Incoming Electromagnetic Wave Research Articles

A Silver Modified Nanosheet Self-Assembled Hollow Microsphere with Enhanced Conductivity and Permeability.

The utilization of sheet structure composites as a viable conductive filler has been implemented in polymer-based electromagnetic shielding materials. However, the development of an innovative sheet structure to enhance electromagnetic shielding performance remains a significant challenge. Herein, we propose a novel design incorporating silver-modified nanosheet self-assembled hollow spheres to optimize their performance. The unique microporous structure of the hollow composite, combined with the self-assembled surface nanosheets, facilitates multiple reflections of electromagnetic waves, thereby enhancing the dissipation of electromagnetic energy. The contribution of absorbing and reflecting electromagnetic waves in hollow nanostructures could be attributed to both the inner and outer surfaces. When multiple reflection attenuation is implemented, the self-assembled stack structure of nanosheets outside the composite material significantly enhances the occurrence of multiple reflections, thereby effectively improving its shielding performance. The structure also facilitates multiple reflections of incoming electromagnetic waves at the internal and external interfaces of the material, thereby enhancing the shielding efficiency. Simultaneously, the incorporation of silver particles can enhance conductivity and further augment the shielding properties. Finally, the optimized Ag/NiSi-Ni nanocomposites can demonstrate superior initial permeability (2.1 × 10-6 H m-1), saturation magnetization (13.2 emu g-1), and conductivity (1.2 × 10-3 Ω•m). This work could offer insights for structural design of conductive fillers with improved electromagnetic shielding performance.

A Study on a Compact Double Layer Sub-GHz Reflectarray Design Suitable for Wireless Power Transfer

The paper presents a novel small-footprint varactor diode-based reconfigurable reflectarray (RRA) design and investigates its power reflection efficiency theoretically and experimentally in a real-life indoor environment. The surface is designed to operate at 865.5 MHz and is intended for simultaneous use with other wireless power transfer (WPT) efficiency-improving techniques that have been recently reported in the literature. To the best of the authors’ knowledge, no RRA intended to improve the performance of antenna-based WPT systems operating in the sub-GHz range has been designed and studied both theoretically and experimentally so far. The proposed RRA is a two-layer structure. The top layer contains electronically tunable phase shifters for the local phase control of an incoming electromagnetic wave, while the other one is fully covered by metal to reduce the phase shifter size and RRA’s backscattering. Each phase shifter is a pair of diode-loaded 8-shaped metallic patches. Extensive numerical studies are conducted to ascertain a suitable set of RRA unit cell parameters that ensure both adequate phase agility and reflection uniformity for a given varactor parameter. The RRA design parameter finding procedure followed in this paper comprises several steps. First, the phase and amplitude responses of a virtual infinite double periodic RRA are computed using full-wave solver Ansys HFSS. Once the design parameters are found for a given set of physical constraints, the phase curve of the corresponding finite array is retrieved to estimate the side lobe level due to the finiteness of the RRA aperture. Then, a diode reactance combination is found for several different RRA reflection angles, and the corresponding RRA radiation pattern is computed. The numerical results show that the side lobe level and the deviation of the peak reflected power angles from the desired ones are more sensitive to the reflection coefficient magnitude uniformity than to the phase agility. Furthermore, it is found that for scanning angles less than 50°, satisfactory reflection efficiency can be achieved by using the classical reactance profile synthesis approach employing the generalized geometrical optics (GGO) approximation, which is in accord with the findings of other studies. Additionally, for large reflection angles, an alternative synthesis approach relying on the Floquet mode amplitude optimization is utilized to verify the maximum achievable efficiency of the proposed RRA at large angles. A prototype consisting of 36 elements is fabricated and measured to verify the proposed reflectarray design experimentally. The initial diode voltage combination is found by applying the GGO-based phase profile synthesis method to the experimentally obtained phase curve. Then, the voltage combination is optimized in real time based on power measurement. Finally, the radiation pattern of the prototype is acquired using a pair of identical 4-director printed Yagi antennas with a gain of 9.17 dBi and compared with the simulated. The calculated results are consistent with the measured ones. However, some discrepancies attributed to the adverse effects of biasing lines are observed.

Enhancement of Quantum Efficiency in Perovskite Solar Cells Through Whispering Gallery Modes from Titanium Oxide Micro‐Resonators

With the aid of 3D full‐field finite difference time–domain simulations, model configurations for thin‐film solar cell devices that include periodically arranged microspheres, exhibiting resonating whispering gallery modes (WGMs), are proposed. The microspheres present, either immersed in perovskite or coated with perovskite layer, between the electron‐ and hole‐transport layers show enhanced current‐conversion efficiency. The presence of WGMs lead to enhancement in the absorption of layer. The incoming electromagnetic wave couples with microsphere and forms confined resonating modes. Different designs are examined for deciding the appropriate position of WGM exhibiting spheres with respect to thin‐film perovskite solar cell (PSC) featuring back reflector and optimized antireflectance coating. Since the incoupling element is lossless, energy stored in microspheres is absorbed efficiently by the underlying active material. This directly contributes to the increment in the current density of the solar cell. Thus, the devices show a higher current density of 23.62 mA cm−1, while that in planar solar cell device shows current density of 13.68 mA cm−1, for the same thickness of perovskite layer. This leads to more than 70% enhancement in the short‐circuit current density than the conventional PSCs device of similar size.

Wideband radar cross-section reduction by a double-layer-plasma-based metasurface

Reduction of the radar cross-section (RCS) is the key to stealth technology. To improve the RCS reduction effect of the designed checkerboard metasurface and overcome the limitation of thin-layer plasma in RCS reduction technology, a double-layer-plasma-based metasurface—composed of a checkerboard metasurface, a double-layer plasma and an air gap between them—was investigated. Based on the principle of backscattering cancellation, we designed a checkerboard metasurface composed of different artificial magnetic conductor units; the checkerboard metasurface can reflect vertically incident electromagnetic (EM) waves in four different inclined directions to reduce the RCS. Full-wave simulations confirm that the double-layer-plasma-based metasurface can improve the RCS reduction effect of the metasurface and the plasma. This is because in a band lower than the working band of the metasurface, the RCS reduction effect is mainly improved by the plasma layer. In the working band of the metasurface, impedance mismatching between the air gap and first plasma layer and between first and second plasma layers cause the scattered waves to become more dispersed, so the propagation path of the EM waves in the plasma becomes longer, increasing the absorption of the EM waves by the plasma. Thus, the RCS reduction effect is enhanced. The double-layer-plasma-based metasurface can be insensitive to the polarization of the incoming EM waves, and can also maintain a satisfactory RCS reduction band when the incident waves are oblique.

Dual-Polarization Conversion and Coding Metasurface for Wideband Radar Cross-Section Reduction

Modern stealth application systems require integrated meta-devices to operate effectively and have gained significant attention recently. This research paper proposes a 1-bit coding metasurface (CM) design. The fundamental component of the proposed CM is integrated to convert linearly polarized incoming electromagnetic waves into their orthogonal counterpart within frequency bands of 12.37–13.03 GHz and 18.96–32.37 GHz, achieving a polarization conversion ratio exceeding 99%. Furthermore, it enables linear-to-circular polarization conversion from 11.80 to 12.29, 13.17 to 18.44, and 33.33 to 40.35 GHz. A second element is produced by rotating a fundamental component by 90°, introducing a phase difference of π (pi) between them. Both elements are arranged in an array using a random aperiodic coding sequence to create a 1-bit CM for reducing the radar cross-section (RCS). The planar structure achieved over 10 dB RCS reduction for polarized waves in the frequency bands of 13.1–13.8 GHz and 20.4–30.9 GHz. A prototype was fabricated and tested, with the experimental results showing a good agreement with the simulated outcomes. The proposed design holds potential applications in radar systems, reflector antennas, stealth technologies, and satellite communication.

Enhancing broadband terahertz absorption via a graphene-based metasurface absorber featuring a rectangular ring and triple crossbars

This study introduces an innovative strategy to achieve a versatile and adaptive terahertz (THz) absorber by leveraging a graphene-based metasurface. This metasurface comprises a rectangular ring, three crossbars and a grounded gold film, all separated by a thin SiO2 layer. The phenomenon of plasmonic hybridization, involving surface and cavity plasmon resonances, enables the interaction between incident THz waves and the proposed graphene-based metasurface, leading to a substantial enhancement in the absorptance bandwidth of the plasmonic system. The enhancement of absorptance can be finely adjusted by modifying the chemical potential (Fermi energy) in graphene and manipulating the structural parameters of the device. A notable feature of our design is its inherent resistance to variations in incident angles and polarization states of incoming electromagnetic waves. The proposed device achieves an absorptance exceeding 80% across a continuous spectrum, exhibiting a bandwidth of approximately 0.90 THz from 0.94 to 1.84 THz. This robust characteristic ensures consistent and reliable performance in diverse scenarios. Our findings present intriguing prospects for various applications centered on wave modulation, which encompass, but are not limited to, THz imaging, filtering, energy harvesting, and tunable sensors.

Package-Less Liquid Phase Sensing Using Surface Acoustic Waves on Lithium Tantalate Oxide.

Surface acoustic wave (SAW) transducers propagating shear waves are compatible with sensing chemical compounds in a liquid phase. However, if the liquid surrounding the sensor possesses a higher permittivity than the piezoelectric substrate, then the interdigitated electrodes for converting the incoming electromagnetic wave to acoustic waves are susceptible to capacitive short-circuiting, leading to excessive insertion losses. By using high-permittivity lithium tantalate oxide (LTO), we demonstrate chemical sensing in water without the need for dedicated microfluidic packaging. Nevertheless, the gravimetric sensitivity of these package-less transmission Love-mode delay lines remains comparable to that of low-permittivity quartz when appropriately tuning the guiding layer of thin film to confine energy to the surface in a Love mode. We extend the transmission line gravimetric sensitivity measurement to a reflective delay line geometry for passive transducers that can be wirelessly probed. For instance, ground-penetrating radar (GPR) can be used for subsurface sensing, here targeting water pollution detection, operating in the 100-500-MHz range. This center frequency was selected as a tradeoff between penetration depth (lower frequency) and antenna size (smaller at higher frequency). Nonspecific binding of proteins detection is shown in the context of biosensing applications.

Printed graphene and its composite with copper for electromagnetic interference shielding applications.

Advances in mobile electronics and telecommunication systems along with 5G technologies have been escalating the electromagnetic interference (EMI) problem in recent years. Graphene-based material systems such as pristine graphene, graphene-polymer composites and other graphene-containing candidates have been shown to provide adequate EMI shielding performance. Besides achieving the needed shielding effectiveness (SE), the method of applying the candidate shielding material onto the object in need of protection is of enormous importance due to considerations of ease of application, reduced logistics and infrastructure, rapid prototyping and throughput, versatility to handle both rigid and flexible substrates and cost. Printing readily meets all these criteria and here we demonstrate plasma jet printing of thin films of graphene and its composite with copper to meet the EMI shielding needs. SE over 30 dB is achieved, which represents blocking over 99.9% of the incoming radiation. Graphene and its composite with copper yield higher green index compared to pure copper shields, implying reduced reflection of incoming electromagnetic waves to help reduce secondary pollution.

Design of a compact filter integrated wideband and circularly polarized antenna array for K-band application

A compact filtering mechanism in the antenna system is required to avoid unwanted incoming electromagnetic waves in the working frequency band. A circularly polarized (CP), wideband, and high gain antenna array co-design with a wide bandpass filter (BPF) for a K-band satellite application at (17.7 to 21.2) GHz is studied in this paper. Antenna array elements with diagonal slots and BPF in the same frequency are compatible. For maximum radiation efficiency, the input impedance of the slotted 16 × 16 elements antenna array is matched to 50 Ω and equal to the output impedance of the BPF in the operating band. To implement the filtering concept, a co-design is modeled and simulated. The suggested wideband BPF and antenna array are integrated on a combined aperture, manufactured, and tested experimentally. Based on the results of the tests, it can be concluded that the suggested filtering antenna array is well matched (|S11| < −15 dB) throughout a wide frequency band of 17.7 GHz to 21.2 GHz. The final structure simulated and measured 3 dB axial ratio covers the functional spectrum with a maximum 25.3 dBi gain. High directive beams with a 20 dB cross-polarization suppression level in E & H planes are simulated and measured. Due to these advantages, the suggested antenna is an attractive option for use in K-band 3U satellite applications to minimize the requirement for extra filtering circuits in the RF system.

A comparative analysis of flexible pvdf based smart films for advanced electromagnetic shielding applications using a machine learning approach

Due to emerging technology, the usage of electronic gadgets has paved a route for the arousal of Electromagnetic Interference (EMI) pollution. Electromagnetic pollution is considered a global threat that can harm all biological systems and technological equipment. To overcome this issue, a suitable shielding material has to be implemented to attenuate the incoming electromagnetic waves. On the other hand, compared to traditional materials, recently, polymers have grabbed excellent responses in various fields of material science and modern chemistry. Specifically, functional polymers are increasing their scope in industry and academia due to their unique features, such as magnetic, catalysis, optical and piezoelectric properties. In this regard, Polyvinylidene Fluoride (PVDF), a well-known semicrystalline polymer from the family of Fluoropolymers, has achieved remarkable in various applications of sensors, actuators, biomedical scaffolds and energy harvesting devices. PVDF has also contributed excellent outcomes as a shielding material as they are transparent to light and flexible. Hence, this research work attempts to fabricate PVDF thin films with various weight percentages of nanofillers such as Zinc oxide (ZnO), Zirconium oxide (ZrO2), and Titanium dioxide (TiO2). Further, all the samples were tested for electromagnetic shielding effectiveness (SE). Further, these experimental results were compared with statistical and computational approaches such as the Gradient Descent Algorithm (GDA) and Response Surface Methodology (RSM). Based on the experimental results, it was observed that the PVDF nanofilm fabricated with 0.3 wt% of ZrO2, 0.5 wt% of TiO2and 0.3 wt% of ZnO nanofillers had achieved a maximum EMI SE of 11.4 dB at X-band frequency of 8–12 GHz.

Multibeam digital metasurface reflectarray antenna for 5G millimeter wave applications

AbstractA phase‐graded multibeam high gain digital metasurface reflector array (DMSRA) antenna for 5G millimeter wave communication is proposed in this letter. The DMSRA unit‐cell element is composed of a dipole loaded with endstubs. The variation of load across the diploe manipulates the reflection phase response of the incoming electromagnetic wave. A discretized phase state of 0° and 180° is obtained for an optimized loaded dipole. The phase states mimic the binary meta bit‐0 and meta bit‐1. The metabits are distributed along the reflecting surface using a digital coding sequence to form multiple beams in the desired direction. A coding sequence of 010101… is employed to design a two‐dimensional phase‐graded metasurface to generate a four‐beam radiation pattern. The designed digital metasurface reflectarray antenna of dimensions is fabricated and measured to validate the performance. The DMSRA is excited by an antipodal Vivaldi antenna positioned at an optimized focal point of 28 mm. The measured results show a four‐beam radiation pattern obtained over the frequency range of 27.5–28.5 GHz along azimuthal and elevation planes, with a peak beam gain of 10.5 dBi at 28 GHz.

Bipartite dielectric Huygens’ metasurface for anomalous refraction

Huygens’ metasurfaces—fundamentally based on Schelkunoff's equivalence principle, Huygens’ metasurfaces consist of a two-dimensional array of Huygens’ sources formed by co-located orthogonal electric and magnetic dipoles. Such metasurfaces provide electric and magnetic responses to an incoming electromagnetic (EM) wave, leading to unidirectional scattering and 2π phase coverage. We herein report a near-reflectionless coarsely discretized dielectric Huygens’ metasurface that performs anomalous refraction, offering a low-loss platform for wave manipulation at high frequencies as compared to their lossy metallic analogue. The coarse discretization dramatically simplifies the design, resulting in a metasurface that is highly efficient, cost-effective and robust. In this paper, the proposed metasurface comprises two meta-atoms per period, and is hence named the bipartite dielectric Huygens’ metasurface. Through full-wave simulations at 28 GHz, we show that the proposed metasurface can reroute an incident EM wave from θ i = 15° to θ t = − 44.5° with a very high efficiency: 87% of the scattered power is anomalously transmitted to θ t . Based on our observations, a coarsely discretized dielectric Huygens’ metasurface platform can be efficacious to design meta-devices with multifaceted functionalities in different frequency regimes.

Computational Modeling for Intelligent Surface Plasmon Resonance Sensor Design and Experimental Schemes for Real‐Time Plasmonic Biosensing: A Review

AbstractThe spectacular physical phenomenon of surface plasmon resonance (SPR) is the essence of present‐day plasmonic sensors. Meanwhile, the unique properties of the interaction between light and matter have been carved out into the development of modern‐day diagnostic biosensors. Plasmons, in simple terms, are oscillating free electrons in metallic nano‐structures triggered by an incoming electromagnetic (EM) wave. With the advantages of real‐time and label‐free bio‐sensing, plasmonic sensors are being utilized in multiple diverse areas of food technology, the bio‐medical diagnostic sector, and even the chemical industry. Although this review will be brief, readers can gain a comprehensive picture of the essential elements by taking a broader look into the exploration of SPR sensor design via simulated studies and representative experimental plasmonic schemes developed for bio‐sensing. In short, the various SPR sensing schemes that researchers have explored to realize enhanced SPR sensitivity are reviewed and summarized. Different experimental plasmonic sensors are also examined in which new SPR excitation schemes have been adopted. These "unconventional" designs, specifically those involving hybrid localized surface plasmon resonance (LSPR)‐SPR excitation, may inspire those in the plasmonic field.

Three-Layered Thin Films for Simultaneous Infrared Camouflage and Radiative Cooling.

With the rapid advancements in aerospace technology and infrared detection technology, there are increasing needs for materials with simultaneous infrared camouflage and radiative cooling capabilities. In this study, a three-layered Ge/Ag/Si thin film structure on a titanium alloy TC4 substrate (a widely used skin material for spacecraft) is designed and optimized to achieve such spectral compatibility by combining the transfer matrix method and the genetic algorithm. The structure exhibits a low average emissivity of 0.11 in the atmospheric windows of 3-5 μm and 8-14 μm for infrared camouflage and a high average emissivity of 0.69 in 5-8 μm for radiative cooling. Furthermore, the designed metasurface shows a high degree of robustness regarding the polarization and incidence angle of the incoming electromagnetic wave. The underlying mechanisms allowing for the spectral compatibility of the metasurface can be elucidated as follows: the top Ge layer selectively transmits electromagnetic waves ranging from 5-8 μm while it reflects those in the ranges of 3-5 μm and 8-14 μm. The transmitted electromagnetic waves from the Ge layer are first absorbed by the Ag layer and then localized in the Fabry-Perot resonance cavity formed by Ag layer, Si layer and TC4 substrate. Ag and TC4 make further intrinsic absorptions during the multiple reflections of the localized electromagnetic waves.

Millimeter-Wave Ferromagnetic Resonance of a Saturated Magnetic Transmission Line

Saturated ferrites exhibit microwave and millimeter wave absorption because they consist of nano- magnetic harmonic oscillators. The absorption frequency and line width are dictated by the strength and range of interactions between the magnetic dipoles. The forced orientation of magnetic dipoles along the magnetic bias results in Zeeman splitting in the energy levels. The incoming electromagnetic wave can excite dipoles to transition between these energy levels. In order to investigate the effects of input frequency and Gilbert damping constant on the electromagnetic properties, a magnetic transmission line model is presented for a saturated ferrite. The enhanced power loss during ferromagnetic resonance is contributed to the strong spike of longitudinal magnetic admittance and transverse magnetic impedance.

A Dual-Polarized Omnidirectional Rectenna Array for RF Energy Harvesting.

In this paper, a dual-polarized omnidirectional rectenna array using a hybrid power-combining scheme is proposed for the applications of RF energy harvesting. In the antenna design part, two omnidirectional antenna subarrays are created to receive horizontally polarized electromagnetic (EM) waves and a four-dipole subarray is produced to receive vertically polarized incoming EM waves. The two antenna subarrays of different polarizations are combined and optimized, so as to reduce the mutual influence between them. In this way, a dual-polarized omnidirectional antenna array is realized. In the rectifier design part, a half-wave rectifying structure is adopted for converting the RF energy into DC energy. Based on the Wilkinson power divider and 3-dB hybrid coupler structure, a power-combining network is designed to connect the whole antenna array and rectifiers. The proposed rectenna array is fabricated and measured under different RF energy harvesting scenarios. All simulated and measured results are in good agreement, which verifies the capabilities of the designed rectenna array.

Scattering of the quantized electromagnetic waves from a bi-anisotropic absorbing magneto-dielectric slab

A canonical quantization of electromagnetic field in the presence of a bi-anisotropic absorbing magneto-dielectric slab is provided. The quantized Maxwell’s equations in the presence of the slab are exactly solved and the time-space dependence of the quantized electric and magnetic fields are obtained. The Fock space of the total system is introduced. The scattering matrix of the bi-anisotropic magneto-dielectric slab is obtained in terms of the susceptibility tensors of the slab. The scattering matrix relates the annihilation operators of the outgoing quantized electromagnetic waves from the slab to the annihilation operators of the incoming quantized electromagnetic waves to the slab. The Fresnel’s coefficients of the bi-anisotropic magneto-dielectric slab are obtained in terms of the susceptibility tensors of the slab. The Fresnel’s coefficients relate the powers radiated by the outgoing quantized electromagnetic waves from the slab to the powers radiated by the incoming quantized electromagnetic waves to the slab. The radiated powers by the outgoing quantized electromagnetic waves are calculated in the special cases that the slab is in the thermal state and the incoming quantized electromagnetic waves to the slab are in the vacuum state and the coherent state.

Electrodynamics under the action of null cosmic strings

A method to study electromagnetic (EM) effects generated by a straight null cosmic string moving in classical EM fields is suggested. The string is shown to induce an additional EM field which can be described as a solution to homogeneous Maxwell equations with initial data set on a null surface, the string event horizon, where the string world-sheet belongs to. The initial data ensure the required holonomy of the string space-time caused by the gravity of the string. This characteristic initial value problem is used to study interaction of plane waves with null strings and perturbations by the strings of the Coulomb fields of electric charges. It is shown that parts of an incoming EM wave crossing the string horizon from different sides of the string are refracted with respect to each other and leave behind the string a wedge-like region of interference. A null string moving near an electric charge results in two effects: it creates a self-force of the charge and induces a pulse of EM radiation traveling away from the charge in the direction close to trajectory of the string.

Extraordinary optical transmittance generation on Si3N4 membranes.

Metamaterials are attracting increasing attention due to their ability to support novel and engineerable electromagnetic functionalities. In this paper, we investigate one of these functionalities, i.e. the extraordinary optical transmittance (EOT) effect based on silicon nitride (Si3N4) membranes patterned with a periodic lattice of micrometric holes. Here, the coupling between the incoming electromagnetic wave and a Si3N4 optical phonon located around 900 cm-1 triggers an increase of the transmitted infrared intensity in an otherwise opaque spectral region. Different hole sizes are investigated suggesting that the mediating mechanism responsible for this phenomenon is the excitation of a phonon-polariton mode. The electric field distribution around the holes is further investigated by numerical simulations and nano-IR measurements based on a Scattering-Scanning Near Field Microscope (s-SNOM) technique, confirming the phonon-polariton origin of the EOT effect. Being membrane technologies at the core of a broad range of applications, the confinement of IR radiation at the membrane surface provides this technology platform with a novel light-matter interaction functionality.

Direction-of-Arrival Estimation With Planar Luneburg Lens and Waveguide Metasurface Absorber

Direction of arrival (DOA) estimation using array antennas is known to have high resolution. However, these algorithms require high computational resources. This paper proposes a unique DOA estimation system without a sophisticated algorithm, using a planar Luneburg lens and a waveguide metasurface absorber. The planar Luneburg lens consists of a convex lens and a waveguide that separates incoming electromagnetic waves from different directions and focuses them at different points on the sides of the convex lens. The metasurface absorber consists of a mushroom-shaped structure that, when placed at the focal point of the lens, behaves like a compact 2D sensor array. Information regarding the intensity and angle of the incident electromagnetic wave can be obtained from the power and position of the sensor element. The resolution of the system is 2.2–2.4 degrees (depending on the sensor position), and the maximum estimation error is within 2.4 degrees in the 5.65 GHz frequency band.