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In this paper, the characteristics of microwave propagation channels in drill pipe bore are analyzed by regarding the drill pipe as an irregular lossy cylindrical waveguide. An attenuation law is modeled using multipath propagation theory and an experimental statistical method. It is shown from physical measurement results that 5″ and $5^{1/2 \\prime \\prime} $ drill pipe bores, widely applied in the field of air drilling, can be used as 2.4 GHz band microwave channels with the caveat that the numerous reflective surfaces in the joint section of the drill pipe produce a great deal of reflected waves. Hence, the drill pipe bore has the characteristics of a dual cluster multipath channel, and multipath fading and delay are the primary factors affecting propagation quality. The study's constructed microwave attenuation model, based on multipath channels, can be regarded as the average attenuation of the unit length in the drill pipe bore, and can be used as the basis for simulation and analysis of the longer drill pipe string. In addition, a large delay between the two clusters leads to a significant increase of the root mean square delay spread. Consequently, multipath fading and delay are the main factors affecting the channel transmission rate.

HighlightsMetal–organic frameworks (MOFs) are used to directly initiate the gelation of graphene oxide (GO), producing MOF/rGO aerogels.The ultralight magnetic and dielectric aerogels show remarkable microwave absorption performance with ultralow filling contents.The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks (MOFs) and graphene oxide (GO) building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications. Herein, we report a facile route for synthesizing MOF/reduced GO (rGO) aerogels based on the gelation of GO, which is directly initiated using MOF crystals. Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal–oxygen covalent or electrostatic interactions. The MOF/rGO-derived magnetic and dielectric aerogels Fe3O4@C/rGO and Ni-doped Fe3O4@C/rGO show notable microwave absorption (MA) performance, simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5 (− 58.1 dB and 6.48 GHz) and 2.8 mm (− 46.2 dB and 7.92 GHz) with ultralow filling contents of 0.7 and 0.6 wt%, respectively. The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation, which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering. This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.

Dedicating to the exploration of efficient electromagnetic (EM) absorption and electromagnetic interference (EMI) shielding materials is the main strategy to solve the EM radiation issues. The development of multifunction EM attenuation materials that are compatible together EM absorption and EMI shielding properties is deserved our exploration and study. Here, the graphene-wrapped multiloculated NiFe 2 O 4 composites are reported as multifunction EM absorbing and EMI shielding materials. The conductive networks configurated by the overlapping flexible graphene promote the riched polarization genes, as well as electron transmission paths, and thus optimize the dielectric constant of the composites. Meanwhile, the introduction of magnetic NiFe 2 O 4 further establishes the magnetic-dielectric synergy effect. The abundant non-homogeneous interfaces not only generate effective interfacial polarization, also the deliberate multiloculated structure of NiFe 2 O 4 strengthens multi-scattering and multi-reflection sites to expand the transmission path of EM waves. As it turns out, the best impedance matching is matched at a lower filled concentration to achieve the strongest reflection loss value of −48.1 dB. Simultaneously, green EMI shielding based on a predominantly EM absorption and dissipation is achieved by an enlargement of the filled concentration, which is helpful to reduce the secondary EM wave reflection pollution to the environment. In addition, the electrocatalytic properties are further examined. The graphene-wrapped multiloculated NiFe 2 O 4 shows the well electrocatalytic activity as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which is mainly attributed to the interconnected structures formed by graphene and NiFe 2 O 4 connection. The structural advantages of multiloculated NiFe 2 O 4 expose more active sites, which plays an important role in optimizing catalytic reactions. This work provides an excellent jumping-off point for the development of multifunction EM absorbing materials, eco-friendliness EMI shielding materials and electrocatalysts.

HighlightsThe size of metal organic frameworks (MOFs) derivatives was manipulated by a spatial confined growth strategy.Dielectric polarization is the dominant dissipation mechanism due to the phase hybridization based on size dependent oxidation motion.The specific reflection loss of synthesized Co/Co3O4 hollow carbon nanocages surpasses most reported MOFs derived counterparts for practical microwave absorption applications.Precisely reducing the size of metal-organic frameworks (MOFs) derivatives is an effective strategy to manipulate their phase engineering owing to size-dependent oxidation; however, the underlying relationship between the size of derivatives and phase engineering has not been clarified so far. Herein, a spatial confined growth strategy is proposed to encapsulate small-size MOFs derivatives into hollow carbon nanocages. It realizes that the hollow cavity shows a significant spatial confinement effect on the size of confined MOFs crystals and subsequently affects the dielectric polarization due to the phase hybridization with tunable coherent interfaces and heterojunctions owing to size-dependent oxidation motion, yielding to satisfied microwave attenuation with an optimal reflection loss of −50.6 dB and effective bandwidth of 6.6 GHz. Meanwhile, the effect of phase hybridization on dielectric polarization is deeply visualized, and the simulated calculation and electron holograms demonstrate that dielectric polarization is shown to be dominant dissipation mechanism in determining microwave absorption. This spatial confined growth strategy provides a versatile methodology for manipulating the size of MOFs derivatives and the understanding of size-dependent oxidation-induced phase hybridization offers a precise inspiration in optimizing dielectric polarization and microwave attenuation in theory.

With the development of nanotechnology, nano-functional units of different dimensions, morphologies, and sizes exhibit the potential for efficient microwave absorption (MA) performance. However, the multi-unit coupling enhancement mechanism triggered by the alignment and orientation of nano-functional units has been neglected, hindering the further development of microwave absorbing materials (MAMs). In this paper, two typical ZIF-derived nanomaterials are self-assembled into two-dimensional ordered polyhedral superstructures by the simple ice template method. The nano-functional units exhibit distinctive dielectric-sensitive behaviors after self-assembling into two-dimensional ordered arrays. The modified 2D ordered polyhedral superstructures not only inherit the atomic-level doping and well-designed shell structure, but also further amplify the loss properties to realize the multi-scale modulated MA response. Satisfactory MA performance in C, X and Ku bands is finally achieved. In particular, the ultra-broadband microwave absorption bandwidth (EAB) of 6.41 GHz is realized at 1.82 mm thickness. Our work demonstrates the two-dimensional ordered array-induced multiscale polarization behavior, providing a direction to fully utilize the potential of wave-absorbing functional units. This work delves into the effects of orientation of ordered nano-units in 2D arrays on electromagnetic shielding. Polyhedral superstructures allow for good performance in the C, X, and Ku bands, with a bandwidth of 6.41 GHz at 1.82 mm thickness.

HighlightsHollow SiC/C microspheres with controllable composition have been successfully synthesized by simultaneously implementing compositional and structural engineering.The optimum dielectric properties (i.e., conductivity loss and polarization loss) and impedance matching characteristics can achieve outstanding microwave absorption performance.Broadband wave absorption (5.1 GHz with only 1.8 mm thickness), high efficiency loss (− 60.8 dB at 10.4 GHz) combined with good environmental tolerance, demonstrate their bright prospects in practice.Microwave absorbing materials (MAMs) characterized by high absorption efficiency and good environmental tolerance are highly desirable in practical applications. Both silicon carbide and carbon are considered as stable MAMs under some rigorous conditions, while their composites still fail to produce satisfactory microwave absorption performance regardless of the improvements as compared with the individuals. Herein, we have successfully implemented compositional and structural engineering to fabricate hollow SiC/C microspheres with controllable composition. The simultaneous modulation on dielectric properties and impedance matching can be easily achieved as the change in the composition of these composites. The formation of hollow structure not only favors lightweight feature, but also generates considerable contribution to microwave attenuation capacity. With the synergistic effect of composition and structure, the optimized SiC/C composite exhibits excellent performance, whose the strongest reflection loss intensity and broadest effective absorption reach − 60.8 dB and 5.1 GHz, respectively, and its microwave absorption properties are actually superior to those of most SiC/C composites in previous studies. In addition, the stability tests of microwave absorption capacity after exposure to harsh conditions and Radar Cross Section simulation data demonstrate that hollow SiC/C microspheres from compositional and structural optimization have a bright prospect in practical applications.

Nowadays, electromagnetic pollution originated from artificial intelligence devices, fifth-generation (5G) cellular networks, as well as ever-increasing electronic devices applying and/or producing electromagnetic waves has excited the global concern. Evidently, the novel threats are springing up as a sleeping giant awaiting to irrupt; thus, the immediate counteraction is inescapable against the augmenting harmful electromagnetic waves. Till date, based on the permeability and permittivity of the materials in the microwave region, diverse microwave absorbing structures have been fabricated to overcome the aforementioned problem. It is worth noting that nanostructures are under the spotlight as a hot spot generated from their incomparable surface area-to-volume ratio tuning polarizability, magnetic features, electrical conductivity, eddy current loss, and other absorbing mechanisms. It should be noted that the secondary pollution produced at the threshold of the absorbing structures is tunable by the impedance matching. Hitherto, the size, shape, and morphology of nanostructures have been manipulated to improve microwave attenuation. The more surface area-to-volume ratio brings the more defect, dipole, and interfacial polarization as well as enhances the interfacial interactions at heterogeneous interfaces providing more multiple reflections and scattering. On the other hand, the intrinsic properties of the absorbing media and their unique interactions at grain boundaries can promote microwave attenuation which have recently attracted a great deal of attention. The obtained results manifest that the morphology and medium influence on microwave absorbing characteristics are the tip of the iceberg investigated by diverse approaches. In this study, a comprehensive prospect is presented using recent researches related to the size, shape, defect, morphology, and medium effect on the microwave absorbing mechanisms paving the way for microwave attenuation. The achieved works have attested that the mentioned parameters are the vital factors influencing the microwave absorbing properties. Graphical abstract

It is essential to manufacture microwave absorbers with strong absorption as well as tunable absorption bands at a low filler content. However, it remains challenging for pure biomass material to reach this goal without loading other components. MoSe 2 , as a transition metal chalcogenide with semiconductor properties, has emerged as a potential microwave absorber filler. Herein, bacterial cellulose (BC)-derived carbon nanofibers/MoSe 2 nanocomposite was fabricated and phosphoric acid was used to dope phosphorus in BC, in which MoSe 2 microspheres were dropped on the BC network like a dew-covered spider web. This unique network structure enhances conductive loss and multiple reflections of the incident wave. The collocation of BC and MoSe 2 is helpful to impedance match and introduces interfacial/dipolar polarization loss; moreover, the P-doping of BC helps to tune the absorption bands. Overall, the optimal reflection loss of undoped one reaches −53.33 dB with only 20 wt.% filler content, whose main absorption peaks focus on X-band. Interestingly, after the P-doping of BC, the main absorption peaks move to Ku-band and the optimal reflection loss gets stronger (−66.84 dB) with the same filler loading. Strong absorption and tunable absorption bands can be realized, and thus wide frequency range is covered. This work is expected to enlighten future exploration of biomass carbon materials on high-performance microwave absorption materials.

Carbon aerogels (CAs) have been considered potential microwave absorption (MA) materials because of intrinsic hierarchical porous structure, low density, and excellent heat resistance. However, CAs always required to be ground into micron-scale powder before being used as microwave absorbers, which will inevitably destroy the hierarchical porous structure. Meanwhile, reproducing the optimized CAs powders is difficult. Herein, CAs microspheres with in-situ mineralized TiO 2 were easily prepared via a sol-gel transition and calcination process. The uniform size of CA microspheres and the loaded TiO 2 on the skeleton of CA yield great microwave attenuation performance while guaranteeing good impedance matching performance. The obtained TiO 2 /CA hybrid presented a minimum reflection loss value of −30.2 dB and a broad effective absorption bandwidth (reflection loss below −10 dB) of 6.2 GHz. The low density, MA performance, and controllable particle size make the novel TiO 2 /CA hybrid promising candidates for MA applications.

Highlights An alternative electromagnetic attenuation pathway is proposed in the MXene-polymer hybrid structure, distinct from conduction loss, for generalizing the results to a wider range of electromagnetic-thermal driven soft materials and devices. By efficiently harvesting and converting electromagnetic energy, the response time of the hybrid polymer to microwave exhibits 87% reduction with merely 0.15 wt% MXene. A new mode of self-powered motion sensing based on deformation-driven piezoelectric effect is developed, enhancing the material’s intelligence. Polymeric microwave actuators combining tissue-like softness with programmable microwave-responsive deformation hold great promise for mobile intelligent devices and bionic soft robots. However, their application is challenged by restricted electromagnetic sensitivity and intricate sensing coupling. In this study, a sensitized polymeric microwave actuator is fabricated by hybridizing a liquid crystal polymer with Ti 3 C 2 T x (MXene). Compared to the initial counterpart, the hybrid polymer exhibits unique space-charge polarization and interfacial polarization, resulting in significant improvements of 230% in the dielectric loss factor and 830% in the apparent efficiency of electromagnetic energy harvest. The sensitized microwave actuation demonstrates as the shortened response time of nearly 10 s, which is merely 13% of that for the initial shape memory polymer. Moreover, the ultra-low content of MXene (up to 0.15 wt%) benefits for maintaining the actuation potential of the hybrid polymer. An innovative self-powered sensing prototype that combines driving and piezoelectric polymers is developed, which generates real-time electric potential feedback (open-circuit potential of ~ 3 mV) during actuation. The polarization-dominant energy conversion mechanism observed in the MXene-polymer hybrid structure furnishes a new approach for developing efficient electromagnetic dissipative structures and shows potential for advancing polymeric electromagnetic intelligent devices.