Characterization and analysis of a POF sensor embedded in different materials: Towards wearable systems for stiffness estimation

Abstract

This paper presents the development, characterization and analysis of an intensity variation-based polymer optical fiber (POF) force sensor using cyclic transparent optical polymer (CYTOP) fiber through side-coupling light source embedded in different materials. Tests with application of vertical force on the sensor with different supports were performed to analyze the sensor responses when embedded in different materials. In addition, vertical force tests along the fiber were performed to analyze the sensor feasibility of detecting the location of applied force. Results of the force characterization on different materials show that the POF-CYTOP force sensor response is related to elastic modulus of the materials. Using the support I, more flexible (elastic modulus of 18.6MPa), the sensor responses presented a high influence of the light coupling, resulting in an increase of the optical power. In contrast, the responses using the support II (elastic modulus of 1.6GPa), presented a decrease of optical power variation with only a minor increase in the optical power when small forces are applied. This is due to the higher strain in the POF, resulting in optical power decrease due to radiation losses and stress-optical effect. Tests with application of the force along the fiber show that the sensor had different sensitivities for impacts located at different distances of the lateral section, leading to the possibility of estimating the impact location using a multiplexed sensor array. The differences in the sensor’s responses over the different supports show the feasibility of using the proposed sensor system for the stiffness assessment in users, where wearable optical fiber sensors can be employed on the real-time estimation of soft tissues, which finds important applications in rehabilitation as well as wearable robotics control and design.