Tunable Microwave Absorption Research Articles

Tunable and efficient microwave absorption from mesophase pitch carbide with designable electromagnetic properties

In order to obtain the microwave absorption (MA) materials with light weight, high efficiency and tunable properties, the carbonized mesophase pitch (CMP) with the variation in carbonization temperatures and particle sizes were prepared and characterized. The carbonization temperature mainly controlled the graphitization degree of the CMP to affect their conductive loss. The carbon residues were generated on the CMP surface when the temperature was higher than 700 °C, which contributed significantly to the polarization loss of the CMP. For scale regulation, the segregation between the particles in the paraffin ring caused by the reduction particles of CMP carbonization at 750 °C (750 CMP) resulted in a significant reduction in conductive losses while improving their impedance matching. The 750 CMP over 300 mesh sieved had the strongest MA properties of −53 dB at 3.49 GHz within 5.5 mm. Moreover, the prepared CMPs were multi-layer compounded and optimized by CST microwave studio. The synergistic effect derived from the improved impedance matching and the enhanced interfacial polarization resulted in significant reflection loss in multi-layer CMP. Overall, these findings lead to the systematically regulation of carbon-based materials for MA, showing an attractive application prospect for the preparation of high-performance MA materials.

Tunable microwave absorption and shielding effectiveness in the nanocomposite of 3D hierarchical flower-like Co3O4 and rod-like polyindole

• 3D hierarchical composites of Co 3 O 4 /polyindole/paraffin were successfully prepared. • Electromagnetic properties of composites improved as the Co 3 O 4 /PIn ratio increased. • A 25 wt% Co 3 O 4 /PIn paraffined composite achieve RL = −21.5 dB and EAB = 3.5 GHz. • Total shielding effectiveness ( SE T ) was increased by the increase of Co 3 O 4 /PIn. • SE T of 25 wt% Co 3 O 4 /PIn paraffined composite was four times higher than 5 wt% one. Due to the rapid development of wireless electronic devices, achieving an excellent microwave absorber is crucial in modern life. The composite of flower-like Co 3 O 4 and rod-like polyindole (PIn) was embedded in the paraffin matrix for tunable microwave absorption performance and shielding effectiveness. Investigation of microwave absorption features of Co 3 O 4 /PIn paraffined composites in the X band frequency range revealed a good performance for 25 wt% Co 3 O 4 /PIn paraffined composite with reflection loss and an effective absorption bandwidth of −21.5 dB and 3.5 GHz (covered ∼ 83% X band). The pretty good microwave absorption performance of this composite originated from magnetic loss (by Co 3 O 4 ), dielectric loss (by PIn), and heat transfer capability (by paraffin). Shielding effectiveness was also increased with the increase of Co 3 O 4 /PIn loading percentage, with a total shielding effectiveness of 28.1 dB with the most contribution from shielding effectiveness for absorption. This work provides an easy and low-cost approach for tunable microwave absorption and shielding effectiveness for practical applications.

Reduced graphene oxide loaded with magnetic nanoparticles for tunable low frequency microwave absorption

Graphene-based microwave absorption materials have been profoundly and extensively investigated because of their excellent properties and is potential absorbing material. However, graphene-based absorbing materials about low-frequency remain to be researched and developed. Here we obtain that Reduced Graphene Oxide (RGO) modified with magnetic xNi/yNiO nanoparticles by a simple hydrothermal method, which presents a large reflection loss (RL) in S-band. The electromagnetic parameters, attenuation constants and impedance matching of xNi/yNiO/RGO composite were analyzed to determine the appropriate ratio of magnetic xNi/yNiO nanoparticles and GO. The maximum RL can reach −46.5 dB with a thickness of 3.6 mm at 3.57 GHz with a loading wax ratio of 15 wt%. The probability of falling on EAB is maximized to cover 94.5% of the S-band. Notably, the RL and efficient absorption bandwidth (EAB) of xNi/yNiO/RGO composite material can be adjusted according to the quarter wavelength matching theory. All the results indicate that xNi/yNiO/RGO composite has a great potential of low frequency absorbing material for low frequency absorbing material research on practical. • xNi/yNiO/RGO was prepared by simple hydrothermal method. • The maximum reflection loss can reach −46.6 dB with a thickness of 3.6 mm at 3.57 GHz. • The probability of falling on EAB is maximized cover 94.5% of S-band. • According to the practical adjustment of raw material proportion to get the required absorbing material.

Frequency-Tunable and Magnitude-Tunable Microwave Metasurface Absorbers Enabled by Shape Memory Polymers

In this article, we demonstrate a new strategy for achieving a kind of shape-controlled tunable microwave absorbers based on shape memory polymers (SMPs). Using the heat-driven shape memory effect of SMPs, a frequency-tunable absorber and a magnitude-tunable absorber are designed. Both of the designs consist of a periodic metallic array printed on both sides of the FR4 substrate, SMPs’ substrate (VeroWhitePlus) in the middle layer, and a metallic ground at the bottom. The equivalent circuit models are introduced to analyze the operational principles of the two absorbers. Furthermore, the functionalities of the designed shape-controlled tunable absorbers are investigated by full-wave simulations. For the frequency-tunable absorber design, the simulated results indicate that the resonant frequency can be tuned from 11.3 to 13.5 GHz with a frequency shift of 2.2 GHz. For the other design, the simulated results show that the reflection coefficient can be tuned from −17.00 to −1.34 dB. The proposed frequency shift responses and magnitude modulation responses are experimentally demonstrated by fabricating two prototypes containing 33 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times33$ </tex-math></inline-formula> units. The above designs overcome the limitation of the traditional electrically adjustable wave absorber requiring an external power supply, providing a new paradigm for the design of tunable devices.

Core-shell FeNi@SiO2 composite with enhanced microwave absorption performance

In this work, a core-shell FeNi@SiO2 composite is constructed by modified Stöber method. Through adjusting the content of Tetra-Ethyl OrthoSilicate (TEOS) to control the thickness of the SiO2 shell, four FeNi@SiO2 powder samples with different SiO2 mass fractions were prepared, where magnetic FeNi@SiO2 microsphere with the core of FeNi is completely coated by SiO2. Herein, the electromagnetic parameters of the composites are effectively tuned by the combination of magnetic FeNi with dielectric SiO2. Results show that when the mass fraction of SiO2 is 35 %, the prepared FeNi@SiO2 powder sample exhibits good absorption performance, the minimum reflection loss (RL) reaches − 36.25 dB at 2.6 mm with the effective absorption bandwidth (RL<−10 dB) of 6 GHz (9.5–15.5 GHz) at 2.0 mm. It is believed that its good absorbing performance originates from the synergistic effect of the conductivity loss, dielectric polarization loss and magnetic loss of core-shell FeNi@SiO2 composite. This work provides a versatile strategy for FeNi@SiO2 composite with unique core-shell structures on excellent and tunable microwave absorption performance.

Preparation of porous CoNi/N-doped carbon microspheres based on magnetoelectric coupling strategy: A new choice against electromagnetic pollution

Magnetoelectric coupling is a key strategy to obtain high-performance microwave absorption materials. Especially for carbon matrix composites, the absorbing capacity can be optimized via the tuning of the graphitization degree and the content ratio of the magnetic and dielectric components. Based on this theory, a simple strategy, consisting of the solvothermal method and annealing in an inert atmosphere, is adopted in this study to combine CoNi magnetic alloys with graphitized carbon into micron-scale composite spherical particles. Additionally, special attention is paid to the correlation among the graphitization degree of carbon matrix, component proportion, and dielectric response ability, so as to achieve a flexible micromorphology design and a tunable microwave absorption performance. When the pyrolysis temperature is offset to the best of 700 ℃, a broadband absorption of 6.61 GHz (reflection loss < − 10 dB) is achieved at an ultrathin matching thickness of 1.9 mm. Adjusting the carbon content can further optimize the impedance matching and realize a high-intensity absorption with a reflection loss of − 72.7 dB. Our work proposes a useful strategy to realize the effective combination of the magnetic and dielectric loss mechanisms and boost the microwave absorption capacity toward achieving the desired broadband and a high-efficiency absorption performance.

Biomass-derived ultralight superior microwave absorber Towards X and Ku bands

Biomass-derived microwave absorbers have attracted extensive attention due to their natural abundance, low cost and eco-friendliness. However, it is still a challenge to achieve superior absorptivity under the extremely low filler content in such absorbers. Herein, we engineer a hybrid of Co3Fe7 alloy nanoparticles (NPs) anchoring on the biomass shaddock peel derived porous carbon nanosheets (CNs) for superlight and efficient microwave absorption. The CNs exhibit attractive graphene-like morphology with Co3Fe7 alloy NPs uniformly dispersing throughout the CNs. It is revealed that the EM parameters could be well controlled by tailoring the deposition ratio of Co3Fe7 NPs to optimize impedance matching. Specifically, the sample with relatively sparse Co3Fe7 NPs exhibit a reflection loss (RL) of –22.3 dB and broad absorption bandwidth of 5.3 GHz in Ku band under the ultralow filler content of only 8.0 wt%. As the deposition ratio of magnetic Co3Fe7 NPs increases, the optimized absorption peak moves to X band with −50.6 dB of RL value and 4.5 GHz of effective absorption, completely covering the whole X band. The elaborative studies demonstrate the significant influence of impedance matching on the ultimate absorption performance. This work paves a new way for the development of biomass-derived composites as superlight and tunable microwave absorber.

Cellular-like sericin-derived carbon decorated reduced graphene oxide for tunable microwave absorption

Sodium hydroxide (NaOH) activation on biomass-derived carbon materials has been a developed strategy to construct the porous and lightweight microwave absorber. However, the resulting random porous structures still remain a formidable challenge to optimize the impedance matching and microwave absorption performance. Here, a sericin-guided NaOH activation and subsequent carbonization process were proposed to synthesize uniform cellular-like sericin-derived carbon decorated reduced graphene oxide (SC/rGO) nanohybrids. The NaOH was used as a bi-functional activator to regulate the self-assembly of sericin protein between graphene oxide lamellas, while the sericin-guided NaOH further in situ activates the nanohybrids to produce uniform cellular nanostructures by carbonization. The abundant natural doped nitrogen and oxygen atoms derived from the industry wastes sericin are in-situ maintained after carbonization, which act as polarization centers to promote the attenuation of microwave energy. Benefiting from these merits, the synthesized cellular-like SC/rGO nanohybrids exhibit excellent impedance matching performance, promoted multiple electromagnetic transmission, excellent relaxation polarization phenomenon and microwave absorption properties. The optimized microwave absorption of SC/rGO40-500 reached −53.68 dB at 15.30 GHz, and the effective absorption bandwidth achieved 4.4 GHz (13.35–17.75 GHz) at the thickness of 1.51 mm with a low surface density of 0.035 g/cm2. Our work demonstrates a novel porous structure design strategy on biomass-derived carbon materials as high-efficiency microwave absorbers.

Ion-Exchange Strategy for Metal-Organic Frameworks-Derived Composites with Tunable Hollow Porous and Microwave Absorption.

Hollow metal-organic frameworks (MOFs) with careful phase engineering have been considered to be suitable candidates for high-performance microwave absorbents. However, there has been a lack of direct methods tailored to MOFs in this area. Here, a facile and safe Ni2+ -exchange strategy is proposed to synthesize graphite/CoNi alloy hollow porous composites from Ni2+ concentration-dependent etching of Zeolite imidazole frame-67 (ZIF-67) MOF and subsequent thermal field regulation. Such a special combination of hollow structure and carefully selected hybrid phase are with optimized impedance matching and electromagnetic attenuation. Especially, the suitable carrier transport model and the rich polarization site enhance the dielectric loss, while more significant hysteresis loss and more natural resonance increase the magnetic loss. As a result, excellent microwave absorbing (MA) performances of both broadband absorption (7.63GHz) and high-efficiency loss (-63.79dB) are obtained. Moreover, the applicability and practicability of the strategy are demonstrated. This work illustrates the unique advantages of ion-exchange strategy in structure design, component optimization, and electromagnetic regulation, providing a new reference for the 5G cause and MA field.

A frequency selective surface loaded two-layer composite for tunable microwave absorption

To obtain tunable microwave absorption, a strategy of constructing a frequency selective surface (FSS) on a two-layer composite is proposed. The designed FSS loaded two-layer composite is composed of a FSS constructed by evenly spaced circular copper sheet, an impedance matching layer (SiO2 fiber reinforced epoxy resin (EP) composite, SiO2f/EP) and a lossy layer. Both simulation and experiments indicate that the SiO2f/EP layer serves as a good impedance matching layer with increased microwave absorption efficiency. By analyzing the distributions of electric field, magnetic field as well as the power loss, the strong resonance should be attributed to the enhanced incident microwave caused by FSS.

Recent Progress in Electromagnetic Interference Shielding Performance of Porous Polymer Nanocomposites—A Review

The urge to develop high-speed data transfer technologies for futuristic electronic and communication devices has led to more incidents of serious electromagnetic interference and pollution. Over the past decade, there has been burgeoning research interests to design and fabricate high-performance porous EM shields to tackle this undesired phenomenon. Polymer nanocomposite foams and aerogels offer robust, flexible and lightweight architectures with tunable microwave absorption properties and are foreseen as potential candidates to mitigate electromagnetic pollution. This review covers various strategies adopted to fabricate 3D porous nanocomposites using conductive nanoinclusions with suitable polymer matrices, such as elastomers, thermoplastics, bioplastics, conducting polymers, polyurethanes, polyimides and nanocellulose. Special emphasis has been placed on novel 2D materials such as MXenes, that are envisaged to be the future of microwave-absorbing materials for next-generation electronic devices. Strategies to achieve an ultra-low percolation threshold using environmentally benign and facile processing techniques have been discussed in detail.

Magnetic-dielectric synergy and interfacial engineering to design yolk–shell structured CoNi@void@C and CoNi@void@C@MoS2 nanocomposites with tunable and strong wideband microwave absorption

Magnetic-dielectric synergy and interfacial engineering to design yolk–shell structured CoNi@void@C and CoNi@void@C@MoS2 nanocomposites with tunable and strong wideband microwave absorption

Coral-like carbon-based composite derived from layered structure Co-MOF-71 with outstanding impedance matching and tunable microwave absorption performance

• Porous coral-like carbon/Co 3 O 4 and carbon/Co materials were prepared for the first time through the calcination of precursor Co-MOF-71. • Pore structure and magnetic properties can be tuned by regulating the calcination temperature. • S500 achieves strong absorption and broad effective absorption under a thin coating thickness. Metal-organic frameworks (MOFs) are considered as a novel type of microwave absorption (MA) material owing to the sufficient pore structure, diverse configurations, and easy-to-control magnetic properties. However, their evolution is limited by the imperfect impedance matching conditions caused by the undesirable microstructure. Herein, two types of novel porous coral-like carbon/Co 3 O 4 and carbon/Co composites have been effectively fabricated for the first time by a facile heat treatment process of precursor Co-MOF-71. The graphitization degree, magnetic property and MA ability of the product can be effortlessly tuned by altering the heat treatment temperature of Co-MOF-71. Remarkably, S500 (Co-MOF-71 calcined at 500 °C) composite displays strong and multi-frequency absorption performance, whose minimum reflection loss (RL) value achieves -36.4 dB with an absorbing thickness of 3.0 mm and attains an effective absorbing bandwidth (RL≤-10 dB) of 5.76 GHz (almost covers whole Ku band) at a thinner coating thickness of 2.5 mm. Such superb MA ability has roots in the coral-like structure derived from the layer Co-MOF-71, sufficient electromagnetic loss. This work ameliorates the MA ability of MOFs through a special nanostructural design, which provides a fresh way for the preparation of novel MA materials.

Low-temperature carbonized biomimetic cellulose nanofiber/MXene composite membrane with excellent microwave absorption performance and tunable absorption bands

2D transition metal carbides and nitrides (MXenes) have gained much interest in microwave absorption. However, the high conductivity of MXenes results in inferior absorption performance. To solve this problem, Cellulose nanofiber (CNF) is compounded with MXenes to build membranes with biomimetic structures. CNF not only contributes to adjusting the electromagentic parameters, but also enhances the microwave attenuation and regulates the absorption band. In this work, nacre-like and loofah-like carbonized CNF/MXenes membranes were successfully prepared. The self-assembly of CNF and MXene avoids the impedance mismatch, and the biomimetic structures enhance conductive loss, polarization loss and multiple reflection. The results show that nacre-like carbonized CNF/MXene membrane (CCM) exhibits absorbing performance with the minimum reflection loss (RLmin) of −42.2 dB and the Effective absorption band (EAB) of 7.12 GHz. Meanwhile, the absorption peaks are mainly concentrated on X-band. Further, as the morphology changes to porous layers, the RLmin of loofah-like CCM increases to −63.8 dB, whose EAB is 7.32 GHz at 2.5 mm, and the main absorption peaks shift to Ku-band. Besides, the possible absorption mechanism of biomimetic composite membranes has been expounded. This work provides a versatile strategy for CNF/MXene composite membrane with biomimetic structures on excellent and tunable microwave absorption performance.

Tunable microwave absorption band via rational design of C@TiC nanospheres

To effectively tune material's microwave absorption band, it is necessary to build a special structure and composition. Titanium carbide nanoparticles decorated carbon nanospheres (C@TiC) were prepared by using carbon nanospheres as a initial structure-directing agent, and their absorption band was tuned by rational design of TiC content. With increasing dosage of tetrabutyl titanate (TBT), absorption band of C@TiC dispersed in paraffin (30 wt%) gradually shifted from Ku to S-band, realizing the adjustment of absorption band. For example, when the amount of TBT was 1.0, 1.5 and 2.0 mL, the minimum reflection loss (RL) of C@TiC was about −49.8, −52.4 and −50.3 dB at 17.4, 13.1 and 6.6 GHz, respectively. Excellent performance was attributed to good impedance match and synergistic effect between carbon spheres and TiC nanoparticles. This in-situ phase transition induced nanoheterostructure would provide a way for microwave absorbers with tunable band.

MoS2 /MXene Aerogel with Conformal Heterogeneous Interfaces Tailored by Atomic Layer Deposition for Tunable Microwave Absorption.

In the design of electromagnetic (EM) wave absorbing materials, it is still a great challenge to optimize the relationship between the attenuation capability and impedance matching synergistically. Herein, a 3D porous MoS2/MXene hybrid aerogel architecture with conformal heterogeneous interface has been built by atomic layer deposition (ALD) based on specific porous templates to optimize the microwave absorption (MA) performance comprehensively. The original porous structure of pristine Ti3C2T x aerogel used as templates can be preserved well during ALD fabrication, which prolongs the reflection and scattering path and ameliorates the dielectric loss. Meanwhile, plenty of heterointerfaces between MoS2 and Ti3C2T x have been fabricated based on conformally ALD‐deposited MoS2 with controlled thickness on the porous surfaces of the templates, which can effectively optimize the impedance matching and transform its response to EM waves from shielding into absorbing. Moreover, the interaction between the attenuation capability and impedance matching can also be modulated by the number of ALD cycle in MoS2 fabrication. After optimization, MoS2/MXene hybrid aerogel obtained under 300 ALD cycles shows a minimum reflection loss of −61.65 dB at the thickness of 4.53 mm. In addition, its preferable lightweight, high surface area, mechanical, and hydrophobicity properties will also be conducive to further practical applications.

A neutron diffraction investigation of high valent doped barium ferrite with wideband tunable microwave absorption

The barium ferrite BaTixFe12−xO19 (x = 0.2, 0.4, 0.6, 0.8) (BFTO-x) ceramics doped by Ti4+ were synthesized by a modified sol—gel method. The crystal structure and magnetic structure of the samples were determined by neutron diffraction, and confirm that the BFTO-x ceramics were high quality single phase with sheet microstructure. With x increasing from 0.2 to 0.8, the saturation magnetization (Ms) decreases gradually but the change trend of coercivity (Hc) is complex under the synergy of the changed grain size and the magnetic crystal anisotropy field. Relying on the high valence of Ti4+, double resonance peaks are obtained in the curves of the imaginary part of magnetic conductivity (μ″) and the resonance peaks could move toward the low frequency with the increase of x, which facilitate the samples perform an excellent wideband modulation microwave absorption property. In the x = 0.2 sample, the maximum reflection loss (RL) can reach −44.9 dB at the thickness of only 1.8 mm, and the bandwidth could reach 5.28 GHz at 2 mm when RL is less than −10 dB. All the BFTO-x ceramics show excellent frequency modulation ability varying from 18 (x = 0.8) to 4 GHz (x = 0.4), which covers 81% of the investigated frequency in microwave absorption field. This work not only implements the tunable of electromagnetic parameters but also broadens the application of high-performance microwave absorption devices.

Nanoporous resorcinol-formaldehyde based carbon aerogel for lightweight and tunable microwave absorption

Porous carbon materials hold great promise for high-performance microwave absorption application. Herein, nanoporous carbon aerogels of different textures were prepared by sol-gel method and pyrolysis. The effects of solution chemistry and carbonization temperature on the microwave absorbing property were discussed. It is found that, the incident electromagnetic energy was attenuated through multiple reflections, conductive loss and polarization loss in the 3D interconnected porous structures. Furthermore, reasonable architecture design and pyrolysis temperature can be employed to achieve favorable microwave absorption capacity of the carbon aerogel that will be a platform for accessing highly controlled structurally light absorbers.

Design of Double-Layer Absorbers Based on Co2y@C Core-Shell Nanofibers and Carbon Nanofibers for High-Efficient and Tunable Microwave Absorption

Design of Double-Layer Absorbers Based on Co2y@C Core-Shell Nanofibers and Carbon Nanofibers for High-Efficient and Tunable Microwave Absorption

Tunable microwave absorption features in bi-layer absorber based on mesoporous CuS micro-particle with 3D hierarchical structure and nanosphere like NiCo2O4

There has been a growing demand for materials with superior absorption capabilities, such as strong absorbing capacity, thin thickness, and light weight, to solve challenges related to EM radiation pollution. While the majority of the research is focused on optimizing material compositions, component microstructure and absorber structure are also critical factors for improving microwave absorption performance. In this research, we show how the microstructure of components and absorber design may increase dissipation features. Solvothermal and hydrothermal methods were utilized for synthesizing mesoporous CuS micro-particles with a 3D hierarchical structure as a dielectric component and nanospheres like NiCo2O4 as magnetic components respectively. The formation of pure phases with the mentioned microstructures was confirmed via XRD, FTIR, UV–Vis, XPS, VSM, FESEM and BET analysis. According to VNA results, the minimum reflection loss can be achieved to −33 dB at 11 GHz with a total thickness of 2 mm in which each layer thickness was considered 1 mm (CuS placed at top layer and NiCo2O4 placed at bottom layer). The RL values of bilayer absorber were strongly affected by both the microstructure of the components and tuning the thickness and arrangement of each layer. We offer a potential technique for enhancing microwave dissipation performance by combining the synergistic effects between the microstructure, thickness and arrangement of layers in a bilayer absorber.