SI Traceability: Current status and future trends for forces below 10 micronewtons
Jon R. Pratt
Measurements related to nano- and micro- scale science, technology, and manufacturing are pushing the limits of detectable mechanical, electrical, and chemical quantities to ever smaller values, raising important questions regarding how best to extend the range of SI traceability. The case in small force measurement is illustrative. At present, the mechanical unit of force is linked to The Kilogram, or a deadweight force of nearly 10 N. Although known with exquisite accuracy and precision on this scale, such a mass- based force standard is of little use to investigators and manufacturers faced with instruments that must accurately determine quantities that are twelve orders of magnitude smaller. In light of this, the world congress of the International Measurement Confederation (IMEKO) convened a round table of researchers from National Metrology Institutes representing the US, Europe, and Asia to discuss and provide an overview of the emerging field of low-force metrology . This paper seeks to capture the information shared in that round table and amplify on its content. The current status of research efforts and standards activities aimed at small force measurement and instrumentation are reviewed. Topics are highlighted that encompass the development of primary realizations of force in the range from hundreds of piconewtons through micronewtons, techniques and devices for the dissemination of traceable small forces, and nascent standards activities surrounding depth sensing indentation and atomic force microscopy. Looking towards the future, trends such as quantum based force and intrinsic force standards based on atomic and molecular interactions are also discussed.