151 research outputs found
Single-electron current sources: towards a refined definition of ampere
Controlling electrons at the level of elementary charge has been
demonstrated experimentally already in the 1980's. Ever since, producing an
electrical current , or its integer multiple, at a drive frequency has
been in a focus of research for metrological purposes. In this review we first
discuss the generic physical phenomena and technical constraints that influence
charge transport. We then present the broad variety of proposed realizations.
Some of them have already proven experimentally to nearly fulfill the demanding
needs, in terms of transfer errors and transfer rate, of quantum metrology of
electrical quantities, whereas some others are currently "just" wild ideas,
still often potentially competitive if technical constraints can be lifted. We
also discuss the important issues of read-out of single-electron events and
potential error correction schemes based on them. Finally, we give an account
of the status of single-electron current sources in the bigger framework of
electric quantum standards and of the future international SI system of units,
and briefly discuss the applications and uses of single-electron devices
outside the metrological context.Comment: 55 pages, 38 figures; (v2) fixed typos and misformatted references,
reworded the section on AC pump
Variational Calibration
The approach to the improving the accuracy of the impedance parameter measurements is described. This approach is based on the well-known variations of the influence of the disturbing factors on the results of measurement. Using these variations, measurement circuit provides the additional number of measurements, equal to the number of the disturbing factors. System of equations describes these results of measurements. The solution of this system eliminates the influence of the appropriate uncertainty sources on the results of measurement and gets the true result of the measured value. In addition, the solution of this system also gets the values of the uncertainty components in every measurement and possibility to monitor the properties of the measurement circuit. Examples of the realization of this method for improving the accuracy of the impedance parameter measurements in different bridges are given
The ampere and the electrical units in the quantum era
By fixing two fundamental constants from quantum mechanics, the Planck
constant and the elementary charge , the revised Syst\`eme International
(SI) of units endorses explicitly quantum mechanics. This evolution also
highlights the importance of this theory which underpins the most accurate
realization of the units. From 20 May 2019, the new definitions of the kilogram
and of the ampere, based on fixed values of and respectively, will
particularly impact the electrical metrology. The Josephson effect (JE) and the
quantum Hall effect (QHE), used to maintain voltage and resistance standards
with unprecedented reproducibility since 1990, will henceforth provide
realizations of the volt and the ohm without the uncertainties inherited from
the older electromechanical definitions. More broadly, the revised SI will
sustain the exploitation of quantum effects to realize electrical units, to the
benefit of end-users. Here, we review the state-of-the-art of these standards
and discuss further applications and perspectives.Comment: 78 pages, 35 figure
Development and characterisation of traceable force measurement for nanotechnology
Traceable low force metrology should be an essential tool for nanotechnology. Traceable
measurement of micro- and nanonewton forces would allow independent measurement
and comparison on material properties, MEMS behaviour and nanodimensional measurement
uncertainties. Yet the current traceability infrastructure in the UK is incomplete.
This thesis describes the incremental development of the low force facility at the National
Physical Laboratory (NPL).
The novel contribution of this thesis has three components. First, specific modifications
to the NPL Low Force Balance were undertaken. This involved developing novel or
highly modified solutions to address key issues, as well as undertaking detailed comparions
with external ans internal traceability references. Second, a triskelion force sensor flexure
was proposed and mathematically modelled using both analytical and finite element techniques,
and compared to experimentally measured spring constant estimates. The models
compared satisfactorily, though fabrication defects in developed prototype artefacts limited
the experimental confirmation of the models. Third, a piezoelectric sensor approach for quasistatic
force measurement was proposed, experimentally evaluated and rejected. Finally, an
improved design for a low force transfer artefact system is presented, harnessing the findings
of the reported investigations. The proposed design combines proven strain-sensing technology
with the advantageous triskelion flexure, incorporating an external stage and packaging
aspects to achieve the requirements for a traceable low force transfer artefact
Programmierbare Josephson-Arrays für Impedanzmessungen
An innovative way of networking two programmable Josephson arrays generating synchronous waveforms for impedance ratio measurements, as the first of its kind, is presented. This pioneering approach of the Josephson Impedance Bridges is far more flexible than conventional bridges at the same level of measurement uncertainty. Results prove that aside from having the capability of measuring
over a wider frequency range, the Josephson bridge permits measurements on two impedances with any value of phase angle between them. In the two-terminal-pair Josephson bridge setup, measurements are made for a 1:1 resistance ratio at the 10-k level in the frequency range between 25 Hz and 10 kHz. Uncertainties reach to levels of better than a few parts in 108 and results agree to the values measured from conventional impedance bridges.
Two methods for four-terminal impedance measurements have been investigated, the potential comparison circuit and the coaxial setup. Both methods are capable of measuring from DC to 6 kHz with uncertainties to 10−8. The four-terminal-pair coaxial setup has potential to decrease the relative uncertainty down to 10−9 once systematic errors are analyzed and canceled. Thermal converter measurements have been made to investigate the effects of transients on stepwise approximated sinewaves. Rms measurements show that transients limit the uncertainty to about 10−6 at 1 kHz. A simple model with an equivalent time constant is presented to evaluate the influence of different parameters on the shape of the transients. It has been experimentally established, at the 10−8 level of uncertainty for the determination of impedance ratios, that the variations of the transients in stepwise approximated waveforms can be neglected when using the fundamental component of rectangular waveforms. Quantization at up to 10 kHz has been confirmed by varying the bias current of the Josephson arrays resulting in constant resistance ratios within the measurement resolution.Ein innovativer Weg, zwei programmierbare Josephson-Schaltungen für Impedanz-Verhältnismessungen zu verknüpfen, wird erstmals in dieser Arbeit präsentiert. Dieser neuartige Ansatz einer Josephson-Impedanzmessbrücke ist flexibler als konventionelle Impedanzmessbrücken bei gleicher Messunsicherheit. Es wird gezeigt, dass neben der Möglichkeit, über einen wesentlich größeren Frequenzbereich zu messen, die Josephson-Impedanzmessbrücke auch Messungen sehr unterschiedlicher Impedanzverhältnisse und beliebiger Phasenwinkel erlaubt. In einer Zwei-Tor-Anordnung der Josephson-Impedanzmessbrücke wurden Messungen für ein 1:1 Widerstandsverhältnis bei 10 k im Frequenzbereich von 25 Hz bis 10 kHz durchgeführt. Die Ergebnisse stimmen mit denen einer konventionellen Messbrücke im Rahmen der Unsicherheit von wenigen 10−8 überein.
Für eine Vier-Tor-Anordnung wurden zwei unterschiedliche Methoden untersucht, eine Spannungsverhältnisschaltung und eine koaxiale Vier-Tor-Anordnung. Letztere hat das Potential, Unsicherheiten von 10−9 zu erreichen, sobald systematische Fehler eliminiert sind.
Um Effekte der Transienten in stufenförmig approximierten Sinuswellen zu untersuchen, wurden Messungen an Thermokonvertern durchgeführt. Diese Effektivmessungen zeigen, dass Transienten die relative Messunsicherheiten auf etwa 10−6 bei einer Frequenz von 1 kHz beschränken. Es wird ein einfaches Modell vorgestellt, das die Form der Transienten in Abhängigkeit der wesentlichen Parameter beschreibt. Experimentell konnte bei Impedanzverhältnismessungen mit einer relativen Messunsicherheit von 10−8 nachgewiesen werden, dass die Variation der Transienten in stufenförmig approximierten Wellenformen vernachlässigbar ist, wenn die fundamentale Komponente eines Rechtecksignals verwendet wird. Quantisierte Plateaus wurden bis zu Frequenzen von 10 kHz gefunden, bei denen die Variation des angelegten Stroms durch die Josephson-Schaltungen keine Veränderung des Impedanzverhältnisses zur Folge hatte
System architecture for real time power management.
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN012449 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Research in electrically supported vacuum gyroscope. Volume 3 - ESVG suspension research Final report
Suspension factors analyzed as part of research on Electrically Supported Vacuum Gyroscope /ESVG/ for spacecraf
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