Broadband Absorption Properties Research Articles

Mechanical and broadband absorption properties of Nextel 610/SiOC composites synergistically enhanced by the interfacial structure design

In this work, BN interphase and Si3N4 matrix were prepared by chemical vapor infiltration (CVI) to optimize the mechanical properties of N610/SiOC composites, and the strengthening and toughening mechanisms were investigated. The results showed that the content and distribution of Si3N4 matrix and the thickness of BN interphase could tailor the strength and toughness of composites simultaneously. The optimal tensile strength of 234 MPa and flexural strength of 338 MPa were obtained by Si3N4 reinforced N610/SiOC composites with a BN interphase thickness of 540 nm, respectively. Meanwhile, free carbon modified BN interphase (BN(C)) and multi-layer “mortise and tenon” joint were designed to optimize the broadband EMW absorption. The impedance-matching “mortise and tenon” joint achieved a wide effective absorption bandwidth (EAB) of 8.4 GHz and a minimum reflection loss (RLmin) of −52.55 dB. This work inspires designing and fabricating CMC with both good mechanical and broadband EMW absorption properties.

Graphene Microflower by Photothermal Marangoni-Induced Fluid Instability for Omnidirectional Broadband Photothermal Conversion.

2-D carbon-based materials are well-known for their broadband absorption properties for efficient solar energy conversion. However, their high reflectivity poses a challenge for achieving efficient omnidirectional light absorption. Inspired by the multilevel structures of the flower, a Graphene Microflower (GM) material with gradient refractive index surface was fabricated on polymer substrates using the UV-intense laser-induced phase explosion technique under the synergistic design of the photothermal Marangoni effect and the fluid instability principle. The refractive index gradient reduces light reflection and absorbs at least 96% of light at incident angles of 0-60° across the entire solar wavelength range (200-2500 nm). Over 90% absorption even at 75° angle of incidence. The light absorption is enhanced by the multiple interferometric phase cancelation and localized surface plasmon resonance, resulting in a steady-state temperature 60 °C higher than ambient conditions under one solar irradiation. The max rate of temperature rise can reach up to 62 °C s-1. The device is then integrated at the hot end of the temperature difference generator at high altitude to ensure continuous and efficient power generation, producing a steady-state power of 196 mW.

Electromagnetic wave absorption in polyaniline coated Y3Fe5O12/Carbon-Black hybrid composites

Y3Fe5O12(YIG)1-x/Carbon-Black(CB)x (0.00≤x≤1.00; 0.25 steps) coated with polyaniline (PANI), forming a core-shell structure, were synthesized by in-situ polymerization following sol-gel and solid-state reactions. The crystalline, surface morphology and magnetic properties of YIG1-x/CBx and PANI@YIG1-x/CBx hybrid composites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM), respectively. Electromagnetic wave (EMW) absorbing properties were investigated by measuring dielectric parameters in the 2–18 GHz frequency range. The reflection loss (RL), impedance matching, and loss tangent were studied in detail. The electromagnetic wave absorbing mechanisms were discussed by considering dielectric and magnetic losses, as well as microstructural properties of the samples. The EMW absorbing performance of the YIG1-x/CBx composites showed a broadband absorption property (7.0 GHz bandwidth at −10 dB reflection loss value) in YIG0.75/CB0.25 composite. When the composites are covered with conductive PANI, the EMW absorbing performance is enhanced in terms of RL (minimum −36.5 dB) and effective absorption bandwidth (EAB) (maximum 10.2 GHz at −10 dB) values due to increasing scattering probability, interfacial polarization and conduction loss of the penetrated EMW. The results showed that a wider absorption frequency range could be obtained by coating PANI on YIG/CB composite.

Multi-scale design of MWCNT/glass fiber/balsa wood composite multilayer stealth structure with wide broadband absorption and excellent mechanical properties

In unmanned aircraft applications, electromagnetic wave (EMW) absorbers suffer from defects in narrow absorption bands and poor mechanical properties. To solve the problems, a lightweight multilayer stealth structure with wide broadband absorption performance and excellent mechanical properties was designed and prepared by adjusting microscopically the number of multi-walled carbon nanotubes (MWCNT) and modulating macroscopically the thickness-matching relationship of the structure to promote the absorption of EMW synergistically. Under the MWCNT of 30 wt% and the depletion layer with the thickness of 0.2 mm, the effective absorption bandwidth (EAB) covers the entire Ku-band while maintaining a minimum reflection loss (RL) of −15 dB. Besides, the radar cross-sectional area attenuation is as high as 23.1 dBm2, as well as the mechanical properties of the radar absorbing structures (RAS) were improved significantly due to the reducing structural density from balsa wood and the enhancement effect of glass fiber mats (GFM). The study constructed balsa-based RAS with excellent EMW absorbing and mechanical properties from both micro-nano scale and macro-structure, providing a research route for designing high-performance and lightweight stealth structures.

Multi-functional switchable terahertz metasurface device prediction by K-nearest neighbor

In this paper, we present the design of a versatile terahertz (THz) device characterized by its multi-functional capabilities including broadband absorption and polarization modulation, achieved through leveraging the temperature-induced phase transition behavior of vanadium dioxide (VO2). Operating in the metallic state of VO2, the device exhibits broadband absorption properties, delivering a remarkable total effective absorption of 2.871 THz with absorption rates exceeding 90 % across the frequency ranges of 8.140∼9.405 THz and 12.740∼14.346 THz. Furthermore, it demonstrates excellent adaptability to large angle incidence. Conversely, in the dielectric state of VO2, the device transitions into a polarization modulation mode, facilitating linear-to-cross-polarization (LTX) and linear-to-circular-polarization (LTC) conversions. Notably, for LTX polarization, the conversion efficiency exceeds 90 % within the 8-11.5 THz range, while for LTC polarization, the ellipticity surpasses 0.8 within the 7.861∼8 THz range. Additionally, we introduce a machine learning (ML) approach to optimize the device parameters, presenting a novel strategy for enhancing the design and optimization of future multifunctional devices.

Design and optimization of double-layer structure for improved electromagnetic wave absorbing characteristic of single-layer foam cement-based materials containing carbon black

Electromagnetic wave (EMW) absorbing properties are increasingly needed in cement-based materials; however, lightweight and broadband absorption properties are challenging to realize. This study aims to create lightweight, broadband, and highly efficient EMW-absorbing materials by investigating a foam cement-based material with single- and double-layer structures containing carbon black (CB). The results revealed that CB significantly affects the mechanical properties and electrical conductivity of foam cement-based materials. The compressive strength of the foam cement-based material containing 1.5 wt% CB with a density of 0.9 g cm−3 can reach 7.0 MPa and has satisfactory workability and conductivity. The dielectric properties of the foam cement-based material can be synergistically controlled by its density and CB content, and obtain favorable electric loss ability. For a single-layer structure, the optimal reflection loss (RL) value of a specimen with 10 mm-thick can reach −29.67 dB with an efficient bandwidth of 0.99 GHz. In contrast, the double-layer structure exhibited remarkable broadband characteristics. When the total thickness of double-layer structure is 10 mm, the optimal two specimens can achieve a minimum RL value of −28.62 and −25.52 dB with a maximum effective bandwidth of 1.49 and 1.87 GHz, respectively. This study proposes single- and double-layer foam cement-based structures with excellent impedance matching and loss attenuation ability, and constructs an effective design method for cement-based materials to achieve lightweight and broadband absorption. In addition, these cement-based materials can be regarded as a new generation of EMW-absorbing materials in the field of construction engineering.

Broadband and Tunable Microwave Absorption Properties from Large Magnetic Loss in Ni–Zn Ferrite

AbstractHighly effective electromagnetic (EM) wave absorber materials with strong reflection loss (RL) and a wide absorption bandwidth (EBW) in gigahertz (GHz) frequencies are crucial for advanced wireless applications and portable electronics. Traditional microwave absorbers lack magnetic loss and struggle with impedance matching, while ferrites are stable, exhibit excellent magnetic and dielectric losses, and offer better impedance matching. However, achieving the desired EBW in ferrites remains a challenge, necessitating further composition design. In this study, impedance matching is successfully enhanced and EBW in Ni–Zn ferrite is broadened by successive doping with Mn and Co , without incorporation of any polymer filler. It is found that Ni0.4Co0.1Zn0.5Fe1.9Mn0.1O4 material exhibits exceptional EM wave absorption, with a maximum RL of −48.7 dB. It also featured a significant EBW of 10.8 GHz, maintaining a 90% absorption rate (RL < −10 dB) for a thickness of 4.5 mm. These outstanding properties result from substantial magnetic losses and favorable impedance matching. These findings represent a significant step forward in the development of microwave absorber materials, addressing EM wave pollution concerns within GHz frequencies, including the frequency band used in popular 5G technology.

Ultrahigh dark and light-improved chloride removal performance of magnetite bismuth oxide thin flakes with low crystallinity

The high concentration of chloride (Cl-) ions in wastewater poses environmental risks. The bismuth oxide (Bi2O3)-based Cl- removal method has gained significant attention due to its high selectivity towards Cl- ions. However, it still faces challenges related to strong acid condition and excessive dosage. Herein, the mixed-ferrites (M-Fe3O4) nanoparticles with broadband absorption property were combined with Bi2O3 to form to the magnetite Bi2O3 (FBO) composites. Due to the space separation of M-Fe3O4 nanoparticles in the thin Bi2O3 flakes, FBO had a loose structure, and its sample after 100 °C treatment (FBO-100) possessed weak crystallinity and the largest specific surface area, which enabled it to possess the highest Cl- removal efficiency of 98.4% at pH = 1 in the dark. Under UV-Vis-NIR irradiation, the Cl- removal efficiencies of FBO-100 at pH = 2, 3, and 5 increased from 71.4%, 56.3%, and 54.5% to 84.6%, 65.5%, and 58.0%, respectively. During the light-irradiated Cl- removal process, the heterostructures of Bi2O3/M-Fe3O4, Bi2O3/BiOCl/M-Fe3O4, and BiOCl/M-Fe3O4 were successively built, and the oxidative photocorrosion of Bi2O3 caused by holes played the predominant role in improving the Cl- removal efficiency, compared with the •OH, Cl•, and O2•− radicals. FBO-100 had stable cyclic Cl- removal performance and high safety, which is expected to be of a good application prospect for Cl- removal.

Optimal design of 3D macro-structures for multi-layer foams achieving ultra-broadband microwave absorption properties and high retention after immersion in brine

A novel flexible microwave absorbing material (C–MCM–FAS) with a cone-shaped sandwich structure is proposed, which is constructed by carbonyl iron-carbon nanotubes/PDMS foams and SiC–morchella biochar/PDMS film. To enhance broadband absorption properties, a three-level scale design has been creatively introduced into C–MCM–FAS, encompassing millimeter, micron and nano scales. The rational structural parameters of C–MCM–FAS are determined by CST simulation, leading to the preparation of C–MCM–FAS with an impressive minimum reflection loss (RLmin) of −43.26 dB and an effective absorption band (EB) covering the entire C2, X, and Ku bands at 11.79 GHz. Encouragingly, the measured results are basically consistent with the simulation results (an RLmin of −35.78 dB and an EB of 14.68 GHz), which verifies the accuracy of the theoretical simulation and the feasibility of the method. It holds great significance that the investigation of the adsorption retention rate of C–MCM–FAS after immersing it in 3.5 wt% NaCl solution for 21 days. The measured RLmin reaches −48.41 dB with a retention rate of 111.9 %, and the EB reaches 8.56 GHz with a retention rate of 72.6 %. This work presents a groundbreaking concept for designing structural absorbers, expecting the C–MCM–FAS to become a strong contender for application in special environments like microwave detection in the nautical field.

Construction of chitosan-derived porous nest-like C/SnO2 materials for microwave absorption

Electromagnetic waves have an irreplaceable role as information carriers in civil and radar stealth fields, but they also lead to electromagnetic pollution and electromagnetic leakage. Therefore, electromagnetic wave absorbing materials that can reduce electromagnetic radiation have come into being. Especially, SnO2 has made a wave among many wave-absorbing materials as an easily tunable dielectric material, but it hardly has both broadband and powerful absorption properties. Here, the nested porous C/SnO2 composites derived from nitrogen-doped chitosan is obtained by freeze-drying and supplemented with carbonization treatment. The chitosan creates a nested cross-linked conductive network that can make part of the contribution to conduction loss. The amino groups contained in the molecule either help promote in situ nitrogen doping and trigger dipole polarization. The multiphase dissimilar interface between the nested carbon layer and the inner clad SnO2 formation is the major inducer of interfacial polarization. It reached intense absorption of −48.8 dB and bandwidth of 5.2 GHz at 3.46 mm. The interfacial polarization is confirmed to be the main force of dielectric loss by simulating the electromagnetic field distribution. In addition, the RCS simulation data assure the prospect of enticing applications of C/SnO2 composites in the field of radar stealth.

Enhancement of photo-thermal performance using hole plasmonic nanofluids

A single nanoparticle with broadband and strong optical absorption property has great significance for expanding its utilization and saving cost in various fields. This work utilizes the near-spherical nanocavities distributed on the surface of a single nanoparticles (named as “hole nanoparticles”) to optimize the optical absorption performance and to reduce the material cost, especially for plasmonic materials. The cavity effect and the localized surface plasmon resonance effect of the hole plasmonic nanofluids can effectively regulate the absorption band to match the solar spectrum and enhance optical absorption property. Apart from gathering the incident light, the cavity effect can enhance the surface resonance effect, then further enhances the optical absorption. Based on the finite-difference time-domain method, the results show that the photothermal conversion efficiency of silver hole nanofluid and titanium nitride hole nanofluid with a cavity size of 10 nm, a cavity depth of 18 nm, and a cavity number of 49 can separately reach 89.1 % and 91 % at just 10 ppm, among which the silver hole nanofluids have higher photothermal conversion efficiency by 15.4 % than the corresponding solid nanofluids. This work provides an efficient strategy to achieve the broadband-spectrum utilization of the single nanoparticle with the low material usage.

A broadband low-profile microwave absorber based on ferromagnetic material doped hybrid stereo metamaterial

This study introduces a ferromagnetic material-doped hybrid stereo metamaterial absorber (HSMA) that has been developed to overcome the limitations in broadband absorption of electromagnetic wave. This metamaterial combines a ferromagnetic block with a blind via in the center and a standing resistive trapezoidal patch together in a stereo meta-atom to enable a continuous and broad absorption band for 90% absorptivity from 2.3 GHz to 40 GHz, with a thickness only as 0.079 times the maximum working wavelength. The hybrid absorber also exhibits angular stability under oblique incidence and polarization insensitivity. Furthermore, a sample of proposed HSMA was fabricated and measured. The broadband absorption properties of such hybrid stereo metamaterial were validated by both simulated and experimental results. Our study provides a promising implementation approach for broadband and low-profile microwave absorbers.

Multifunctional carbon dots reinforced gelatin-based coating film for strawberry preservation

The development of safe, non-toxic, multifunctional nano preserved materials with excellent performance has become a hot research topic. Multifunctional Sophora Japonica extract (95% rutin)-derived carbon dots (R-CDs) were prepared by hydrothermal method. The π-π conjugation structure of R-CDs enabled them UV broadband absorption properties. The excellent antioxidant properties of R-CDs were attributed to the presence of the sp2 carbon in core and a large number of hydroxyl groups at the edges, and their degradation rate of potassium permanganate and scavenging activity of superoxide anion radical were better than that of ascorbic acid. The presence of CO bond may be the site for the generation of reactive oxygen species (ROS) and thus they could kill Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis) and Listeria monocytogenes (L. monocytogenes) at a concentration of 2 mg/mL and inhibited the growth of fungi (Botrytis cinerea). Then R-CDs were uniformly dispersed in gelatin-based solution, and the as-prepared films had smooth surface, good hydrophilicity, strong mechanical properties and good biocompatibility. With the increase of R-CDs addition, the tensile strength increased and then decreased, and the elongation at break rose to 358%. The film inherited the broadband UV absorption, antioxidant and antibacterial properties of R-CDs. The storage period of strawberries was prolonged after coating. The variety and abundance of microorganisms on the surface of strawberries was reduced and the growth of harmful bacteria was inhibited. This work provides more possibilities for the application of nanomaterials in fruit preservation.

Tunable broadband terahertz absorption and shielding of bioderived graphitic carbon microspheres

The rapid advancement of Terahertz (THz) science and technology has led to a growing interest in electromagnetic interference (EMI) shielding in the THz frequency region. There is an urgent need for broadband and tunable devices capable of absorbing terahertz (THz) waves to effectively eliminate undesired THz interference. In this regard, this work demonstrates the facile synthesis of graphitic carbon microspheres from turpentine oil (a natural carbon source) and its broadband absorption and shielding properties in the THz frequency region from 0.2 THz to 1.6 THz. Advanced characterization techniques like XRD, FESEM, RAMAN, and XPS have been employed to explore the structural, microstructural, and elemental properties of graphitic carbon microspheres (GCMs). Herein, an effort has been made to discuss the underlying mechanism for THz absorption by GCMs. The minimum shielding efficacy reaches −27.5 dB covering the broad frequency region from 0.2 to 1.6 THz with a matching thickness of ∼3.75 μm, signifying that more than 99% of the THz radiations can be shielded. Also, GCMs are exhibiting exceptional terahertz absorption (∼86%) spanning from 0.2 to 1.6 THz for the same sample thickness. Our findings reveal valuable insights into the THz shielding properties of graphitic carbon thin films without any complex element doping or functionalization, shedding light on their suitability for future THz-based devices.

A Review of Nitrogen-Doped Graphene Aerogel in Electromagnetic Wave Absorption.

Graphene aerogels (GAs) possess a remarkable capability to absorb electromagnetic waves (EMWs) due to their favorable dielectric characteristics and unique porous structure. Nevertheless, the introduction of nitrogen atoms into graphene aerogels can result in improved impedance matching. In recent years, nitrogen-doped graphene aerogels (NGAs) have emerged as promising materials, particularly when combined with magnetic metals, magnetic oxides, carbon nanotubes, and polymers, forming innovative composite systems with excellent multi-functional and broadband absorption properties. This paper provides a comprehensive summary of the synthesis methods and the EMW absorption mechanism of NGAs, along with an overview of the absorption properties of nitrogen-doped graphene-based aerogels. Furthermore, this study sheds light on the potential challenges that NGAs may encounter. By highlighting the substantial contribution of NGAs in the field of EMW absorption, this study aims to facilitate the innovative development of NGAs toward achieving broadband absorption, lightweight characteristics, and multifunctionality.

Broadband ultra-thin Long-Wave InfraRed metamaterial absorber based on trapezoidal pyramid array

The ultra-thin absorber in the long-wave infrared band plays an important role in imaging, sensor, and energy collection. Various perfect absorbers in the long wave infrared band have been designed, however, the absorption bandwidth and structural thickness still limit their application. Here, we propose an ultra-thin perfect absorber composed of a periodic Ti trapezoidal pyramid array, on GaAs dielectric spacer layer, with Ti reflection substrate. Due to the excitation of propagating surface plasmon resonance and local surface plasmon resonance, the average absorptivity about 93.6% in the 8–15 μm band is obtained, which is insensitive to the polarization angle and incidence angle. The resonance characteristics of the structure are studied through the electrostatic theory, and the broadband absorption properties for varied geometric parameters are analyzed using the multipole decomposition method. Meanwhile, we achieved the absorptivity more than 90% at 9.1–17.1 μm by changing the dielectric spacer layer structure of the absorber, and the average absorptivity is 92.1%.

Optimization design of 3D-printed pyramid structure for broadband electromagnetic wave absorption

Aiming to improve the bandwidth of the absorber, which is more favorable for applications in military and civil fields, a novel FeSiAl/polylactic acid (PLA) composites pyramid was fabricated by fused deposition molding (FDM) 3D printing technology. The study investigated the impact of the geometric parameters of the unit structure on the absorption intensity and bandwidth of electromagnetic (EM) wave (EMW). The results show that the pyramid structure achieves a minimum reflection loss (RLmin) of − 37.2 dB. The cell structure of the pyramid structure features a period length of 22.5 mm, a base thickness of 0.5 mm, a cell thickness of 7.0 mm, and an upper surface edge length of 6.0 mm. These parameters result in a RL below − 10 dB within the frequency band of 6.7–18 GHz. Meanwhile, the effective absorption bandwidth (EAB, for RL below −10 dB) of TE polarization exceeds 11 GHz when the incident angle changes from 0° to 50°, and the EAB value of TM polarization still reaches 6.9 GHz at 70°. The broadband absorption properties of the proposed absorber are attributed to the synergistic enhancement effect of the structure and material.

Enhancing broadband and intense microwave absorption properties of flaky FeSiCr powder by coating SiO2

Flaky FeSiCr@SiO2 composites with broadband and intense absorption were successfully synthesized by modified Stöber method. The phase, microstructure and morphology of flaky FeSiCr@SiO2 composites were investigated by XRD, FT-IR, SEM and TEM, confirming the successful preparation of SiO2 coating. The thermal behavior of flaky FeSiCr@SiO2 composites was analyzed by TGA/DSC. The results showed that the oxidation resistance of the coated FeSiCr powder was promoted. The electromagnetic wave absorption properties of samples with different contents of tetraethyl orthosilicate (TEOS) were systematically investigated. The sample synthetized with 10 ml TEOS possesses the optimal absorption performance, which is attributed to the synergistic effect of magnetic loss and dielectric loss. The minimum reflection loss is −65.3 dB at 4.4 GHz. And the maximum effective absorption bandwidth is 6.0 GHz with only a 1.5 mm thickness. In particular, by controlling the thickness of the absorber, the effective absorption bandwidth can reach 13.3 GHz (2.9–16.2 GHz), covering the entire C and X bands. Thus, the flaky FeSiCr@SiO2 composites can be used as high-performance microwave absorption materials.

A nanocomposite metamaterial with excellent broadband microwave absorption performance and good mechanical property

The microwave absorbers draw great attentions in addressing the electromagnetic pollution issues and the electromagnetic stealth needs. However, it remains a challenge to realize the microwave absorbers with thin thickness, broadband absorption and good mechanical properties simultaneously. Inspired by the special microstructures of papilio palinurus's wing and beetle’s elytra, nanocomposite metamaterial with excellent broadband microwave absorption and good mechanical property was designed and fabricated. The Carbonyl iron-Carbon nanotubes-epoxy nanocomposites were firstly synthesized for fabricating the designed metamaterial. Slab made of the synthesized nanocomposites can realize 7.04 GHz effective absorption bandwidth (i.e., EAB, reflection loss (RL) ≤-10 dB) with thickness of 1.28 mm. Unit cell size parameters optimization of designed metamaterial was then conducted with the multi-population genetic algorithms, in which both the microwave absorption bandwidth and microwave absorption intensity were set as the optimized target. The optimized bioinspired nanocomposite metamaterial possesses 31.7 GHz EAB and −47 dB minimum RL value with thickness of only 6 mm, and its compressive strength is 33.78 MPa. The proposed bioinspired metamaterial strategy in this paper provides an efficient way for designing metamaterials with excellent broadband microwave absorption performance and good mechanical properties.

Design and Preparation of Flexible Graphene/Nonwoven Composites with Simultaneous Broadband Absorption and Stable Properties

As the world moves into the 21st century, the complex electromagnetic wave environment is receiving widespread attention due to its impact on human health, suggesting the critical importance of wearable absorbing materials. In this paper, graphene nonwoven (RGO/NW) composites were prepared by diffusely distributing graphene sheets in a polypropylene three-dimensional framework through Hummers' method. Moreover, based on the Jaumann structural material design concept, the RGO/NW composite was designed as a multilayer microwave absorber, with self-recovery capability. It achieves effective absorption (reflection loss of -10 dB) in the 2~18 GHz electromagnetic wave frequency domain, exhibiting a larger bandwidth than that reported in the literature for absorbers of equivalent thickness. In addition, the rationally designed three-layer sample has an electromagnetic wave absorption of over 97% (reflection loss of -15 dB) of the bandwidth over 14 GHz. In addition, due to the physical and chemical stability of graphene and the deformation recovery ability of nonwoven fabric, the absorber also shows good deformation recovery ability and stable absorption performance. This broadband absorption and extreme environmental adaptability make this flexible absorber promising for various applications, especially for personnel wearable devices.