Mun-Seog Kim

Analog-to-digital conversion for low-frequency waveforms based on the Josephson voltage standard

A waveform synthesizer adopting a superconductor–normal metal–superconductor junction array has been developed, which can generate arbitrary stepwise waveforms with a number of quantum-voltage steps up to 1 V level amplitude. As an application of the synthesizer, we have built a sampling voltmeter that measures the differential voltages between a sinusoidal waveform produced by a semiconductor-based ac source and the Josephson waveforms. We carried out extensive sampling measurements for a 50 Hz sine wave with 1 V amplitude, applying sampling apertures in the range of 55 µs ≤ta ≤ 130 µs and using Josephson waveforms with 32, 60, 80 and 100 quantum steps. From the measurements, the amplitude of the ac waveform was determined with a type A uncertainty (k = 2) of 0.15 µV. Also, we elucidated how the phase jitter in the ac waveform is reflected in the overall uncertainty for the measurements. The type B uncertainty due to the jitter is at least one order of magnitude smaller than the type A uncertainty.

All-around dual source impedance bridge

Two terminal dual source impedance bridge was configured using commercial voltage calibrators. The bridge performance was evaluated by measuring 1 to 1 resistance ratio at 1 kHz using 1 kΩ and 10 kΩ resistors. The same bridge was used for the resistance (R) to the inductor (L) and the capacitor (C) ratio measurements by adjusting the phase between the voltage sources. Then, the AC resistance value was found from the R : C ratio. This simple two terminal dual source impedance bridge proved its reliable and versatile measurement capability.

A pulse-driven Josephson arbitrary waveform synthesis system as a quantum AC voltage standard in KRISS

We report our progress in the Josephson arbitrary waveform synthesis system in KRISS. The system is based on the pulse-driven Josephson junction array, and currently we routinely produce arbitrary waveforms up to 100 mVrms amplitude with distortions smaller than 100 dBc. Precision waveform synthesis results are presented. Our future works will include AC-DC thermal transfer measurement and quantum noise source for Johnson noise thermometry.

Voltage linearity evaluation for a high-speed digitizer adopted to a quantum sampling voltmeter

We report the linearity evaluation for a high-speed digitizer NI 5922, which is adopted to a quantum sampling voltmeter. The evaluation has been carried out for three units of the digitizer using a reference voltmeter with a 14-bit arbitrary waveform generator as a dummy voltage source. The three units show totally different behaviors in terms of the voltage linearity which might be described with different polynomial functions of input voltage. In the conference, we will present results of the linearity evaluation for the three units using a programmable Josephson voltage standard.

Power calibration system based on Josephson sampling voltmeter

This paper describes system setup, based on a Josephson sampling voltmeter for precision power calibration. The waveforms generated by voltage and current sources, which are applied to a power meter under test, are transformed to 1-V level voltage signals and measured by a single Josephson voltmeter with a uncertainty (k = 2) less than 0.5 μV/V.

Measurement and analysis of earth's magnetic field based on low-magnetic field standards

The Cheongyang (CYG) observatory has been built to measure earths magnetic field and to study prediction of earthquake and space weather. The equipments of the CYG observatory are a 3-axis fluxgate magnetometer, an overhauser effect proton magnetometer, a declination/inclination magnetometer and a data logger. A Cs-4He atomic magnetic resonance magnetometer was used to correct the measured data obtained by the proton magnetometer. All the measurement equipments were calibrated using magnetic field standard system maintained at KRISS. The Measurement results show a variation of the baselines less than 5 nT within one year, which is the most critical requirement criteria for joining the INTERMAGNET (International Real-time Magnetic Observatory Network).

Application of a pulse-driven ac Josephson voltage standard to ac-dc difference measurement in KRISS

The pulse-driven ac Josephson voltage standard (ACJVS) system has been operated stably in Korea Research Institute of Standards and Science(KRISS). We have improved the system operation so that the distortion has been reduced compared to our previous report [1]. Since this system can generate arbitrary waveform with quantum-mechanically precise voltages, it can be applied to precision ac electrical measurements. We will present single-tone waveform synthesis results at different amplitudes and frequencies for ac metrology purpose, and will describe our preliminary result on ac-dc difference measurement using ACJVS and a commercial thermal transfer standard.

An H-T diagram characterizing the activation barriers obtained from the magnetic relaxation of HgBa2Ca2Cu3O8+δ thin film

The magnetic relaxation of an epitaxial HgBa 2 Ca 2 Cu 3 O 8 + δ (Hg-1223) thin film was measured at several fields and temperatures. After the activation energy and the normalized relaxation rate had been analysed, the U-j characteristics were mapped on the H-T diagram. The power-law region with a creep exponent of μ ≃ 7/9, which indicates large bundle creep, became a logarithmic region in the small μ limit as j went far below j c . From this analysis, we found that a large bundle of flux acts like a single vortex, the size of which was temperature independent. This behaviour is quite different from that of other cuprate superconductors. Also, the crossover temperature, T b , between the power-law and the logarithmic regions was inversely proportional to H β . The fitting of T b (β) on the H-T diagram is in good agreement with the field exponent of β ≃ 0.4 that was obtained from the scaling of U e f f (H).

Effects of powder alignment on determination error of spin reorientation angle of cone anisotropy

Abstract The effects of powder alignment on the determination error of the spin reorientation angle (SRA) from polycrystalline magnetization curves have been examined. A theoretical calculation showed that highly aligned powder is desired to determine the SRA with a high degree of accuracy. The effect of powder alignment on the SRA-error decreases when the SRA is increased. The SRA of Nd 2 Fe 14 B determined from the magnetization measurements of magnetically aligned powder coincided with the value reported on single crystals, and the determination error was evaluated to be within 1°.

Bilateral comparison of 10 kΩ resistance standards between KRISS and the BIPM

This paper reports the results of an ongoing bilateral key comparison at 10 kΩ resistance standards between KRISS and the BIPM. Two 10 kΩ travelling resistance standards of the BIPM were measured at KRISS against a 100 Ω transfer standard by using a homemade cryogenic current comparator (CCC) bridge system. The value of the transfer standard resistor maintained at KRISS is calibrated against the quantized Hall resistance at plateau i = 2 using the same CCC. The measurement result shows that the equivalence of about -1 × 10-9 in the resistance calibrations between the two institutions is much smaller than the measurement uncertainty of 32 × 10-9(k=2).