The Impact of Permanent Magnet Geometry on the Reading of Soft Magnetic Barcodes Using Magnetoresistive Sensors

Encoding information in patterns printed with magnetic ink can extend the usability of barcode and QR code technologies to applications that do not require a line of sight between the sensor and the code. Such an implementation garners an interest in security, track-and-trace, and recyclable packaging applications. Previous work has demonstrated a device that can read a barcode obscured by a layer of opaque and 1 mm thick material. However, given that the most widespread magnetic toners are soft magnetic, a permanent magnet (PM) is needed in the system alongside the sensor to magnetically bias the barcode, which affects the sensor sensitivity. Here, we describe a protocol to evaluate the impact of different PM geometries on the performance of the sensor and validate it with experimental results, enabling active feedback for integration in the scanner system. As a result, we have reached an improved geometry that increases the reading distance of the device to at least 2 mm. This study is also useful for other applications that require optimization of the interaction between a PM and a magnetic sensor (e.g., nanoparticle tracking in magnetoresistive biosensors).