Papers by Keyword: Electromagnetic Wave Absorber

Abstract: The titanite-based ceramics with nominal composition CaTi_1-xM_ySiO₅ (0≦x≦1, M = Mn, Sn, Zr (y = x), and M = Nb (y = 4x/5)) in which part x of Ti sites are replaced by several kinds of atoms had remarkable increase in both the real and imaginary parts of complex relative permittivity around x = 0.0125~0.1 compared with those of pure titanite CaTiSiO₅ ( x = 0) at 70 GHz. Real part varied from 3 to 43, and the imaginary part from 0 to 12 (tangent delta from 0 to 0.28). No reflection condition is fulfilled for M = Zr when x = 0.05, d/λ₀ =0.042, and for M = Nb in both cases when 0 < x < 0.0125, d/λ₀ = 0.05 and 0.1 <x < 0.2, d/λ₀ =0.042, where d is thickness of the plate sample and λ₀ is the wavelength of incident electromagnetic wave. The dominant dielectric dispersion may occur due to difference of ionic polarization between Ti⁴⁺ ions and Mn⁴⁺, Sn⁴⁺, Zr⁴⁺, or Nb⁵⁺ ions relative to O^2- ions, which becomes inactive and saturates around x = 0.0125~0.05. From the measurement of the lattice parameters, a, b, c, and the angle β, characterizing monoclinic crystal structure, this saturation may have close correlation with some structural rearrangement of constituting atoms, Ti and substituted M atoms in CaTi_1-xM_ySiO₅

Abstract: The purpose of this research is to observe the influence of carbon from rice husk charcoal composition at Unsaturated Polyester Resin/Carbon (UPR/C) composite as electromagnetic wave absorber. In this research, carbon has been synthesized from rice husk charcoal. Characterization with SEM-EDX and FT-IR showed that the carbon consists of C, O, and Si atoms. Characterization with XRD showed that carbon from rice husk charcoal is amorf with the maximum value of 2θ is 22,86^o, respectively. Carbon from rice husk charcoal then is used as a composite filler with UPR as the composite matrix with ratio filler/matrix such as 5:95; 10:90; 15:85; 20:80 and 25:75 (%w/w). Characterization with VNA is done at the frequency range of 8-12 GHz. It has been found that the composite which contains filler carbon 20% exhibits optimum reflection loss of peaks with-19,5909 dB at 10.60 GHz. The result showed that inside UPR/C composite can be used as an electromagnetic wave absorber.

Abstract: We have investigated of composite (1-x)Ba_0.5Sr_0.5Fe_11.7Mn_0.15Ti_0.15 / xLa_0.7Ba_0.3MnO₃ by conventional ceramic method. The sturcture of composite and complex impedance are carried out by XRD, SEM and Impedance Spectroscopy. With changing the weight ratio from x=0; 0.3; 0.5 and x=1 the phase exhibit the composite behavior. Very interestingly, for the case of the case of weight ratio x=0.5 and 0.7 showed the complex impedance with xemicircle pattern in frequency range from 1 KHz to 1 MHz.

Abstract: A low-cost composite electromagnetic wave absorber made of sendust dispersed in resin was developed that does not contain any rare metals. In this study, spherical sendust particles with average particle sizes of approximately 5 and 20 μm were dispersed in polystyrene resin at volume ratios in the range 2040 vol% to broaden the absorption frequency bandwidth at frequencies above 10 GHz. The optimal volume ratios of sendust with average particle sizes of approximately 5 and 20 μm were found to be approximately 30 and 35 vol%, respectively. Electromagnetic wave absorbers can be flexibly designed by controlling the volume ratio of spherical sendust particles in resin.

Abstract: Nd₅Fe₉₂B₃ alloy was induction-melted. The α-Fe compounded low content of Nd₂Fe₁₄B nanocomposites were prepared using a melt-spinning method, subsequent annealing treatment, and ball milling. The complex permittivity, permeability of composites was measured in the 0.5-18 GHz frequency range. The permeability spectra exhibits relaxation type characteristic. The α-Fe/Nd₂Fe₁₄B composites shows an excellent microwave absorption property (reflection loss: RL<-20dB) in 9-17GHz with thin matching thickness 1.6-2.5 mm, due to the cooperate effect of magnetic loss and dielectric loss. α-Fe/Nd₂Fe₁₄B nanocomposites are thought to be a good microwave absorbers in GHz microwave range.

Abstract: In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability μ_r^*, the relative complex permittivity ε_r^*, and return loss were investigated for a composite made of Ni-Zn ferrite and SiO₂. When ferrite particles were dispersed and isolated in an SiO₂ medium, the frequency dependence of μ_r^* was different from that for a composite made of SiO₂ particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO₂ was selected, the return loss was less than −20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO₂ particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO₂ medium.

Abstract: To design an electromagnetic wave absorber with good absorption properties at frequencies above 1 GHz, the frequency dependences of the relative complex permeability μr*, the relative complex permittivity εr*, and return loss were investigated for the composite made of both sendust (an alloy of Al 5%, Si 10%, and Fe 85%) and aluminum particles dispersed in polystyrene resin. It was found that the frequency dependence of μr* for this composite can be changed by adjusting the particle size of aluminum and the volume mixture ratio of sendust and aluminum. Therefore, a flexible design of an absorber with good absorption characteristics was proposed based on the ability to control μr*. The composite made of both sendust and aluminum was found to exhibit a return loss of less than −20 dB in the frequency range of not only several GHz but also around 20 GHz if appropriate volume mixture ratio and particle size were selected.