The quantum limits of micromachined gravity sensors

“该项目将研究微机械重力传感器可实现的最终性能。目标是开发现有的0.25 ng/rtHz硅传感器，这是目前惯性硅传感器在一定程度上达到的最高分辨率，以前作为火星微震仪交付给NASA，但应用于重力传感。尽管MEMS技术通常受到电子或悬架中的热力学噪声的限制，但我们现在已经将这些限制降低到足够低的程度，似乎量子效应正在设定最终性能。该项目的第一阶段是探索量子力学在这些传感器中发挥的限制作用。我们相信，在我们的位置传感器的电极上的表面状态可能起着重要的作用。如果是这样的话，微制造可能能够通过一种工程方法来最小化这些状态的贡献。这项工作可能会提出一种方法，以尽量减少“补丁”的影响，一个有问题的噪声源，为高精度传感器。硕士工作将涉及建模使用有限元分析的电子状态，特别是表面电位的变化对电容测量的影响，并产生第一原理估计的噪声地板。这种建模将被扩展到考虑不同的电极几何形状。随着基本限制更好地量化，博士可以继续研究设计贸易，以优化传感器的几何形状，然后在一系列可能的部署下构建和实验室测试这些。"

"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. "