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Hwang S.-M.,Korea Research Institute of Standards and Science | Korber R.,Physikalisch - Technische Bundesanstalt | Korber R.,Magnicon GmbH | Kim K.,Korea Research Institute of Standards and Science | And 4 more authors.
IEEE Transactions on Applied Superconductivity

Recent efforts in the development of ultralow field nuclear magnetic resonance (NMR) have focused on increasing prepolarizing field ( {\rm B}-{\rm p}) strength. The strong {\rm B}-{\rm p}, which is up to hundreds of milliteslas, is mandatory for high-quality NMR signals. However, {\rm B}-{\rm p} needs to be completely removed within milliseconds so that spin relaxation signal measurement can take place before the sample magnetization wears off. In a previous study, where we compared three pick-up coils made of Nb, NbTi, and Pb, we found that only the pick-up coil made of Pb, which is a type-I superconductor, was unaffected by the strong magnetic field from the {\rm B}-{\rm p} coil and produced a sharp NMR signal. The other coils made of type-II superconductors all began to suffer from a degraded NMR signal with {\rm B}-{\rm p} above a certain threshold. Here, we show detailed measurement of magnetization loops of NbTi and Pb wires and argue that the counter pulse strategy suggested in our previous study can minimize the trapped flux and recover the spin relaxation signal. We argue that this counter pulse strategy can be applied to superconducting {\rm B}-{\rm p} coils, so that the counter pulses can neutralize flux trapped inside the {\rm B}-{\rm p} coil due to its strong internal field, thereby dramatically increasing the limit on the {\rm B}-{\rm p} strength. © 2002-2011 IEEE. Source

Hwang S.-M.,Korea Research Institute of Standards and Science | Kim K.,Korea Research Institute of Standards and Science | Kyu Yu K.,Korea Research Institute of Standards and Science | Lee S.-J.,Korea Research Institute of Standards and Science | And 4 more authors.
Applied Physics Letters

In ultra-low field nuclear magnetic resonance (ULF-NMR) with strong prepolarization field (Bp), type-II superconducting pick-up coils may be vulnerable to flux pinning from the strong Bp. Pick-up coils made of NbTi, Nb, and Pb were evaluated in terms of acquired NMR signal quality. The type-II pick-up coils showed degraded signals above 61mT maximum exposure, while the Pb pick-up coil exhibited no such degradation. Furthermore, a negative counter pulse following a strong Bp was shown to follow magnetic hysteresis loop to unpin the trapped flux in the type-II pick-up coil and restore the NMR signal. © 2014 AIP Publishing LLC. Source

Drung D.,Physikalisch - Technische Bundesanstalt | Gotz M.,Physikalisch - Technische Bundesanstalt | Pesel E.,Physikalisch - Technische Bundesanstalt | Barthelmess H.J.,Magnicon GmbH | Hinnrichs C.,Magnicon GmbH
IEEE Transactions on Instrumentation and Measurement

We have developed a binary compensation unit for balancing measurement bridges with cryogenic current comparators (CCCs) commonly used in resistance metrology. We present the basic design ideas for the new microcontroller- operated module. It offers balance over a gapless range of resistance ratios of the resistors to be compared. The binary setup allows for convenient calibration when being combined with a binary CCC. The calibration can be performed using the CCC's control electronics and software. Examples of measurements demonstrate the unit's high flexibility and stability of resistance calibration well below one part in 109 over a period of 21 hours. © 1963-2012 IEEE. Source

Engert J.,Physikalisch - Technische Bundesanstalt | Heyer D.,Physikalisch - Technische Bundesanstalt | Beyer J.,Physikalisch - Technische Bundesanstalt | Barthelmess H.-J.,Magnicon GmbH
Journal of Physics: Conference Series

Reliable and traceable thermometry is a demanding task at low temperatures. Recently, we have developed a dc SQUID-based noise thermometer, the magnetic field fluctuation thermometer (MFFT), for practical thermometry in the low temperature range [1]. Its operational principle is based on the Nyquist theorem ensuring a linear characteristic over a wide range of temperatures. This makes the MFFT capable to replace a variety of secondary thermometers, which are normally used in the low temperature range. For the first time, we report on MFFT measurements over more than 3 decades in temperature from about 1.6 K down to below 1 mK The deviations from a high-accuracy realization of the PLTS-2000 are found to be ≈ 1%. © Published under licence by IOP Publishing Ltd. Source

Beyer J.,Physikalisch - Technische Bundesanstalt | Schmidt M.,Physikalisch - Technische Bundesanstalt | Engert J.,Physikalisch - Technische Bundesanstalt | Alivaliollahi S.,Magnicon GmbH | Barthelmess H.J.,Magnicon GmbH
Superconductor Science and Technology

The magnetic-field fluctuation thermometer (MFFT) is a noise thermometer that has been developed for thermometry in sub-Kelvin refrigerators. Meaningful MFFT operation requires a prior measurement at one known temperature in the temperature range of operation. From this reference measurement a set of calibration parameters is determined that characterizes the thermometer. Aiming at improving the measurement quality of the MFFT and extending its acceptance, we have developed a setup and procedure for reference measurements at temperatures directly traceable to the PLTS-2000. The reference measurements allow the assessment of methods to determine the uncertainty of a MFFT measurement. Temperature measurements with relative uncertainties of <1% can be obtained within measurement times of ≈10 s. © 2013 IOP Publishing Ltd. Source

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