A new infinitesimal computational approach to calculating frequency-domain electromagnetic response

For controlled source audio frequency magnetotellurics (CSAMT) which supported by traditional dipole hypothesis theory, the observations point should be located in far source zone. However, during field measurements, due to limited transmitter power, the distance between transmitter and receiver is usually not too large. Sometimes, field measurements are carried out in the near source zone, and the traditional dipole hypothesis will produce large errors under such condition. So, the errors between the approximate solution of traditional dipole approximation and the exact solution of the long grounded-wire source are firstly studied in this paper. Moreover, relative error distribution between exact solution of the long grounded-wire source and electric dipole source variations with different frequencies has been analyzed. It finds that the traditional dipole hypothesis bring large errors in the near source zone and no longer be satisfied to such condition. As a further study, a new 'harmonic point charge' solution for CSAMT, instead of the traditional dipole hypothesis, is proposed in this paper, which lay a foundation to realize near source prospecting and obtain more accurate near source responses in frequency domain electromagnetic.