Flow Sensor Based on the Snap-Through Detection of a Curved Micromechanical Beam

Abstract

We report on a flow velocity measurement technique based on snap-through detection of an electrostatically actuated, bistable micromechanical beam. We show that induced elecro-thermal Joule heating and the convective air cooling change the beam curvature and consequently the critical snap-through voltage (VST). Using single crystal silicon beams, we demonstrate the snap-through voltage to flow velocity sensitivity of dVST/du ≈ 0.13 V s m−1 with a power consumption of ≈ 360 μW. Our experimental results were in accord with the reduced order, coupled, thermo-electro-mechanical model prediction. We anticipate that electrostatically induced snap-through in curved, micromechanical beams will open new directions for the design and implementation of downscaled flow sensors for autonomous applications and environmental sensors.

Analytical Study of the Snap-Through and Bistability of Beams With Arbitrarily Initial Shape

“…It can be noticed that the solution and expressions derived in this section are similar to those obtained in [55]. This is due to the fact that the solution in [44,55] is approximated as an infinite sum of the modes of buckling of a straight beam (same as for the homogeneous problem (11)) and the initial shape is similar to one of these modes of buckling.…”

“…Bistable beams exhibit additional advantages, such as their simplicity, passive holding, low actuation energy, small footprint, large stroke with small restoring forces, and negative stiffness zone. These advantages make bistable beams suitable for an increasing number of applications at different scales, such as space applications [1], biomedical [2], energy harvesting [3,4], resonators [5], actuators [6] accelerometers [7], shock sensors [8], gas sensors [9], pressure sensors [10], flow sensors [11], grippers [12], mechanisms with large displacement and small actuation stroke [13], switches [14], relays [15], memory devices [16], logics [17], lamina emergent frustrum [18], statically-balanced mechanisms [19], soft robotics [20], constant force mechanisms [21,22], bistable positioning [23][24][25][26], and multistable devices [27][28][29][30][31][32].…”

Snap-induced flow in a closed channel

“…Snap instability can be actuated in various ways, including the application of a point force (Pandey et al 2014) or the utilization of electrostatic and capillary forces (Krylov et al 2008;Fargette, Neukirch & Antkowiak 2014) or thermal effects (Boisseau et al 2013;Kessler et al 2018). These actuation methods drive a system towards a marginal stability state, from which only a small perturbation will drive the instability.…”

2.5D Flexible Wind Sensor Using Differential Plate Capacitors

“…However, the thermal anemometer requires high power consumption to form a temperature field. In this regard, the pressure anemometer uses some passive devices, such as resistors, inductors, and capacitors, to convert wind information into electrical signals, achieving extremely low power consumption [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. However, in practice, the sensitive elements are directly exposed to the air and are susceptible to the interference of dust particles, leading to a decline in reliability.…”