Manfredi O F, Mills R S, Schirru M M, Dwyer-Joyce R S
Leonardo Centre for Tribology, University of Sheffield, Sheffield S1 3JD, UK.
Leonardo Centre for Tribology, University of Sheffield, Sheffield S1 3JD, UK.
Ultrasonics. 2019 Apr;94:332-339. doi: 10.1016/j.ultras.2018.08.002. Epub 2018 Aug 7.
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.
监测金属制品内润滑油粘度的能力对许多行业都很重要，比如汽车、航空航天和食品行业等等。金属 - 液体界面处的声阻抗失配会限制超声信号传输，从而限制了该技术的适用性和灵敏度。在这项工作中，我们提出使用连续重复啁啾（CRC）剪切波来放大对液体粘度的可测量声学响应。该技术能使多次反射在部件内部叠加并形成准静态驻波，其振幅谱取决于固 - 液边界的状况。将共振频率为5MHz的裸元件剪切超声换能器以一发一收的布置方式粘结到铝板的下表面，以测量与上表面接触的液体。使用从0.5到9.5MHz、持续10ms的连续重复频率扫描对换能器进行脉冲激励。对于一系列标准粘度的油观察所得驻波的振幅谱，以此作为校准程序，从中获得驻波反射系数（S）。对17种粘度范围从1080到6.7mPa·s的混合油进行了测量。还通过在金属与液体界面之间添加聚酰亚胺匹配层（ML）对该技术进行了评估。然后将超声粘度测量值与使用传统实验室粘度计进行的测量值进行比较。结果发现，与单频脉冲相比，CRC方法显著提高了金属 - 液体界面处粘度测量的灵敏度，且具有低成本信号生成和采集硬件要求的优点。CRC方法还能够进行即时快速响应测量，因为信号实时响应，无需等待回波脉冲。
