In this paper, we develop the theoretical basis and carry out numerical studies on a new Differential Target Antenna Coupling (DTAC) method for imaging objects within the earth. The DTAC method uses a separate transmitter and a rotating receiver to collect the magnetic field data. The DTAC method uses at least two frequencies. One frequency is used as a reference signal to establish the null direction at that frequency, and then a different frequency is used to measure the change in the null at that new frequency. We can also use an arbitrary number of frequencies with just one reference frequency for wide-bandwidth measurements. By comparing the characteristics of the null magnetic fields at these two or more frequencies, this technique allows one to precisely determine the orientations of the measuring array from the measured data. This allows for the nulling out of the overwhelming effects of the layered earth, thereby allowing for the measurement of the much smaller target response. In this paper, we have assumed a horizontal array with an intended separation between transmitter and receiver of the order of kilometers and a very powerful transmitter. The depth of investigation in this case was also of the order of kilometers. This type of array is applicable to natural resource investigations, e.g., mining, geothermal, and petroleum.

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