接地导线源电磁场全域有效趋肤深度

Effective skin depth of whole EM field due to a grounded wire source

为了更好地推进广域电磁法的发展和应用,本文以接地长导线源为例,研究了可控源电磁场全场域的有效趋肤深度.利用频域电偶极源在均匀半空间产生电磁场的闭合表达式,计算了不同电磁场分量定义的有效趋肤深度,并讨论了在不同频率、不同偏移距、不同电导率情况下,有效趋肤深度的变化特性.根据有效趋肤深度随偏移距的变化特征以及与平面波趋肤深度之间的关系,利用多项式拟合的办法在五个不同频率范围内给出了适用于全场域的有效趋肤深度快速估算公式.研究结果表明:不同分量定义的有效趋肤深度是不同的,但是它们随偏移距、频率、电导率等参数的变化趋势是类似的,而且在一定范围内都趋近于平面波趋肤深度.理论模型的研究表明,有效趋肤深度可以作为测量参数选取和数据解释工作的参考依据.

The effective skin depth of whole electromagnetic field due to a grounded wire source in a homogeneous half-space was defined as the depth at which the amplitude falls to 1/e of the value at the surface. With the closed form expression of EM fields generated by a grounded horizontal harmonic electric dipole in a homogeneous half-space, effective skin depths of different EM components were calculated and their variations with different parameters were studied as well. It depicts that effective skin depth due to grounded wire source depends on frequency, offset, conductivity and field components. But all the curves show similar characteristic variation, and the effective skin depth approaches to plane wave skin depth at some certain value for all parameters. According to the relationship between effective skin depth and plane wave skin depth and the offset, a fast estimate formula for effective skin depth was achieved using polynomial fitting method. A theoretical example demonstrates that the effective skin depth can be used as one of effective aids for estimating the optimum parameters in EM survey design and data interpretations.