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The eigenfunction solution of electromagnetic radiation and scattering from a multilayer uniaxial bianisotropic circular cylindrical scatterer is presented. The expressions for the electric and magnetic field equations are decomposed into transverse and longitudinal components. The boundary conditions are enforced by matching the transverse and axially directed fields at the interfaces between regions with different constitutive parameters. Matrices are constructed from the linear algebraic equations to solve the unknown series coefficients. On the one hand, numerical results are presented for the near zone fields and radar cross section in the two dimensional case. On the other hand, numerical solutions are presented for the radiation pattern when a dipole is present in the vicinity of the cylindrical scatterer in the three dimensional case. Results obtained using the eigenfunction series for the multilayer uniaxial bianisotropic circular cylindrical scatterer are in excellent agreement with results in existing literature and solutions computed using other formulations. [ABSTRACT FROM AUTHOR]

The development of microwave shielding nanocomposites based on recycled hematite nanoparticles, oil palm empty fruit bunch (OPEFB), and polytetrafluoroethylene (PTFE) was the main focus of this study. The complex permeability (μ′–jμ″), complex permittivity (ε′–jε″), reflection coefficient (S11), and transmission coefficient (S21) were determined using rectangular waveguide (RWG) connected to a vector network analyzer (VNA) in the frequency range of 8.2–12.4 GHz. The power loss, reflection loss, and total shielding effectiveness (SE) were calculated using the scattering parameters obtained through RWG. The results showed that the nanocomposites' microwave shielding properties can be controlled by tuning the percentage of Fe2O3 nanofiller in the nanocomposites. The values of ε′, ε″, μ′, and μ″ were enhanced by increasing the content of the recycled Fe2O3 nanofiller in the nanocomposites. At 10 GHz, the power loss values obtained for the nanocomposites ranged between 8.52 and 15.64 dB, while at 12.4 GHz, a maximum value of 16.32 dB was achieved by 25 wt%. nanocomposite. The total SE also increased with increasing Fe2O3 loading and a maximum value of 21.2 dB was achieved by 25 wt% nanocomposite at 12.4 GHz. The Fe2O3‐OPEFB‐PTFE nanocomposites have the potential to be used in microwave shielding applications in the frequency range 8.2–12.4 GHz. [ABSTRACT FROM AUTHOR]

Recently, modern wireless communication applications are extended to call high frequency bands including millimeter waves for 5G systems. Therefore, the propagation properties of such waves in different media have attracted many researchers. In this work, the results of the S-parameters measurements of mortar with four thicknesses are obtained using a nondestructive free space measurement technique for the frequency bands from 8GHz up to 32GHz. The obtained results of the dielectric properties and loss factors for the prepared mortar samples are realized. The variation in both the reflection and transmission coefficients and the dielectric properties with curing time conditions of mortar structure is examined. The dielectric properties of water are realized using the proposed method to subtract the effects of water contents from the prepared mortar samples. The effects of the sample thickness and relaxation frequency are considered. The obtained measurements are compared to the simulated results based on a full wave simulation software package of CSTMWS algorithms. Finally, excellent agreements are achieved between the simulated and measured results. [ABSTRACT FROM AUTHOR]

Magnetite (Fe3O4) have been thoroughly investigated as microwave absorbing material due to its excellent electromagnetic properties (permittivity and permeability) and favorable saturation magnetization. However, large density and impedance mismatch are some of the limiting factors that hinder its microwave absorption performance (MAP). Herein, Fe3O4 nanoparticles prepared by facile co-precipitation method have been coated with citric acid and embedded in a polyvinylidene fluoride (PVDF) matrix. The coated Fe3O4 nanoparticles were characterized by X-ray diffraction spectrometer (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). COMSOL Multiphysics based on the finite element method was used to simulate the rectangular waveguide at X-band and Ku-band frequency range in three-dimensional geometry. The citric acid coated Fe3O4/PVDF composite with 40 wt.% filler loading displayed good microwave absorption ability over the studied frequency range (8.2–18 GHz). A minimum reflection loss of −47.3 dB occurs at 17.9 GHz with 2.5 mm absorber thickness. The composite of citric acid coated Fe3O4 and PVDF was thus verified as a potential absorptive material with improved MAP. These enhanced absorption coefficients can be ascribed to favorable impedance match and moderate attenuation. [ABSTRACT FROM AUTHOR]

RS-4050 is a rigid epoxy based magnetic castable microwave absorbing material; it has been used in many areas of waveguide application as a microwave waveguide terminations and dummy loads. In recent years, there is a demand for composites material with lower dielectric constant higher loss factor for microwave application. This research, the effect of soda lime silica (SLS) on structural and complex permittivity of soda lime silica-high density polyethylene (SLS-HDPE) composites was conducted in order to explore the possibility of substituting RS-4050 with SLS-HDPE composites as a microwave waveguide terminations and dummy loads. Elemental weight composition of the SLS glass powder and HDPE was identified through scaling of different percentage of SLS and HDPE. X-ray diffraction (XRD) was used to investigate the crystallinity behavior of SLS-HDPE composites. The proposed SLS-HDPE composites material was studied at frequencies 8 to 12 GHz. The study was conducted using waveguide Agilent N5230A PNA technique. The effect of microwave frequency on complex permittivity properties for SLS-HDPE composites of different percentages of SLS and HDPE (10% SLS-90% HDPE, 20% SLS-80% HDPE, 30% SLS-70% HDPE, 40% SLS-60% HDPE, and 50% SLS-50% HDPE) were investigated. Results showed the diffraction patterns reveal good amorphous quality with a genuinely properties structure. The microwave frequency and composites percentages significantly influenced the complex permittivity (real and imaginary) properties of the composites. Moreover, the complex permittivity increased as the percentage of SLS filler increased in the host matrix HDPE as a result of increased in composite density due to less volume being occupied by the filler as the percentage increased. The complex permittivity of the smallest and largest percentages of SLS (10% and 50%) was (2.67-j0.05) and (3.45-j0.35), respectively. The study revealed that the best sample for waveguide application as microwave terminator is 50% SLS as it has the highest dielectric constant, highest loss factor, and highest loss tangent as compared to 10% SLS to 40% SLS. Also 50% SLS has the highest absorption properties as compare to 10% SLS, 20% SLS, 30% SLS, or 40% SLS. The XRD physical structure of the SLS-HDPE composites revealed the absorption characteristics of different percentages of the materials. The SLS-HDPE composites can be applied in the area of waveguide as a microwave waveguide terminations and dummy loads. [ABSTRACT FROM AUTHOR]

This study attempts to develop a soil moisture measurement system with a monopole antenna sensor, mini-VNA Tiny and a mobile phone respectively. The mini-VNA Tiny is a compact vector network analyzer (VNA) with a USB connection to a smartphone or a tablet. There are 17 sets of data which have been collected from 15 different spots with varying soil moisture content. The actual moisture content on site was collected from TRIME-PICO 64/32 sensor. Upon collection, it was necessary to calibrate the resistance obtained from the mini-VNA between 1 MHz and 3 GHz. The data obtained from the study shows that the resonances of the antenna resistance shift to the left on the frequency spectrum as moisture content increases. A linear model relating the resistance and actual moisture content was developed from this study with coefficient of determination (R²) value of 0.723 at 13 MHz. This value is much less than the anticipated R² = 0.95 for accurate measurement of soil moisture with monopole antenna at microwave frequency. This could be due to the 0.60 cm thickness of the monopole antenna which may not be suited for soil moisture measurement. Nonetheless, this study demonstrates the potential application of an inexpensive and portable mini-VNA Tiny and smartphone system for sensing applications. [ABSTRACT FROM AUTHOR]

Oil palm fresh fruit bunch (OPFFB) is the main export product of the oil palm industry. A good oil palm is between 17 to 18 weeks of age with full fruitless maturity. An automated detection system should be implemented to determine the OPFFB's maturity and expedite the harvesting process. Various automated detection methods have been proposed for conventional method replacement. In a preliminary study, a new oil palm fruit sensor was proposed for detecting the maturity of OPFFB, and a microstrip ring resonator was designed for determining the moisture content in oil palm fruit. The coaxial feeder of the microstrip ring was a Sub-Miniature A (SMA) stub contact panel with outer and inner conductors of 4.1 mm and 1.3 mm, respectively. The measurement system consisted of a sensor and a PC controlled network analyzer. This system was tested successfully on seeds and fruits of oil palm with various degrees of maturity. The microstrip ring resonator operated between 2.2 and 3 GHz and required low frequency that enabled the electromagnetic field in the first half of the ring resonator to be transferred to the second half and subsequently cause the collinearity of the maximum field points in the feed lines and resonator. [ABSTRACT FROM AUTHOR]

This paper reports a study of the microwave absorption properties of multiferroic BiFeO3 (BFO) epoxy resin composites. The effects of various sintering temperatures on the crystalline phase of BFO and its microwave absorption characteristics were critically analyzed. BFO nanoparticles were synthesized by mechanical activation high energy ball milling (HEBM) with post heat treatment over various temperatures ranging from 700 to 800 °C. The XRD results showed by using the HEBM method, BFO phase is formed at a lower sintering temperature of 700 °C compared to conventional solid state reaction due to the enhanced diffusion rates. The phase composition and the grain sizes had significant influence on the permeability, permittivity and reflection loss values of BFO composites measured by a network analyzer in the frequency range from 8 to 18 GHz. It was observed that the purity fraction of BFO phase and the grain sizes increased with the sintering temperature. By increasing the sintering temperature up to 775 °C, the microwave absorption properties were enhanced over a broad working frequency range corresponding to the reflection loss below − 10 dB (i.e. 90% absorption) due to crystalline phase changes. BFO samples sintered at 775 °C demonstrated higher absorption ability with RLmin − 40.5 dB over a 1.31 GHz bandwidth, showing that BiFeO3 has great potential as a microwave absorbing material. [ABSTRACT FROM AUTHOR]

Microwave-absorptive polymer composite materials provide protection against interference to communication systems caused by microwave-inducing devices. Microwave-absorptive polymer composites were prepared from polylactic acid (PLA) biocomposite blended with oil palm empty fruit bunch (OPEFB) fiber and commercial Iron oxide (Fe2O3) as filler using the melt-blending method. The composites characterization was carried out using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The coefficient of reflection S11 and coefficient of transmission S21 of the composites for various Fe2O3 filler percentages were determined using a rectangular waveguide in connection with microwave vector network analyser (HP/Agilent model PNA N5227). These coefficients were then used to calculate microwave-absorption properties (in decibels). XRD analysis showed that increasing amounts of reinforced material (Fe2O3) reduces the crystallinity of the composites. SEM data indicated that Fe2O3 filler ratio increased in the composites, and adhesion to the cellulose fiber grew gradually until the highest percentage of filler was added. The complex relative permittivity and relative permeability were obtained within the broad frequency range of 8-12 GHz at room temperature for various percentages of filler and were measured by the transmission/reflection method using a vector network analyser. Fe2O3 embedment in OPEFB/PLA was observed to have resulted in enhancing the dielectric and magnetic properties. The values of permittivity and permeability increased with increasing Fe2O3 filler content. Theoretical simulation studied the relation between ε′ and ε″ of the relative complex permittivity in terms of Cole-Cole dispersion law. The result indicated that the processes of Debye relaxation in Fe2O3/OPEFB/PLA, the unique dielectric characteristics of Fe2O3 cannot be accounted for by both the Debye dipolar relaxation and natural resonance. Results further showed that the material transmission, reflection, and absorption properties could be controlled by changing the percentage of Fe2O3 filler in the composites. [ABSTRACT FROM AUTHOR]

Basic research on recyclable, renewable and biodegradable polymer composite materials reinforced with natural fibers is increasingly growing. In this article, we characterize agricultural waste by determining its dielectric properties for microwave absorber application. Recently, polymer composites reinforced with natural fibers are increasingly used in dielectric and aircraft applications. We used a Thermal Hake blending machine to blend oil palm empty fruit bunch with polycaprolactone grain to make a homogeneous powder. The functional groups of the resulting composites were then analyzed through Fourier transform infrared spectrometry. Thermogravimetric and differential thermogravimetric analyses were performed to determine the thermal degradation behaviors of the composites. The tensile strength, tensile modulus and elongation at break of the composites were measured in an Instron universal testing machine. A rectangular waveguide and open‐ended coaxial probe connected to a microwave network analyzer (PNA) Agilent N5230A PNA‐L was used to measure the reflection coefficient S11 and transmission coefficient S21 values and the dielectric properties of the composite materials. Results showed that the thermal stability and dielectric properties of the polymer composites decreased as the fiber content increased. The composites exhibited potential as microwave absorbers at microwave frequencies. POLYM. COMPOS., 39:E1778–E1787, 2018. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: A five‐port ring reflectometer‐probe system was developed to measure relative permittivity of normal and tumorous breast tissues in frequency range from 1.6 to 2.75 GHz. The calibration procedures of the study reflectometer and the coaxial probe were described in detail. In this study, the synthetic breast tissues have been used, which are the Triton TX‐100‐water mixture at different ratios that mimic dielectric properties of normal and tumor breast tissue samples. The comparative studies of reflection coefficient and dielectric properties of the synthetic mixture samples were conducted using study reflectometer‐probe system and commercial vector network analyzer with Keysight (formerly Agilent) 85070E dielectric probe. Maximum mean errors of the linear magnitude, phase, dielectric, and loss factor measurements were recorded to be 0.02, 6.1°, 2.21, and 1.60, respectively. These measurements were significantly distinguishable for normal and tumorous breast tissues. [ABSTRACT FROM AUTHOR]

A material description was established for oil palm empty fruit bunch (OPEFB) fibre waste for microwave absorber applications by determining its dielectric properties with respect to fibre size and frequency. The proposed OPEFB material was studied at frequencies from 1 to 4 GHz. The study was conducted using the open-ended coaxial probe (OECP) HP85071C technique. The effect of microwave frequency on complex permittivity properties for powdered OPEFB and compressed OPEFB with different particle sizes (100, 200, 300, 400, and 500 μm) were investigated. Results showed that the microwave frequency and particle size significantly influenced the complex permittivity (real and imaginary) properties of the samples. Moreover, the complex permittivity decreased as the powder fibre size increased. The complex permittivity of the smallest and largest powder fibre sizes (100 and 500 μm) were (2.050 - j 0.197) and (1.934 - j 0.137), respectively; and the complex permittivity of the smallest and largest compressed OPEFB fibre sizes (100 and 500 μm) were (3.799 - j0.603) and (3.326 - j0.486), respectively. The compressed OPEFB complex permittivity was higher than that of the OPEFB powder. [ABSTRACT FROM AUTHOR]

The dielectric and magnetic behaviour and thermal properties of composites based on nickel-zinc ferrite (NZF) filler can be improved by the addition of various types of materials. Amongst others, ferrite-polymer composites have been subjected to a wide range of research, due to their extensive applications: electromagnetic interference shielding, microwave absorption, electrodes and sensors. Currently, the interest in scientific and technical searches for the potential outcomes of ferrite-polymer materials due to their different uses in applications such as telecommunication applications, microwave devices and electromagnetic interference shielding has been growing stronger. The dielectric and magnetic behaviour and thermal properties for such composite materials depend on size, shape and the amount of filler addition. Nickel-zinc ferrite material was prepared using the conventional solid-state reaction technique. This study highlights the development of microwave-absorbing material from NZF by adding natural fibres, Oil Palm Empty Fruit Bunch (OPEFB) and polycaprolactone (PCL). OPEFB is considered in this study because it is a solid waste product of the oil palm milling process which is widely and cheaply available. The use of OPEFB in this product may save the environment from oil palm solid waste. A Thermal Hake blending machine was used in blending the powder structure of NZF + OPEFB + PCL, which made it homogeneous. These composites were characterized by the use of Fourier transform infrared (FTIR) spectrometry and scanning electron microscopy (SEM). The thermal degradation behaviour of the composites was analyzed using thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) thermograms. The effective permittivity and effective permeability was obtained over a broad frequency range from 8 to 12 GHz at room temperature. It was observed that the values of effective permittivity and permeability increased as the content of NZF content increased. A rectangular waveguide connected to a microwave vector network analyser (PNA) (HP/Agilent model PNA E8364B) was employed in measuring the reflection coefficient S11 and transmission coefficient S12 parameters of composites for different percentages of NZF filler. This parameter was then used in calculating the microwave absorbing properties (dB). [ABSTRACT FROM AUTHOR]

Effect of In ion substitutions on yttrium iron garnet samples' morphology, magnetic properties and dc electrical resistivity was examined closely and reported in this study. A series of polycrystalline garnet ferrites with composition of YFeInO (0 ≤ x ≤ 0.5) were prepared by using the mechanical alloying technique. The morphological properties of the samples was analysed by using a TEM, XRD, FESEM and EDX. The electrical dc resistivity of the samples was investigated as a function of temperature and composition by using a Picoammeter, the complex permeability was analysed by using an Impedance Materials Analyzer meanwhile microwave properties was measured by using VNA. The lattice constant increases as In content increases which can be understood by the difference in ionic radii of In ions replacing the smaller Fe ions. The grain size also increased with In content, indicating that the In ion acts as a grain growth promoter. Both complex permeability components, µ′ and µ″ reaching about 92.75 and 85.03 respectively at x = 0.3; later decreased with further In substitution. This result is synchronized with FMR linewidth which manifests magnetic loss of the samples. By correlating the phase analysis, morphology, electrical resistivity and complex permeability results, it is believed that there was an increase in number of crystalline-growth regions with increasing In content, which together increased a total mass of ferromagnetic grains with the latter starting to dominate the samples. The results also showed that In ions increase the dc resistivity of the system. [ABSTRACT FROM AUTHOR]

The dielectric properties of four types of rhizomes from Zingiberaceace families, namely Java turmeric, Mango ginger, Black turmeric and Turmeric were measured. The non-destructive measurement technique was adopted for the measurement using HP-85070B open-ended coaxial line probe coupled with a computer-controlled Automated Network Analyzer (ANA) at the frequency range of 0.13-20 GHz which is in the microwave frequency region. The dielectric properties of all samples are presented graphically to show the dependence of these properties on moisture content and frequency. The results show that the dielectric properties of samples follow the trend of dielectric properties of deionised water. The dielectric constant decreased with increase in frequency and the dielectric loss factor decreased in low frequency before increasing at 1.5 GHz and above. The penetration depths for all samples were calculated. The results show that they were only dependent upon the moisture at low frequency (≤ 10 GHz). [ABSTRACT FROM AUTHOR]

Six-port reflectometer is well-known for its ability to measure magnitude and phase-shift of microwave signal using four power detectors that perform magnitudeonly measurements. This paper presents the development of an innovative symmetric ring junction as four-port reflectometer for complex reflection coefficient measurements. It reduces the number of required detectors to two. Design optimization, new calibration modeling and algorithm are discussed in details for this four-port reflectometer. The developed four-port reflectometer is compared to five-port reflectometer and vector network analyzer. It is found that the measured magnitude and phase-shift show good performance in comparison with the commercial vector network analyzer and the five-port reflectometer. [ABSTRACT FROM AUTHOR]

This paper describes a detailed study on the application of an open ended coaxial probe technique to determine the permittivity of NixZn1-xFe2O4 in the frequency range between 1 GHz and 10 GHz. The x compositions of the spinel ferrite were 0.1, 0.3, 0.5, 0.7, and 0.9. The NixZn1-xFe2O4 samples were prepared by 10-hour sintering at 900°C with 4°C/min increment from room temperature. Particles showed phase purity and crystallinity in powder X-ray diffraction (XRD) analysis. Surface morphology measurement of scanning electron microscopy (SEM) was conducted on the plane surfaces of the molded samples which gave information about grain morphology, boundaries, and porosity. The tabulated grain size for all samples was in the range of 62 nm–175 nm. The complex permittivity of Ni-Zn ferrite samples was determined using the Agilent Dielectric Probe Kit 85070B. The probe assumed the samples were nonmagnetic homogeneous materials. The permittivity values also provide insights into the effect of the fractional composition of x on the bulk permittivity values NixZn1-xFe2O4. Vector Network Analyzer 8720B (VNA) was connected via coaxial cable to the Agilent Dielectric Probe Kit 85070B. [ABSTRACT FROM AUTHOR]

Bio-composites of oil palm empty fruit bunch (OPEFB) fibres and polycaprolactones (PCL) with a thickness of 1 mm were prepared and characterized. The composites produced from these materials are low in density, inexpensive, environmentally friendly, and possess good dielectric characteristics. The magnitudes of the reflection and transmission coefficients of OPEFB fibre-reinforced PCL composites with different percentages of filler were measured using a rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in the X-band frequency range. In contrast to the effective medium theory, which states that polymer-based composites with a high dielectric constant can be obtained by doping a filler with a high dielectric constant into a host material with a low dielectric constant, this paper demonstrates that the use of a low filler percentage (12.2%OPEFB) and a high matrix percentage (87.8%PCL) provides excellent results for the dielectric constant and loss factor, whereas 63.8% filler material with 36.2% host material results in lower values for both the dielectric constant and loss factor. The open-ended probe technique (OEC), connected with the Agilent vector network analyzer (VNA), is used to determine the dielectric properties of the materials under investigation. The comparative approach indicates that the mean relative error of FEM is smaller than that of NRW in terms of the corresponding S21 magnitude. The present calculation of the matrix/filler percentages endorses the exact amounts of substrate utilized in various physics applications. [ABSTRACT FROM AUTHOR]

In industrial equipment and home appliance applications, the electromagnetic compatibility compliance directive (ECCD) demands that electromagnetic interference side effects be eliminated or marginally minimized. The equipment must not disturb radio and telecommunication as well as other appliances. Additionally the ECCD also governs the immunity of such equipment to interference and seeks to ensure that this equipment is not disturbed by radio emissions when used as intended. Many types of absorbing materials are commercially available. However, many are expensive and not environmentally friendly. It is in the light of the above that we studied the electromagnetic absorption properties of ZnO-PCL nanocomposites prepared from cheap and abundant resources which are environmentally friendly (zinc and polycaprolactone). The test was carried out using a microstrip, open ended coaxial probe, and vector network analyzer. Amongst other findings, result showed that the ZnO-PCL nanocomposite has the capability of attenuating microwave frequency up to −18.2 dB due to their very high specific surface areas attributed to the nanofillers at 12 GHz. [ABSTRACT FROM AUTHOR]

The role of indium (In) substitution in the dynamics of ferrimagnetism, structure and microstructure of yttrium iron garnet (YIG) employing sintering temperature as a temporary agent of composition and microstructural changes was examined closely and reported in this study. The nanoparticles of YIG powder samples with various In content (x = 0.0, 0.1, 0.2, 0.3, 0.4) were prepared via the mechanical alloying (MA) technique. A brief, yet revealing characterization of the samples was carried out by using a transmission electron microscopy, X-ray diffraction, Raman spectroscopy and scanning electron microscopy to analyse the structural and morphological properties, whereas B-H hysteresis graph and LCR-meter were used to measure the magnetic and thermo-magnetic behaviour respectively. The X-ray diffraction analysis of the samples prepared via the MA indicates the formation of single phase YIG structure at much lower sintering temperature than that in the conventional ceramic technique. The lattice constant increases as In content increases which obeys Vegard's law due to the larger In ions replacing the smaller Fe ions. The grain size also increased with In content, indicating that the In ion acts as a grain growth promoter. The saturation induction increased reaching about 699.1 G for x = 0.3 and decreased with further In substitution. Three stages of ordered magnetism formation were identified which attributed to development of crystallinity and larger grains for magnetic domain accommodation. The Curie temperature shows a decrement of 60 °C for In content changes from x = 0.0 to x = 0.4 due to weakening of superexchange interactions. Raman shifts from 268.1 to 272.2 cm with increasing In content were observed due to stress developed in the YIG crystal structure. Possible mechanisms contribute to these properties are discussed in this paper. [ABSTRACT FROM AUTHOR]