An Experimental and Analytical Study of Hybrid Accelerometers

Abstract

Hybrid accelerometers comprise sensor elements from different technologies, capable of combining two output signals into a highly linear response. Typically, a piezoaccelerometer would be combined with a MEMS accelerometer to extend an otherwise AC coupled response down to DC. The complementary filter function is an effective and distortion-free method for combining a DC capacitive sensing element that is critically damped with an AC piezosensing element; however, this method does not work well with lightly damped DC sensing elements. A detailed examination was undertaken of the issues that arise when combining AC and DC sensing elements where the damping factor of the DC sensor element is < 1, as is the case with many MEMS piezoresistive accelerometers. Results include earlier work with a prototype hybrid accelerometer, as well as a later analytical model to investigate in detail the complex interaction between system parameters that lead to distortion, nonlinearity and changes in impulse response when lightly damped DC sensing elements are combined. The analysis concludes with a post-processing method investigated for the removal of spurious transformation coefficients that currently preclude the use of lightly damped DC sensors.