Micromachined Thermal Accelerometer without Proof Mass

Abstract

Since a few years, micromachining technologies have been widely developed for the market of inertial sensors because they permit to achieve low cost production, sensor miniaturization and mass manufacturing. The conventional accelerometers and inclinometers measure generally the displacement or the deformation of a proof mass (or seismic mass), whose the mobility is the principal disadvantage and is responsible of their low shock survival rating and their fragility during very high accelerations such as those produced at the time of the firing of shells. Piezoresistive or capacitive detection are the most common principles used to convert the acceleration into output voltage but they have some disadvantages: high temperature dependence and great influence of mounting stress for the piezoresistive accelerometers, electromagnetic interference and parasitic capacitance for the capacitive ones. The first micromachined thermal accelerometers were studied by Dauderstädt and coworkers [1]–[3] but a proof mass was still present. It consisted of a heater at a temperature T and a suspended mass used as a heat sink at T 0. When an acceleration was applied, the suspended heat sink moved, the distance, heat flow and temperature difference between the two elements changed and thermopiles were used to measure T − T 0.