Tunable Electromagnetic Wave Research Articles

In Situ Synthesis of Heterostructured Fe–Ni Nanowires with Tunable Electromagnetic Wave Absorption Capabilities

In Situ Synthesis of Heterostructured Fe–Ni Nanowires with Tunable Electromagnetic Wave Absorption Capabilities

Comment on: “Tunable surface waves supported by graphene-covered left-handed material structures” [Opt. Commun. 489 (2021) 126874

In a recent article (Yaqoob et al., 2021), Yaqoob et al. studied the tunable electromagnetic surface wave propagation on the graphene-covered left-handed material (LHM) slab backed by the perfect electric conductor (PEC). They derived the dispersion relations for both transverse electric (TE) and transverse magnetic (TM)-polarized surface waves, and then used the relations for two types of LHMs according to the spectral range, i.e., GHz- and THz-LHM. The present Comment points out although the system under consideration (i.e., graphene-covered LHM) is itself physically challenging, the results for THz-LHM are also rather unreal because the frequency regime to accomplish the calculations falls within the high THz frequency band. In such a frequency band, the conductor substrate no longer behaves like a PEC and thus the results are rather unreal when considering THz-LHM. We note that the metal, for example, gold or silver may be modeled as a PEC, but only for a few THz. Moreover, when considering GHz-LHM, we obtain new forms of dispersion relations for both TE and TM surface waves. We find that our dispersion relations do not agree with the results obtained by Yaqoob et al.

Carbon cloth based flexible electromagnetic wave absorbing materials loaded with Co3O4 array and tunable electromagnetic wave absorption performance

The demand for flexible electromagnetic wave (EMW) absorbing materials has increased, highlighting the importance of designing efficient and adaptable EMW absorbing materials. In this study, flexible Co3O4/carbon cloth (Co3O4/CC) composites with high EMW absorption properties were prepared via a static growth method and annealing process. The composites exhibited remarkable properties, with the minimum reflection loss (RLmin) and maximum effective absorption bandwidth (EAB, RL ≤ –10 dB) of –54.43 dB and 4.54 GHz, respectively. The flexible carbon cloth (CC) substrates exhibited outstanding dielectric loss due to their conductive networks. Moreover, the uniformly and tightly organized Co3O4 arrays on the flexible CC substrate played a crucial role in fine-tuning the impedance matching and facilitating abundant multiple scattering and interface polarization. This study proposes a promising approach to preparing flexible Co3O4/CC composites with a significant reference value for the field of flexible EMW.

Tunable and broad-band electromagnetic wave absorption using W-type Hexaferrites in 1–40 GHz range

W-type Sr-hexaferrites, Sr0.75Ca0.25Zn2-xCoxFe16O27 (0.0 ≤ x ≤ 2.0), were synthesized, and their magnetic and electromagnetic (EM) wave absorption properties were investigated. As x increased from 0.0 to 2.0, the saturation magnetization value increased and reached a maximum at x = 1.25, followed by a decrease, while the magnetic anisotropic field (Hani) decreased and showed a minimum at x = 1.0, then increased again. The variation in Hani could be controlled by adjusting the value of x, which also changed the ferromagnetic resonance (FMR) frequency and enabled control over the frequency band of EM wave absorption. It is demonstrated that the EM wave absorption is primarily controlled by imaginary part of permeability (μ") induced by FMR. Composite of the W-type hexaferrite-epoxy (10 wt%) with x = 0.75–2.0 showed a broad-band EM wave absorption in the 1–18 GHz range, while the composites with x = 0–0.4 showed it in the 26.5–40 GHz. The x = 1.25 sample satisfied RL < − 10 dB in the 7–17 GHz range with a thickness of 2.1 mm, while x = 0.3 sample satisfied RL < − 10 dB in the 27–39 GHz with a thickness of 0.8 mm. Sr0.75Ca0.25Zn2-xCoxW is a very promising material for tunable wideband EM wave absorbers in 1–40 GHz range.

Heterogeneous and hierarchical ni/C/SiO2 composite with tunable electromagnetic wave absorption

Structure design, conductivity regulation and electromagnetic matching are important to optimize the electromagnetic wave (EMW) absorbing properties. Therefore, exploring a strategy which kill these three birds with one stone is extraordinary. In this work, the heterogeneous and hierarchical Ni/C/SiO2 composite with tunable EMW absorption properties was synthesized through a simple calcination process. The introduction of SiO2 and Ni prompted a relatively large hole generated in the center of carbon fiber and formed hierarchical porous structure with the circumambient small holes which extended the propagation path of EMW, realized multiple reflection and scattering and endowed sufficient interfacial polarization. Meanwhile, the SiO2 and Ni nanoparticles played an important role in conductivity regulation and electromagnetic matching. Owing to the ingenious hierarchical porous structure and synergistic effect of multiple loss mechanisms, the Ni/C/SiO2-0.5 exhibited the optimal absorption properties with the maximum reflection loss (RL) of −47.65 dB at 3.1 mm with the filler content of 10 wt%. This research would provide a novel strategy for the exploitation route of the EMW absorbing materials.

Construction of 1D Heterogeneous Co/C@Ag Nws With Tunable Electromagnetic Wave Absorption And Shielding Performance.

In this study, silver nanowires (Ag NWs) are synthesized at first, and then the 1D heterogeneous Co/C@Ag NWs with a kebab- and popsicle-like microstructures are constructed by in situ growth ZIF-67 on Ag NWs combined with calcination. Results show that the EM wave prevention performance of composites depends on the loading of Co/C particles threaded on the Ag NWs. The popsicle-like structure with high Co/C loading gives Co/C@Ag NWs excellent EM wave absorption performance, which achieved a minimum reflection loss (RLmin ) of -44.5dB with a low filling of 30wt.% in paraffin; while the kebab-like structure with low Co/C loading shows good electromagnetic interference (EMI) shielding effectiveness (SET ) of 30.2dB at the same filler ratio. The enhanced EM wave absorption performance is attributed to the synergy of multiple energy dissipation mechanisms including dielectric loss, magnetic loss, polarization loss, eddy-current loss, multiple reflection loss, as well as proper impedance matching; the good EMI shielding performance is mainly due to the conduction loss brought by the Ag NWs with ultrahigh conductivity. This work provides a reference for the design of electromagnetic wave prevention material with tuned absorption and shielding performance.

Direct ink writing of thermoresistant, lightweight composite polyimide honeycombs with tunable X-band electromagnetic wave absorption properties

Direct ink writing of thermoresistant, lightweight composite polyimide honeycombs with tunable X-band electromagnetic wave absorption properties

Manipulation of Impedance Matching toward 3D-Printed Lightweight and Stiff MXene-Based Aerogels for Consecutive Multiband Tunable Electromagnetic Wave Absorption

Highly conductive MXene material exhibits outstanding dissipation capability of electromagnetic (EM) waves. However, the interfacial impedance mismatch due to high reflectivity restricts the application of MXene-based EM wave absorbing materials. Herein, a direct ink writing (DIW) 3D printing strategy to construct lightweight and stiff MXene/graphene oxide aerogels (SMGAs) with controllable fret architecture is demonstrated, exhibiting tunable EM wave absorption properties by manipulating impedance matching. Noteworthy, the maximum reflection loss variation value (ΔRL) of SMGAs is -61.2 dB by accurately modulating the width of the fret architecture. The effective absorption region (fE) of SMGAs exhibits consecutive multiband tunability, and the broadest tunable fE (Δf) is 14.05 GHz, which could be continuously tuned in the whole C- (4-8 GHz), X- (8-12 GHz), and Ku-bands (12-18 GHz). Importantly, the hierarchical structures and the orderly stacking of filaments endow lightweight SMGAs (0.024 g cm-3) with a surprising compression resistance, which can withstand 36 000 times its own weight without obvious deformation. Finite element analysis (FEA) further indicates that the hierarchical structure facilitates stress dispersion. The strategy developed here provides a method for fabricating tunable MXene-based EM wave absorbers that are lightweight and stiff.

Preparation of microcrystalline graphite/zinc ferrite composites with enhanced and tunable electromagnetic wave absorption using a high-temperature ball milling method

Microcrystalline graphite (MG)/zinc ferrite (ZFO) composites were prepared by a high-temperature ball milling method. The magnetic and microwave absorption properties of MG/ZFO composites were analyzed in the frequency range of 2.0–18.0 GHz. The results showed that MG has a favorable impact on the microwave absorption capacity of ZFO. The composites containing 10 wt% MG had a minimum reflection loss of −62.90 dB, which is almost a factor of 12 higher than for pure ZFO, and their effective absorption bandwidth (EAB, RL<−10 dB) covers frequency range of 5.84–7.92 GHz for a matching thickness of 3.9 mm, and for a matching thickness of 1.8 mm, the EAB covers frequency range of 12.87–17.70 GHz. A probable mechanism of microwave absorption for MG/ZFO composites is based on a synergistic combination of dielectric and magnetic losses. The attractive properties of prepared composites indicate that they are promising and competitive materials for use in microwave absorption.

Rational manipulation of composition and construction toward Zn/Co bimetal hybrids for electromagnetic wave absorption

• Zn@Co and Co@Zn Zn/Co bimetal hybrids were fabricated by bi-orientation etching strategy. • The components and constructions are regarded as major factors determining electromagnetic properties. • The RL min and f E of Zn@Co-C-2h reached -34.99 dB and 5.52 GHz (2.00 mm), respectively. Rational manipulation of multi-metal hybrids with controllable compositions and constructions is evolving as an efficacious strategy for tunable electromagnetic (EM) characteristics and EM wave (EMW) absorption. Herein, a novel bi-orientation etching approach is proposed to regulate the chemical compositions and hybridization construction of Zn/Co hybrids, thence meeting the synergistic interaction among diverse compositions for ultra-high EMW absorption. Attributing to the stepwise heterometallic modification by Zn in Co-ZIFs (Zn@Co-ZIF) and Co in Zn-ZIFs (Co@Zn-ZIF), corresponding pyrolysis products with variable Zn/Co atomic concentration and hybridization states (Zn@Co-C, Co@Zn-C) can be obtained. The Co species was confirmed to have a positive impact on both the dielectric and magnetic response, while an appropriate amount of Zn hybridization in Co substance further enhanced the synergistic effect between multiple loss mechanisms, promoting the minimum reflection loss and effective absorption bandwidth of Zn@Co-C reached -34.99 dB and 5.52 GHz (2.00 mm), respectively. Finally, this work reveals the composition and construction dependency of bimetal hybrids on EMW absorption, which can be a strong reference for developing EMAs with diverse hybridization structures.

Microstructure optimization strategy of ZnIn2S4/rGO composites toward enhanced and tunable electromagnetic wave absorption properties.

Although microstructure optimization is an effective strategy to improve and regulate electromagnetic wave (EMW) absorption properties, preparing microwave absorbents with enhanced EMW absorbing performance and tuned absorption band by a simple method remains challenging. Herein, ZnIn2S4/reduced graphene oxide (rGO) composites with flower-like and cloud-like morphologies were fabricated by a convenient hydrothermal method. The ZnIn2S4/rGO composites with different morphologies realize efficient EMW absorption and tunable absorption bands, covering a wide frequency range. The flower-like structure has an optimal reflection loss (RL) of up to -49.2 dB with a maximum effective absorption bandwidth (EAB) of 5.7 GHz, and its main absorption peaks are concentrated in the C and Ku bands. The minimal RL of the cloud-like structure can reach -36.3 dB, and the absorption peak shifts to the junction of X and Ku bands. The distinguished EMW absorption capacity originates from the uniquely optimized microstructure, complementary effect of ZnIn2S4 and rGO in dielectric constant, and synergy of various loss mechanisms, such as interfacial polarization, dipole polarization, conductive loss, and multiple reflections. This study proposes a guide for the structural optimization of an ideal EMW absorber to achieve efficient and tunable EMW absorption performance.

Hierarchical composite foams possessing an electric network layer modified with MoS2by atomic layer deposition as high-performance and tunable absorbers

The construction of three-dimensional (3D) electric network structures is playing a crucial role in improving the electromagnetic energy attenuation ability in the design and synthesis of efficient and tunable electromagnetic waves absorbers.Herein, an extraordinary carbonized melamine skeletons (CMS) @ knitted Ni/N-doped carbon nanotubes (NCNTs) structure (labeled CK), in which the hollow CMS wrapped with 3D electric network layer is constructed via the intertwining of in-situ grown NCNTs, has been rationally designed and successfully fabricated through the anchoring of nickel hydroxide and pyrolysis processes. Meanwhile, the efficient and tunable microwave absorption performance of the CMS @ knitted Ni/NCNTs @ MoS2 (CKM) is achieved by introducing MoS2 into the 3D electric network layer via atomic layer deposition. The optimal microwave absorption performance can be observed in involved absorbers with a filling ratio of only 3.97 %, whose minimum reflection loss reaches up to −96.13 dB at a thickness of 2.62 mm and maximum effective absorption bandwidth is 8.2 GHz at 3.2 mm. By manipulating the loads of MoS2, the coverage of X-band and Ku-band can be implemented with a 6.68 % filling load at an absorber thickness of 2.5 and 1.9 mm, respectively. The construction of the unique microstructure and regulation of MoS2 loads are demonstrated to be feasible pathways for the production of efficient and tunable electromagnetic waves absorbers in future.

N-doped carbon nanofiber embedded with TiN nanoparticles: A type of efficient microwave absorbers with lightweight and wide-bandwidth

In this work, TiN-embedded in N-doped carbon nanofiber (TiN/NCNF) composites were synthesized by the electrospinning method and heat treatment process subsequently. The TiN/NCNF composites possess different TiN nanoparticles (TiNNPs) content, which can acquire by tuning the percentage of TiNNPs in the polyacrylonitrile precursor solutions. The study shows that TiN/NCNF composites hold more intense and tunable electromagnetic wave (EMW) absorption capabilities, as the embedded TiNNPs with more defects lead to enhanced electrical conductivity and cause room-temperature ferromagnetic. As a result, TiN/NCNF composites can achieve the well-matched impedance and contribute to significant electromagnetic wave attenuation capabilities due to their more interfacial polarization, defect dipole relaxation polarization, enhanced conductance loss, and magnetic loss caused by the defect, resulting in excellent microwave absorbing performance. When the mass fraction of the TiN/NCNF composites (S2 sample with nominal 3 wt% TiNNPs content) was only 30% in the absorbing coating, the optimal reflection loss (RL) value was achieved in − 45.19 dB at 15.6 GHz with a thickness of 1.91 mm, corresponding efficient absorption bandwidth (RL≤−10 dB) of 4.93 GHz. This work provides a novel method of realizing lightweight, wide-bandwidth, and efficient microwave absorbing characteristics of carbon fiber absorbents, using obtained particles from defect engineering strategies as loaded ones. As may be expected, the TiN/NCNF composites would have a significant potential application prospect as microwave absorbing materials.

Lightweight porous cobalt-encapsulated Nitrogen-Doped Carbon nanotubes for tunable, efficient and stable electromagnetic waves absorption

To eliminate the hazards of electromagnetic radiation, lightweight and efficient electromagnetic waves absorbing (EWA) materials with long-term stability are highly desired. Herein, novel bamboo-like carbon nanotubes wrapped with controllable-sized Co magnetic nanoparticles (Co@CNT) are successfully prepared via a simple calcination strategy. The terminal EWA properties can be effectively tuned by adjusting filler loading, calcination temperature and template usage. Specifically, via controlling the calcination temperature, strong absorption capabilities located at X, C and Ku bands can be achieved. Finally, the optimized Co@CNT displays a superior EWA performance with −53.5 dB absorption intensity and 5.64 GHz effective bandwidth under 1.85 mm thin thickness and 6 wt% low filler loading, being in line with the development of innovative EWs absorber. This remarkable performance is attributed to dielectric loss, magnetic loss, multiple reflections, and moderate impedance matching. Furthermore, through hydrophobic modification by methyltrimethoxysilane (MTMS), it exhibits a significant improvement in stability and still keeps a strong absorption of −59.05 dB after acidic solution immersion. This work sheds a light on the design and synthesis of advanced EWA materials with lightweight, strong absorption, hydrophobicity, and stability merits.

Hollow spherical NiFe-MOF derivative and N-doped rGO composites towards the tunable wideband electromagnetic wave absorption: Experimental and theoretical study

N-doped rGO (N-rGO) based nano materials are considered to be competent candidates for absorbing electromagnetic waves (EMWs), owing to the low filler loading and abundant relaxation polarization losses. With a unique multistage porous structure, NiFe@N–C/rGO, derived from the composite of NiFe-MOF anchoring on GO nanosheeets, was successfully constructed by a facile solvothermal method and high-temperature annealing technique. Adjusting the ratio of GO is an effective strategy to optimize the EMWs absorption performance to a large extent. At a filler loading of 20 wt%, when the content of graphene is 30 mg, the corresponding product NiFe@N–C/rGO-30 is found to have a minimum reflection loss (RLmin) of −72.28 dB at 10.82 GHz, and an effective absorption bandwidth (EAB, RL ≤ −10 dB) is 5.25 GHz (12.43–17.68 GHz) under the matching thickness of 2.46 mm, its EAB dramatically reached 7.14 GHz (9.74–16.88 GHz) when the graphene content was increased to 90 mg at 2.04 mm matching thickness, which covers most of the X and Ku radar frequency band. Combined with the analysis of the electronic and surface structures of NiFe@N–C/rGO composites, the formation energy and dipole moment were calculated to reveal the mechanism of EMWs absorption within them. The results show that the N-doped structure is more stable than the vacancy modification, where the pyridinic-N is the source of dipole relaxation polarization under high-frequency electromagnetic field. The combination of experimental and theoretical research reveals the inherent mechanism of EMWs attenuation in as-prepared composites, paving an inspirational route for controllable high performance absorbing materials.

Investigation into wideband electromagnetic stealth device based on plasma array and radar-absorbing materials

Manipulation of electromagnetic waves is essential to various microwave applications, and absorbing devices composed of low-pressure gas discharge tubes and radar-absorbing materials (RAM) can bring new solutions to broadband electromagnetic stealth. The microwave transmission method is used to measure the physical parameters of the plasma unit. The designed structure exhibits superior absorption performance and radar cross-section (RCS) reduction capability in the 2–18 GHz band, with unique absorption advantage in the S and C frequency bands. It is found that the combination of the plasma and the RAM can significantly broaden the absorption frequency band and improve the absorption performance with excellent synergistic stealth capability. Experimental and simulation results present that broadband, wide-angle, tunable electromagnetic wave absorption and RCS reduction can be achieved by adjusting the spatial layout of the combined plasma layer and the type of RAMs, which creates opportunities for microwave transmission and selective stealth of equipment. Therefore, the wave manipulation by combined plasma array and RAM provides a valuable reference for developing numerous applications, including radar antenna stealth, spatial filter, and high power microwave shielding.

Accordion-like reduced graphene oxide embedded with Fe nanoparticles between layers for tunable and broadband electromagnetic wave absorption

Electromagnetic wave absorbers constructed by reduced graphene oxide (rGO) and magnetic nanoparticles are extremely desirable for enhancing electromagnetic wave absorption performance due to the effective integration of the properties of dielectric and magnetic materials. However, the arrangement of graphene sheets and the growth of magnetic nanoparticles have always been challenging. Herein, an in-situ growth process has been used to successfully prepare accordion-like graphene with homogeneously distributed Fe nanoparticles in the confined structure via ion absorption and pyrolysis. The as-prepared Fe/layered rGO composites show excellent electromagnetic wave absorption performance with thin thickness, low filler loading, and broad effective absorption bandwidth (EAB). The minimum reflection loss of the composites achieves −54.6 dB with 20 wt% filler loading, and the tunable EAB reach 6.8 GHz (2.2 mm with 10 wt% filler loading) and 4.6 GHz (2.8 mm with 30 wt% filler loading), which can cover the entire Ku-band and X-band. The mechanism analysis indicates that the superior absorption performance is attributed to the multi-component loss mechanism, enhanced impedance matching degree and attenuation ability caused by the synergistic effect of layered rGO sheets and magnetic nanoparticles. This work opens up a new avenue for constructing accordion-like graphene-based composites as highly efficient electromagnetic wave absorbers.

A mechanically tunable electromagnetic wave harvester and dual-modal detector based on quasi-static van der Waals heterojunction

Electromagnetic (EM) wave harvesting and detection have many implications for self-powered human health monitoring and robot intelligence. Heterojunction-based energy harvesters and detectors can convert various forms of energy into electricity. Here, we report a mechanically tunable electromagnetic wave harvester (EMH), operated by quasi-static contact of a metal/indium gallium zinc oxide/metal van der Waals heterojunction. The proposed EMH behaves as a rectenna responding to low-frequency signals (80–400 MHz), where the electrode works as an antenna, the heterojunction between two separated layers works as a rectifying diode, and the parallel structure works as a capacitor. It is found that the pressure on the EMH plays an important role on regulating electronic interfaces and thus the output characteristics. The two output states (on/off states) of the EMH can be reversibly controlled by mechanical pressure. The proposed design and mechanism have been verified by various materials pairings and structures, which proves their great universality. The simple-structure EMH can continuously generate DC power for 10 hours without signal attenuation. It can supply power to a capacitor, a LED and a resistive load inverter, which demonstrates its application potential as an energy source. Moreover, the EMH can work as a sensor to qualitatively detect electromagnetic waves in the ambient environment and pressure. This work has proposed a novel solution to harvest and detect electromagnetic energy by van der Waals heterojunction in a mechanically controllable way, providing new possibilities for wearable electronics, intelligent robots, and Internet of Things.

The flexible carbon fibers@ZIF–67 decorated with MoS2 layers towards tunable and high–performance electromagnetic wave absorption

Hierarchical structural design has been proved to be a new strategy for fabricating high-performance microwave absorbers, so some researchers use low–dimensional components to construct continuous networks for better performance. In this work, the novel hierarchical carbon fibers@ZIF–67@MoS2 film with tunable and efficient electromagnetic wave (EMW) absorption performance was obtained by the electrostatic spinning of ZIF–67 in the interior of carbon fibers and subsequent hydrothermal of MoS2. By the synergistic effects from the ZIF–67 particles increasing the magnetic loss and MoS2 at the outer layer improving the impendence matching, the absorption property of CPZM–1 could be summarized as follow: the optimal reflection loss(RL) was −72.7 dB with a thickness of 2.6 mm at 10.0 GHz and the corresponding effective absorption bandwidth (EAB) of 9.8 GHz covered whole X and Ku band. Moreover, by adjusting the load of ZIF–67, CPZM–5 achieved the maximum EAB of 12.5 GHz.

Controllable thermal treatment of reduced graphene oxide for tunable electromagnetic wave absorption performance

The complex process of reduced graphene oxide (RGO) preparation hindered its merits of lightweight, high surface area, and notable dielectric loss in electromagnetic (EM) wave absorption performance. This work introduced a controllable ethanol-assisted hydrothermal and annealing treatment to simplify the preparation of RGO with improved agglomeration and achieved tunable EM wave absorption performance. Among series of RGO materials fabricated with different annealing temperatures, the optimized RGO achieves a strong reflection loss of −49.9 dB with a thickness of 3.9 mm, and a broad effective absorption bandwidth of 7.65 GHz with a thickness of 3.1 mm based on a 2 wt% filler content in the matrix. The vacancy defect density and C/O ratio of RGO were demonstrated to be correlated to the behavior of conductive loss and polarization relaxation for RGO and the interface reflection of EM wave. This controllable thermal treatment successfully enabled the simple preparation of RGO with reduced agglomeration and tunable EM wave absorption and effectively contributed to fabricating other carbon-based dielectric/magnetic materials as high-efficiency electromagnetic absorbers in future.