Detecting Magnetic Ink Barcodes With Handheld Magnetoresistive Sensors

Information encoding in barcodes using magnetic-based technology is a unique strategy to read data buried underneath non-transparent surfaces since a direct line-of-sight between the code and the reader is not required. This technology is of particular interest in secure labeling and recyclable packaging applications. However, current magnetic reading heads, such as those employed for magnetic ink character recognition (MICR), need to be placed in contact with the magnetic structures, limiting the depths at which the information can be read. This article describes a strategy to overcome that limitation by replacing the traditional inductive heads with tunnel magnetoresistive (TMR) sensors. Soft-magnetic codes can be printed using conventional LaserJet toners and, by having their magnetization set with a permanent magnet (PM) included in the device, the resulting magnetic field can be read using a TMR sensor. We demonstrate that such a device can read barcodes at depths of at least 1 mm. It can also resolve individual structures as thin as $200 ~\mu \text{m}$ when used in contact.