Yao Jiamin, Wu Kang, Guo Meiying, Wang Lijun
State Key Laboratory of Precision Measurement Technology and Instruments, Tsinghua University, Beijing 100084, China.
Rev Sci Instrum. 2021 May 1;92(5):054503. doi: 10.1063/5.0049925.
For absolute gravimeters, which play important roles in geophysics and geological exploration, an ultra-low-frequency vertical vibration isolator is necessary to achieve the required measurement precision. A novel active vibration isolator that uses a geometric anti-spring (GAS) structure has been proposed by our team at Tsinghua University previously, but its performance is mainly limited by the large-scale drift in the detection signal of the system. In this paper, after a brief theoretical introduction to the overall system, recent improvements in this novel vibration isolator are presented. The main improvements to the isolator are the use of new blades in the GAS structure and the addition of an extra compensation circuit to eliminate the drift. The improved prototype has a resonance period of 29.2 s and a continuous working time of several days, as compared with the resonance period of 19.2 s and a working time lasting only several minutes of the previous prototype. Experiments show that the improved prototype performs well in the homemade T-1 laser-interferometry absolute gravimeter. The standard error of the mean (SEM) of a 50-drop measurement performed in Tsinghua University is reduced significantly from 404 μGal (1 μGal = 1 × 10 m s) without the vibration isolator to 10.8 μGal with the improved prototype at its best level. Additionally, the SEM of a 50-set measurement (including 800 drops) lasting for 25 h achieves 5.9 μGal with the improved prototype.
对于在地球物理学和地质勘探中发挥重要作用的绝对重力仪而言，需要一种超低频垂直隔振器来实现所需的测量精度。此前，我们清华大学团队提出了一种采用几何反弹簧（GAS）结构的新型主动隔振器，但其性能主要受系统检测信号中大规模漂移的限制。本文在对整个系统进行简要理论介绍之后，阐述了这种新型隔振器最近的改进情况。对该隔振器的主要改进包括在GAS结构中使用新叶片以及增加一个额外的补偿电路来消除漂移。改进后的原型机共振周期为29.2秒，连续工作时间可达数天，而之前的原型机共振周期为19.2秒，工作时间仅持续几分钟。实验表明，改进后的原型机在自制的T - 1激光干涉绝对重力仪中表现良好。在清华大学进行的50次下落测量中，平均标准误差（SEM）从没有隔振器时的404微伽（1微伽 = 1×10⁻⁸米/秒²）显著降低至改进后的原型机最佳水平时的10.8微伽。此外，使用改进后的原型机进行持续25小时的50组测量（包括800次下落），SEM达到5.9微伽。
