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Volume 149
Issue 6
IEE Proceedings - Science, Measurement and Technology
Volume 149, Issue 6, November 2002
Volumes & issues:
Volume 149, Issue 6
November 2002
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- Author(s): Lesley CA Henderson
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 297 –298
- DOI: 10.1049/ip-smt:20020766
- Type: Article
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- Author(s): N.E. Fletcher ; T.J.B.M. Janssen ; A. Hartland
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 299 –301
- DOI: 10.1049/ip-smt:20020744
- Type: Article
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p.
299
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Measurements of the slopes (ΔI/ΔVg)n of the acoustoelectric current plateaux In=nef for n=1 and 2 have been made, as a function of the bath temperature T in the range 0.3 to 4.2 K. Electrons, constrained in one-dimensional channels, are transported by a surface acoustic wave of frequency f≈2.8 GHz, generated by transducers deposited on a GaAs heterostructure. The channel width is controlled by the application of voltages Vg to Schottky gates also deposited on the heterostructure. The normalised slopes S=(ΔI/ΔVg)n/(ΔI/ΔVg)n−1→n are compared with those calculated using a model describing the device behaviour proposed by Flensberg et al. In this model S is related to an effective temperature Teff, which can be greater than T. The measurements indicate that for n=1, Teff has a minimum value of 1.65±0.1 K corresponding to a minimum value of S≈10−3. - Author(s): P. Kleinschmidt ; J.M. Williams ; N.E. Fletcher ; T.J.B.M. Janssen
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 302 –304
- DOI: 10.1049/ip-smt:20020758
- Type: Article
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p.
302
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A cryogenic current comparator (CCC) bridge for quantum Hall resistance ratio measurement has been constructed. Compared to previous CCC systems at the National Physical Laboratory, UK, the new system differs in two aspects. Firstly, it uses a type-II CCC, i.e. the ratio windings are on the outside and the detection winding is on the inside. This has the advantage that the CCC can be made very compact and fits into a standard storage Dewar. Secondly, the bridge electronics uses a digital servo and the SQUID feedback loop is disabled during current reversals. The overall relative measurement uncertainty of the system is of the order of 10−9. - Author(s): T.J. Witt
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 305 –312
- DOI: 10.1049/ip-smt:20020640
- Type: Article
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p.
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Although arrays of Josephson junctions are today's primary reference standards of voltage, they are used by only 30 to 40 national metrology institutes around the world and perhaps a comparable number of primary metrology laboratories. Nearly all traceable voltage measurements are linked to Josephson standards by chains containing electronic DC voltage standards referenced to Zener diodes. These typically take the form of small, rather easily transportable instruments that provide outputs of 10 V and 1.018 V. The specified stability over a 1-year period of the 10 V outputs of the best Zener standards is quite good, of the order of one part in 106 of the nominal output voltage, and, by modelling temporal drift and correcting for environmental influences, output voltages can be predictable, over periods of several weeks or more, to within a few parts in 108. However, given that the demonstrated reproducibility of 10 V Josephson standards is of the order of a few parts in 1010 of the nominal output, an enormous increase in measurement uncertainty occurs in going from Josephson standards to Zeners. The various effects that limit the reproducibility of Zener standards, including drift, pressure, temperature and humidity effects and, ultimately, 1/f noise, are reviewed. - Author(s): P. Kleinschmidt ; P.D. Patel ; J.M. Williams ; T.J.B.M. Janssen
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 313 –316
- DOI: 10.1049/ip-smt:20020759
- Type: Article
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p.
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Arrays of Josephson junctions have been used successfully for many years as the primary standard of voltage. A recent development has been the fabrication of arrays, based on non-hysteretic Josephson junctions, which allows the voltage output to be changed almost instantaneously. When these arrays are divided into binary segments a ‘digital-to-analogue converter’ with quantum accuracy is created. The properties of two types of array, a SINIS array, using intrinsic shunting of the Josephson junctions, and a SIS array with external, on-chip shunting have been investigated. The accuracy of the generated voltages and AC properties of the arrays when driven with a purpose-built, programmable current bias source are discussed. It is anticipated that a Josephson standard having waveforms with calculable rms values of AC voltage will soon be available. - Author(s): L.X. Liu ; S.W. Chua ; C.K. Ang
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 317 –319
- DOI: 10.1049/ip-smt:20020745
- Type: Article
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p.
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Preliminary results of AC–DC difference measurements using a thermal voltage converter with range resistor under humidity change conditions are reported. The AC–DC difference measurement results, from a Holt-11 thermal converter at 100 and 200 V and frequency range from 40 Hz to 100 kHz, have shown that a first-order differential equation can be used to model this phenomenon. The humidity coefficients for the model are found to be frequency dependent and the time constants are related to the changes of humidity. - Author(s): R.G. Jones
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 320 –322
- DOI: 10.1049/ip-smt:20020767
- Type: Article
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The electrical conductivity of water is used in many industries as an indication of the purity of the water. A system for the traceable measurement of the conductivity of water in the range 0.01 S/m to 1 S/m is described. The method is based on the measurement of the resistance of a column of water of accurately known dimensions. There is an electrode polarisation effect and the convention is to extrapolate the conductivity as a function of inverse frequency to find the value at zero inverse frequency. The temperature coefficient of the conductivity is 2% per Kelvin at 25°C and this limits the uncertainty of the measurement to about ±0.14 % of value in the present system. - Author(s): I.J. Youngs ; A.S. Treen ; G. Fixter ; S. Holden
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 323 –328
- DOI: 10.1049/ip-smt:20020647
- Type: Article
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The basis of a quantitative design process for solid broadband human tissue simulant materials is described. It is shown that the complex permittivity spectra of human tissue is not well represented by simple effective media theory (equivalent to using a single Debye-type dielectric relaxation), but that it can be represented by a percolative response. A solid two-layer spherical phantom with material properties representative of human head tissue over the frequency range 1 MHz to 10 GHz has been designed and tested. Such a simple phantom geometry was selected to assist, through validation, the development of related electromagnetic computer models. The dielectric properties of the simulant materials were tailored using appropriate quantities of a conducting filler dispersed in an insulating thermosetting plastic matrix. The two materials exhibit both a dielectric constant and an AC conductivity comparable (to first approximation) to that of human grey matter and fat. The phantom was constructed by injection moulding. The uniformity of the electromagnetic properties throughout the phantom and their temperature dependence were both assessed using broadband dielectric spectroscopy. - Author(s): K. Holland and J. Howes
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 329 –332
- DOI: 10.1049/ip-smt:20020639
- Type: Article
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p.
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Knowledge of the performance of power sensors and mixers is vital to the uncertainty analysis of the RF and microwave attenuation calibration systems held at the National Physical Laboratory (NPL). Recently the facilities used to characterise these components have been improved with the aim of measuring the response to ±0.0003 dB over a 40 dB range from 10 MHz to 60 GHz. The principal changes to the original linearity measurement systems have been the selection of the highly repeatable attenuator, used to generate a step change in the RF signal, and the way in which the detector in the mixer measurement system is operated. Measurements on these systems have been used to re-assess the National Attenuation system capabilities and to select the optimal operating conditions for the mixers and power sensors used in them. - Author(s): J. Randa and W. Wiatr
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 333 –337
- DOI: 10.1049/ip-smt:20020488
- Type: Article
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p.
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Uncertainties in noise-parameter measurements, obtained using a Monte Carlo simulation of the measurements, are presented. Sets of data were generated to simulate measurements on a low-noise amplifier, with given uncertainties in the underlying measurements, including the standard noise temperature (hot or cold), ambient temperature, reflection coefficients of the terminations, scattering parameters of the amplifier, power measurements, and variations in the connections. Each set of simulated measurement results was analysed to determine the “measured” noise parameters, and the standard deviation of the set of measured noise-parameter values was computed to determine the uncertainty in each noise parameter. Results are presented for the noise-parameter uncertainties for different values of the underlying measurement uncertainties. - Author(s): M. Rodríguez
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 339 –344
- DOI: 10.1049/ip-smt:20020646
- Type: Article
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p.
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In the past, considerable attention has been devoted to the effect of recessed connections on the accuracy of vector network analyser (VNA) calibrations. Recession, defined as the gap between connectors, produces a discontinuity in the transmission line, which can be modelled as a short section of line with a different characteristic impedance. The parameters which define this discontinuity are the diameter and length of the intermediate section. The diameter is that of the male connector pin and the length is a function of the recession and/or protrusion of both connectors. Together with the diameter of the outer conductor, these parameters allow the calculation of the characteristic impedance of the section and the reflection coefficient of the termination. Simulations of the performance of a mismatch airline are presented in order to assess the correctness of our model. Subsequently, the same model is applied to the open-short-sliding load calibration of a vector network analyser. We show that the effects of recession during calibration and/or measurement can be predicted with the aid of computer simulations. Finally, the theoretical predictions are compared with results obtained experimentally. - Author(s): R.D. Pollard
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 149, Issue 6, p. 345 –350
- DOI: 10.1049/ip-smt:20020763
- Type: Article
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p.
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The state-of-the-art in lightwave network analysis is reviewed. Existing commercial instruments use simple architectures which limit the type of calibrations that are available for lightwave S-parameter measurements. However, recent research at The University of Leeds has demonstrated the feasibility of using reversible test sets and modular approaches, which offer the option of full two-post self-calibration routines for the first time. Experimental results for the error-corrected S-parameter measurement of optical, optoelectronic and electro-optic two-ports are presented.
Editorial: Electromagnetic measurements
Temperature as a limitation to the accuracy of SETSAW devices as quantum standards of current
Cryogenic current comparator bridge for quantum Hall resistance ratio measurements
Maintenance and dissemination of voltage standards by Zener-diode-based instruments
Investigation of binary Josephson arrays for arbitrary waveform synthesis
High voltage AC–DC difference measurements under humidity step changes
Measurements of the electrical conductivity of water
Design of solid broadband human tissue simulant materials
Improvements to the microwave mixer and power sensor linearity measurement capability at the National Physical Laboratory
Monte Carlo estimation of noise-parameter uncertainties
Modelling the effect of port recession on VNA one-port calibrations
Developments in lightwave S-parameter measurement techniques
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