Agile lensing-based non-contact liquid level optical sensor for extreme environments

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t a r t i c l e i n f o To the best of the author's knowledge, demonstrated is the first opto-fluidic technology-based sensor for detection of liquid levels. An opto-fluidic Electronically Controlled Variable Focus Lens (ECVFL) is used to change the spatial intensity profile of the low power optical beam falling on the liquid surface. By observing, tuning and measuring the liquid surface reflected intensity profile to reach its smallest size, the liquid level is determined through a beam spot size versus ECVFL focal length calibration table. Using a 50 μW 632.8 nm laser wavelength liquid illuminating beam, a proof-of-concept sensor is tested using engine oil, vegetable oil, and detergent fluid with measured liquid levels over a 75 cm range. This non-contact Radio Frequency (RF) modulation-free sensor is particularly suited for hazardous fluids in window-accessed sealed containers including liquid carrying vessels in Electromagnetic Interference (EMI) rich environments. Liquid level sensors are used extensively in various industrial applications where the liquid depths have to be monitored with robustness, reliability, and repeatability. Many industrial processes and aerospace platforms involve toxic and combustible fluids, including fluids under extreme temperatures (e.g., cryogenic conditions), pressures and radioactivity. In addition, fuel cells for scalable renewable energy storage also require the monitoring of caustic liquid levels. Typically, such liquids are stored in mechanically robust large volume tanks with small optical windows for basic liquid visual viewing. Given these hazardous liquid tank conditions, it is generally not possible to insert any type of sensor into the tank cavity as the sensor module can suffer degradation with liquid contact, apart from acting as a potential trigger for liquid chemical or electrical instability. As the container is sealed, a wired sensor, whether optical [1–15] or electrical [16,17] or ultrasonic [18] is highly intrusive and suffers from the additional problem of having no access point for wire insertion into the tank. A non-contact optical sensor such as a laser radar sensor [19,20] is a preferred sensor for the hazardous liquid environment, although this type of sensor requires phase-sensitive RF electronics that can be expensive and EMI sensitive. The use of ultrasound …