  We report on a flow sensing approach based on deflection monitoring of micro
beams buckled by the compressive thermal stress due to electrothermal Joules
heating. The air stream convectively cooling the device affects both the
critical buckling values of the electric current and the postbuckling
deflections of the structure. After calibration, the flow velocity was obtained
from the deflections measurements. The quasi-static responses of 2000 microns
long, 10 microns wide and 30 microns high single crystal silicon beam
transduced using image processing were consistent with the prediction of the
reduced order model, which couples thermoelectric, thermofluidic and structural
domains. The deflection sensitivity of 1.5 microns/(m/s) and the critical
current sensitivity of 0.4 mA/(m/s) were registered in the experiments. Our
model and experimental results collectively demonstrate feasibility of the
sensing approach and further suggest that simple, robust and potentially
downscalable beam-type devices may have use in flow velocity and wall shear
stress sensors.
