Papers by Gerd Willenberg
Physik Journal, 1999
Alliances between members of the visual communication division of the Association for Journalism ... more Alliances between members of the visual communication division of the Association for Journalism and Mass Communication (AEJMC) and the National Press Photographers Association (NPPA) can be strengthened without sacrificing the basic liberal arts principles promoted by R. 0. Blanchard and W. G. Christ in their book "Media Education and the Liberal Arts." For example, a new journal, "Visual Communication Quarterly," seeks to increase interest among both professionals and scholars and helps to build alliances that benefit all parties, photojournalism educators, students, and practitioners. "Visual Communication Quarterly" was launched for several reasons, but one reason was to increase the flow of information from photojournalism educators to practitioners, since no journal was fulfilling that role exactly. Two potential problems that faced the founders of this journal were: (1) obtaining funding; and (2) finding a sufficient supply of quality research. The first problem was solved when the editors of "News Photographer" agreed to absorb the costs and bind the journal as an insert in their magazine. The second problem did not seem formidable, but in fact finding quality articles is no small task. To address this problem, only 9 articles will appear in each of the 1995 issues instead of 12, though the overall length of the journal will not change. (Includes 13 notes.) (TB)
29th Conference on Precision Electromagnetic Measurements (CPEM 2014), 2014
We present the comparison of results from the generation and the measurement of direct currents i... more We present the comparison of results from the generation and the measurement of direct currents in the pA range, performed with traceable state-of-the-art methods at highest accuracy. The currents were generated with the capacitor charging method, and measured with the first prototype of a novel picoammeter developed at PTB. The results confirm the agreement between both methods and the linearity of the new picoammeter at an uncertainty level of few µA/A. Also, they shed light on the ac-dc difference of capacitors, crucial for current generation with the capacitor charging method.
Physik Journal, 1999
Alliances between members of the visual communication division of the Association for Journalism ... more Alliances between members of the visual communication division of the Association for Journalism and Mass Communication (AEJMC) and the National Press Photographers Association (NPPA) can be strengthened without sacrificing the basic liberal arts principles promoted by R. 0. Blanchard and W. G. Christ in their book "Media Education and the Liberal Arts." For example, a new journal, "Visual Communication Quarterly," seeks to increase interest among both professionals and scholars and helps to build alliances that benefit all parties, photojournalism educators, students, and practitioners. "Visual Communication Quarterly" was launched for several reasons, but one reason was to increase the flow of information from photojournalism educators to practitioners, since no journal was fulfilling that role exactly. Two potential problems that faced the founders of this journal were: (1) obtaining funding; and (2) finding a sufficient supply of quality research. The first problem was solved when the editors of "News Photographer" agreed to absorb the costs and bind the journal as an insert in their magazine. The second problem did not seem formidable, but in fact finding quality articles is no small task. To address this problem, only 9 articles will appear in each of the 1995 issues instead of 12, though the overall length of the journal will not change. (Includes 13 notes.) (TB)
29th Conference on Precision Electromagnetic Measurements (CPEM 2014), 2014
We present the comparison of results from the generation and the measurement of direct currents i... more We present the comparison of results from the generation and the measurement of direct currents in the pA range, performed with traceable state-of-the-art methods at highest accuracy. The currents were generated with the capacitor charging method, and measured with the first prototype of a novel picoammeter developed at PTB. The results confirm the agreement between both methods and the linearity of the new picoammeter at an uncertainty level of few µA/A. Also, they shed light on the ac-dc difference of capacitors, crucial for current generation with the capacitor charging method.
A standard method for picoammeter calibrations is the capacitor charging technique, which allows ... more A standard method for picoammeter calibrations is the capacitor charging technique, which allows generating traceable currents in the sub-nA range. However, its accuracy is limited by the ac-dc differences of the capacitances involved. The Ultrastable Low-noise Current Amplifier (ULCA) is a novel high-precision amperemeter for direct current measurements in the pA range, developed at PTB. Its amplifier stages, based on resistor networks and op-amps, can be calibrated traceably with a cryogenic current comparator (CCC) system. We compare the results from both independent calibration routes for two different ULCA prototypes. We find agreement between both methods at an uncertainty level below 10 microA/A, limited by the uncertainty of the currents generated with the capacitor charging method. The investigations confirm the superior performance of the new ULCA picoammeter.
A standard method for picoammeter calibrations is the capacitor charging technique, which allows ... more A standard method for picoammeter calibrations is the capacitor charging technique, which allows generating traceable currents in the sub-nA range. However, its accuracy is limited by the ac-dc differences of the capacitances involved. The Ultrastable Low-noise Current Amplifier (ULCA) is a novel high-precision amperemeter for direct current measurements in the pA range, developed at PTB. Its amplifier stages, based on resistor networks and op-amps, can be calibrated traceably with a cryogenic current comparator (CCC) system. We compare the results from both independent calibration routes for two different ULCA prototypes. We find agreement between both methods at an uncertainty level below 10 microA/A, limited by the uncertainty of the currents generated with the capacitor charging method. The investigations confirm the superior performance of the new ULCA picoammeter.
Metrologia, 2011
The Electron Counting Capacitance Standard currently pursued at PTB aims to close the Quantum Met... more The Electron Counting Capacitance Standard currently pursued at PTB aims to close the Quantum Metrological Triangle with a final precision of a few parts in 10 7. This paper reports the considerable progress recently achieved with a new generation of single-electron tunnelling devices. A five-junction R-pump was operated with a relative charge transfer error of five electrons in 10 7 , and was used to successfully perform single-electron charging of a cryogenic capacitor. The preliminary result for the single-electron charge quantum has an uncertainty of less than two parts in 10 6 and is consistent with the value of the elementary charge.
IEEE Transactions on Instrumentation and Measurement, 1985
The ampere may be realized by combining the results of two different NMR experiments. In contrast... more The ampere may be realized by combining the results of two different NMR experiments. In contrast to the well-known meth-F ods, we describe here a novel approach whereby the first-order influence " "VI, of the geometrical dimensions of the coils is eliminated by using one NI B, coil for weighing and for producing a magnetic flux density to which Xmg that of the low-field experiment is related.
IEEE Transactions on Instrumentation and Measurement, 2005
A capacitance standard based on the definition of capacitance = is realized if a capacitor is cha... more A capacitance standard based on the definition of capacitance = is realized if a capacitor is charged with a known number of electrons (is the elementary charge), and the voltage across the capacitor is measured [1]. If is measured by means of a Josephson voltage standard, is solely determined by quantum numbers and fundamental constants. Presently, Physikalisch-Technische Bundesanstalt (PTB) is setting up this experiment using a special type of single-electron pump, the so-called r-pump [2], for transferring electrons one by one onto a cryogenic vacuum capacitor with the decadic capacitance = 1 pF. We report on the progress in the setup with emphasis on the characterization of the single-electron tunneling elements. We describe the modifications of the single-electron circuit that are necessary to implement the capacitor charging experiment by using a four-or five-junction r-pump.
IEEE Transactions on Instrumentation and Measurement, 2003
The European COUNT project exploits two complementary single electron tunneling devices for use i... more The European COUNT project exploits two complementary single electron tunneling devices for use in electrical current metrology: a single electron pump as a current source and a single electron counter as a current meter. An electron pump has been developed with on-chip resistors in order to suppress cotunneling. The intended accuracy is 1 ppm for a current of a few picoampere. Apart from being a quantum current standard, the electron pump could also be the basis of a capacitance standard. A coaxial tunable cryogenic capacitor of 1 picofarad has been developed for this purpose. A passive electron counter based on a single electron transistor embedded in a resonant tank circuit has been further investigated and developed in order to reach both high sensitivity and high counting speed. The intended accuracy is 10 ppm for a current of a few picoampere.
IEEE Transactions on Instrumentation and Measurement, 2003
IEEE Transactions on Instrumentation and Measurement, 2009
We report on the progress and new results in the setup of the electron counting capacitance stand... more We report on the progress and new results in the setup of the electron counting capacitance standard (ECCS) at Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany. Considerable progress has been made in the operation of the single-electron circuit and in the incorporation of a cryogenic capacitor into the millikelvin refrigerator setup. The single-electron tunneling (SET) circuit comprised a five-junction, single-electron R-pump that showed an electron retention time of more than 600 s, and the circuit was successfully used for the deterministic shuttle transfer of charge packets consisting of few electrons. In addition, the cryogenic capacitor was tested, and its performance was found to be suitable for a high-precision ECCS experiment.
IEEE Transactions on Instrumentation and Measurement, 2009
We report on the development of a novel highly linear voltage ramp generator to be used for the t... more We report on the development of a novel highly linear voltage ramp generator to be used for the traceable calibration of picoamperemeters. The generator is based on two digital-toanalog converters, one of them being used to compensate for the differential nonlinearity of the other one. The generator is completely controllable by a computer, its voltage slope dV /dt is adjustable between 1 and 1000 mV/s. During a ramp running between −10 and +10 V, the slope shows a relative variation of only 1.3 • 10 −5 (relative standard deviation). Due to a small output filter time constant of only 10 ms, we are, for the first time, able to conduct dynamic measurements of picoamperemeters with no sacrifice of linearity.
IEEE Transactions on Instrumentation and Measurement, 1987
The error sources which have proven to be dominant in our previous γ′p experiments are discussed ... more The error sources which have proven to be dominant in our previous γ′p experiments are discussed and improvements in the experimental setup to reduce their influence on the coil-constant determination below the 1-ppm level are described. In particular, the problems involved in flux profile measurements by means of a SQUID magnetometer are considered.
IEEE Transactions on Instrumentation and Measurement, 2001
For use in our single-electron charging experiment, a novel cryogenic vacuum capacitor has been d... more For use in our single-electron charging experiment, a novel cryogenic vacuum capacitor has been developed which is superior to the previous parallel-plate design. Due to its coaxial design consisting of a long cylindrical center electrode and a shorter cylindrical ring electrode, it is inherently stable against mechanical vibrations and thermal cycling. Electrical insulation is achieved by the exclusive use of sapphire, which promises extremely low leakage currents.
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Papers by Gerd Willenberg