Papers by Keyword: Microwave Absorber

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Authors: Katsuyoshi Hotta, Hiroyuki Shimizu, Y. Watanabe, Haruo Hirose
Abstract: The purpose of this study is to examine the basic characteristics of the single layer type microwave absorber in X band. Samples were produced from Bi system (2223) superconductor powder and metallic powder and inserted into a wave guide system where the complex reflection intensity was measured (The short circuit method) by using the vector network analyzer[1]. As the result, at the room temperature (300K), the reflection loss is apt to increase with increasing the content of the Bi system superconductor powder. Furthermore, the measured value of the reflection loss agreed with the value calculated from the complex permittivity εr* . At liquid nitrogen temperature (77K) where the superconductor powders are in the superconducting state, some differences occurred between the calculated value and the measured one of the reflection loss. For the metallic powders, copper powder showed good agreement between the calculated and the measured of reflection loss. For the magnetic material, it was concluded that the theoretical formula under consideration of complex permeability μr* should be derivated.
Authors: Hasnain Abdullah, Asmalia Zanal, Mohamad Hakim Ahya Ilmudin, Mohd Nasir Taib, Juliana Md Sharif, Mohamad Khairul Nizam Malek, Rohaiza Baharudin, Ida Rahayu Mohamed Noordin, Ahmad Rashidy Razali
Abstract: Radiation Absorbing Material (RAM) is used to absorb radiations of electromagnetic wave surrounding us. Thus, the multiple layers’ microwave absorber using biomass composite materials could be one of the solutions to address the problem. In order to effectively absorb the radiation of electromagnetic wave, the multiple layers’ absorber is characterized to optimize the performance of the absorber. The characterization is made by varying biomass composite material contents, thickness and other possible considerations. CST Microwave Studio software is first used to design and simulate the multiple layers’ absorber to estimate its performance. Development of multiple layers’ prototype is carried out to test its performance at free space environment. Free space dielectric measurement method is used to determine the value of multiple layers’ absorber dielectric. The dielectric value is then used in CST software in order to make the simulation more precise. Free space arch which is connected to Agilent Analyzer is used to measure absorption of multiple layers’ microwave absorber.
Authors: Jin Bong Kim, Sang Kwan Lee, Chun Gon Kim
Abstract: In this paper, we have studied the permittivities of E-glass fabric/epoxy composite laminates containing three different types of carbon-based nano conductive fillers such as carbon black (CB), carbon nano fiber (CNF) and multi-wall carbon nano tube (MWNT). The measurements were performed for permittivities at the frequency band of 0.5 GHz ~ 18.0 GHz using a vector network analyzer with a 7 mm coaxial air line. The experimental results show that the complex permittivities of the composites depend strongly on the natures and concentrations of the conductive fillers. The real and imaginary parts of the complex permittivities of the composites were proportional to the filler concentrations. But, depending on the types of fillers and frequency band, the increasing rates of the real and imaginary parts with respect to the filler concentrations were all different. At the frequency of 10 GHz, the rates in the CNF filled composite and the MWNT filled composite were much larger then those of the CB filled composite. Between the CNF filled composite and MWNT filled composite, however, the former showed a little higher increasing rates than the other. These different rates can have great effect on the thickness in designing the single layer microwave absorbers. The effect of the different rates was examined by using Cole-Cole plots; the plot is composed of a single layer absorber solution line and permittivity lines of these three types of composites.
Authors: Erfan Handoko, Iwan Sugihartono, Mangasi Alion Marpaung, Maulana Randa, Mudrik Alaydrus, Nofrijon Sofyan
Abstract: Microwave absorption characteristics of double layer of barium hexaferrite attached on the silica to from a composite on the basis of wave propagation theory have been investigated. Barium hexaferrite, BaFe12O19, was synthesized through ceramic method from stoichiometric mixtures of BaCO3 and Fe2O3 as precursors. The mixture was pelletized under the pressure of 10 MPa and sintered at 1100 °C for 5 hours. Silica in the forms of powder was purified by using HCl. The crystal structure of the samples was characterized using X-ray diffraction (XRD), microstructure was examined using scanning electron microscope (SEM), hysteresis curves recorded by PERMAGRAPH techniques, whereas the microwave absorbing properties for X-band was recorded using a vector network analyzer (VNA). Relative complex permeability and permittivity, and reflection loss values were calculated at given thickness according to transmittance line theory within the range 8.2–12.4 GHz. Based on this study, the layer dimension and frequency that results in low reflection loss can be estimated from the material properties of the barium hexaferrite/silica composite material.
Authors: M.L. Gregori, M.S Pinho, R.C. Lima, J.C.S. Leandro, Tsuneharu Ogasawara
Authors: Syarifah Nor Faizah Syed Abdul Rahman, Norazah Abdul Rahman, Siti Shawalliah Idris, Noor Fitrah Abu Bakar, Roslan Mokhtar, Zakiuddin Januri, Muhammad Fareezuddin Mohamad Khalil
Abstract: Application of microwave absorber (MWA) does affect the yield of microwave pyrolysis process. In this study, activated carbon and graphite have been used as microwave absorbers and the results were then compared with the microwave pyrolysis process without microwave absorber. The yield of solid and liquid increased while the yield of gas decreased with the application of MWA. Chemical functional group inside MWA also affected by the microwave pyrolysis process and energy content of MWA slightly increased from 24.54 MJ/kg to 29.57 MJ/kg and 32.17 MJ/kg to 32.24 MJ/kg for activated carbon and graphite, respectively.
Authors: Hui Bin Zhang, Li Wei Deng, Nan Zhang, Pei Heng Zhou, Jian Liang Xie, Long Jiang Deng
Abstract: We simulate, fabricate and measure a microwave absorber by introducing metamaterial design method to magnetic material. The proposed absorber is composed of periodic copper wire array, magnetic material coated on copper wires, a foam substrate and a bottom metal plane. The results show a nearly perfect absorption peak around 8.7GHz (simulated) and 7.6GHz (measured). Even though the electric and magnetic field distribution indicate that the absorption is a typical metamaterial absorption, the power loss is neither Ohmic nor dielectric loss but magnetic loss, which is different from typical metamaterial absorber. The skillful introduction of the magnetic loss improves the absorption performance, including the absorption bandwidth and intensity. The designed absorber shows an effective application of the magnetic material, which is only 1/60000 volume proportion of the total absorber. Dependences of the absorption on frequency and the coating volume of the magnetic material manifest that the coated magnetic material can adjust the absorption peak position and intensity. The absorber can be an attractive candidate of electromagnetic wave absorber.
Authors: Endyas Pratitajati, Azwar Manaf
Abstract: Perovskite lanthanum manganites, especially those doped LaMnO3 (LMO), have shown potentials for applications in magnetic electronic functional materials. Partial substitution of La ion with divalent ions or Mn ion with trivalent ions gives rise to new properties. Substituted LMO has ability for absorbing electromagnetic waves. In this paper, we report recent investigations on substituted LaMnO3 with designated La(1-x)BaxFe0.25Mn0.5Ti0.25O3 (x= 0, 0.25, 0.75, 1) compositions. Materials were prepared by mechanical alloying technique. After heat treatments at sintering temperatures 1100°C, 1200°C and 1300°C to the quasi-crystalline powders, presence of material phases were confirmed by XRD. Single phase material was obtained in samples of 0.25 x < 0.75 compositions. Mean crystallite size of sintered materials showed that crystallites were in a nanocrystalline regime. It is then concluded, during mechanically alloyed sintering powder materials, solid-state reaction and crystallisation promoted formation of particles containing nanocrystallites. Microwave absorption data showed that materials with large amount of substituted Ba ion gives broad absorption profiles. Total substitution of La by Ba ions (x=1) has significantly changed absorption profile. Smaller mean crystallite sizes indicated an increase in reflection loss value. In this report, empirical relationship between nanostructure and absorption profile of material is discussed.
Authors: Wisnu Ari Adi, A. Manaf
Abstract: The synthesis and characterization of the magnetic materials of La0.8Ba0.2Mn (1-x)TixO3 system (x = 0 0.7) by mechanical alloying process have been performed. This magnetic material is prepared by oxides, namely La2O3, BaCO3, MnCO3 and TiO2. The mixture was milled for 10 h and then sintered at 1000 ° C for 10 h. The refinement results of x-ray diffraction pattern showed that the doping concentration (x < 0.5) was a single phase, which has a structure monoclinic (I12/a1) with lattice parameters a = 5.5169(5) Å, b = 5.5437(5) Å and c = 7.8553(7) Å, = 90o and 89.75(1) o, V = 240.25(4) Å3 and 6.345 The microstructure analysis showed that the particle shapes was polygonal with the varied particle sizes distributed homogeneously on the surface of the samples. We concluded that the maximum number of titanium atoms substituting manganese atom is around x ~ 0.43 without changing the structure of this system.
Authors: Hasnain Abdullah, Asmalia Zanal, Mohd Nasir Taib, Ida Rahayu Mohamed Noordin, Wan Khairuddin bin Wan Ali, Rusnani Ariffin, Samihah Abdullah, Rohaiza Baharudin, Ahmad Takiyuddin Abdullah
Abstract: The most important part to be highlighted in developing a reliable microwave absorber is the material used to fabricate the absorber. As an alternative in managing the increase of the oil palm residues throughout the country, this study is focusing on developing a microwave absorber coating using oil palm fly ash. The software uses for design and simulation of microwave absorber is CST Microwave Studio (CST MWS) which enables the fast and accurate analysis of high frequency devices. The simulation design is fabricated to a number of layers which is coated by oil palm ash as a lossy element. The measurement and performance are carried out in the high broadband frequency of 8 to 12 GHz (X-band).
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