Microwave Loss Mechanisms Research Articles

In situ loading of ZnO on hierarchical porous carbon derived from banana-peel waste to enrich mechanism for microwave absorption

Biomass has received widespread attention due to its easy availability, low cost, and environmental friendliness as an electromagnetic wave absorber candidate. Inspired by the natural porosity of biomass, the three-dimensional (3D) porous carbon materials derived from banana peels were prepared via coordination and pyrolysis carbonization. A conductive network of biomass-zinc complexes was constructed by introducing Zn2+ to coordinate with organic polymers. Hierarchical porous carbon/ZnO composites with a 3D skeleton network were obtained, which demonstrated outstanding electromagnetic wave absorption performance with an effective absorption bandwidth (EAB) of 6.72 GHz and the reflection loss (RL) of −44.18 dB. The banana peel-derived porous carbon (BPC) embedded with ZnO particles brings about conductive loss and interface polarization, further enriching the microwave loss mechanisms. This work offers a fresh idea for creating a green, sustainable, and high-value functional carbon-based composite material.

Study on microwave absorption performance of nickel cobalt bimetallic nanosheet arrays @ hydrophilic carbon cloth composite with core-sheath structure

Magnetic metal/carbon matrix composites have gained significant attention as vital microwave absorption materials (MAMs) in recent years, owing to their multifarious microwave loss mechanisms, adjustable chemical composition, and microstructure. In this study, we describe the successful synthesis of nickel-cobalt bimetallic nanosheet arrays @ hydrophilic carbon cloth (NiCo-BNSAs @ HCC) composites with a distinctive core-sheath structure, low density, and high toughness using a solvothermal method followed by a high-temperature pyrolysis process. Despite their low density and high toughness, these composites exhibit outstanding MA properties at low matching thicknesses. Among them, S2 exhibited the minimum reflection loss (RLmin) of −75.4 dB at 1.35 mm, with its optimal effective absorption bandwidth (EAB, RL＜−10 dB) extending to 3.6 GHz at 1.10 mm. Our analysis indicates that the incorporation of NiCo-BNSAs nanosheets not only enhances the multiple scattering of EM waves but also improves interfacial polarization loss and dipole polarization loss. This study provides valuable insights into the rational construction of high-performance magnetic metal/ carbon matrix MAMs with a core-sheath structure.

Recent progress on the electromagnetic wave absorption of one-dimensional carbon-based nanomaterials

The rapid development of electronic information technology and the use of high-power electrical equipment have led to the increasingly serious problem of electromagnetic interference (EMI). Therefore, it is of great significance to study electromagnetic wave absorbing (EWA) materials with good absorbing properties. Compared with other wave absorbing materials, carbon-based nanomaterials such as silicon carbide (SiC), carbon nanotube (CNT), carbon nanowire (CNW) and carbon nanofiber (CNF) have the advantages of low density, large specific surface area/aspect ratio and excellent dielectric properties, which make them stand out. However, impedance mismatch caused by high conductivity and a single microwave loss mechanism seriously affect the absorption performance. In order to overcome the above shortcomings, surface modification, component control, structural design and other methods have been widely used in EWA materials in recent years to improve their absorption performance. In this review, we introduce the mechanism of microwave absorption and summarizes the research progress of one-dimensional carbon based nanomaterials and their composites. The preparation methods and microwave absorption properties of one-dimensional carbon based nanocomposites with different components, morphologies, and microstructures were discussed in detail. Finally, the challenges and future development prospects of one-dimensional carbon based nanomaterials were summarized, providing reference for the development of high-performance microwave absorbing materials.

Controlled Synthesis of MOF-Derived Nano-Microstructure toward Lightweight and Wideband Microwave Absorption.

Correlating metal-organic framework (MOF) synthesis processes and microwave absorption (MA) enhancement mechanisms is a pioneer project. Nevertheless, the correlation process still relies mainly on empirical doctrine, which hardly corresponds to the specific mechanism of the effect on the dielectric properties. Hereby, after the strategy of modulation of protonation engineering and solvothermal temperature in the synthesis route, the obtained sheet-like self-assembled nanoflowerswereconstructed.Porous structures with multiple heterointerfaces, abundant defects, and vacancies are obtained by controlled design of the synthesis procedure. The rearrangement of charges and enhanced polarization can be promoted. The designed electromagnetic properties and special nano-microstructures of functional materials have significant impact on their electromagnetic wave energy conversion effects. As a consequence, the MA performance of the samples has been enhanced toward broadband absorption (6.07GHz), low thickness (2.0mm), low filling (20%), and efficient loss (-25dB), as well as being suitable for practical environmental applications. This work establishes the connection between the MOF-derived materials synthesis process and the MA enhancement mechanism, which provides insight into various microscopic microwave loss mechanisms.

Detailed microwave loss mechanisms for nanocomposites of La-doped BaFe12O19 and polyaniline

To mitigate the undesirable effects of electromagnetic pollution on the precise instrument, biological health, and human life, high-efficiency microwave-absorbing materials (MAMs) have been pursued by the scientific community. MAMs also have important potential for information security, 5G, energy harvesting, reduced radar cross-section, and military stealth technology. In this work, magnetic/dielectric composites of La-doped BaFe12O19 (La-BaM) and polyaniline (PANI) were developed to be MAMs. Composites with no and 30% of La concentration (named M0-C and M3-C, respectively) showed poor microwave absorption performance with reflection loss (RL) values of about −20 dB, meaning 99% of the incident microwave was absorbed. The effective absorption bandwidths (EABs) were narrow, with values of 0.70 and 1.55 GHz, respectively. In contrast, the microwave absorption performance of composites with 10% and 50% of La concentration (named M1-C and M5-C, respectively), reached excellent values in both RL and EAB of −47.83 and −43.53 dB and 3.98 and 3.43 GHz, respectively. These RL values implied that 99.99% of the incident microwave could be absorbed. The superior microwave absorption properties of M1-C and M5-C composites could be attributed to their excellent impedance matching, better natural ferromagnetic resonance, exchange resonance, and better attenuation constant. The loss mechanism of microwave energy in La-BaM/PANI composites could be attributed to interfacial polarization at the interfaces of two phases, dipole polarization and micro-current and conductive loss (from PANI), eddy current (from La-BaM), multiple reflection and scattering (from the dispersion of PANI into La-BaM), as well as thermal energy dissipation (from embedding La-BaM/PANI into the epoxy matrix).

Microwave polarization conversion and reflection loss mechanism of complementary-modeled Rossler-based chaotic metamaterial

The complementary-modeled Rossler chaotic metamaterial (CRCM) with FR-4 dielectric layer is proposed to design metamaterial absorber with multi-resonance peaks. Under “master-slave” boundary condition in high-frequency structure simulator (HFSS) software, the electric field between adjacent boundaries presents phase difference which can simulate an infinite array. The research results show that the CRCM demonstrates multi-resonant peaks from 4 GHz to 10 GHz, and the area of metal patterned-layer can obviously regulate the resonant peaks. The CRCM presents a linear polarization conversion peak around 5.80 GHz, its polarization conversion ratio (PCR) is near 100%. The PCR is also larger than 80% from 5.56 GHz to 5.95 GHz. Through the surface current density distribution and the comparison between the CRCM and complementary-modeled double ring metamaterial (CDRM), the main factors generating polarization conversion are the asymmetry of metal pattern layer and magnetic resonance caused by reverse current. The CRCM also has two strong absorption peaks located at 6.31 and 9.37 GHz, respectively. Dielectric loss and ohmic loss are the main microwave loss mechanisms proved by volume and surface power loss density distribution. The resonant frequencies derived from [Formula: see text] resonant circuit are well consistent with the simulation data and measurement results.

The difference in microwave loss mechanism between nano- and micron-sized Ag particles

Separated E/H-field heating in microwave cavities enables us to examine the microwave loss mechanisms. We prepared mixtures of SiO2 particles (having almost no microwave loss) and Ag particles with micrometer- and nano-sizes. Their average impedance and dielectric constants were measured. Electric conductivity exhibited percolation behavior at a specific threshold of Ag fraction. When the mixtures were heated in the separated fields, H-field heating was dominant in all the fraction ranges for the micrometer-sized Ag mixture. However, E-field heating was dominant below the percolation threshold for the nano-sized Ag mixture, and above the threshold, the H-field became dominant. This change in heating rates indicates the change in the energy loss mechanism. According to the size dependence of the induction current loss in a metallic sphere, the loss becomes less effective below the size of skin depth, namely, in the nano-size region. The permittivity of nano-sized Ag particles was estimated by an approximated Lindhard’s equation, which was input into the Maxwell–Garnett mixing model for predicting the effective complex permittivity of the mixture. It was possible to interpret the measured permittivity dependence on the Ag fraction.

Optimization of microwave absorption properties of flaky FeSiAl magnetic alloy by surface modification

The surface modified flaky FeSiAl magnetic microwave absorbing material was prepared by controlled oxidation heat treatment, and was compounded with MOFs (Metal Organic Frameworks) material. The dielectric polarization characteristics and the microwave loss mechanism for the heterogeneous structure are analyzed. The obtained MOFs@FeSiAl balances the electromagnetic wave attenuation ability and the impedance matching, thus achieving excellent microwave absorbing properties. The effective absorption bandwidth (≤ −20 dB) of the composite material covers 3 ∼ 16 GHz when the coating thickness is from 1.5 to 5.0 mm. The minimum value of the reflection loss (RLmin) reaches − 71.5 dB when the frequency is 5.68 GHz, and the coating thickness is 3.85 mm. The research scheme of pre-oxidation and then composite with MOFs materials not only realizes the controllable preparation of high-performance FeSiAl composites, but also enhances the stability and corrosion resistance of the material. This work provides a new way to realize in situ composite of high permeability alloy materials and MOFs materials.

Selective coding dielectric genes based on proton tailoring to improve microwave absorption of MOFs

Regulating dielectric genes of hollow metal-organic frameworks is a milestone project for microwave absorption (MA). However, there is still a bottleneck in deciphering the contribution of various dielectric genes, making it hard to expand the MA potential from selective encoding gene sequences. Herein, a custom-made proton tailoring strategy is used to build a controllable cavity, and meticulously designed thermodynamic regulation promotes the rearrangement of carbon atoms from disorder to order, thus enhancing the characteristics of charge transfer. Meanwhile, the defect-configuration transformation from heteroatom to vacancy and geometric configuration of hollow structure increase the polarization-related dielectric genes. Therefore, MA performance is enhanced towards broadband absorption (6.6 ​GHz, 1.78 ​mm) and high-efficiency loss (−62.5 ​dB), making samples suitable for complex open electromagnetic environments. This work realizes the tradeoff between dielectric gene sequences and provides a profound insight into the functions and sources of various microwave loss mechanisms.

Loss mechanisms in TiN high impedance superconducting microwave circuits

Aluminum-based platforms have allowed to reach major milestones for superconducting quantum circuits. For the next generation of devices, materials that are able to maintain low microwave losses while providing new functionalities, such as large kinetic inductance or compatibility with CMOS platform, are needed. Here, we report on a combined direct current and microwave investigation of titanium nitride films of different thicknesses grown using CMOS compatible methods. For microwave resonators made of 3 nm thick TiN, we measured large kinetic inductance LK ∼240 pH/sq, high mode impedance of ∼4.2 kΩ while maintaining microwave quality factor ∼105 in the single photon limit. We present an in-depth study of the microwave loss mechanisms in these devices that indicates the importance of quasiparticles and provide insight for further improvement.

Ni/NiO/SiO2/C nanofibers with strong wideband microwave absorption and robust hydrophobicity

Multifunctional microwave absorbers with robust hydrophobicity and enhanced wave absorption are of great significance for human health and the martial applications. Herein, carbon nanofibers (CNFs) inlaid with Ni/NiO and SiO2 nanoparticles were prepared by electrospinning and in-situ annealing method. Contrast experiments at different annealing temperatures had been conducted to illustrate the formation process and microwave loss mechanism of Ni/NiO/SiO2/CNFs. At the annealing temperature of 550 °C, the optimal reflection loss (RL) of −40.1 dB was reached at 16.6 GHz with a thickness of 2.5 mm, the effective absorption bandwidth (EAB) was 5.2 GHz. The maximum EAB of 8.0 GHz was obtained as the thickness close to 3.0 mm, covering the half of X band and entire Ku band. It was worth mentioning that the introduction of nano SiO2 into the Ni/NiO/CNFs annealed at 550 °C could refine the nanoparticles of Ni, promote the formation of Ni, improve the complex permittivity, and ultimately widen the EAB. Moreover, the contact angle (CA) of the Ni/NiO/SiO2/CNFs membranes annealed at 450, 550, 650 and 750 °C was 154.3°, 138.7°, 142.2° and 144.9°, respectively, illustrating that the products were of robust hydrophobicity. Therefore, the as-prepared NFs are promising in multifunction wave absorbers.

Influence of synergistic effect of Mn valence state and oxygen vacancy concentration on microwave absorbing properties of CaMnO3

The research of microwave absorption material has great significance for solving electromagnetic pollution and military security. Manganite perovskite has huge potential for developing into a fine microwave absorption material due to its adjustable electromagnetic property, while the mechanisms are still being explored. Therefore, we aim to explain the microwave loss mechanism of manganite perovskite with the double exchange interaction of Mn ion. Orthorhombic structure CaMnO3 was effectively synthesized, and the Mn valence state and oxygen vacancy concentration were changed by doping at Ca-site, while the total number of Mn ions remained intact. Ba, Sr, La, Sm, and Ce were the doping ions employed. Analyses revealed that the microwave absorption performance of CMO was linked to the Mn valence state and oxygen vacancy concentration. The Sr-CMO with the optimal microwave attenuation capability had the most Mn3+ ions and its dielectric loss is primarily due to polarization relaxation loss. In the microwave attenuation mechanism of La-CMO, which had the least oxygen vacancy content, conductive loss played a larger role. Through the double exchange interaction of Mn, the synergistic impact altered the microwave absorption performance. Hence, we can manipulate Mn valence state and oxygen vacancy concentration to improve the microwave absorption performance of CaMnO3, and the technique might be applied to other Mn-based absorbents.

Synthesis of bowknot-like N-doped Co@C magnetic nanoparticles constituted by acicular structural units for excellent microwave absorption

Nanoparticles with high roughness and complex surface have strong reflection and scattering ability for electromagnetic wave, which can extend the propagation path of electromagnetic wave in absorbing coating, thus exhibiting better microwave absorbing performance. Constructing complex surface has been considered as an effective way to improve the microwave loss ability of microwave absorbers. In this paper, a novel bowknot-like N-doped Co@C magnetic nanoparticle constituted by acicular structural units (BNCoC) has been designed and prepared. Its precursor (BNCoCP) is synthesized by solvothermal method and converted into BNCoC by subsequent vacuum calcination. The main structure of BNCoC is N-doped carbon with Co nanoparticles embedded in it. BNCoC contains dielectric and magnetic components that has both dielectric loss and magnetic loss capabilities. Under the synergistic effect of its unique structure, BNCoC exhibits excellent absorbing performance with a minimum reflection loss of −47.6 dB@11.0 GHz@2.7 mm. Furthermore, the effects of calcination temperature and filler content on microwave absorbing performance are investigated. The electromagnetic parameters are analyzed in depth to reveal the microwave loss mechanism. This work reports a novel high-efficiency microwave absorber with unique structure. It provides a new method for microstructure design of microwave absorbing materials.

The electromagnetic response of composition-regulated honeycomb structural materials used for broadband microwave absorption

The undesirable absorption bandwidth is the main limitation for the application of microwave absorbing materials. Noting that the design of structure and composition of absorbing coating allows it to obtain a satisfying absorption bandwidth and to avoid weight increasing, honeycomb and its sandwich structures coated by various absorbant have been developed and measured using an arch measurement system over 2−18 GHz. To further understand the absorption mechanisms of honeycomb structural materials, simulation based on finite element method and transmission line theory is performed to analyze the different responses to the applied microwave between honeycomb structural materials and uniform-medium slab materials. The proper composition design allows control over the microwave loss mechanisms, which optimize the coating to possess both of the dielectric and magnetic advantages. For the honeycomb structural materials, the magnetic resonation is found for the first time, which is resulting from the periodic honeycomb walls on both sides of the dielectric cavity (consisting of the aramid paper interlayer and vacuum hexagonal prisms). In addition, the conversion of structure from solid to honeycomb brings about changes in impedance, propagating path, effective wavelength, effective attenuation area, microwave phases, and inductive coupling effect, etc., which result in a better microwave absorbing performance. The honeycomb sandwich structure coated by CIP/CB/EP with the weight ratio of 4:0.03:1 shows the absorption bandwidth of ∼9.8 GHz for reflection loss (RL) lower than -10 dB which covers part of the S and C bands and almost the whole X and Ku bands.

Microwave absorbing properties of La1-x Ba x MnO3 (x=0.1,0.2,0.3,0.4,0.5) nano-particles

Electromagnetic wave absorbing materials have always been a research hotspot in military and civil fields. La1-x Ba x MnO3 nanocrystalline powders were prepared by sol-gel method. XRD analysis shows that La1-x Ba x MnO3 is a single perovskite structure, and the lattice constant changes with the doping amount. SEM analysis shows that La1-x Ba x MnO3 is basically spherical with an average particle size of about 80 nm. The relationship between the complex permittivity and permeability with microwave frequency was measured by microwave vector network analyzer. According to the measured data, the microwave reflectivity and loss factor of the sample were calculated, and the microwave loss mechanism of the sample was discussed. The results show that x has a great influence on the absorbing properties of La1-x Ba x MnO3. When x is 0.2 and the thickness is 1.6mm, the absorption bandwidth above 10dB reaches 2.1GHz and the maximum absorption value is 25dB. The microwave loss of La1-x Ba x MnO3 mainly comes from the dielectric polarization loss of perovskite materials, it also comes from conductivity loss, magnetic loss and interface polarization loss due to Ba doping and nano effect.

Low-loss (1-x)Ba0.6Sr0.4La4Ti4O15-xCaTiO3 microwave dielectric ceramics with medium permittivity

In the present work, a series of (1-x)Ba0.6Sr0.4La4Ti4O15-xCaTiO3 (x = 0.02, 0.03, 0.05, 0.1 and 0.2, BSLT-CT) functional ceramics were synthesized via co-firing the mixtures of Ba0.6Sr0.4La4Ti4O15 and CaTiO3 powders. Crystal structure and microwave dielectric properties were investigated together thermally stimulated depolarization currents (TSDC). Scanning electron microscopy (SEM) would be explored. X-ray diffraction confirms that these compounds display a single hexagonal phase with perovskite structure and the diffraction peaks shift to high angles with increasing CaTiO3 content. Raman spectra uncover Oh symmetry deviation and distortions of oxygen octahedra. The variation of the CaTiO3 addition has a direct impact on the dielectric properties of the (1-x)BSLT-xCT ceramics at microwave frequency. TSDC was conducted to acquire the defects associated with extrinsic microwave loss mechanism. The main type of defect in BSLT-CT is oxygen vacancy (VO••), namely involving in-grain and across-grain relaxation. The increase of CaTiO3 prompts the increase of oxygen vacancy concentration, which may induce microwave loss. At x = 0.2, the microwave dielectric properties of specimens are εr = 47.1, Q × f = 41,200 GHz and τf = −5.3 ppm/°C, respectively.

Trimetallic FeCoNi@C Nanocomposite Hollow Spheres Derived from Metal-Organic Frameworks with Superior Electromagnetic Wave Absorption Ability.

Organic ligands and metal ions in the metal-organic frameworks (MOFs, a type of porous magnetic metal/carbon nanocomposites obtained through high-temperature carbonization) have caused widespread concerns in the field of microwave absorption because of the existence of various microwave loss mechanisms in these materials. However, MOF-driven microwave absorbing materials with high absorption intensity and wide absorption band still require further research and development. In this work, hollow sphere trimetallic FeCoNi@C microwave absorbing materials via high-temperature carbonization were obtained using FeCoNi-based MOF-74 (FeCoNi-MOF) as the precursor. The effects of different carbonization conditions on the microwave absorption properties of the materials were studied. FeCoNi-MOF-74 annealed at 700 °C showed superior microwave absorption capacity, where the RL value reached -64.75 dB at 15.44 GHz corresponding to the actual application thickness of the absorber (only 2.1 mm), and the minimum RL values reached -69.03 dB at 5.52 GHz. Furthermore, the as-prepared sample can fully cover the Ku band and X band at only 2.1 and 3.1 mm, respectively. The maximum EAB reached 8.08 GHz (9.92-18 GHz) when the thickness of the absorber was 2.47 mm. Such remarkable absorption performance is attributed to the synergetic effects between the multiple loss mechanisms of the FeCoNi@C, and the improved impedance matching characteristic came from the hollow sphere morphology.

MnFe2O4-coated carbon nanotubes with enhanced microwave absorption: Effect of CNT content and hydrothermal reaction time

Carbon nanotubes (CNT) coated with magnetic nanoparticles are promising microwave absorbing materials with high performance. Despite several previous investigations, the relationship between intrinsic composition and preparation conditions of this composite material to its microwave loss mechanisms and absorbing properties have not yet been fully understood. We present a convenient and cost-effective hydrothermal method to deposit crystalline manganese iron oxide (MnFe2O4) over CNT. Adjusting the hydrothermal reaction time and CNT content allows control over the microstructure of the resulting CNT-MnFe2O4 nanocomposite and its microwave absorbing properties, resulting in a better microwave absorber than pure MnFe2O4. Composites synthesized at 150 °C for 10 h with 10 wt% CNT reveal a reflection loss as high as −38 dB at 5.7 GHz for an absorber thickness of 5 mm and frequency bandwidth (RL < −10 dB) up to 3.59 GHz. As the hydrothermal reaction time is reduced to 1 h, the minimum reflection loss increases significantly to −41 dB at 11.8 GHz for a 2 mm coating thickness. Defects and functional groups on the surfaces of CNT act as nucleation sites for MnFe2O4 and help reduce agglomeration, which decreases overall particle size. Microwave absorbing mechanisms are also discussed. Coating CNTs with manganese iron oxide increases microwave dissipation by enhancing conduction loss, interface polarization, relaxation polarization, and magnetic loss, including the contributions of eddy current and natural resonance, which are all related to the reaction time and CNT content. Consequently, the synthesis-property relationship could potentially be used to design CNT-based nanomaterials that have more effective microwave absorption.

Microwave electromagnetic and absorption properties of SiO2/C core/shell composites plated with metal cobalt

A facile method has been developed to fabricate magnetic core/shell SiO2/C/Co sub-microspheres via the pyrolysis of SiO2/PANI (polyaniline) and electroless plating method. The electromagnetic parameters of these SiO2/C and SiO2/C/Co composites were measured and the microwave reflection loss properties were evaluated in the frequency range of 2–18 GHz. The results show that the dielectric loss of SiO2/C composite increases with the increase of carbonization temperature and the magnetic loss enhances due to the deposition of cobalt on the SiO2/C sub-microspheres. The reflection loss results exhibit that the microwave absorption properties of the SiO2/C/Co composites are more excellent than those of SiO2/C composites for each thickness. The maximum effective absorption bandwidth (reflection loss ≤ −10 dB) arrives at 5.0 GHz (13.0–18 GHz) for SiO2/C/Co composite with 1.5 mm of thickness and the minimum reflection loss value is −24.0 dB at 5.0 GHz with 4.0 mm of thickness. The microwave loss mechanism of the SiO2/C/Co composites was also discussed in this paper.

Loss mechanism and microwave absorption properties of hierarchical NiCo2O4 nanomaterial

Understanding the loss mechanism of microwave absorption is of great significance for the design and fabrication of low-cost, high-efficient and light-weight microwave absorbing materials. In this study, the microwave absorption of a hierarchical NiCo2O4 nanomaterial synthesized via a hydrothermal method and a subsequent annealing process was investigated in detail. The effects of the annealing temperature on the phase evaluation and microwave absorption properties were also investigated to reveal the microwave loss mechanism of NiCo2O4 nanostructures. The results show that the Debye relaxation and superior electric conductivity of NiCo2O4 are beneficial to its excellent microwave absorption performance. This study will be useful for the fundamental understanding of microwave absorption in NiCo2O4 nanomaterial, and for the design of a novel microwave absorbent.