The quantum limits of micromachined gravity sensors

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"This project will investigate the ultimate performance achievable with a micromachined gravity sensor. The goal is to develop an existing 0.25 ng/rtHz silicon sensor, the highest resolution presently achieved by an inertial silicon sensor by some margin, and previously delivered to NASA as a Mars microseismometer, but with application to gravity sensing. Although MEMS technology is generally limited by thermodynamic noise, either in the electronics or the suspension, we have now pushed these limits low enough that it appears that quantum effects are setting the ultimate performance. The first stage of this project is to probe the limiting role that quantum mechanics is playing in these sensors. It is believed that surface states on the electrodes of our position transducer may be playing an important role. If so, microfabrication may be able to minimise the contribution through an engineered approach to dimensionally constraining these states. This work might suggest a way to minimise the "patch" effect, a problematic noise source for ultrahigh precision sensors.The MSc work will involve modelling using finite element analysis of the electron states, and in particular the effect of the variation of surface potentials on the measurement of capacitance and producing a first principles estimation of the noise floor. This modelling will be extended to consider different electrode geometries. With the fundamental limitations better quantified, the PhD can proceed to investigate design trades to optimise sensor geometries, and then to build and lab test these under a range of possible deployments. "