Effect of Overheat and Direct Flow Loading on the MEMS Bistable Flow Sensor

TL;DR

This study investigates how overheat ratios, flow loading, and vibrations influence the snap-through behavior of a MEMS bistable flow sensor, revealing energy-efficient operation and environmental sensitivities.

Contribution

It provides the first direct experimental observation of the beam profile during snap transitions and highlights the effects of flow angles and vibrations on sensor performance.

Findings

Overheat ratio can be lower than in conventional thermal sensors.

Flow angles and vibrations significantly affect critical voltages.

First direct observation of beam profile during snap transitions.

Abstract

We present the findings from an experimental study of a MEMS flow sensor in which an initially curved, double-clamped bistable microbeam is the primary sensing element. Our research explores how the overheat ratio, direct flow loading, and turbulence-induced vibration affect the sequential snap-through (ST) buckling and snap-back (SB) release of an electrostatically actuated beam heated by an electric current. The sensor is fabricated from highly doped single-crystal silicon using a silicon-on-insulator (SOI) wafer. Positioned at the chip's edge, the microbeam is exposed to airflow, enabling concurrent dynamic response measurements with a laser Doppler vibrometer and a video camera. Our research demonstrates that the overheat ratio can be significantly lower for this sensing principle than conventional thermal sensing elements, pointing to the potential for substantial energy savings. We also emphasize the significant impact of flow angles and vibrations on the critical ST and SB voltages, which are vital for the flow sensor's output. Additionally, we introduce the first direct experimental observation of the beam profile's time history during the snap-through /snap-back transition. The potential impact of this research lies in developing more robust MEMS flow sensors with enhanced sensitivity and a better understanding of their response to environmental factors, which could have broader applications in fields such as aerospace, environmental monitoring, and industrial process control.