Design of hierarchical core-shell ZnFe2O4@MnO2@RGO composite with heterogeneous interfaces for enhanced microwave absorption

In order to overcome the problems caused by electromagnetic pollution, the design and development of high-performance microwave absorbers is urgently required. In this work, a hierarchical ZnFe₂O₄@MnO₂@RGO composite was successfully fabricated via a facile and rapid hydrothermal method. Its unique core-shell structure and synergistic effect between multiple components are beneficial for electromagnetic wave absorption. The morphology, elemental composition, microstructure and microwave absorption characteristics were systematically studied. With a filler loading of 20 wt%, the composite presents a minimum reflection loss (R_Lmin) of ?46.7 dB and an effective absorption bandwidth (EAB) as wide as 5.2 GHz at a thickness of 2.5 mm. The superior absorption ability profits from a special microstructure, good impedance matching, multiple attenuation features, interfacial polarization, and the synergistic effect of dielectric and magnetic loss. Consequently, this work lays a foundation for the design of high-performance electromagnetic wave absorbers with multicomponent heterogeneous structures.     

Dielectric and microwave absorption properties of CB doped SiO2f/PI double-layer composites

Carbon black (CB) with contents of 5.5?wt% and 15?wt% filled quartz glass fiber reinforced polyimide (SiO_2f/PI) composite were designed and prepared. A double-layer absorbing material was designed using the two composites materials as a matching layer and an absorption layer, respectively. The microwave absorption property of single-layer and double-layer composites is calculated according to transmission line theory. The results show that the microwave absorbing property of double-layer composite is better than that of single-layer at the same thickness. When the 5.5?wt%CB doped SiO_2f/PI composite is used as the matching layer with a thickness of 0.7?mm and 15?wt%CB doped SiO_2f/PI composite is used as the absorption layer with a thickness of 0.9?mm, the RL (reflection loss) of the composite reaches a minimum value of ?46.18?dB at 16.07?GHz. Meanwhile, the bandwidth of RL?≤??5?dB is 5.87?GHz and the bandwidth of RL?≤??10?dB is 3.95?GHz.     

Double-layer electromagnetic wave absorber based on barium titanate/carbon nanotube nanocomposites

The electromagnetic wave absorption properties of double-layer barium titanate/carbon nanotube (BTO/CNT) nanocomposites were evaluated. The BTO/CNT nanomaterials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy. The reflection loss (R.L.) of the samples was calculated based on the measured complex permittivity and permeability. The minimum R.L. of single-layer BTO/CNT 30 wt% nanocomposites sample with a thickness of 1.1 mm reached ~−30.3 dB (over 99.9% absorption) at 13.8 GHz, and the bandwidth of the reflection loss less than −10 dB (over 90% absorption) was 1.5 GHz. The double-layer composites consist of BTO/CNT 30 wt% (absorption layer) with thickness of 1.0 mm and BTO 30 wt% (matching layer) with thickness of 0.3 mm showed a minimum R.L. of ~−63.7 dB (over 99.9999% absorption) at 13.7 GHz, and the bandwidth of the reflection loss less than −10 dB was 1.7 GHz. Wider response bandwidth, >1.7 GHz also can be achieved with different designs of double-layer absorbers. The R.L. significantly improved and wider response bandwidth can be obtained with double-layer composites. The capability to modulate the absorption and bandwidth of these samples to suit various applications in different frequency bands indicates that these nanocomposites could be an excellent electromagnetic wave absorber.     

Rational construction of wideband electromagnetic wave absorber using hybrid FeWO4-based nanocomposite structures and tested by the free-space method

In this research, we developed a wideband electromagnetic wave absorber suitable for the X-band frequency by using a unique hybrid nanocomposite structure made of FeWO₄ embellished with Ag₃PO₄ nanopowders. Simple chemical hydrothermal and microwave-aided hydrothermal procedures were used to successfully produce single-phase spherical-like FeWO4 and FeWO4@Ag3PO4 nanocomposite powders. Using XRD, FTIR, VSM, FESEM, and VNA methods, the phase constituents, morphological, magnetic, and electromagnetic properties of the produced nanocomposite materials were assessed. The resin-based nanocomposite absorber sample allows to obtain a maximum reflection loss of ?21 dB with a matching thickness of 1.8 mm at the ferromagnetic resonance of 10.4 GHz with a 3.8 GHz effective absorption bandwidth, which is evaluated using the waveguide technique, when the filler loading percentage reaches 40 wt percent (S40). S40 had superior impedance matching capabilities, a wide effective absorption bandwidth, and a high absorption capacity when compared to other produced absorber samples. The best sample is prepared for free-space testing with the dimension of 200 × 200 mm and an optimum thickness of 1.8 mm, and the results demonstrate a good agreement between the waveguide and free-space technique results. This absorber sample's wideband absorption capacity was attained by adjusting the magneto-electric composition and enhancing the interfacial characteristics brought on by the core-shell construction. In this study, a design approach for efficient microwave absorbers based on a magneto-electric hybrid nanocomposite structure is presented, using waveguide and free-space experimental methods in two different ways.     

Single and double-layered Tri-band Microwave absorbing materials

Absorbers at microwave frequencies with multiple frequency-band response are particularly important for use in military for stealth technology. Specially, ferrite based absorbing materials are significant for electromagnetic shielding and signal attenuation. The enhancement of reflection loss of ferrites along with carbonaceous materials are even more beneficial. Recently double-layer absorbers have extensively studied to meet the requirements of advanced absorbing materials in multiple frequency-band response. It still remains a challenge how to determine the type and thickness to couple the impedance-matching-layer to the absorption-layers for a double-layer absorber. We applied hydrothermal method to prepare Fe₃O₄ nanoparticle and combine them with either graphene oxide (GO) or reduced graphene oxide (rGO) to prepare a composite of specific quality to obtain Fe₃O₄@GO and Fe₃O₄@rGO nanocomposite. We studied microwave attenuation capabilities of single and double-layer absorbers containing these two materials. We have demonstrated that with a thin impedance matching layer as a first layer and an absorbing layer behind this layer for the double-layered absorber has much higher reflection loss (RL) than a single-layer. The Fe₃O₄@rGO composite as a single-layer absorber shows the best microwave absorption performance with RL close to −30 dB in all three microwave bands (X, Ku and K bands). The use of a double-layer structure as Fe₃O₄@GO as impedance matching layer and Fe₃O₄@rGO as absorbing layer exhibits the best absorption of −50 dB. This is much larger than the single-layered absorbers at all three frequency-bands. Such a performance is superior to many reported ferrite-based carbonaceous composites. Therefore, a double-layer absorber is best suited to coat the whole body of the aircraft or missiles to evade satellite detection, a preparation towards new-generation weapons for future warfare. Before performing the absorption studies we have characterized the ferrites, GO and rGO materials with various microstructural and magnetic characterizations.     

Facile synthesis of Mn3O4 hollow polyhedron wrapped by multiwalled carbon nanotubes as a high-efficiency microwave absorber

Investigating lightweight and high-efficiency electromagnetic wave (EM) absorbers is evolving as a desirable approach to solve the electromagnetic pollution. In this study, Mn₃O₄ hollow polyhedron wrapped by multiwalled carbon nanotubes (Mn₃O₄/MWCNTs) was successfully prepared by one-step hydrothermal treatment. Interestingly, the Mn₃O₄ polyhedron as a unique hollow structure can serve as a microwave receiver and the incident EM waves hardly escape in the intricate networks, which could be repetitiously attenuated and consumed. The Mn₃O₄/MWCNTs composite with a filler loading of 20 wt% exhibits most outstanding EM absorption performance over the whole frequency of 2–18 GHz. The optimal reflection loss (R_L) achieves −53.8 dB at 11 GHz, and the effective absorption bandwidth (R_L exceeding −10 dB) reaches 4.1 GHz (9.1–13.2 GHz) with a thickness of 2.5 mm. The effective absorption bandwidth (R_L < −10 dB) up to 13.7 GHz (85% absorption over 2–18 GHz) was achieved by adjusting the thickness from 1.5 to 4 mm. The remarkable EM absorption performances benefit from the synergistic effects of suitable impedance matching, dielectric loss, interfacial polarizations and relaxation polarizations. These results indicate that Mn₃O₄/MWCNTs composite with lightweight and high-efficiency microwave absorption properties could serve as a prospective microwave absorber in practical applications.     

Fabrication of hexagonal cerium oxide nanoparticles decorated nitrogen-doped reduced graphene oxide hybrid nanocomposite as high-performance microwave absorbers in the Ku band

With the aim to obtain microwave absorbers simultaneously possessing broad absorption bandwidth, strong absorption intensity and thin matching thickness, nitrogen-doped reduced graphene oxide decorated by cerium oxide particles (NRGO/CeO₂) hybrid nanocomposite was prepared through a hydrothermal and calcination two-step route. Results of micromorphology analysis showed that numerous hexagonal CeO₂ nanoparticles were evenly anchored on the crumpled surfaces of NRGO. Moreover, both nitrogen doping and hybridization with RGO could notably strengthen the microwave absorption capacity of CeO₂. Remarkably, the NRGO/CeO₂ hybrid nanocomposite exhibited the minimum reflection loss of ?57.2 dB at 13.4 GHz (Ku band) under a matching thickness of 1.66 mm and maximum absorption bandwidth of 4.6 GHz (from 13.2 to 17.8 GHz) at an ultrathin thickness of only 1.5 mm. Meanwhile, the hybrid nanocomposites displayed strong absorption intensity (≤-20 dB, 99% absorption) in almost the whole measured thicknesses range. Furthermore, the relationship between absorption intensity and filler loadings was uncovered. The potential microwave absorption mechanisms were further revealed. Therefore, this work opened a novel idea for designing RGO-based hybrid nanocomposites as high-performance microwave absorbers.     

Synergistic effect of polyindole decoration on bismuth neodymium ferrite powder for achieving wideband microwave absorber

Recently, composite materials with outstanding absorption properties, like extraordinary absorbing capability, light weight, and thin in size, are required to solve the challenges of electromagnetic pollution. In addition, most of the work is based on the optimization of absorber material structure, and microstructure. In the current work, we improved the reflection loss feature of Bi_0.5Nd_0.5FeO₃ nanopowders via decoration with polyindole polymer by tuning the filler loading of the nanocomposite in the matrix. XRD, UV–Vis, XPS, and FESEM were used to determine the physicochemical features of the as-prepared nanocomposite. The minimum RL was lowered further with the increasing filler loading at 25 wt%. The lower RL of ?22 dB was noticed for 2.2 mm thickness at 11.5 GHz. The maximum value of the SE_R for a 25 wt% sample was 5.5, whereas 19 dB and 24.5 dB values were recorded for SE_A and SET, respectively. The resonance peak above 11.5 GHz demonstrated the better outcome of the absorber at high frequency. Good impedance matching characteristics, conductive features, dielectrics, and magnetic losses were all credited with the excellent reflection loss and electromagnetic interference shielding efficiency. The as-prepared nanocomposite materials that have been proven are interesting prospects for electromagnetic reflection loss and interference shielding that is lightweight, flexible, and extremely effective.     

High temperature anti-oxidative and tunable wave absorbing SiC/Fe3Si/CNTs composite ceramic derived from a novel polysilyacetylene

With the rapid development of high power electromagnetic (EM) equipment and high-speed aircraft, the powerful and high oxidation-resistance absorbers are fundamentally desirable for the EM field. Herein, a novel high temperature anti-oxidative SiC/Fe₃Si/CNTs composite is synthesized by a facile polymer derived ceramic (PDC) route from a Fe-containing polysilyacetylene (PSA). The microstructure of as-prepared SiC/Fe₃Si/CNTs composite absorber is featured by micro-sized SiC ceramic grains with spherical Fe₃Si nanoparticles and carbon nanotubes (CNTs) attached to. The vector network analyzer tests show a tunable wave-absorbing performance by adjusting the thickness of layer, and the effective bandwidth (the reflection loss < −10 dB) is 3.3–16.8 GHz for the sample S-1400 (heat treatment at 1400 °C in nitrogen flow). The minimal RL value is −41.2 dB at 10.5 GHz at a thickness of 2 mm and an effective bandwidth is nearly 4 GHz (12.9–16.9 GHz) at the thickness of only 1.5 mm. Moreover, after the oxidation treatment at 800 °C in the air, this absorber maintains the main structure and shows a good high temperature oxidation resistance. This absorber still remains excellent wave absorption property, in view of a minimal RL value of −40 dB at the thickness of 3 mm and a bandwidth of 4.8 GHz (10.4–15.2 GHz) at the thickness of 2.5 mm. The mechanism of high EM wave absorption performance is studied and attributed to the impendence matching, polarization, and the magnetic properties. Thus, the SiC/Fe₃Si/CNTs composite is a promising EM absorber for high-temperature EM wave-absorbing applications.     

Optimized impedance matching and enhanced attenuation by heteroatoms doping of yolk-shell CoFe2O4@HCN as highly efficient microwave absorbers

Microwave absorbing (MA) materials with yolk-shell structures have been extensively studied in impedance matching. However, the impedance matching achieved by the complementary effect of the core and the shell does not determine the reflection of the microwaves upon the occurrence at the first incidence. The interaction between the outer layer of materials and the electromagnetic waves significantly impacts the MA properties of materials. In this study, the impedance matching improvement method of the shell structure was further explored by preparing CoFe₂O₄@HCN (honeycomb carbon with N-doping) through the hydrothermal method followed by hydrolysis, polymerization, etching, and annealing. The resulting structure with heteroatoms doping provided the novel CoFe₂O₄@HCN with excellent impedance matching and multiple loss mechanisms contributing to MA process. The absorber with a filler loading of 40% exhibited an RL_min of −68.03 dB with a matching thickness of 2.5 mm. The efficient absorbing bandwidth reached 5.92 GHz (a change from 11.92 to 17.84 GHz) at 1.99 mm thickness. Interestingly, these findings look promising for future synthesis and application of yolk-shell structure microwave absorbers.     

Investigation on microwave absorption characteristics of ternary MWCNTs/CoFe2O4/FeCo nanocomposite coated with conductive PEDOT-Polyaniline Co-polymers

In this study, ternary MWCNTs/CoFe₂O₄/FeCo nanocomposite coated with conductive PEDOT-polyaniline (PA@MW/F/C) co-polymers were synthesized by microwave-assisted sol-gel followed in-situ polymerization methods. The phases, crystal structures, morphologies, magnetic and electromagnetic features of the as-prepared samples were identified via XRD, SEM, XPS, VSM, and VNA respectively. Absorption characteristics were investigated in the frequency (12–18 GHz) Ku band. XRD, VSM and SEM analysis confirmed the partial reduction process of CoFe₂O₄ and successfully decorated magneto-dielectric particles with co-polymers. By measuring electromagnetic features of the samples, it was found that coating magneto-dielectric particles with conductive co-polymers improved the permittivity and dielectric constant, accordingly affecting the impedance matching characteristic and attenuation constant performance. Moreover, exchange coupling behavior was found significant impacts on the microwave absorption properties. PA@MW/F/C coated nanocomposite revealed the maximum reflection loss of ?90 dB at 13.8 GHz with 4 GHz effective bandwidth and 1.5 mm thickness. Due to the enhanced interfacial polarization, impedance matching and exchange coupling effects of the as-prepared nanocomposite, it owns excellent microwave absorption properties, which can be applied as an absorber with distinguishing features (strong absorption, thin thickness, and broadest effective bandwidth).     

Design of controlled-morphology NiCo2O4 with tunable and excellent microwave absorption performance

In recent years, the high-performance microwave absorbers with strong loss, broad frequency bandwidth, thin thickness and light weight have been intensively investigated to address the problem of electromagnetic pollution and improve stealth technology. Considering the fact that microwave absorption performance is quite sensitive to morphology, studying NiCo₂O₄ with different morphologies is a valuable step towards developing a high-performance microwave absorber. The different morphologies are prepared by adjusting the addition of the structure-directing agent NH₄F. When the amount of added NH₄F is 1 mmol, a flower-like NiCo₂O₄ morphology (NC–F1) is obtained with a large specific surface area of 158.97 m²/g and pore volume of 0.3525 cm³g^-1, which easily generates conductive loss, polarization loss, and multiple scattering, thereby enhancing its microwave absorption performance. The maximum reflection loss reaches −50.3 dB at 3 mm, and the effective bandwidth is 4 GHz with the matching thickness of 2 mm when the fill ratio is only 30 wt% in the epoxy resin. As the thicknesses range from 1.5 mm to 5 mm, the effective bandwidth is 14.2 GHz (3.8 GHz–18 GHz) and covers the entire C, X, and Ku bands. Therefore, the defined-morphology NiCo₂O₄ is expected to be a novel wide-band and strong-loss microwave absorber.     

Decoration of worm-like Cu2S particles on CuCo2S4 micro-spheres: An effective strategy to improve the electromagnetic dissipation feature

Civilization can be shielded from the dangerous electromagnetic spectrum by using microwave absorption materials, however, absorbing electromagnetic radiation with thin thickness and high bandwidth remains a challenge, especially at scales that are significant. Herein, we propose a novel architecture where worm-like Cu₂S particles are decorating CuCo₂S₄ micro-spheres were decorated, and this method is thought to be a successful one for enhancing the created nanocomposite's ability to dissipate electromagnetic radiation. Changing the filler loading percentage allows the nanohybrids' electromagnetic characteristics and microwave dissipation effectiveness to be efficiently changed. This leads to the creation of ultra-bandwidth absorbers with thin thickness, which are then tested using waveguide and free-space techniques. The sample with a thickness of 1.4 mm has a maximum reflection loss of ?18 dB and a maximum bandwidth of 3.6 GHz. The hetero-structures, multi-interfaces, and multiple relaxations phenomena, as well as the combined effects of the two components, are credited with the superior microwave absorption performance compared with the state-of-the-art. This finding demonstrates that CuCo₂S₄/Cu₂S nanohybrids pave the way for the development of future high-performance microwave absorption materials.     

Flexible BaTiO3/SiC@PbTiO3/epoxy composite films with enhanced dielectric performance at high frequency

Flexible polymer composites with high dielectric constants and low dielectric losses at high frequencies are highly desired in microwave and RF applications. However, a high dielectric constant is often obtained at the expense of flexibility because a high loading of filler is needed. In this work, we synthesize a core-shell structured 1D filler by coating high-dielectric-constant PbTiO₃ onto the surface of low-thermal-expansion-coefficient SiC nanofibers, which are then incorporated into the epoxy matrix together with BaTiO₃ nanoparticles to form the multi-phase BaTiO₃/SiC@PbTiO₃/epoxy composite film. A high dielectric constant (35 at 100 Hz and 20 at 5 GHz) and a low dielectric loss (0.023 at 100 Hz and 0.13 at 5 GHz) are achieved as the filling content of SiC@PbTiO₃ and BaTiO₃ is 5.24 wt% and 80 wt%, respectively. Prediction models of the effective dielectric constant of polymer-based composites reveal that a continuous polarization network is constructed in the composites owing to the physical contact between BaTiO₃ and PbTiO₃. The construction of the multi-phase filler provides a feasible way to effectively adjust and improve the dielectric properties of polymer-based composite films.     

Synthesis and microwave absorption properties of bamboo-like β-SiC nanowires

Lightweight and strong microwave adsorption property have become the foremost crucial factors in the practical application of modern microwave absorbers. This study mainly dealt with synthesize of bamboo-like β-SiC nanowires with high-performance microwave absorption property via a polymer pyrolysis CVD (PPCVD) approach. The PPCVD process was conducted by cleverly placing the polymer powders into two temperature zones to produce reactant gases with alternating concentrations. The morphological study revealed that the nodes exhibited abundant stacking faults as compared to the stem segments, which was beneficial for the microwave losses. The optimal reflection loss value of −35.47 dB was gained at 18 GHz corresponding to 2.0-mm absorber thickness, and the corresponding −10 dB bandwidth (>90% absorption) was 3.22 GHz. It has turned out that the as-prepared nanowires could be applied at different frequencies by adjusting the thickness. Especially, it exhibits a good prospect in the fields of ultrathin absorbers. Furthermore, the microwave absorption mechanisms of the nanowires were explored. This present investigation has opened a high-efficient facile approach to develop ultrathin, lightweight, and high-performance microwave absorbers.     

Fabrication of hierarchical PANI@W-type barium hexaferrite composites for highly efficient microwave absorption

Hexagonal barium ferries is a promising and efficient microwave (MW) absorbing material, but the low dielectric loss and poor conductivity have limited their extensive applications. In this work, a simple tactic of coating conductive polymer PANI on hexaferrite BaCo₂Fe₁₆O₂₇ is presented, wherein the dielectric properties are customized, and more significantly, the electromagnetic loss is greatly enhanced. As displayed from structural characterizations, PANI were coated equably on the surface of hexaferrite grains by an in-situ polymerization process. The outcomes exhibit the as-prepared PANI@hexaferrite composite has remarkable electromagnetic wave absorption capacity. When the thickness is 6.0 mm, the minimal RL of ?40.4 dB was achieved at 2.9 GHz. The effective absorption bandwidth (RL < ?20 dB) of 0.65 GHz, 0.53 GHz, 0.65 GHz, 0.52 GHz, 0.46 GHz and 0.39 GHz was achieved separately when the thickness ranges from 4 to 9 mm. The highly efficient MW absorbing performance of PANI@hexaferrite composite were the consequence of multiple loss mechanisms and perfect impedance matching. It is demonstrated that the PANI@hexaferrite composite with excellent MW absorption performance is expected to be potential MW absorbers for extensive applications.     

A new multicomponent material based on carbonyl iron/carbon nanofiber/lanthanum–strontium–manganite as microwave absorbers in the range of 8–12 GHz

We report the design of a new multicomponent microwave absorber in the X band based on carbonyl iron (CI)/carbon nanofiber (CNF)/lanthanum–strontium manganese oxide (LSMO). The citrate precursor method has been used to synthesize LSMO nanopowder. The phase identification has been investigated using XRD patterns. Scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA) are used to analyze the morphology of the different components and the magnetic, electromagnetic and microwave absorption properties of the final composite absorbers. To the best of our knowledge, the use of this class of multicomponent microwave absorber, has not been explored before. The results indicate that substituting CI by increasing amounts of CNF and LSMO, not only decreases the weight of the designed absorber, but also has a synergistic effect that promotes its attenuation properties. The absorber of 2 mm thickness and only 30 wt% of loading ratio exhibits an average reflection loss of −8.75 dB over the range 9–12 GHz, while its corresponding absorber without LSMO has only a RL around −5 dB.     

Core-shell MXene/nitrogen-doped C heterostructure for wide-band electromagnetic wave absorption at thin thickness

MXenes have been utilized to fabricate electromagnetic wave (EMW) absorbers owning to large aspect ratio, high electronic conductivity, and favorable hydrophilicity. In this work, the core-shell MXene/nitrogen-doped (N-doped) C heterostructure was firstly prepared via HCl and LiF etching, in-situ polymerization, and carbonization. When mixed with paraffin at a low filler loading of 30 wt%, the MXene/N-doped C hybrid reached a wide effective absorption bandwidth of 5.0 GHz (13.0 GHz–18.0 GHz) at a thin thickness of 1.72 mm. The stronger ability of attenuating EMWs promoted the absorption performance of MXene/N-doped C, overcoming the deficiency in the characteristics of impedance compared with its counterparts. This work provides a new insight in manufacturing MXene-based absorbers to alleviate EMW pollution by delicate structural design and effective multi-component strategy.     

Efficient single and bi-layer absorbers of CaTiO3 micro-cubes and polypyrrole nanotubes composites for enhanced microwave absorption in X and Ku band

The present study is focused on the investigation of the absorption properties of the bi-layer absorber with different thickness and orientation approaches. Improvement in absorption exclusively depends on the various parameters as interfacial polarization, multiple reflections among layers, conduction loss, phase cancellations, and shape anisotropy, etc. By considering these parameters. Calcium titanate micro-cubes CaTiO3 (CTO) and polypyrrole nanotubes (PPy) nanocomposites were prepared and microwave absorption from single layer coaxial absorbers having M1 = CaTiO₃+15 wt% polymer and M2 = CaTiO₃+30 wt% polymer were determined. Different layer orientations and thicknesses of the bi-layer absorber were optimized by CST software. FESEM, XRD, VSM, and VNA were used to find out the microstructural, phase, morphology, magnetic, and absorptions properties in microwave region. The values of the RL from M1 and M2 are ?24 dB and ?32 dB for 2.5 mm thickness. However, the RL response absorber with 2 mm thickness shows ?19 dB and ?11 dB. The bi-layer absorber with M1 and M2 having 0.5/0.5 mm (lower/upper) arrangement layer depicted minimum loss in Ku band. It is expected that CTO/PPy absorbers are versatile absorbers for Ku and X band purposes.     

Comparative study of microwave absorption properties of Ni–Zn ferrites obtained from different synthesis technologies

Spinel ferrites are widely used for electromagnetic wave (EMW) absorption applications. In this study, spinel Ni–Zn ferrites with excellent microwave absorption properties were synthesized. Their EMW absorption characteristics and interaction mechanisms were studied to lay the foundation for the study of the role of Ni–Zn ferrite as a magnetic substrate for composites. Herein, Ni_0·5Zn_0·5Fe₂O₄ was prepared by the hydrothermal method (H-NZFO) and the sol–gel auto-combustion method (S-NZFO); both samples exhibited distinct microwave absorption properties. The S-NZFO absorber (thickness = 3.72 mm) demonstrated the best dual-zone microwave absorption with two strong reflection loss peaks at 5.1 and 10.5 GHz. The corresponding effective absorption bandwidth (EAB) reached 9.0 GHz, which covered part of the S-band and all of the C- and X-bands. These results were attributed to the high saturation magnetization, outstanding complex permeability, and multiple magnetic loss channels of S-NZFO. The H-NZFO sample exhibited excellent absorption capability and matching thickness. At a thickness as low as 1.71 mm, the minimum reflection loss (RL_min) of the H-NZFO absorber reached -60.2 dB at 13.1 GHz. The maximum bandwidth corresponding to RL below -10 dB was 4.6 GHz. These results can be attributed to small particle size, high complex permittivity, and multiple dielectric loss channels of H-NZFO. The observed wide effective absorption bandwidth of S-NZFO and strong microwave absorption capability of H-NZFO suggest the potential of both materials as substrates for efficient microwave absorbers in military as well as civilian absorption applications.