Results from a novel direct magnetic gradiometer^*

Abstract

Development is continuing on a novel direct magnetic gradiometer that uses a string as its single sensing element. A string driven by an AC current and vibrating in its second order ‘S’ shaped mode is used to directly measure the magnetic gradient. The sensitivity is measured to be 0.4 nT/m/√Hz in the laboratory. Long-term drift is very low, and static measurements are made in the field with precision 0.2 nT/m. Laboratory measurements of moving iron spheres of various volumes demonstrate the accuracy of the sensor. By combining the sphere measurements with forward modelling of a hypothetical mineral deposit, we illustrate the utility of the gradiometer for airborne surveying. A 20 m line survey on the ground demonstrates the performance of the gradiometer in the field. These experimental and numerical results indicate that such a system is potentially viable for airborne and ground deployment and there is no reason the sensor could not be used in other applications.