Traceable small force metrologyAbstractThe measurement of small forces is needed in a large variety of applications like micro-assembly factories,and robotics, MEMS, nano-manipulation, biological and biomedical research, material characterisation, etc.The development of these applications is being hindered by the fact that small force measurement is nottraceable to the SI. This SRT calls for the development, in strong collaboration with industry, of newtraceable primary standard systems for small forces. This includes the improvement of high precision masscomparators, the evaluation and development of new primary standards, the development of positioningsensors with a resolution of a few nm, as well as the development of the appropriate transfer standards.Conformity with the Work ProgrammeThis Call for JRPs conforms to the EMRP Outline 2008, section on “Grand Challenges” related to Industry &Fundamental Metrology on pages 9 and 25.KeywordsMicro force, traceability of small forcesBackground to the Metrological ChallengesThe ability to measure small forces are key to a large variety of scientific research fields like biology,micromechanics, physics, material science or medicine. The establishment of SI traceable primary standardsin this area will significantly improve the comparison of results and the comprehension of new phenomenon.For instance it would allow microbiology research to make the step forward from qualitative to quantitativeobservations in some areas. Micro forces are also used in medical applications like the new imagingtechnique based on the vibration response to a micro-force used in cardiac surgery where the insertion ofcardiac valve is piloted by micro force sensors to avoid vein lesions.Depth sensing indentation and atomic force microscopy (AFM) are two techniques that are typically used innano- and biomechanics. In material science, instrumented indentations are used for the determination ofhardness and elastic modulus, through relations between applied force and indenting depth. These methodshave been extended to forces of a few nN and a displacement of few nm for example for characterisingcoatings and films used in the automotive or semiconductor industry. AFM has a resolution of nanometresand can probe interaction forces with a resolution of pN, and so is used for determining the mechanicalproperties of nano-materials and for measuring interactions between molecules.Although these methods are currently used in material science, industry and bio-technology, they canproduce ambiguous results because of the lack of traceability. Mechanical properties established by meansof nano-indentation instruments from different manufacturers often do not agree with each other and Young’smodulus measured by AFM using different cantilevers can differ by orders of magnitude. Theseinconsistencies are hindering a successful commercialisation of nano- and bio-technology.The establishment of traceability for small forces, covering a range from mN down to some tenth of µN willneed a strong collaboration between European metrology institutes and instrument manufacturers. Thedevelopment of fast and high precision load cells, needed for instance in real-time application ofbiotechnology, will require industrial effort in the field of dynamic force measurement.
SI traceable force metrology