Transmission Of Electromagnetic Waves Research Articles

Asymmetric transmission of linearly polarized electromagnetic waves using chiral metamaterials with constant chirality over a certain frequency band

In this study, a dynamic chiral metamaterial (MTM) structure leading to an asymmetric electromagnetic (EM) wave transmission for linear polarization is presented. The structure is composed of square-shaped resonator with gaps on both sides of a dielectric substrate with a certain degree of rotation. The dynamic structure is adjustable via various parameters to fit any desired frequency ranges. Theoretical and experimental analysis of the proposed structure are conducted and given in detail. The suggested model can provide constant chirality over a certain frequency band and thus, it can be used to design myriad novel devices such as EM transmission and antireflection filters, and polarization rotators for desired frequency regimes.

Exploring superluminal transmission of electromagnetic waves through dielectric barriers and causality: a pedagogical insight

A pedagogical insight into models for determining the transit time of electromagnetic waves through dielectric barriers is presented. The meaning of this time is analyzed and the issue of superluminal propagation (propagation with a velocity higher than light velocity) is discussed in relation to the principle of causality. These analyses are illustrated with examples and comparison of results obtained with the models presented here. This paper is addressed to postgraduate physics students in the their early studies who have acquired a suitable grounding in classical electrodynamics. The main objective is to motivate these students to research these subjects further.

Electromagnetic waves reflection, transmission and absorption by graphene–magnetic semiconductor–graphene sandwich-structure in magnetic field: Faraday geometry

Electrodynamic properties of the graphene–magnetic semiconductor–graphene sandwich-structure have been investigated theoretically with taking into account the dissipation processes. Influence of graphene layers on electromagnetic waves propagation in graphene–semi-infinte magnetic semiconductor and graphene–magnetic semiconductor–graphene sandwich-structure has been analyzed. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such structure have been calculated. The size effects associated with the thickness of the structure have been analyzed. The possibility of efficient control of electrodynamic properties of graphene–magnetic semiconductor–graphene sandwich-structure by an external magnetic field has been shown.

Hybrid composite low-observable radome composed of E-glass/aramid/epoxy composite sandwich construction and frequency selective surface

Low-observable radomes are generally fabricated in the shape of a composite sandwich construction whose faces are made of either an E-glass/epoxy or aramid/epoxy composite because both composites have low interference electromagnetic (EM) wave transmission characteristics. However, the E-glass/epoxy and aramid/epoxy composites have different EM and mechanical properties; therefore, they might be used simultaneously as the hybrid composite face for a low-observable radome to better exploit their properties selectively.In this study, a hybrid composite low-observable radome employed in the X-band frequency range was designed as the composite sandwich construction composed of E-glass/aramid/epoxy hybrid composite faces, a polymethacrylimide (PMI) foam core and a frequency selective surface (FSS). Then, the EM wave transmission characteristics were evaluated with a 3-dimensional (3-D) numerical simulation and verified with a free space measurement method. Finally, the mechanical performances were measured by the 3-point bending test and compared to the results of conventional low-observable radomes.

Dual-band asymmetric electromagnetic wave transmission for dual polarizations in chiral metamaterial structure

In this paper, we propose a chiral metamaterial structure that enables dual-band asymmetric transmission effect for different linearly polarized electromagnetic waves. The metamaterial is composed of metallic spirals with two split-ring resonators sandwiching a dielectric slab and connecting with via hole. Strong one-way transmission of two orthogonally polarized waves at different frequency bands has been confirmed through both full-wave simulation and test on fabricated prototype at the microwave band. Analysis also shows such asymmetric transmission can be attributed to the induced asymmetric current distributions in the spiral that support strong polarization conversion and cross-polarization transmission. By scaling down the metamaterial structure, the concept could also be utilized at other frequency bands, such as submillimeter or even terahertz band and find applications in designing one-way electromagnetic wave devices or polarization spectral filters.

Design, Fabrication and Characterization of Fused Silica-Based Composites with an LTCC-Derived FSS

Laminated composites with a frequency selective surfaces (FSS) or more complex metamaterials are potential radome materials due to their unique characteristics of electromagnetic wave transmission. For making high-temperature resistant radomes, metamaterials or laminated composites with an FSS should be based on ceramic substrates. However, the processing methods for ceramic metamaterials are very limited and the conventionally used LTCC technique suffers from the shortcoming of large sintering shrinkage rates, which unfortunately impede the production of ceramic-based metamaterials. In this paper, a novel method of a low temperature co-fired ceramic (LTCC) technique combined with a technique of ceramic joining via green tapes was developed to fabricate the fused silica ceramic laminates sandwiched with the FSS. It was found that the newly developed composites with the FSS unit cells of the Ag-Pd strips exhibited near zero shrinkage of the unit cells, showed predictable transmission efficiencies of electromagnetic microwaves, and were able to overcome the poor transmission efficiencies below 11 GHz of the pure fused silica ceramic plates with an identical thickness.

Reflected and Transmitted Powers of Electromagnetic Waves through a Ferrite-Dielectric Photonic Crystal

In this work, reflection and transmission of electromagnetic wave by a periodic ferrite-dielectric photonic crystal are investigated theoretically and numerically. The ferrite material is described and its main parameters are given in detail. After the construction of the problem, the reflection and transmission coefficients are derived in a closed form by a transfer matrix method. The reflected, transmitted, and loss powers of the crystal are calculated using these coefficients. In the numerical results the mentioned powers are computed and illustrated as a function of frequency, angle of incidence, dielectric thickness, and applied magnetic field intensity when the damping coefficient changes.

Reflected and Transmitted Powers of Electromagnetic Waves through a Ferrite-Dielectric Photonic Crystal

In this work, reflection and transmission of electromagnetic wave by a periodic ferrite-dielectric photonic crystal are investigated theoretically and numerically. The ferrite material is described and its main parameters are given in detail. After the construction of the problem, the reflection and transmission coefficients are derived in a closed form by a transfer matrix method. The reflected, transmitted, and loss powers of the crystal are calculated using these coefficients. In the numerical results the mentioned powers are computed and illustrated as a function of frequency, angle of incidence, dielectric thickness, and applied magnetic field intensity when the damping coefficient changes.

Characterization of Radome Materials Comprising LTCC-Derived FSS on a Quartz Glass Plate

Frequency selective surfaces (FSS) and recent metamaterials (MTM) have shown unique electromagnetic characteristics and are of potential benefits for radome applications. To make the radomes/windows high-temperature resistant, the substrates of the frequency selective surfaces or metamaterials should be made of ceramic/glass-based materials of a low dielectric constant and a low loss tangent. However, fabricating ceramic/glass-based FSS or MTM is always challenging. In this paper, a constrained low-temperature co-fired ceramic (LTCC) technique was used to produce quartz glass-based radome material consisting of a frequency selective surface (FSs) layer embedded in a surface laminate. Due to the constrained sintering shrinkage, the geometry and the dimensions of the unit cells of the FSs were not subjected to significant variations and thus the measured electromagnetic (EM) wave transmission spectra matched those of the computer simulation results quite well. This preliminary work marks the beginning of our long-term efforts toward the goal of achieving high-temperature resistant, highly electromagnetic wave transparent, as well as carefullydesigned and fabricated radome materials.

Microwave properties of materials with dolomite and ilmenite structures

Frequency dependences of transmission and reflection coefficients of electromagnetic waves are experimentally studied at frequencies ranging from 12 to 38 GHz. It is demonstrated that dolomite and corundum samples exhibit relatively low reflectances and absorbances in several spectral intervals. The results of microwave measurements are compared with the structural state and phase composition of the samples.

Resonance transmission of electromagnetic wave through a thin dielectric rod

Squeezing and transmitting electromagnetic energy through structures with transverse dimensions very much smaller than the operating wavelength assumes an importance in various microwave and optical fields. We present a means using resonance transmission whereby electromagnetic waves inside rectangular waveguides are significantly squeezed and efficiently transmitted in a thin dielectric rod. At resonance frequencies, electromagnetic waves form an integer number of resonance magnetic dipoles along the rod. With these dipoles alternately arranged, the phase shift between the two ends of the rod is 0° or 180° on whether their number is even or odd. The experimental results are in agreement with the theory and simulated results. This proposed resonance transmission has many applications in microwave devices such as couplers, filters, and phase inverters.

A systematic approach to enhance off-axis directional electromagnetic wave by two-dimensional structure design

In this study, we propose a two-dimensional (2D) dielectric structure tailored by a systematic design approach on the exit side of a metallic aperture to enhance the off-axis electromagnetic (EM) wave. We adopted a phase field method based topology optimization scheme and designed an arbitrary 2D dielectric structure in order to steer outward beaming through an aperture to a specific direction. Beyond previous one-dimensional structure, we proposed an arbitrary 2D dielectric structure through the introduced design process defining not only x- but also y-directional dielectric structural boundaries simultaneously and experimentally confirmed enhanced EM wave transmission to a desired direction.

Transmission of Electromagnetic Waves in Softmaterial Waveguides

We report here experimental data for transmission of electromagnetic waves through a variety of softmaterial structures made of plastic tubes and ionic solutions, as compared to that in the free space. The results firmly support the theory on softmaterial waveguides in the environment of ionic solutions. This is a solid step towards a better understanding of the underlying physics for the electrical communication in biosystems through axons and membranes. It also offers valuable insight for further experiments with artificial materials at the nanoscale, and experiments in live animals.

Reflection and transmission of electromagnetic waves at a temporal boundary

We consider propagation of an electromagnetic (EM) wave through a dynamic optical medium whose refractive index varies with time. Specifically, we focus on the reflection and transmission of EM waves from a temporal boundary and clarify the two different physical processes that contribute to them. One process is related to impedance mismatch, while the other results from temporal scaling related to a sudden change in the speed of light at the temporal boundary. Our results show that temporal scaling of the electric field must be considered for light propagation in dynamic media. Numerical solutions of Maxwell's equations are in full agreement with our theory.

3 μm aperture probes for near-field terahertz transmission microscopy

The transmission of electromagnetic waves through a sub-wavelength aperture is described by Bethe's theory. This imposes severe limitations on using apertures smaller than ∼1/100 of the wavelength for near-field microscopy at terahertz (THz) frequencies. Experimentally, we observe that the transmitted evanescent field within 1 μm of the aperture deviates significantly from the Bethe dependence of E ∝ a3. Using this effect, we realized THz near-field probes incorporating 3 μm apertures and we demonstrate transmission mode THz time-domain near-field imaging with spatial resolution of 3 μm, corresponding to λ/100 (at 1 THz).

ELECTROMAGNETIC WAVE PROPAGATION IN THE FINITE PERIODICALLY LAYERED CHIRAL MEDIUM

The transmission and reflection coefficients of electromagnetic waves propagating through the finite periodically layered chiral structure are defined both theoretically (using the propagation matrix method) and experimentally. The coefficients of the propagation matrix of the periodically layered chiral medium are obtained. The boundaries of the forbidden bands for a periodic medium, whose unit cell consists of two different chiral layers were determined. It is shown that the boundaries of the forbidden bands do not depend on the chirality parameter of the layers. It is found that for certain values of the layers thicknesses, the forbidden band widths tend to zero and that the proposed method for calculation of the reflection and transmission coefficients can be used to determine the effective constitutive parameters of artificial chiral metamaterials. The transmission and reflection coefficients of plane electromagnetic waves propagated through the finite periodically layered chiral structure were determined experimentally for 20-40 GHz range. A good agreement between the experimental results and theoretical studies of the forbidden band spectrum for the structure under research has been shown.

Antireflection Coating at Metamaterial Waveguide Structure by Using Superlattices (LANS)

The characteristics of electromagnetic wave reflection and transmission by multilayered structures consisting of a pair of left-handed material (LHM) and superlattices (LANS) slabs inserted between two semi-infinite dielectric media are investigated for photovoltaic and solar energy applications. Maxwell’s equations are used to determine the electric and magnetic fields of the perpendicular polarized wave incident at each layer. Snell’s law is applied and the boundary conditions are imposed at each layer interface to calculate the reflected and transmitted coefficients of the structure. The reflected, transmitted powers are determined using these coefficients by a recursive method. The reflected and transmitted powers are computed in both visible and microwave spectral band with the appropriate LHM for each band and appropriate location of LANS in the structure. They are illustrated as a function of the incident wavelength, angle of incidence, magnetic fraction of LANS and thickness of the slabs with the emphasis on the appropriate refractive indices. I found that, zero reflectance and maximum transmittance of the incident powers are achieved for visible spectral band at a single frequency if LHM and LANS have the same refractive index of opposite signs with the same width and more magnetic material of LANS while the reflected power is zero for less magnetic material of LANS in the microwave spectral band which realizes antireflection coating in this structure.

Analysis of one-dimensional electromagnetic wave transmission characteristics of plasma based on a kinetic theory model

This paper utilizes a kinetic theory model to gain the accurate electromagnetic (EM) wave characteristics in the plasma region, based on the solution of Maxwell-Boltzmann (MB) equation system. The system is solved by finite-difference time-domain (FDTD) algorithm, which gives the results of the electric field intensity and particle velocity distribution function. Furthermore, the validity and effectiveness of the proposed method is verified by comparing the results of reflection coefficient and transmission coefficient of the wave that impinges on plasma plate region with that of the analytic solution.

井中雷达的瞬态电磁波传输特性及实验验证

井中雷达的瞬态电磁波传输特性及实验验证

Mobile Communication and its Adverse Effects

Mobile phone became almost essential part of daily life for all generation of people. It functions with the help of transmission of electromagnetic waves from towers to the cell phones in the micro wave frequency region. The energy carried by the waves is not only useful for mobile communication but also produce adverse affects on the users' health as well as to all living beings which are in the radiation area. The paper aims to discuss some of the possible dark side of health concern by the usage of cell phone and radiation from the towers. It also aims to suggest the possible remedies to minimize the health problems.The Himalayan Physics Vol. 4, No. 4, 2013 Page: 51-59 Uploaded date: 12/23/2013