A method for reducing the influence of mechanical disturbances in a magnetic field measuring system which uses a loop positioned in the field and oscillatable due to interaction between the field and a current in the loop, the loop being supplied by an alternating current having a frequency considerably higher than the mechanical resonant frequency of the loop, employs a signal which is a component of the mechanical resonant frequency of the loop; the signal being fed back to the loop to obtain damping of mechanical oscillations.
A magnetic field sensor device (2) is described that comprises an oscillatory member (8) and current control means (6). The current control means (6) is arranged to pass an alternating current (AC) along at least first (10) and second (12) current paths provided through the oscillatory member (8) and is arranged to provide magnetic gradiometer mode operation (i.e. to measure magnetic field gradient) in which current flow through the first current path (10) is in substantially the opposite direction to current flow through the second current path (12). The current control means (6) can also prove magnetometer mode operation (i.e. to measure magnetic field strength). The magnetic field sensor (2) may be used in a compass.
