The Effect of Sensor Size on Axial Gradiometer Performance

In this paper, we examine the influence of sensor size, sensor spacing (gradiometric base), and distance from dipole source on the performance of a single-axis gradiometer positioned along the dipole axis. The case of a finite base gradiometer with ideal sensors is considered, then the influence of finite-size sensing elements is modeled, and finally, a comparison with experimental results obtained with two ring-core and race-track fluxgates and two anisotropic magnetoresistors (AMRs) is evaluated. Some of the effects found may be counterintuitive, and especially in close proximity of the dipole source, the gradient cannot be further modeled by simplified uniaxial approximation because of the active element size. Full Biot-Savart field model was considered in those cases.