Christopher Paul Fell

A preliminary investigation of thermo-elastic damping in silicon rings

Zeners model for thermo-elastic loss, when applied to uniform beams undergoing flexural vibrations, gives theoretical predictions of mechanical Q-factor that often agree well with experimental measurements. The use of silicon ring resonators in MEMS devices is now becoming increasingly common. This paper considers the application of Zeners theory to thin, circular rings and presents a simple expression for the Q-factor associated with in-plane flexural modes of vibration. The theoretical predictions are shown to be in good agreement with experimental measurements for a practically relevant range of ring sizes. The relationships between ring dimensions, ambient temperature and Q-factor are explored.

Precision mode matching of MEMS gyroscope by feedback control

This paper reports on mode matching of a MEMS gyroscope using simplified displacement feedback and reduces the frequency split between the two modes to less than 0.01 Hz. Mode matching is shown to improve the gyro performance significantly and reduce the bias stability from 3 degree/hour to 0.5degree/hour. The displacement feedback matching scheme provides an in situ matching control that may augment the generally coarser electrostatic tuning method. The control has been realized in a high performance DSP based rate gyroscope control system and experimental results show the effectiveness of the control algorithm.

Control Scheme to Reduce the Effect of Structure Imperfections in a Rate Integrating MEMS Gyroscope

In this paper, a control scheme is presented for a rate integrating microelectromechanical system ring gyroscope that reduces the effects of structural imperfections on the precession of an ellipse used to describe the structural vibration of the gyroscope. Modeling is provided that demonstrates the potential increase in gyroscope measurement accuracy on implementation of the control scheme. Furthermore, the description of the gyroscope dynamics used provides an alternative description of the effect of drive mistuning. Finally, experimental results are provided that demonstrate the viability of the proposed control scheme.

A digital signal processing-based control system for a micro-electromechanical systems vibrating gyroscope with parametric amplification and force rebalance control:

This article reports a digital signal processing-based digital implementation of a micro-ring gyroscope control system that can be programmed to operate in open loop with parametric amplification or closed loop with force rebalance control according to bandwidth and dynamic range requirements. Parametric amplification is directly applied to the secondary mode and amplifies the Coriolis response by an order of magnitude. In order to improve the dynamic range and bandwidth performance of the gyroscope, force rebalance control loops are designed for the vibrations both in-phase and in quadrature with the Coriolis response. Experimental results show parametric amplification of the Coriolis response by a factor of 11 and correspond to an improvement in the signal-to-noise ratio by a factor of 9.5. The effectiveness of the force rebalance control is shown experimentally, and both the measurement bandwidth and the dynamic range have increased beyond the test capability of the rate table.

Multichannel and multiaxis inertial sensor concepts based on vibrating structures

Single-axis rate sensors (rate gyroscopes) that utilize Coriolis coupling between a single pair of modes of a simple vibrating structure have been widely researched and are being used in increasing numbers in a range of aerospace, automotive and other applications. To meet market demands for such sensors, there are now significant pressures to reduce cost and size and to improve basic performance. Size and cost reduction will be achieved via MEMS technology, but size reduction and performance improvement are often conflicting requirements. This paper examines some smart alternatives to simple size reduction. The presented concepts allow more information to be measured by a single sensor structure by using more of the available spectrum of vibration modes available in the sensor structure. The concepts are illustrated in the form of a multi-channel rate sensor based on a vibrating cylinder and a multi-axis rate sensor based on a vibrating ring. Test results from prototype sensors are presented.