The dynamics of degenerate mode MEMS sensors

This presentation discusses the vibration characteristics of structures which have cyclic symmetry and shows how their properties can be exploited to design MEMS resonators which have independent modes of vibration sharing a common natural frequency. Particular examples, such as a gyroscope and a mass sensor, are described and important issues related to their manufacture identified. Imperfections, accidentally or deliberately introduced, will always break the cyclic symmetry of the ideal structure and introduce a dynamic coupling which produces a ‘split' in the modal frequencies. Methods of minimising or exploiting this frequency split are described as well as techniques for resonance excitation and detection. Optical characterisation of the sensors using surface profilometery and laser Doppler is also described.