Gauge Factor of Graphene Piezoresistor for Surface Acoustic Wave Gyroscope Instrumentation

Abstract

Surface Acoustic Wave gyroscopes are gyroscopes that have no suspended structures and hence have the potential of operation under high shock and vibration environments. Typically, gyroscopes have two electromechanical resonators; a drive resonator which couples energy into the sense resonator through the Coriolis force. Challenges in SAW gyroscope instrumentation include the matching of drive and sense resonance frequencies, matching to 50 ohm impedance for electronics, and maximizing sensitivity while minimizing noise. In addition, the sensitivities to accelerations and other physical effects such as temperature swings need to be minimized. Piezoresistive graphene transducers, with high sensitivity, and ultralow mass density and negligible loading of SAW waves, and matching to 50 ohm by proper sizing, can provide a pathway to improving SAW gyroscope performance. In this thesis, we study the electrode design and the alignment of graphene piezoresistive transducers in a two-port SAW resonator to maximize the sensitivity obtained by a biasing technique. By applying an external bias, current induced by SAW in graphene resistors can be canceled and large sensitivity at this bias point can be obtained. To characterize the sensitivity of graphene electrodes, we vary the widths, lengths and placement of the piezoresistor. We calculate the effective gauge factor using the measured displacement as a function of RF amplitude. We have discovered that the piezoresistors of lambda/4 width, aligned between the node and antinode of the primary SAW will be the most sensitive configuration equivalent to an effective gauge factor of 1 x 10^8. This high gauge factor, enabled by fast digital processing, can lead to highly sensitive SAW gyroscopes and other electromechanical sensors.