Analysis of an ultrasonic viscosity measurement cell with mode conversion

Theoretical and experimental analyses of a cell that measures the viscosity of liquids using longitudinal to shear wave mode conversion are presented. The measurement method is based on the determination of the complex reflection coefficient (magnitude and phase) of shear waves at a solid-liquid interface. The cell is composed of an ultrasonic transducer, a water buffer, an aluminum prism, a PMMA buffer rod and a sample chamber. In order to simulate the cell, a unidimensional model composed by acoustic and electroacoustic transmission lines is implemented using matrix operations. The simulation of viscosity as a function of signal-to-noise ratio, and the temperature dependence, which affects the measurement values if there are gradients inside the cell, are studied. The results show the behavior of the measurement cell to obtain the viscosity error. The cell was tested with olive oil at 3.5 MHz as a function of the temperature. The experimental results agree with those measured by a rotational viscometer for stabilized temperatures.