A liquid-filled buoyancy-driven convective micromachined accelerometer

A novel class of accelerometer, based on the buoyancy of a heated fluid within a micromachined cavity, has previously been developed and reported. Based on dimensional analysis and computational modeling, it is predicted that the sensitivity of the accelerometer can be increased by several orders of magnitude over previously reported results by choosing a suitable liquid as the working fluid, though this increased sensitivity comes at the cost of an increased response time. A liquid-filled accelerometer is constructed; its sensitivity and response time are measured, and shown to be consistent with theoretical predictions and with the results of finite-element analysis. It is noted that the existing literature provides no basis for predicting the effect of Prandtl number on the sensitivity and response time of the accelerometer. The prediction of response time requires analysis of the transient response of the heated fluid to a sudden acceleration. This is a novel problem: previous studies of transient convection have focused on the effects of a newly imposed temperature differential in an existing gravity field, rather than a newly imposed acceleration on an existing thermal field. An approximate expression for response time as a function of radius ratio and Prandtl number is developed by curve-fitting to the results of FLOTRAN simulation.