Abstract
A novel method, which was called a slope method, has been proposed to measure fluid density by the micro-cantilever sensing chip. The theoretical formulas of the slope method were discussed and established when the micro-cantilever sensing chip was under flexural and torsional vibrations. The slope was calculated based on the fitted curve between the excitation and output voltages of sensing chip under the nonresonant status. This measuring method need not sweep frequency to find the accurate resonant frequency. Therefore, the fluid density was measured easily based on the calculated slope. In addition, the micro-cantilver was drived by double sided excitation and free end excitation to oscillate under flexural and torsional vibrations, respectively. The corresponding experiments were carried out to measure the fluid density by the slope method. The measurement results were also analyzed when the sensing chip was under flexural and torsional nonresonant vibrations separately. The measurement accuracies under these vibrations were all better than 1.5%, and the density measuring sensitivity under torsional nonresonant vibration was about two times higher than that under flexural nonresonant vibration.
Highlights
Vibration methods are widely used in online measurements of fluid density [1,2,3].Micro Electromechanical Systems (MEMS) technology has increasingly been used to fabricate vibration sensors [4,5,6]
A new simple silicon straight tube was tested as a fluid density sensor in the study of Najmzadeh [8]; the length of the proposed tube was 2.65 cm, and the volume of the fluid sample was only 9.3 μL
The slope between driving and output voltages of a sensing chip under nonresonant status was inversely proportional to the density of the surrounding fluid
Summary
Vibration methods are widely used in online measurements of fluid density [1,2,3].Micro Electromechanical Systems (MEMS) technology has increasingly been used to fabricate vibration sensors [4,5,6]. Vibration methods are widely used in online measurements of fluid density [1,2,3]. MEMS sensors need only a micro-scale fluid sample to measure its density, viscosity or other parameters. Corman [7] presented a fully low-pressure encapsulated and closed-loop operated resonant fluid density sensor, where the required sample volume was only 35 μL. A new simple silicon straight tube was tested as a fluid density sensor in the study of Najmzadeh [8]; the length of the proposed tube was 2.65 cm, and the volume of the fluid sample was only 9.3 μL. The micro-cantilever is one of most common structures used for MEMS vibration devices, as it is simple and reliable [9]. Wilson [10] showed that piezoelectric-excited millimeter-sized cantilever (PEMC)
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