Fluorescence-Based Optical Flow Sensor with Direction-Independent Response

Abstract

Non-contact flow-sensing technologies have attracted increasing attention in various fields, such as microfluidiccontrol and underwater flow monitoring. In this study, an optical flow-sensing principle based on the fluorescence response of aphosphor-attached hollow pillar is proposed. The hollow structure of the ethylene propylene diene monomer pillar serves as anoptical waveguide, delivering blue excitation light from an LED to a phosphor bead attached to the pillar tip, where red fluorescenceis emitted and subsequently detected. Flow-induced deformation of the pillar causes a slight inclination of the phosphor, resultingin measurable variations in the detected fluorescence intensity. The fluorescence response was quantitatively analyzed under differentflow rates (0？3000 mL/min) and directions (frontal and lateral) using three pillars with different outer diameters (Ø2.8, Ø3.8, andØ4.8 mm). The results show a consistent decrease in the fluorescence intensity with an increasing flow rate and rapid recovery oncethe flow ceases. Smaller-diameter pillars exhibit higher sensitivity, and the overall response remains independent of the flowdirection. These findings demonstrate that the proposed fluorescence-based optical sensor provides a simple and effective approachfor multidirectional flow detection and can be applied to precise flow measurements in microfluidic and underwater environments.