共查询到20条相似文献,搜索用时 15 毫秒
1.
A differential T , Ω formulation using nonconformal elements is presented. It is an extension of the T integral formulation. The method has been used as the basis of a finite-element code that handles the open boundary problem of eddy-current analysis in fully 3-D conductors. The results obtained with this formulation for different treatments of the boundary conditions at infinity are shown and compared among themselves and with respect to a T integral formulation. The efficiencies are compared in terms of storage occupation, CPU time, and accuracy 相似文献
2.
Biro O. Preis K. Renhart W. Vrisk G. Richter K.R. 《IEEE transactions on magnetics》1993,29(2):1325-1328
A finite element formulation of current-driven eddy current problems in terms of a current vector potential and a magnetic scalar potential is developed. Since the traditional T -Ω method enforces zero net current in conductors, an impressed current vector potential T 0 is introduced in both conducting and nonconducting regions, describing an arbitrary current distribution with the prescribed net current in each conductor. The function T 0 is represented by edge elements, while nodal elements are used to approximate the current vector potential and the magnetic scalar potential. The tangential component of T is set to zero on the conductor-nonconductor interfaces. The method is validated by computing the solution to an axisymmetric problem. Problems involving a coil with several turns wound around an iron core are solved 相似文献
3.
In order to obtain hexagonal ferrites with improved characteristics for application in the field of the magnetic recording, the ferrimagnetic Sr(NiTi)x Fe12-2xO19 system is studied. Preliminary investigations suggested that NI is more effective than Co in reducing the magnetic anisotropy of hexaferrites. The system was analyzed as a function of the degree of substitution x and of the reaction temperature T R and time τ. The reactivity of the mixtures and their magnetic characteristics (σ, H c, H A, T c) were measured, and from the χT(H ) data it was possible to distinguish between single-domain or polydomain particles. The results are presented. The influence of the extraneous magnetic phases on the coercive field value was also studied and a preliminary investigation of the relation between coercive and anisotropy fields was carried out 相似文献
4.
Karim R. Seed R. Oliver S.A. Widom A. Vittoria C. 《IEEE transactions on magnetics》1989,25(5):3221-3223
Modified electron spin resonance (ESR) techniques were used to measure low-field (<200 Oe) microwave absorption of high-T c cuprates YBa2Cu3O7-x. A series of experiments on polycrystalline and single-crystal samples in which the angle between the DC and the modulating magnetic fields was varied showed that the microwave absorption obeys results predicted from thermodynamic considerations of fluxoids. The absorption takes place in the normal regions created by flux penetration at low fields in these samples. The change in magnetically modulated microwave absorption on passing through T c is explained by the decrease in absorption that occurs when part of the sample becomes superconducting and by the rapid variation of the penetration depth near T c. The technique is an extremely sensitive method of detecting superconductivity in very small samples and for studying the superconducting state. Possible applications such as microwave attenuators, magnetic memories, and gaussmeters are discussed 相似文献
5.
Barwicz A. Bellemare D. Morawski R.Z. 《IEEE transactions on instrumentation and measurement》1990,39(1):76-79
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 V 1(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 相似文献
6.
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 PbZn1.9Fe15.3O25.8 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 σs=108 emu×g-1, and the Curie temperature was T c=600±20 K 相似文献
7.
Zhihui Liu 《IEEE transactions on magnetics》1991,27(3):3409-3411
The temperature dependence of magnetization in Sm3Fe 20Cx (x =0.3, 0.6, 0.8) and Sm2Fe16.5C1.0 intermetallic compounds with rhombohedral structure has been analyzed using molecular field theory. On the basis of a two-sublattice model, the molecular field coefficients are calculated using a numerical fitting method. The Curie temperature and the Fe-Fe, Sm-Fe, Sm-Sm magnetic interaction energies for the compounds are determined from these coefficients. The results show that the increase of the Curie temperature (T c) with the increase of carbon content x is attributed mainly to the enhancement of the Fe-Fe exchange interaction energy caused by carbon atoms added 相似文献
8.
Kawaji S. Nagashima N. Kikuchi N. Wakabayashi J. Ricketts B.W. Yoshihiro K. Kinoshita J. Inagaki K. Yamanouchi C. 《IEEE transactions on instrumentation and measurement》1989,38(2):270-275
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)) ΩSI-NML which can also be expressed as 6453.2(1.000,000,52(8)) ΩSI-NML. This R H (4) value gives a value for h /e 2 which is about 0.3 p.p.m. larger than the value for h /e 2 derived from the anomalous moment of the electron, using the quantum electrodynamics (QED) theory 相似文献
9.
Williams E.R. Jones G.R. Jr. Ye S. Liu R. Sasaki H. Olsen P.T. Phillips W.D. Layer H.P. 《IEEE transactions on instrumentation and measurement》1989,38(2):233-237
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 相似文献
10.
11.
A real vector X in n dimensions whose components are sinusoidally varying with time can be represented by an n -dimensional complex factor Ze jωt whose real part is X . In different real coordinate systems, the components of X transform linearly, but the amplitudes of the components of Z transform nonlinearly. The author describes a method to reconstruct the relative phases of the (complex) components of Z (and, therefore, of X ) based on the amplitude measurements of its n components in an orthogonal coordinate system and at least 2n -3 additional amplitude measurements in different directions. The author shows the necessary and sufficient condition on these additional directions to ensure uniqueness of the phase and polarization reconstruction for any arbitrary vector X , and presents an algebraic method for the reconstruction which offers substantial reduction in computing time over the method of reconstruction by nonlinear optimization. The result of this phase of reconstruction is the complete characterization of the polarization of X except for chirality 相似文献
12.
Cage M.E. Dziuba R.F. Van Degrift C.T. Yu D. 《IEEE transactions on instrumentation and measurement》1989,38(2):263-269
The quantum Hall effect is being used to monitor the US legal representation of the ohm, or as-maintained ohm, ΩNBS. Measurements have been made on a regular basis since August 1983. Individual transfers between the quantized Hall resistance R H and the five 1-Ω resistors which comprise ΩNBS can be made with a total of one standard deviation (1σ) uncertainty of ±0.014 p.p.m. This uncertainty is the root-sum-square of 32 individual components. The time-dependent expression for R H in terms of ΩNBS is: R H=25812.8[1+(1.842±0.012)×10-6 =(0.0529±0.0040)(t -0.7785)×10-6 /year] ΩNBS, where t is measured in years from January 1, 1987. The value of ΩNBS is, therefore, decreasing at the rate of (0.0529±0.0040) p.p.m./year 相似文献
13.
Jau Hwang Ho Chung Len Lee Tan Fu Lei 《IEEE transactions on instrumentation and measurement》1990,39(4):642-648
An ellipsometry technique for measuring the arbitrary refractive index profile of composite thin films is presented. The refractive index profile is obtained through a successive partitioning and computation process on measured data points with the aid of a φ0/T plot, which reduces errors. Analyses of the required number of data points in the partitioned sections, the errors caused by the inappropriate partitioning, and the cumulative errors are performed. A Δφ0/T plot is used to monitor the overall cumulative errors of the computation. Experimental examples using this technique to measure the refractive index profile of O-N-O and O-N composite thin films are included and results are compared with those obtained by Auger electron spectroscopy. It is shown that this method is sensitive enough to determine the refractive index profile to a resolution of 20 Å 相似文献
14.
An improved T -Ω method that can analyze magnetic fields produced not only by eddy currents but also by magnetizing currents is proposed. The method is applied to the analysis of 3-D eddy-current models with holes. The usefulness of the method is investigated by comparing calculated results with measured results and with results obtained by the A -Φ method. The T -Ω method has the advantage that the CPU time can be considerably reduced when most of the analyzed region is current-free and the eddy current flows two-dimensionally. The method is especially effective when the shape of the winding is simple and the distribution of magnetizing current is known beforehand. It is not effective when most of the analyzed region is current-carrying 相似文献
15.
Co-Cr layers deposited on Ge underlayers were investigated with ferromagnetic resonance (FMR). The thickness of the Co-Cr layers and the substrate temperature (T s) during deposition were varied. Measurements with a vibrating sample magnetometer showed that an increase of T s results in an increase of both the bulk saturation magnetization M s and the perpendicular coercivity H c⊥. The FMR spectra, obtained with the applied field perpendicular to the sample, showed two resonances for all layers. The effective anisotropy field is positive for both resonances. The difference in effective anisotropy field does not change with thickness of the layer, but increases with increasing T s. From this it is clear that the two resonances are not due to magnetic inhomogeneities in the growth direction, but must be due to lateral magnetic inhomogeneities. Inhomogeneities in composition, resulting in different values of M s, or in geometric structure, resulting in different values of the demagnetizing factor N d, are the most probable causes of the observed effects 相似文献
16.
In high fields where the magnetization is approaching saturation, the resolved magnetic polarization I can be expressed by a power series of the inverse of external field H as: I=Is-b/H 2-c/H3 . . ., or alternatively in terms of the reversible permeability μrev=1+(2b/H3+3c/H4+ . . .)/μ0 where I s is the spontaneous magnetic polarization and b , c , are constants. These equations express the law of approach to saturation magnetization. The coefficient b for a cubic crystal has been deduced as b =0.0762/Is[K+1.5(λ100-λ 111)σ]2, where σ is the applied stress and others are magnetic constants. The values of reversible permeability μrev under biasing field H were measured for carbon steels with applied stresses. The results showed that the square root of 2b changed linearly with the applied stress, The values of magnetic constant K andλ100 -λ111 were calculated, They agreed with the standard values, but were affected by chemical composition and heat treatment of materials, especially in λ100-λ111 相似文献
17.
Many design objectives can be expressed more directly in terms of circuit parameters, such as capacitance and inductance, than in terms of the field vectors E and B . A simple, although radical, change is suggested to provide a closer link between the field and circuit views. The electric potential φ and magnetic vector A are defined, in energy terms, as the primary field quantities, and they are visualized as measures of the capacitance and inductance, respectively. E and B become auxiliary symbols denoting derivatives, so that the customary roles of the potentials and field vectors are reversed. Some of the practical advantages of the change are examined and are illustrated by example 相似文献
18.
《IEEE transactions on instrumentation and measurement》1989,38(1):64-73
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 相似文献
19.
Shida K. Wada T. Nishinaka H. Segawa K. Igarashi T. 《IEEE transactions on instrumentation and measurement》1989,38(2):252-255
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 /e 2 is estimated to be 25,812.8064 ΩSI 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) 相似文献
20.
Fabbricatore P. Musenich R. Parodi R. Vaccarone R. 《IEEE transactions on magnetics》1990,26(6):3046-3051
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: R αl n 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 相似文献