Coaxial Bridge Research Articles

A Full-Wave Analysis of a Coaxial Waveguide Slot Bridge using the Fourier Transform Technique

Electromagnetic wave scattering from a coaxial waveguide slot bridge is theoretically investigated. The Fourier transform/series technique is utilized to constitute a set of simultaneous equations for the discrete modal coefficients. The residue calculus is applied to transform the scattered-field integral representations into fast-converging series forms. Numerical computations illustrate the behavior of scattering in terms of the slot geometry, the incident mode, and the operating frequency.

On Strategies for Automatic Bridge Balancing

Automatic balancing of coaxial AC impedance bridges asks for simple, robust and efficient strategies suitable to be easily implemented on PC controllers. The paper considers the problem of balancing a bridge with n detectors to be equivalent to the problem of finding the root of a complex-valued vector function F. To avoid electrical modeling of the bridge, F is considered generally unknown except at specific points evaluated by experiment. In this framework, efficient root-finding strategies can be employed; in particular, secant method and two generalizations of it to the case n>1 are proposed. Experimental results on a test circuit are given.

Linear Frequency Dependence in AC Resistance Measurement

The frequency dependence of AC resistors as well as the AC quantum Hall resistance shows sometimes unexpected linear terms of the order of 1/spl middot/10/sup -7/ kHz/sup -1/. Three reasons for measuring linear terms are identified as systematic effects of the coaxial bridge and the compared resistors.

A QHE-Based System for Calibrating Impedance Standards

Coaxial transformer bridges applied to a newly formed system for calibrating impedance standards are described. In this system, an R-R bridge characterizes reference quantum Hall devices as well as directly links them to 12906.4 /spl Omega/ or 10000 /spl Omega/ standard resistors. These resistors, in turn, serve as reference standards in capacitance calibrations made by a multifrequency quadrature R-C bridge and a C-C bridge. Finally, by means of a multifrequency double-balance L bridge, 1- and 10-nF capacitors calibrated in this manner are linked to inductance standards whose values range from 1 to 100 mH.

Unequalized Currents in Coaxial AC Bridges

In a coaxial ac bridge with imperfect current equalization, the comparison of two standard resistors shows a linear frequency dependence. Unequalized currents load the magnetic cores in the coaxial bridge and result in effective loss factors of certain capacitances of the compared resistors. To avoid this systematic effect in any coaxial bridge used for the precise calibration of impedance standards, a correct arrangement of current equalizers is absolutely necessary.

Evaluation of coaxial bridge systems for accurate determination of the SI Farad from the DC quantum Hall effect

An evaluation of the four-terminal-pair equal power 100 : 1, quadrature and 10 : 1 coaxial bridge systems for the traceable determination of NPL 10 pF primary capacitance standard from the DC quantum Hall effect is reported. This was instigated to resolve the small but significant discrepancies observed in the NPL measurements during the recent EUROMET and CCEM comparisons. A formal bilateral comparison between NPL and BIPM was conducted (involving EUROMET two-terminal-pair and BIPM three-terminal capacitance standards) to establish a new degree of equivalence between the two laboratories for the 10 pF and 100 pF capacitance measurements at 1 kHz and 1.592 kHz. The majority of results show agreement within the estimated 2σ combined relative standard uncertainty of measurement of the two laboratories. However, the best agreement was obtained for the EUROMET two-terminal-pair 10 pF and 100 pF capacitance standards with a mean difference between NPL and BIPM results of (21.9 ± 117) nF/F and (51.4 ± 117) nF/F, respectively, at 1.592 kHz.

Accurate analysis of coaxial waveguide slot bridge

Accurate analysis of coaxial waveguide slot bridge

Accurate analysis of coaxial waveguide slot bridge

Accurate analysis of coaxial waveguide slot bridge

Accurate analysis of coaxial waveguide slot bridge

Accurate analysis of coaxial waveguide slot bridge

Coaxial Waveguide Slot Bridge Cell for Liquid Substances Study

The experimental method suggested suppose the studying of energy characteristics of slot bridge (SB) cells in the multi mode operating regime based on the preliminary numerical investigation of scattering resonant characteristics of SB (solution of boundary value problem and investigation of eigen frequencies and relevant field modes). The configuration of experimental model of SB cell is computed accordingly to required frequency band and preliminary information about dielectric parameters of materials chosen for tests. Ethanol scattering characteristics of SB cell are computed by software, developed on the base of rigorous solution of the boundary value problem, providing numerical data with any required accuracy.

Phase border and density determinations in the critical region of (carbon dioxide+ethane) determined from dielectric permittivity measurements

We have determined the (p,T, ρ,x) phase boundaries in three mixtures of {(1−x)CO2+xC2H6}, withx=(0.25166, 0.49245, and 0.73978), in the vicinity of the critical locus from measurements of the relative dielectric permittivity εr. We combined accurate measurements of εrwith the Clausius–Mossotti relationship to determine the density. Measurements of εrwere made with two apparatuses: a reentrant cavity resonating at 375 MHz, and a coaxial cylindrical capacitor and bridge operating at a frequency of 1 kHz. The phase border was determined with uncertainties of approximately 0.5 per cent in density and 0.06 K in temperature, the latter corresponding to a fractional uncertainty of 1.2·10−3in pressure. The uncertainties in temperature and pressure resulted from the size of the temperature steps that were used; smaller values could be attained. The uncertainty in density resulted from uncertainty in the parameters relating the density to εr.

AC QHE-based calibration of resistance standards

A coaxial transformer bridge for QHE-based calibration of resistance standards has been developed. An eight-decade two-stage inductive voltage divider forms ratio arms of the bridge and triple-series connection of the reference QHE sample to the bridge is employed. Frequency characteristics of LEP heterostructures have been measured by comparing them against resistors with calculable frequency dependences. Two quadrifilar, Gibbings's type resistors with nominal values of 12 906 /spl Omega/ and 6353 /spl Omega/ have been used in this measurement.

Accurate AC Measurements of the Quantized Hall Resistance from 1 Hz to 1,6 kHz

Accurate measurements have been made of the quantized Hall resistance (QHR) corresponding to the quantum number i = 2, RH (2), of two GaAs-based heterostructures using alternating current in the frequency range from 1 Hz to 1,6 kHz. The QHR is compared with a conventional ac reference resistance standard (Vishay type) of the same nominal value. The measurements are made with an alternating current comparator bridge at 1 Hz and with a coaxial ac bridge from 400 Hz to 1,6 kHz. The quantum Hall effect (QHE) sample is connected to the coaxial bridge using a double series connection. An analysis of the circuit properties of the sample shows that this technique of connection is sufficient to define the QHR as a four terminal-pair impedance. It also avoids perturbing effects from small capacitances between the terminals of the sample and from inductive reactances in series with the terminals. At frequencies up to at least 1,6 kHz a central region on the Hall resistance plateau has been observed for which the Hall resistance RH (2) is independent of the magnetic flux density to within 1 part in 108. The ratio of RH (2) to the reference resistance varies by less than 2 parts in 107 from 1 Hz to 1,6 kHz. A significant part of this variation is probably due to the frequency dependence of the reference resistance itself.

A method for precise RF admittance measurement

An improvement in the theory of the dual admittance bridge with self-calibration ability for precise RF measurement is described. The approach to the bridge function analysis extends utilization of its high resolution and accuracy in immittance standardization into the UHF range. No detailed information about the bridge's internal structure is needed for the theory, which describes it as a multiport device. Thus, the theory has not only contributed to bridge arrangement, but also enables simple and efficient calibration of measurement equipment based on the classical twin-T admittance bridge. Improvement in the accuracy and frequency range of the calibrated equipment should be expected. The theory has been verified on a special coaxial bridge circuit at 100 and 1000 MHz. >

Coaxial AC Bridges

Coaxial AC Bridges

A Method for Remote Use of Hot Wire Anemometer

Hot-wire anemometer remote operation, discussing coaxial cable length, terminal connection and bridge current

A coaxial bridge with helical line sample holders as a nuclear quadrupole resonance detector

The main advantages of the spin resonance detector described are high sensitivity, the absence of line distortions, low microphonics and a wide frequency range. The spectrometer is particularly suited for pure nuclear quadrupole resonance measurements. As an example, the nuclear quadrupole resonance line of 81Br in NaBrO3 at 150 MHz has been observed with a calculated power ratio S/N of about 5 × 106, using a lock-in system of 0.1 Hz bandwidth. The amplifier noise (noise figure 4 dB) reduced it to an actual value of 5 × 104. The detector consists of a commercially available coaxial bridge (Siemens Rel 3 R 251 b) which has been modified. The performance of the bridge is analysed and the optimum working conditions are discussed. The results are in good agreement with experiment. For single crystal studies, helical line sample holders have been developed.

Annealing of Oblique-Incidence Permalloy Films

The anisotropy of evaporated Permalloy films (composition near zero magnetostriction) deposited on glass at 45° to the substrate normal and at a substrate temperature of 200°C has been studied after anneal for several hours at 300°C. After anneal the room temperature easy axis of films with positive magnetostrictionis in the original direction. However, films with negative magnetostriction develop a new room temperature easy axis 90° to the original one; at 300°C the easy axis is in the original direction. Application of a large magnetic field in any direction during anneal does not influence the final magnetic anisotropy in either case. These effects are qualitatively explained by assuming the anneal to increase the tension along the long axis of oblique-incidence chains, a process which converts surface energy into strain energy. Anisotropy was measured by resonance in a coaxial bridge over the frequency range 50 Mc to 2100 Mc. A rectangular coaxial cavity is used which can be heated to 500°C in a vacuum of 10−6 mm Hg; continuous angular orientation of the film is possible with a resolution of ±0.5°. Bridge balance is good enough to permit samples of less than 100 A thickness to be measured.