Inertial unit for multi-motion detection

Monitoring motion parameters are increasingly important in automotive and robotics applications, where cheap sensors are highly desirable. A silicon micromachined structure 0.5X2cm in size was designed and fabricated, which can detect not only translational acceleration, but angular acceleration or rate simultaneously and independently, which has a particular merit since it theoretically allows single point detection of all 6 axis of freedom using only three sensors. This is accomplished by capacitive detection of the displacement and the tilt of the seismic mass, symmetrically suspended by two torsion bars. The expected linear dependencies of the output signal on translational and angular accelerations, as well as quadratic dependency on angular rate could be verified. It is shown, that the dynamic response is improved by vacuum packaging.