Apodized pickup coils for improved spatial resolution of SQUID magnetometers

Publisher Website
Google Scholar
Abstract
The spatial resolution of a SQUID magnetometer is known to be determined by the size of the magnetometer pickup coil and the distance of this coil from the source of the magnetic field. With the advent of spatial‐filtering techniques for converting magnetic field maps to current density images, it is clear that the quality and spatial resolution of the current image is also affected by the detailed characteristics of the transfer function between the current sources and the pickup coil. We show that the quality of a current image can be improved over that obtained with conventional pickup coils by using a multiturn pickup coil whose interturn spacing is adjusted to provide a source‐coil transfer function with specific characteristics. This process is functionally equivalent to apodization techniques applied in optical image processing, in which the aperture function of the telescope is adjusted to improve spatial resolution. In coil design, the process of apodization involves designing a magnetometer coil whose transfer function has its first zero at a relatively large spatial frequency. Using apodization, we can decrease coil size and increase the number of turns without a large increase in coil inductance. Our model calculations demonstrate that apodization allows us to optimize the ability of a coil design to image a current distribution, subject to the constraints of signal‐to‐noise ratio, spatial resolution, and coil inductance.

This publication has 12 references indexed in Scilit: