MEMS shear stress sensors: promise and progress

Department of Mechanical and Aerospace Engineering
IUTAM Symposium on Flow Control and MEMS 09/2006; DOI: 10.2514/6.2004-2606

ABSTRACT This paper reviews existing microelectromechanical systems (MEMS)-based shear stress sensors. The promise and progress of MEMS scaling advantages to improve the spatial and temporal resolution and accuracy of shear stress measurement is critically reviewed. The advantages and limitations of existing devices are discussed. Finally, unresolved technical issues are summarized for future sensor development.

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    ABSTRACT: A numerical study with spectral element method for a dynamic resonant shear stress sensor concept is presented in this paper, in which the numerical model of the sensor consisted of an unsteady three-dimensional boundary layer model for the flow and a simple mechanical model for the sensor itself. Spectral element method was used to explore fluid flow properties around the sensor in the three-dimensional boundary layer model. The three-dimensional unsteady spectral element method code was first verified with Blasius solutions in a flat plate boundary layer flow. The sensor's sensitivity to wall shear stress was then numerically determined in a laminar boundary layer. Finally, the physical mechanism of the dynamic resonant shear stress sensor was analyzed by using the verified model. The results showed that the sensitivity of the dynamic resonant shear stress sensor was due to the energy lost produced by the oscillating interaction between the sensor and fluid flow.
    Journal of Fluids and Structures 07/2013; 40:356-365. DOI:10.1016/j.jfluidstructs.2013.03.016 · 2.23 Impact Factor
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    ABSTRACT: In this paper, we present carbon nanotube (CNT) based thermal shear stress sensors integrated inside optically transparent Polymethylmethacrylate (PMMA) microfluidic systems. The sensors were fabricated on PMMA substrates by batch assembling multi-walled carbon nanotubes (MWNTs) as sensing elements between microelectrode pairs using AC dielectrophoretic (DEP) technique. PMMA chambers were fabricated using SU-8 molding/hot-embossing technique. Then, the PMMA substrate with a micro chamber and vortex micropump was bonded to the other PMMA substrate embedded with the MWNT sensor array to form a closed flow chamber. Experiments showed that the CNT sensors could detect volumetric air flow rate in the order of 10 -8 m 3 /s inside this microchannel system. We have also proved that upon exposure to constant liquid (DI-water) flow, the electrical resistance of the CNT sensor was found to increase linearly at low activation current of 100μA. And a linear relation between the change of output resistance and one-third power of flow rate was observed for flow rate from 0.3 to 2.3m/s. This result proved that the CNT sensors work with the same principle as conventional MEMS based thermal shear stress sensors, but only require ultra-low activation power (~μW) to achieve comparable sensitivity, which is three orders of magnitude lower than conventional MEMS polysilicon based flow sensors.
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