Investigation of the Metrological Properties of Magnetic Field Sensors Used in Popular Smartphones for the Shoe Size Determination System

This article presents a study on the metrological properties of smartphone magnetometers and their application in determining the correct shoe size. The research focuses on using magnetometers in smartphones to measure the magnetic field generated by magnetic markers placed inside shoes. To measure foot dimensions, smartphone embedded position sensors and image analysis were employed to determine key foot parameters accurately. Measurements were conducted under controlled conditions using triaxial Helmholtz coils, which generated a precise magnetic field. Linearity, sensitivity, offset, and measurement uncertainty were evaluated in several popular smartphones. The results indicate that the accuracy of magnetometer measurements depends on the quality of the smartphone. Electromagnetic interference, especially in cheaper devices, can introduce noise that affects data quality. Extended averaging periods help reduce noise and improve measurement accuracy. Smartphone magnetometers can be effectively utilized for precise magnetic field measurements, provided the device is calibrated correctly and the measurement method is appropriately adjusted. Certain limitations, such as noise from electromagnetic interference and its impact on data quality, remain challenging. Nonetheless, the study’s findings are promising, especially in applications such as shoe sizing systems, where accurate measurements of the inside of the shoe are essential for a proper fit of the shoe to the foot.