Incoming Electromagnetic Wave Research Articles

Mechanically tunable dual-band metamaterial absorber at ultra-high frequency

We numerically demonstrated a dual-band metamaterial absorber (MPA) operating in low frequency range based on a flexible polyimide substrate. For the flat configuration, two absorption peaks are obtained at 450 MHz and 1.47 GHz with absorption over 90%. The ratios of the periodicity of unit cells and thickness to the longest absorption wavelength are 1/12 and 1/114, respectively. Especially, our MPA is insensitive with polarization and stable with the oblique incidence angle of incoming electromagnetic waves. The proposed MPA maintains an absorption over 90% when incident angle is increased up to 60o. Furthermore, since structure is wrapped and attached to cylindered surfaces (the varying radii from 200 to 500 mm), new absorption peaks can be obtained at higher frequency range. For both flat and curvature states, the absorption mechanism is explained by the magnetic resonance and the perfect impedance matching phenomena.

Recoverable Broadband Absorption Based on Ultra-Flexible Meta-Surfaces

In this work, we demonstrated a tunable metamaterial perfect absorber (MPA) with broadband absorption by tuning the different states of flexible sandwiched structures (graphene conductive ink/rubber/metallic layers). The broadband absorption spectrum was tuned mechanically by changing the concave-up/down states of flexible hemispherical unit-cells. When the unit-cell was concave-up, our proposed MPAs played as a broadband absorber with a fractal bandwidth (FBW) of 107% (since an absorption over 90% ranges from 5.28 to 17.6 GHz) at the normal incidence; at the same time, this broadband absorption feature could remain well at large incident angles up to 40 deg. and regardless of polarization of the incoming electromagnetic waves. In the case of the concave-down state, a narrow FBW of only 6.8% was noticed. These results could promote great application potential, such as regarding advanced stealth devices, advances in the biomedical and the communication fields, and more.

Calculated attenuated total reflection (ATR) for analyzing surface plasmon polaritons

The electromagnetic waves propagate in the interface between metal and dielectric can be simply called surface plasmon polariton. The surface plasmon polaritons were produced by the coupling of incoming electromagnetic waves and collective vibrations of free charges on metal surface. The generation of surface polaritons may be done using attenuated total reflection (ATR) method which was based on total internal reflection. The method can be performed numerically by analyzing reflections on each involved interfaces. The generated surface plasmon polaritons were represented by the appearance of the dip in the ATR spectroscopy. In this paper, we presented the ATR spectroscopy for surface plasmon polaritons generated on gold-castor oil interface. The results showed the predicted dispersion relation from calculated ATR of the surface plasmons polaritons were in good agreement with the dispersion relation from the theory.

Broadband solar absorption by chromium metasurface for highly efficient solar thermophotovoltaic systems

We report a broadband metasurface solar absorber composed of refractory material chromium (Cr) for the intermediate structure of a solar thermophotovoltaic (STPV) system that can overcome the Shockley–Queisser limit for efficient solar energy harvesting. The metasurface absorber exhibits high broadband absorptance with an average higher than 90% for 300–1200 nm. The self-passivation property of chromium ensures resistance to oxidation and corrosion, besides the benefit of being a low-cost material having stability at higher temperatures. The proposed absorber forms one part of the intermediate structure, whereas the emitter forms its second part. The emitter shapes the incoming electromagnetic (EM) waves to have energies just above the PV cell bandgap to assist in efficient electron-hole pair generation. The proposed STPV system can achieve PV cell efficiency of 43.2% with an efficiency greater than 42% in a broad color temperature range of 1597–2573 K, which is comparable to the state-of-the-art. The innovation in our work comes from efficiency enhancement through the hybridization of selectivity and broadband response of the proposed absorbers and emitter. The designs are also subjected to detailed analyses to understand the mechanism behind their performance. Moreover, a robustness check is performed to know which design parameters are crucial to acquiring such results.

Design of Multilayered 2D Nanomaterial Composite Structures for EMI Shielding Analysis.

It is still very challenging to effectively design nanocomposite microstructures with significantly improved electromagnetic interference shielding effectiveness (EMI SE). Herein, we developed a facile method for fabrication of molybdenum disulfide/graphene nanoplatelets (MoS2/GNPs) nanocomposites, in which GNPs are utilized as highly effective electrical transport materials, while MoS2 resolves the agglomeration problem of GNPs. GNPs also serve as an efficient cluster of electrical transport systems and dampen the incoming electromagnetic wave. Two types of samples are synthesized and compared in context of EMI SE values: physically mixed composite and layered samples. The sandwiched MoS2 between GNP layers showed an EMI SE of ∼24 dB, which was an almost 14% improvement relative to MoS2/GNPs nanocomposites exhibiting an EMI SE value of ∼21 dB, both containing 0.5 wt % GNPs. This work provides a new strategy for the design of multifunctional nanocomposites using the simple low-cost vacuum filtration method for EMI shielding for future applications.

One-Dimensional Photonic Serial Asymmetric Loops Structure Containing Three Defects

We study in this work, the occurrence of defects modes in the transmission spectrum and the band structure of a perfect photonic asymmetric serial loops structure (ASLS) utilized for narrow-band filtering. The perfect structure presents large photonic bandgaps that result from the modes of the loops resonances and the system periodicity. Besides that, the existence of defects within this perfect ASLS, whether at the segment or loop level, or both of them, causes the appearance of two, three, or four defect modes within gaps with good transmission rates and high-quality factors. These defects modes are extremely sensitive to changes in structural parameters. This system can be used to filter or guide the incoming electromagnetic waves. The interface response theory has been used to accomplish the analytical calculation. Green's function of the full system is determinated using this method. It allows us to calculate the dispersion relation and the transmission rate. Therefore, this paper can provide ideas for the design of multi-channel tunable filter using for frequency division multiplexing and microwave and signal processing.

Nanoporous Anodic Alumina Photonic Crystals for Sunlight Harvesting Applications: A Perspective

Nanoporous anodic alumina (NAA) fabricated by anodization of aluminum is a versatile platform material with tailorable geometric, optical, and chemical features for specific light‐based technologies and applications. Recent advances in anodization technology have enabled a new generation of NAA‐based photonic crystals (PCs)—periodic dielectric nanoporous structures that selectively allow, forbid, and confine the flow of incoming electromagnetic waves of specific wavelengths across their structure. NAA–PCs provide exciting new opportunities to engineer light–matter interactions with versatility across the broad spectrum, from UV to IR. But despite these fundamental advances, demonstrations of sunlight‐harvesting technologies based on NAA–PCs are still limited. Herein, an up‐to‐date summary of recent advances in NAA–PC technology is provided, and proof‐of‐concept demonstrations and future pathways to propel this versatile platform material across sunlight‐harvesting technologies such as photocatalysis, photoelectrocatalysis, photothermal energy conversion, and solar cells are discussed.

Electromagnetically Induced Transparency and Fano Resonances Base on Coaxial Photonic Waveguide Made up of Asymmetric Loop and Resonators

In the actual work, we present the phenomenon of electromagnetically induced transparency (EIT) and Fano resonances by one-dimensional microwave coaxial waveguides for the aim to achieve a filtering system either by transmission or by reflection with very high performance. Our proposed system is composed of coupled asymmetric loops of lengths d2 and d3, and two asymmetric resonators of lengths d5 and d6. This system creates the resonance modes, which are sensitive to certain lengths, while they are insensitive to other lengths. The very narrow EIT resonance appears as a maximum transmission peak stuck between two transmissions zeros, this EIT is due to the interaction of the Eigen modes of symmetric resonators and the incident electromagnetic waves. On the other hand, a resonance near to a zero of transmission is called a Fano resonance, its appearance is due to the interaction between the Eigen modes of symmetric loops and the incoming electromagnetic waves. The theoretical results are obtained using the continuous medium interface response theory, which allows calculating the Green function of composite systems and the transmission rate T. This structure can be utilized for electromagnetic filtering by transmission or reflection with high transmittance and good quality factor. According to these results, this filtering system can be used in the field of microwave communication antennas.

Fractal metamaterial based multiband absorber operating in 5G regime

Multiband absorption is the interest of the microwave communities due to several applications in sensing, filtering, and stealth. Usually, the stacking of metal and dielectric multilayered structures form a multiband absorber which makes the device bulky and costly. In this paper, we investigate a multiband absorber based on a single-layered fractal metasurface for the 5G applications. The unit cell of the fractal metasurface is comprised of six ring-shaped symmetric split-ring resonators (SRRs) connected back-to-back with each other. The absorptivity is investigated in the 5G microwave regime (22–36 GHz) for various obliquities at different substrate thicknesses. Simulation results show that the proposed fractal metasurface has several absorption peaks in different 5G bands. Furthermore, measured results agree well with the simulation results. The proposed absorber can play an important role in 5G applications wherein sensing the angle of incidence and polarization of the incoming electromagnetic waves is desired.

Experimental verification of ill-defined topologies and energy sinks in electromagnetic continua

It is experimentally verified that nonreciprocal photonic systems with continuous translation symmetry may have an ill-defined topology. The topological classification of such systems is only feasible when the material response is regularized with a spatial-frequency cutoff. We experimentally demonstrate that adjoining a small air layer to the relevant material interface may effectively imitate an idealized spatial cutoff that suppresses the nonreciprocal response for short wavelengths and regularizes the topology. Furthermore, it is experimentally verified that nonreciprocal systems with an ill-defined topology may be used to abruptly halt the energy flow in a unidirectional waveguide due to the violation of the bulk-edge correspondence. In particular, we report the formation of an energy sink that absorbs the incoming electromagnetic waves with a large field enhancement at the singularity.

The first family of application-specific integrated circuits for programmable and reconfigurable metasurfaces

Reconfigurable metasurfaces are man-made surfaces, which consist of sub-wavelength periodic elements—meta-atoms—that can be reconfigured to manipulate incoming electromagnetic waves. However, reconfigurable metasurfaces developed to-date, have limitations in terms of loading impedance range, reconfiguration delay and power consumption. Also, these systems are costly and they require bulky electronics and complex control circuits, which makes them unattractive for commercial use. Here, we report the first family of CMOS application-specific integrated circuits that enable microsecond and microwatt reconfiguration of complex impedances at microwave frequencies. Our approach utilizes asynchronous digital control circuitry with chip-to-chip communication capabilities, allowing simple and fast reconfiguration via digital devices and user-friendly software. Our solution is low-cost and can cover arbitrary board-to-board metasurfaces, with different sizes and shapes.

Detection, Estimation and Radiation Formation Using Smart Antennas for the Spatial Location

The Electromagnetic (EM) waves are impinging on the base station from all the directions, Equally Spaced Uniform Linear Antenna Array (ESULA) are used to process these incoming EM waves to Detect and Estimate the directions of the mobile transmitters. After the process of Detection and Estimation, Electronic Beamforming is used to provide the narrow sharper beam towards the detected user. This Detection, Estimation and Beamforming plays a key role in variety of use cases like Radar, Wireless Communication and Sonar based systems. Smart Antenna Systems are implemented using two strategies namely Direction of Arrival (DoA) and Beamforming (BF). Direction of Arrival is a mechanism of Detecting and Estimating the directions of the mobile transmitters. Beamforming on the other hand is a process of transmission of the EM waves towards the source in a specific direction and providing the Spectral Nulls to other Interfering users. To increase the user capacity and to enhance the user experience Spatial Location based Spatial Division Multiple Access (SDMA) technology is used. To improve the overall performance of the smart antenna systems energy and packet delivery is majorly focused on specific source directions rather than using blind transmission strategy. In this paper performance analysis of algorithms for Direction of Arrival methods as well as the Beamforming methods have been performed. Experimental simulations are conducted and comparison is done with respect to Bias, Resolution and Time complexity for the Direction of Arrival methods. Noise Subspace Method (NSM) DoA algorithm consistently delivered the optimal bias, high resolution detection of the user location in spatial domain and provided lesser time complexity for both the scenarios which uses fewer antenna elements or larger number of antenna array elements at the base station. Similarly for the case of Beamforming methods the Mean Square Error and Beam-directions have been compared.

Quality Evaluation of Lemon Cordial Stored at Different Times with Microwave Heating (Pasteurization)

Consumer interest in food quality and safety has shifted over time, as consumers increasingly prefer minimally processed items. As a result, numerous non-thermal approaches have been implemented due to their potential to preserve the nutritional profile of products along with lengthening their storability. Microwaving, a green processing technique, volumetrically heats the product because of the interactions developed between charged ions, polar water molecules of foodstuff and the incoming electromagnetic waves. The study was mapped out to investigate the effect of microwave exposure time (60, 90 and 120 s) at fixed power (1000 W) and frequency (2450 MHz) on physicochemical properties, phytochemical constituents, antioxidant potential and microbial counts of lemon cordial stored at refrigerated temperature (4 ± 2 °C). The mentioned parameters were analyzed after an interval of 30–90 days. Statistical findings illustrated a highly significant (p ≤ 0.01) impact of microwave treatment and storage on titratable acidity, pH, total soluble solids, total phenolic contents, total flavonoids contents, antioxidant potential and total plate count. Sample microwaved for 120 s showed the highest pH values (2.45 ± 0.050), total soluble solids (56.68 ± 2.612 °B) and antioxidant activity (1212.03 ± 716.5 µg—equivalent of ascorbic acid per 100 mL of cordial); meanwhile, it exhibited the lowest total plate counts (1.75 ± 0.144 Log 10 CFU/mL). Therefore, microwaving can be suggested as a suitable alternate to traditional pasteurization techniques as well as to chemical preservatives.

Reconfigurable Intelligent Surface (RIS) in the Sub-6 GHz Band: Design, Implementation, and Real-World Demonstration

Here, we first aim to explain practical considerations to design and implement a reconfigurable intelligent surface (RIS) in the sub-6 GHz band and then, to demonstrate its real-world performance. The wave manipulation procedure is explored with a discussion on relevant electromagnetic (EM) concepts and backgrounds. Based on that, the RIS is designed and fabricated to operate at the center frequency of 3.5 GHz. The surface is composed of 2430 unit cells where the engineered reflecting response is obtained by governing the microscopic characteristics of the conductive patches printed on each unit cell. To achieve this goal, the patches are not only geometrically customized to properly reflect the local waves, but also are equipped with specific varactor diodes to be able to reconfigure their response when it is required. An equivalent circuit model is presented to analytically evaluate the unit cell’s performance with a method to measure the unit cell’s characteristics from the macroscopic response of the RIS. The patches are printed on six standard-size substrates which then placed together to make a relatively big aperture with approximate planar dimensions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$120 \times 120$ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The manufactured RIS possesses a control unit with a custom-built system that can control the response of the reflecting surface by regulating the performance of the varactor diode on each printed patch across the structure. Furthermore, with an introduction of our test-bed system, the functionality of the developed RIS in an indoor real-world scenario is assessed. Finally, we showcase the capability of the RIS in hand to reconfigure itself in order to anomalously reflect the incoming EM waves toward the direction of interest in which a receiver could be experiencing poor coverage.

Reconfigurable Intelligent Surface Based Orbital Angular Momentum: Architecture, Opportunities, and Challenges

Orbital angular momentum (OAM) has gained a lot of attention due to its potential in enhancing the spectral efficiency for wireless communications. Using different OAM modes, multiple independent data streams are simultaneously transmitted by using spatial distribution of helical phase, which enables OAM as a new form of multiple access technique for wireless communications. Controlling the phases of incoming electromagnetic waves, the reconfigurable intelligent surface (RIS) is suitable for implementing OAM. In this article, an RIS-based OAM framework is introduced. The basic concepts and features of RIS and OAM are presented. Then classifications and comparisons of different RIS-based OAM schemes are summarized. Simulation results verify that RIS-based OAM transmission can achieve nearly 100 percent higher spectral efficiency of wireless communication systems compared to the conventional RIS scheme.

Efficient arbitrary polarized light focusing by silicon cross-shaped metaatoms

The functionality of most of the metasurfaces that have been investigated so far, especially in illuminations with arbitrarily linearly polarized incident light, are restricted to x- or y-polarized incoming light. In particular, filtering out one of the two orthogonal polarizations of the incoming electromagnetic wave loses the incident light energy and limits the potential performance of the metasurface. In this study, by utilizing the cross-shaped silicon metaatoms that support the simultaneous excitation of electric and magnetic dipoles under the illumination of both x- and y- orthogonal polarizations, we overcome the polarization-restricted functionality of the metalenses. By selecting the metaatoms arrangement in the metalens structure, which follows the hyperbolic phase profiles for both x- and y-polarized incoming light waves at the same time, we obtain the light intensity distribution with the extended depth of focus (EDOF) or enhanced intensities at the focal spot with the focusing efficiency 65% for the numerical aperture of 0.7. Utilizing metaatoms with the ability to control the two orthogonal incoming polarizations develops a new methodology for using the full potential and intensity of the arbitrary polarized incoming light. The present design concept of metaatoms has several advantages that are not limited to metalenses alone but can be applied in all metasurfaces realized to have good efficiency. Finally, the proposed metalenses are suitable for imaging, optical tweezers and lithography applications, where subwavelength light intensity distributions with EDOF are the most desirable property.

M-Type Barium Hexaferrite-Based Nanocomposites for EMI Shielding Application: a Review

The electromagnetic radiation emission at high radio frequency causes electromagnetic interference (EMI) which is a serious issue. EMI shielding materials are necessary to shield the incoming electromagnetic waves to prevent this problem. Hence, the advancement of high-performance EMI absorbers with flexibility, strong absorption, and extensive bandwidth has gained great attention. Recently, M-type barium hexaferrite as EM interference absorber has gained much interest, owing to their high magnetic loss, high saturation magnetization, flexibility, low cost, high Curie temperature, and strong absorption. Furthermore, due to high density, the incorporation of other dielectric loss fillers such as conductive polymers, graphene, and carbon nanotubes are studied as an essential way to improve the microwave’s absorption. In this review, we present the EMI theory and also summarize modern improvements in the fabrication of barium hexaferrite-based materials comprising substituted barium ferrite and chemical integrations with conductive polymers, graphene, CNTs, and multicomponent composites. The key points of increasing the EMI absorption in barium hexaferrite-based materials are to regulate the EM properties, improving the impedance match, and expanded the loss mechanisms.

Diffraction of electromagnetic waves by an anomalously transmitting metasurface half-plane in anisotropic plasma

The paper deals with the scattering of magnetic polarized electromagnetic plane waves by a anomalously transmitting metasurface half-plane, located in anisotropic plasma. Such a medium occurs for cold magnetized plasma, in which a static magnetic field exists. In this case the permittivity of the medium is expressed as a tensor, the elements of which are functions of the magnetostatic field, electron’s mass and charge and angular frequency of the plasma. The metasurface half-plane transmits part of the incoming electromagnetic wave with a different angle from the angle of incidence, absorbing the remaining part. First of all, we will obtain the scattered geometric optics wave by subtracting the incident field from the total geometric optics wave. Then the kernel of a physical optics type scattering integral will be constructed with the aid of the integral theory of diffraction. The uniform diffracted magnetic field will be obtained from the physical optics integral. The total magnetic field will be evaluated as a sum of the total geometric optics and diffracted waves. The behaviours of the derived fields will be analyzed numerically.

EVIDENCE OF HUMAN INTER-TISSUE BIOELECTROMAGNETIC TRANSFER: THE HUMAN BLOOD TISSUE INTRINSIC BIOELECTROMAGNETIC ENERGY TRANSFERRING ONTO A MINIORGAN

Basically the human hair consists of a follicle a.k.a root penetrating the skin and an outer skin structure commonly called the shaft. The hair follicle has been classified as a miniorgan having its own cells divisions; aging stages and also demonstrated to emit electromagnetic radiation. The intent of this manuscript is to demonstrate via in vitro experiments evidence of human inter-tissue electromagnetic energy transfer through a glass slide, namely from human blood tissue to the previously described miniorgan or follicle. &#x0D; The mechanism behind this new finding was possible due to the introduction in 2015 of a tabletop optical microscopy method designed to display plants and animal tissue electromagnetic energy emissions. Essential to present finding is the described property of anisotropic crystals of full absorption of incoming electromagnetic radiation waves. K3Fe is an anisotropic crystal. For example, a single layer human blood smear was sandwiched (SDW) by a second glass slide. On the top slide of the SDW, a freshly plucked in toto human hair was then covered by drops diluted K3Fe. Control experiments had repeatedly shown orderly semicircular periodic crystals of K3Fe triggered by the electromagnetic waves emitted by the hair follicle. Prior experiments by this author, have hinted at a “bioelectromagnetic cross-talk” between the follicle and blood. This was seen when there was physical contact between the follicle and blood drops on a glass slide. In the present experiments there is no direct tissue contact, the energy is transmitted through a 1 mm glass barrier. The data herein presented introduces Bioelectromagnetic Fields (BEMFs) energy from human blood onto a miniorgan. This energy is shown penetrating a 1 mm glass slide barrier. Further research is warranted to assess the physiological implications of the human blood tissue as a molecular and BEMFs energy source.

Structural, Magnetic and Microwave Absorption Characteristics of Ba&lt;sub&gt;1-x&lt;/sub&gt;La&lt;sub&gt;x&lt;/sub&gt;Fe&lt;sub&gt;12&lt;/sub&gt;O&lt;sub&gt;19&lt;/sub&gt; (x = 0; 0.1; 0.2;0.3;0.5;0.7)

In this study, effect of La substitution on the microstructure, magnetic properties and microwave absorption characteristics of Ba1-xLaxFe12O19 (x=0, 0.1, 0.2, 0.3, 0.5, 0.7) is reported. The samples were synthesized through mechanical alloying and solid reaction a temperature 1200 °C for 2 hours. A single-phase material occurred only at x = 0 and 0.1. Additional second phases were existing in all samples with x ≥ 0.2 which led to multi-phase materials. The single phase (x = 0 and 0.1) has a relatively uniform particle size distribution with a mean crystallite size 138 nm. Additional phases of respectively Fe2O3 and LaFe2O3 were identified in all samples with x ≥ 0.2. Effect of La substitution is to decrease the magneto crystalline anisotropy constant and the saturation magnetization. The latter is due to a decrease in mass fraction of the main magnetic phase. All Ba1-xLaxFe12O19 samples have superior microwave characteristics which able to absorb more than 99 % the incoming electromagnetic wave entering the material. The absorption bandwidth is found relatively wide within the frequency range 8-12 GHz.