Long-Path Evanescent-Wave Elastic Fiber for Liquid Level Sensing in Deformable Vessels

Timely and accurate monitoring of intravenous infusions can effectively improve the safety and reliability of the infusion process. An optical-fiber evanescent-wave sensor is suitable for liquid-level monitoring because it provides high security, is corrosion resistant, and is unaffected by electromagnetic interference. Liquid-level monitoring at slightly large depths requires an optical-fiber evanescent-wave sensor to possess the ability to transmit evanescent waves over long distances. In this study, we provide a feasible design strategy and a fabrication process for highly elastic polymer fibers that can transmit evanescent waves over extremely long distances (>50 cm). Such an elastic fiber exhibits excellent mechanical properties and is capable of reversibly sustaining strains up to 110% while transmitting light. Based on such an elastic polymer-fiber evanescent-wave sensor, we have developed a liquid-level monitoring system for an infusion bag that provides error compensation and self-adapts to high temperatures. The reference channel in the sensor compensates for the additional optical loss due to deformations of the companion leaky channel in real time, ensuring accurate and stable liquid-level monitoring even when the system is deformed. The system provides consistent and high-quality liquid-level monitoring performance for commonly used intravenous liquids such as a 5% glucose solution and a 0.9% normal saline solution. It can thus help solve problems caused by shortages of medical staff and can provide a safe treatment process for patients.