In this study, a novel adaptive infrared (IR) camouflage film based on one-dimensional (1D) quasi-photonic crystal (PC) with phase-change material Ge2Sb2Te5 (GST), is theoretically demonstrated. The ...designed film shows high emissivity state at low temperature and low emissivity state at high temperature, via the transition between amorphous and crystalline phase of GST. Moreover, the quasi-PC structure, designed with top optimized layers, possesses low emissivity property by splicing constructive interference (CI) peaks. In particular, the designed quasi-PC film is more conducive to the IR camouflage with variable object temperature (To), compared to those with static emissivity. This study provides a significant pathway to 1DPC application for adaptive IR camouflage and other technologies that rely on controlling the transfer of thermal radiation.
•A new one-dimensional quasi-photonic crystal (PC) structure with top optimized layers is designed.•Phase-change material Ge2Sb2Te5 (GST) is introduced as alternate layer material into quasi-PC.•Infrared emissivity can be modulated by phase changing of GST.•This film can be applied to adaptive infrared camouflage for variable temperature object.
An ultra-thin low-frequency broadband microwave absorber (MWA) based on a magnetic rubber plate (MRP) and cross-shaped structure (CSS) metamaterial (MM) was presented numerically and experimentally. ...The designed composite MWA is consisted of the MRP, CSS resonator, dielectric substrate and metallic background plane. The low-frequency absorption can be easily adjusted by tuning the geometric parameter of the CSS MM and the thickness of MPR. A bandwidth (i.e. the reflectance is below −10 dB) from 2.5 GHz to 5 GHz can be achieved with the total thickness of about 2 mm in experiments. The broadband absorption is attributed to the overlap of two resonant absorption peaks originated from MRP and CSS MM, respectively. More importantly, the thickness of the composite WMA is much thinner (
λ
/40;
λ
is the operation center frequency), which could operate well at wide incidence angles for both transverse electric and transverse magnetic waves. Thus, it can be expected that our design will be applicable in the area of eliminating microwave energy and electromagnetic stealth.
General metasurfaces (MSs) can realize low observability of radar by manipulating the polarization mode and transmission direction of the electromagnetic (EM) waves. Here, we propose the radar trap ...model to realize EM wave imprisonment. This three-layer model is composed of the transmission polarization converter, the connected dielectric substrate and the reflection polarization converter. Using Jones calculation as a guide, we optimized the geometric parameters of the upper and lower layers to realize specific polarization conversion functions. The middle layer is regarded as the support and matching layer. On this basis, the combined radar trap model can realize the imprisonment of EM waves between upper and lower layers, which is attributed to the cooperative effect of asymmetric transmission and polarization conversion. We further verified the feasibility and correctness of our investigations through two kinds of model designs based on linear and circular polarization conversion mechanisms. Good agreements are observed between simulation and experiment. Even though the design presents a narrow operating bandwidth, it still provides novel ideas for developing radar stealth technology.
In this paper, magnetic iron fibers of 3–10
μm diameter and an adjustable aspect ratio were synthesized successfully by a method involving pyrolysis of carbonyl under a magnetic field. A surface ...modification technology was also investigated. The electromagnetic parameters of the iron-fiber–wax composites were measured using the transmission/reflection coaxial line method in the microwave frequency range of 2–18
GHz. The results show that the prepared iron-fiber–wax composites exhibit high magnetic loss that can be further improved after phosphating. On the other hand, the complex permittivity was significantly decreased after phosphating. As a result, this kind of iron fiber may be useful for thin and lightweight radar-absorbing materials.
Development of microwave absorbing materials (MAMs) with strong and broadband absorption at thin thickness to address electromagnetic radiation and interference is still a huge challenge. Herein, ...bimetallic oxalate rod-derived NiFe/Fe3O4@carbon rods (NiFe/Fe3O4@CRs) composites as MAMs were structured by a facile coprecipitation followed by a carbothermal reduction process. The multiple interfaces existing in the composite can enhance the dielectric loss, and the rod structure can decrease the density of the NiFe/Fe3O4@carbon. The composite shows excellent microwave absorption properties. The minimum reflection loss (RL) value reaches −44.9 dB at an absorber thickness of 2.2 mm, and the efficient absorption bandwidth (RL ≤ −10 dB) is 5.1 GHz with a small thickness of only 1.58 mm. The high-performance microwave absorption mechanisms of the as-prepared NiFe/Fe3O4@CRs composites were mainly attributed to the synergistic of impedance matching, magnetic loss, and electrical loss. This work opens up a new prospect for developing high-performance microwave absorbers.
•Novel heterogeneous structured dendritic Fe3O4@PANI composites were prepared.•The Fe3O4@(HCl doped PANI) exhibited an outstanding EAB of 6.08 GHz at only 2.1 mm.•The Fe3O4@(dedoped PANI) displayed ...the RLmin of −53.08 dB at 3.04 GHz and an excellent EAB (4.1 GHz at1.3 mm).•The multiple loss mechanisms and improved impedance matching synergistically enhanced EMW absorption performance.
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Fe3O4, as a typical absorber, its electromagnetic wave (EMW) absorption properties are far from meeting the requirements of practical application due to its poor impedance matching. In this study, three kinds of novel heterogeneous structured composites, dendritic Fe3O4@(HCl doped PANI), Fe3O4@(p-TSA doped PANI) and Fe3O4@(dedoped PANI), were prepared via hydrothermal method combined with thermal reduction and in-situ polymerization, and their phase composition, microscopic morphologies, static magnetic properties, EMW absorption performance and absorption mechanisms were investigated. The results showed that the introduction of different medium doped and dedoped PANI greatly enhanced the EMW absorption performance of Fe3O4. The outstanding advantages of Fe3O4@(HCl doped PANI) were that the widest effective absorption bandwidth (EAB) up to 6.08 GHz in a relatively thin thickness of 2.1 mm. And the Fe3O4@(dedoped PANI) composite achieved strong absorption ability (− 53.08 dB@3.04 GHz) at low frequency in a relatively thin thickness (4.9 mm). The remarkable improvement of EMW absorption performance of dendritic Fe3O4@PANI composites could be attributed to the introduction of dissipation mechanisms, the optimization of impedance matching characteristics and the formation of appropriate conductive network microstructure. The dendritic Fe3O4@PANI composites are promising EMW absorption materials and have great practical application value.
Integrated lightweight metastructures with microwave absorption and mechanical properties are of great significance in practical applications, but so far relevant study is still lacking. In this ...paper, an integrated lightweight gradient honeycomb metastructure (GHM) was proposed using 3D printing and screen printing technologies. Using the equivalent circuit method (ECM), we provided an in-depth analysis of how to broaden the absorption bandwidth and derived the mathematical formula of the equivalent resistance of the hexagon loop. The simulation results reveal that the proposed metastructure has the characteristics of broadband absorption, polarization insensitivity, oblique incidence stability, and radar cross section (RCS) suppression in the operating frequency range. The measured results are in good agreement with the simulation ones. In addition, the compression test results show that the metastructure has good compression strength. This work provides a route to achieve integrated metastructures with thin, lightweight, excellent absorption and mechanical properties.
In this paper, we present a novel design of a dual and broadband metamaterial absorber (MMA) based on a compact meander wire structure resonator in the terahertz (THz) region. The simulation results ...indicate that the absorbance is greater than 90% around 1.19 THz and 1.64-2.47 THz. The dual and broadband high level absorption mainly originates from the mixtures of the electric and magnetic resonance response with higher-orders of the proposed structure. The high absorption performance can be obtained at large angles of polarization and incidence for both transverse magnetic (TM) and transverse electric (TE) waves. Multiple reflection interference theory is used to analyze the mechanism of the MMA, and the theoretical results agree well with simulations. Furthermore, the absorption properties of the MMA can be adjusted easily by changing the geometric parameters of the unit-cell structure. Owing to its favorable performance, the proposed MMA could find many potential applications in bolometric imaging, stealth and communications in the THz region.
•We calculate the relative permittivity chart to guide the design of specific materials with particular microwave absorption (MA) properties.•Design composites are prepared and characterized to ...realize the temperature-insensitive MA properties.•The temperature-insensitive and enhanced MA properties are believed to be the cooperative effect of dielectric loss and impedance matching.•Prepared meta-structure can realize a reflection loss less than −5 dB at 8.2–18.0 GHz in the temperature range of 25–1100 °C.
Developing high-temperature microwave absorption (MA) materials remains a challenge in the field of radar stealth. Here, we propose a design concept of meta-structure for temperature-insensitive and broadband MA. The three-phase TiB2/Al2O3/MgAl2O4 composites are prepared to realize the temperature-insensitive MA properties, which is ascribed to the interaction of different components in terms of the electrical conductivity, dipolar polarization and interfacial polarization as temperature increases. On this basis, we design and fabricate a three-layer meta-structure composed of the SiO2 ceramics as environmental adaptation layer, the patch-type and flat composites as MA layers. Compared with flat composites, the meta-structure can optimize its effective permittivity, thereby realizing enhanced MA properties at elevated temperatures. This meta-structure can realize a reflection loss (RL) less than −5 dB at 8.2–18.0 GHz in the temperature range of 25 °C to 1100 °C. The experiment matches well with the simulation. The temperature-insensitive and enhanced MA properties are attributed to the consequence of the combination of traditional absorbing materials and metamaterial structures.
Fe55Ni45 fiber has been fabricated by magnetic-field-induced thermal decomposition of iron pentacarbonyl Fe(CO)5 and nickel tetracarbonyl Ni(CO)4. Fe55Ni45 fiber presents the face-centered-cubic ...(FCC) structure (γ-phase) characterized by X-ray diffraction (XRD) and fibrous morphology observed by scanning electron microscope (SEM). It is shown that with the increase of induced magnetic field, the diameter of the fiber can be increased from 5 to 8 μm and its corresponding aspect ratio is decreased from 60–80 to 20–40. The complex permittivity and permeability of Fe55Ni45 fiber-filled composites are measured in x-band (8–12 GHz) with the transmission and reflection waveguide method. The results show that Fe55Ni45 fiber of smaller diameter (5 μm) and higher aspect ratio (60–80) exhibits higher complex permittivity and permeability. The reflection loss (RL) measurement reveals the thin composites filled with Fe55Ni45 fibers possess low RL value.
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