Modeled Performance of a Long Baseline Planar SQUID Gradiometer for Biomagnetism

In this paper, the performance of a first order planar SQUID gradiometer with a long baseline, with regard its application to biomagnetism, is presented. In particular, we report on the analysis of the device response to the current dipole which is the most fundamental model used in biomagnetism. The planar gradiometer is arranged to measure the field components. The results have been compared with those of an axial SQUID gradiometer having the same baseline, pickup coil´s size and the same SQUID design parameters. The performance study involves the computation of the magnetic flux measured by the sensors in the presence of a current dipole and the minimum detectable dipole as function of both off-axis and on-axis distance from the gradiometer. A comparative study as a function of sensor baseline has been also performed. Furthermore, the spatial resolution has been investigated by computing the response of both sensor type to a pair of current dipoles. The results have shown that the dipole current sensitivity of a planar gradiometer, (which measures the tangential magnetic fields), is better than those of the axial gradiometer suggesting that it is possible to employ planar gradiometers in multichannel systems for biomagnetism.