Method of suppressing spurious magnetic signals detected by a magnetic gradiometer

摘要

A method of suppressing spurious magnetic signals in a magnetic gradiometer comprises providing two gradiometers S1, S2 spaced apart with their sensitive axis aligned in the same direction; applying a reference magnetic signal to the gradiometers, which is distinguishable from the said spurious signals, and analysing the signals form the gradiometers and the reference signal to derive a signal indicative of the target signal. The reference and spurious magnetic signals may be from near field sources to the gradiometers and the target signals for a far field source. The output signal form one gradiometer is subtracted from that of the other to provide a first signal containing information about the spurious signals. A second signal with information about the reference signal is provided and used in conjunction with a gradiometer signal to produce a third signal. The three signals are processed to obtain a signal indicative of the target signal. The reference magnetic signal may be provided by an alternating current flowing in a conductive loop 1 formed around the gradiometers S1, S2. The first and third signals may be low-pass filtered 4, 6 to the same bandwidth.