International Journal of Applied Electromagnetics and Mechanics - Volume 10, issue 2

Authors: Sikora, R. | Sikora, J. | Pańczyk, B.

Article Type: Research Article

Abstract: Nuclear reactor coolant tubes are routinely inspected using eddy current methods. Classical methods rely on either human or automatic interpretation of impedance plane trajectories generated by differential eddy current probes to determine the condition of the tube. An alternative approach is to use a modified version of the Electrical Impedance Tomography (D.C. Barber and J. Sikora, 1995) (in this case called the Eddy Current Tomography) for the material coefficient imaging in a certain sub-region of the tubing. The problem can be defined as the inverse problem involving the estimation of the material coefficients (conductivity \gamma ) (S.-y. Hahn …et al., 1995). In order to solve the inverse problem it is necessary to carry out the sensitivity analysis that provides the gradient of the objective function F . The main goal of this paper is to present the adjoint variable method, an efficient tool for gradient calculation. Show more

DOI: 10.3233/JAE-1999-133

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 10, no. 2, pp. 91-103, 1999

Authors: Yang, J.S. | Zhang, W.

Article Type: Research Article

Abstract: A high voltage piezoelectric transformer working with thickness-shear modes is proposed. For the analysis of the proposed transformer, one-dimensional equations for coupled thickness-shear and flexural motions of a piezoelectric beam with rectangular cross section are employed and are simplified by thickness-shear long wave approximation. Free vibration frequency equation and modes are obtained which exhibit the mechanism of the transformer. The analysis is for piezoelectric materials of arbitrary anisotropy. A ceramic thickness-shear transformer is discussed as an example.

DOI: 10.3233/JAE-1999-131

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 10, no. 2, pp. 105-121, 1999

Authors: Zimmels, Y.

Article Type: Research Article

Abstract: Relative and absolute thermodynamic permeabilities are defined as system variables and supplements to the classical point permeability, which expresses the ratio of \mathbf{B} to \mathbf{H} , at the position where these vectors exist. The thermodynamic permeability gives a measure for the net contribution of a system to the energy stored in the field, and as such it reflects also the effect of constraints that are imposed on this field. If the system is permeable, then a fixed \mathbf{B} field involves a negative absolute thermodynamic permeability, whereas the reverse is true in a fixed \mathbf{H} …field. It is shown that weighted average permeabilities of systems that are either connected in parallel, with \mathbf{H} being uniform across them, or in series, with \mathbf{B} being uniform, are a direct consequence of related thermodynamic permeabilities. Derivatives of point permeabilities and thermodynamic permeabilities are used to define sets of field dependent temperature, pressure and chemical potential. Whereas the field dependent temperature, pressure and chemical potential are functions of a derivative of the point permeability, the pressure is a function of such a derivative as well as of the thermodynamic permeability. Examples of thermodynamic permeabilities which are obtained for toroids of different properties and for a sphere in a uniform field are illustrated and discussed. It is shown that in the case of the sphere, the thermodynamic permeability reflects the effect of partition of its own energy within and outside its physical boundaries. Furthermore, the field dependent entropy, temperature, pressure and chemical potential, of the matter enclosed within the sphere depend on properties of its own as well as on those of its surroundings. Finally, the results obtained for magnetic fields apply to electric fields once the relevant magnetic variables are replaced by their electric counterparts. Show more

DOI: 10.3233/JAE-1999-132

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 10, no. 2, pp. 123-141, 1999

Authors: Sablik, M.J. | Rubin, S.W.

Article Type: Research Article

Abstract: This paper investigates the problem of magnetostrictive generation of elastic waves in steel pipes. The elastic waves are generated by alternating current in a coil about the pipe in a static axial magnetic field. Electromagnetic theory is used to develop solutions for changing electromagnetic fields induced in the pipe, which are needed for coupling magnetostrictively to elastic waves. Elastic wave equations with magnetostrictive driving terms are then solved for the elastic wave solutions. The elastic wave solutions so generated correspond to the L(0,1) and L(0,2) modes for a cylinder, for the frequency range and cylinder geometry considered. Other cylindrical modes …do not appear because of the axisymmetric way in which the waves are generated. Comparison with experimental data shows good agreement with the elastic wave dispersion found numerically from the theory. Predictions are made for the wave amplitudes at various frequencies, incorporating both radial and longitudinal displacements into the total amplitude. Show more

DOI: 10.3233/JAE-1999-137

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 10, no. 2, pp. 143-166, 1999

Authors: Sablik, M.J. | Lu, Yichi | Burkhardt, G.L.

Article Type: Research Article

Abstract: This paper describes continued investigation of magnetostrictive generation of elastic waves in steel pipes via alternating current through a coil about the pipe in the presence of a longitudinal static magnetic field. In paper I, electromagnetic theory was used to find solutions for changing electromagnetic fields induced in the pipe. The solutions were used to obtain magnetostrictive forcing terms in an elastic wave equation for solutions appropriate to continuity of normal stresses across cylindrical boundaries. It was found that longitudinal {\rm L}(0,1) and {\rm L}(0,2) elastic wave modes could be propagated for the frequency range considered. …The amplitudes of these waves were dependent on the magnetostrictive forcing terms, which were in turn attributable to the alternating electromagnetic fields. In this paper, measurements are reported for the a.c. magnetic permeability of a steel pipe as a function of frequency and static magnetic field. These values are inserted into the model, and after other appropriate substitutions, predictions for wave amplitudes generated in the pipe are compared against experimental measurements. Show more

DOI: 10.3233/JAE-1999-138

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 10, no. 2, pp. 167-176, 1999

Authors: Mognaschi, Ezio Roberto | Calderwood, James Henry

Article Type: Research Article

Abstract: An electrostatic motor has been designed and built, and its construction is described. It was capable of running either as an induction motor or as a synchronous motor, depending on the electrical characteristics of the rotor material. The critical factor determining which behaviour is exhibited appears to be the time constant of the rotor material. Analytical expressions are given for the mechanical torque developed when the machine is running in each mode. When mechanical torque was applied to the axle of the unenergised machine, it was observed that an ac emf appeared at the terminals and the machine was therefore …operating as a generator. Show more

DOI: 10.3233/JAE-1999-135

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 10, no. 2, pp. 177-183, 1999