Fiber-Optic Viscometer Based on Damping Rate of Off-Core Microsphere Cantilever

Viscosity governs fluid motion and has broad applications in scientific research, biomedicine, and industry. This paper proposed and demonstrated a compact all-fiber viscometer based on an off-core optical fiber cantilever integrated with a microsphere to form interferometer for high sensitivity viscosity sensing via vibrational damping analysis. The cantilever's free end is immersed in the test liquid and driven by a mechanical actuator, while the viscosity-dependent damping is extracted from the optical response of an interferometric cavity formed between the off-core fiber and the microsphere. The phase delay between the excitation and vibration signals serves as the primary sensing parameter for viscosity measurement in real-time. The all-fiber architecture ensures a miniaturized footprint and requires only a small sample volume (∼50 μL). Experimental validation demonstrates a strong correlation between the measured phase delay and viscosities ranging from 1.144 mPa·s to 8.029 mPa·s. The proposed viscometer offers a robust and practical solution for real-time viscosity monitoring in biomedical diagnostics, industrial process control, and microfluidic systems.