Tracking metallic objects by information incorporated therein

摘要

The subject of the invention is method and device system for entering and retrieving information in the surface layer of objects made of solid matters. The information is entered with a (concentrated) beam directed to the surface and having a power density selected to induce permanent change at least in the surface layer of the material's structure in a way that the power density of the beam is smaller that the power density of the beam causing visible deformation, but bigger than that of the beam that causes (within the order of magnitude of the beam's diameter) inhomogeneities commensurable with the structural inhomogeneities generally present in the material. The invention can be used for all materials, the structure or internal stress of which can be modified with high energy density surface treatment (at the location of the treatment) (specially with the local laser treatment of ferromagnetic material).