A proposed superconducting magnetic levitation system intended to monitor stability of the unit of mass

Abstract

To monitor the stability of the kilogram a total uncertainty not exceeding 1 to 2 parts in 108 is required. Although a comparison of "mechanical" and "electrical" energy by the superconducting magnetic levitation method is viable in principle for this purpose, a more elaborate design of electromechanical system for levitation is required. A design for the system based on a combination of flat elements is suggested. The single element takes the form of a flat rectangular coil, produced by photolithography, and a superconducting plane located near and parallel to the coil. The characteristics of the element have been calculated in two versions. The first is meant for use in levitation, the second as part of a magnetic guide.

Mass determination with the magnetic levitation method—proposal for a new design of electromechanical system

“…A novel method for manufacturing single crystal layers is to evaporate pure niobium (99.99%) on the surface of a sapphire crystal plate (coating thickness of niobium about 1 µm) [26]. Such heteroepitaxial Nb/α-Al 2 O 3 structures have been proposed to reduce energy losses in the levitation method [27]. Sapphire is inflexible, light and nonmagnetic.…”

“…Figure 3.Measurement set-up of the levitation method with a repulsed body. The voltage is determined with the aid of a known inductance L ref[27].…”

Measuring the gravitational acceleration using a superconducting magnetic levitation system

“…Then the equation of oscillations for the levitated body becomes isomorphic to that for a simple pendulum of length . The natural, angular frequency of free small-amplitude oscillations, , is thus given by (11) and hence (12) which is the required result. This allows the gravitational acceleration to be determined in terms of (i) the frequency of free small-amplitude oscillations about an arbitrary preset position, and (ii) the effective length of a simple pendulum, which in turn can be found from measurements of the parameters which describe the system configuration.…”

“…Then, as described in [10], we may express the angular frequency, , of oscillations of amplitude as δ (20) with the relative correction δ where (-) and (-) are the factors of and , respectively, in the power-series expansion on the right of (10). Using (10) and (11) gives…”

“…As indicated above, the expression in the brackets on the right side of ( 21) is defined by the geometric features of the system so its value can be reduced to an admissible level, at least in the close vicinity of one point whose extent is of the order of peak-to-peak amplitude of the oscillations, by deliberate changes in the configuration of the system. An example of changes of this kind can be found in [11], which considers the use of an additional coil placed above the levitated body to neutralize the nonlinearity of the sytem. There, it is shown that full neutralization is possible and, for the situation considered in the vicinity of the fullcompensation point , δ can be written in the form δ…”