The AG currency detection PCB, which is available from Rhopoint
Components, contains an array of 20 to 60 giant magneto resistive (GMR)
sensors that detect magnetic fields in currency and other secure
documents using magnetic ink for validation purposes. The beauty of this
system is its non-contact operation. The assembly is placed 1mm from the
currency or document path, in contrast to inductive heads, which are
pressed against the target and often cause jamming in high-speed
transport mechanisms.