面向海空重力测量的高精度硅谐振梁加速度计研究

Sea-air gravimetry is one of the main techniques to determine the regional Earth’s gravity field data efficiently, which gives rise to more urgent demands on various high-performance gravity sensors. Silicon resonant accelerometer (SRA), as one of the high-performance microelectromechanical accelerometers, has been proven to be one of most promising candidates for high accuracy applications. However, its long-term error characteristics has not been investigated intensively to date. In order to achieve a sea-air gravimetry accuracy better than 1mGal, this project will focus on optimal design and long-term error suppression of a dedicated small dynamic range SRA to produce high sensitivity and high accuracy. The error mechanism and its physical model of the SRA will be intensively investigated firstly in order to clarify its propagation rules and potential suppression methods. The optimal design of both the sensing structure and bulk micromachining process will then be conducted according to the specific performance requirements of sea-air gravimeters. Both the digital vibration amplitude control and parameter optimization of two tuning fork resonators will be conducted to explore effective solutions to suppress their nonlinear vibration and temperature drift. The optimal model estimation and test methods of the SRA dominant errors will be investigated experimentally to explore the effective techniques which will greatly improve its overall accuracy by a combination of precise error model identification and real-time compensation. The expected bias and scale factor stability of the SRA prototype will reach 1μg and 1ppm per month, respectively, by employing various error suppression techniques. It is expected that the SRA will be qualified to be used as a novel high-performance inertial sensor for sea-air gravity surveys.

海空重力测量作为快速高效获取区域地球重力场数据的主要技术手段，对高精度重力传感器的需求日益迫切。硅谐振梁加速度计作为微机电加速度计的重要发展方向，近年来已展现出高精度的优势，但其长时间误差特性有待深入研究。本课题以实现海空重力测量精度1mGal为目标，研究低量程、高灵敏度、高精度硅谐振梁加速度计的优化设计与长期误差抑制技术。研究内容包括①研究加速度测量误差的作用机理和物理模型，阐明误差传播规律及抑制途径；②针对海空重力仪需求，探索加速度计敏感结构和体硅工艺的优化设计方法；③研究谐振器数字稳幅技术与参数优化方法，探明抑制双端音叉谐振器非线性振动与温漂的途径；④研究规律性误差模型的最优估计及实验方法，探索通过误差标校与补偿技术提高精度的有效途径。通过课题研究，实现硅谐振梁加速度计零偏和标度因数月稳定性分别优于1μg和1ppm，为我国海空重力测量仪器探索出一种新型高精度重力传感器。

高精度加速度计是海空重力仪的核心传感器，要求具体极高的分辨率和长期稳定性。硅谐振梁加速度计作为微机电加速度计的重要发展方向，已展现出高精度、高分辨率的优势，有望满足动基座重力测量对小型高精度加速度计的应用需要。本项目重点研究了低量程、高灵敏度硅谐振梁加速度计的优化设计与误差抑制技术，研制了多套高精度加速度计原理样机，解决了制约硅谐振梁加速度计精度的主要技术瓶颈和关键科学问题。取得的研究成果包括：1）提出了两种低温漂结构设计方案和一种低应力贴片工艺，温漂误差的差分抑制效果显著，温漂系数可降低至4.02 μg/°C，15天的零偏稳定性为1.4μg，已表现出极高的长时间精度水平；2）完成了硅微谐振梁加速度计噪声建模分析与低噪声优化设计，白噪声水平降低至0.38μg/Hz1/2，阈值低至0.63ug；3）成功探索出了高灵敏度硅微谐振梁加速度计的体硅加工工艺路线，标度因数从200Hz/g提升至1000Hz/g；4）设计并实现了一种基于连续时间标记法的精密频率测量系统，在15kHz~25kHz输入频率范围内，频率测量的相对分辨率均在1.8ppb以内；5）提出了基于两个谐振器的谐振频率随温度变化特性的实时高精度温度测量方法，通过高低温实验对加速度计的零偏和标度因数温漂进行了误差建模，温漂补偿后零偏和标度因数误差均减小了一个量级以上；6）研制了基于精密温控的加速度计样机，恒温精度优于±0.01℃，连续30天的长时间零偏稳定性达到1.77μg，利用样机监测了潮汐引起的重力变化，对持续6天测试数据的分析表明，二者的相关系数达到0.84，充分验证了高灵敏度谐振梁加速度计具有极高的分辨率。研究工作表明，高精度谐振梁具备应用于长航时、高精度惯性导航及海空重力测量的能力。