In the area of textile-integrated sensors, polymer optical fibers (POF) have been used for measuring various vital parameters, such as heart rate, oxygen saturation, and respiratory rate. They have become more and more popular for sensing applications due to increased homogeneity. However, the flexibility has often been a bottleneck for integration.
Here we present the melt-spinning as well as the optical and mechanical characterization of POFs from different commercial urethane/siloxane block copolymers. The fibers could be produced continuously without preparation of a preform at speeds of up to 30 meters per minute. The fiber diameter correlated directly with the drawing speed. The fiber is extruded with a single-screw extruder and a 2 mm-diameter die. No additional material layer is coated on top of the fiber. Thus, air acts as a cladding and allows for total reflection of guided light at the interface due to the much lower refractive index.
The produced fibers were analyzed regarding their appearance and homogeneity as well as optical properties including light attenuation along the fiber and pressure losses. Attenuation spectra were taken for the visible light and near-infrared spectrum. The pressure losses are based on the deflection of light in the waveguides. This effect was analyzed during load cycles in respect to the fiber diameter and composition and the siloxane chain length with varying loads. Additionally, long-term signal output was investigated.
To create a sensing system, the fibers were integrated into a carrier fabric. Due to the high flexibility of the POFs, good drapeability is possible and high comfort during wear of the textile is achieved.
Possible applications are multifold due to the reliability of the such produced POFs. The calibrated pressure fibers can be used for logging of respiratory rate as well as for designing a pressure-sensing map. Even a tactile sensor for research on body movement can be imagined.