An optimisation approch to determine the electromagnetic properties of lanthanum iron garnet filled PVDF-polymer composite at microwave frequencies

In this study, an optimization approach is shown to improve the accuracy of the Nicholson and Ross Weir (NRW) method to determine both the complex permittivity and permeability of the lanthanum iron garnet-filled PVDF-polymer nanocomposite loaded in a rectangular waveguide. The complex permittivity and permeability values were in turn used in Finite Element Method to calculate the S-parameter and were found to be in good agreement with the measured values

Electromagnetic properties of polytetrafluoroethylene at microwave frequencies using finite element modeling waveguide adapter

Experimental and theoretical approaches were shown great potential to determine electromagnetic properties of dielectric materials at microwave frequencies. In this study, the application of Finite Element Modeling (FEM) of waveguide adapter was utilized to investigate the distribution of electric and magnetic fields intensity of Polytetrafluoroethylene (PTFE) as dielectric sample. Essentially, the electric and magnetic fields intensity in various regions of waveguide were obtained. The computations of the reflection and transmission coefficients of dielectric sample were determined by implementation of Finite Element Methods and Nicolson-Rose-Wire (NRW) method as well. The results were compared with the experimental achievement results using the waveguide adapter in conjunction with a Vector Network Analyzer (VNA) at Microwave frequencies. The general observation indicate that, the level of transmission was greater than reflection for PTFE as dielectric material sample. Furthermore, among the two applied methods, the FEM is more accurate than the NRW method

Determination reflection and transmission coefficients of lanthanum iron garnet filled PVDF-polymer nanocomposite using finite element method modeling at microwave frequencies

In our previous work, the lanthanum iron garnet-filled PVDF-polymer nanocomposite has been prepared. The reflection and transmission coefficients of PVDF/LIG were measured using rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) at X-band frequencies (8 GHz 12 GHz). In this study, the distribution of electric field intensity of PVDF/LIG which was loaded in rectangular waveguide was simulated based on Finite Element Method (FEM) formulation to show the essential differences of intensity of emitted electrical field. The computations of reflection and transmission coefficients of PVDF/ LIG were determined by using implementation FEM modeling rectangular waveguide. The FEM results were compared with the experimental achievement results using the rectangular waveguide. An excellent agreement between measured and simulated results was obtained based on the values of mean relative errors

Method of Moment Analysis Using Open-Ended Coaxial Sensor in Determination of Corn Reflection Coefficient

The present thesis is a critical study on the use of an open-ended coaxial sensor for the estimation of moisture content of corn with various degrees of fruit ripeness at (25+1)oC. The fruit’s state of ripeness depends on moisture content. The permitivity is in direct relation with the amount of water in corn texture’ in other words, The higher the amount of water in the corn texture is, the higher the permittivity goes. An open-ended co-axial line has been used as an electromagnetic sensor or probe for various industrial and scientific applications. These applications are based on the principle that the characteristics of the echo signal produced by the co-axial opening depend upon the sample material terminating the probe. Thus, if the aperture admittance characteristics can be precisely formulated, then the electrical parameters of the sample can be found. The sensor was studied based on the calculation of reflection coefficient using an integral admittance approach and Method of Moment (MOM). The Method of Moment is one of the most important general methods which are used for solving electromagnetic-field problems. It begins with a brief mathematical foundation of the general method. Then, the various specializations are described, accompanied with relevant references to illustrate the pitfalls and shortcomings, as well as the advantages, as compared to other methods. So finally, their algorithms are easily programmable on computer. The computation of reflection coefficient of the corn was programmed using MATLAB software for the admittance approach and Method of Moment (MOM). The results were compared with the measured reflection coefficient using the open-ended coaxial sensor in conjunction with a vector network analyzer (VNA). The sensor operating between 1 GHz and 5 GHz was fabricated from a 2.05 mm and 0.65 mm, outer and inner diameters respectively. The measuring end of the sensor was calibrated by a transmission line procedure. The integral admittance formulation was simplified into a series expression. The local truncation errors of the series approximation were critically analyzed. The two-dimensional MOM was used to solve the rotationally symmetric region of the open-ended coaxial line. The MOM results are closed to the measurements data than calculated admittance formulation. The maximum absolute errors of MOM and measurement results for magnitude and phase reflection coefficient are less than 0.02 and 0.1 rad, respectively, compared with 0.05 and 0.2 rad of admittance formulation and measurement results, respectively. A calibration equation has been developed based on the relationship between the measured moisture content obtained by the oven drying method and the phase of the reflection coefficient of the sensor. The moisture content predicted by the sensor was in good agreement with those obtained using the standard oven drying method with its absolute error within 5 % moisture content, when tested on 114 different corn samples. The model successfully evaluated the complex permittivity for different ripeness stages of corn mesocarp as a function of frequency, moisture and ionic conductivity, as well as the bulk density. The software is also used to calculate reflection coefficient from complex permittivity in frequency between 1 GHz and 5 GHz

Reflection and transmission coefficient of yttrium iron garnet filled polyvinylidene fluoride composite using rectangular waveguide at microwave frequencies

The sol-gel method was carried out to synthesize nanosized Yttrium Iron Garnet (YIG). The nanomaterials with ferrite structure were heat-treated at different temperatures from 500 to 1000 °C. The phase identification, morphology and functional groups of the prepared samples were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), respectively. The YIG ferrite nanopowder was composited with polyvinylidene fluoride (PVDF) by a solution casting method. The magnitudes of reflection and transmission coefficients of PVDF/YIG containing 6, 10 and 13% YIG, respectively, were measured using rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in X-band frequencies. The results indicate that the presence of YIG in polymer composites causes an increase in reflection coefficient and decrease in transmission coefficient of the polymer

Electromagnetic properties of lanthanum iron garnet filled PVDF-polymer composite at microwave frequencies using finite element method (FEM) and Nicholson–Ross–Weir (NRW) method

In our previous work, the lanthanum iron garnet-filled PVDF-polymer nanocomposite has been prepared. The real and imaginary parts of relative permittivity and permeability of mentioned sample were obtained simultaneously using the Nicholson-Ross-Weir (NRW) method based on the measurement of the reflection and transmission coefficients of the materials. In this study, the electric field distribution and attenuation at rectangular waveguide loaded sample were investigated based on the Finite Element Method (FEM). The computations of the reflection and transmission coefficients (S-parameters) were implemented using both the FEM and NRW methods. The results were compared with the measured reflection and transmission coefficients using the rectangular waveguide in conjunction with an Agilent N5230A PNA-L Vector network analyzer (VNA) at X-band frequencies (8 GHz- 12 GHz). The results of the relative error indicated that, among the two applied methods, the FEM is more accurate than the NRW method

Key Immune Cell Cytokines Affects the Telomere Activity of Cord Blood Cells In vitro

Purpose: Telomere is a nucleoprotein complex at the end of eukaryotic chromosomes and its length is regulated by telomerase. The number of DNA repeat sequence (TTAGGG)n is reduced with each cell division in differentiated cells. The aim of this study was to evaluate the effect of SCF (Stem Cell Factor), Flt3 (Fms- Like tyrosine kinase-3), Interleukin-2, 7 and 15 on telomere length and hTERT gene expression in mononuclear and umbilical cord blood stem cells (CD34+ cells) during development to lymphoid cells. Methods: The mononuclear cells were isolated from umbilical cord blood by Ficoll-Paque density gradient. Then cells were cultured for 21 days in the presence of different cytokines. Telomere length and hTERT gene expression were evaluated in freshly isolated cells, 7, 14 and 21 days of culture by real-time PCR. The same condition had been done for CD34+ cells but telomere length and hTERT gene expression were measured at initial and day 21 of the experiment. Results: Highest hTERT gene expression and maximum telomere length were measured at day14 of MNCs in the presence of IL-7 and IL-15. Also, there was a significant correlation between telomere length and telomerase gene expression in MNCs at 14 days in a combination of IL-7 and IL-15 (r = 0.998, p =0.04). In contrast, IL-2 showed no distinct effect on telomere length and hTERT gene expression in cells. Conclusion: Taken together, IL-7 and IL-15 increased telomere length and hTERT gene expression at 14 day of the experiment. In conclusion, it seems likely that cells maintain naïve phenotype due to prolonged exposure of IL-7 and IL-15