Waveguide Method Research Articles

Measurement of the Complex Dielectric Constant of Materials Based on a Ridge Waveguide

Abstract—The problem of determining the complex dielectric constant of materials in the centimeter and millimeter wavelength ranges is solved using the waveguide method with an double-ridged waveguide. The use of a segment of an double-ridged waveguide as the measuring cell made it possible to expand the operating frequency range and increase the measurement accuracy due to localization of the electromagnetic field energy in the space between metal ridges. The electromagnetic fields of hybrid types of waves in the double-ridged waveguide were calculated by the partial region method taking into account the peculiarities of the electromagnetic field on the metal and dielectric ridges. The results of measuring the complex dielectric constant for samples made of ebonite, Teflon, and fiberglass are presented.

Диэлектрические характеристики эпоксидной смолы, модифицированной тетраэтоксисиланом, в миллиметровом диапазоне

In this work, the influence of alkoxysilanes introduced into the epoxy resin was studied. That was done in order to study the possibility of using the obtained binders in composite materials with increased radio transparency in the millimetre microwave radio band. Determination of the modified epoxy resin dielectric characteristics in the millimetre microwave radio transparency was carried out by the waveguide method. The measuring complex consisted of a precision measuring line P1-31, a tunable generator on a Gann diode (30-38 GHz), a ferrite gate, and a section of a standard-section waveguide. Based on measurements of the minimum position displacement of the standing wave coefficient by known propagation constants, the free-space wavelength λ0 for a given operating frequency, and the critical wavelength in the waveguide λcr, the loss angle tangent tg(δ) and the permittivity ε were calculated. Calculations of the permittivity ε, the angle of the dielectric loss tg(δ) and the radio transparency loss-ΔР were performed in the MathСad. Moisture absorption of samples was determined by holding them in a desiccator with a humidity of 98 %. The samples were kept in a tightly closed desiccator for 24 hours at a temperature of 25 oC. In addition, the relative moisture absorption was determined using the increase in mass. It was found that the introduction of tetraethoxysilane in the composition in an amount of 1.5-3.5% leads to a decrease in the tangent of the dielectric loss angle. The optimum is observed in the range of the modifier concentration of 2.5-3.5%. This fact confirms that at these concentrations there is a complete interaction of TEOS alkoxygroups with epoxy resin epoxygroups.

Design and Optimization Methodology of Coplanar Waveguide Test Structures for Dielectric Characterization of Thin Films

This paper describes an accurate design method of coplanar waveguide (CPW) test structures on characterizing dielectric properties of thin films with arbitrary thickness. Current CPW measurement method has difficulty in providing accurate dielectric properties of films with extremely small thickness. To address this issue, an optimized algorithm is presented to generate proper geometric parameters of CPW test structures for films with different thickness. To validate the accuracy of the proposed design methodology, various test cases of CPW structures with different dimensions have been designed and implemented, the extracted dielectric properties (e.g., dielectric constant and loss tangent) from the S-parameters of the different test cases are compared to the benchmark results simulated by accurate electromagnetic tool Ansys HFSS. It demonstrates the efficacy of the proposed optimized method on quickly producing correct dimensions of CPW test lines for accurate properties characterization of thin films.

Investigations on europium aluminum incorporated polymer composite optical waveguide amplifier

The gain performance of 50-iun core diameter graded-index (GI) multimode europium aluminum benzyl methacrylate (Eu-Al/BzMA) waveguide was investigated by numerically solving rate and propagation equations using MATLAB. At a fixed waveguide length of 10 cm and gain medium concentration of 13 wt.%, optical gain was found to be dependent on pump power and input signal power. This paper utilized a 532 nm wavelength pump with power varied from 100 mW to 500 mW, together with low (-30 dBm) and high (0 dBm) input signal powers, within the amplification range of 580 to 640 nm wavelength. With the highest pumping power of 500 mW and the lowest input signal power of -30 dBm, a 29-dB optical gain with wavelength of 617 nm was observed from forward pumping amplification. For comparison, an identical waveguide in terms of properties was fabricated through an innovative fabrication method for polymer waveguide—the Mosquito method. The fabricated waveguide was then experimentally tested for -30 dBm input signal power with 200 mW pump power in the attempt to realize future real-world applications of short reach networks such as in Local Area Network (LAN) and in-vehicle optical interconnects.

Free and steady forced vibration characteristics of elastic metamaterial beam

The propagation of elastic waves in infinite elastic metamaterials (EMs) is studied by using the effective medium theory (EMT). However, when EMs are applied in engineering practice, finite EM structures should obviously be the most cases, in which the propagation of elastic waves corresponds to the problem of vibration. Therefore, it is necessary to establish a reasonable vibration analysis method for typical EM waveguides and investigate their unique modal characteristics and related vibration characteristics. At present, the relevant exploration is relatively limited, especially analytical analysis. As one typical EM finite structure, an EM beam was chosen to be investigated in this study. Based on the EMT, the Euler beam theory is extended to the analysis of EM finite beams, and the analysis process of free and steady forced vibration is established, the particular characteristics are revealed, including the gathering of natural frequencies in the vicinity of band edges, the absence of natural frequencies within bandgap (BG), and the particular modal correspondence before and after BG. Then, the formation mechanisms of the characteristics are explained from the perspective of standing waves. The obtained results may give insights into the vibration analysis of other finite EM structures, such as EM rods, shafts, plates, and shells.

Achieving full effective microwave absorption in X band by double-layered design of glass fiber epoxy composites containing MWCNTs and Fe3O4 NPs

The glass fiber epoxy composites containing MWCNTs and Fe3O4 NPs were manufactured by composites liquid molding process. The microwave absorbing properties of single-layered and double-layered glass fiber/MWCNTs/epoxy and glass fiber/Fe3O4 NPs/epoxy composites were evaluated. The reflection loss(RL) were calculated by the measured complex permittivity and permeability using waveguide method by vector network analyzer. Based on the mechanism analysis and deficiency of single-layer absorber, the double-layered composites were fabricated by using matching layer and absorbing layer to enhance the microwave absorption performance, which can be modulated by tailoring the electromagnetic parameters and thicknesses of each layer. The optimized microwave absorbing properties of double-layered composites with minimum RL of −45.7 dB and full X-band effective absorption can be achieved when the total thickness of the matching layer and absorbing layer is 1.8 mm, which can be attributed to synergistic effect of improved impedance matching characteristic and superior microwave attenuation characteristic of the absorbing layer. The combined utilization of dielectric loss and magnetic loss absorbent and their double-layered structure design shows great design flexibility and diversity and can be a promising candidate for designing high performance microwave absorbing materials.

A Study on the Fused Deposition Modeling Process of Graphene/Nano-Fe3O4 Composite Absorber and its Absorbing Properties of Electromagnetic Microwave

Graphene/polylactic acid; nano-Fe3O4/polylactic acid; and graphene/nano-Fe3O4/polylactic acid composite absorbers are independently produced by fused deposition modeling technology. The effects of the content of graphene and nano-Fe3O4 on absorbing properties are investigated. After measuring the electromagnetic parameters using the waveguide method, the absorbing property is characterized according to the transmission line theory. The distribution of graphene and nano-Fe3O4 in the matrix is observed by scanning electronic microscopy (SEM). The results show that the graphene and nanometer ferroferric oxide multicomponent absorbing agent helps to form a synergistic absorbing effect. In the frequency range 8.2–18.0 GHz; the absorber has the greatest absorbing property when the content of graphene and nanosize Fe3O4 are 5 wt% and 20 wt%, respectively.

Electromagnetic methods for determining grain humidity

The article considers the waveguide and resonator methods for measuring the dielectric constant. It is shown that the dielectric constant in the microwave range is a linear function of grain density, and the transverse resonator can be used to determine the moisture content of a moving grain flow.

Model of the propagation of very low-frequency beams in the Earth–ionosphere waveguide: principles of the tensor impedance method in multi-layered gyrotropic waveguides

Abstract. The modeling of very low-frequency (VLF) electromagnetic (EM) beam propagation in the Earth–ionosphere waveguide (WGEI) is considered. A new tensor impedance method for modeling the propagation of electromagnetic beams in a multi-layered and inhomogeneous waveguide is presented. The waveguide is assumed to possess the gyrotropy and inhomogeneity with a thick cover layer placed above the waveguide. The influence of geomagnetic field inclination and carrier beam frequency on the characteristics of the polarization transformation in the Earth–ionosphere waveguide is determined. The new method for modeling the propagation of electromagnetic beams allows us to study the (i) propagation of the very low-frequency modes in the Earth–ionosphere waveguide and, in perspective, their excitation by the typical Earth–ionosphere waveguide sources, such as radio wave transmitters and lightning discharges, and (ii) leakage of Earth–ionosphere waveguide waves into the upper ionosphere and magnetosphere. The proposed approach can be applied to the variety of problems related to the analysis of the propagation of electromagnetic waves in layered gyrotropic and anisotropic active media in a wide frequency range, e.g., from the Earth–ionosphere waveguide to the optical waveband, for artificial signal propagation such as metamaterial microwave or optical waveguides.

The use of cenospheres for the production of spheroplastics with high dielectric characteristics, obtained from ash of thermal power plant operating on solid fuel

Current work investigates problems of smoke emissions utilization from thermal power plants operation on solid fuel. During the work of this TPP type, a significant amount of ash is formed. During flotation, a pop-up fraction consisting of hollow spherical particles – cenosphere is distinguished from it. One of the promising applications of the cenospheres is their use as a filler in the production of spheroplastics. Cenospheres ecological safety was studied for the presence of heavy metals and the impact of water hoods on bioorganisms. Cenospheres’ shell chemical composition was determined using an X-ray fluorescence spectrometer «Cпeктроскaн». It is determined that the censosphere consists mainly of aluminium oxide and silicon oxide, and heavy metals are presented in trace amounts. Micro-organisms’ test reactions of the daphnia magna showed the absence of toxic characteristics in the cenospheres. Considering tests results, it was concluded that use of the cenospheres in spheroplast was safe. Based on the unique composition of cenosphere shell made of aluminum and silicon oxides, it was concluded that they should be used as dielectric materials. Dielectric characteristics of spheroplastics on the basis of cenosphere and connector, polymethylphenylsiloxane resin of domestic manufacture, in the field of centimeter microwave radio range are studied by the waveguide method. The research results showed that the dielectric characteristics of spheroplastics are at a very high level. The use of polymethylphenylsiloxane connector allows not only to increase the dielectric characteristics and durability of spheroplastics, but also partially reduce the combustibility and flammability of structures.

Dielectric and Emissive Properties of Sorghum (Jowar) Vegetation at C-Band Microwave Frequency

Abstract Microwave interaction with earth resources like soil and vegetation provides useful information for remote sensing techniques. Such interaction is mainly governed by a complex dielectric property of target material. This paper reports on laboratory measurements of complex dielectric constant of sorghum vegetation (leaves) at room temperature (30°C), at C-Band microwave frequency. Von Hippel (shorted waveguide) method is used to conduct the measurements. The measurements were performed for freshly cut sorghum leaves as a function of moisture content by using automated C-Band microwave bench set up with movable reflector. The least square fitting technique is used to calculate dielectric constant (e'), dielectric loss (e'') and errors in their measurements. Emissivity and radiometric brightness temperature is estimated from measured dielectric properties at different angle of incidence for dry and moist sorghum leaves using Fresnel equations. This study is useful for interpretation of microwave remote sensing of vegetation and applications specifically in agriculture

Scalable self-supported FeNi3/Mo2C flexible paper for enhanced electromagnetic wave absorption evaluated via coaxial, waveguide and arch methods

Scalable self-supported FeNi3/Mo2C flexible paper with satisfactory impedance matching and multiple loss mechanisms to allow excellent wave absorption performance.

Attenuation and Shielding Performance of Wood-Polymer Composites Synthesized via Melt-Blend Technique

In the recent, filler-polymer composites researches have been on the rise due to its implication to electromagnetic interference (EMI) applications. The composition, morphology and surface rheology of the filler-polymer composites play an immense role in determining the electrical, mechanical, and optical properties. In this paper, the preparation and characterization of micro-composites of wood (biodegradable waste material)/polycaprolactone (PCL) composites are reported. The micro-composites were prepared using melt blend technique via the solid state route. This method was selected because of its numerous advantages compared to other methods such as being easy, cheap with mass production of materials. To determine attenuation, rectangular waveguide (RWG) method was used. The magnitudes of the transmission coefficient (S21) from the waveguide measurement were used to determine the attenuation of the wood-PCL composite substrate with respect to different percentages of wood filler. Result from the measurement showed amongst others that as the filler content increases, the attenuation increases. The highest magnitude for attenuation was calculated for the 62.5% wood-PCL composites with a value of -6.46 dB and the least attenuation was calculated for the 12.5% wood micro filler, which value gave -3.34 dB which is good for low shielding applications. Scanning electron microscope (SEM) was used to study the surface morphology of the samples.

Enhanced microwave absorption properties of nickel-coated carbon fiber/glass fiber hybrid epoxy composites-towards an industrial reality

The Nickel-coated carbon fibers (NiCFs)/glass fibers (GFs) hybrid epoxy composites were manufactured by employing papermaking technology to produce NiCFs/GFs paper followed by composites liquid molding. The microwave absorbing properties of single-layered and double-layered NiCFs/GFs hybrid epoxy composites were evaluated. The reflection loss (RL) were calculated by the measured complex permittivity and permeability using waveguide method by vector network analyzer in the X-band (8.2–12.4 GHz) range. The double-layered composites were fabricated by using matching layer and absorbing layer to enhance the microwave absorption performance. The enhanced microwave absorbing properties of double-layered composites with minimum RL of −48.1 dB and effective absorption bandwidth of 3.2 GHz in the X band can be achieved when the total thickness of the matching layer and absorbing layer is 2.5 mm, which is attributed to synergistic effect of improved impedance matching characteristic and superior microwave attenuation capability of the absorbing layer, demonstrating that the NiCFs/GFs hybrid epoxy composites can be a promising candidate of high performance microwave absorbing materials for realizing industrialization.

Lightweight open cell aluminum foam for superior mechanical and electromagnetic interference shielding properties

In the present investigation, a simple and cost-effective method is described for preparing lightweight open cell aluminum foam by impregnating of aluminum powder into a substrate polyurethane foam template. Aluminum powder impregnated polyurethane foam was converted into open cell aluminum foam by several heat treatments inert as well reduce atmospheric pressure. The different concentrations of slurries of aluminum powder in acetone were used in combination with substrate foams to prepare open cell foams of relative density in the range of 0.08–0.22. The open cell aluminum foam prepared by this sacrificial template techniques is found to possess a compressive strength of 6.2 MPa. Electromagnetic interference shielding of aluminum foam was measured in X-band frequency region (8.2–12.4 GHz) using waveguide method. The electromagnetic interference shielding of aluminum foam with relative density of 0.22 is found −44.6 dB. This technique is fast, very economic and highly reproducible which may help the commercialization of such open cell aluminum foam for various applications.

Usage and Experimental Tests of the Modified Waveguide Method for Measurement of the Complex Permittivity and Permeability of Materials

Results of the numerical experiment are presented, which allow considerably extending the range of the waveguide method capabilities in determination of the complex permittivity of materials. Two main methodological errors are estimated, which affect the measurement accuracy and are related to errors in determination of the sample boundary positions in the measuring section and to presence of an air gap between the sample and the wide wall of the waveguide. Calculations are performed in the centimeter and millimeter ranges for materials with a large real component of the permittivity (e1 ⩾ 25) and tangents of the dielectric loss angle tan δe varying between 0.1 and 0.2. Ways of decreasing the errors are proposed. To decrease the measurement error caused by the inaccurate positioning of the sample boundaries, it is proposed to use measuring section-flanges with the length equal to the length of the sample. To decrease the error caused by the air gap between the sample and the wide wall of the waveguide, it is proposed to fill the gap with a nonconducting paste composed of finely dispersed copper powder mixed with petrolatum. The centimeter-range experiment on determination of the complex permittivity of high-ohmic silicon shows an appreciable decrease in the measurement error when the air gap is filled with the above paste. The presented method also allows the complex permeability of a material to be determined. The real component μ1 of the complex permeability of silicon as a dielectric is unity. This is experimentally confirmed.

Preparation and Performance of Si3N4 Hollow Microspheres by the Template Method and Carbothermal Reduction Nitridation.

Silicon nitride (Si3N4) hollow microspheres with smaller particle size and narrower distribution can be used to prepare closed-cell ceramics as the pore-forming agent to improve heat insulation performance and wave-transparent performance of porous Si3N4 ceramics. In this work, Si3N4 hollow microspheres with a diameter of about 1 μm and a wall thickness of approximately 150 nm were prepared by using the template method combined with the carbothermal reduction nitridation method. The optimum preparation temperature of the Si3N4 hollow microspheres is 1450 °C. The morphology, microstructure, and phase composition of the prepared Si3N4 hollow microspheres were characterized. The formation mechanism of the Si3N4 hollow microspheres was discussed. The dielectric properties of Si3N4 hollow microspheres were measured using the waveguide method at 8.2-12.4 GHz. The results show that the wave-transparent performance of the Si3N4 hollow microspheres is similar to those of α-Si3N4 particles. It can be used as the pore-forming agent or matrix for preparing lightweight, heat-insulating, wave-transparent, and high-strength porous Si3N4 ceramics.

Design and Analysis of Substrate Integrated Waveguide (SIW) for High Frequency Applications

In this paper, substrate integrated waveguide has been designed and analyzed for high frequency applications. As high frequency suffers attenuation due to metal waveguide, atmospheric attenuation and Rain fade etc.A improved waveguide method is adapted known as Substrate Integrated Waveguide. SIW is transition between micro-strip antenna and Dielectric filled Waveguide antenna. SIWs are planar structures so they can be fabricated over PCBs and can be easily integrated with supplementary transmission lines. In the study, the different parameters like electric field generated, transmission gain and return loss is evaluated. Results are calculated over a frequency ranging from 6 GHz to 11 GHz.

Polarizability Extraction of Above-Half-Space Transversal Dipole Scatterers Using a Fast Waveguide-Based Approach

We present a semi-analytical method to extract transverse polarizability parameters of an arbitrary bi-anisotropic sub-wavelength scatterer both in homogeneous medium and placed at the boundary of two simple (homogeneous, isotropic, and linear) media. Using this technique, polarizability parameters of various dielectric and/or metallic scatterers are obtained, effectively. In this method, a scatterer is placed at the middle of a rectangular waveguide which in general is filled by two different simple media in either sides of the scatterer. The waveguide is designed so that the two TE10 and TE01 fundamental modes are propagating in a given frequency band. All 16 transverse polarizabilities are fast obtained having 16 different generalized scattering parameters (S-parameters). The S-parameters are associated with excitations at two different ports of the waveguide and the two different modes (TE10 and TE01). Comparing to existing polarizability extraction methods, the presented waveguide method is easy to run, fast and almost accurate. In order to validate the method, we present three examples including omega particle and magneto-dielectric sphere in free-space and an electric resonance particle, placed on top of a dielectric half-space.

Characterization of Transmission and Reflection of Ku Band Split Ring Resonator Reflectarray using Waveguide Method

In this paper, the analysis, design, and measurement of a split ring resonator reflectarray is presented. The 6 different designs of reflectarray are simulated to analyze the effect of splits position on resonance frequency. The SRR reflectarray which covered highest frequency bandwidth at Ku-band is fabricated and tested. In the fabrication, FR4 substrate is used. The S-parameter measurements of the fabricated reflectarray are performed by waveguide method. The obtained results have good reflection characteristics for a wide frequency range from 12 GHz to 16.5 GHz in Ku-band. The maximum value of reflection is achieved approximately at 15.3 GHz frequency