Measurement Of Mutual Impedance Research Articles

Noninvasive Conductivity and Temperature Sensing Using Magnetic Induction Spectroscopy Imaging

The work presents a perspective in evaluating electromagnetic tomography reconstruction through a spectral eddy current imaging arrangement. Embarking from an established analytical basis, the spectroscopic relation of a metallic conductive body to its physical properties is revealed via multifrequency mutual impedance measurement. Characteristics are evident, from either modeling or experiment, on certain frequency ranges that discriminate the object’s circumstances. Both the amplitude ratio and phase-contrast image spectrum show information on the conductivity and structure of a target considered pivotal for industrial applications. Two test cases are reported: liquid metal structure determination and contactless temperature evaluation of a remote/hidden medium/object. Using eddy current-based spectroscopic imaging data and appropriate calibration, this work, for the first time, demonstrates a novel thermal mapping system. This is a wireless and inductive-based temperature mapping device that can have great potential applications where none of the existing thermal measuring devices could work noninvasively.

Evaluation of EIT systems and algorithms for handling full void fraction range in two-phase flow measurement

In the aqueous-based two-phase flow, if the void fraction of dispersed phase exceeds 0.25, conventional electrical impedance tomography (EIT) produces a considerable error due to the linear approximation of the sensitivity back-projection (SBP) method, which limits the EIT’s wider application in the process industry. In this paper, an EIT sensing system which is able to handle full void fraction range in two-phase flow is reported. This EIT system employs a voltage source, conducts true mutual impedance measurement and reconstructs an online image with the modified sensitivity back-projection (MSBP) algorithm. The capability of the Maxwell relationship to convey full void fraction is investigated. The limitation of the linear sensitivity back-projection method is analysed. The MSBP algorithm is used to derive relative conductivity change in the evaluation. A series of static and dynamic experiments demonstrating the mean void fraction obtained using this EIT system has a good agreement with reference void fractions over the range from 0 to 1. The combination of the new EIT system and MSBP algorithm would significantly extend the applications of EIT in industrial process measurement.

Modeling of Cluster's electric antennas in space: Application to plasma diagnostics

The main characteristics of the long‐boom electric antennas installed on board the Cluster satellites are derived from finite element modeling in a kinetic and isotropic space plasma, in the frequency range of about 1–100 kHz. The model is based on the surface charge distribution method in quasi‐static conditions. The impedances of both types of antenna, i.e., the double‐wire and the double‐probe, are computed versus the frequency normalized with respect to the local plasma frequency and for several different Debye lengths. Most of the code outputs are checked using analytic estimations for better understanding of the involved physical mechanisms. As a by‐product, the effective length of the double‐probe antenna and the mutual impedance between the two antennas are computed by the code. It is shown that if it had been possible to implement such measurements on board, one would have been able not only to determine accurately the electric characteristics of the antennas but also to estimate the local plasma parameters. Nevertheless, an interesting feature predicted by the model has been checked recently in orbit by running a special mode of operation for testing the mutual impedance measurement. The preliminary results are globally consistent with the predictions, except that they suggest that our Maxwellian model for the electron distribution should be revised in order to explain the unexpected low‐frequency response. After analysis of the electron flux measurements obtained simultaneously, it appears that a rough adjustment of the electron distribution with a two‐component distribution allows us to account for the observations.

A technique for the measurement of mutual impedance of monolithic solid‐state quasioptical oscillators

AbstractA technique for the measurement of mutual impedance of monolithic solid‐state quasioptical oscillators is described. Varying the spacing between one oscillator and its mirror image causes a frequency shift that can be used to calculate mutual coupling. The theory is confirmed through measurements of a 51‐GHz monolithic IMPATT oscillator.

Design of a transducer element for an acoustic mutual impedance measurement experiment

A companion paper in this session has described an experiment to measure the acoustic mutual impedances in a resonant, close-packed sonar array [S.C . Thompson, J. Acoust. Soc. Am. Suppl. 1 82, S2 (1987)]. This experiment requires the use of special measurement transducers in place of the elements in the array under study. There were several special requirements for these transducers: (1) high mechanical input impedance at the element radiating face; (2) accurate knowledge of the transducer electromechanical impedance matrix; and (3) radiating face dimensions that are identical to those of the elements of the array under study. The first requirement reduces the effects of interelement coupling and, consequently, reduces the sensitivity in the calculations to errors in the measurement. The second acknowledges that the electromechanical impedance matrices of the transducer elements are needed in the calculation. The third requirement provides a measurement array with the same mutual impedance coefficients as the array under study. A prototype transducer element that seems to meet these requirements is a doubly resonant piston element. The element is designed so that the operating band of the array under study falls between the two resonant frequencies of the measurement transducer. The design and performance of this element will be described.

Acoustic Models of Radio Antennas

The large number of independent variables in antenna arrays make it advisable to develop means for rapidly surveying the field patterns which may be obtained. The advantages in the use of acoustic models for this purpose are shown. Two analogous acoustic antennas are developed, one for the measurement of fields at a distance and the other for fields close to the antenna. The procedure which can be followed in setting up the models and making measurements is outlined. Advantages are demonstrated for the acoustic model in the study of nonsinusoidal current distributions, and their effect on the field pattern. The measurement of mutual impedance between antennas may be conveniently carried out with one of the models. The arrangement for phasing and magnitude control in a multiunit array are shown. The field of an acoustic model is shown in comparison with the field of an actual array which it simulates.