4,035 research outputs found
Waveform characterization of calibration-pulse generators for EMI measuring receivers
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents the waveform characterization of calibration pulse generators intended to evaluate the response to pulses of the weighting detectors in CISPR 16-1-1 measuring receivers. First, the standard requirements of the reference pulses are described, and the pulse generators calibration methods based on waveform measurements are briefly discussed. Then, high-resolution time domain measurements are used for characterizing the waveforms of a commercial calibration-pulse generator in terms of rise/fall time, pulse width, mean voltage of the upper state, repetition frequency, and area. Moreover, the results above are used for estimating the spectral density of the impulses, their corresponding quasi-peak level, the pulses bandwidth, and the breakpoint frequencies. Finally, the measurement uncertainty is estimated for CISPR bands A, B, and C/D. Results are in good agreement with other calibrations performed during an intercomparison exercise and the uncertainty satisfy the target ±0.5 dB and 1% given in standards for the impulse area and pulse repetition frequency respectively.Postprint (author's final draft
Waveform Approach for Assessing Conformity of CISPR 16-1-1 Measuring Receivers
An alternative approach for assessing the conformity of electromagnetic interference measuring receivers with respect to the baseline CISPR 16-1-1 requirements is proposed. The methodâs core is based on the generation of digitally synthesized complex waveforms comprising multisine excitation signals and modulated pulses. The superposition of multiple narrowband reference signals populating the standard frequency bands allows for a single-stage evaluation of the receiverâs voltage accuracy and frequency selectivity. Moreover, characterizing the response of the weighting detectors using modulated pulses is more repeatable and less restrictive than the conventional approach. This methodology significantly reduces the amount of time required to complete the verification of the receiverâs baseline magnitudes, because time-domain measurements enable a broadband assessment while the typical calibration methodology follows the time-consuming narrow band frequency sweep scheme. Since the reference signals are generated using arbitrary waveform generators, they can be easily reproduced from a standard numerical vector. For different test receivers, the results of such assessment are presented in the 9 kHzâ1 GHz frequency range. Finally, a discussion on the measurement uncertainty of this methodology for assessing measuring receivers is given.Postprint (author's final draft
Time-Domain Measurement of Broadband Coherent Cherenkov Radiation
We report on further analysis of coherent microwave Cherenkov impulses
emitted via the Askaryan mechanism from high-energy electromagnetic showers
produced at the Stanford Linear Accelerator Center (SLAC). In this report, the
time-domain based analysis of the measurements made with a broadband (nominally
1-18 GHz) log periodic dipole array antenna is described. The theory of a
transmit-receive antenna system based on time-dependent effective height
operator is summarized and applied to fully characterize the measurement
antenna system and to reconstruct the electric field induced via the Askaryan
process. The observed radiation intensity and phase as functions of frequency
were found to agree with expectations from 0.75-11.5 GHz within experimental
errors on the normalized electric field magnitude and the relative phase; 0.039
microV/MHz/TeV and 17 deg, respectively. This is the first time this agreement
has been observed over such a broad bandwidth, and the first measurement of the
relative phase variation of an Askaryan pulse. The importance of validation of
the Askaryan mechanism is significant since it is viewed as the most promising
way to detect cosmogenic neutrino fluxes at E > 10^15 eV.Comment: 10 pages, 9 figures, accepted by Phys. Rev.
Uncertainty analysis in the measurement of switching losses in GaN FETs power converters
© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper analyses the method for measuring the switching losses in Gallium Nitride (GaN) Field Effect Transistors (FETs) employed in highly efficient power electronics applications, particularly in DC-DC converters. In this regard, the switching losses are measured through the integration of the product of the voltage multiplied by the current during the turn-on and turn-off intervals of the switching process. The objective of this analysis is to identify, model, correct/minimize and quantify the main contributions to the switching lossesâ measurement uncertainty following a top- down approach. First, a set of general specifications for a suitable test bench is given. Subsequently, the distortion of the oscilloscope-probe system and the influence of the current shunt is studied along with a method for correcting the waveform distortion. Then, based on the model describing the general measurement method, the individual sources of uncertainty are stripped down, giving guidance regarding how to estimate each of them. Finally, such individual contributions to the switching losses measurement uncertainty are propagated and combined following the guidelines of the "Guide to the Expression of Uncertainty in Measurement".This research work is carried in the framework of the ADVENT project (Grant Number: 16ENG06 ADVENT) which is supported by the European Metrology Programme for Innovation and Research (EMPIR). The EMPIR initiative is co-funded by the European's Horizon 2020 research and innovation programme and the EMPIR Participating States.Postprint (author's final draft
Conversion from linear to circular polarization in FPGA
Context: Radio astronomical receivers are now expanding their frequency range
to cover large (octave) fractional bandwidths for sensitivity and spectral
flexibility, which makes the design of good analogue circular polarizers
challenging. Better polarization purity requires a flatter phase response over
increasingly wide bandwidth, which is most easily achieved with digital
techniques. They offer the ability to form circular polarization with perfect
polarization purity over arbitrarily wide fractional bandwidths, due to the
ease of introducing a perfect quadrature phase shift. Further, the rapid
improvements in field programmable gate arrays provide the high processing
power, low cost, portability and reconfigurability needed to make practical the
implementation of the formation of circular polarization digitally. Aims: Here
we explore the performance of a circular polarizer implemented with digital
techniques. Methods: We designed a digital circular polarizer in which the
intermediate frequency signals from a receiver with native linear polarizations
were sampled and converted to circular polarization. The frequency-dependent
instrumental phase difference and gain scaling factors were determined using an
injected noise signal and applied to the two linear polarizations to equalize
the transfer characteristics of the two polarization channels. This
equalization was performed in 512 frequency channels over a 512 MHz bandwidth.
Circular polarization was formed by quadrature phase shifting and summing the
equalized linear polarization signals. Results: We obtained polarization purity
of -25 dB corresponding to a D-term of 0.06 over the whole bandwidth.
Conclusions: This technique enables construction of broad-band radio astronomy
receivers with native linear polarization to form circular polarization for
VLBI.Comment: 11 pages 8 figure
Correction of environmental magnetic fields for the acquisition of Nuclear magnetic relaxation dispersion profiles below Earthâs field
V.Z. acknowledges funding from EPSRC under grant number EP/J500045/1, âA UK Magnetic Resonance Basic Technology Centre for Doctoral Trainingâ. Aspects of the work were funded by EPSRC grant EP/K020293/1, âZero-Field MRI to Enhance Diagnosis of Neurodegenerationâ. This project has also received funding from the European Unionâs Horizon 2020 research and innovation program under grant agreement No 668119, project âIDentIFYâ. The authors are grateful to Mr. G.P. Ashcroft and Dr. W. Mathieson for providing access to the biological samples used.Peer reviewedPublisher PD
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