Quantized Hall resistance measurements

The quantized Hall resistances, R_H(4), of Si MOSFETs were measured at ≈0.5 K in a magnetic field of 15 T. The value of R_H(4) was determined in terms of the Commonwealth Scientific and Industrial Research Organization (CSIRO) realization of the SI ohm. A weighted mean of three determinations gave a value for the quantity R_H(4) of (6453.203,36(52)) Ω_SI-NML which can also be expressed as 6453.2(1.000,000,52(8)) Ω_SI-NML. This R_H (4) value gives a value for h/e² which is about 0.3 p.p.m. larger than the value for h/e² derived from the anomalous moment of the electron, using the quantum electrodynamics (QED) theory     

A low field determination of the proton gyromagnetic ratio in water

The proton gyromagnetic ratio in H₂O is measured by the low-field method. γ'_p(low)=2.67513376×10⁸ s^-1 T^-1 (0.11 p.p.m.), leads to a value of the fine structure constant of α^-1=137.0359840 (0.037 ppm) and a value for the quantized Hall resistance in SI units of R_H=25812.80460 Ω (0.037 p.p.m.). To achieve this result, the dimensions of a 2.1-m solenoid were measured with an accuracy of 0.04 μm, and the NMR (nuclear magnetic resonance) frequency of a water sample was measured in the field of the solenoid     

A measurement of the NBS electrical watt in SI units

The National Bureau of Standards (NBS) electric watt in SI units to be: W_NBS/W=K_W =1-(16.69±1.33) p.p.m. The uncertainty of 1.33 p.p.m. has the significance of a standard deviation and includes the best estimate of random and known or suspected systematic uncertainties. The mean time of the measurement is May 15, 1988. Combined with the measurement of the NBS ohm in SI units: Ω_NBS/Ω=K_Ω =1-(1.593±0.022) p.p.m., this leads to a Josephson frequency/voltage quotient of E_J=E₀[1+(7.94±0.67) p.p.m.] where E₀=483, 594 GHz/V     

Widely extended new method for measuring the impedance (CxRx) at high frequencies withapplications

A method is described for the accurate measurement of the equivalent parallel capacitance C_x and resistance R_x of very high loss materials at high frequencies. The important characteristic of the method is its capability of measuring the value of C_x extending from 10^-2 to 10⁶ pF and R_x from 10 to 100×10⁶ Ω. The authors measure the humidity of tea leaves and rockwool by measuring the capacitance C_x of specimens irrespective of the value of R_x     

A reevaluation of the NML absolute ohm and quantized Hallresistance determinations

Several electrical and geometrical aspects of the National Measurement Laboratory (NML) calculable capacitor are reexamined for effects of wear and other possible causes of error. A new set of quantized Hall resistance measurements is made and related to the NML realization of the SI ohm based on the calculable capacitor. The results of these measurements may be expressed as R_H=25812.8 (1.000,000,363 (66)) Ω     

New realization of the ohm and farad using the NBS calculablecapacitor

Results of a realization of the ohm and farad using the US National Bureau of Standards (NBS) calculable capacitor and associated apparatus are reported. The results show that both the NBS representation of the ohm and the NBS representation of the farad are changing with time, Ω_NBS at the rate of -0.054 p.p.m./year and F_NBS at the rate of 0.010 p.p.m./year. The realization of the ohm is of particular significance because of its role in assigning an SI value to the quantized Hall resistance. The estimated uncertainty of the ohm realization is 0.022 p.p.m. (1σ), while the estimated uncertainty of the farad realization is 0.014 p.p.m. (1σ)     

A precise measurement of QHR at NIM [quantized Hall resistance]

Equipment for precise measurement of the quantized Hall resistance (QHR) at the National Institute of Metrology (NIM), Beijing, China, is described. The essential parts in this equipment are a resistance comparator of one-to-one ratio with a comparison uncertainty of 3×10^-8 and two specially designed resistor networks used for determining of the ratio between 12906.4035 Ω of QHR at i=2 and 10 kΩ or 1 kΩ. The transfer procedure from QHR to 10 kΩ or 1 kΩ can be completed easily with this equipment by a few one-to-one comparisons with a total uncertainty of 5×10^-8     

SI value of quantized Hall resistance based on ETL's calculablecapacitor

The SI value of the quantized Hall resistance based on Electrotechnical Laboratory's (ETL) calculable capacitor is presented. Some improvements for previous measurement systems were made and some of the measurement techniques were changed. Based on measurements of ETL, the value of h/e² is estimated to be 25,812.8064 Ω_SI with a systematic uncertainty of 0.24-p.p.m. root-sum-square (r.s.s.) and a random error of 0.11-p.p.m. at one standard deviation (1σ)     

Comparison of quantized Hall resistances RH(2) andRH(4) of a GaAs/AlGaAs heterostructure device

Quantized Hall resistances R_H(4) and R_H(2) of a GaAs/AlGaAs heterostructure were compared with reference resistors whose values are close to h/4e² or h/2e². The values of the reference resistors were compared with a 100 ohm standard resistor via a cryogenic current comparator (CCC) resistance bridge. Results showed that (4×R_H(4)-2×R_H(2))/2×R_H (2)=(0.037±0.019)×10^-6     

Digital correction of A/D conversion error due to multiplexingdelay

A measurement channel which consists of a multiplexer, sample-and-hold circuit, and analog-to-digital (A/D) converter is studied. It is designed for the synchronous sampling and measurement of two or more voltage signals V₁(t), V ₂(t), . . ., but the finite time of A/D conversion (ΔT) makes it impossible to acquire consecutive samples closer in time than ΔT. This can become a source of measurement error if further processing of the measurement data is based on the assumption of ideal synchronism. It has been found that interpolation filters, developed from the Lagrange polynomial interpolation, are useful tools for solving the problem of correction. An illustrative example of their use is presented     

Accuracy of measurements of the quantized Hall resistivity by adirect current comparator type potentiometer: calibration using aJosephson potentiometer

The accuracy of measurements of the quantized Hall resistivity (QHR) by a direct-current-comparator (DCC)-type potentiometer is estimated based on a linearity calibration of the potentiometer using a Josephson potentiometer. The power coefficient contribution to the nonlinearity of the DCC potentiometer was found to be 0.15±0.02 p.p.m./(100 mV)² at 18.5±0.5°C in 1985 and 0.21±0.03 p.p.m./(100 mV)² at 20.5±0.5°C in 1988. The possibility of accurate measurements of the ratio QHR/R _STD with uncertainties less than 0.05 p.p.m. by the DCC potentiometer is discussed     

Properties of the W-type hexaferritePbZn2Fe16O27

W-type Pb-hexaferrites were prepared by standard ceramic methods. The lattice constants found by refinement were a=0.59140±0.00006 nm and c=3.29209±0.00041 nm. The X-ray density of a typical composition PbZn_1.9Fe_15.3O_25.8 was ρ=5.32 g/cm³ and the Vickers microhardness value h _v=6 kN/mm². A plot of the saturation magnetization versus temperature is given. The extrapolated value of the saturation magnetization (H→∞, T→0) was σ_s=108 emu×g^-1, and the Curie temperature was T_c=600±20 K     

Global iterative solution of dielectric spectroscopy equations

A global method is presented for solving the permittivity equations for open- and short-circuited coaxial lines of general length for broadband measurements by iterating the recurrence schemes z_n+1=c cot z_z and z _n+1=c tan z_n, respectively, and their inverses. The global iteration theory of Fatou and Julia (see J. L. Howland and R. Vaillancourt, Num. Math., vol.46, 323-337, 1985), coupled with linear extrapolation and interpolation and Steffensen's acceleration procedure, supplies starting values and guarantees convergence even near double roots. When R_Z⩾0 for open, and R_Z⩽0 for short circuit terminations Newton's method, with appropriate starting values, converges to the desired roots. A combination of the three iterative schemes results in an almost global method of solution. Numerical results are quoted     

A transformer-ratio bridge for the measurement of small loss angles

A development in the architecture of transformer-ratio bridges for the measurement of the loss angles of low-pass dielectrics is described. This has led to a sensitive and accurate bridge capable of measuring loss angles with a detection limit of 1×10^-8 rad (S /N=1 at a bandwidth of 1 Hz of the detector) and an accuracy of a few percent in the 10^-6 and higher ranges in the frequency range from 200 Hz to 200 kHz. The readout of the bridge is computer controlled and has an automatic capacitive balance. The most important characteristics of the bridge and their influence on the sensitivity and accuracy are discussed. Measurements as a function of frequency are presented as an example. The bridge can be used in numerous applications concerning the characterization of dielectric materials     

Determination of the tesla-to-ampere ratio for the KRISS/VNIIMγ'P-experiment

Tesla-to-ampere ratio giving the largest error in the γ'_P-low-field-experiment has been determined using a modified noncontacting method. The total uncertainty of 0.164×10 ^-6 has been attained. The constant of a solenoid and the γ'_P-value have been corrected for magnetic susceptibility of air. The result is γ'_P=2.675 154 18×10⁸ s^-1 T^-1 (Tesla BI-90) with the total uncertainty of 0.18×10^-6     

Direct comparison of two independent Josephson voltage standards at1 V and precision measurements up to 10 V

Two Josephson voltage standards have been compared using a room-temperature electronic nanovoltmeter with a peak-to-peak noise of about 2 nV at the 1-V level corresponding to a RMS uncertainty of 4×10^-10. The excellent stability in maintaining the desired voltage steps makes it possible to obtain recorder traces comparing Nb/Al₂O₃/Nb Josephson standards with Weston cells and Zener reference standards at 1 V and 10 V. At 10 V the best result shows a peak-to-peak noise of 250 nV corresponding to a RMS uncertainty of 5×10^-9 for a Zener reference and 50 nV corresponding to 1×10^-9 for a series connection of nine Weston cells. As an example for the application of the Josephson standard as a potentiometer the deviation in the linearity of a digital voltmeter is confirmed to be on the order of 0.1 p.p.m. in the range from -10 V to +10 V     

Grain size dependence of coercivity and permeability innanocrystalline ferromagnets

Amorphous ribbons of composition Fe_74.5-xCu_xNb₃Si_13.5B₉ (x=0, 1 at.%) have been annealed between about 500°C and 900°C. This produced a series of crystallized samples with grain sizes between about 10 nm and 300 nm and with coercivities H _c and initial permeabilities μ_i varying over several orders of magnitude. The best soft magnetic properties (H _c≈0.01 A/cm and μ_i≈80×10³ ) were observed for the smallest grain sized of about 10 nm. With increasing grain size D, coercivity steeply increases following a D⁶-power law (up to D≈50 nm). H_c then runs through a maximum of H_c≈30 A/cm and decreases again for grain sizes above 150 nm according to the well-known 1/D law for polycrystalline magnets. The initial permeability was found to vary in a similar manner, essentially being inversely proportional to coercivity. The variation of the soft magnetic properties with the average grain size is discussed and compared with the predictions of the random anisotropy model and other theories for the magnetization reversal     

Effect of the n value and the field inhomogeneity on thequench current of superconducting cables [magnet winding]

A model developed to obtain a relation connecting the critical current and the quench current of superconducting (S/C) cables is described. The model is based on the hypothesis that the heat produced inside the cable is only due to the ohmic dissipation, and it is only removed by thermal exchange with the liquid helium bath. The ohmic dissipation is calculated by supposing that the electrical resistance of the S/C cable at the transition to normal state is: Rαlⁿ where l is the current and n (n value) is an integer number. To calculate the function R(I), the field inhomogeneity at the conductor due to the self-field is taken into account, introducing the effective critical field