Method for full magnetic gradient tensor detection from a single HTS gradiometer

Abstract

A new method to measure the full magnetic gradient tensor (FMGT) using a single rotating high-temperature superconducting planar first-order gradiometer is described. Determining the FMGT provides valuable additional information about magnetic sources and their anomalies and, critically, the location of magnetic targets with less ambiguity and with fewer survey lines required. This paper presents both a theoretical description and experimental demonstration of the single sensor system that can, in principle, extract all the magnetic gradient tensor components, with suitable referencing and/or field cancellation procedures. The technique involves rotating the planar gradiometer mounted on an angled plinth about the vertical axis of the sensor package. The technique works by shifting gradient terms to harmonics of the rotating frequency, above the 1/f noise of the device, and allows extraction of all the components in the frequency domain. Additional referencing enables compensation for the non-ideal gradiometer response and provides a more accurate measurement of contaminated gradient components. Laboratory results show tracking of a moving dipole target and these are compared to a modelled response, both with and without field compensation.