The Economy

Magnetic memories and sensors are part of our every day's life. Every computer possesses a hard disk drive on which digital information is stored in a nanometer thick magnetic thin film. Magnetic sensors are used e.g. in hard disks to read out the stored information but also in other fields like the automotive sector. Like in all other fields of information technology such magnetic memories and sensors will have to work faster and faster to meet the requirements of future applications. Consequently also the test and measurement capabilities must be improved to test e.g. the ultra fast writing of hard disks and other magnetic memories or the response time of magnetic sensor elements.A research team of PTB Braunschweig and University of Bielefeld has now developed a new and versatile technique to study the ultra fast magnetization dynamics of magnetic nanostructures simply by measuring their electrical resistance. When a magnetic...

Within a cooperation with the university of Göttingen, the PTB is developing a technique that allows for a quantitative and traceable determination of the magnetization and the stray field of nanostructures. This technique combines magneto-optic measurements and magnetic force microscopy. Applying newly developed mathematical techniques the sample magnetization is calculated from the stray field data measured by magneto-optics.
By means of this method calibration samples for magnetic force microscopy can be characterized and thus, a traceable magnetic measurement with this extremely high resolution technique is made possible.The application of a magneto optical indicator film (MOIF) allows for a quantitative imaging of the stray field Hz on length scales between several mm to 300 nm. The signal can be calibrated by using well known external fields. However, inverse magneto-static calculation techniques are necessary for the determination...

As the quantum Hall resistance can now be precisely measured also with alternating current, its application as a quantum standard of capacitance is possible. To this end a cryogenic system with two quantum Hall devices has been set up. It allows to realize a quadrature bridge employing two independent ac quantum Hall resistors. In effect, this shortens the measurement-chain to a 10 pF capacitor. Also the resistors' thermal noise is much smaller than that of conventional room-temperature resistors. This permits to operate the quadrature bridge at a lower voltage which allows to dispense with the laborious determination of the voltage-dependence of a capacitor. Altogether, a lower uncertainty can be expected. In any case, the measurement-chain requires reliable ac bridges. Such bridges allow a high precision but are susceptible to systematic effects. It is therefore planned to carefully scrutinize and improve the bridges. Eventually this...

Terahertz-Strahlung mit Frequenzen zwischen 100 GHz und einigen THz ist nichts anderes als sanfte Wärmestrahlung mit besonderen Eigenschaften und wird schon seit vielen Jahren in wissenschaftlichen Anwendungen wie der Radioastronomie, der Atmosphärenforschung und der Laborspektroskopie genutzt. Die Erzeugung nutzbarer Terahertz-Wellen gestaltet sich allerdings schwierig. Durch das Aufkommen neuartiger optoelektronischer Strahlungsquellen hat das Gebiet jedoch mittlerweile eine technologische Reife erzielt, die kommerzielle Anwendungen ermöglicht. Erste Messsysteme zur Detektion von Hautkrebs, für die Personenkontrolle an Flughäfen oder zur Qualitätskontrolle von Industrieprodukten wurden bereits entwickelt. Aufgrund des zunehmenden Bedarfs an freier Bandbreite wird über kurzreichweitige Kommuni kationssysteme bei Frequenzen von 300 GHz und darüber nachgedacht. Wie breiten sich diese Wellen aber in Innenräumen aus und welche...

Die derzeit erreichbaren niedrigen Messunsicherheiten von einigen 10-6 in der Leistungsmesstechnik sind den Abtastverfahren oder aber thermisch-basierten Messverfahren vorbehalten. Für die thermisch-basierten Messverfahren verfügt die PTB mit den von ihr entwickelten planaren Thermokonvertern über ideal geeignete RMS-Sensoren.

Die Ermittlung der Wirkleistung zwischen den beiden am Eingang des Multiplizierers anstehenden Wechselspannungen erfolgt über die Bestimmung des Effektivwertes der Summe und der Differenz dieser Spannungen mittels AC-DC Transfer. Zur Bildung der Summen- bzw. der Differenzspannung werden Summierverstärker und ein Inverter herangezogen, die aufgrund ihres Aufbaus sehr geringe Eigenfehler aufweisen.

Das im Bild dargestellt Design des Multiplizierers gestattet die Kompensation der statischen Eigenfehler der Summierverstärker. Diese ergeben sich zwangsläufig aus den immer vorhandenen geringen Differenzen zwischen...

For the calibration of amperemeters traceable current sources are required. In the current range between 1 fA and 100 pA the most favourable and hence most frequently applied method relies on charging or discharging an air capacitor. A linearly increasing or decreasing voltage V is applied to an air capacitor. The resulting charging current I=C·dV/dt is used to calibrate the amperemeter.
In the past, for this purpose a voltage-ramp generator had been used which was built entirely in analog electronics. It had a very good linearity and therefore delivered a very constant calibration current, but at the expense that prior to each ramp start a period of several minutes was required to reset the integration capacitor to a defined state. This prevented the application for measurements where the dynamic behaviour of an amperemeter had to be investigated.
In order to make this feasible, a novel voltage-ramp generator has been designed which...

A Josephson Waveform Synthesizer, developed by PTB in cooperation with NPL in Great Britain, has been used to perform an "in-situ" calibration of the sampling voltmeter which is at the heart of the PTB primary power standard for electrical power. Besides reducing the measurement uncertainty, this provides direct traceability to a quantum standard for the voltage measurements in the power standard.In the past few years precision waveforms with accuracies better than 1 part in 107 at power frequencies have been available from series arrays of shunted Josephson junctions operated as digital to analog converters with fundamental accuracy. PTB has progressed in its efforts to integrate such a Josephson waveform synthesizer into its primary power standard. The sampling voltmeter in the power standard can thus be continuously calibrated leading to a reduction in the uncertainty for the measure-ment of active, reactive and apparent power at the...