From AssemblyMag Device reads data matrix codes though paint
Researchers at NASA’s Marshall Space Flight Center (Huntsville, AL) have developed a way to read Data Matrix codes even if they are obscured by paint or coatings.
The technique requires that the Data Matrix code be printed on the part with a magnetic material. A specially designed scanner can then read the code either optically or magnetically.
The magnetic marks can be read under conditions that would render optical methods useless. For example, the scanner can read the codes through contaminants, in the dark, or under bright light that would wash out conventional markings. In addition, assemblers can use the technology to deliberately hide Data Matrix codes for security reasons