Liquid Viscosity Measurement Using a Vibrating Flexure Hinged Structure and a Fiber-Optic Sensor

A novel viscosity measurement system based on a miniature 3D printed parallelogram flexure hinge structure and a fiber-optic sensor is developed. Lorentz forces are applied to excite the structure vibration at various frequencies, and the fiber-optic sensor is used to measure the amplitude and phase responses without the electromagnetic interference. The system is modeled as a single oscillator by taking into account the liquid-induced mass and damping as well as the additive stiffness due to the liquid viscoelasticity. By curve fitting of the experimentally obtained amplitude and phase responses based on the analytical model, the viscosity and the additive stiffness can be obtained. This method can help differentiate the effect of the viscosity and elasticity on the response of the sensing structure. By implementing this method, accurate viscosity measurements over a large range of 1–1045
$\text {mPa} \cdot \text {s}$
are demonstrated with the errors of <3.7% for all the test samples. It is also confirmed in the experiment that the liquid-induced additive stiffness is strongly related to the liquid storage modulus.