精密扭摆研究

本研究旨在提高扭摆精度。扭摆采用大理石——这取自地球的天然材料作摆盘;通过试验,挑选了Q值高、内耗小、剪切模量温度系数接近于零的恒弹性合金丝作为吊丝。特别是,我们把Saxl类型的每周期吸合一次的间断振荡摆回复到小阻尼情况下的自由振荡摆,减少对摆振动的人为干预;增加真空条件,以减少周围环境干扰,延长了阻尼时间;同时在摆盘中央安放多面反射镜环,增加测量点,变一周期仅测一次时间为同一周期测四次以上。这就提供了用计算机求阻尼振荡方程θi=Ae^-t_i/τsin(ωt_i+φ)数值解的条件,不但可直接测得周期T的变化,而且可望计算得振幅A、阻尼时间τ、初相角φ的变化。另外,在光电接收方面也作了一些改进。通过这些措施,我室的精密扭摆对周期的探测精度已比美国Saxl 1964年发表第一篇文章时的扭摆精度提高100倍;比其运转17年,经一再改进的扭摆精度提高10倍。测量有效数字6位至7位,周期相对误差一般达2×10^-6,最佳状况可达8×10^-7,基本达到预期设计要求,为将来探测引力异常,“区分长期间与短期间内频率起伏”提供了可能性。 关键词：

THE INVESTIGATION OF THE PRECISION OF TORSIONAL PENDULUM

Our pendulum disk is made of natural marble. The suspended wire is made of isoelastic alloy which has been chosen through repeated testing for it's high quality factor, low internal exhaustion and almost zero thermoelastic coefficisnt. A low-damping free oscillating pendulum is set up instead of the discontinuous pendulum which is electro-magnetically attracted against a stop once every swing. Thus artificial disturbance to the pendulum is reduced. The pendulum is put in a vacuum-tight chamber to avoid environmental disturbance and lengthen the damping time. Besides, a multi-faceted reflective mirror ring is located at the centre of the pendulum disk. As a result, the number of times of measurement is increased from one to four or more within a certain period. This makes it possible to numerically solve the damping oscillating equations θ_i= A exp(-t_i/τ) sin(ωt_i + φ) (i = 1, 2, 3, 4) by means ofcomputer. Therefore, not only can variations of period be measured directly, the variations of amplitude A, damping time τ and initial phase φ can also be calculated. Some modifications have been made on the system of light-electric accepter. Now, the precision detecting period with our torsional pendulum is one-hundred times higher than that of Dr. Saxl's as reported in his first article concerning pendulum in 1964, and ten times higher than the precision of his pendulum in 1970, which is the result of seventeen years of efforts in making improvements. The effective numbers obtained with our setup have reached six to seven figures, and the relative error of period is 2×10^-6, or even 8×10^-7 in the best case. Basically, the desired requirements have been satisfied. This will provide the possibility of detecting gravitational abnormal phenomena and making a distinction between the frequency fluctuation during a long period of time and that during a short period of time.