Abstract The ultrasonic reflection from a lubricated interface has been widely analyzed to measure fluid film thickness, with different algorithms being applied to overcome measurement accuracy and resolution issues. Existing algorithms use either the amplitude or the phase angle of the ultrasonic interfacial reflection. In this paper, a new algorithm (named the “exact model – complex”) that simultaneously utilizes both the amplitude and the phase of the complex ultrasonic reflection coefficient is proposed and mathematically derived. General procedures for theoretical analysis in terms of measurement accuracy and uncertainty are proposed and applied to the new algorithm, the beneficial features of which (as compared to other existing algorithms) can be summarized as: 1) a direct calculation, instead of an iterative approximation, 2) guaranteed maximum measurement accuracy, and 3) acceptable measurement uncertainty. None of the existing methods have showed this combination of benefits. Moreover, two groups of raw data from previous experimental studies are utilized to further validate the practical feasibility of the new algorithm. Overall, the proposed “exact model – complex” algorithm fully exploits the potential of ultrasonic reflection for oil film thickness measurement, with an accurate and a convenient calculation suited to practical implementation.

中文翻译：

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超声波界面反射的精确分析解决方案可实现最佳油膜厚度测量

摘要 来自润滑界面的超声波反射已被广泛用于测量流体膜厚度，并应用不同的算法来克服测量精度和分辨率问题。现有算法使用超声波界面反射的幅度或相位角。在本文中，提出了一种同时利用复数超声反射系数的幅度和相位的新算法（命名为“精确模型-复数”）并通过数学推导出来。提出了在测量精度和不确定度方面进行理论分析的一般程序并将其应用于新算法，其优点（与其他现有算法相比）可以概括为：1）直接计算，而不是迭代近似, 2) 保证最大测量精度，以及 3) 可接受的测量不确定度。现有的方法都没有显示出这种好处的组合。此外，利用先前实验研究的两组原始数据来进一步验证新算法的实际可行性。总体而言，所提出的“精确模型-复杂”算法充分利用了超声波反射在油膜厚度测量中的潜力，计算准确、方便，适合实际实施。