Raja Nishanth, Balasubramaniam Krishnan, Periyannan Suresh
Centre for Non-Destructive Evaluation, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India.
Rev Sci Instrum. 2019 Apr;90(4):045108. doi: 10.1063/1.5054638.
This paper reports on an ultrasonic waveguide sensor for liquid level measurements using three guided wave modes simultaneously. The fundamental wave modes longitudinal L(0,1), torsional T(0,1), and flexural F(1,1) were simultaneously transmitted/received in a thin stainless steel wire-like waveguide using a standard shear wave transducer when oriented at an angle of 45° to the axis of the waveguide. Experiments were conducted in non-viscous fluid (water) and viscous fluid (castor oil). It was observed that the flexural F(1,1) wave mode showed a change in both time of flight (due to the change in velocity and dispersion effects) and amplitude (due to leakage) for different levels (0-9 cm) of immersion of the waveguide in a fluid medium. For the same level of immersion in the fluid, the L(0,1) and the T(0,1) modes show only a relatively smaller change in amplitude and no change in time of flight. The experimental results were validated using finite element model studies. The measured change in time of flight and/or the shift in central frequency of F(1,1) was related to the liquid level measurements. Multiple trials show repeatability with a maximum error of 2.5% in level measurement. Also, by monitoring all three wave modes simultaneously, a more versatile and redundancy in measurements of the fluid level inside critical enclosures of processing industries can be achieved by compensating for changes in the fluid temperature using one mode, while the level is measured using another. This ultrasonic waveguide technique will be helpful for remote measurements in physically inaccessible areas in hostile environments.
本文报道了一种同时使用三种导波模式进行液位测量的超声波波导传感器。当标准剪切波换能器与波导轴线成45°角放置时，在细不锈钢丝状波导中同时发射/接收基波模式纵向L(0,1)、扭转T(0,1)和弯曲F(1,1)。实验在非粘性流体（水）和粘性流体（蓖麻油）中进行。观察到，对于波导在流体介质中不同浸没深度（0 - 9厘米），弯曲F(1,1)波模式在飞行时间（由于速度变化和色散效应）和幅度（由于泄漏）上均表现出变化。对于在流体中相同的浸没深度，L(0,1)和T(0,1)模式仅在幅度上表现出相对较小的变化，而在飞行时间上没有变化。实验结果通过有限元模型研究得到验证。测量得到的F(1,1)飞行时间变化和/或中心频率偏移与液位测量相关。多次试验表明具有可重复性，液位测量的最大误差为2.5%。此外，通过同时监测所有三种波模式，利用一种模式补偿流体温度变化，同时用另一种模式测量液位，可在加工行业关键封闭空间内实现更通用且冗余的液位测量。这种超声波波导技术将有助于在恶劣环境中物理上难以到达的区域进行远程测量。
