Kajian Terhadap Prestasi Penumpas EMI Ferit Mg-Zn dan Ni-Zn Pada Frekuensi Radio

Gangguan elektromagnet (EMI) merupakan salah satu daripada pencemaran gelombang yang mengganggu alat-alat elektronik untuk berfungsi dengan baik. Bahan penyerap gelombang EMI diperlukan untuk menyerap gangguan gelombang yang terhasil. Ferit merupakan bahan yang sangat baik dan sesuai untuk digunakan sebagai penyerap gangguan EMI. Projek yang telah dilakukan ini telah mengkaji kesan penggunaan komposisi ferit yang berbeza berasaskan kepada Ni-Zn dan Mg-Zn terhadap sifat penyerapan bahan menggunakan sampel berbentuk toroid. Pemilihan komposisi tersebut adalah bertujuan untuk mendapatkan pelebaran jalur impedans dengan nilai impedans yang tinggi pada julat frekuensi < 100 MHz. Penggunaan Mg-Zn ferit pula adalah untuk mengurangkan kos pembuatan kerana MgO adalah di antara bahan mentah yang paling murah. Sebanyak tiga set sampel telah disediakan dalam projek ini. Analisis bahan yang dilakukan adalah terhadap kesan ketakisotropan magnet, parameter-parameter histeresis, keliangan dan saiz butir, kerintangan elektrik dan sifat-sifat intrinsik yang lain serta faktor-faktor ekstrinsik yang boleh mempengaruhi tahap penyerapan gangguan gelombang (EMI). Sifat bahan yang terpenting sekali yang perlu diperhatikan adalah impedans yang magnitud dan ciri frekuensinya sangat penting dalam menghasilkan ciri bahan penyerap yang berkualiti dan mampu menyerap banyak gangguan pada frekuensi berbeza yang terhasil daripada penjanaan isyarat harmonik. Butir-butir yang diperolehi melalui projek ini mempunyai saiz yang keeil dan tidak seragam. Saiz butir yang sedemikian memaksa dinding domain menyerap lebih banyak tenaga untuk membebaskan diri daripada kesan terpin pada sempadan butir. lni menghasilkan kehilangan tenaga yang tinggi, iaitu nilai Z yang tinggi diperolehi. Seeara tidak langsung, sifat penumpasan yang baik telah dapat dihasilkan. Akhirnya, projek yang telah dijalankan ini telah berjaya mencapai objektif yang dikehendaki iaitu untuk mendapatkan nilai Z yang tinggi dengan menggunakan sampel set 1. Sampel-sampel S1, S2, S3 dan S4 didapati memiliki nilai impedans yang melebihi nilai impedans sampel rujukan D28 dalam julat frekuensi 1 MHz ke 150 MHz

Effects of Non-Stoichiometry on Magnetic Properties and Microstructure of Ni₀.₃Zn₀.₇Fe₂ ±ₓO₄ and Mg₀.₅Zn₀.₅Fe₂ ±ₓO₄

Various non-stoichiometric compositions of Ni-Zn ferrites and Mg-Zn ferrites were investigated. The samples were prepared by the conventional sintering method while being subjected to an air annospheric condition. The measurement of magnetic properties such as magnetic permeability, magnetic loss, Curie temperature, magnetic flux density and microstructure were performed to understand the magnetic properties of samples prepared by systematic compositional changes. X-ray diffraction results indicate that the samples are in good crystalline form. Curie temperature variation can be explained on the basis of Neel's two sub-lattices model and could be due to distribution of magnetic ions between two sub-lattices. The dependence of magnetic permeability with temperature shows that the trends exhibited by all the samples are similar. With increase in temperature, permeability increases gradually and then shows sudden drop at the Curie point because the anisotropy constant decreases more rapidly than the saturation magnetization. The dependence of permeability on iron oxide content obeys globus model. The change of permeability in the cation-deficient region is caused by the positive contribution of the anisotropy constant to the total anisotropy during conversion of Fe3+ ions to Fe2+ ions. However, for the anion-deficient region, the variation in permeability is mainly accounted to be due to microstructural changes. The loss factor and the quality factor were also calculated and this study has revealed that the iron oxide concentration is a determining factor for high quality ferrites. Finally, this study shows that high permeability values of Ni-Zn and Mg-Zn ferrites occur in the cation-deficient region with x = 0.002-0.006 weight percent

Milling time and BPR dependance on permeability and losses of Ni0.5Zn0.5Fe2O4 synthesized via mechanical alloying process.

Ni0.5Zn0.5Fe2O4 has been synthesized using mechanical alloying method with two variables (milling time and ball-to-powder weight ratio (BPR)) were varied in order to study its effect on the magnetic properties of the material. The effects of these two variables were studied using XRD, SEM, TEM and later by impedance analyzer with the frequency range from 1 MHz to 1.8 GHz. The results obtained however show that there are no significant trends to relate the milling time and BPR with the permeability and losses of the material studied. After being sintered at 1150 °C, all the effects of alloying process seem to diminish

The effect of milling time on Ni0.5Zn0.5Fe2O4 compositional evolution and particle size distribution

Problem statement: This study involved an investigation to ascertain the diffusion of NiO and ZnO into the tetrahedral and octahedral sites using mechanical alloying method. The effect of mechanical alloying towards particle size was also reported. Approach: NiO, ZnO and Fe2O3 precursors were mechanically alloyed to synthesis ultrafine powders of Ni0.5Zn0.5Fe2O4. Various milling times were employed to study the effect of milling time on the materials. The ultrafine powder was sampled after each milling time and further characterized using XRD to investigate the phases of the powder and the crystallite size, SEM for the morphology and TEM for particle size investigation. Results: The XRD spectra indicated the precursors reacted during milling with the diffusion of ZnO and followed by NiO into their respective crystallographic sites. SEM micrographs showed the agglomeration of powders due to high energy milling and TEM images proved the particles of the materials were of nanosize. Conclusion: It was concluded that samples prepared using mechanical alloying technique appear to be a potential method for large production due to the possible reduction of cost and also reduction of particle size against milling time