A high-accuracy viscosity sensor based on an optimized quartz tuning fork resonator

Abstract This paper presents the design, structural optimization, and implementation of a high-accuracy viscosity sensor based on a custom-designed quartz tuning fork (QTF). Unlike standard commercial resonators, the QTF in this study was specifically optimized using finite element method, identifying the fourth-order in-plane inverting mode as the optimal working mode to minimize support coupling. By optimizing the cantilever geometry, we increased the natural resonant frequency from 15.652 kHz to 21.44 kHz, significantly enhancing sensitivity and interference immunity. A compact hardware system based on a field-programmable gate array was developed for robust open-loop frequency sweep detection. We specifically proposed a dual-layer modeling strategy, integrating a physics-based model to ensure theoretical monotonicity with an efficient polynomial approximation for real-time computation. Calibration experiments using methyl silicone oils revealed a strong quadratic relationship ( R 2 = 0 .999 ) between the peak voltage and fluid viscosity. Validation with a certified standard fluid (8.92 mPa·s) demonstrated a measurement error of only 0.13 mPa·s. These results confirm that the proposed sensor system achieves high accuracy and stability, offering a cost-effective solution for embedded industrial fluid monitoring.