ANALYTICAL INVESTIGATIONS INVOLVED IN A MICROCANTILEVER FOR GAS DETECTION

Abstract
MEMS has been identified as one of the most promising technologies for the 21st Century and has the potential to revolutionize both industrial and consumer products by combining silicon-based microelectronics with micromachining technology. Its techniques and micro system based devices have the potential to dramatically change all of our lives and the way we live. A cantilever is the simplest mechanical structure and hence it gains its significance. In the cantilever sensors the basic principle of measurement would be by measuring the change in resonant frequency or the peizoresistivity based on the displacement. The Resonant frequency is the frequency that produces the maximum displacement that a vibrating body can achieve. The change in resistance value of a conductor due to applied force resulting in strain and displacement is called piezoresistive effect. This paper briefs about the analytical aspects in designing a microcantilever. Initially the modelling of the cantilever is dealt followed by the mandatory equations for both the frequency and resistance measurement. Followed by the the ppmv to mass conversion, so that we can effectively incorporate it in the gas sensing stream. The microcantilever as a gas sensor has wide applications.
Keywords: Cantilever, resonant frequency, piezoresistance
I.Introduction
Numerous components and devices from calculators to mobile phones and computers applied in our daily lives are fabricated using microtechnology. In sensor applications the expectations are a robust, reliable, inexpensive, portable device with low power consumption. A microcantilever fits into this as the simplest device which could be easily fabricated. Any mechanical structure will have an inherent resonant frequency. The fundamental operation of a cantilever will be that when a force is applied at the free end the cantilever will deflect creating a strain across its surface, it means that there would be a displacement from the original position and the inherent frequency will also be altered. Thus depending on the force applied the resonant frequency changes and the resistivity changes. These are the factors which are to be determined to infer the amount of force that is applied. The resonant frequency can be determined by applying an a/c signal to the cantilever and making it vibrate and then check for the amplitude. The piezoresistance can be obtained by connecting the cantilever resistor across in a wheatstone bridge setup and checking for the imbalance. The analytical investigations will help in verifying the experimental results and will also help us in optimization before going for the fabrication process.