Papers by Keyword: Permittivity

Abstract: This study explores the formulation of dielectric composite material derived from Ananas comosus (pineapple) waste for 5 GHz microstrip antenna applications. Cellulose extracted from pineapple leaves was incorporated into an epoxy matrix to achieve a permittivity (ε_r) of 4.13. Morphological analysis revealed cellulose fiber particles averaging 1.60 μm in diameter, embedded within a composite matrix rich in carbon and oxygen. EDX analysis confirmed composition percentages of 62.07 wt.% carbon, 33.95 wt.% oxygen, and 3.98 wt.% sodium. Antenna performance evaluation demonstrated an optimal reflection coefficient, S₁₁, of -32 dB at 5.30 GHz in simulations, meeting FCCs 5G band specifications. The three-dimensional radiation patterns from the simulations confirmed efficient power radiation, with a gain of 4.246 dBi, indicating the suitability of the dielectric composite for effective signal transmission and reception. Experimental results showed an S₁₁ of -22 dB at 5.15 GHz, validating robust performance within the 5 GHz range. These findings underscore the potential of pineapple waste-derived composites in advancing sustainable antenna technology.

Abstract: Multifunctional materials refer to the types of materials that possess enhanced mechanical, electrical, and thermal properties. In this work, nano silica and Carbon Black (CB) are added to epoxy polymer as an effort to improve the thermomechanical and dielectric properties of the composites. Filler loadings are varied from 0.1 wt.%, up till 5 wt.%. The thermomechanical properties are measured from Dynamic Mechanical Thermal Analysis (DMTA) while the dielectric properties are measured from Vector Network Analyser (VNA). The synergistic effects of combining both fillers (keeping them at 1:1 wt.% ratio) are also assessed. It was found that the value of glass transition temperature (T_g) increased from 56.85°C (neat epoxy) to 59.8°C (5 wt.% CB). The T_q values further increased to 64.7°C, for 5 wt.% hybrid fillers (2.5 wt.% silica + 2.5 wt.% CB), demonstrating the synergistic effects by employing dual fillers. By adding single and dual fillers, the values of storage Modulus, E’ remains almost constant for both glassy (40°C) and rubbery region (100°C), regardless of the loadings employed. The values of real permittivity, e_r’ was also measured for dual fillers in the frequency range between 300 kHz to 18 GHz. The highest value of e_r’ was 5.5 F/m, which was measured for both 1.5 mm and 2.0 mm sample thickness of 5 wt.% hybrid fillers (2.5 wt.% silica + 2.5 wt.% CB). This study highlights the thermomechanical and dielectric properties improvement of epoxy composites by incorporating dual fillers.

Abstract: Materials with high dielectric properties have become interested due to their important applications, mainly in electronics and energy storage. This study assesses the dielectric properties of epoxy composites containing silver nanoparticles (AgNPs) and carbon nanotube (CNT) composite materials. These samples' permittivity and reflective properties were measured using Vector Network Analyser (VNA) within the X-band frequency (8.2 – 12.4 GHz). Samples were prepared at various loading (0.1-5 wt.%), with various thickness of (0.5, 1.0, 1.5 and 2.0 mm). Regardless of the fillers loading and sample thickness, it was found that the values of real permittivity, er', remain constant along the frequency range. At the same sample thickness, it was found that the values of both er' and er'' increase as loading increases, indicating the function of AgNPs and CNT in enhancing the dielectric and electrical conductivity properties of epoxy composites, respectively. The highest value of er' is recorded as 5 F/m (at f = 8.2 GHz), measured at 5 wt.% loadings and 0.5 mm sample thickness. Measurement on S₁₁ parameters at f = 8.2 GHz indicated that the SE_R values are between 9 dB and 15 dB, with no obvious pattern observed, regardless of the fillers loading and sample thickness. This study highlights the dielectric properties improvement of epoxy composites by incorporating dual fillers.

Abstract: Heating polymers by microwaves is not common. In order to quantify the ability of micro-wives to heat different type of polymers, a bench measuring the dielectrics characteristics of polymers is built, and a numerical modeling of the waves-polymers interaction is achieved. Finite elements method is introduced to solve the Maxwell equations [6-8] and the energy equation. A series of numerical simulations test are performed: convergence tests are realized and the heating power distribution in the sample is obtained. Using the power distribution, we studied a transient heating process of a polymer (CAPA) sample by microwave. In order to validate the numerical approach, we set-up an experimental bench to heat the sample by microwave and measure temperature distribution, using optical fiber and pyrometers. A vector analyzer (VNA). [6, 9-12] is used to check the quality of the microwave cavity The results of the numerical simulations of the wave propagation are presented and the amplitude of the electric field is compared to the experimental measurement: good agreement is observed. In terms of polymer heating, numerical results of temperature field and experimental measurements are also compared: an efficient heating is observed.

Abstract: Various filling fractions of silver silica nanocomposites (Ag-SiO₂ NC) were successfully synthesized via sol-gel technique and deposited onto indium tin oxide via electrophoretic deposition (EPD). Ag-SiO₂ NC was investigated using X-ray diffraction, FTIR spectroscopy, Uv-vis and transmission electron microscopy. The XRD and Uv-vis results revealed that Ag-SiO₂ NC is stable with a filling fraction of 0.6 in the dielectric medium with excellent absorption peak. Spectroscopy Ellipsometry shows that the effective permittivity and refractive index obtained from this filling fraction are -0.88 and 0.90, respectively. We discovered a ragged of metamaterial properties at negative permittivity.

Abstract: In the present paper we demonstrate and compare different properties of Bi and Bi_1-xSb_x thin films placed on polyimide (PI) substrate in frequency range from 0.2 to 1.0 THz. Bi films with a thickness of 40, 105 and 150 nm have been studied as well as 150 nm Bi_1-xSb_x solid solutions with Sb concentration of 5, 8, 12 and 15 %. An effective refractive index and permittivity of whole substrate/film structures have been derived by using terahertz time-domain spectroscopy (THz-TDS) method. These measurements have shown the positive phase shift in PI substrate with a thickness of 42 μm and revealed that it is barely transparent in studied frequency range, but the whole substrate/film structure provides the negative phase shift of terahertz wave. It was shown that the permittivity depends on mobility of charge carriers which is driven by film thickness and antimony content.

Abstract: The design of artificial metamaterial (MTM) has been proposed as an effective medium with extracted scattering parameter by applying Nicolson-Ross-Weir (NWR) equation to achieved negative permittivity and permeability. The novel architecture of ‘Folded-Line’ Left-handed metamaterial (FL-LHM) consist of split ring resonator SRR is designed and modified using LC lump elements analysis to extend bandwidth and operational frequency at 6 GHz to 12 GHz. In this study, we proposed metamaterial novel unit cell designs and simulate the performance in terms of the distribution of electric and magnetic fields, absorption, transmittance and reflectance. The unit cell of FL-LHM as medium allows controlling electromagnetic waves can cause backwave propagation is observed electromagnetic response that current induced in the closed FL-LHM unit cell. This design has its own advantage in term of FL-LHM parameter width, thickness, and absorption bandwidth and transmittance wavelength, might be severely important for particular purposes such as waveguiding or sensing application.

Abstract: The dual metallic components, i.e., iron-aluminum particles were distributed in alumina matrix to fabricate lossy cermets. The electromagnetic parameters including ac conductivity, the complex permittivity and permeability were investigated. With the increase of filler fractions, the conductive carriers instead of the dipoles played a primary role in conductive and dielectric properties. Hopefully, the cermets composites could be promising candidates for electromagnetic wave attenuation and shielding.

Abstract: Applied research tries to offer new materials from the slag mortars. Basic research tries to explore these engineered materials from the perspective of all the possible test methods. Modern vector analyzer R&S ZNC with a coaxial probe DAK-12 from Speag company was used to determine permittivity and dielectric loss factor of the beams and interesting spectrums of electric resistance were measured for samples with varying content of carbon powder. Carbon contributes from the viewpoint of electrical properties, for example it improved antistatic properties of the floor. In addition to the vector analyzer – the simpler measuring unit was also used. In a frequency range of 40 Hz to 1 MHz values of electrical resistance and permittivity values of the beams with different content of graphite powder, labeled Cond 896 were determined. The higher content of graphite powder increases the electrical conductivity; building materials based on cement are becoming more measurable using electromagnetic measuring methods. The most striking change in the relative conductivity was observed at excitation frequency of the external electric field of 1 kHz. At high frequencies of electrical excitation field from 10 MHz to 3 GHz values of the real part of permittivity were determined by vector analyzer. These measurements are among the building materials used rarely and they open new possibilities of diagnostics.

Abstract: In this paper, C/SiO₂ composites were fabricated by self-assembly process combined with heat treatment. The X-ray diffraction (XRD) analysis, SEM and impedance analyzer were used to investigate the microstructure and radio-frequency dielectric properties of the composites. The results showed that the matrix of C/SiO₂ composite with a periodical structure formed by the hexagonal stacking of SiO₂ microspheres. The sheet carbon distributes in pores formed by SiO₂ microspheres and act as the functional phase in the composite. The results indicate that the permittivity of C/SiO₂ composite could be easily adjusted by controlling the content of Carbon in the composite. Both real and imaginary parts of the permittivity increase with the content of carbon, but decrease with the frequency.