Directionally-conductive, optically-transparent composites by magnetic alignment

Ferromagnetic metal spheres (silver-coated Ni, 0.5-2% in volume) dispersed in a thin layer of transparent polymer medium were subjected to a vertical magnetic field for alignment into the chain-of-spheres (or column) configuration. When the polymer was solidified, the resultant composite contained vertically aligned, but laterally isolated, columns of conductive particles in a sheet of transparent matrix. The sheet material transmitted in excess of 90% of incident light in the visible range, and was highly conductive only in the thickness direction. While optically and electrically anisotropic, the magnetic columns in the composite exhibited an essentially isotropic magnetic behavior for the given height and spacing of the columns. The material, if suitably modified, may be useful as a transparent position sensor for visual communication devices such as touch-sensitive screens or write pads