Presence Of Eddy Currents Research Articles

Skin depth and complex magnetic susceptibility: An experimental alternative approach

A different approach in the discussion of the skin effect in a metal cylinder, is described, where the presence of eddy currents is assumed to be a consequence of an equivalent static magnetization. A low-cost, easy to build mutual inductance bridge is used to measure the equivalent magnetic susceptibility—a function of the skin depth. The use of a lock-in amplifier as a null detector clearly shows the concept of complex magnetic susceptibility. The electrical resistivity of a copper rod is measured as an application thereof. The results are shown and compared to theory achieving excellent agreement.

Magnetization of a nonlinear ferromagnetic semi-infinite plate by a short coil, in the presence of eddy-currents

The paper deals with the evaluation of magnetic fields in a system of a relatively long-conductive ferromagnetic strip with nonlinear characteristic. The field is produced by an a.c. excited relatively short coil wound around the strip. The investigated system is similar to a magnetic field sensor system (described recently) which employs nonlinear eddy current effects in the sensing process. The analysis in the paper depends on linearization of the magnetic vector-potential equations by assuming that all field components are sinusoidal everywhere, and by imposing an appropriate change of μ with the material depth. The linearization process enables the integration of the field equations by Fourier transform. The evaluated results compare favorably to experimental results.

A mobility analogy equivalent circuit of a magnetostrictive transducer in the presence of eddy currents

The equivalent circuit in the mobility analogy of a magnetostrictive transducer in the presence of eddy currents is derived. This equivalent circuit is used to predict the effect of eddy currents on the efficiency, the electrical impedance, the transmitting responses, and the receiving sensitivity of a magnetostrictive transducer. Lumped-parameter equivalent circuits are also presented which use approximations to the exact theory to simply and accurately predict the efficiency and electrical impedance of a transducer with eddy currents within a frequency range of practical interest near the clamped characteristic frequency. It was found that the eddy current theory predicted a sharp drop in the eddy current loss in a narrow frequency range just past resonance. This effect was experimentally observed by Savage and Abbundi [IEEE Trans. Magn. 14, 545 (1978)].

Rare earth iron magnetostrictive underwater sound transducer

A low-frequency, resonant, longitudinally vibrating piston-type rare earth iron underwater sound transducer using rods of 27% terbium – 73% dysprosium iron (Tb0.27Dy0.73Fe1.95) is described. The performance of the rare earth iron transducer is compared with the performance of the same transducer with identical ceramic active elements. Data on transmitting current response, transmitting voltage response, free-field voltage sensitivity, coupling coefficient, efficiency, and linearity are presented. An equivalent circuit is presented which predicts the performance of the transducer in the presence of eddy currents and demagnetization. The predicted performance of a laminated transducer is compared with that of an unlaminated transducer. Advantages and disadvantages of the rare earth iron material are discussed.

Finite element analysis of the skin effect in current carrying conductors

The current density distribution in a conductor of finite size is affected by the presence of eddy currents in the conductor. This phenomenon, generally known as skin effect, causes ohmic losses in the conductors and alters their magnetic induction. This paper presents an analysis of skin effect phenomena using the triangular finite element method. The results obtained by this method are compared with those of classical one-dimensional analysis for (i) a conductor in free space and (ii) a conductor in the presence of an iron boundary.

Mechanism of alumina buildup in tundish nozzles during continuous casting of aluminum-killed steels

During continuous casting of aluminum-killed steels, the pouring rate through the tundish nozzle often diminishes, posing serious operating problems. This happens because a buildup of microscopic alumina particles at the nozzle orifice effectively decreases the nozzle orifice diameter and causes constriction of the liquid-steel pouring stream. There are two major aspects of the constriction problem: (1) the source of the depositing particles, and (2) the mechanism by which the particles deposit at the nozzle orifice. Detailed microscopic examination of the buildup of alumina particles in nozzles from various casting trials and petrographic examination of the nozzle refractory indicated that the particles depositing at the nozzle orifice were already present in the melt because of deoxidation and reoxidation processes. A model proposed herein explains why and how the alumina particles deposit and stay at the nozzle orifice. The model considers a microscopically thin boundary layer at the nozzle bore where the velocity of the liquid steel approaches zero. Particles passing close to the refractory surface and in the slow-moving boundary layer attach to the wall and to each other. The presence of eddy currents in and close to the turbulent boundary layer increase the particle to particle collision. Such collisions of the particles thrown from outer region of boundary layers with the already attached particles keep on dumping the particles toward the refractory surface. The high interfacial energy of alumina inclusions in steel is a driving force for particles to attach to the refractory wall and to each other, and high-temperature sintering then occurs to form a network of alumina particles.

Lunar Magnetic Field Measurements, Electrical Conductivity Calculations and Thermal Profile Inferences

Steady magnetic field measurements of magnitude 30 to 100 γ on the lunar surface impose problems of interpretation when coupled with the non-detectability of a lunar field at 0.4 lunar radius altitude and the limb induced perturbations of the solar wind reported by Mihalov et al. at the Explorer orbit. The lunar time varying magnetic field clearly indicates the presence of eddy currents in the lunar interior and allows calculation of an electrical conductivity profile. The problem is complicated by the day-night asymmetry of the Moon's electromagnetic environment, the possible presence of the TM mode and the variable wave directions of the driving function. The electrical conductivity is calculated to be low near the surface, rising to a peak of 6 × 10−3Ω−1 m−1 at 250 km, dropping steeply inwards to a value of about 10−5Ω−1 m−1, and then rising toward the interior. A transition at 250 km depth from a high conductivity to a low conductivity material is inferred, suggesting an olivine-like core at approximately 800 °C, although other models are possible.

Analysis of Self-Saturating Magnetic Amplifier in the Presence of Eddy Currents

Analysis of Self-Saturating Magnetic Amplifier in the Presence of Eddy Currents