Optimization of eddy-current compensation☆

The bulk of the article is concerned with a critical discussion of inductive, electrodeless techniques that enable the resistivity of a metal to be investigated, especially by the use of massive samples, with or without the presence of a strong magnetic field. The principal methods are the following: modification of the inductance of a coil by a metal core, eddy current decay, `hard' helicons in a rigidly mounted sample, `soft' helicons in an elastically mounted sample and torque on a sphere turning in a steady transverse field. The theory underlying the methods is expounded, but greatest attention is paid to the variety of disturbing effects that can introduce significant errors, and to the refinements of technique and analysis needed to minimize them. Although the literature is reviewed in some detail, much of the material is new. In an introduction the problems of conventional measurements, by four-terminal methods, in the presence of strong magnetic fields are outlined, particularly the `current-jetting' effects that can cause disastrous errors. This review was completed in January 1972.

http://iopscience.iop.org/article/10.1088/0034-4885/35/2/304/pdf

Electrodeless methods for conductivity measurement in metals

While the literature contains many contactless resistivity measurement methods suitable for fairly large spherical, cylindrical and rectangular geometries, few of these are designed for small samples. After a literature review, a variable-temperature technique which is well adapted to small circular wafers is presented.

https://iopscience.iop.org/article/10.1088/0022-3719/18/8/010/pdf

Contactless resistivity measurements: a technique adapted to graphite intercalation compounds

Mechanical spectroscopy, electrical resistivity and X-ray diffraction measurements were performed on commercial WE 43 magnesium alloy with different thermal histories in order to determine the precipitation processes which appears within the temperature range between room temperature and 823 K. It has been found out that the precipitation process at temperatures of about 650 K promotes two stages of precipitations. The first occurring at earlier times produces an increase of the modulus and the later one leading to softening by growing of precipitates and a decrease of solid solute concentration in the matrix. The damping spectrum in WE 43 magnesium alloy shows three grain boundary damping peaks. The characteristic grain boundary peak of magnesium at 450 K, a grain boundary peak related to the solute atoms at 490 K and a grain boundary peak related to precipitates at grain boundaries at 520 K.

Effects of precipitation processes on damping and elastic modulus of WE 43 magnesium alloy

Measurements are reported of the electrical conductivity of solutions of Cs, Ca, Sr, Ba, and Yb in liquid ammonia. Cs-NH${7}_{3}$ solutions were studied at concentrations above 6 mole% metal (MPM) and at temperatures from 200 to 300 K. Cesium and ammonia can apparently be mixed in any proportion near room temperature. In the case of the other metals, the concentration range is from 2 to 7 MPM at temperatures between 190 and 250 K. The observed conductivities ranged from 200 to 16 000 ${\ensuremath{\Omega}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The conductivity was observed to increase with temperature, except for Cs-N${\mathrm{H}}_{3}$ solutions above 30 MPM. The present results are compared with those available on other metal-ammonia solutions, and with the behavior of simple liquid metals. In addition, the phase diagrams of the solutions are reported.

Conduction in Concentrated Solutions of Several Metals in Liquid Ammonia

A systematic analysis is presented of the conditions in which the measurements of resistivities of metallic samples by the eddy current decay method give meaningful and accurate results. Coil sample geometry and material parameters are examined by means of equivalent circuits, and ways of extracting the desired information from the signal are discussed. We report selected measurements on critical parameters. A carefully designed and tested apparatus for the accurate determination of resistivity at room and helium temperatures with an operational logarithmic amplifier has been constructed. Most of the important conclusions of this study are displayed in graphical form to assist workers in the field.

A. Bernalte

Papers

Analysis of Resistivity Measurements by the Eddy Current Decay Method