Focus on Metrology in Electricity and Magnetism

Guest Editors


François Piquemal, Laboratoire national de métrologie et d'essais, France
Gert Rietveld, Van Swinden Laboratorium, The Netherlands (CCEM president).


Artist view of the network of Carbon atoms which constitutes the graphene and the motion of a charge carrier under magnetic field. The quantization of energy associated to this motion is at the origin of the quantum Hall effect used to implement the electrical resistance standard. Credit: Anthony Carlone

Scope

Over the past decades, the field of electromagnetic precision measurements has strongly developed driven by progress in science and technology and evolving needs in industry. This focus issue collates papers that describe the state of the art and new challenges in a broad variety of disciplines of electromagnetic metrology. These range—to name a few examples—from quantum electrical standards that provide a quantum basis for electrical measurements and drive the revision of the SI, to microwave metrology reaching unprecedented uncertainties and extending its frequency range up to the THz regime, and applied measurements for the electrical power industry.

Ever since the first international congress of electricity in 1881, the field of electrical precision measurements is a strongly developing area driven by progress in science and technology and evolving needs in industry. Quantum standards were discovered and further developed to the level that today they not only provide the ideal and widespread quantum basis for all our electrical measurements worldwide but also are an important driving force for revising the SI.

Significant progress has also been made in the many derived quantities that characterize the field of electromagnetic metrology such as alternating voltage and current, impedance, radiofrequency power and S-parameters, magnetism, electromagnetic fields, high voltage and high current. In fact, electromagnetic metrology is unique in the large measurement and frequency range of its many derived quantities, as reflected in the extensive number of calibration measurement capabilities contained in the Key Comparison Data Base of the BIPM.

Recognising this significant progress in electromagnetic metrology, still much development is required and new challenges lay ahead both in existing areas as new evolving areas, as for example identified by the 2011 "Big problems in electromagnetics" strategy document of the CCEM:

  • Quantum standards for industry and AC metrology
  • Electronic kilogram
  • Electrical and magnetic measurements at the nanoscale
  • Waveform metrology
  • THz metrology
  • Metrology for smart grids

This focus issue reviews the state of the art and describes the challenges in these and other disciplines of electromagnetic measurement science. It aims to provide insight in the latest developments of the field and provide inspiration for new research to researchers at universities and metrology institutes worldwide.

Focus issue papers

Open access
Robustness of single-electron pumps at sub-ppm current accuracy level

F Stein et al 2017 Metrologia 54 S1

We report on characterizations of single-electron pumps at the highest accuracy level, enabled by improvements of the small-current measurement technique. With these improvements a new accuracy record in measurements on single-electron pumps is demonstrated: 0.16 µA · A−1 of relative combined uncertainty was reached within less than 1 d of measurement time. Additionally, robustness tests of pump operation on a sub-ppm level revealed a good stability of tunable-barrier single-electron pumps against variations in the operating parameters.

Establishing traceability for the measurement of scattering parameters in coaxial line systems

M Zeier et al 2018 Metrologia 55 S23

Scattering parameters are fundamental quantities in radio frequency and microwave metrology. Traceability to SI units for these measurements is established with the help of calculable standards. Progress has been made over recent years in characterizing these standards. Major steps forward have been achieved with advanced modelling of the entire standard, including connector interface and with the use of multivariate uncertainty evaluation, taking correlations fully into account. The improvements have led to more consistent, more accurate measurements.

Open access
Epitaxial graphene for quantum resistance metrology

Mattias Kruskopf and Randolph E Elmquist 2018 Metrologia 55 R27

Graphene-based quantised Hall resistance standards promise high precision for the unit ohm under less exclusive measurement conditions, enabling the use of compact measurement systems. To meet the requirements of metrological applications, national metrology institutes developed large-area monolayer graphene growth methods for uniform material properties and optimized device fabrication techniques. Precision measurements of the quantised Hall resistance showing the advantage of graphene over GaAs-based resistance standards demonstrate the remarkable achievements realized by the research community. This work provides an overview over the state-of-the-art technologies in this field.

Impedance bridges: from Wheatstone to Josephson

Frédéric Overney and Blaise Jeanneret 2018 Metrologia 55 S119

This paper reviews the recent evolution of the measurement techniques in the area of impedance measurement from the Wheatstone bridge to the most advanced Josephson-based digital impedance bridge. The progress in the development of high sampling rate, high accuracy digital-to-analog and analog-to-digital converters has led to the development of digital impedance bridges that have profoundly modified the landscape of impedance metrology. Although these new bridges do not yet outperform the traditional transformer-based bridge in terms of accuracy, they significantly improve their measurement capabilities and flexibility by allowing a complete automation, a full coverage of the complex plane, arbitrary bridge ratios and extended frequency range. In addition, after the redefinition of the International System of Unit, they will contribute to the realization of the henry and the farad by establishing a direct link between the quantized Hall resistance and the capacitance or inductance standards.

Waveform metrology: signal measurements in a modulated world

Paul D Hale et al 2018 Metrologia 55 S135

We review the waveform metrology program developed over many years at the National Institute of Standards and Technology. The goal of this program is to provide a measurement service capable of characterizing both temporal and frequency-domain instrumentation used with high-speed communication systems. Under our program, full waveforms as functions of both time and frequency are the target measurands. From these functional waveforms, traditional parametric descriptions can be derived. Furthermore, we give temporal waveforms and their frequency-domain representations consistent and equal consideration, with traceability to the International System of Units. To support this traceability, we emphasize voltage and current waveforms, their relationships, and the ability to transform both nominal values and their uncertainties from one domain to the other.

Impact of the latest generation of Josephson voltage standards in ac and dc electric metrology

Alain Rüfenacht et al 2018 Metrologia 55 S152

For decades, the quantum behavior of Josephson junctions has been employed as intrinsic standards for voltage metrology. Conventional dc Josephson voltage standards have been the primary standards for voltage, programmable Josephson voltage standards have been implemented in calibration services and precision measurements, such as the Planck constant, and Josephson arbitrary waveform synthesizers have been employed in ac voltage calibrations and precision measurements of the Boltzmann constant. With the anticipated redefinition of the Système International d'Unités, all types of Josephson voltage standards will become intrinsic standards and equivalent realizations of the unit volt. Here we review the state-of-the art performance, best practices, and current impact of these systems for various applications, with an emphasis on ac voltage metrology. We explain the limitations of each system, especially regarding the many potential systematic errors that affect their accuracy and performance for specific applications.

Selected articles published in Metrologia:

Open access
Metrology in electricity and magnetism: EURAMET activities today and tomorrow

F Piquemal et al 2017 Metrologia 54 R1

Metrology dedicated to electricity and magnetism has changed considerably in recent years. It encompasses almost all modern scientific, industrial, and societal challenges, e.g. the revision of the International System of Units, the profound transformation of industry, changes in energy use and generation, health, and environment, as well as nanotechnologies (including graphene and 2D materials) and quantum engineering. Over the same period, driven by the globalization of worldwide trade, the Mutual Recognition Arrangement (referred to as the CIPM MRA) was set up. As a result, the regional metrology organizations (RMOs) of national metrology institutes have grown in significance. EURAMET is the European RMO and has been very prominent in developing a strategic research agenda (SRA) and has established a comprehensive research programme. This paper reviews the highlights of EURAMET in electrical metrology within the European Metrology Research Programme and its main contributions to the CIPM MRA. In 2012 EURAMET undertook an extensive roadmapping exercise for proposed activities for the next decade which will also be discussed in this paper. This work has resulted in a new SRA of the second largest European funding programme: European Metrology Programme for Innovation and Research.

A novel two-terminal-pair pulse-driven Josephson impedance bridge linking a 10 nF capacitance standard to the quantized Hall resistance

S Bauer et al 2017 Metrologia 54 152

In this paper the realization of a two-terminal-pair impedance bridge based on pulse-driven Josephson arrays will be presented. This bridge was used to link a 10 nF capacitance standard to the quantized Hall resistance at 1233 Hz. With pulse-driven Josephson arrays the setup for a quadrature bridge can be reduced dramatically. For the combination of the AC quantum Hall resistance and a 10 nF capacitance standard, most of the uncertainties caused by contact resistances in a two-terminal-pair definition were circumvented by a triple-series connection of the AC quantum Hall resistance. The capacitance value obtained by the new Josephson impedance bridge was compared to the results from a transformer-based ratio bridge and agrees within 1.3 parts in 108. Sources of systematic uncertainties were investigated and the combined relative uncertainty of the bridge was determined to be less than $1\times {{10}^{-8}}$ (k  =  1) and 13.9 nF F−1 (k  =  1) for the link of the 10 nF capacitance standard.

Josephson-based full digital bridge for high-accuracy impedance comparisons

Frédéric Overney et al 2016 Metrologia 53 1045

This paper describes a Josephson-based full digital impedance bridge capable of comparing any two impedances, regardless of type (R-C, R-L, or L-C), over a large frequency range (from 1 kHz to 20 kHz). At the heart of the bridge are two Josephson arbitrary waveform synthesizer systems that offer unprecedented flexibility in high-precision impedance calibration, that is, it can compare impedances with arbitrary ratios and phase angles. Thus this single bridge can fully cover the entire complex plane. In the near future, this type of instrument will considerably simplify the realization and maintenance of the various impedance scales in many National Metrology Institutes around the world.

Broadband fully automated digitally assisted coaxial bridge for high accuracy impedance ratio measurements

Frédéric Overney et al 2016 Metrologia 53 918

This paper describes the principle of a new fully automated digitally assisted coaxial bridge having a large bandwidth ranging from 60 Hz to 50 kHz. The performance of the bridge is evaluated making $1:1$ comparisons between calculable ac resistors. The agreement between the calculated and the measured frequency dependence of the resistors is better than $5\cdot {{10}^{-8}}$ at frequencies up to 5 kHz, better than $1\cdot {{10}^{-7}}$ up to 20 kHz and better than $0.8\cdot {{10}^{-6}}$ up to 50 kHz. This bridge is particularly well suited to investigate the ac transport properties of graphene in the quantum Hall regime.

Evaluating the measurement uncertainty of complex quantities: a selective review

B D Hall 2016 Metrologia 53 S25

This paper reviews a selection of topics related to the evaluation and expression of measurement uncertainty in complex quantities, which are prevalent in electromagnetic measurements at radio and microwave frequencies. Methods appropriate for complex quantities are presented that extend those described, for real-valued quantities, in the Guide to the Expression of Uncertainty in Measurement.

Validation of the ultrastable low-noise current amplifier as travelling standard for small direct currents

D Drung et al 2015 Metrologia 52 756

An interlaboratory comparison of small-current generation and measurement capability is presented with the ultrastable low-noise current amplifier (ULCA) acting as travelling standard. Various measurements at direct currents between 0.16 nA and 13 nA were performed to verify the degree of agreement between the three national metrology institutes involved in the study. Consistency well within one part per million (ppm) was found. Due to harsh environmental conditions during shipment, the ULCA's transfer accuracy had been limited to about  ±0.4 ppm. Supplemental measurements performed at PTB indicate that further improvements in accuracy are possible. Relative uncertainties of 0.1 ppm are achieved by applying on-site calibration of the ULCA with a suitable cryogenic current comparator.

Direct comparison of a 1 V Josephson arbitrary waveform synthesizer and an ac quantum voltmeter

Ralf Behr et al 2015 Metrologia 52 528

AC Josephson voltage standards based on pulse-driven Josephson arrays (Josephson arbitrary waveform synthesizer—JAWS) have recently achieved an output voltage of at least 1 V root-mean-square. An ac quantum voltmeter (ac-QVM) based on a 2 V programmable Josephson array has been used to verify the quantization level of the new JAWS by performing a direct comparison in the frequency range from 30 Hz to 2 kHz. The comparison has demonstrated an excellent agreement between the two quantum standards of better than 1 part in 108. Sources for systematic errors have been investigated. The overall uncertainty is found to be better than 1.2 parts in 108 (k = 1) for measurements at a frequency of 250 Hz and 1 V amplitude.

Open access
Precision measurement of a potential-profile tunable single-electron pump

Myung-Ho Bae et al 2015 Metrologia 52 195

We performed a precision measurement of the current from a single-parameter electron pump, where the potential-profile for a quantum dot was manipulated by multiple top-metal gates. In an optimally tuned condition, driven with a sinusoidal-waveform microwave at f = 0.95 GHz, B = 11 T, and T = 0.3 K, the relative deviation of the pump current from ef, δIp/ef ≡ (Ip − ef)/ef was measured to be (−0.92  ±  1.37) ppm. Our experiment reproduces the current quantisation accuracy of a previous measurement of a single-parameter pump, but in a device fabricated using very different geometry, thereby indicating that accurate single-parameter pumping is insensitive to device details.

Open access
Calibration of bridge-, charge- and voltage amplifiers for dynamic measurement applications

Leonard Klaus et al 2015 Metrologia 52 72

Measuring amplifiers are used for transducer output signal conditioning in many dynamic measurement applications. For a traceable measurement, a calibration of all components of the measuring chain—and therefore of the conditioning amplifiers, too—is mandatory. In this paper methods for a dynamic calibration of different types of conditioning amplifiers are presented. Measurement uncertainties and calibration results for typical amplifiers are discussed.