Papers by Keyword: Dielectric Permittivity

Abstract: This study investigates the fabrication of a cylindrical dielectric resonator antenna (CDRA) using ceramic microwave dielectric composites as a resonator. The composites (1-x) Li₃MgNbO₅-(x) Sr₃V₂O₈ (x=0.25-0.40) have been synthesized via the conventional solid-state reaction method, incorporating 1% B₂O₃ to lower the sintering temperature. The 0.70-0.30 composite exhibited optimal microwave dielectric properties with a dielectric constant (ε_r) of 19.20, a quality factor (Q x f) of 3738 GHz, and a temperature coefficient (τ_f)of -43 ppm/°C. These characteristics render the 0.70-0.30 composite suitable for CDRA applications. The experimentally obtained microwave dielectric parameters were used to simulate the CDRA design using the High-Frequency Structure Simulator design software. A single-feed cylindrical antenna has been fabricated using this composite material as a resonator with a radius × height of 5×6 mm², mounted on an FR4 substrate measuring close to 25×25×1.6 mm³ and Cu strip as a feed line. The simulated and experimentally measured parameters, including S11, voltage standing wave ratio, and radiation pattern, demonstrated excellent agreement, validating the composite's efficacy for antenna design.

Abstract: A mathematical model of diffraction of electromagnetic microwaves on explosive materials with different physical and electromagnetic parameters has been developed. The model was constructed by solving Maxwell's equation for two surfaces separating three dielectric materials, in particular air, explosive material, and the substrate on which the explosive material is located. Different types of soil and wood are considered as the substrate material, which meets the conditions for demining large areas of the locality. The results of the numerical calculation showed that 67 % to 92 % of the energy of electromagnetic radiation is concentrated in the explosive material. In this case, trinitrotoluene, which is placed on dry sand, has the highest absorption rates, while wet wood, due to its high coefficient of dielectric permittivity, successfully transmits electromagnetic microwaves through its surface. The obtained models and numerical results are considered as theoretical basis for predicting the effectiveness of remote methods of detection and disposal of explosive materials using electromagnetic microwaves. The obtained results showed that this method will be least effective for explosive materials placed on wet wood. In this case, the lowest reflection coefficient is observed that complicates the search for explosive material and the lowest absorption coefficient that complicates the artificial detonation of explosive material due to its heating under the influence of electromagnetic microwaves.

Abstract: The solid polymer electrolyte (SPE) consists of polylactic acid (PLA) with different compositions of lithium perchlorate (LiClO₄) were prepared by using the solution casting method. The conductivity and dielectric properties of the SPE system were studied by using an impedance spectroscopy technique with a frequency ranging from 0.1 Hz to 100 MHz. The optimum composition of the LiClO₄ in the PLA based electrolyte system is 50 %. The highest ionic conductivity value of the PLA-LiClO₄ electrolyte is 2.66 x 10^-5 Scm^-1. The dielectric permittivity, ɛ′ shows high magnitude in the lower frequency due to electrode polarization (EP) effect and become to decrease at high frequency. The magnitude of ɛ′ increases up to 50 % of LiClO₄ in the electrolyte system. The loss tangent was used to measure the relaxation time of the electrolyte system. The shortest relaxation time is PLA- LiClO₄ polymer electrolyte system is 7.98 × 10−6 s. The electric modulus, M′ and M′', increases with frequency, indicating that the force of charge carriers increases in depletion and accumulation regions at room temperature.

Abstract: In this work, PVDF/BaTiO₃ nanocomposites consisting of polyvinylidene fluoride (PVDF) as matrix and BaTiO₃ (BT) as fillers were prepared by ball milling and hot-pressing process. It is known that nanofillers content and frequency affect the effective dielectric permittivity of the nanocomposites materials. Therefore, a developed model based on deep neural network (DNN) was used to study the effect of the input parameters on the dielectric permittivity of the nanocomposites. The volume fraction (vol%) of BT and frequency of alternating current (AC) were selected as the input parameters and the effective dielectric permittivity as the output response. The results show that the developed DNN model was able to predict the effective dielectric permittivity of PVDF/BT nanocomposites with a correlation coefficient (R) of 0.997. Thus, our study confirmed the accuracy and efficiency of the developed DNN model for predicting the relative dielectric permittivity of PVDF/BT nanocomposites.

Abstract: Herein, we have developed a Cr³⁺ doped Al₂O₃ of a hierarchical nanostructure by a simple two-step synthesis. A pure AlO(OH)⋅αH₂O, as synthesized in forms of small tubular fibers by hydrolysis of Al-metal sheets, is easily doped with selective Cr³⁺ dosages up to 2.0 mol% using an aqueous CrO₃. As-synthesized samples exhibit XRD of a single phase Cr³⁺: Al₂O₃ of a rhombohedral crystal structure. Average pore-volume is decreased as 98.1, 89.8, and 61.5 cm³-g^-1 in the 0.5, 1.0 and 2.0 % Cr% doped samples, with average pore radius of 1.70, 2.17 and 1.90 nm, respectively, as measure from BET specific surface area. Local Al-O vibrations exhibit IR bands of 400 to 1200 cm^-1 intrinsic of oxygen polygons. At room temperature, a duly tailored dielectric permittivity of 480 is obtained in a 2.0 mol% Cr³⁺:Al₂O₃ and that is enhanced progressively on heating it over 25 to 300 °C, showing a value 6700 at 300 °C in phonon induced dynamics of charge carriers, useful for solid-state electronics.

Abstract: Determination of the electromagnetic parameters is an important tool to evaluate the microwave-absorbing characteristic of a novel material. In this context, our research was carried out to investigate the electromagnetic parameters of nanocomposites samples obtained by inclusion of nanostructured Fe₇₂Al₂₃V₅ powders in a resin matrix. Nanostructured Fe₇₂Al₂₃V₅ powders were synthesized by high-energy mechanical alloying (MA) route and characterized using a scanning electron microscopy (SEM). The nanostructured Fe₇₂Al₂₃V₅ powders were dispersed in an epoxy resin matrix. Nanocomposites bulk samples of rectangular section and given thickness were shaped for electromagnetic characterization in an X-band metallic rectangular waveguide. Electromagnetic characterization was performed in terms of measured S_ij scattering parameters. Dielectric permittivity and magnetic permeability spectra were extracted over the microwave X-band via the transmission/reflection technique. Obtained results exhibit how the nature and size of the inclusions affect the electromagnetic parameters in the X-band frequencies.

Abstract: In this work, the uses of giant dielectric constant of Y₂NiMnO₆ ceramics were investigated in the frequency range from 1 kHz to 3 MHz. The Y₂NiMnO₆ ceramics were sintered at 1400 °C for 6, 12, 18 and 24 hours, respectively. The dielectric properties of Y₂NiMnO₆ ceramics were examined in dc bias from 0 to 1.5 volt at room temperature. We found that all sintering times displayed high dielectric permittivity at frequencies below 10⁵ Hz, above which the values decreased significantly, applied dc bias also reduced dielectric permittivity. The peak of dielectric loss decreased significantly at high dc bias due to decreased contribution of dc conductivity in grain ceramics. This research has characterised electrical properties of Y₂NiMnO₆ ceramics which maybe suitable for electronic components including batteries and capacitors.

Abstract: The dielectric permittivity (ε) of Y₂NiMnO₆ ceramics prepared by sintering at 1400 °C over 6 to 24 hours was investigated. The response of the ceramics was measured from 1 kHz to 3 MHz, with the influence of a fixed dc bias from 0 to 1.5 V and temperature from 40 °C to -60 ^oC. Increasing dc bias was found to reduce ε' at low frequencies, while at higher frequencies the dc bias had less influence on ε'. At 40 °C a sharp transition from high to low ε' occurred starting at ~100 kHz, as the temperature of the ceramic was lowered, the transition shifted to lower frequencies. This behaviour is attributed to the charge ordering of Ni²⁺ and Mn⁴⁺ ions and the thermal effect on the ions energy.

Abstract: Structural features and dielectric behavior of polymeric systems based on tetrazole are investigated after combining them with potassium nitrate (KNO₃) and potassium chloride (KCl). It was found that the salt additives added to the system exist in the form of the singular crystallites that is the closed inclusions chaotically distributed inside polymeric matrix. Injection of potassium nitrate increases the value of dielectric permittivity on the studied interval of frequencies. Potassium chloride reduces the value of dielectric permittivity of the polymeric system in the field of high frequencies, and increases it in the field of low frequencies. Addition of salt increases the specific conductivity of composites that indicates increase in degree of dissociation of ionogenic substances. In the studied systems, ionogenic substances, besides salt additives, including water and remains of catalysts.

Abstract: Liquid crystal (LC) polymer, composited with inorganic filler, has a broad application prospect in electronic and electrical industry. In this research, permittivity (ε_r) and dielectric loss tangent (tanδ) of LC composites under different temperatures and frequencies were investigated, and activation energies were calculated and analyzed. At low temperatures and high frequencies, LC composites exhibited well dielectric properties. ε_r changed a little (3.6~4.0) in temperature range of-60°C~160°C when frequency was higher than 10Hz, but increased sharply when temperatures was higher than 100°C and frequency was lower 10Hz. The tanδ increased sharply with increasing temperature when temperatures was higher than 100°C and frequency was lower than 10²Hz, and when frequency was above 10²Hz, the value of tanδ changed gently (10^-3~10^-2). The peak of tanδ would translate to higher frequencies direction with increasing temperature in tanδ-frequency curve, and to higher temperatures direction with increasing frequency in tanδ-temperature curve. Activation energy is calculated by fitting the peak of the imaginary of the electric modulus, and activation energy is 0.43eV in low temperature and 1.59eV in high temperature.