Non-invasive measurement of lubricating oil viscosity using an ultrasonic continuously repeated chirp shear wave

Abstract

The ability to monitor the viscosity of lubricating oils within metallic products is of interest to many industries, these being the automotive, aerospace and food industries to name a few. Acoustic mismatch at the metallic-liquid interface restricts ultrasonic signal transmission and so limits applicability and sensitivity of the technique. In this work, we propose the use of a continuously repeated chirp (CRC) shear wave to amplify the measurable acoustic response to liquid viscosity. The technique enables multiple reflections to superimpose inside the component and form a quasi-static standing wave whose amplitude spectrum depends on the condition at the solid-liquid boundary. Bare element shear ultrasonic transducers of 5 MHz resonant frequency were bonded to the lower surface of an aluminium plate in a pitch-catch arrangement to measure liquid in contact with the upper surface. Transducers were pulsed using a continuously repeated frequency sweep, from 0.5 to 9.5 MHz over 10 ms. The amplitude spectrum of the resulting standing wave was observed for a series of standard viscosity oils, which served as a calibration procedure, from which the standing wave reflection coefficient (S), was obtained. Measurements of 17 blended oils ranging in viscosity from 1080 to 6.7 mPa s were made. The technique was also evaluated with the addition of a polyimide matching layer (ML) between the metallic and liquid interface. Ultrasonic viscosity measurement values were then compared to measurements made using a conventional laboratory viscometer. The CRC method was found to significantly improve the sensitivity of viscosity measurement at a metal-liquid interface when compared to a single frequency burst with the benefit of low cost signal generation and acquisition hardware requirements. The CRC method is also capable of instant rapid response measurements as the signal responds in real time without the need to wait for a returning pulse.

Characterising the mechanical properties of soft solids through acoustics and rheology, exemplified by anhydrous milk fat

“…In the field of shear acoustics 27 a highly attenuated shear wave propagates over just a few wavelengths and much more slowly 28 than the longitudinal wave. Oscillatory shear rheology 29 shares much in common with shear acoustics.…”

Desenvolvimento de célula para medição de viscosidade por ultrassom com conversão de modo interna.

“…Esse fenômeno foi descrito primeiramente por Mason et al (1949). A teoria que utiliza o método de reflexão das ondas de cisalhamento na determinação da viscosidade de líquidos pode ser encontrada em diversos artigos e livros (WHORLOW, 1992;MANFREDI et al, 2019e SCHIRRU et al, 2019.…”