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A chirp filter is a linear device that is designed to give a surface-acoustic-wave (SAW) signal delay which varies substantially with frequency. It is also called dispersive delay line (DDL). Such devices are often used in pulse-compression radar systems, and for real time Fourier transformations. A prototype chirp filter with a time-bandwidth product of 4000 (= 10µs; = 400MHz) has been developed based on black YZ-cut Lithium Niobate (YZ-LiNbO3). This type is called Reflective Array Compressor (RAC), and the schematic structure is shown in Figure 1.
LiNbO3 is strongly piezoelectric and therefore especially suitable for the design of large bandwidth SAW filters. An inter digital transducer (IDT) is used to transform a microwave signal into a surface acoustic wave propagating along the substrate surface. Vice versa, due to the duality of the piezoelectricity, the surface acoustic wave can also be detected by an IDT and be transformed...

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In the `Electron Counting Capacitance Standard´ experiment a capacitor is charged by a well-known number of electrons, and the voltage developing is measured using a Josephson voltage standard. Eventually the `Electrical Quantum Triangle´ can be realized by tracing the capacitor's capacitance to the von-Klitzing constant, which tests the consistency of the three fundamental electrical quantum effects (quantum-Hall, Josephson and the single-electron tunnelling effect). The realization of the Electrical Quantum Triangle with an uncertainty of a few parts in 107 is considered an important milestone on the way to a new system of units, being entirely based on fundamental constants. PTB, as one of few metrology institutes world-wide, pursues the setup of this experiment for some time past (Fig. 1).
In the last year the operation of a five-junction single-electron tunneling (SET) pump, fabricated at PTB, was tested for the first time. Here, a...

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The apparatuses designated for the transmission of electrical energy from the power plant to the consumer are tested in a series of expensive acceptance tests before being put into operation. This includes short-circuit tests of high-voltage breakers with high alternating currents and tests of arresters with impulse currents. In particular, the measurement of short-circuit currents, superimposed by exponentially decaying DC currents with amplitudes of several 100 kA, is rather difficult. The measuring shunts, used traditionally for this purpose, have very large dimensions and must be water-cooled in extreme cases to draw off the heat of the power consumption, at least partially.
Rogowski coils are well suited for the almost wattless and unloaded measurement of high alternating and impulse currents. Because of their non-magnetic core, they have a negligible nonlinearity which is of advantage for reliable calibration at small currents....
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In einem durch die VW-Stiftung geförderten Vorhaben sollen die Herstellung, die physikalischen und chemischen Eigenschaften und mögliche Anwendungen von frei aufgehängten, monolagigen "Nanoblättern" untersucht werden. Die drei beteiligten Partner sind Arbeitsgruppen der Universität Bielefeld, der Universität Heidelberg und der PTB. Die Nanoblätter bilden ultradünne Membranen mit der Dicke eines einzelnen Moleküls (1-2 nm). Sie basieren auf vernetzten, selbstorganisierenden Monoschichten, die sich von ihrem Substrat ablösen lassen und als freistehendes Nanomaterial stabil sind. Wir wollen mechanische Eigenschaften wie Moduli, Zugfestigkeiten und Resonanzfrequenzen untersuchen. Auch die elektrischen Eigenschaften wie Leitfähig- keit und Kapazität, und chemische Eigenschaften wie Oberflächenfunktionalisierung und Gasadsorption sollen charakterisiert werden. Mögliche Anwendungen dieser Nanoblätter könnten ultradünne, elektronentransparente...

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In der PTB werden seit etwa 15 Jahren Strukturen gefertigt, deren laterale Abmessungen im sub-µm Bereich liegen. Seit dieser Zeit wurde auch ein Rasterelektronenmikroskop zur Untersuchung der im Reinraumzentrum gefertigten Dünnschichtstrukturen eingesetzt. Zum Jahreswechsel 2006/2007 wurde dieses Gerät durch ein neues Gerät der Firma Zeiss (Supra 40 Abb. 1) ersetzt. Dieses bietet gegenüber dem Vorgängermodell deutlich bessere Abbildungseigenschaften (Abb. 2 ) und kann so den gesteigerten Anforderungen gerecht werden.


Bild 1: Neues hochauflösendes Rasterelektronenmikroskop Zeiss Supra 40 im Reinraumzentrum


Bild 2: Abbildung einer Einzelelektronenschaltung mit dem alten (a) und mit dem neuen Rasterelektronenmikroskop (b)

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Mit einem neuen Messverfahren kann man die Induktivität und die Güte einer Spule aus dem Wirkwiderstand und der Zeitkonstante eines Wechselstromwiderstandes bestimmen. Das Verfahren kombiniert Elemente der klassischen Brückentechnik (Wagner-Erdung) mit der digitalen Synthese von Signalen und ihrer Abtastung unter Anwendung der diskreten Fourier-Transformation (DFT). Zur Erprobung wurde die Induktivität einer 100-mH-Spule bei der Messfrequenz 1 kHz mit einer abgeschätzten Standardmessunsicherheit (k = 1) von 2 x 10-6 aus einem 1-k Wechselstromwider- abgeleitet.

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Mit dem Eintritt Bulgariens in die EU ergab sich die Notwendigkeit, die korrekte Rück- führung der dortigen nationalen Normale für Wechselspannung durch einen interna- tionalen Vergleich sicherzustellen. In einem bilateralen Vergleich zwischen dem BIM in Bulgarien und der PTB wurden 3 Volt Wechselspannungen bei Frequenzen von 55 Hz, 1 kHz, 20 kHz und 100 kHz gemessen. Die Messwerte zeigen eine sehr gute Überein- stimmung (degree of equivalence) von besser als 8 µV/V. Es wurde eine Verbindung zu dem Key Comparison CCEM-K6.a hergestellt, an dem die PTB früher teilge- nommen hatte. Der bilaterale Vergleich wurde als EUROMET.EM-K6.a in die Daten- bank des BIPM aufgenommen.

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The novel method is based on a single airline one-port measurement which is performed with the pre-calibrated vector network analyzer. By applying a sophisticated numerical analyzing scheme to the measured broadband data set, the complexvalued residual system error parameter of the analyzer can be extracted over the entire frequency range. From the error terms, a second-order calibration of the analyzer can be performed. The method enables an easy performance check of mechanical calibration kits as well as of electronic calibration units. In collaboration with PTB WG 8.42 und in cooperation with Rohde & Schwarz, the method is currently extended to 2-port measurements. A corresponding publication has been awarded at the 69. ARFTG conference 2008 for best paper.

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The Josephson junctions with Al2O3-double barriers (SINIS junctions) used at PTB for programmable voltage standards can be damaged during the rather complex fabrication process. The reason why some critical currents strongly deviate from the average value is not known. A technological alternative are SNS junctions with only one normal conductor as effective tunnel barrier. They may reduce the problem of process-induced damages to a minimum and would, moreover, simplify the fabrication process. However, due to the low resistivity of the normal conductors used up to now, programmable voltage standards on the basis of SNS junctions could only be driven at frequencies up to 20 GHz. A new technology recently developed at NIST has the potential to overcome the frequency limit set by the IcRn-product (Ic: critical current, Rn: normal resistance of the junction). This technology is using a co-sputtered high-resistive NbxSi1-x alloy embedded...

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DC-SQUIDs (SQUID: Superconducting QUantum Interference Device) are investigated for their usability as phase quantum bits (qubits) within the EU-project "EuroSQIP" in cooperation with the CNRS in Grenoble. In collaboration with our partners at the CNRS an optimized SQUID circuit was designed, including a high frequency supply and filter structures. The SQUID circuits were fabricated from Nb/AlOx/Nb trilayers at PTB, using electron beam lithography, reactive ion etching and chemical-mechanical polishing of an SiO2 insulating layer. After a first examination of the SQUID structures at 4,2 K, some appropriate circuits were selected and characterized in detail in a dilution refrigerator at mK temperatures in Grenoble. The measurements demonstrated that the DC-SQUID can be operated as a qubit, i.e. as a two level quantum system. The SQUIDs showed a coherence time of Rabi-oscillations which is typical for phase qubits. The results demonstrate...

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