Sensory-Hair-Based Flow Sensor

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A flow sensor with a sensory hair structure consisting of a cantilever and a strain gauge was fabricated. The cantilever measured 1.5 mm in length, 600 μm in width, and 80 μm in thickness, and was made of SU-8 which is often used for fabrication of microstructures having high aspect ratios. The strain gauge was made of Au/Cr thin film at the bottom of the cantilever, and showed a linear relationship between the rate of change of its resistance and deflection of the cantilever. Although the fabricated sensor had a small gauge factor, it was as sensitive as that of a silicon strain gauge because the cantilever material, SU-8, had smaller Young's modulus by two digits compared to that of silicon, and therefore the cantilever was much easier to deflect. When air and other fluids approached the cantilever, it was bent and the flow rate was measured by deflection of the cantilever.Moreover, a sensor for detecting angular acceleration based on a semicircular canal structure model was developed using the technique described above. The flow sensor was attached to the sidewall of a circular channel of 2 mm in width and 5 mm in radius. When an angular acceleration was applied to the channel, motion of the liquid filled inside the channel caused deflection of the cantilever and change in resistance of the strain gauge. The angular acceleration of 16.7 rad/sec^2 generated resistance change which was then converted to an output voltage of nearly 20 mV when amplified by 300. The sensor is less sensitive in terms of responsiveness because it relies on liquid motion. However, it retains a big advantage of permitting much smaller cross-talk with angular accelerations around other axes.