Advancements in Microwave Absorption Motivated by Interdisciplinary Research.

Microwave absorption materials (MAMs) are originally developed for military purposes, but have since evolved into versatile materials with promising applications in modern technologies, including household use. Despite significant progress in bench-side research over the past decade, MAMs remain limited in their scope and have yet to be widely adopted. This review explores the history of MAMs from first-generation coatings to second-generation functional absorbers, identifies bottlenecks hindering their maturation. It also presents potential solutions such as exploring broader spatial scales, advanced characterization, introducing liquid media, utilizing novel toolbox (machine learning, ML), and proximity of lab to end-user. Additionally, it meticulously presents compelling applications of MAMs in medicine, mechanics, energy, optics, and sensing, which go beyond absorption efficiency, along with their current development status and prospects. This interdisciplinary research direction differs from previous research which primarily focused on meeting traditional requirements (i.e., thin, lightweight, wide, and strong), and can be defined as the next generation of smart absorbers. Ultimately, the effective utilization of ubiquitous electromagnetic (EM) waves, aided by third-generation MAMs, should be better aligned with future expectations.

Positive Charge Holes Revealed by Energy Band Theory in Multiphase Tix O2x-1 and Exploration of its Microscopic Electromagnetic Loss Mechanism.

Although numerous experimental investigations have been carried out on the problem of defect engineering in semiconductor absorbers, the relationship among charge carrier, defects, heterointerfaces, and electromagnetic (EM) wave absorption has not been established systematically. Herein, the new thermodynamic and kinetic control strategy is proposed to establish multiphase Tix O2 x -1 (1 ≤ x ≤ 6) through a hydrogenation calcination. The TiOC-900 composite shows the efficient EM wave absorption capability with a minimum reflection loss (RLmin ) of -69.6 dB at a thickness of 2.04 mm corresponding to an effective absorption bandwidth (EAB) of 4.0 GHz due to the holes induced conductance loss and heterointerfaces induced interfacial polarization. Benefiting from the controllable preparation of multiphase Tix O2 x -1 , a new pathway is proposed for designing high-efficiency EM wave absorbing semiconducting oxides. The validity of the method for adopting energy band theory to explore the underlying relations among charge carriers, defects, heterointerfaces, and EM properties in multiphase Tix O2 x -1 is demonstrated for the first time, which is of great importance in optimizing the EM wave absorption performance by electronic structure tailoring.

In-situ construction of Cr2O3@ATO hybrid pigment towards synergetic enhancement of visible light-infrared-radar compatible stealth.

Multiband compatible stealth engineering with controllable visible light-infrared (VIS-IR) features and radar wave absorption is urgently needed to improve the survivability of advanced military equipment. Cr2O3 has good visible light stealth performance under green background, but it is lack of IR and radar multi-band stealth properties. Herein, a core-shelled Cr2O3@stannic antimony oxide (ATO) structure was developed to enhance the IR-radar compatible stealth properties of Cr2O3 by in-situ precipitation method, concurrently maintaining its visible light stealth property. The morphology, conductivity, and infrared stealth properties of the Cr2O3@ATO hybrids were influenced by the calcination temperature, and the IR and radar stealth performance were tunable by ATO content. The lowest emissivity of Cr2O3@ATO pigments is 0.852, reduced by 10% than pure Cr2O3. The Cr2O3@ATO filled silicone resin coatings possessed good thermal stability and IR stealth stability. Benefiting from the enhanced interfacial polarization and conductive loss, the Cr2O3@ATO exhibited an effective absorption bandwidth of 2 GHz in the X band, with respect to pure Cr2O3 without radar absorption property. The Cr2O3@ATO structure opens an avenue for advanced VIS-IR-Radar compatible stealth materials.

A novel plasma-sprayed Ti4O7/carbon nanotubes/Al2O3 coating with bifunctional microwave application.

High-performance microwave absorption coatings are critically required in the stealth defense system of military platforms. Regrettably, just optimizing the property but neglecting the application feasibility seriously inhibits its practical application in the field of microwave absorption. To face this challenge, the Ti4O7/carbon nanotubes (CNTs)/Al2O3 coatings were successfully fabricated by a plasma-sprayed method. For the different oxygen vacancy-induced Ti4O7 coatings, the enhanced ε' and ε'' values in the frequency of X-band is due to the synergistic manipulation of conductive path, defects and interfacial polarization. The optimal reflection loss of Ti4O7/CNTs/Al2O3 sample (0 wt% CNTs) is -55.7 dB (8.9 GHz of 2.41 mm), while the electromagnetic interference shielding effectiveness of Ti4O7/CNTs/Al2O3 sample (5 wt% CNTs) increases to 20.5 dB as the enhanced electrical conductivity. In special, the flexural strength of Ti4O7/CNTs/Al2O3 coatings first increases from 48.59 MPa (0 wt% CNTs) to 67.13 MPa (2.5 wt% CNTs) and then decreases to 38.31 MPa (5 wt% CNTs), demonstrating that an appropriate amount of CNTs evenly dispersed in the Ti4O7/Al2O3 ceramic matrix can effectively play the role of CNTs as the strengthening phase of the coatings. This research will provide a strategy by tailoring synergistic effect of dielectric loss and conduction loss for oxygen vacancy-mediated Ti4O7 material to broaden the application of absorbing or shielding ceramic coatings.

Balancing Between Polarization and Conduction Loss toward Strong Electromagnetic Wave Absorption of Hard Carbon Particles with Morphology Heterogeneity.

The heterostructure and hierarchical morphology of carbonaceous absorbents play an important role in the construction of high-performance electromagnetic wave absorbing materials. Herein, novel micron-scale hard carbon particles with morphology heterogeneity were developed as lightweight superior electromagnetic wave absorbents via a facile and ecofriendly process. The as-prepared hard carbon particle composed of pseudographite and a highly disordered region shows a unique heterostructure. Concurrently, constructing a multilevel geometric shape and size can cause a decrease of the percolation threshold and an excellent balance between polarization and conduction loss, which enhances the electromagnetic wave absorption significantly. The composites (thickness d = 2.36 mm) filled with morphology-heterogeneity hard carbon particles (15 wt %) achieve an excellent electromagnetic wave absorption with a minimum reflection loss of -78.0 dB at 10.2 GHz and effective absorption bandwidth (<-10 dB) of 3.1 GHz (8.8-11.9 GHz). Compared to the traditional carbonaceous absorbents with complex microstructures and/or multiple chemical components, this work presents a feasible idea for the development of an efficient carbonaceous absorbent to realize practical applications.

Effects of Multi-Components on the Microwave Absorption and Dielectric Properties of Plasma-Sprayed Carbon Nanotube/Y2O3/ZrB2 Ceramics.

Carbon nanotube (CNT)-reinforced Y2O3/ZrB2 ceramics were fabricated via planetary ball milling and atmospheric-pressure plasma spraying for the first time. The phase composition, micromorphology, and electromagnetic (EM) wave absorption performance of the Y2O3/ZrB2/CNT hybrid was investigated from 8.2 to 12.4 GHz. Both the real and imaginary parts of the complex permittivity were enhanced as the ZrB2 and CNT content increased. The Y2O3/ZrB2/CNT hybrids corresponded to a ZrB2 content of 15 wt.%, and the CNT content was 2 wt.% and showed an exceptional EM wave absorption capability, with a minimum reflection loss of -25.7 dB at 1.9 mm thickness, and the effective absorption band was in a full X-band. These results indicate that an appropriate CNT or ZrB2 content can tune the complex permittivity and absorption performance of the Y2O3/ZrB2/CNT ceramics.

SiC-Coated Carbon Nanotubes with Enhanced Oxidation Resistance and Stable Dielectric Properties.

Carbon nanotubes (CNTs) coated with SiC coating was successfully prepared by pyrolysis of polycarbosilane (PCS) used as a precursor. The function of pyrolysis temperature on the oxidation resistance and the dielectric properties of CNTs/SiC were studied in X-band. The results demonstrate that the obtained dense SiC film can prevent the oxidation of CNTs when the pyrolysis temperature reaches 600 °C. Correspondingly, after heat treatment is at 400 °C for 200 h, the mass loss of P-600 is less than 1.86%, and the real and imaginary parts of the dielectric constant nearly keep constant (ε' from 14.2 to 14, and ε″ from 5.7 to 5.5). SiC-coated CNTs have a better oxidation resistance than pristine CNTs. Therefore, this work, with a facile preparation process, enhances the oxidation resistance of CNTs at high temperature for a long time and maintains a stable dielectric property, which means CNTs/SiC composites can be good candidates for applications in the field of high-temperature absorbers.

Flexible and Transparent Ferroferric Oxide-Modified Silver Nanowire Film for Efficient Electromagnetic Interference Shielding.

Transparent and flexible electromagnetic interference (EMI) shielding film is highly desirable due to the fast-growing flexible electronics. A silver nanowire (Ag NW) film is considered to be an ideal candidate for a transparent and flexible EMI shielding film but suffers low EMI shielding effectiveness (SE) at high transparency and poor bending durability. Herein, we introduce ferroferric oxide (Fe3O4) into a Ag NW film and demonstrate a robust EMI shielding film, which exhibits SE of 24.9 dB at 8.2 GHz and optical transparency of 90%. Fe3O4 exhibits roles of the improved absorption loss for electromagnetic radiation due to its high permeability, the enhanced reflection loss for electromagnetic radiation by increasing the conductivity of Ag NWs film, and the improved stability for the enhanced adhesion of the Ag NW EMI shielding film. Our work provides a facile method for high-performance transparent EMI shielding film, which exhibits great potential for protection for electronic devices.