Fabrication of clay soil/CuFe2O4 nanocomposite toward improving energy and shielding efficiency of buildings

Sol-gel derived ceramic nanoparticles as an alternative material for microstrip patch antenna in WLAN applications

In the fast-evolving realm of communication technology, microstrip patch antennas (MPAs) are in high demand owing to their compact size, lightweight, inexpensive, ease of integration, and compatibility with modern electronic devices. This research focuses on the synthesis of ZnAl2O4Ca (ZAC) ceramic nanoparticles using an economical sol-gel method suitable for microstrip patch antenna applications. The structural analysis study of ZAC nanoparticles confirmed the polycrystalline nature with 8.1 nm of crystallite size whereas an investigation of functional groups showed the corresponding vibration modes. Morphological investigation revealed the spherical grains having their mean diameter of 12.32 nm. The dielectric property's examination, revealed the dielectric permittivity of 13, loss tangent of 0.02, and conductivity of 67 μΩ-1 cm-1. Furthermore, a prototype patch antenna fabricated using ZAC ceramics demonstrated a dual-band performance at frequencies 2.8 GHz and 4.8 GHz, with return losses of - 25.78 dB and - 28.5 dB, respectively. This work suggests the suitability of ZAC ceramic nanoparticles for use in WLAN applications.

Dendrimer-assisted defect and morphology regulation for improving optical, hyperthermia, and microwave-absorbing features

Electromagnetic pollution and cancer are phenomena that essentially endanger the future of humanity. Herein, multiple approaches are being proposed to solve the aforementioned issues. Recent studies have demonstrated that by regulating the morphology, defect, and phase of materials, their microwave absorbing, optical, and hyperthermia properties are tunable. Calcium ferrite with proper dielectric, magnetic, and biocompatible characteristics was chosen as a substantial candidate to promote its microwave-absorbing properties by regulating its structure. Spinel CaFe2O4 was synthesized through sol-gel and solvothermal routes and its phase, defect, and morphology were manipulated using innovative procedures. Glucose was applied as conventional defecting and templating agent; interestingly, a dendrimer was designed to bear and form nanoparticles. More importantly, a novel reductive process was designed to fabricate one-put Ca/Fe3O4 using a solvothermal method. Particularly, polypropylene (PP) was employed as a practical polymeric matrix to fabricate the eventual product. Structures were molded at a low filling ratio to evaluate their optical and microwave-absorbing performance. As expected, defects, morphology, and phase play a pivotal role in tuning the optical and microwave-absorbing properties of calcium ferrite derivates. Interestingly, the dendrimer-assisted (D-A) formation of CaFe2O4 demonstrated a fascinating reflection loss (RL) of 70.11 dB and an efficient bandwidth (RL ≤ -20 dB) of 7.03 GHz with ultralow thickness (0.65 mm) and filling ratio (10 wt%), attaining proper shielding efficiency (SE) and hyperthermia desirable for its practical application as a material for shielding buildings and cancer therapy. The presented perspective develops new inspirations for architecting microwave absorbing/shielding materials with advanced applications in therapeutic issues.

A reconfigurable ultra-broadband transparent absorber combined with ITO and structural water

In this paper, a reconfigurable transparent metamaterial absorber consisting of a double-layer indium tin oxide (ITO) complementary resonant structure with a structural water-based substrate is proposed. The double-layer resonant pattern gives rise to two stable resonant peaks, and the loading of the water-based substrate can enhance the microwave absorption of the overall structure. By adjusting the thickness of the water layer in the substrate, the microwave absorption performance of the structure can be switched between dual-band and ultra-broadband, with more than 90% efficient microwave absorption covering the frequency range of 6.1 GHz-35.2 GHz. The absorption mechanism is revealed by analyzing the structure surface current as well as the equivalent dielectric constant. We also experimentally verified its microwave absorption and optical transparency properties. Due to its excellent tunable microwave absorption performance and high optical transparency, the proposed absorber has a large application value in stealth devices and optical windows.

Microwave absorbing characteristics of porphyrin derivates: a loop of conjugated structure

Microwave absorbing architectures have gained a great deal of attention due to their widespread application in diverse fields, especially in refining electromagnetic pollution. The aim of this study is to investigate the metamaterial characteristics of porphyrin derivatives as conjugated rings in the microwave region and evaluate the influence of electron-withdrawing and donating groups on microwave attenuating performance. Initially, an innovative microwave curing procedure was applied to synthesize the derivates; following that, the phenyl, aniline, and nitrophenyl-coupled structures were identified by XRD, FTIR, FESEM, and DRS analyses. The optical features illustrated that the characteristic band gap of the conjugated loops is obtained and that the optical performance can be manipulated by coupling the functional groups. Eventually, the achieved results demonstrated that the best microwave absorbing performance is related to aniline-coupled porphyrin with a maximum reflection loss (RL) value of -104.93 dB at 10.09 GHz with 2.80 mm in thickness attaining an efficient bandwidth (EB) (RL ≤ 10 dB) higher than the X-band. Noticeably, polyethylene (PE) was applied as an absorbing matrix presenting a meaningful idea for the development of practical microwave absorbers as a new generation of electromagnetic refining and stealth materials. The presented research provides precious inspiration to tailor novel microwave absorbing materials with metamaterial capability to promote their microwave absorbing performance.

Symbiotic strategy of Cu on CuFe2O4 realizing high-efficiency electromagnetic wave absorption

Low complex permittivity and easy magnetic agglomeration prevent ferrites from achieving high-efficiency electromagnetic wave (EMW) absorption owing to the resultant narrow absorption bandwidth. Existing composition- and morphology-controlled strategies have made limited progress in fundamentally improving the intrinsic complex permittivity and absorption performance of pure ferrite. In this study, Cu/CuFe₂O₄ composites were synthesized using a facile and low-energy sol-gel self-propagating combustion, and the metallic Cu content was adjusted by changing the ratio of the reductant (citric acid) to the oxidant (ferric nitrate). The symbiosis and coexistence of metallic Cu with ferritic CuFe₂O₄ increases the intrinsic complex permittivity of CuFe₂O₄, which can be regulated by changing the metallic Cu content_. Moreover, the unique ant-nest-like microstructure overcomes the issue of magnetic agglomeration. Because of the favorable impedance matching and strong dielectric loss (interfacial polarization and conduction loss) provided by the moderate metallic Cu content, S0.5 concurrently displays broadband absorption with an effective absorption bandwidth (EAB) of 6.32 GHz at an ultrathin thickness of 1.7 mm and strong absorption relying on minimum reflection loss (RL_min) of -48.81 dB at 4.08 GHz and 4.0 mm. This study provides a new perspective for improving the EMW absorption performance of ferrites.

Multi-Band Polarization-Insensitive Metamaterial Absorber for Microwave Based on Slotted Structure and Magnetic Rubber

A design method of five-band polarization-insensitive metamaterial absorber (MMA) based on the slotted structures and the magnetic rubber is proposed for L-, S-, C-, X-, and Ku-band applications. The slotted structures of the top layer, which evolved from two square rings, are used to excite multi-resonance. The range of the electromagnetic (EM) parameters of a magnetic rubber substrate, which is used to adjust the equivalent impedance of the absorber to match the free space impedance in different bands, is estimated using the impedance matching principle. A series of magnetic rubber substrates based on the estimated EM parameters are prepared and measured, whose thickness is only 0.7 mm, meeting the thin design requirements. The absorption of the proposed absorber greater than 90% at 1.7 GHz, 3.87 GHz, 5.96 GHz, 9.4–10.4 GHz, and 14 GHz is achieved when the doping amount of the carbonyl iron powders is 200%. The absorbing performance of the absorber with measured EM parameter agrees well with the theoretical estimates, which validates the accuracy of the proposed design method.