Approach for sub pT, room temperature magnetic sensors

Some of the major contributions to noise in magnetic sensors can only be reduced by increasing the size of the sensor. Here we present an approach for reducing 1/f noise in large magnetic sensors. The approach is based on modulating the field by rotating a disc containing permalloy flux concentrators or flux guides. The disc rotation is driven by an air turbine. Modulation frequencies as high as 76 Hz have been achieved, but higher modulation frequencies will be achieved in our new design. Low frequency signals appear as sidebands around the modulation frequency. The magnetic sensor used is a magnetoelectric sensor. Magnetoelectric sensors have achieved sensitivities of 2nT at 1 Hz. By using modulation to operate at the mechanical resonance frequency of magnetoelectric sensors it should be possible to achieve sub pT/Hz^1/2 at 1 Hz. Here we discuss the progress and problems in achieving this goal.