Milligram mass metrology using an electrostatic force balance
Gordon A. Shaw, Julian Stirling, John A. Kramar, Alexander D. Moses, Patrick J. Abbott, Richard L. Steiner, Andrew D. Koffman, Jon R. Pratt, Zeina J. Kubarych
Although mass is typically defined within the International System of Units (SI) at the Kilogram level, the pending redefinition of the SI provides an opportunity to realize mass at any scale using electrical metrology. We propose the use of an electromechanical balance to realize mass at the milligram level using SI electrical units. The use of a concentric-cylinder vacuum gap capacitor allows us to leverage the highly precise references available for capacitance, voltage and length to generate an electrostatic reference force. Weighing experiments performed on 1 milligram and 20 milligram artifacts show slightly lower uncertainty than similar experiments performed by subdividing the kilogram. The measurement is currently limited by the stability of the materials composing the mass artifacts and the changes in adsorbed layers on the artifact surfaces as they are transferred from vacuum to air.