Distributed Em Parlmeters Of An Ungrokmded Horizontal Loop .4Nd Their Relation To The Near-Si-Rface Geoei,Ectrical Features

A horizontal transmitter loop is the principal part of many prospective TEM and FEM systems. In shallow<br>TEM geoelectric studies a loop with low electrical inertia has to be used to avoid a convolution problem. Up<br>to now an equivalent circuit with lumped inductance, capacitance, and resistance is widely used to simulate<br>loop’s parameters (e.g., resonance frequency) and intrinsic response. However, in-field measurements with<br>loops of different size have shown a lumped circuit to be unadequate in simulating early time and/or high<br>frequency loop responses. To account for these experimental results a system with distributed parameters has<br>to be used rather than an equivalent lumped circuit. The system is formed by the loop itself and the underlying<br>it shallow ground. Both oscillating and damped current and voltage transients as well as the frequency<br>response of such a system could be studied in detail on the basis of the transmission line theory and specially<br>designed computer simulating technique. It has been found from the in-field measurements that oscillating<br>transients are sensitive to local earth’s geoelectric structure and meteorological conditions.