Papers by Keyword: Complex Permittivity

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: Three-dimensional flower-like nickel-ferrite composites were successfully synthesized via decomposition of the nickel-iron alkoxide precursors by varying the ratio of iron and nickel ion in the solution. The overall morphology and size of the particles had no obvious change compared with the precursors. The high-frequency absorption properties of the composites were investigated in a frequency range of 2-18 GHz. The reflection loss and bandwidth varied with the nickel ratio and thicknesses of the compositions, showing valuable prospect in high-frequency wave attenuation. The wave absorbing mechanism was also discussed, which could be attributed to the dielectric loss, magnetic loss, and the synergetic effect.

Abstract: In this paper we designed a microwave material measurement system by using slotted line waveguide.Compared with the VNA,this system have the smaller size and lower cost.Considering the test technical specifications, test methods of complex permittivity of microwave materials, and the performance of test system,we used the short-circuited line method to test the complex permittivity of the microwave material, and used the TI DSP [1] (TMS320C6747) as a minimum core processor system. Developed a set of X-band automatic slotted line system, this paper carried out the design of the prototype test system and the programing of the system's automated testing software. Finally,we used the measuring system to test two kinds of sample(fiberglass and quartz) and compare the result with the other result testing by the VNA.it is not difficult to conclude the measured result is relatively accurate.

Abstract: A double-ridge waveguide resonator loaded with rod like dielectric material was analyzed based on the electromagnetic simulation software HFSS and microwave resonant cavity perturbation technique in this paper. The perturbation method is used to calculate the complex permittivity of the material due to the change of the resonator's tiny change. The calculation expression of complex permittivity was deduced and proper test system was built for the validation at several specific frequencies, the resonant parameters of the cavity were measured by the external Agilent vector network analyzer, according to the calibration of standard quartz sample, the complex permittivity of the quartz, sapphire and PTFE samples were calculated. Experimental result showed that the method has a good performance for measuring the complex permittivity of low dielectric loss dielectric materials.

Abstract: The measurement of the complex permittivity of big structure composite material has always been a key and difficulty in the preparation of electromagnetic functional materials. In this paper the average dielectric constant inversion of coconut fiber/gypsum composite in S band is studied based on λ/4 absorption spectrum. First the absorbing effects of the prepared coconut fiber gypsum composite materials are tested with method of flat reflection. Then the equivalent complex permittivity is inversed with the inversion theory. Further the experimental verification is preceded that the theoretical and experimental absorbing curves whose peak positions are respectively at 3.05GHz and 2.45GHz are quite matched. And the study shows that this method is scientific and effective, and it can provide technical support for the baroque electromagnetic functional composite materials.

Abstract: In this paper, an improved coaxial measurement system with a newly designed coaxial fixture is presented. The electromagnetic parameters of samples are retrieved from the scattering parameters measured by a vector network analyzer (VNA) at microwave frequencies. The measurements of air and PTFE in the range of 1~6 GHz were carried out to verify the reliability and the accuracy of this measurement system. By using frequency-sweep and data processing techniques, the multiplicity of roots is eliminated. The results show that this system can effectively be applied to measure the material electromagnetic parameters of absorbing materials with high accuracy in a wide frequency band.

Abstract: Real and Imaginary parts of Complex Dielectric Permittivity (ε’ and ε” ) of Sandy Loam soil have been measured in the frequency range 150 MHz – 2.4 GHz using a Vector Network Analyzer at varied Moisture contents, Salinity and Biomass. The Emissivity of the soil for normal incidence was also calculated from measured values of Complex Permittivity. The measured permittivity data show strong dependence on moisture content. Salinity causes higher permittivity and dielectric loss. Biomass appears to enhance the permittivity data due to increase in porosity of the soil. The emissivity of the soil was observed to decrease with increasing soil moisture and soil salinity, but it increases with biomass.

Abstract: Complex permittivity spectra of 1-Propanol (1-PrOH), Fluorobenzene (FB) and their binary mixtures are obtained in radio and microwave frequency range using Vector network analyzer (VNA) operating in the frequency range 0.3 MHz to 3.0 GHz and standard microwave benches operated at 9.1 GHz and 19.61 GHz. Static dielectric constant (ε₀) and high frequency limiting dielectric constant (ε_∞1) for binary mixtures of 1-PrOH and FB are obtained by extrapolating the complex permittivity data towards low frequency side and high frequency side on complex plane plots. Optical dielectric constant (ε_∞ = n²) for binary mixtures are measured using Abbe's refractometer. Excess static dielectric constant (ε₀)^E, Kirkwood correlation parameters (g, g^eff and g_f) and Bruggeman factor (f_B) are determined from the values of static dielectric constant (ε₀) and optical dielectric constant (ε_∞). These parameters have been discussed to explore the molecular interaction between the molecular species.

Abstract: The complex relative dielectric function ε*(ω) = ε’- jε” of anisole (AN), 1-heptanol (1-HeOH) and their binary mixtures of varying concentration have been measured using Precision LCR meter in the frequency range 20 Hz to 2 MHz at 303 K. The electrical/dielectric properties of the liquid samples are represented in terms of intensive quantities namely, complex relative dielectric function ε*(ω), electrical modulus M*(ω), electrical conductivity σ*(ω) and extensive quantities, i.e. complex admittance Y*(ω) and complex impedance Z*(ω). All of these presentations are used to explore various processes contributed in the electrical/dielectric properties of the mixtures of two polar liquids.

Abstract: As electric insulators of the copper conductors in the electric generators of alternative current or in electric motors of high tension, there are used with priority the composite crosslinked mica-epoxy. Pre-impregnated band with solvent was introduced, the impregnation being performed with phenolic-novolac resin. The studied material got superior dielectric properties at function temperatures corresponding to the insulation class F(155C). Its main components are: mica paper (53%), glass cloth (13%) and the basic epoxy phenolic-novolac resin. The complex permittivity and conductivity were determined with the Time Domain Spectrometer (TDS); the apparatus allows the determination of the electric values in the domain of frequencies: very large domain of frequencies. The temperature varied in the domain 23-190C with the help of an oven. The purpose of this article is to report the dielectric properties of mica-epoxy-novolac composite insulator, for which very few data have so far been published.