Results from a novel direct magnetic gradiometer*

Abstract. Development is continuing on anovel directmagnetic 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/HHz 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 20m 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. Key words: aeromagnetic, magnetic gradiometer, survey, tensor