Sensitivity analysis and comparison of frequency-domain electromagnetic system configurations

The responses of electromagnetic (EM) systems in the frequency-domain depend on the transmitting frequency and configuration between the transmitter and receiver under certain geological environments. In order to reduce the noise from the primary field for improving the sensitivity of the EM system, special techniques have to be employed. A sound analysis for the coil configurations can help the EM system design. This paper addresses the theoretical sensitivity analysis of coil configuration EM systems. By analysis and comparison, we see that the null configurations can also receive the second field generated by the three-dimensional targets located in the shallow subsurface. This configuration is less sensitive to the geometric setting errors than the perpendicular configuration is. These characteristics can be applied to simplify the high-frequency EM system design for near-surface applications. Test results show that the null configuration is sensitive to image small three-dimension targets located in the shallow subsurface even though the residual primary field is not cancelled.