Force multiplier in a microelectromechanical silicon oscillating accelerometer

Abstract

This thesis describes the third generation design of a silicon oscillating accelerometer (SOA.) The device is a micromachined vibrating beam accelerometer consisting of two tuning fork oscillators attached to a large proof mass. When accelerated along the input axis, the proof mass exerts a force on the oscillators, causing their natural frequencies to shift in opposing directions. Taking the difference of these frequencies gives a measurement of the applied acceleration. A significant feature in the new design is a force multiplying lever arm which connects the oscillators to the proof mass. With this addition, the surface area of the proof mass is reduced by a factor of four, while the scale factor and axial resonant frequency of the previous design is retained. All vibration modes of the device are identified, and stiffness nonlinearity in the oscillators is investigated. A method to compensate for thermally induced acceleration errors is also introduced. Testing of the fabricated device is shown to agree with model predictions.