Multiplexed in-Series Macro-Bend Fiber Sensors for Personal Authentication Through Foot Recognition

Abstract

This work proposes a new tactile sensing system for biometric authentication. The system operates based on the response of multiplexed optical fiber macro-bend sensors to plantar pressure. The setup contains a set of 6 in-series sensors installed in holes drilled in a foot-shaped slab of Polymethyl Methacrylate. Each sensor is a loop of standard single-mode telecommunication fiber with 2.5 mm radius, encapsulated with silicone elastomer. The instrumentation required for interrogation includes only a broadband visible light source and a ultraviolet-visible spectrometer. Personal authentication is based on recognizing the unique pattern of pressures applied by the person's foot in the metatarsal, outside of the foot arch, and heel areas monitored by the 6 sensors. The light spectrum transmitted by the set of multiplexed sensors in the spectral range from 400 nm to 800 nm carries information about the magnitude of the pressure applied on each sensor by the foot. The distribution of pressures exerted by different individuals alters the geometry of the macro-bends, resulting in spectral changes in transmitted light that allow personal authentication. Principal component analysis and support vector machine method are responsible for foot recognition. Data analysis returned hit rates greater than 85% for 6 different feet.