Highlights from the SI Broader Scope projects

Whether for disease diagnosis or to manufacture energy efficient engines, the SI underpins all measurements across the globe. The SI Broader Scope call has focused R&D to advance measurement standards and SI units and to prepare an efficient European measurement infrastructure based on National Measurement Institute collaboration.

The European Union and national governments invested 37 million Euro in collaborative metrology focused research, involving research groups in 28 European NMIs and Designated Institutes (DIs), and 28 academic groups. The research addressed key needs for SI unit redefinitions and increased traceability for chemical,radio-biological and sub-nano measurements.

Silicon spheres for routine kilogram-SI links

The ability to redefine the kilo in 2018 will rely on determining the Planck constant using two different methods. One method balances a kilogram weight and a force generated by the current in a coil of wire within a magnetic field and the other relies on counting atoms in a silicon sphere. Resolving small discrepancies between the different electrical balances used to generate the kilogram experimentally and remove inconsistencies between the balancing and atom counting methods were remaining problems hampering the kilograms redefinition. The EMRP project Realisation of the awaited definition of the kilogram - resolving the discrepancies has enabled the international community to pool resources and successfully get agreement between these techniques.

Over the longer-term, the atom-counting method will make the kilogram definition accessible to any laboratory capable of carrying out surface characterisations and volume measurements. Relatively inexpensive natural silicon spheres will be usable as mass transfer standards. Spheres may transform the kilograms traceability chain and significantly increase the number of labs able to experimentally achieve an SI definition of the kilogram. 

Innovation in optical measurement standards

Optical technologies are important for many applications from fibre optic communication networks to earth observation and healthcare. To take advantage of LED technologies, new highly accurate measurement standards are needed to support SI traceability in radiometry – the measurement of light in any part of the electromagnetic spectrum. EMRP project New primary standards and traceability for radiometry has developed a new radiometry standard based on Predictable Quantum Efficiency Detectors (PQED) that for the first time can be easily used by calibration and testing laboratories, improving access to the candela, the SI unit of luminous intensity. The PQED provides a direct link to the fundamental constants used in the SI redefinition, therefore it does not require calibration using any other method.

A milestone in angle metrology

Ensuring that the world’s most precise mirror, to be installed in the new European X-ray Free Electron Laser Facility (XFEL) in Hamburg (Germany) is defect free, relies on measurement technology that can identify system imperfections of only a few atoms in size. EMRP project Angle Metrology has enabled manufacturers of optical components for the beam line to demonstrate conformance to onerous specifications. Working at the boundaries of measurement capability, the project developed advanced facilities and a new two-axis calibration method for the autocollimators that are used to make contactless angle measurements of complex optical surfaces. Improving the quality of high intensity light beams supports European materials research which is fundamental to future innovations in many scientific fields, such as improved films for solar panels.

Developing next-generation SI impedance standards

Precise measurements of impedance – the resistance a circuit presents to an alternating current – is vital in modern electronics. Impedance values are currently defined using the Quantum Hall Effect, which can be scaled to create a range of impedance values depending on the number of windings in the two transformers used. Josephson Bridges, based on dual alternating current Josephson voltage standards, enable unprecedented flexibility in high-precision impedance calibrations but these take a long time to achieve stability. EMRP project Automated impedance metrology extending the quantum toolbox for electricity has developed and validated a software driven Josephson Bridge that can automatically set impedance ratios, allowing multiple ratios to be achieved rapidly with a single instrument.

Developing next-generation SI voltage standards

Quantum devices based on superconducting Josephson junctions can create small but highly reliable voltage outputs. These have great potential for use as future industrial voltage standards provided they can be scaled up and used to calibrate transfer devices that operate at room temperature. EMRP project A quantum standard for sampled electrical measurements has demomstrated the feasibility of using Josephson junctions as a precise SI linked calibration standard that matches industrial requirements. For the first time, a prototype voltage standard, based on multiple arrays that each contain thousands of junctions, has been assembled into a single unit capable of producing the 1 volt standard required by many sensing, electronics and communications applications.

Innovation in sub-nanometre dimension accuracy

Advanced analytical instruments, such as Atomic Force Microscopes and Scanning Electron Microscopes, are being used to make nanoscale dimension measurements, but their users need improved calibration standards to have confidence in the measurements made. Existing standards, based on precisely machined blocks of material to form nano-sized steps, is a time-consuming process that produces standards down to only 6 nm. EMRP project Crystalline surfaces, self assembled structures, and nano-origami as length standards in (nano)metrology successfully created silicon lattices with reproducible step height and lateral features that demonstrate the feasibility of using crystal lattices for sub-nanometre dimension measurements. Further evaluation of this new capability is needed to ensure its international acceptance and to enable this type of standard to be used in nanoscale dimension measurements.