COMPUTATION OF TRANSIENT ELECTROMAGNETIC FIELD FROM A RECTANGULAR LOOP OVER STRATIFIED EARTHS
矩形大定源层状模型瞬变电磁响应计算

The paper introduces a new method for computing the transient electromagnetic (TEM) response from a large rectangular loop over a layered earth. In the method, the large loop is spanned by fictitious squares. The response from each square are then summed up as that of the large loop. In frequency domain, the superposition leads the vertical magnetic field to be expressed as a standard Hankel integral, whose integrand contains the addition of 0-order Bessel functions involving the distance from the center of each square to calculating point. Time-domain response can then be cosine transformed directly from the frequency domain result. The error of the method stems from the approximation of square loop by circular one, and comparing with analytical response of half space, relative error is less than 10~(-3) with only 16 squares used.