Measurement of remanent magnetic moment using a torsion pendulum with single frequency modulation method

In Tian Qin spaceborne gravitational-wave detectors, the stringent requirements on the magnetic cleanliness of the test masses demand the high resolution ground-based characterization measurement of their magnetic properties. Here we present a single frequency modulation method based on a torsion pendulum to measure the remanent magnetic moment mr of 1.1 kg dummy copper test mass, and the measurement result is(6.45 ± 0.04(stat) ± 0.07(syst)) × 10^(-8)A · m^(2). The measurement precision of the mr is about 0.9 n A · m^(2), well below the present measurement requirement of Tian Qin. The method is particularly useful for measuring extremely low magnetic properties of the materials for use in the construction of space-borne gravitational wave detection and other precision scientific apparatus.

New measuring method of fiber alignment in precision torsion pendulum experiments

Testing the extreme weak gravitational forces between torsion pendulum and surrounding objects will indicate new physics which attracts many interests.In these measurements,the fiber alignment plays a crucial role in fulfilling high precision placement measurement,especially in measuring the deviation between the fiber and source mass or other objects.The traditional way of the fiber alignment requires to measure the component of the pendulum body and then transfer to the torsion fiber by some complicated calculations.A new method is reported here by using a CCD camera to get the projection image of the torsion fiber,which is a direct and no-contact measurement.Furthermore,the relative position change of the torsion fiber can also be monitored during the experiment.In our experiment,the alignment between the fiber and the center of the turntable has been operated as an example.Our result reaches the accuracy of several micrometers which is higher than the previous method.

Influence of the colored noise on determining the period of a torsion pendulum

Based on statistical properties, two typical models are considered to calculate the uncertainties for some random noise sequences on the period extraction of a torsion pendulum, which is important and instructive in the measurement of gravitational constant G with the time-of-swing method. An expression of the uncertainty for the period measurement is obtained, which is dependent on the ratio ？t/（1/λ） where ？t is the interval of the sample time and 1/λ is the length of the correlation time. The result of processing experimental data shows that as the interval of the sample time ？t gradually shortens, the uncertainty of the period becomes smaller, and further when the ratio ？t/（1/λ） is less than 1, the uncertainty remains substantially unchanged.

Ultra-High Sensitivity Viscometer Based on a Torsion Pendulum

Based on a conventional torsion pendulum,we develop a forced oscillation viscometer with ultra-high viscosity sensitivity of 2×10^（-7）Pa·s working at frequencies near the resonance.The viscosity is achieved by exploiting the phase lag for the angle displacement behind the torque,instead of the resonant curve,i.e.,the variation of angle displacement amplitude versus frequency.The general formula for the measurement of the visco-elasticit.y of complex fluids is also presented.With such precision it is easy to measure tiny change in viscosity result from circumstantial influences.Deionized water and two kinds of NaCl aqueous solutions are chosen to demonstrate the performance of our home-made torsion pendulum-based viscometer.

Determination of the thermal noise limit in test of weak equivalence principle with a rotating torsion pendulum

Thermal noise is one of the most fundamental limits to the sensitivity in weak equivalence principle test with a rotating torsion pendulum. Velocity damping and internal damping are two of many contributions at the thermal noise, and which one mainly limits the torsion pendulum in low frequency is difficult to be verified by experiment. Based on the conventional method of fast Fourier transform, we propose a developed method to determine the thermal noise limit and then obtain the precise power spectrum density of the pendulum motion signal. The experiment result verifies that the thermal noise is mainly contributed by the internal damping in the fiber in the low frequency torsion pendulum experiment with a high vacuum. Quantitative data analysis shows that the basic noise level in the experiment is about one to two times of the theoretical value of internal damping thermal noise.

Design and fabrication of a full elastic sub-micron-Newton scale thrust measurement system for plasma micro thrusters

In this work,a force measurement system is proposed to measure the thrust of plasma microthruster with thrust magnitude ranging from sub-micro-Newtons to hundreds micro-Newtons.The thrust measurement system uses an elastic torsional pendulum structure with a capacitance sensor to measure the displacement,which can reflect the position change caused by the applied force perpendicular to the pendulum axis.In the open-loop mode,the steady-state thrust or the impulse of the plasma micro-thruster can be obtained from the swing of the pendulum,and in the closed-loop mode the steady-state thrust can be obtained from the feedback force that keeps the pendulum at a specific position.The thrust respond of the system was calibrated using an electrostatic weak force generation device.Experimental results show that the system can measure a thrust range from 0 to 200μN in both open-loop mode and closed-loop mode with a thrust resolution of 0.1μN,and the system can response to a pulse bit at the magnitude of 0.1 m N s generated by a micro cathode arc thruster.The background noise of the closed-loop mode is lower than that of the open-loop mode,both less than 0.1 m N/Hz in the range of 10 mHz to 5 Hz.

Exploring Extra Dimensions in Spectroscopy Experiments

We propose an idea in spectroscopy to search for extra spatial dimensions as well as to detect the possible deviation from Newton＇s inverse-square law at small scale, and we take high-Z hydrogenic systems and muonic atoms as illustrations. The relevant experiments might help to explore a more than two extra dimensions scenario in the brane world model proposed by Arkani-Hamed, Dimopoulos, Dvali （ADD） and to set constraints for fundamental parameters such as the size of extra dimensions.

Relationship between Magnetomechanical Damping Capacity and Vibration Modes

The mathematical expressions for magnetomechanical damping capacity are presented by applying Smith-Birchak's model in torsion pendulum and cantilever beam.The peak value ψ_p is found to be related to physical parameters and material constants in the form Kλ_s=αψ_pε_p.which can be used to estimate the magnetostrictive constant λ_s from the damping capacity-strain amplitude curve.A good agreement of experimental data and theoretical prediction was observed in HIDAMETS Cr15A13NiCu.

On the Possibility to Construct Gravitational Eye

The possibility of modifying a conventional Cavendish torsion pendulum into a half-armed pendulum oscillator to measure the horizontal gravitational acceleration is discussed. A new kind of gravitational detector, gravieye, as we named, can be made by a proper combination of such oscillators to ＂see＂ remote objects and to be used, e.g. to detect the movement of huge mass at a long distance.

An Improved Model to Characterize Drill-String Vibrations in Rotary Drilling Applications

A specific model is elaborated for stick-slip and bit-bounce vibrations,which are dangerous dynamic phenomena typically encountered in the context of rotary drilling applications.Such a model takes into account two coupled degrees of freedom of drill-string vibrations.Moreover,it assumes a state-dependent time delay and a viscous damping for both the axial and torsional vibrations and relies on a sawtooth function to account for the cutting force fluctuation.In the frame of this theoretical approach,the influence of rock brittleness on the stability of the drill string is calculated via direct integration of the model equations.The results show that the rock brittleness has a great influence on the rotational speed and bit depth.

A MODIFIED TORSION PENDULUM FOR MEASURING THE SHEAR MODULUS OF A SINGLE MICRO-SIZED FILAMENT

A modified torsion pendulum apparatus is developed for measuring the shear modu- lus of single filaments with uniform micro-sized diameter. A single filament fixed at both ends and with a ring-shaped mass attached at the middle is used as a clamped-clamped torsion pendulum. The shear modulus of single filaments can be expressed as a function of the oscillation frequency of the torsion pendulum. The oscillation motion is measured with a CCD laser displacement sensor, and its frequency is determined by the Fast Fourier Transform （FFT） method. The shear moduli of three types of filaments： copper wires, tungsten wires and carbon fibers are accurately measured with this technique. It is found that the size effect in shear moduli of both copper wires and tungsten wires is minor. Finally, the error analysis of our measurement technique is presented in detail.