Piezoelectric bimorph as a high-sensitivity viscosity resonant sensor to test the anisotropy of magnetorheological fluid.

Abstract

In this paper, we present a device which is very sensitive for small changes in the viscosity of the investigated fluid. The main part of the device is a piezo-electric bimorph which consists of the brass shim with two piezo-ceramic layers on the opposite sides. One of them is responsible for generating vibrations, whereas the second one is meant to measure system response which is produced by the damping properties of the surrounding fluid. During the experiment, the cylindrical bar is forced to move by the series of sinusoidal waves with different frequencies and at constant amplitudes. The probe is immersed in the fluid and then the amplitude vs frequency and phase vs frequency curves are obtained. Next, one can determine the viscosity according to a proper mathematical model. The resonant frequency is related to the damping coefficient which depends on the viscosity of the surrender fluid and immersion depth of the probe. The coefficients necessary for calculating viscosity are obtained by fitting the resonance curve to the amplitude vs frequency data obtained from the experiment. The device has been applied to study the anisotropy of magnetorheological fluids. The weak anisotropy of viscosity has been observed. The highest value of viscosity was observed in the case of viscosity measurement in the direction orthogonal to the magnetic field and the lowest in the direction parallel to the magnetic field.