The MICR head is the part of a scanner that reads magnetic ink, such as the characters printed at the bottom of a check. The acronym MICR stands for Magnetic Ink Character Recognition.
Check scanners read the magnetic characters, or MICR line, on a check by imparting a magnetic charge to the ink just before passing it over the reader. The MICR head does not “see” the characters, but instead detects the magnetic signal strength in a straight line horizontally, resulting in a wave pattern. Each number is designed to have its own uniquely identifiable waveform — the reason why MICR characters are printed with odd “machine-like” shapes and exaggerated features.
Over extended use, the MICR head may become worn down and need to be replaced because the repeated rubbing of paper against it actually wears down the metal. This usually happens over a period of years, after scanning hundreds of thousands of checks.