Hiding Information in Silver and Carbon Ink
“We used silver and carbon ink to print an image consisting of small rods that are about a millimeter long and a couple of hundred microns wide,” said Ajay Nahata from the University of Utah, leader of the research team. “We found that changing the fraction of silver and carbon in each rod changes the conductivity in each rod just slightly, but visually, you can’t see this modification. Passing terahertz radiation at the correct frequency and polarization through the array allows extraction of information encoded into the conductivity.”
Research paper.
Nutty Professor • December 13, 2016 9:33 AM
Maybe that explains the fancy copper-colored ink on the new US $100 bills… an efficient way to scan and track serial numbers?