HTS SQUID microscope head with permalloy flux guide

In order to improve the spatial resolution of an HTS SQUID microscope, permalloy rods with sharpened tip angles of 50° to 170° were placed in front of a SQUID as magnetic flux guides. A current carrying meander line on a printed circuit board with lines and spaces of two widths, 0.3 mm and 0.5 mm, was used as a magnetic field source. The magnetic field distribution was better resolved with the smaller tip angle. Also, a rod with a smaller tip diameter of curvature of 30 μm could resolve the magnetic field distribution better than one with a 100 μm diameter. It was further found that using a magnetic shield around the magnetic flux guide to suppress the inefficient magnetic field allowed the magnetic field image to be better resolved. The limits of the system´s spatial resolution were examined with a 100 μm wide meander line. Magnetized laser-printed characters of font size from 2 points to 5 points were also imaged. It was found that this method has a higher magnetic sensitivity and spatial resolution than a large SQUID system, and allows the position and distance from the sample to be adjusted.