Incident Electromagnetic Wave Research Articles

Effect of graphene on absorption spectrum of Si/SiO2 multilayer

In recent decades, photonic crystals have emerged as a key technology in several fields, including light management, photovoltaics, detection, and lasing. This success can be attributed to the ability to regulate electromagnetic waves, which can be achieved by, through a variety of techniques, disruption the periodicity of crystals. In this study, the introduction of graphene as a material defect in a one-dimensional photonic crystal consisting of six Si/SiO2 patterns is subjected to investigation. The calculations are performed using the transfer matrix method, with the experimental data serving as the input, following a protocol that involves exploring the variation of the absorption spectra as a function of the parameters of the material system and the incident electromagnetic wave. The findings illustrate that the absorption peak exhibits a pronounced dependency on the positioning of the material defect, the graphene layer thickness, and the incident angle. This paves the way for a more detailed inquiry into its potential utility in the domain of detection.

Enhancing electromagnetic interference mitigation: A comprehensive study on the synthesis and shielding capabilities of polypyrrole/cobalt ferrite nanocomposites

In a society increasingly infiltrated by digital and networking technologies, designing electromagnetic interference (EMI) shielding materials is critical for safeguarding sensitive electronic equipment and ensuring the smooth functioning of essential communication networks. This study focuses on the optimization of the properties of cobalt ferrite (CoFe2O4)/polypyrrole (PPy) nanocomposites made by in-situ polymerization used for electromagnetic (EM) shielding based on their magnetic and dielectric losses. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA) were employed to study the materials' physical and chemical characteristics. The findings demonstrate that the magnetic and electric properties of the materials composed of CoFe2O4 and PPy are substantially altered by the integration of CoFe2O4 and PPy. Adding PPy to CoFe2O4 reduces the real and imaginary parts of magnetic permeability, and the conductivity, dielectric constant, and dielectric loss are increased. These effects are advantageous for EM shielding applications. The high electromagnetic shielding performance mainly results from the enhanced interfacial polarization induced by interface region among CoFe2O4 and PPy molecules. The influence of the PPy matrix in altering the dielectric and magnetic loss factors (tanδE and tanδM) of the embedded ferrite particles is pronounced. Although CoFe2O4 shows excellent attenuation characteristics, it cannot optimally match impedance with free space, particularly at higher frequencies. In addition, material thickness and shielding efficiency adjust the reflection loss (RL) performance. The prepared composites can attenuate more than 95 % of the incident electromagnetic waves. This study emphasizes the benefits of employing composite materials in EMI shielding designs and the combined advantages of conductive and magnetic materials.

Hyperspectral Analysis of Silicon Nanowires Manufactured Through Metal-Assisted Chemical Etching

Abstract This study used hyperspectral imaging to analyze localized near-field interactions between incident electromagnetic waves and silicon nanowire (SiNW) arrays manufactured through catalytic etching of Si wafers for different durations. The results revealed that the unetched upper surface area on Si wafers and reflection of incident light decreased with increasing etching time. A light reflection band peaking at approximately 880 nm was generated from arrays etched for more than 1 h. We used six separate hyperspectral images to analyze the wavelength-dependent spatial optical responses of the fabricated SiNW arrays. The images revealed hot spots of light reflection from unetched Si surfaces in the wavelength range of 470–750 nm and a resonant peak at 880 nm for a photonic crystal derived from a random SiNW array. Accordingly, hyperspectral imaging enables the assessment of localized optical responses of SiNW arrays, which can then be optimized to cater to various applications.

Second harmonic generation based on graphene hyperstructure for higher resolution and performance on top of achieving fundamental wave detection in theory

In this paper, an innovative one-dimensional graphene hyperstructure (GHS) is proposed, allowing for the concurrent detection of multiple physical parameters in both the fundamental and second harmonic generation. The sensing characteristics of GHS pertaining to magnetic field strength (B), incident electromagnetic wave angle (θ), and graphene thickness (dgt) are systematically investigated. Moreover, through the incorporation of second harmonic generation alongside fundamental detection, higher resolution and performance are achieved. The findings indicate an expansion of the measurement range for B, θ, and dgt, from 0.3∼0.5 T, 35∼55°, and 1∼6 layers to 0.3∼1 T, 35∼65°, and 1∼10 layers, providing increased flexibility and adjustability. Additionally, by leveraging nonlinear effects and widening the Fabry-Perot cavity width, this structure effectively enhances the quality factor (Q) from 2.94 × 102 to 1.95 × 105, resulting in a substantial improvement in sensing performance. This development holds tremendous promise in surpassing the diffraction limit and addressing high-Q value sensing requirements. In comparison to conventional detectors, the GHS not only enhances detection efficiency but also harbors the potential for multiple physical quantities detection. This forward-looking research is pivotal in its successful resolution of detector performance limitations, ushering in novel possibilities across diverse domains.

A Low-Profile and Ultra-Wideband Pancharatnam-Berry Coding Metasurface for High-Efficiency and Wide-Angle Circular Polarization Anomalous Reflection.

The manipulation of electromagnetic waves using metasurfaces is important in areas such as stealth and communication. In this paper, we reported on the use of an element-based polarizer for the first step, which enables the incident electromagnetic waves to integrate into the cross-polarized waves with a relative bandwidth of 88% within 15-37.1 GHz. Then, an eight-element coding metasurface based on the Pancharatnam-Berry phase is presented for circular polarization anomalous reflection. The simulated values show that our work can achieve a high-efficiency (94%) and wide-angle (70°) anomalous reflection under normal incidence. The simulated values present good agreement with the experimental values. Our work reveals the ability to manipulate the waves and electromagnetic stealth.

Engineering of N doped carbon@FeCo alloy hollow spheres: Remarkable mid-frequency electromagnetic wave absorption performance exhibited by unique porous and wrinkled surface structure

The modulation of the shape and design of microstructures plays a crucial role in enhancing the efficient absorption of electromagnetic waves in absorbers. The electromagnetic parameters and scattering effects of these materials are directly influenced by their morphological characteristics. In this study, polystyrene microspheres were used as templates for a two-step in-situ growth process: Initially, Fe₃O₄ was coated onto the surfaces of these microspheres, followed by the in-situ growth of Fe-Co Prussian blue analogs. The rational design of electrical parameters during the conversion process was calculated and analyzed using Density Functional Theory. The precursor was calcined at various temperatures to generate a unique porous wrinkled surface hollow nanostructure. This nanostructure not only facilitates multiple reflections and scattering of incident electromagnetic waves but also promotes the occurrence of multiple interface polarizations. Doping with nitrogen and oxygen elements introduced abundant dipole polarization, thereby enhancing the electromagnetic wave attenuation capability of the composite material. The Fe3O4@PBA composite material synthesized at 600°C achieved a minimum reflection loss of −57.01 dB and a maximum effective absorption bandwidth of 4.58 GHz (7.52–12.1 GHz) at a thickness of 4 mm, covering nearly the entire X-band. This method provides a means to enhance magnetic loss by temperature adjustment to control the magnetic components in composite materials, providing a systematic approach to designing the microstructure of materials used for absorbing electromagnetic waves.

A Flexible and Optical Transparent Metasurface Absorber with Broadband RCS Reduction Characteristics.

Metasurface absorbers (MSAs) are of significant importance in a wide range of applications, such as in the field of stealth technology. Nevertheless, conventional designs demonstrate limited flexible characteristics and a lack of transparency, hence constraining their suitability for certain radar stealth applications. This study introduces a novel MSA operating in the broad microwave range, which exhibits both optical transparency and flexibility. The structure consists of a flexible substrate made of polyvinyl chloride (PVC), along with a resistive film composed of indium tin oxide (ITO). The proposed structure exhibits the ability to effectively absorb over 90% of the energy carried by incident electromagnetic (EM) waves across the frequency range of 9.85-41.76 GHz within an angular range of 0° to 60°. In addition, to assess the efficacy of the absorption performance, an examination of the radar cross-section (RCS) characteristics is conducted. The results indicate a reduction of over 10 dB across the aforementioned broad frequency spectrum, regardless of the central angle.

A dual-band polarization independent dielectric metasurface-based absorber for sensing application in the visible light regime

We present a dual-band, polarization-independent dielectric terahertz absorber exhibiting near-perfect absorption and minimal reflection at frequencies of f 1 = 419 THz and f 2 = 528 THz. Using electromagnetic theory, we modeled the structure to derive the surface electric admittance and magnetic impedance of the metasurface, elucidating the conditions required for perfect absorption in terms of inverse electric and magnetic polarizabilities. The absorber features a tunable symmetrical design, facilitating precise frequency adjustment by modifying structural parameters and ensuring polarization independence for perpendicularly incident electromagnetic waves. This scalable and versatile absorber, constructed from readily available materials, is optimally suited for applications in resource detection, imaging, sensing, and medical diagnostics, attributed to its simplicity, cost-effectiveness, and high performance.

Asymmetric and mechanically enhanced MOF derived magnetic carbon-MXene/cellulose nanofiber films for electromagnetic interference shielding and electrothermal/photothermal conversion

The prosperity of wearable and microelectronic devices tremendously facilitates to exploit thin and flexible composite films with multifunction. Free-standing MXene films have aroused considerable interest in the fields of electromagnetic interference (EMI) shielding and thermal management because of brilliant electrical conductivity, distinctive layered architecture and remarkable localized surface plasmon resonance effect. Nevertheless, the inferior mechanical strength and potential performance degradation in humid environments seriously constrain their practical applications. In this regard, robust and multifunctional CoNi-MOF-74 derived magnetic carbon/cellulose nanofibers (CNF)-MXene/CNF composite films with Janus architecture were successfully constructed via two-step vacuum-assisted filtration technology. The rational arrangement of functional fillers effectively improves the impedance matching, promoting the incident electromagnetic waves to enter the films for consumption. Constructing double-layered structure could induce the generation of “absorption-reflection-reabsorption” dissipation manner, dramatically enhancing EMI shielding performance. The bi-layered magnetic carbon/CNF-MXene/CNF composite membranes (0.1 mm in thickness) realize a fascinating EMI shielding effectiveness of 68.86 dB and a superior absorption efficiency of 58.82 dB. Meanwhile, the brilliant conductivity and significant localized surface plasmon resonance effect of MXene/CNF layer endow the composite films with excellent electrothermal/photothermal conversion capability, greatly broadening application prospects. The steady temperature of the composite films is as high as 112.9 °C within 10 s under the low driven voltage of 3.0 V and the saturation temperature reaches up to 154.2 °C within 15 s at the light intensity of 1500 W/m2, respectively. Moreover, the plentiful hydrogen bonding interaction and compact interfacial combination jointly enable the composite films to possess robust mechanical flexibility, satisfying the demands in practice. This work supplies a prospective guidance for preparing flexible and multifunctional composite films with Janus architecture, revealing great application potential in wearable and microelectronic devices even under harsh conditions.

Multi-band ultrathin reflective metasurface for linear and circular polarization conversion in Ku, K, and Ka bands

Linear polarization (LP) and circular polarization (CP) holds paramount importance in Ku, K, and Ka bands for satellite based communication, and remote sensing applications. Satellite based remote sensing applications face challenges like atmospheric attenuation, noise & interference, and signal degradation. Moreover, satellite based communication application demands CP in two distinct, non-adjacent frequency bands with orthogonal polarizations at greater oblique angles, considering the unpredictable incidence angles of electromagnetic (EM) waves. Addressing these challenges, an innovative metasurface polarization converter is proposed to operate efficiently across the Ku-band (13.5–18.0 GHz), K-band (18.0–26.5 GHz), and Ka-band (26.5–38.5 GHz) frequency ranges. The converter achieves left-handed circular polarization (LHCP) in the Ku- and Ka-bands within the frequency ranges of 14.57–15.65 GHz and 27.47–33.85 GHz for y-polarized incident EM waves. Additionally, it provides right-handed circular polarization (RHCP) in the K- and Ka-bands at 17.27–23.92 GHz and 35.87–38.32 GHz for y-polarized incident EM waves. The LP conversion ratio exceeds 95% in the frequency bands of 15.97–16.85 GHz, 24.70–26.65 GHz, and 34.37–35.45 GHz for y-polarized, LHCP, and RHCP incident EM waves, respectively. The metasurface exhibits robust performance up to incidence angles of 45 degrees under oblique conditions. Experimental validation using traditional board-circuit manufacturing demonstrates close agreement between measured co- and cross-polarized reflection coefficients and simulations in the 13.5–18 GHz, and 24–38.5 GHz frequency range. Thin metasurface with a thickness of only 0.64 = 0.013λo mm, the proposed design outperforms existing studies in the literature, establishing its competitive edge in terms of structure and performance.

Rational construction of dicarbonous CB/CNT@PI composites toward low filler loading and low-frequency electromagnetic wave absorption.

With the application of low frequency radar and the demand for stealth of high temperature resistant components, it is increasingly urgent to develop absorbing materials with both low frequency and high temperature resistant properties. Here, we successfully prepared various carbon/polyimide composites as low-frequency electromagnetic wave absorbing materials by simple blending method. The well-designed mesh lap structure introduces a large amount of free space, further optimizing the impedance matching of the material. At the same time, the multiple loss mechanism formed by the combination of carbon black dominated polarization and carbon nanotube dominated conductive loss enhances the loss of incident electromagnetic wave. The results showed that only 10 wt% filler loading of the CB/CNT@PI is achieved in the low frequency range (1-4 GHz) with a minimum RL strength of - 18.3 dB, which has obvious advantages compared with other works in recent years. This study provides a way for the design and preparation of resin-based absorbing materials.

A near-infrared metastructure to realizing polarization conversion and sensing based on the electromagnetic induced reflection

A multifunctional metastructure (MS) working in the near-infrared band is proposed that achieves linear to circular polarization conversion (LTCPC) and electromagnetically induced reflection (EIR). In addition, due to the use of reflected electric fields to overcome the influences of near-infrared band thermal radiation, MS has a good multifunctional sensing detection. The given MS is composed of a four-layer stacked structure. From the substrate to the top layer (along the +z-direction), it consists of silver, a silicon dioxide layer, and two layers of silicon (Si) resonators. Each layer of the Si resonator has four holes created by rotation. By breaking the symmetry of the upper and lower Si layers of MS, the deviation of the rotation angle of the upper and lower holes is introduced, so the MS achieved a near-infrared EIR with an ultrahigh quality factor (Q-factor). Under electromagnetic wave incidence, at 187.89 THz, the Q-factor of MS's reflection peak reaches 2441.25. Due to the unique shapes of the two resonator layers' holes, the axial ratio (AR) is less than 3 dB between 187.844 THz and 187.871 THz, realizing LTCPC. Utilizing the relationship between the optimal polarization conversion frequency point (the frequency corresponding to the lowest AR) and the environmental refractive index, the MS can be used for detecting cancer cells with a sensing sensitivity (S) of 37.24 THz/RIU (36.06 THz/RIU). By introducing the alcohol into the MS, the refractive index of the alcohol to be measured. MS achieved the detection function of the alcohol solution volume fraction, with an S reaching 33.32 THz/RIU, and a figure of merit as high as 154.202. Finally, the related parameters and polarization angle are discussed. The effects of different parameters on EIR and AR also are analyzed. The innovation of this paper lies in the realization of EIR, and a method to improve the Q-factor of near-infrared EIR by rotating the structure is proposed. The combination of a high Q-factor and polarization conversion overcomes the disadvantage that both are difficult to achieve together, and the EIR is easier to detect than the electromagnetically induced transparency. The design also has potential applications in biomedical sensors and industrial production.

Polarization-insensitive cross-polarization converter with high frequency selectivity based on an antenna-resonator-antenna module

In this paper, a novel transmission-type polarization-insensitive frequency selective polarization converter (PIFSPC) is proposed. The overall structural scheme of the proposed PIFSPC is based on an antenna-resonator-antenna (ARA) module, which is composed of a receiving patch antenna, double “S-shaped” half-wavelength resonators, and a transmitting patch antenna. By adopting cross-coupling, high frequency selectivity is achieved, and through the utilization of a staggered rotationally symmetric structure, polarization insensitivity is attained. The prototype possesses four transmission poles and two zeros on the polarization conversion spectrum, and it shows insensitivity to the polarization direction of incident electromagnetic waves. The frequency selectivity of the prototype at the lower and upper band edges is 425 dB/GHz and 283 dB/GHz respectively. The cross-polarization conversion rate (PCR) is over 95% within the passband from 4.93 GHz to 5.09 GHz for arbitrarily polarized azimuth incident waves, and its thickness is merely 0.052λ0. The operation bandwidth and frequency selectivity of the prototype can be readily altered. A prototype is fabricated and measured, with excellent consistency between simulations and experiments. It indicates the feasibility of integrating frequency selection and polarization conversion. The proposed PIFSPC has extensive application prospects in enhancing the anti-interference ability and electromagnetic compatibility in the fields of communication, measurement, and microwave detection.

One dimensional multilayer structure for kerosene adulteration detection in petrol and diesel

Abstract We aim to design a multilayer periodic structure to detect the kerosene adulteration in the petrol and diesel fuels on a single processing setup. We built the structure by arranging TiO2 and SiO2 layers periodically in alternate manner with empty space at the middle. The optical response of the designed structure is then theoretically studied using transfer matrix method. Empty space of the design is filled with different kerosene adulterated petrol and diesel samples for inspecting structure response to incident electromagnetic waves. Theoretical calculations affirm that the proposed structure is capable to detect the fuel adulteration efficiently. Critical performance parameters like sensitivity, quality factor, figure of merit and limit of detection are calculated to check the effectiveness of the sensor. We also optimized the sensitivity of sensors design through modifying the defect thickness as well as angle of incidence of electromagnetic waves, and provides poly fit formula. It is observed that the sensitivity of sensor to detect kerosene adulteration in fuels highly depends on defect thickness and light incidence angle. An efficient sensor possessing high quality factor and figure of merit is realized from the designed structure that is capable of detecting 10 − 5 RIU.

Enhancing Defect-Induced Dipole Polarization Strategy of SiC@MoO3 Nanocomposite Towards Electromagnetic Wave Absorption

HighlightsOxygen-vacancy-rich SiC@MoO3 nanocomposite with strong reflection loss (− 50.49 dB at 1.27 mm thickness) and broadband absorption band (8.72 GHz at 2.68 mm thickness) were constructed via in situ etching strategy.The presence of oxygen vacancy leads to an increased conductive loss and defect-induced dipole polarization, which plays significant role in attenuating the incident electromagnetic wave.

Key parameters to optimize the photothermoelectric effect of thermoelectric materials

Recently, photothermoelectric effect of thermoelectric materials has been hotly explored to develop self-powered and large bandwidth photodetectors working at ambient conditions. However, the key parameters for optimized photothermoelectric effect are still elusive. Here, based on the two-temperature model under static condition, we theoretically studied the key parameters to optimize the photothermoelectric performance of thermoelectric materials. Results verify that when the incident electromagnetic wave only generates electronic intra-band excitation, there is an ideal carrier concentration to optimize the photothermoelectric voltage; when the wavelength of a detected electromagnetic wave can resonantly excite quasi-particle (like phonons) except electrons, the photothermoelectric voltage can be enhanced significantly around the resonant wavelength regime; and when the electronic inter-band transition can be excited by an electromagnetic wave, photothermoelectric voltage is significantly increased due to the high optical absorption. As an example, the theoretical dependence of the photothermoelectric voltage of SnSe on wavelength is in line with the experimental result. This work elucidates the crucial parameters of thermoelectric materials to achieve the ideal photothermoelectric performance.

MoSe2 nanosheets implanting on 3D hollow carbon sphere for high-efficiency electromagnetic wave absorption

Carbon-based electromagnetic wave absorption (EMA) materials are extensively studied due to their unique advantages. Nevertheless, impedance matching issues was still constraining their further research. Consequently, we successfully synthesized MoSe2 nanosheets implanting on 3D hollow carbon sphere (HCS@MoSe2) composites with core–shell structure. The complex core–shell structure high-entropy composites provided multiple dissipation mechanisms for efficient dissipation of incident electromagnetic wave energy. The implanting MoSe2 nanosheets optimized the dielectric constant of the composites, thus ensuring optimal impedance matching. The HCS@MoSe2-1 composites exhibit excellent EMA properties and a significant minimum reflection loss (RLmin) of −56.19 dB. And HCS@MoSe2-1 had an ultra-wide effective absorption bandwidth (EAB) of 7.43 GHz. The significant EMA capability attributed to the synergistic effects of conductive loss, polarization loss, and optimized impedance matching. This work paved a new path for synthesizing transition metal selenide-modified carbon-based composite materials, offering great potential as high-performance materials for EMA applications.

Enhanced electromagnetic interference shielding via surface-bound molecules and synergistically amplified polarization and triboelectrification

Achieving high-performance electromagnetic interference (EMI) shielding materials with ultra-low reflectivity, minimal volume, and light weight is challenging. This study addresses this by introducing a nanofiber (NF)-based structure composed of MXene nanoflakes and ferroelectric barium titanate oxide (BTO) nanoparticles embedded within polyurethane (PU) fibers, and surface-bound branched polyethyleneimine (PEI(b)) on the NFs. This design enhances the flexibility and lightness of the EMI shielding materials while effectively minimizing reflectivity. A key approach in this study is the functionalization of the NFs with branched polyethyleneimine (PEI(b)), which reduces reflectivity and enhances EMI shielding effectiveness (SE). The surface-bound molecules increase the effective surface area, improving the absorption efficiency of incident electromagnetic waves without adding weight or volume. Additionally, the surface-bound PEI(b) molecules synergistically enhance the polarization of the embedded BTO nanoparticles and amplify the triboelectric charging effect, crucial for achieving ultra-low reflectivity and high EMI SE. Combining the optimized composite NF design with these enhancement methods, this study achieves significant advancements in EMI SE, reaching an EMI SE of 72 dB, an absolute EMI SE (SSEt) of 28,460 dB·cm²g−1, and a reflectivity of 0.09, all without increasing weight or volume. This approach exemplifies how the strategic application of surface-bound molecules can enhance EMI shielding effectiveness and achieve ultra-low reflectivity through the effective expansion of the absorption surface and synergistic enhancement of piezoelectric and triboelectric effects.

A novel oxide ceramic matrix composite with integrated high-temperature EMW absorption and mechanical performance

Oxide ceramic matrix composites (OCMC) are extensively used as thermal structural materials due to good high-temperature resistance, mechanical properties, and oxidation resistance, but they are rarely regarded as electromagnetic wave absorbing materials due to the high resistivity of oxide ceramics/fibers. However, high-performance Al2O3 fiber can be used to design and fabricate OCMC with integrated high-temperature microwave absorbing and mechanical properties by introducing dielectric material into Si-based ceramic matrix. The N610/Si3N4-SiOC composites have the prior mechanical performance because the uniformly distributed Si3N4 matrix made the fiber bear effectively. After that, the Sc2O3 modified SiOC matrix was filled into inter- and intra-fascicular pores forming interfacial polarization, dipole polarization, multiple reflection and scattering to attenuate the incident electromagnetic wave (EMW). The effective absorption bandwidth (EAB) and the minimum reflection coefficient (RCmin) of N610/Si3N4-SiOC(Sc) composites at the thickness of 2.75 mm reach 3.0 GHz and −42 dB in the X band, respectively. In addition, the EMW absorption performance of the composite is relatively stable with EABmax and RCmin of 3.5 GHz and −41 dB in 4–18 GHz at high temperatures. This work provides a strategy for designing and fabricating OCMC with excellent mechanical properties and EMW absorption properties.

Uniformity improvement of microwave heating with switchable frequency selective surface

Microwave heating has attracted interests in many industrial applications, yet heating inhomogeneity remains a critical issue. This study proposes a novel approach to enhance microwave heating uniformity employing a switchable frequency selective surface (FSS). The PIN diodes in each FSS unit cell can be toggled ON or OFF by controlling voltage biases, enabling the FSS to either reflect or transmit incident electromagnetic waves. Placing this switchable FSS in front of a heating cavity wall creates a dynamic reflecting boundary, which, through periodic alterations of the FSS and metallic wall, effectively improves the heating uniformity. To validate this method, we simulated the heating of a potato sample at 2450 MHz using COMSOL Multiphysics and conducted experimental tests. Both simulation and experimental results demonstrate that the proposed method significantly enhances microwave heating uniformity across various materials and sample sizes. This work provides a promising solution for designing microwave heating reactors.