X-band Frequency Research Articles

Multilayered silver nanowires and graphene fluoride-based aramid nanofibers for excellent thermoconductive electromagnetic interference shielding materials with low-reflection

Multilayered films composed of alternating layers of graphene fluoride (GF) and silver nanowires (AgNWs) in an aramid nanofiber (ANF) matrix were fabricated. The films were prepared by sequential vacuum filtration of GF@ANF and AgNWs@ANF suspensions to obtain multilayered composite architectures. The multilayered GF@ANF/AgNWs@ANF films exhibited exceptional mechanical flexibility and strength, with tensile strength up to 130 MPa and 5000 bending cycles with negligible performance deterioration. The films displayed remarkably high electromagnetic interference (EMI) shielding effectiveness up to 54 dB in X-band frequencies, attributed to the multiple internal reflections in the multilayered structure. EMI shielding was dominated by absorption rather than reflection, enabling attenuation of incident microwaves without secondary pollution. The multilayered films also exhibited ultrahigh in-plane thermal conductivity of up to 45 W/mK, owing to the thermally conductive GF and AgNWs networks. The EMI shielding effectiveness and thermal conductivity were retained after temperature and bending cycling. The composite films also demonstrated excellent flame retardancy. This study provides an effective route toward concurrent enhancement of multi-functional properties through architectural engineering at the nanoscale. The combination of robust EMI shielding, mechanical flexibility, thermal management, and fire safety highlights the potential of rationally designed multilayered composites for practical applications in 5 G wearable electronics devices, communications systems, and radar technologies.

Dielectric characterization analysis of natural fiber based hybrid composite for microwave absorption in X-band frequency

Dielectric characterization analysis of natural fiber based hybrid composite for microwave absorption in X-band frequency

Morphology dependent EMI shielding performance of Ag-Ni core-shell nanowires

The proposed work reports a facile chemical reduction method for synthesizing the hierarchical silver-nickel core-shell nanowire structures with controllable morphologies by varying the Ag concentration. The growth of Ni shells around the Ag core to make thorny and smooth Ag-Ni core-shell nanowires is studied for addressing electromagnetic interference (EMI). The synthesized Ag-Ni nanowires show better EMI shielding effectiveness (SE) than Ni nanowires with much-improved absorption loss (SEA). Due to high electrical conductivity (8630 S cm−1), magnetic permeability (44.1 emu/g), and heterojunction core-shell interfaces, the bimetallic nanowires flakes exhibit exceptional average EMI SE of 90.5 dB in the X-band frequency range (8–12 GHz) with a thickness of 0.11 mm, taking specific EMI SE to 822.72 dB/mm. In addition, the EMI shielding performance of the smooth Ag-Ni nanowires showed a 45% enhancement in SEA with marginal change in reflection loss (SER) compared to the thorny ones, indicating high absorption of EM waves. The unique core-shell nanowires with high aspect ratio with tunable physical properties can be ideal candidates for futuristic applications in microwave absorption and electromagnetic interference shielding.

Microwave dielectric characterization studies of PVDF-TrFE-Nafion blended films

The solution-based casting method fabricates the free-standing pure PVDF-TrFE, PVDF-TrFE-Nafion blended films and tests them for structural, morphological, and microwave studies. The X-ray diffraction pattern and FTIR spectrum confirmed the formation of the ferroelectric β-phase of PVDF-TrFE. The surface morphology of blended films is studied by scanning electron microscope (SEM), and noticeable changes in the morphological features are observed in the blended films resulting from the differences in the nucleation process in these films. Then using the open-ended coaxial probe method, the complex permittivity measurements were carried out over a large frequency range, from 0.5 GHz to 50 GHz. These results were verified with the Transmission-Reflection method using a rectangular waveguide in the X-band and Ku-band frequency range. The microwave absorption properties of the blends are also studied in the same frequency range. The stability of the dielectric properties and low microwave absorption indicates that the blending of PVDF-TrFE with Nafion results in a new potential material for high frequency flexible capacitor applications.

Evaluation of electromagnetic characteristics of 3D-printed radar absorbing structures based on three-dimensional period pattern surface

This paper aims to assess the electromagnetic (EM) characteristics of 3D-printed radar absorbing structures (RASs) based on three-dimensional period pattern surface (3D PPS) within the X-band frequency range (8.2–12.4 GHz). The assessment is validated through HFSS software, a 3D printer (Markforged, X7), and a scanning free-space measurement (SFM) system. Firstly, the analysis indicates that the EM characteristics of RASs based on 3D PPS are impacted by impedance matching in the thickness direction and the scattering of EM waves at the edges. The utilization of Onyx (Chopped carbon fiber/Nylon) reveals variations in resonance frequencies and EM wave absorption performance contingent upon the surface shape. Furthermore, significant differences in the variations of EM characteristics are observed even for RASs with the same surface shape but different materials. Secondly, the measurement results of 3D-printed RAS specimens based on PPS using Onyx exhibit similar trends to the analysis results obtained with the SFM system. Ensuring precise measurement results requires specific measurement conditions tailored to each surface shape, along with an examination of the EM characteristic distribution across the entire specimen area. This is crucial due to variations in the size, number, and range of reflected EM waves in the time domain. The analysis and measurement techniques presented in this study hold applicability in designing 3D-printed RASs that demand high EM wave absorption performance, whether under normal or oblique incident EM waves.

Electromagnetic and microwave absorption properties of flexible fabric coatings containing Ag decorated spherical graphene powders with FSS incorporation

Flexible textile microwave absorbing materials own the advantages of flexibility, foldability and cuttability, have become a research hotspot in electromagnetic stealth technology. In this study, a microwave absorbing coating was prepared on a fabric substrate using Ag decorated spherical graphene (SG) as the absorbent. XRD results demonstrated the metallic Ag ion was successfully reduced. TEM photographs showed the silver nanoparticles were stuck to the spherical graphene. The complex permittivity was enhanced after compositing with Ag particles. Along with the increase of silver content from 0 to 20 wt%, the complex permittivity rises from 3.29–0.42j to 6.93–2.22j owing to its higher electric conductivity and stronger relaxation effect. Meanwhile, the flexible coating containing Ag decorated spherical graphene (Ag@SG) also exhibited better microwave absorption performance. The minimum reflection loss (RLmin) for the coating with a thickness of 3.0 mm was −15 dB. And the effectively absorbing broadband (EAB) is located at 9.08–11.52 GHz. In addition, the microwave absorbing performance was greatly enhanced after being combined with periodic frequency selective surface (FSS). The EAB was obtained over the entire X-band frequency range, and the RLmin value achieved −41.72 dB at 10.25 GHz. What's more, the coating owned an EAB in a wide range incident angle of 60°–90°. This work was help to developing high performance flexible fabric coating containing Ag decorated spherical graphene with FSS incorporation.

A miniaturized ultra-wideband filter with high rejection and selectivity based on dual-notch bands.

A novel compact and highly selective Ultra Wide Band (UWB) filter is proposed using multimode resonator (MMR) technology. To begin with, the filter's ultra-wideband performance is achieved by coupling a stepped-triangular multimode resonator with input-output feedlines. Furthermore, dual-notch band characteristics are realized at 6.80 GHz and 9.82 GHz, employing asymmetric coupled lines and the split ring resonator (SRR) methods. Eventually, by using a Defected Ground Structure (DGS), the filter's correct transmission zero is deepened, further enhancing the out-of-band suppression performance at higher frequencies. The measured results are in excellent agreement with the experimental results, and the filter has a passband range of 3.52-11.68 GHz, a center frequency of 7.59 GHz, an insertion loss of just 0.61 dB, and a return loss of more than 18 dB. The transmission zeros have a rejection capability of more than 47 dB attenuation, and the rectangular coefficient of the filter is 1.34, which is outstanding for filtering out the interference signals in the parasitic passband with superior selectivity. The overall structure is compact, and the size is just 0.41λg×0.20λg. The filter can be used for UWB system filtering and also to avoid interference from some Wireless Local Area Network (WLAN) IEEE 802.11 series and x-band satellite link frequency bands.

Design and analysis of X-band metamaterial absorber

This study introduces a novel metamaterial absorber operating in X-band frequency range, characterized by two resonating peaks. The proposed structure consist of four circular sectors connected by two cross resonators enclosed by a circular strip with the dielectric between them. FR4 is used as a substrate backed by a copper ground plane. Simulation results reveal that the reflection co-efficient remains consistently below -10dB across the entire X-band, ensuring effective absorption of incident electromagnetic waves. Moreover, the absorber achieves 100% absorptivity with the gain of -25dB under normal incidence. The validity of absorber performance is confirmed through impedance plot and Voltage Stand Waving Ration (VSWR) analysis, verifying the accuracy of S11 parameter. Furthermore, the proposed structure has a compact size of 0.1666 λ. The absorber’s robust performance validated through numerical analysis, positions it as a compelling candidate for various X-band applications, including radar systems, communication devices, and stealth technology. This research establishes the proposed metamaterial absorber as a promising solution for X-band electromagnetic wave attenuation needs, offering both superior performance and compact design.

Liquid-templated graphene aerogel electromagnetic traps.

For decades, the inherently reflective nature of metallic electromagnetic (EM) shields and their induced secondary EM pollution have posed significant challenges for sensitive electronics. While numerous efforts have been made to develop superior EM shielding systems, the issue of reflection dominancy in metallic substrates remains unresolved. Herein, we addressed this long-lasting obstacle by pairing metallic shields with ultra-lightweight (density of 3.12-3.40 mg cm-3) elastic anti-reflection aerogels, altering their shielding mechanism from dominant reflection (reflectance >0.8) to absorption (absorbance >0.7) by trapping EM waves inside the aerogel. The aerogel EM traps were generated using interfacial complexation, yielding engineerable filamentous liquid structures. These served as templates for aerogel creation through a follow-up process of freezing and lyophilization. The engineerable lossy medium of aerogels benefits from a multi-scale porous construct with the combined action of dielectric and conduction losses, highly dissipating the EM waves and minimizing the reflections. Notably, declining the diameter of aerogel filaments promoted its absorption dominancy, rendering it a potent dissipating medium for EM waves. Pairing a metallic substrate with filamentous aerogel EM traps has resulted in an exceptionally effective absorption-dominant shielding system, achieving absorbance levels between 0.70-0.81. This system offers a shielding effectiveness of 53-89 dB within the X-band frequency range. This innovation addresses a persistent issue in shielding science related to the reflective characteristics of metallic substrates, effectively inhibiting their induced EM reflections.

Using characteristic mode theory to design and analyze an X-band polarization conversion metasurface

This paper proposes a new framework based on the characteristic modes analysis (CMA) to design polarization conversion metasurfaces (PCMs). This approach relies on the information inferred from the characteristic currents of the dominant modes (DMs). To demonstrate the advantages of this strategy, a multi-functional PCM is designed for the X-band frequencies. Besides, this paper expands and develops the characteristic mode rotation (CMR) method to investigate the intrinsic behavior of PCMs. Based on the extended CMR method, the physical concepts behind polarization conversion purity and angular stability at the resonance frequencies are revealed in a new manner. Finally, a prototype of the designed polarizer is fabricated and its reflection coefficients are measured. A great agreement between simulation and measurement results is obtained.

Experimental and theoretical study on the electromagnetic shielding performance of polymer nanocomposites consisting of basalt fiber and CNTs

In this paper, we substantiated the mechanism behind the absorption and multiple reflection shielding in the nanocomposites (2 mm in thickness) consisting of basalt fiber loaded with carbon nanotubes and polydimethylsiloxane when exposed to an electromagnetic wave of the X-band frequency (8.2–12.4 GHz). The experimental results confirmed that the interface polarization, capacitor-like structure, together with internal conducting networks contributed to the electromagnetic shielding effect in the material. Furthermore, calculation and simulation were employed to analyze the propagation of electromagnetic wave within the nanocomposites, giving direct evidence that the electromagnetic irradiation could be efficiently absorbed while the reflection loss played a marginal role in this process. The findings of this study shed light on the structural design and optimization of the nanocomposites for high-efficiency electromagnetic shielding.

Multi-objective optimization of a compact wideband antenna using grey relational analysis

In this article, a wide bandwidth along with compactness is achieved using a multi-objective optimization technique in a simple X-band antenna structure. The grey relational analysis is used to predict S11, bandwidth and gain for specific combinations of corner-cut length (lc), slot length (ls), and slot width (wst) of the proposed antenna. The effect of corner-cut length, slot length, and slot width on S11, −10 dB bandwidth, and antenna gain is also analyzed. This paper discusses a slotted patch antenna that can cover the X-band frequency range. The modifications involve adding four corner-cut and a parallelogram-shaped slot to the rectangular patch along with a tapered feedline, resulting in a wide bandwidth of 1.55 GHz (9.7 GHz to 11.25 GHz). The proposed compact antenna (23 mm × 32 mm × 1.575 mm) has a peak gain of 8.8 dBi at 10 GHz and can be used in radar communication. An equivalent circuit analysis is done and S11 of the circuit is matched with simulated and measured results. It is appropriate for use as a unit element in an antenna array due to its clear and straightforward design.

Electromagnetic interference shielding performance of lanthanum ferrite with MWCNT and graphene in the polyethylene polymer matrix in X-band frequency

In the present study, a combination of Lanthanum ferrite (LaFeO3) magnetic nanoparticles with multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNP) was prepared and used as conducting filler. As prepared Nanofillers were incorporated with the Low-density polyethylene (LDPE) with the melt blending process. The polymer composite was used to study the electromagnetic interference (EMI) shielding behaviour from 8.2 to 12.4 GHz. The electromagnetic (EM) wave shielding was ascribed to the dielectric and magnetic loss phenomena by incorporating graphene, MWCNT, and LaFeO3. The maximum shielding effectiveness of 33.57 dB was obtained with the critical concentration of 50:5:40:5 wt% sample.

Temperature-dependent conduction mechanism of NiO@Carbon@Polypyrrole nanomaterial with EMI shielding characteristics

A simple hydrothermal technique and in-situ chemical oxidative polymerization of pyrrole monomer yield the functionalized NiO@C@PPy nanomaterial for electromagnetic shielding applications. The crystal structure, morphology, dielectric and electromagnetic shielding (EMI) performance in the X-band (8.2–12.4 GHz) is thoroughly studied. Impedance spectroscopy is utilized to study the electrical response of a NiO@C@PPy pellet. This study focuses on the modulations of relaxation time with frequency at different temperatures. In the NiO@C@PPy composite, a semiconductor-to-metal transition (SMT) is observed, at 328 K. The conduction mechanism of NiO@C@PPy is explained based on the carrier hopping transport model in Ni2+ and Ni3+ ions. It is evident from the activation energy value (Ea ≈ 0.32 eV) determined from impedance, conductivity, and dielectric data that the relaxation and conduction processes correspond to the same electro-active region. Using the variable range hopping (VRH) model localization length of the carrier is calculated to be 1.56 Å. The NiO@C@PPy sample demonstrated enhanced conductivity and low dielectric values which are vital in EMI shielding applications. Consequently, the electromagnetic interference shielding effectiveness is found to be 21.9 dB of NiO@C@PPy in the X-band frequency range. This composite material is a good candidate for high frequency shielding applications.

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.

Polypyrrole coated carbon fiber/ magnetite/ graphene oxide reinforced hybrid epoxy composites for high strength and electromagnetic interference shielding

Carbon fiber reinforced polymer composites (CFRPs) are in huge demand in the aviation industry for reducing fuel consumption despite their unfavorable electromagnetic interference (EMI) shielding properties. The present work aims to improve the mechanical properties and EMI shielding effectiveness (SE) of polypyrrole (PPy) coated carbon fibers/graphene oxide (GO)/magnetite nanoparticles (MP)/ epoxy hybrid composites. For this purpose, PPy was coated on desized woven carbon fibers (CFs) woven mats via electrophoretic deposition. Graphite oxide and magnetite nanoparticles were synthesized through improved Hummers’ method and modified Massart’s method, respectively. GO was synthesized via ultra-sonication of graphite oxide, with its average thickness determined to be ∼ 1.4 nm as verified by atomic force microscopy (AFM). Solution mixing method and vacuum centrifugal mixing were utilized to disperse GO in epoxy resin. Porosity-free composites were fabricated using the vacuum bag technique. PPy coating, graphite oxide, GO and MP were characterized by scanning electron microscopy (SEM), AFM and Fourier transform infrared spectroscopy (FTIR). The SEM images showed the globular morphology of the deposited PPy on CFs. Hybrid composites containing CFPPy-0.2 wt% GO-0.2 wt% MP showed ∼52%, ∼24%, ∼60% and ∼25% increase in tensile strength, Young’s modulus, toughness, and elongation, respectively, compared to neat CF-epoxy composite. All hybrid composites prepared in this work have SE > 30 dB and could be promising lightweight and high-strength materials for EMI shielding applications in the X-band frequency range.

Ultrathin MXene film interaction with electromagnetic radiation in the microwave range

The quick progress in communication technologies demands superior electromagnetic interference (EMI) shielding materials. However, achieving a high shielding effectiveness (SE) with thin films, which is needed for microscale, flexible, and wearable devices, through absorption of EM radiation remains a challenge. 2D titanium carbide MXene, Ti3C2Tx, has been shown to efficiently reflect electromagnetic waves. In this paper, we investigated the electromagnetic shielding of ultrathin printed Ti3C2Tx films and recorded absorption up to 50% for 4 nm-thick films. This behavior is explained by impedance matching. Analysis of the sheet impedance in the X-band frequency range allows us to correlate the EMI shielding mechanism with the electrical conductivity measured within the same range. The average bulk in-plane conductivity for 4 to 40 nm-thick films reaches 106 S/m, while the average relaxation time is estimated at around 2.3 ps. Our figures of merit are similar to those reported for ultrathin metal films, such as gold, showing that an abundant MXene material can replace noble metals. We demonstrate that the MXene conductivity mechanism does not change from direct current to THz. The conventional method of reporting EMI SE is correlated with absolute values of transmitted, reflected, and absorbed power, which allows us to interpret previous results on MXene EMI shielding. Considering the easy deposition of thin MXenes films from solution onto a variety of surfaces, our findings offer an attractive alternative for shielding microscale devices and personal electronics.

X-band frequency selective surface with low loss and angular stability

A bandpass frequency selective surface (FSS) with low loss and angular stability based on three metal layers is proposed in this paper. The top and bottom resonant layers are coupled through a metal ring layer to build the FSS structure. The equivalent circuit model is derived to explain the operation principle of the proposed FSS. In the design, two transmission zeros (TZs) are generated at both sides of the passband contributing to the high selectivity performance. Furthermore, current distributions are given to analyze the generation mechanism of the TZs. The performance of the proposed FSS is insensitive to the polarization and angle of the incident wave. To verify the performance, a prototype of the FSS is fabricated, whose measured results agree with the simulated ones. The FSS shows low-profile of about 0.07λ (λ is the free space wavelength at the center frequency).

A SIW Based Leaky Wave Antenna for Aerospace Applications in X Band

In the rapidly advancing field of aerospace communication and radar systems, the demand for high performance antennas operating in the X-band frequency range has increased significantly. For high speed communication, precise navigation, and accurate detection the antenna in X band is required. In this paper, the design and analysis of a substrate integrated waveguide (SIW)-based antenna for aerospace applications operating at a frequency of 10.5 GHz. The proposed antenna design integrates the benefits of SIW technology, such as low loss, compact size, and compatibility with planar fabrication techniques, making it suitable for space-constrained aerospace platforms. The antenna had gain of 9.34 dBi, s11 of design is -28.3 at 10.5 GHz. The radiation pattern is approximately omnidirectional.

Ti3C2Tx MXene/delignified wood supported flame-retardant phase-change composites with superior solar-thermal conversion efficiency and highly electromagnetic interference shielding for efficient thermal management

The development of form-stable phase-change material (PCM) with solar-thermal harvest, electromagnetic interference (EMI) shielding, and flame-retardancy is crucial for efficient building energy management and conservation. Herein, novel Ti3C2Tx MXene/delignified wood supported form-stable phase-change composites (PMPCMs) with superior solar-thermal conversion efficiency, highly EMI shielding effects, and excellent flame-retardancy were fabricated by alkaline boiling delignification, ammonium dihydrogen phosphate (ADP) and MXene deposition, and melted n-octadecane impregnation. Benefiting from the powerful surface tension and capillary force of the wood-based support materials, PMPCMs can effectively encapsulate the melted n-alkane molecules and inhibit their leakage. The differential scanning calorimetry results showed that PMPCMs possessed superior n-octadecane encapsulation yield and high thermal energy storage density (166.9–191.6 J/g). Decorating delignified wood by MXene significantly improved the solar-thermal storage efficiency (up to 88.4 %) and EMI shielding performance of PMPCMs. The average EMI shielding effectiveness of PMPCM-10 was enhanced to 34.12 dB in X-band frequency range of 8.2–12.4 GHz. Moreover, with the introduction of the flame-retardant ADP, the peak heat release rate (pHRR) and total heat release (THR) of PMPCMs decreased noticeably, demonstrating the enhanced flame retardancy of delignified wood supported phase-change composites. In summary, PMPCMs exhibited superior application prospects in building energy management and electromagnetic shielding fields.