Digital spatial filter made from a SQUID array

A linear array of high transition temperature SQUID, has been configured to work as digital spatial filters. The SQUID filters can be configured to obtain a desired spatial frequency response. We describe their design using a technique known as Frequency Sampling, which consists of specifying a discrete spatial frequency response for the SQUID array spatial filter. We then apply that sequence to the inverse Discrete Fourier Transform to get the spatial domain gain of each SQUID and the baseline. Several designs for spatial band-pass filters are proposed and checked experimentally. The results show that while keeping or even increasing the noise rejection obtained with conventional gradiometers, the SQUID filters preserve the original signal characteristics of the source.