation to a depth that may extend to a few kilometers. To measure conductivity and permittivity of the formation, a sensor consisting of an array of transmitters and receivers is lowered in the borehole. Coils form the basic element of the antenna arrays. Accurate evaluation of the coil impedance in presence of complex sensor structure is essential in evaluating performance of the antenna system. This paper introduces a numerical method based on superposition principle and edge current model to compute impedance of a coil with thin wires at high frequency. Both axial and tilted coils are studied. Numerical results are validated by comparing them with measurements.