A MEMS-Based Flow Rate and Flow Direction Sensing Platform with Integrated Temperature Compensation Scheme

Rong-Hua Ma,Chia-Yen Lee,Dung-An Wang,Tzu-Han Hsueh

doi:10.3390/s90705460

Abstract

This study develops a MEMS-based low-cost sensing platform for sensing gas flow rate and flow direction comprising four silicon nitride cantilever beams arranged in a cross-form configuration, a circular hot-wire flow meter suspended on a silicon nitride membrane, and an integrated resistive temperature detector (RTD). In the proposed device, the flow rate is inversely derived from the change in the resistance signal of the flow meter when exposed to the sensed air stream. To compensate for the effects of the ambient temperature on the accuracy of the flow rate measurements, the output signal from the flow meter is compensated using the resistance signal generated by the RTD. As air travels over the surface of the cross-form cantilever structure, the upstream cantilevers are deflected in the downward direction, while the downstream cantilevers are deflected in the upward direction. The deflection of the cantilever beams causes a corresponding change in the resistive signals of the piezoresistors patterned on their upper surfaces. The amount by which each beam deflects depends on both the flow rate and the orientation of the beam relative to the direction of the gas flow. Thus, following an appropriate compensation by the temperature-corrected flow rate, the gas flow direction can be determined through a suitable manipulation of the output signals of the four piezoresistors. The experimental results have confirmed that the resulting variation in the output signals of the integrated sensors can be used to determine not only the ambient temperature and the velocity of the air flow, but also its direction relative to the sensor with an accuracy of ± 7.5° error.

Highlights

Flow measurement is an essential task in many fields, including environmental monitoring, process control, medical instrumentation, air conditioning systems, weather forecasting systems, and so forth.For many years, flow sensing was accomplished using large-scale mechanical flow meters such as anemometers, turbines, Pitot tubes and so forth
The flow direction sensor consists of a crossform configuration of four free-standing cantilevers, each patterned with a pizeoresistor
The passage of air over the sensor surface prompts a deflection of the cantilevers, which in turn produces a measurable change in the output signals of the four resistors from which the direction of the air flow can be derived

Summary

Introduction

Flow sensing was accomplished using large-scale mechanical flow meters such as anemometers, turbines, Pitot tubes and so forth. MEMS-based flow sensors have a smaller size, a greater sensitivity, a faster response and a lower power consumption than their traditional counterparts. They are integrated with other IC devices and can be mass produced at a low cost. The literature contains a wealth of proposals for MEMS-based sensors for a diverse range of flow sensing applications [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]

Methods

Results

Conclusion