Waveguide Measurements Research Articles

Carbon nanotubes films in glass fiber polymer matrix forming structures with high absorption and shielding performance in X-Band

Thin films based on carbon nanotubes materials are used to form layered structures for electromagnetic absorption and shielding applications over X-Band. Measurements in a WR-90 waveguide with a Vector Network Analyzer are carried out to determine the dielectric characteristics of the materials. Samples of graphene and carbon nanotubes are constructed in an epoxy resin polymeric matrix as a one-layer structure. A two-layer structure based on epoxy resin and glass fiber combined with carbon nanotubes films is also examined. Films have a thickness of around 70 μm and have a significant effect in the attenuation of the electromagnetic field. A decrease of more than 20 dB in the Transmission Coefficient can be achieved even with few carbon nanotubes films placed intermediately in a glass fiber polymer matrix. Simulated results compared to measurements of the waveguide setup show satisfactory agreement. Planar layers composed of the above materials are also examined for electromagnetic absorption and shielding performance. A one-layer planar structure that consists of the above carbon nanotubes films in a glass fiber polymer matrix and has a total thickness of 2.7 mm is proposed. It is intended for high shielding effectiveness applications presenting a shielding effectiveness variating between 27 dB and 42 dB over X-Band. However, for both high shielding and absorption applications, a two-layer planar structure with a total thickness of 5.7 mm is designed. The structure consists of successive carbon nanotubes films in a glass fiber polymer matrix as the bottom layer and carbon nanotubes in an epoxy resin matrix as the top layer. The structure presents a shielding effectiveness between 27 dB and 40 dB over X-Band while absorption can reach 95% around 10 GHz. As shown, adding carbon nanotubes in film structure, even with a thickness in the order of μm, inside a polymer matrix can greatly increase the electromagnetic shielding and absorption performance showing also a high attenuation of electromagnetic field.

A 2D Gaussian beam launcher applied in parallel plate waveguide field mapping systems

Abstract3D Gaussian beam generation techniques have been studied by many researchers, while the problem of 2D Gaussian beam generations have not been addressed fully. However, 2D Gaussian beams are still useful in research and applications. This article presents the mechanism, design, simulation, and measurement of a 2D Gaussian beam launcher, which allows the easy control of the width and the location of Gaussian beam waist. The proposed Gaussian beam launcher consists of a radiator array fed with the designable excitation phase and magnitude to each radiator, so as to generate the necessary boundary condition that the Gaussian beam can be excited and propagate. Both simulation and measurement results are nearly identical with the profile of the lowest order 2D Gaussian beam mode. The proposed 2D Gaussian beam launcher is suitable as the excitation source of parallel plate waveguide measurement systems. By integrating tunable components, it can be easily extended in the future to control Gaussian beam parameters dynamically.

Experimentally realization of dual nonlinear dielectric resonance and electromagnetic characteristics of Manganese-doped ZnO NPs in X-Band

In this paper, the electromagnetic details of Manganese-doped Zinc Oxide (Mn–ZnO) nanoparticles (NPs) were measured using the waveguide measurement method in the frequency range 8–12.5 GHz. The evaluations have been utilized by the Nicolson-Ross-Weir method for electromagnetic properties such as permittivity and permeability. The results indicate, dual nonlinear dielectric resonance in X-band at 9.446 and 10.47 GHz. The equivalent circuit and simulated waveguide structure are inserted to explain and verify the dual dielectric resonance. Consequently, Inductance-Capacitance properties are detected by the obtained impedance regarding the reaction of the NPs to the electromagnetic waves and, the outgoing power for the simulated waveguide has a sharp drop at around the two main resonance domains. The evaluated magnetic susceptibility quantity affirms that the Mn–ZnO NPs act as ferro and paramagnetic material at less and above than 10.39 GHz.

Characterization of Tiled Architecture for C-Band 1-Bit Beam-Steering Transmitarray.

A new implementation of a beam-steering transmitarray is proposed based on the tiled array architecture. Each pixel of the transmitarray is manufactured as a standalone unit which can be hard-wired for specific transmission characteristics. A set of complementary units, providing reciprocal phase-shifts, can be assembled in a prescribed spatial phase-modulation pattern to perform beam steering and beam forming in a broad spatial range. A compact circuit model of the tiled unit cell is proposed and characterized with full-wave electromagnetic simulations. Waveguide measurements of a prototype unit cell have been carried out. A design example of a tiled 10 × 10-element 1-bit beam-steering transmitarray is presented and its performance benchmarked against the conventional single-panel, i.e., unibody, counterpart. Prototypes of the tiled and single-panel C-band transmitarrays have been fabricated and tested, demonstrating their close performance, good agreement with simulations and a weak effect of fabrication tolerances. The proposed transmitarray antenna configuration has great potential for fifth-generation (5G) communication systems.

Dual-band multi-bit programmable reflective metasurface unit cell: design and experiment.

Programmable reflective metasurfaces that combine the features of reconfigurable phased array antennas and reflectors are an effective solution for radar and modern communication systems. However, most of the demonstrated active metasurfaces support tunable responses for a specific frequency band. Thus, we propose a programmable metasurface that combines the advantages of multi-bit phase quantization and dual-band operations. To actively control the diverse functions, two PIN diodes are integrated on the radiating element, and these diodes are controlled by the biasing voltage. The unit cell is fabricated, and experimental characterization is performed in the waveguide measurement setup. The proposed design can be applied for imaging and high-capacity wireless communications.

Development of lightweight carbon nanotube-based epoxy nanocomposite shield for broadband electromagnetic interference shielding: estimating shielding effectiveness and experimental validation

Lightweight carbon nanotube (CNT)-based epoxy nanocomposite shield with 0.5 mm thickness are fabricated at various CNT concentrations for broadband electromagnetic interference shielding in this work. The electromagnetic parameters of the samples measured using impedance spectroscopy are used to estimate shielding effectiveness in the X and Ku frequency bands using finite element-based method. The shielding effectiveness obtained using the finite element model at 2 wt.% CNT concentration in the X and Ku bands are 19 dB and 26 dB which agrees well with experimental results obtained using waveguide measurement which amounts to 20 dB and 27 dB, respectively. The finite element model developed for the estimation of shielding effectiveness provides promising results in both X and Ku bands which are experimentally validated. Shielding effectiveness of the prepared samples in the Ku band is superior to that in the X band. High values of shielding in both X and Ku bands qualify it as a good broadband shield with minimal thickness and less weight and cost. Absorption phenomenon dominates the shielding mechanism in both these bands due to the dielectric losses and the electron-rich skeletal structure of CNT. The dominance of absorption loss increases as the frequency shifts from X to Ku band qualifying the developed nanocomposite material as a good broadband shield covering both X and Ku bands.

Spray Pyrolysis Synthesized and ZnO–NiO Nanostructured Thin Films Analysis with Their Nanocomposites for Waveguiding Applications

In this work, we have prepared ZnO, NiO, and nanocomposites ZnO–NiO thin films elaborated by the chemical method of spray pyrolysis on glass substrates at a temperature of 480°C. The prepared samples have been analyzed by means of the X-ray diffraction (XRD), UV-visible spectrophotometry, micro-Raman and m-lines spectroscopies techniques. The structure of the thin ZnO films is hexagonal of the wurtzite type with a preferential orientation along the axis (002). The size of the crystallites, deduced from the XRD measurements, varies between 25 and 43 nm. The NiO films crystallize in the cubic structure with the size 4 nm of the crystallites. The micro-Raman study confirms the XRD results showing the presence of the vibrational modes characteristics of the wurtzite structure of ZnO and the cubic structure of NiO. The obtained films have an optical transmission varying from 60 to 95% in the visible region. The forbidden optical band energies, deduced from the transmittance, are 3.28 and 3.89 eV for the ZnO and NiO films, respectively. The optical waveguiding measurements carried out on pure ZnO and ZnO–NiO films show single-guided modes behavior (TE0 and TM0). These measurements have allowed deducing the thickness and the refractive index values which are respectively 250 nm and 1.89 for ZnO, 165 nm and 1.80 for ZnO–NiO thin films.

Microwave-absorption characteristics of polyaniline-coated multi-walled carbon nanotube composites

ABSTRACT In this study, the microwave-absorption characteristics of multi-layered radar-absorbing structures (RASs) were investigated. Electrical-grade glass (e-glass)/epoxy composites containing modified multi-walled carbon nanotubes (MWCNTs) were fabricated. The poly aniline (PANI) coated MWCNTs was obtained by in-situ polymerisation of aniline in the presence of MWCNTs. The PANI-coated MWCNTs (PCNTs) were then used as reinforcements in the polymer matrix, and their morphologies, microstructures, thermal stabilities, and microwave-absorbing properties were investigated. The complex permittivity and permeability of the composites were measured and found to have increased with increasing filler concentration. Microwave absorbing properties were analysed via waveguide measurement. The three-layered RASs reinforced with PCNTs having a thickness of 4 mm exhibited a RL of –5 dB over the entire X-band and a reflection peak of –24.53 dB at 10.0 GHz. Hence, the epoxy/PCNTs composites are suitable for use in microwave-absorption applications.

Unveiling photophysical and photonic phenomena by means of optical gain measurements in waveguides and solutions

The increasing number of solution-processed laser compounds that can be implemented as low-cost, flexible, and/or integrated devices, makes necessary the development of reliable methods to delineate all their amplifying signatures and thus to open the door to appropriate cross-sample comparisons. Seeking to solve this problem, a new formalism to retrieve the losses and the optical gains from Amplified Spontaneous Emission (ASE) spectra as a function of the excitation density has been recently reported. In this manuscript, we explore the potential of this methodology to unveil relevant information on the photonic properties of the waveguiding devices and on the photophysics of the active materials. We demonstrate that the Variable Pump Intensity method opens the door to understand the relationship between the ASE thresholds and the optical gains and losses, it enables the extraction of the scattering/modal losses of the passive devices, and it can unveil the presence of leaky-modes and excited state absorption. In contrast, it does not perform too well in samples with multiple active species in its current implementation. We have substantiated all these findings using organic semiconductor thin films, several dye-doped polymer thin films and solutions of boron hydride.

Measurement of nickel doped zinc oxide NPs resonance frequencies and electromagnetic properties in X-Band

In this work, the advantages of X-Band lead us to extract and study the electric and magnetic properties of Nickel (Ni) doped Zinc Oxide (ZnO) nanoparticles (NPs). So as to attain the proposed characteristics, waveguide measurement approach has been performed. And in order to extract the stated properties such as permittivity and permeability from the scattering parameters, Nicolson-Ross-Weir method has been utilized. Hence, both capacitance and inductance behaviors have been observed through the attained complex impedance considering the response of the Ni–ZnO NPs to the electromagnetic wave incident. Subsequently, results show that inductance, capacitance and resistance behaviors of Ni–ZnO NPs change around the two main resonance frequencies (8.767 GHz and 10.47 GHz). The attained magnetic susceptibility characteristic confirms that the Ni–ZnO NPs is ferromagnetic over the frequency of 8–9.746 GHz and paramagnetic up to 12.5 GHz.

High luminance and high see‐through head‐mounted displays with beam‐splitter‐array waveguides

AbstractWe have developed head‐mounted displays with high transmittance and luminance, which could be utilized outside safely without dimming glasses. We first specified required optical performance specifications by considering user's safety and usability. In order to ensure that the user is able to recognize both surrounding environment and the image of the head‐mounted display, we set the target specification that the transmittance is higher than or equal to 85%, and the luminance contrast ratio is larger than or equal to 1.15 with display image of white solid pattern. We then developed the beam‐splitter‐array waveguide to achieve the requirements. It has advantages in high efficiency and high see‐through property. In order to determine configuration of the waveguide, we have performed optical ray trace simulation. We also established versatile waveguide measurement method applicable to different‐type waveguides. By utilizing the waveguide we have developed, we made a prototype of a head‐mounted display (HMD) with high transmittance 94% and high luminance 4.8 × 103 cd/m2 and thus luminance contrast ratio 1.25 under the sun. With these advantages, our HMD is suitable for usage outside including applications of work support systems where dimming effect is not preferred, and the HMD is used under the sun.

Noise and bias in off-axis digital holography for measurements in acoustic waveguides.

This paper discusses noise and bias in the method of holographic interferometry applied to the study of acoustics phenomena. The influence of noise on the measurement of acoustic pressure is described by an analytical approach. Relationships to quantify the minimum measurable fluid density and acoustic pressure are given by taking into account the experimental parameters of the setup. These parameters are related to the spatial bandwidths, number of electrons in pixels, readout noise, and quantization noise. Experimental results show that theoretical relations are relatively close to experimental data and that the lower pressure measurement limit is on the order of 15 Pa for the acoustics pressure. The case of waveguides excited by an internal or external acoustic source is investigated. Specifically, for the case of studies in thermoacoustics, this paper demonstrates that the parasitic coupling of vibrations can be compensated. The proposed method is based on the determination of the amplitude and phase of the parasitic oscillation, requiring a few assumptions related to the physics of the underlying phenomenon. Successful compensation is obtained and yields experimental data in agreement with the theoretical predictions.

Measurement of the characteristics of protective screens for microwave radiation made of thin conductive fibers

In thin conductive fibers, which diameter is much smaller than the wavelength, under certain conditions, a very strong absorption of the microwave radiation can occur. The absorption efficiency factor can reach several thousand. It is suggested to use this effect for creation of protective screens. The absorption of radiation occurs in segments of graphite fibers with a diameter of tens micrometers (12…15 μm), which are randomly arranged on the paper or polyethylene film substrate. With such arrangement of fibers, characteristics of the screen do not depend on the radiation polarization. An advantage of the screens is also the uniformity of the frequency characteristics of transmission, absorption and reflection of radiation. The paper describes experiments on measurement of the transmission, reflection and absorption of radiation by screens in the centimeter wave range. The screens were placed in free space under different angles of the incident radiation. The measurement results were compared with the results obtained during measurements in waveguides. As it turned out, the results obtained by both methods are consistent. This makes it possible to recommend waveguide methods based on reflectometers. They are more convenient, fast and accurate than free space measurement methods.Formulas for estimating the transmission, absorption and reflection of screens are given.

A new compact dual-band perfect absorption ultrathin planar metasurface energy harvester in X- and V-bands with a wide incident angle

In this paper, we design and simulate a new dual-band ultrathin metasurface energy harvester (EH) in X- and V-bands. One of the significant advantages of the proposed EH is the efficiency, which is more than 70% over 170° of the TM-polarized oblique incident angles at f = 10 GHz. The full-wave simulation results show that the maximum harvesting efficiencies of 93.4% (in 10.1 GHz) and 84.3% (in 42.86 GHz) are obtained by the TM 75°-polarized and the normal incident waves, respectively. Besides, half-power bandwidths (ratios) are about 1.12 GHz (11.08%) and 2.36 GHz (5.5%), respectively. The designed unit-cell is miniaturized using a C-shaped slot with the dimensions of 0.1λ0 × 0.1λ0 × 0.008λ0 at the lowest resonance frequency (λ0 = 30.12 mm). To analyze the physical mechanism of energy harvesting, the full-wave simulation results of the current and electric field distributions at two resonance frequencies are presented. We demonstrate how the rotation of the load around the metallic via can affect the resonance frequency and the other characteristics of the EH at the X-band. We validate the load’s rotation effects using the waveguide measurement method as well. Finally, we show that the location of the metallic via has a greater impact compared to the load’s rotation using the full-wave numerical simulation at the X-band.

A broadband polarized artificial magnetic conductor metasurface

We present an artificial metasurface comprised of a metallic monolayer having a designed functionality of an Artificial Magnetic Conductor (AMC). The metasurface is designed to operate as a broadband AMC for incident electromagnetic waves polarized in a specific direction, while it works as a pass-band filter for waves orthogonally polarized to the previous direction. Hence the design presents a dual polarization-specific functionality, that of a broadband AMC, or that of a transparent dielectric. In this paper we have selected design parameters scaling the AMC behavior at mm-wave frequencies, but the design can be scaled in other frequency bands of choice. A metasurface sample has been fabricated and characterized via Ka-band waveguide measurements which have validated the approach. Applications on antenna substrates have also been demonstrated through full-wave electromagnetic simulations.

Experimental Characterization of Positive and Negative Dielectric Constants and Artificial Anisotropy of Meta-materials in the Microwave Range

This paper could be considered as a part of the invited talk “Metamaterials and Their Characterization in the Microwave Range” presented on the 8th International Workshop and Summer School on Plasma Physics (IWSSPP’2018, Kiten, Bulgaria), which has been dedicated to the classification, development, characterization and main applications of the metamaterials as one of the key issues of the modern technologies in the microwave, terahertz and optical regions. The experimental characterization of the actual equivalent dielectric parameters of the engineered artificial metamaterials is an important task in their design, nevertheless the existing relatively good correlation between the numerical simulations of these materials by 3D simulators and their measurements. The aim of the presented investigations is to give a helpful comparison between the most popular characterization methods based on free-space, waveguide and resonance measurements in the microwave range. The description of these methods has been based on the following principle: different metamaterials with surface metal inclusions have been selected and their main characteristics – equivalent dielectric constants in different directions (dielectric anisotropy) and the equivalent conductivity have been compared. A special attention has been directed to the description of measurements of positive and negative values of the permittivity, detection of artificial magnetic properties and resonance behaviour of the conductivity of the considered metamaterials.

High loss liquid dielectric characterization: Comparison of microwave waveguide and resonator measurement techniques

AbstractThe microwave waveguide and resonator methods are compared as applied to the experimental determination of the dielectric properties of high loss liquids. A differential microwave waveguide cavity for measuring high loss liquids complex permittivity in a small volume has been designed and studied. This cavity consists of two circular waveguide cells with central rods made of quartz and surrounded by high loss liquid tested. The cells have different lengths to eliminate complex propagation coefficient measurement errors due to the diffraction effect on the ends of the layered waveguide cells. We have measured the wave amplitude and phase coefficients for the waveguide cavity to estimate physical properties of a high loss liquid under test. The resonant frequencies and the Q-factor of a semi-disk dielectric resonator with high loss liquid filling a capillary have been measured. We have selected water-ethanol solutions as a high loss liquid under test for both techniques. We have determined the measurement sensitivity for these two techniques. The measuring results are discussed. Both the waveguide and resonator methods provide comparable sensitivity and can be successfully used for the complex permittivity characterization of high loss liquids in small volumes.

Microwave absorber based on encapsulated expanded graphite-silicone composite as meta-“atom” for X-band application

In this work, a wideband microwave resonating-type absorber is investigated in terms of metal backed metamaterial absorber (MMA). Expanded graphite-silicone (EG-Si) composite is encapsulated in the flexible silicone rubber matrix to build periodic unit cell of the MMA. Microwave material characterization of the EG-Si composites with different weight percentages (1, 3, 5, 7, 9 and 11 wt. %) is carried out at X-band frequency range. CST simulation is performed to optimize the unit cell parameters i.e. a wideband absorption with at least −10 dB absorption bandwidth (BW) throughout the X-band is obtained. Simulation is also carried out to check the polarization and incident angle dependency of the absorber’s absorption performance. The resonance and absorption mechanism of the absorber are investigated with the help of simulated electric field, magnetic field and current density inside the unit cell. The absorption of the prototype absorbers is experimentally measured by waveguide measurement technique.

Microwave absorption performance enhancement using glass fiber-reinforced polymer nanocomposites containing dielectric fillers in X-band

Microwave absorption properties of radar absorbing structures in X-band frequency have been investigated using carbon-based dielectric filler materials. These structures are composed of E-glass/epoxy laminates filled with various wt% (0–2.5 with an increment of 0.5) of graphene and multiwalled carbon nanotubes individually. Composite fabrication has been done using high-pressure resin transfer molding (HPRTM). The pertinent electromagnetic (EM) parameters of composite structures are measured using the waveguide measurement technique in X-band. From the results, a single-layered polymer composite with 2.5% graphene contains better absorption than others. Among multilayered structures, the 11-layered composite structure has shown the best absorption performance (reflection loss (RL) = −21 dB) which is equal to 99.9% of incident EM radiation absorption in X-band. It is found that the single-layered structure has shown ineffective absorption performance compared to the multilayered structure under low weight concentrations. Moreover, a mathematical model to predict RL of different combinations of multilayered structures based on EM wave theory is proposed for the calculation of optimum layer combination for minimizing time and money. The predictions of the mathematical model are validated for the 11-layered structure using experimentation.

Analysis of the electromagnetic properties of eco‐friendly transparent wood

AbstractIn this study, we fabricated transparent wood that can replace transparent building materials, such as glass or plastic, and analyzed its electromagnetic properties through experiments. The results of the dielectric constant measurement experiment revealed that the electromagnetic properties of the fabricated transparent wood differ from those of conventional wood. The waveguide measurement method was used to investigate the electromagnetic wave transmission and reflection properties of the transparent wood. The results were compared with those of a simulation, and agreement between the results was confirmed. We found, by studying the electromagnetic shielding performance through an indium tin oxide coating, that the proposed transparent wood can be used as an eco‐friendly electromagnetic shielding material.