The torsion pendulum suspended by fused silica fiber has been widely utilized in gravitational experiments. For a practical torsion pendulum, which oscillates with a certain amplitude, the second-order, third-order, and higher-order terms of the angle should be considered, as a result, the quality factor ($Q$) is dependent on the amplitude. This work focuses on the nonlinearity of the fused silica fiber, whose $Q$ value reaches the order of magnitude of $1\times {10}^5$ or higher. The influence mechanism of amplitude on the $Q$ value of the torsion pendulum is analyzed using kinematics theory, and the amplitude modulation has been carried out to measure the coupling coefficient. Two fused silica fibers with diameters of 55 and 46 $\text{μ}\mathrm{m}$ are measured in turn, when the amplitude is reduced from tens of milliradians to several milliradians, the $Q$ value increases observably. The determined change coefficients ${\gamma }_0$ of two fused silica fibers are 0.031(3)/mrad and 0.030(2)/mrad, respectively, which agree well with each other. For the 55-$\text{μ}\mathrm{m}$-diameter fused silica fiber, the change rate of $Q$ value reaches $5.1(5)\times {10}^4/$mrad. This means that the $Q$ value is extremely dependent on the amplitude, thus this effect should be considered in gravitational experiments, especially in the evaluation of fiber anelasticity or to improve the measurement sensitivity of torque.

Close

PrevNext

View figure in article

• Classical mechanics
• Elasticity
• Internal friction
• Laboratory studies of gravity
• Metrology
• Bend & torsion tests
• Chaos & nonlinear dynamics
• Precision measurements