Transparent Thermally Tunable Microwave Absorber Prototype Based on Patterned VO2 Film

Paramagnetic CoS2@MoS2 core-shell composites coated by reduced graphene oxide as broadband and tunable high-performance microwave absorbers

Designing multifunctional integrated composites is a viable approach to meet the diverse requirements in complex environments. By incorporating microwave absorption capability into mullite insulation tiles, it becomes feasible to simultaneously achieve both microwave absorption and thermal insulation effectiveness within a single system, thereby enhancing the materials' adaptability and efficiency. In this study, mullite insulation tiles were utilized as support structures, and polymer‐derived SiCN (PDC‐SiCN) ceramic aerogel with microwave absorption properties was loaded onto the mullite through the high‐pressure impregnation‐pyrolysis technique to fabricate SiCN/mullite insulation tile composite (SM composite). With the inclusion of SiCN aerogel, the SM composite, after one impregnation‐pyrolysis cycle, exhibited exceptional microwave absorption performance, whose minimum reflection loss was −49.24 dB (99.99% microwave absorption) at 15.84 GHz, and effective absorption bandwidth was 9.23 GHz. Additionally, due to the synergistic effect between mullite and SiCN aerogel, the SM composite demonstrated significantly reduced thermal conductivity in 25–1000°C (.064–.086 W·m −1 ·K −1 ), much lower than that of mullite insulation tiles (.076–.156 W·m −1 ·K −1 ). The superior combination of excellent microwave absorption and low thermal conductivity properties makes the SM composite an ideal stealth/thermal insulation integrated material in a thermal protection system operating in a high‐temperature environment.

Effects of thermal treatment on the characteristics of boron and tantalum-doped ZnO thin films deposited by the electrospraying method at atmospheric pressure

In the present paper the experimental results of the effect of sol-gel processing temperature on the physical properties of the TEOS based silica aerogels are reported and discussed. The aerogels were produced by the two step sol-gel process at various temperatures in the range of 26–70∘;C followed by supercritical drying using methanol solvent extraction. A remarkable reduction in the gelation time was observed from three and a half days at room temperature to a mere 18 hours at 50∘;C. The best quality aerogels in terms of low density and high optical transmission were obtained for 6 hours hydrolysis time. The aerogels were characterized by the measurements of bulk density, volume shrinkage, porosity, refractive index and optical transmission. Monolithic aerogels with ultra low density (∼0.018 g/cm3), extremely high porosity (∼99%) and optimum optical transmission at 700 nm (∼75%) were obtained for the molar ratio of TEOS:MeOH:acidic water:basic water at 1:99:10.42:14.58 respectively.

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Interfacial design of sandwich-like CoFe@Ti3C2Tx composites as high efficient microwave absorption materials

We propose a broadband tunable metamaterial absorber with near-unity absorption in the terahertz regime based on a target-patterned graphene sheet. Due to gradient diameter modulation of the graphene sheet and circular symmetry of the unit cell, broadband and polarization-independent properties are achieved in the absorber. A full-wave numerical simulation is performed, and the results show that the absorber's bandwidth of 90% terahertz absorption reaches 1.57 THz with a central frequency of 1.83 THz under normal incidence. At oblique incidence, the broadband absorption of the absorber remains more than 75% over a wide incidence angles up to 60°for the transverse electric (TE) mode and 75°for the transverse magnetic (TM) mode. Furthermore, tunable property is implemented and the peak absorption of the absorber can be tuned from 19% to near 100% by changing the Fermi energy of the graphene sheet from 0 to 0.9 eV via electrostatic doping. The absorber is scalable to the infrared and visible frequencies, which could be used as tunable sensors, filters and photovoltaic devices.

Outstanding comprehensive performance versus facile synthesis: Constructing core and shell-interchangeable nanocomposites as microwave absorber

This paper reports a facile strategy for one-step synthesis of graphene anchored with super-tiny (< 5 nm) nickel nanoparticles (graphene@Ni) with high perfomance microwave absorption. The phase structure, morphology and magnetism of graphene@Ni were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM), respectively. The magnetic Ni nanoparticles with 2.45 nm in average size are densely anchored on the surface of graphene. The electromagnetic characteristics of graphene@Ni compounds were measured by vector network analyzer using a coaxial line method in the frequency range of 1–18 GHz. The reflection loss (RL) of graphene@Ni reaches − 53.92 dB at 9.5 GHz with a thickness of 2.8 mm, and the maximum effective absorption bandwidth with RL values lower than − 10 dB is 5.44 GHz covering from 11.45 to 16.89 GHz at a thickness of 2.1 mm, showing that both of the RLmin and absorption bandwidth for graphene@Ni are obviously enhanced with thinner thickness compared to pure Ni NPs and graphenes. The real RL of graphene@Ni modified aramid fabrics/bismaleimide composite laminate is also measured for comparison, which is basically consistent with simulated results of graphene@Ni. Therefore, the graphene@Ni compounds have advantage in practice for high performance microwave absorption applications.

A novel micromachined thermal emitter for fast transient temperature operation is presented. Compared to most commercial available thermal emitters, the one here presented is able to operate in a pulsed mode. This allows the use of lock-in techniques or pyrodetectors in the data acquisition without the use of an optical chopper for light modulation. Therefore, these types of thermal emitters are very important for small filter photometers. Several hot-plate suspension concepts were studied in order to find a design with excellent mechanical stability and high thermal decoupling. In contrary to the classical spider suspension design, a novel approach based on a non-axis-symmetric design is presented. The thermal emitters are fabricated using silicon on insulator technology and KOH-etching. The emitters are heated with Pt-meanders. For temperature determination an additional Pt-structure is deposited onto the hot-plates. The emitters are mounted in TO-5 housings using a ceramic adhesive and gold wire bonding. The used operation temperature is 750°C. In pulsed operation it’s important to have a large modulation depth in terms of thermal radiation intensity in the needed spectral range. The maximal reachable modulation depth ranges from ambient temperature to steady state temperature. A modulation frequency of 5 Hz still allows using nearly the maximum modulation depth. A parameterized finite element model was realized and adapted to the measured data. This was the basis for the numerical optimization procedure for a new improved design.

CuAlO2, with a relative higher conductivity than other ceramics, is a potential candidate in microwave absorption fields. Herein, to enhance the wide-range efficient microwave absorption property of CuAlO2 powders, Fe-doped CuAlO2 powders were synthesized via a facile sol–gel method. The X-ray diffraction results displayed that 5 at.% Fe doping CuAlO2 powders maintained the original delafossite structure and excessive Fe doping could destroy the structure of CuAlO2. When the Fe doping content increased to 20 at.%, FeAl2O4 phase formed. The Fe doping had significant effects on the electromagnetic parameters of samples. Compared with pure CuAlO2, the Fe-doped CuAlO2 powders have a higher e″ and µ″, which is beneficial to improve the electromagnetic absorption property. The calculated reflection loss curves demonstrated that the sample with at.% Fe doping displayed the most excellent microwave absorption property in thickness of 3.93 mm, showing a minimum reflection loss of − 20.5 dB at the frequency of 9.86 GHz and reflection loss below − 10 dB in the whole measured frequency. Compared with other potential high temperature microwave absorption materials, Fe-doped CuAlO2 powders exhibit a wide-range microwave absorption property.

Carbon-based composites have triggered tremendous attention in the development of high-efficiency microwave absorbers, due to their compatibility, light weight, and high microwave absorption. However, fabricating carbon-based absorbers with a strong absorption ability in a broad frequency range is challenging. Hence, a facile strategy was used to produce Co@C derived from a zeolitic imidazolate framework (ZIF)@ graphene. The Co@C@RGO composite was obtained by annealing the ZIF67/GO nanocomposite precursor at 650 °C in a nitrogen atmosphere. Due to the magnetic loss induced by the Co particles, the dielectric loss generated by the carbon skeletons and graphene, and the interfacial polarization between the components, the hierarchical composite exhibits superior electromagnetic (EM) wave absorption properties. The optimal reflection loss (RL) of the Co@C@ RGO composite can be up to −67.5 dB at 2.6 mm, and the effective bandwidth (≥−10 dB) is 5.4 GHz (10–15.4 GHz) with a thickness of 2 mm at 20 wt% loading. The dipolar polarization caused by graphene, as well as enhanced impedance matching, synergistic effect and interfacial effect among the components, increase the microwave absorption performance of the composite. This work may open a new path to use the Co@C@RGO composite with its high-efficiency EM wave properties as an absorber.

Parallel polymer tandem solar cells containing comb-shaped common electrodes

In order to solve the problem of insufficient oxidation resistance and corrosion resistance of magnetic metal absorbent represented by carbonyl iron powder, a wave absorbing composite material which consists of different filling mass proportions of the atomized electrolytic stainless steel powder and paraffin wax is investigated. The electromagnetic (EM) characteristics and absorbing performance of the proposed composite material were tested with Agilent N5234A vector network analyzer in a frequency range of 2–18GHz. The experimental results show that the real and imaginary parts of the dielectric permittivity of stainless steel powder/paraffin composites will increase with the filling mass fraction in the test frequency band, while the real part of the permeability [Formula: see text] decreases with the increase of the mass fraction, and the imaginary part [Formula: see text] increases with the increase of the mass fraction. At a thickness of 3 mm, with the filling mass fraction increasing from 20 wt.% to 60 wt.%, the peak frequency of reflection loss (RL) moves to low frequency from 17.92 GHz to 16 GHz. Meanwhile, the minimum reflection loss (RL[Formula: see text]) also shows a downward trend, and the RL[Formula: see text] value with a filling mass fraction of 60 wt.% is −8.93[Formula: see text]dB. It can be seen that stainless steel powder shows good microwave absorbing performance, and it has excellent anti-oxidation, and anti-corrosion properties. Based on the excellent performance of stainless steel powder, its absorption performance is expected to be further improved through multi-layer optimization design, so as to meet the needs of electromagnetic protection in harsh environments.

Kirchhoff's law shows that reciprocal materials have equal spectral emissivity at two symmetric polar angles, which is a fundamental limit for a thermal emitter to achieve a small angular divergence in the normal direction. Nonreciprocal materials allow violation of Kirchhoff's law as the emissivity at the two symmetric polar angles can be different. However, achieving strong nonreciprocal thermal radiation near zero angle is challenging. In this work, to reduce the power consumption of a light source for e.g. gas sensing, an ultra‐high‐directional nonreciprocal thermal vertical emitter is proposed, with a periodic structure of magneto‐optical material. When B = 3 T or 1.5 T, magneto‐optical lattice resonances enable the near‐perfect emissivity at 22.36 µm or 22.99 µm at zero angle. The strong nonreciprocity contributed by the collective modes allows for a near‐complete violation of Kirchhoff's law at small angles of ±1°. The nonreciprocal emitters have a very small angular divergence (≈1°), which is better than that of the state‐of‐the‐art thermal emitters. The highly directional nonreciprocal thermal emission is robust despite ±25% change in material loss and ±5% fluctuation in structural parameters. This work should inspire the design of high‐directional nonreciprocal thermal emitters and their applications in high‐resolution thermal imaging, infrared gas sensing, biomedical breath monitoring, and so on.