Real Part Of Relative Permittivity Research Articles

Surfactant assisted tuning of electrical conductivity, electromagnetic interference shielding effectiveness, wetting properties of poly(lactic acid)-expanded graphite-magnetite nanocube hybrid bio-nanocomposites

The study aimed at demonstrating polyvinylpyrrolidone (PVP) amount is critical for tuning electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of poly(lactic acid)-expanded graphite (ExGr)-magnetite (Fe3O4) nanocube hybrid nanocomposites. An optimum loading of PVP (1 wt.%) was found to disperse the nanofillers resulting in enhanced electrical conductivity and EMI SE in the X-band dominated by the absorption mechanism. The electrical conductivity enhancement in hybrid nanocomposites was not only attributed to the network formation between fillers but also to the thickness of the coated surfactant layer. The inter-junction capacitance and real part of relative permittivity of the hybrid nanocomposites were also enhanced at 1 wt.% PVP addition in comparison to 0 wt.% and 2 wt.% surfactant loading. The water contact angle was found to depend on the surface roughness of the film, which varied with both PVP and ExGr loadings. These PLA-based hybrid nanocomposites can be used as microwave-absorbing material.

Hyperfine Structure of Regolith Unveiled by Chang’E-5 Lunar Regolith Penetrating Radar

This work presents the results of the Lunar Regolith Penetrating Radar (LRPR), installed at the bottom of the Chang’E-5 (CE-5) lander, which is the first antenna-array radar deployed for the investigation of an extraterrestrial body. Radar imaging results unveiled a hyperfine structure for the top 2.5-m-thick lunar regolith with an unprecedented high resolution of 5 cm. The interpretation of the results permitted to state that subsurface regolith is dominated by fine grains with abundant rock fragments. The radar imaging results were also used to drive the drilling process until a fragment jammed the core inlet at about 100-cm underground. Laboratory measurements of the samples returned at Earth allow to estimate the real part of relative permittivity and the loss tangent, which are 3.04 ± 0.02 and 0.014 ± 0.002, respectively.

Impact of Filled Materials on the Heating Uniformity and Safety of Microwave Heating Solid Stack Materials

Microwave heating of solid stack materials is common but bothered by problems of uneven heating and electric discharge phenomena. In this paper, a method introducing fluid materials with different relative permittivity is proposed to improve the heating uniformity and safety of solid stack materials. Simulations have been computed based on the finite element method (FEM) and validated by experiments. Simulation results show that the introducing of fluid materials with proper relative permittivity does improve the heating uniformity and safety. Fluid materials with the larger real part of relative permittivity could obviously lower the maximum modulus value of the electric field for about 23 times, and will lower the coefficient of variation (COV) in general, although in small ranges that it has fluctuated. Fluid materials with the larger imaginary part of relative permittivity, in a range from 0 to 0.3, can make a more efficient heating and it could lower the maximum modulus value of the electric field by 34 to 55% on the whole studied range. However, the larger imaginary part of relative permittivity will cause worse heating uniformity as the COV rises by 246.9% in the same process. The computed results are discussed and methods to reach uniform and safe heating through introducing fluid materials with proper relative permittivity are proposed.

Compositionally controlled plasmonics in amorphous semiconductor metasurfaces.

Amorphous bismuth telluride (Bi:Te) provides a composition-dependent, CMOS-compatible alternative material platform for plasmonics in the ultraviolet-visible spectral range. Thin films of the chalcogenide semiconductor are found, using high-throughput physical vapor deposition and characterization techniques, to exhibit a plasmonic response (a negative value of the real part of relative permittivity) over a band of wavelengths extending from ~250 nm to between 530 and 978 nm, depending on alloy composition (Bi:Te at% ratio). The plasmonic response is illustrated via the fabrication of subwavelength period nano-grating metasurfaces, which present strong, period-dependent plasmonic absorption resonances in the visible range, manifested in the perceived color of the nanostructured domains in reflection.

Low temperature sintered magneto-dielectric ferrite ceramics with near net-shape derived from high-energy milled powders

Nanosized Ni0.70Zn0.25Co0.05Fe1.90Mn0.02O4 ferrite ceramics were fabricated from high-energy ball milled powder mixtures with various ratios of Fe2O3/Fe as starting materials, in order to achieve magneto-dielectric materials with near net shape behavior for practical applications. The ferrite ceramics were obtained by sintering the milled powder compacts at 800 °C for 4 h, with a linear expansion of less than 4% as compared to the green pellets. The ceramics had an average grain size of less than 200 nm. The real part of relative permittivity decreases with increasing percentage of Fe2O3 used in the starting mixtures. The sample from the powder mixture with 50% Fe2O3 exhibits promising magneto-dielectric properties at frequencies of up to 90 MHz, which can be used for miniaturization of antennas at very high frequency (VHF) band.

Investigation of dielectric constant variations for Malaysians soil species towards its natural background dose

The correlation of natural background gamma radiation and real part of the complex relative permittivity (dielectric constant) for various species Malaysian soils was investigated in this research. The sampling sites were chosen randomly according to soils groups that consist of sedentary, alluvial and miscellaneous soil which covered the area of Batu Pahat, Kluang and Johor Bahru, Johor state of Malaysia. There are 11 types of Malaysian soil species that have been studied; namely Peat, Linau-Sedu, Selangor-Kangkong, Kranji, Telemong-Akob-Local Alluvium, Holyrood-Lunas, Batu Anam-Melaka-Tavy, Harimau Tampoi, Kulai-Yong Peng, Rengam-Jerangau, and Steepland soils. In-situ exposure rates of each soil species were measured by using portable gamma survey meter and ex-situ analysis of real part of relative permittivity was performed by using DAK (Dielectric Assessment Kit assist by network analyser). Results revealed that the highest and the lowest background dose rate were 94 ± 26.28 μR hr−1 and 7 ± 0.67 μR hr−1 contributed by Rengam Jerangau and Peat soil species respectively. Meanwhile, dielectric constant measurement, it was performed in the range of frequency between 100 MHz to 3 GHz. The measurements of each soils species dielectric constant are in the range of 1 to 3. At the lower frequencies in the range of 100 MHz to 600 MHz, it was observed that the dielectric constant for each soil species fluctuated and inconsistent. But it remained consistent in plateau form of signal at higher frequency at range above 600 MHz. From the comparison of dielectric properties of each soil at above 600 MHz of frequency, it was found that Rengam-Jerangau soil species give the highest reading and followed by Selangor-Kangkong species. The average dielectric measurement for both Selangor-Kangkong and Rengam-Jerangau soil species are 2.34 and 2.35 respectively. Meanwhile, peat soil species exhibits the lowest dielectric measurement of 1.83. It can be clearly seen that the pattern of dielectric measurement for every soil at the frequency above 600 MHz demonstrated a specific distribution which can be classified into two main regions which are higher and lower between the ranges of 1.83 to 2.35. Pearson correlation analysis between the frequency of 100 MHz and 2.6 GHz with respect to exposure rate for every soil species was r = 0.38 and r = 0.51, respectively. This indicates that there was no strong correlation between both parameter, natural background dose and soils dielectric for each soils sample. This factor could be contributed by major and minor elements contained in each soils sample species, especially Ferum, Fe and Silica, Si.

Preparation, characterization and microwave absorbing properties of FeNi alloy prepared by gas atomization method

In this work, Fe–50 wt%Ni alloy was synthesized by nitrogen gas atomization method. The phase composition, morphology, element composition and saturation magnetization of the alloys were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence spectrometer (XRF) and vibrating sample magnetometer (VSM). The electromagnetic parameters and microwave absorbing properties of the microwave absorbing material made from silicone rubber and the as-prepared FeNi alloy were also studied using vector network analyzer (VNA) and transmission line theory. The results show that the particle size of most of the particles is less than 150 μm, and the average particle size is about 48 μm. The Fe–50 wt%Ni powder has a spherical shape, and the main phase composition is FCC (Fe, Ni) alloy. The as-atomized FeNi alloy possesses low coercivity and high specific saturation magnetization. As the frequency increases, the real part of relative permittivity and relative permeability of the Fe–50 wt%Ni/silicone rubber absorber decrease, while the imaginary part of relative permittivity increases. The Fe–50 wt% Ni alloy/silicone rubber absorbers with 0.8–4 mm thickness exhibit adjustable microwave absorbing properties in the range of 1–18 GHz.

The dielectric response of La0.5Ca0.5−xSrxMnO3 (0.1≤x≤0.4) manganites with different magnetic ground states

The dielectric behavior of half doped manganites La0.5Ca0.5−xSrxMnO3 (0.1≤x≤0.4) with varying magnetic ground states has been studied. The real part of relative permittivity as a function of temperature ε′(T), exhibits a maximum around the ferromagnetic (TC) and charge ordering transition (TCO) temperatures accompanied with high dielectric losses. The activation energies obtained for x=0.1 and 0.3 samples below TCO are the same ∼0.12 eV, whereas the relaxation time constant varies in the range 2.8×10−9 s–6.03×10−11 s. In contrast to samples having x≤0.3, for x=0.4 doping, the dielectric permittivity exhibits a strong temperature dependence in the vicinity of magnetic phase transitions. This behavior may be correlated with the presence of competing magnetic interactions (magnetic polarons) close to the magnetic transitions.

Controllable Waveguide Bandstop Filter Using S-Shaped Ring Resonators

In a novel application a slab of S-shaped ring resonators is used to fill a rectangular waveguide for the construction of a band-rejection waveguide filter with adjustable bandwidth and cutoff frequency. Results obtained from theoretical analysis, simulation and measurement of a specific structure are presented. Then, by using finite element simulation, we show that the cutoff frequency and stopband bandwidth of the filter can be controlled by changing the slab substrate properties (permittivity and thickness) and its position inside the waveguide. Results also show that varying the real part of relative permittivity of the slab substrate from 1 to 6, while keeping its physical thickness fixed (0.508 mm), the cutoff frequency drops from 10.6 to 6.9 GHz. On the other hand, when the physical thickness of slab substrate changes from 0.508 mm to 4 mm while keeping its permittivity fixed (ε r = 2.2), the filter cutoff frequency decreases from 8.8 to 5.9 GHz. We show that the width of rejection band of the filter can be decreased from about 4.7 GHz to about a few MHz by increasing the distance of the slab from the central plane of the waveguide.

COMPARATIVE INVESTIGATION OF RESONANCE CHARACTERISTICS AND ELECTRICAL SIZE OF THE DOUBLE-SIDED SRR, BC-SRR AND CONVENTIONAL SRR TYPE METAMATERIALS FOR VARYING SUBSTRATE PARAMETERS

This paper introduces a planar µ-negative (MNG) metamaterial structure, called double-sided split ring resonator (DSRR), which combines the features of a conventional SRR and a broadside-coupled SRR (BC-SRR) to obtain much better miniaturization at microwave frequencies for a given physical cell size. In this study, electromagnetic transmission characteristics of DSRR, BC-SRR and conventional SRR are investigated in a comparative manner for varying values of substrate parameters which are thickness, the real part of relative permittivity and dielectric loss tangent. Simulation results have shown that magnetic resonance patterns of all these three structures are affected in a similar way from variations in permittivity and in loss tangent. However, changes in substrate thickness affect their resonance characteristics quite differently: In response to decreasing substrate thickness, resonance frequency of the SRR increases slowly while the bandwidth and the depth of its resonance curve do not change much. For the DSRR and BC- SRR structures, on the other hand, resonance frequency, half power bandwidth and the depth of resonance curve strongly decrease with decreasing substrate thickness. Among these three structures, all having the same unit cell dimensions, the newly suggested DSRR is found to reach the lowest resonance frequency, hence the smallest electrical size, which is a highly desired property not only for more effective medium approximation but also for miniaturization in RF design. The BC-SRR, on the other hand, provides the largest