The cross-sectional shape of microchannels is, dependent on the fabrication method, never perfectly circular. Consequently, the channels deform with the pressure, which is a non-ideal effect in flow sensors, but may be used for pressure sensing. Multiple suspended channels with different lengths were modeled, fabricated, and characterized to verify the use and the scalability of this effect for pressure sensing. Furthermore, it is shown that the pressure dependence can be distinguished from the Coriolis effect in microfabricated Coriolis mass flow sensors, enabling the measurement of the pressure next to flow and density with only the flow sensor itself. In addition, this allows for further improvement in the accuracy of the flow measurement by correcting for the small pressure dependence.[2016-0236]
A micro Coriolis flow sensor accurately measures small mass flows without being affected by properties of the fluid. This paper presents a micro Coriolis mass flow sensor driven by PZT thin film piezoelectric actuators, which allows a combination of large actuation force, low power dissipation and virtually no self-heating. The sensor was fabricated using surface channel technology, resulting in a tube diameter of 40 µm and a thin silicon-rich silicon nitride tube wall of 1.2 µm thick, with a few additional steps to form the integrated piezoelectric actuators. The integrated actuators can actuate the sensor into both swing mode and twist mode. Both actuation modes were evaluated for different fluids and the results are presented in this paper. In the case of swing mode actuation, an optical readout was used to detect the resulting Coriolis movement, resulting in a relatively low sensitivity. In the case of twist mode actuation, a capacitive readout was used and, in comparison to previously published devices, a high mass flow sensitivity was achieved thanks to an optimized readout design. The measurement results show the read-out noise has a standard deviation of 0.15% of the full scale of 1.8 gh −1 when actuated in the twist mode.
We have realized a micro Coriolis mass flow sensor that is actuated by integrated lead zirconate titanate (PZT) thin film actuators, allowing low voltage, low power actuation compared to current actuation methods. The integrated PZT thin film actuators are deposited on top of silicon-rich silicon nitride (SiRN) fluidic microchannels by pulsed laser deposition (PLD). In this paper we present the fabrication process and first characterization results, including a mass flow measurement with nitrogen flow using a Polytec MSA-400 laser Doppler vibrometer to detect the Coriolis induced motion of the sensor tube. The measurement results confirm that the sensor output is proportional to mass flow up to 14 mg/min.
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