Number 165 (Story #2), February 17, 1994 by Phillip F. Schewe and Ben Stein A SCANNING MAGNETIC FLUX MICROSCOPE , a device that can map magnetic fields with a spatial resolution of about 80 microns and a field sensitivity of 7 pico-Tesla-Hz**-1/2, has been developed by a Maryland-Berkeley collaboration (contact Frederick Wellstood, 301-405-7649). The detector uses a 77-K superconducting quantum interference device to sense tiny magnetic fields from a sample which moves back and forth beneath the SQUID in 1-micron steps. For practice, the scientists made a picture of the face of George Washington as it appears on the one- dollar bill. The accurate likeness is composed of the measurements of the enhanced fields in the vicinity of the tiny droplets of magnetic ink used on all greenbacks. The scientific uses of the magnetic microscope include prospecting for the characteristic fields emanating from microscopic nuggets of superconductor buried inside otherwise non-superconducting samples. The microscope can also be used to image poorly-magnetic materials such as thin copper patterns on printed circuit boards by measuring the faint magnetic fields that arise from eddy currents induced in the copper. (R.C. Black et al., 3 January 1994, Applied Physics Letters.)