Naim Derebasi

Interlaminar Flux Density Distribution at Joints of Overlapping Stacked Electrical Steel and Amorphous Ribbons

The design of joints in a transformer core significantly affects the transformer’s efficiency. Air gaps cause variations in the flux distribution at the joints of the laminations, which depend on the geometry. Two similar samples consisting of electrical steel strips and amorphous ribbons were made. The spatial flux distributions were determined using an array of search coils for each sample. 2D models of these samples were created and examined by finite element analysis. The magnetic flux distribution for each lamination in the samples was computed. The results show that the flux density in amorphous ribbons above and below the air gap starts to approach saturation at lower flux density levels than for electrical steel. The flux density measured using the search coil under the air gap is increased in amorphous ribbons and decreased in the electrical steel with increasing frequency.

Giant Magneto–Impedance Effect in Thin Zinc Oxide Coated on Co-Based (2705 X) Amorphous Ribbons

ZnO film coated Co-based (2705 X) amorphous ribbons are prepared by the successive ionic layer adsorption and reaction technique. The influence of coating on giant magneto-impedance (GMI) has been investigated over a frequency range from 0.1 to 3.5 MHz and under a static magnetic field between -8 and +8 kA/m. The highest GMI ratio of 15.63% was obtained in the coated Co-based amorphous ribbons which is 80% higher than the sample without coating. The results indicate that the surface coating process plays an important role in the GMI effect.

Prediction of dynamic hysteresis loops of nano-crystalline cores

Dynamic hysteresis loops of a range of nano-crystalline cores have been obtained over a wide frequency range (1-50kHz). A dynamic hysteresis model from measurements using an artificial neural network trained by the delta-bar-delta learning algorithm has been developed. The input parameters include the geometrical dimensions of cores, peak magnetic induction and magnetizing frequency. The results show the neural network model has an acceptable estimation capability for dynamic hysteresis loops of toroidal nano-crystalline cores.

Localized Flux Density Distribution Around a Hole in Non-Oriented Electrical Steels

A mechanical strain occurring during the drilling or punching of a hole on electrical sheets will cause deterioration of the magnetic characteristics around the hole. The result is that, when the sheet is magnetized parallel to the edge, the magnetic flux density has changed its orientation around the hole. In this paper, variation of localized flux density distribution around a hole was investigated from the search coils located at 0°, 25°, 45°, and 65° angles corresponding to the center of holes with diameters 10 and 20 mm in non-oriented electrical steel sheet with the dimensions of 300 mm length, 30 mm wide, and 0.50 mm thick standard sample. The localized peak flux density and magnetic field strength were measured over the peak flux density ranges 0.1-0.5 T at 50-400 Hz. A minimum peak flux density was obtained from the search coil, which is located at 65°, whereas maximum flux density was measured from the coil located at 0° angle.

Influence of Geometrical Factors on Performance of Thermoelectric Material Using Numerical Methods

Prediction of the performance of thermoelectric cooling material (figure of merit, ZT) was carried out by simulated results obtained from the finite element method (FEM) as a training dataset with an artificial neural network. A total of 87 input vectors for the ZT obtained from the four thermoelectric cooling (TEC) modules modeled using the FEM analysis were available in the training set to a back-propagation artificial neural network. An average correlation and maximum prediction error were found to be 100% and 0.01%, respectively, for the ZT after training. The standard deviation of the values was 0.05%. A set of test data, different from the training dataset was used to investigate the network performance. The average correlation and maximum prediction error were found to be 99.92% and 0.07%, respectively, for the tested TEC module. A thermoelectric module produced based on the numerical results was shown to be a promising device for use in cooling systems.

Performance of Novel Thermoelectric Cooling Module Depending on Geometrical Factors

A geometrical shape factor was investigated for optimum thermoelectric performance of a thermoelectric module using finite element analysis. The cooling power, electrical energy consumption, and coefficient of performance were analyzed using simulation with different current values passing through the thermoelectric elements for varying temperature differences between the two sides. A dramatic increase in cooling power density was obtained, since it was inversely proportional to the length of the thermoelectric legs. An artificial neural network model for each thermoelectric property was also developed using input–output relations. The models including the shape factor showed good predictive capability and agreement with simulation results. The correlation of the models was found to be 99%, and the overall prediction error was in the range of 1.5% and 1.0%, which is within acceptable limits. A thermoelectric module was produced based on the numerical results and was shown to be a promising device for use in cooling systems.

Dynamic hysteresis modelling for nano-crystalline cores

This paper presents an artificial neural network approach based on dynamic Preisach model to compute hysteresis loops of nano-crystalline cores. The network has been trained by a Levenberg-Marquardt learning algorithm. The model is fast and does not require tremendous computational efforts. The results obtained by using the proposed model are in good agreement with experimental results.

Large gyromagnetic effect in as-cast and post-production treated amorphous wires

Abstract The large gyromagnetic effect (LGE) in highly positive magnetostrictive Fe 77.5 Si 7.5 B 15 amorphous as-cast, furnace annealed with and without axial tension, current annealed, and transverse field annealed wires was investigated. A slight decrease in the rotation frequency of the LGE was observed in the annealed samples. Results on the influence of a localised dc bias field on the LGE of as-cast and furnace annealed samples are reported for the first time. The localised dc bias field applied along the length of the wires significantly influences both frequency and direction of the wires’ rotation.

Influence of oxide layer coating on giant magneto-impedance response in amorphous ribbons

Cobalt-rich amorphous ribbon (Fe5.85Co72.15Mo2B15Si5) 13 mm in length and 5 mm in width were coated with different oxide layers in order to improve their GMI response. The coating process was performed using a chemical Successive Ionic Layer Adsorption and Reaction (SILAR) technique at room temperature. Oxide layer coated ribbons were imaged by an Atomic Force Microscopy (AFM). The variations in oxide layers and their roughness were studied to elucidate the cause of the improvements in GMI ratios in amorphous ribbons.

The Asphaltene Coating Effect on GMI Response in Fe4.3Co68.2Si12.5B15 Amorphous Microwires

The asphaltene was extracted from asphalt cement with penetration grade 60, which is extracted from crude Libya petroleum. The asphalt cement was taken from Tüpraş Refinery in Izmit-Turkey. The asphalt cement was dissolved in 10 times excess volume of benzene, precipitated in a further 10 times excess volume of petroleum ether with a boiling range of 40–60°C (i.e., 1 part asphalt cement, 10 parts benzene, and 100 parts petroleum ether). The resultant precipitate was collected by filtration and dried. The asphaltene so obtained was dark brown semi-solids. The percentage of asphaltene in the asphalt cement was 30% by weight. Fe4.3Co68.2Si12.5B15 amorphous microwires, with a diameter of 120 μm and 12 cm long, were coated with these paramagnetic asphaltene molecules. The giant magneto-impedance effect was experimentally measured on uncoated and asphaltene coated Co-rich amorphous wires. In the asphaltene coated sample, a very high value of the giant magneto-impedance effect ratio up to 42% was achieved at 4.0 MHz. As far as is known, such a giant magneto-impedance enhancement is reported for the first time by an asphaltene coating process.