Preparation of Spinel and Garnet Ferrites and Identification of Their Magnetic-Energy Losses

The objective of this work was to explain the magnetic-energy loss mechanisms of some magnetic materials. The study was divided into three parts., The first part involved fabrication of NiZn-based and YIG ferrites in toroidal and pellet form, employing ceramic processing technique of the starting oxides. Characterisation of chemical, microstructural, magnetic, electrical, mechanical and thermal properties were carried out. In the second part, sol-gel method was employed to obtain high quality and fine-grained microstucture. The Y3FeS012 and NiFe204 samples were fabricated using this technique. The third part dealt with some preliminary studies on the magneto-optical Kerr effect, which were carried out on the NiFe204 and YSFeS012 samples. The characterisation of samples in the first part was divided mainly into two parts: the extrinsic-microstructure properties and the intrinsic-composition properties. The results showed that the initial permeability, relative loss factor, impedance, power loss, quality factor, saturation induction, core loss, coercive force, curie temperature and temperature coefficient of the sintered samples depended chiefly on both the microstructure and the composition of the samples. Adopting ZnO, which acted as a modifier, in the NiZn ferrite series (first premise) had greatly influenced the magnetic properties of the samples, as occurrence of Zn loss was a major factor that affected the grain growth kinetics. Adopting an iron-deficit composition (second series) was fruitful when high density and wide operating frequencies were required in the NiZn ferrite composition. Samples with excess Fe203 (third series) were deleterious in terms of losses due to the formation of Fe2+. There was no significant contribution of the zero magnetostriction affecting the magnetic and electrical properties that was concluded from this premise. CoO was seen to affect the growth anisotropy in the rich NiO content (fourth premise) and thus affected the microstructure of the samples. Interesting, however, was sample with composition Nio.8Zno.2Fe204 that gave very homogeneous and moderate grain size (:::::10.9 flm) exhibited large -KJ , played a dominant role in the frequency extension. Evidence by the reduced permeability, it was believed that the damping of domain wall was restricted by the anisotropy effects. Simultaneously, the relative loss factor was significantly reduced at higher frequencies. In the fifth premise where both C0 2 + and Fe 2 + were adopted in the excess non NiZn based composition, the C02+ content was believed to stabilise the domain wall movement at high frequencies. When a small concentration of cobalt with the formula Nio.70COO.0191sZno.27S8SFe2.00S04.00S was adopted, a vast decrease of power loss was seen to occur. It was speculated that C02+ ions diffused or moved through the vacancies and hence caused them to reside in the vacancies created by the slight iron excess. This reduced the stress and strain created by them and as a result, power loss was reduced significantly. In the second part of this work, high quality and fine grained single-phase ferrite (-0.9 Ilm) was obtained by using the sol-gel technique. Finally, Kerr rotation (Nl deg) was observed for both the NiFe204 and Y3Fes012 samples. Kerr rotation was accompanied by optical energy reflection . This was actually a measure of energy reflected when ferromagnetic order exists. This shed new light in the area of magnetooptic

Development of Low-Loss Nizn-Based Ferrite Materials for High-Frequency Applications

This work is an initial response to the demand for miniaturisation of electronic circuits and the shift to higher operating frequencies which has led to the development of high-density low-loss ferrites. In order to meet this demand, a number of necessities, such as fine-grained and homogeneous microstructure, low power loss, weak temperature dependencies of losses and of course reasonable cost of production are required. The first part of the work was to develop the required material by manipulation of composition. NiZn-based ferrites with various additives such as MgO, CuO, TiCh, CoO and CaO were chosen and the low loss property was attained. Subsequently, a systematic crucial approach was started to further minimise the losses and to extend the operating frequency range. Green compacts with a particle size average (PSA) of 1.2um, a sintering temperature of about 1140°C and only air atmosphere were needed to reach the research targets. In conclusion, a composition-microstructure design technique has been successfully developed, which is capable of producing ferrite materials with the desired magnetic properties

High saturation induction for Bi-substituted yttrium iron garnet prepared via sol gel technique

Y3.0-xBixFe5O12 samples (x = 0.2 and 0.4) were prepared via novel sol-gel and conventional solid-state techniques. The effect of bismuth in both techniques was investigated in terms of shrinkage,density, hysteresis and initial permeability. Sharp and clear diffraction XRD lines with highest peak appear at about 32° of the 2θ, for all the powders sintered at 900°C and 1250°C for both techniques. In evaluating the magnetic properties, it was observed that the saturation induction (1.1902kG) of sample prepared via sol-gel technique (Y2.8Bi0.2Fe5O12) is more than 200% higher than sample with the same formula prepared via conventional technique. Fine grained microstructure with average grain size of about 5μ m and higher shrinkage, about 11% were observed from the samples prepared via sol gel technique. It is concluded that samples prepared via sol gel technique appear to be an attractive route due to the possible reduction of cost of production and the enhanced magnetic and structural properties of the sample

Observation of cotton-like bismuth oxide (β-Bi2O2.5) prepared via pulsed laser ablation deposition

Monoclinic bismuth oxide (α-Bi2O3) nanoparticles were prepared via precipitation method and irradiated with a pulsed laser forming thin films. Their phase and surface morphological properties were investigated using x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The XRD analysis shows the phase transformation to a partially crystalline tetragonal phase β-Bi2O3 thin film. The SEM micrograph of the nanoparticles, with an average crystal size of 72 nm, was seen to form a thin film with a peculiar structure, coined as “cotton-likeâ€�, is attributed to the high surface energy absorbed by the nanoparticles during ablation. The HR-TEM micrograph shows the particulate with a clearly defined interlayer spacing

Carbon nanopipe catalysed by as-prepared NiO nanoparticles

Carbon nanopipes catalyzed by high purity nickel oxide (NiO) nanoparticles were reported. The nanocrystals catalysts were first prepared using precipitation technique and characterized using x-ray diffraction (XRD), energy dispersive x-ray (EDX) and scanning electron microscopy (SEM) and subsequently used as catalyst for the formation of nanotubes. Pure phase, rhombohedral nickel oxide formation was identified from the XRD data, with the major peak located at 43.29o of the 2θ degree corresponding to a (202) plane. A pulsed laser ablation deposition technique (PLAD) was used to produce the CNTs. From the SEM micrograph, deposited CNTs shows a web-like structure, while the HR-TEM reveals carbon nanopipes with a length of 10 micron and diameter of 430 nm, suggesting that the nanocrystals aggregate and forms bigger cluster consequence of the ablation process

Modeling of Antenna for Deep Target Hydrocarbon Exploration

Nowadays control source electromagnetic method is used for offshore hydrocarbon exploration. Hydrocarbon detection in sea bed logging (SBL) is a very challenging task for deep target hydrocarbon reservoir. Response of electromagnetic (EM) field from marine environment is very low and it is very difficult to predict deep target reservoir below 2km from the sea floor. This work premise deals with modeling of new antenna for deep water deep target hydrocarbon exploration. Conventional and new EM antennas at 0.125Hz frequency are used in modeling for the detection of deep target hydrocarbon  reservoir.  The  proposed  area  of  the  seabed model   (40km ´ 40km)   was   simulated   by using CST (computer simulation technology) EM studio based on Finite Integration Method (FIM). Electromagnetic field components were compared at 500m target depth and it was concluded that Ex and Hz components shows better resistivity contrast. Comparison of conventional and new antenna for different target  depths  was  done in  our  proposed  model.  From  the results, it was observed that conventional antenna at 0.125Hz shows 70% ,86% resistivity contrast at target depth of 1000m where   as   new   antenna   showed   329%, 355%   resistivity contrast at the same target depth for Ex and Hz field respectively.  It  was  also  investigated  that  at  frequency of0.125Hz, new antenna gave 46% better delineation of hydrocarbon at 4000m target depth. This is due to focusing of electromagnetic waves by using new antenna. New antenna design gave 125% more extra depth than straight antenna for deep target hydrocarbon detection. Numerical modeling for straight  and  new antenna  was also done to know general equation for electromagnetic field behavior with target depth. From this numerical model it was speculated that this new antenna can detect up to 4.5 km target depth. This new EM antenna may open new frontiers for oil and gas industry for the detection of deep target hydrocarbon reservoir (HC

Multi-Layer Perceptron Neural Network for Air Wave Estimation in Marine Control Source Electromagnetic Data

Marine Control Source Electro-Magnetic (MCSEM) survey is a technique for remote identification of sub-sea floor structures of the earth's interior using Electro-Magnetic (EM) signals. Air wave signal is major problem associated with the data recorded by this technique in shallow water environment. The air wave signals are parts of the EM signals that propagate from EM source via the atmosphere and induced along air/sea surface. These air wave signals has the ability to limit and mask the electromagnetic response of a subsurface resistive body so that signals from subsurface, possibly containing valuable information about a resistive hydrocarbon reservoir is hardly distinguishable. This paper presents the application of a feed forward multi-layer perceptron neural networks model for estimation of air waves in MCSEM survey data based on offset and sea water depth values. The proposed model has 3 hidden layers with sigmoid activation function, an output layer with purelin transfer function and Levenberg-Marquardt (trainlm) as the training function. Simulated airwave data for ten sea water depths from 1000m to 100m at interval of 100m were used as the training data. Coefficient of multiple determination and Mean Square Error (MSE) obtained from the multi-layer perceptron model and the estimation with multiple linear regression model are compared. Preliminary results demonstrate that multi-layer perceptron neural networks are a viable technique for the estimation of air waves in MCSEM data

Multiple zones surveillance system using RFID

Monitoring and tracking the activities of individuals (or objects) in multiple zones or areas simultaneously is quite a challenging task. It is a very common practice to use observation cameras or to have security personnel to guard the specified areas. However, area surveillances using these common methods may become tedious when the activities to watch out for increases. More cameras as well as manpower are needed to cater for the increment of activities for each zone. On top of that, should anyone (or objects) vacates or trespasses the designated areas, it would take some time to identify them, hence resulting complexity in tracing their whereabouts. To overcome these challenges, we propose a surveillance system for multiple zones using RFID technology. Individuals or objects to be monitored are tagged using RFID tags that hold unique identification. Each zone is allocated with one RFID reader, which will transmit the information of activities of the respective zones to the host computer in the control room. The security personnel in the control room would be able to identify which individual or objects that are out of their designated zones or trespassing to another zone based on the tags that has been detected by the reader. Should the tags are removed without authorization, alarm will be generated. Every activity transactions are recorded in a database for future references or actions. A case study of inmate tracking system is conducted and demonstrated to prove the capability of the proposed method

Electromagnetic properties of polytetrafluoroethylene at microwave frequencies using finite element modeling waveguide adapter

Experimental and theoretical approaches were shown great potential to determine electromagnetic properties of dielectric materials at microwave frequencies. In this study, the application of Finite Element Modeling (FEM) of waveguide adapter was utilized to investigate the distribution of electric and magnetic fields intensity of Polytetrafluoroethylene (PTFE) as dielectric sample. Essentially, the electric and magnetic fields intensity in various regions of waveguide were obtained. The computations of the reflection and transmission coefficients of dielectric sample were determined by implementation of Finite Element Methods and Nicolson-Rose-Wire (NRW) method as well. The results were compared with the experimental achievement results using the waveguide adapter in conjunction with a Vector Network Analyzer (VNA) at Microwave frequencies. The general observation indicate that, the level of transmission was greater than reflection for PTFE as dielectric material sample. Furthermore, among the two applied methods, the FEM is more accurate than the NRW method

An optimisation approch to determine the electromagnetic properties of lanthanum iron garnet filled PVDF-polymer composite at microwave frequencies

In this study, an optimization approach is shown to improve the accuracy of the Nicholson and Ross Weir (NRW) method to determine both the complex permittivity and permeability of the lanthanum iron garnet-filled PVDF-polymer nanocomposite loaded in a rectangular waveguide. The complex permittivity and permeability values were in turn used in Finite Element Method to calculate the S-parameter and were found to be in good agreement with the measured values