Transmission Of Electromagnetic Waves Research Articles

Plasma characteristics and broadband electromagnetic wave absorption in argon and helium capacitively coupled plasma* *Project supported by the Key Research and Development Plan of Anhui Province, China (Grant No. 201904a07020013).

A one-dimensional self-consistent calculation model of capacitively coupled plasma (CCP) discharge and electromagnetic wave propagation is developed to solve the plasma characteristics and electromagnetic wave transmission attenuation. Numerical simulation results show that the peak electron number density of argon is about 12 times higher than that of helium, and that the electron number density increases with the augment of pressure, radio frequency (RF) power, and RF frequency. However, the electron number density first increases and then decreases as the discharge gap increases. The transmission attenuation of electromagnetic wave in argon discharge plasma is 8.5-dB higher than that of helium. At the same time, the transmission attenuation increases with the augment of the RF power and RF frequency, but it does not increase or decrease monotonically with the increase of gas pressure and discharge gap. The electromagnetic wave absorption frequency band of the argon discharge plasma under the optimal parameters in this paper can reach the Ku band. It is concluded that the argon CCP discharge under the optimal discharge parameters has great potential applications in plasma stealth.

The effect of microspheres surface morphology on the enhanced microwave absorbing properties of MWCNTs

Polystyrene (PS) microspheres with special morphology of bowl-shaped were synthesized by simple dispersion polymerization. The SEM results showed that the diameter of bowl cavity is about 1.4 μm, and many small cavities appeared at the reverse side of the bowl cavity. The absorber hybrids of bowl-shaped PS@MWCNTs were constructed using bowl-shaped PS microspheres with multi-walled carbon nanotubes (MWCNTs) via π-π stacking effect, and the absorbing performance were investigated. Compared with PS@MWCNTs hybrids, the bowl-shaped PS@MWCNTs hybrids demonstrate excellent absorbing performance, the reflection loss(RL) is -34.92 dB at 13.01 GHz in thickness of 2.0 mm, while the reflection loss(RL) of PS@MWCNTs is -22.42 dB. When the thickness of bowl-shaped PS@MWCNTs hybrids is 2.8 mm, the reflection loss(RL) can reach -38.57 dB, and the effective absorption bandwidth (RL ≤ -10 dB) is as high as 4.81 GHz (6.45–11.26 GHz). The results indicated that the existence of bowl cavity structure is vital to the energy attenuation of incident electromagnetic wave due to the enhancement of impedance matching, electromagnetic wave transmission path and multiple reflection in the interior of absorbing materials.

Investigation of the coupling efficiency between graded index photonic crystal-based flat lenses and various types of waveguides

The importance of transmission, guiding and delivery of electromagnetic waves to the targeted part of a photonic circuit, leads to design couplers with high coupling efficiency. In the present work, we apply two types of photonic crystal-based flat lenses for designing the couplers. The lenses are made of annular $${\text{ ZrO }}_{{2}}$$ rods with a triangular structure embedded in air. To design the lenses, the outer radius of the annular cylinders is kept constant while the inner radius follows two linear and parabolic functions. At the next step, the lenses are placed along a slot waveguide, conventional photonic crystal waveguide and funnel-form photonic crystal waveguide, separately, for creating coupled structures. The incident light is focussed by the graded index flat lenses and transmits through the waveguides. In the following, we study the coupling efficiency of all mentioned structures, using finite-difference time-domain and plane wave expansion methods. The results reveal that the coupled funnel-form waveguide with the linear lens gives the highest coupling efficiency, which is $$7.49\,\text{ dB }$$ and shows great improvement compared to the previous works.

Electromagnetic Characterization of a Multiwalled Carbon Nanotubes-Silver Nanoparticles-Reinforced Polyvinyl Alcohol Hybrid Nanocomposite in X-Band Frequency.

This study presents the electromagnetic (EM) characterization of a multiwalled carbon nanotubes (MWCNT)–silver nanoparticles (AgNP)-reinforced poly(vinyl alcohol) (PVA) hybrid nanocomposite fabricated via the solution mixing technique. Primarily, the structure and morphological properties of the PVA/MWCNT–AgNP hybrid nanocomposite are confirmed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The complex permittivity (ε*) and permeability (μ*), as well as the electromagnetic scattering parameters are measured using a PNA network analyzer equipped with X-band waveguide. The results showed an enhanced permittivity (ε′ ≈ 25) value of the hybrid nanocomposite in the frequency range of 8–12 GHz. However, the permeability decreased to almost zero (μ′ ≈ 0.4) since the inclusion of AgNP with an average particle size of 40 nm is not susceptible to magnetization and causes higher magnetic losses (tan δμ) than dielectric losses (tan δε). Remarkably, the hybrid nanocomposite reduced transmission of electromagnetic (EM) wave by nearly 60% in comparison to PVA/MWCNT. This is attributed to the enhanced absorption and reflection at the nanotubes, and metal–dielectric interfaces have induced multiple internal reflections owing to the porous structure of the nanocomposite. The prospect of the PVA/MWCNT–AgNP hybrid nanocomposite is favorable as a thin absorbing material for EM shielding applications.

A polynomial model of transmission and reflection of electromagnetic monochromatic plane waves in lossless, non-magnetic multilayer thin films subjected to an external transverse voltage

A polynomial approach is adopted to simulate the optical-electrical response of a multilayer thin film subjected to an applied transverse voltage. Each layer in the thin film is modelled by a propagation matrix, while the coupling between any two adjacent layers at an interface is modelled by an interface matrix. Each layer in the multilayer thin film in the present approach is treated as a capacitor coupled to the next so that the multilayer film is modelled as an effective capacitor which is constructed by a series of coupled capacitors. The electric charges accumulated at the interface between adjacent ‘capacitors’ can be modulated by the transverse voltage. The model is constructed to describe only lossless and nonmagnetic materials. The reflection and transmission of multilayer MgO/CaF2 thin films with a selected number of layers and structure, subjected to a tunable transverse potential, are simulated with a home-grown code implementing the model. The numerical results indicate that non-trivial optical responses can be conveniently predicted with the code, providing a handy simulator for designing and optimizing desired optical functionality of an arbitrary lossless multilayer thin film by tuning the transverse potential and the geometrical and electrical parameter of the structure.

Theoretical Analyses and Experimental Research on Transmission of Electromagnetic Wave Passing through Concrete Materials Surface

Simplified theoretical model of electromagnetic wave propagation on concrete materials surface is established first by only considering the normal incidence case. In order to investigate the impact of concrete component to the wave transmission, concrete materials specimens with different composite were casted, which were tested by electromagnetic pulse testing method. Study shows that the transmission rate is only relevant with the concrete materials relative dielectric parameter. The greater relative dielectric constant, the smaller transmission rate in materials surface is. Among all this concrete casting components, unit volume water content has the most obvious influence on transmission rate. To change the transmission rate of electromagnetic wave, it is necessary to control the unit volume water content in concrete materials design process.

Monolithic‐Integrated Multiplexed Devices Based on Metasurface‐Driven Guided Waves

AbstractThe appearance of metasurfaces has solved the difficult problems of bulkiness, the complexity of traditional optics, and arbitrary optical response controlling. However, most free‐space metasurfaces and existing integrated metadevices do not meet the criteria of full on‐chip integration toward low loss and high information transmission capacity. Here, by decorating silicon‐on‐insulator waveguides with metasurfaces, one can realize the arbitrary phase and intensity manipulation of guided waves. Four‐channel multiplexer is demonstrated with inherent advantages of low loss and independent transmission of electromagnetic waves in x and y directions. As proof‐of‐concept demonstrations, monolithic‐integrated multiplexed orbital angular momentum (OAM) and holographic generators are developed at 1550 nm to realize high information transmission capacity, low loss, and low crosstalk. Specifically, when the electromagnetic wave is incident from x, −x, y, and −y directions, four kinds of OAM mode with different topological charge values (−1, +1, +2, and −2), and four different holographic images of the letter “U,” “C,” “A,” and “S” can be obtained with the four‐channel multiplexed OAM generator and holographic display device, respectively. The design methods proposed here are expected to open a new perspective for future versatile utilization of driven guided waves to achieve numerous functionalities.

Transmission enhancement effect of electromagnetic wave in non-uniform collisional plasma

The effect of plasma on the transmission properties of electromagnetic waves and its application have always been one of the key research directions of electromagnetic theory and technology and plasma physics. The enhancement effect of collisional plasma on electromagnetic waves is a classic subject of the interaction between electromagnetic waves and plasma. Based on the transmission characteristics of electromagnetic waves in medium, this paper takes plasma as a special medium, and carries out experimental, theoretical and simulation studies on the transmission characteristics of high power microwave (HPM) atmospheric plasma and a certain range of electromagnetic waves under certain experimental conditions. The study found that the plasma formed by the S-band HPM under a vacuum of 50 Pa has a great influence on the electromagnetic wave transmission characteristics of different frequencies, and the electromagnetic wave transmission signal enhancement effect occurs regularly within a certain frequency range. A series of transmission waveforms of continuous electromagnetic waves of different frequencies passing through the HPM plasma area were obtained, and the waveforms were normalized. At 32.4 GHz, the transmission coefficient of continuous electromagnetic waves passing through the plasma area with plasma is about twice as high as that through the area without plasma. A simulation model was established, and the transmission coefficient distribution curve in the range of 31.5−32.5 GHz was obtained. The electromagnetic wave passing through the plasma showed a transmission enhancement effect, and at some frequency points, there was a transmission enhancement of about 1.9 times. The research results provides important technical support for the application of plasma in stealth, emergency communications, and black barrier communications.

Dielectric properties and electromagnetic wave absorbing performance of granular polysilicon during 2450 MHz microwave smelting

The dielectric properties and electromagnetic wave absorbing performance of granular polysilicon have important influences on microwave smelting efficiency. In this study, the dielectric parameters (dielectric constant, dielectric loss factor and loss tangent) of granular polysilicon were measured from room temperature (25 °C) to 800 °C at 2450 MHz by using the cylindrical cavity perturbation method, and the reflection loss of granular polysilicon was calculated according to the theory of electromagnetic wave transmission line, and then the effects of temperature on microwave absorbing performance was analyzed. The results indicated that the dielectric constant and dielectric factor loss of granular polysilicon change little before 300 °C, but when the temperature is higher than 300 °C, the dielectric constant and dielectric loss factor increase gradually. The microwave absorbing performance of granular polysilicon fluctuates with the increase of granules thickness, there are multiple absorption peaks, and the position and intensity of absorption peaks change with the increasing temperature. This study provides theoretical guidance for the optimization of smelting process parameters of granular polysilicon and the design of microwave smelting equipment.

Effects and characterisations of pulse electrodeposition parameters of silver in terms of scattering parameter and surface roughness for waveguides operating at high frequencies

The signal quality of antennas and waveguides in the transmission of electromagnetic waves are very much dependent on the surface finish of these devices. Effects of pulse parameters on the surface properties of silver coatings of the copper substrates have been analysed in terms of surface roughness and S-parameter (scattering parameter). The duty cycle, frequency and average current density were used as three pulse parameters. Three levels were selected for each parameter in the experimental design. The surface finish was found to be directly proportional to duty cycle and average current density but inversely proportional to frequency. The S11 scattering parameter observations were made relative to a gold-plated reference coupon. It was analysed that the smoother surface had more reflection power in terms of S11 parameter thus decreasing the loss of radiation.

Effects and characterisations of pulse electrodeposition parameters of silver in terms of scattering parameter and surface roughness for waveguides operating at high frequencies

The signal quality of antennas and waveguides in the transmission of electromagnetic waves are very much dependent on the surface finish of these devices. Effects of pulse parameters on the surface properties of silver coatings of the copper substrates have been analysed in terms of surface roughness and S-parameter (scattering parameter). The duty cycle, frequency and average current density were used as three pulse parameters. Three levels were selected for each parameter in the experimental design. The surface finish was found to be directly proportional to duty cycle and average current density but inversely proportional to frequency. The S11 scattering parameter observations were made relative to a gold-plated reference coupon. It was analysed that the smoother surface had more reflection power in terms of S11 parameter thus decreasing the loss of radiation.

Flexible multilayered films consisting of alternating nanofibrillated cellulose/Fe3O4 and carbon nanotube/polyethylene oxide layers for electromagnetic interference shielding

Along with the integration and miniaturization of modern electronics, electromagnetic radiation and heat accumulation have become the increasingly serious problem. However, it is still greatly challenging to achieve high electromagnetic interference (EMI) shielding effectiveness (SE) and thermal conductivity (TC) simultaneously in polymeric composite films. Herein, flexible and tough nanofibrillated cellulose/Fe3O4&carbon nanotube/Polyethylene oxide (NFC/Fe3O4&CNT/PEO) films featured with alternating multilayered structures were successfully prepared by a facile alternating vacuum-assisted filtration (AVF) method. The conductive CNT/PEO acted as the EMI shielding layer; the polymeric NFC/Fe3O4 played the role as supporting substrate and synergistically enhanced the EMI shielding performance. Thus, alternating multilayered NFC/Fe3O4&CNT/PEO films exhibited the high electrical conductivity of 3.9 × 103 S/m, excellent EMI SE of 30.3 dB, and thermal conductivity of 9.53 W m−1 K−1. In addition, NFC/Fe3O4&CNT/PEO films showed wonderful mechanical properties with a tensile strength of 36.03 MPa, a toughness of 2.98 MJ/m3, and an elongation at break of 19.1%, due to strong hydrogen bonding between NFC and PEO and hierarchical “zigzag” cracks. Interestingly, alternating multilayered structures could highly improve the toughness and ductility of composite films, in contrast to pure NFC. In the actual EMI shielding application measurement, NFC/Fe3O4&CNT/PEO films were proved to effectively block the electromagnetic wave transmission. This effort opens a creative avenue for designing and constructing flexible and tough composite films with both excellent EMI shielding performance and fascinating heat removal ability.

Indirect Photon-counting Detector (PCD) for Transmission Imaging

Photon-counting detectors (PCDs) are replacing energy integrating detectors in electromagnetic wave transmission imaging to achieve high performance. The purpose of this study was to develop an indirect PCD system for transmission imaging. The detector module is a combination of scintillator and SiPM, the SiPM is insensitive to magnetic field and operating at low voltage. A 2D array of a GAGG coupled with SiPM, positioning logic circuit, and preamplifier were enclosed in housing that sealed from light. A channel reduction circuit was used to identify the channel from the positioning logic circuit, and then output an analog pulse signal corresponding to the valid channel. The pulse signal measurements were performed using a oscilloscope. The profile analysis of the flood map confirmed that each point was distinct in both the center and peripheral regions. Additionally, the letters engraved on the phantom in the images were confirmed. Therefore, the indirect PCD system has potential for transmission imaging. Our future work will design an indirect PCD for low-energy photon detection and multi-energy imaging.

Research of electromagnetic characteristics of planar chiral metastructures based on composite helices components taking into account the heterogeneous Bruggeman model

In this work a mathematical model of a chiral metamaterial is constructed which based on composite fine-wire helices components, which takes into account the properties of chirality, heterogeneity and dispersion. When constructing the model the chiral metamaterial was considered as a heterogeneous system and described by the Bruggeman model. Inthis work, analytical relationships were obtained for calculating the resonance frequencies of composite helices components. Thedispersion properties of the metamaterial were described using the well-known Condon model. As an example of using the constructed mathematical model, we solved the problem of the reflection (transmission) of a plane electromagnetic wave of linear polarization from a planar layer of the chiral structure under study based on composite helices microelements. A system of linear algebraic equations was obtained to determine the reflection and transmission coefficients of the main and cross-polarized field components. As a result of the numerical simulation, the frequency-selective properties of the metastructure were discovered and the frequencies at which the electromagnetic wave is captured by the planar layer of the metastructure were revealed. A similar effect can be used to creation of frequency selective concentrators (hubs) of microwave energy.

Propagation matrix for electromagnetic interaction through electrostatically and magnetostatically biased graphene sheet

The reflection and transmission of plane electromagnetic waves on monolayer graphene are studied theoretically in this paper. From an electromagnetic point of view, monolayer graphene is described as an “infinitely thin” graphene sheet characterized by a surface conductivity, and based on a microscopic quantum dynamical approach, the graphene sheet becomes anisotropic in the presence of both an electrostatic and a magnetic bias. In this work, starting from boundary conditions and phase-matching conditions, the propagation matrix for the analysis of the interaction between an electromagnetic field and thin graphene sheet which is biased electrostatically and magnetostatically, and then characterized by an anisotropic conductivity, is derived. Furthermore, the analytical solutions of co- and cross-polarization reflective and transmittance coefficients through an anisotropic graphene planar surface are obtained from the proposal matrix above, which couples the fundamental transverse electric (TE) polarization and transverse magnetic (TM) polarization and includes the possible effects of electrostatic and/or magnetostatic bias. In conclusion, the cross-polarization reflective coefficient of TE wave and that of TM wave are equal, and their cross-polarization transmittance coefficients have opposite phase. Finally, a new propagation matrix for stratified medium containing anisotropic graphene interfaces is deduced by embedding the matrix across graphene sheet mentioned above into the traditional propagation matrix for isotropic stratified medium. The proposed new matrix can be used to investigate the propagation properties of plane wave in a complex structure of layered medium and anisotropic conductivity interfaces (including graphene sheet) analytically and quickly, and represents a very simple tool for the relevant analysis and design.

Diffraction Focusing of Electromagnetic Radiation by Transmission through Sub-Wavelength Nanoapertures

It is shown theoretically, that the phenomenon of radiation focusing in a small region of the near zone inside a dielectric film can present due to electromagnetic wave transmission through sub-wavelength nanoapertures. The confirmation is based on the rigorous theory of plane wave diffraction by a slot in a perfectly conducting screen of finite thickness in the presence of a plane dielectric film on a substrate, which plays the role of a radiation detector.

Structure and performance control of porous Si3N4 ceramics fabricated by freeze-drying process

Effects of glycerin and silica sol on the structure and performance of porous Si3N4 ceramics that were prepared via freeze-drying were studied. Adding glycerol affected growth process of ice crystals, changed pore structural from bimodal peaks to triple peaks distribution, and formed regular honeycomb structure. This improved mechanical properties and electromagnetic wave transmission properties of Si3N4 ceramics. Therefore, adding glycerol changed mesoscopic morphology of the material. For porous Si3N4 ceramics with 72.5% porosity, flexural strength was 38 MPa, compressive strength was 42.6 MPa, and dielectric constant was 1.75 in the frequency range of 12.4–18 Hz as the amount of added glycerol increasing to 5 wt%. By reducing the sintering eutectic point of the system, the addition of silica sol promoted sintering shrinkage and formed new phases. Thus, pore size distribution was changed from bimodal to unimodal. Moreover, dielectric constant of samples increased from 2.25 to 3.5. Finally, structure and performance of porous Si3N4 ceramics were controlled via addition of glycerol and silica sol.

Manipulation of topological beam splitter based on honeycomb photonic crystals

The intriguing discoveries of quantum spin Hall effect of electrons and its analogy in photon systems have renovated several concepts in condensed matter physics. Here we emulate topological edge states at microwave frequencies utilizing honeycomb photonic crystals with elliptical rods made of silicon material, and a novel topological beam splitter is implemented and analyzed. Robustness against perturbations provides the beam splitter with extremely strong transmission stability. Noticeably, suppressing the backward transmission of electromagnetic wave mitigates undesirable reflection interference. The numerical analysis results reveal that the splitting ratio obtained is in the range of 0.5–1.5 and the maximum transmittance value can reach up to 97% in this system. Besides, by appropriately adjusting the configuration parameters of photonic crystals, the location of operating frequency can be tuned to match different cases. The proposed structure has tremendous potential applications in the field of all-optical integrated circuits and will promote the practicability of photonic topological insulators in the communication domain

High-Pressure THz ESR

In solid-state physics, pressure is an essential parameter, which can continuously change the interaction between electrons. The combination of terahertz electron spin resonance (THz ESR) with pressure is a powerful approach to clarify the spin state under pressure from the microscopic point of view, especially for quantum magnets. The most important feature of our high-pressure THz ESR system is that our pressure cell ensures the high pressure and wide frequency range using ceramics in internal parts, which are well balanced in terms of toughness and transmittance of electromagnetic waves. This approach allowed to very accurately describe the spin state under pressure. In this review, high-pressure ESR systems are reviewed with a focus on those in the high-frequency region. In addition, we show differences between other systems and our system. Moreover, we show the usefulness of our system by showing application examples of several magnetic materials of interest.

Attenuation constant measurements of clear glass samples at the low terahertz band

The technical performance requirements from wireless communication networks are continuously rising. One method to satisfy the demands is increasing the carrier frequency to the millimetre wave or low terahertz band spectrum to utilise wider operation bandwidth. In order to facilitate the studies in this frequency range, the corresponding electromagnetic (EM) wave properties, channel attributes and material characteristics need to be analytically formulated. In line with these, this Letter initially presents the theoretical expressions governing the EM wave transmission across a conducting medium. Then, by using the relative parameter quantities in the proposed attenuation constant ( ) computation technique, the results of the measurements performed between 260 and 350 GHz for the clear window glass samples of different thicknesses are given. This Letter concludes with the evaluation of the outcomes.