High-performance Microwave Absorption Materials Research Articles

Enhanced dielectric loss induced by the doping of SiC in thick defective graphitic shells of Ni@C nanocapsules with ash-free coal as carbon source for broadband microwave absorption

The rapid development of microelectronic devices means increasing attention is being paid to the exploration of high-performance microwave absorption materials. Enhanced dielectric loss is an effective way of improving microwave absorption performance. Here, we report that Ni@C nanocapsules with ash-free carbon as a carbon source, functionalized by the doping of SiC in a thick defective graphitic shell, demonstrate enhanced dielectric losses at the gigahertz level, and energy transfer from permeability to permittivity at 14.24 GHz. Compared with Ni@C nanocapsules, which have ethanol as a carbon source, the same absorption band and absorption intensity can be obtained with a thinner absorber in the present Ni@C nanocapsules, and the frequency corresponding to maximum reflection loss exhibits a red shift for the same absorbing thickness. At 5.12 GHz, the maximum reflection loss value of the present Ni@C nanocapsules can reach −49.99 dB for a planar absorber with a thickness of 5.1 mm. Experimental results coupled with theoretical simulations reveal the electromagnetic losses of the present Ni@C nanocapsules originating from the core–shell interfacial polarization and dipole polarization of the doping of SiC in the defective graphitic shell.

Wood-based straightway channel structure for high performance microwave absorption

Microwave absorption (MA) materials have gained wide range of applications including satellite communications, radar detections, etc. Here, for the first time we designed high-performance porous biomass-pyrolized carbon (PBPC) based on natural wood. The PBPC with orderly parallel channel structure is on the top among all MA materials, showing excellent MA performance with maximum reflection loss (RL) of −68.3 dB and absorption bandwidth (RL ≤ −10 dB) up to 7.63 GHz. Furthermore, we predict the reflection loss by calculation and point out regulation of electrical conductivity would maximize MA performance. The combination of renewability, easy mass production and simple fabrication provides PBPC practical application value, and the strategy of channel structure design followed by permittivity adjustment casts a light for accessing new high-performance MA materials.

Ultra-broad polypyrrole (PPy) nano-ribbons seeded by racemic surfactants aggregates and their high-performance electromagnetic radiation elimination

Ribbon-like nano-structures possess high aspect ratios, and thus have great potential in the development of high-performance microwave absorption (MA) materials that can effectively eliminate adverse electromagnetic radiation. However, these nano-structures have been scarcely constructed in the field of MA, because of the lack of efficient synthetic routes. Herein, we developed an efficient method to successfully construct polypyrrole (PPy) nano-ribbons using the self-assembly aggregates of a racemic surfactant as the seeds. The frequency range with a reflection loss value of lower than −10 dB reached 7.68 GHz in the frequency range of 10.32–18.00 GHz, and surpassed all the currently reported PPy nano-structures, as well as most other MA nano-materials. Through changing the amount of surfactant, both the nano-structures and MA performance can be effectively regulated. Furthermore, the reason behind the high-performance MA of PPy nano-ribbons has been deeply explored. It opens up the opportunity for the application of conducting polymer nano-ribbons as a lightweight and tunable high-performance MA material, especially in applications of special aircraft and flexible electronics.

Switching the electromagnetic properties of multicomponent porous carbon materials derived from bimetallic metal-organic frameworks: effect of composition.

Porous carbon materials have long been regarded as promising candidate for high-performance lightweight microwave absorption materials owing to their strong attenuation abilities, tunable dielectric properties and low density. Nevertheless, previous work mainly focused on binary composites (usually carbon and magnetic fillers), which show limited loss mechanisms. The effect (except temperature) on the interfacial polarization and electromagnetic properties has rarely been investigated. Thus, a series of bimetallic zeolitic imidazolate frameworks (BMZIFs) with designed compositions and highly porous structures were selected to be converted to porous carbon-wrapped semiconductors (ZnO, Co3ZnC) and magnetic metal (Co) composites. Strong dielectric loss capabilities could be provided by graphitic carbon and enhanced interfacial polarization induced by multiple components and unique microstructures. By changing the molar ratio of Zn/Co under a fixed carbonization temperature, the interface of this multicomponent system could be adjusted, which influenced the electromagnetic properties. When evaluated as microwave absorption material, a reflection loss of -32.4 dB could be achieved with a broad effective frequency bandwidth of 5.24 GHz at only 1.9 mm. This work may provide an effective method to modify the physical and chemical properties of porous carbon materials with a desired complex structure and excellent microwave absorption performance.

Ferromagnetic hierarchical carbon nanofiber bundles derived from natural collagen fibers: truly lightweight and high-performance microwave absorption materials

High-performance microwave absorption materials with a broad bandwidth and strong intensity have significant applications in both civil and military areas.

Bio-inspired fabrication of hierarchical Ni-Fe-P coated skin collagen fibers for high-performance microwave absorption.

In the present investigation, skin collagen fiber (CF) with a well defined hierarchical 3D fibrous structure was employed for the bio-inspired fabrication of high-performance microwave absorption materials. The hierarchical 3D structure of the CF was retained in the CF@Ni-Fe-P composites, and the formation of the Ni-Fe-P coating on the CF surface was identified by XRD and XPS analysis. Based on the electromagnetism parameter measurements, the maximum reflection loss (RL) of the CF@Ni-Fe-P composites reached -31.0 dB, and the width of the absorption band where reflection loss values exceeded -10.0 dB covered the whole Ku-band and some parts of the X-band (9.5-18.0 GHz). The complex permittivity and complex permeability measurements indicated that electronic loss and magnetic loss were involved in the CF@Ni-Fe-P composites for microwave absorption. In addition, due to the magnetic properties of the Ni-Fe-P coating, these CF@Ni-Fe-P composites exhibited excellent magnetic characteristics with high saturation magnetization and low coercivity values. The present investigation indicates a new possibility for the bio-matrix-based fabrication of high-performance microwave absorbing materials with lightweight and efficient absorption properties.

Excellent microwave absorption property of Graphene-coated Fe nanocomposites

Graphene has evoked extensive interests for its abundant physical properties and potential applications. It is reported that the interfacial electronic interaction between metal and graphene would give rise to charge transfer and change the electronic properties of graphene, leading to some novel electrical and magnetic properties in metal-graphene heterostructure. In addition, large specific surface area, low density and high chemical stability make graphene act as an ideal coating material. Taking full advantage of the aforementioned features of graphene, we synthesized graphene-coated Fe nanocomposites for the first time and investigated their microwave absorption properties. Due to the charge transfer at Fe-graphene interface in Fe/G, the nanocomposites show distinct dielectric properties, which result in excellent microwave absorption performance in a wide frequency range. This work provides a novel approach for exploring high-performance microwave absorption material as well as expands the application field of graphene-based materials.

Microwave absorption properties of helical carbon nanofibers-coated carbon fibers

Helical carbon nanofibers (HCNFs) coated-carbon fibers (CFs) were fabricated by catalytic chemical vapor deposition method. TEM and Raman spectroscopy characterizations indicate that the graphitic layers of the HCNFs changed from disorder to order after high temperature annealing. The electromagnetic parameters and microwave absorption properties were measured at 2–18 GHz. The maximum reflection loss is 32 dB at 9 GHz and the widest bandwidth under −10 dB is 9.8 GHz from 8.2 to 18 GHz for the unannealed HCNFs coated-CFs composite with 2.5 mm in thickness, suggesting that HCNFs coated-CFs should have potential applications in high performance microwave absorption materials.

One-step seeding growth of controllable Ag@Ni core–shell nanoparticles on skin collagen fiber with introduction of plant tannin and their application in high-performance microwave absorption

Controllable magnetic Ag@Ni core–shell nanoparticles (NPs) have been designed and constructed on the bayberry tannin (BT) grafted skin collagen fiber (SCF) though a simple one-step route. Due to the mild and naturally occurring reduction ability of BT, when the SCF-BT made contact with the mixture of Ag+/Ni2+ solution, BT was able to preferentially reduce Ag+ into Ag NPs, and subsequently, the formed Ag NPs served as in situ seeds for the over growth of magnetic Ni shell by the reduction of NaBH4. The systematic TEM and EDS analysis confirmed that the as-prepared Ag@Ni NPs on SCF-BT were a typical core–shell structure. Magnetic study of core–shell NPs indicated that their magnetic properties could be tuned by modulating their shell thickness with the change of Ag+/Ni2+ molar ratio. The diameter and size distribution of SCF-supported Ag@Ni core–shell NPs also can be controlled by varying the grafting degree of BT on SCF, as characterized by TEM. A novel and important application of these SCF-supported Ag@Ni core–shell NPs composites is use as high-performance microwave absorption materials in the whole X-band, C-band and some part of S-band with maximum reflection loss (RL) of −51 dB. The further analysis of electromagnetic parameters indicated that the enhancement of dielectric loss properties of SCF-supported Ag@Ni core–shell NPs is introduced by the multiple defective site polarization and interfacial polarization in bimetallic interface. In addition, owing to the combinated magnetic property on the nickel shell, the SCF-supported Ag@Ni core–shell NPs also exhibited a significant eddy current effect and anisotropic energy effect for the microwave absorption. To the best of our knowledge, this is the first time to explore tailoring the magnetic property, electromagnetic property and microwave absorption performance of functional core–shell NPs by tuning their core–shell microstructures. The present work has a significant potential for the development of novel, lightweight, low-cost, flexible and highly efficient microwave absorbing materials.