Efficient simultaneous electromagnetic transmission or reception at different frequencies in electromagnetic mapping

DETAILED DESCRIPTION We claim: 1.
Electromagnetic exploration apparatus comprising means for simultaneously transmitting electromagnetic fields of three different frequencies, means for receiving transmitted electromagnetic fields of three different frequencies, at least one of said transmitting means and said receiving means including three air cored coils each lying in its own plane and having an axis perpendicular to its plane, said coils being mounted with their axes at least substantially parallel and with their planes closely spaced and at least substantially parallel, each coil being overlapped sufficiently with respect to the other two coils that the mutual inductance of said three coils is at least substantially zero.




Description:
This invention relates generally to methods and apparatus for electromagnetic exploration for electrically conducting ore bodies and like electrically conducting anomalies.
The general method is very well known and widely used.
One transmits an alternating electromagnetic field into an area to be explored; the alternating electromagnetic field induces eddy currents in an electrically conducting ore body or like anomaly; the eddy currents give rise to an electromagnetic field of their own and affect the resultant electromagnetic field in the area; and the existence of the eddy currents and hence the anomaly is detected by detecting the resultant electromagnetic field in the area.
Transmitter and receiver coil arrangements vary, the frequencies used vary, the measured characteristics of the resultant field that is measured vary and the apparatus used to create and measure the field varies in the practice of the general method.
Differing variations suit differing conditions.
This invention is particularly concerned with airborne electromagnetic exploration equipment and methods where the transmitting equipment and the receiving equipment is mounted on an aircraft and where two or more electromagnetic fields of different frequencies are transmitted and received in the search for hidden electrically conducting anomalies