The influence of fluid boundary conditions on bio-inspired acoustic flow sensor

One common approach to creating a flow sensor is to fabricate sensing elements that extend perpendicularly from the substrate, which typically provides sensor anchorage. However, this approach is impractical due to fabrication challenges, structural fragility, and integration constraints. This paper explores an alternative packaging method that integrates the sensor into a silicon chip for protection. Since this integration introduces boundary conditions from the substrate, which negatively affect sensor performance, the substrate is removed to modify the fluid boundary condition by transferring the sensing element to a designed cavity (3400 μm length, 1690 μm width, and 500 μm depth). This process eliminates surrounding material while preserving the sensor element for comparison before and after substrate removal. To illustrate this effect, the study presents examples that, while not optimized as flow sensors, could still demonstrate how boundary conditions influence sensor performance. Results indicate that removing the substrate increases viscous damping due to air interaction while reducing damping from substrate boundaries. This leads to lower pressure-referred noise levels and a higher signal-to-noise ratio. These findings could be useful for alternative packaging methods, where the substrate beneath the sensor is completely removed through back-etching. This approach provides protection while simultaneously preserving sensor performance.