Small Angle Scattering of X-Rays

In this work, the authors proposed a thin artificial structure that could give rise to the strong reduction of both radar wave reflection and infrared thermal emission. This is realized by the subtle combination of two specifically designed metasurface layers that control the infrared emission and microwave absorption, respectively. Our measurement shows that the fabricated sample could have wideband absorption from 3–8 GHz with attenuation efficiency larger than 90% up to incident angles of 30°. In the infrared atmosphere window, it gives a very low emission value of about 0.2. These results show that our sample is practically very promising for the application of a radar-infrared bi-stealth technology.

A radar-infrared bi-stealth structure based on metasurfaces

Effects of diameter and hollow structure on the microwave absorption properties of short carbon fibers

Self-assembled monolayers of a 6-nitro BIPS spiropyran (SP) modified with a disulfide-terminated aliphatic chain were prepared on polycrystalline gold surfaces and characterized by UV/vis absorption, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopies (XPS). The SAMs obtained are composed of the ring-closed form (i.e., spiropyran) only. Irradiation with UV light results in conversion of the monolayer to the merocyanine form (MC), manifested in the appearance of an N+ contribution in the N 1s region of the XPS spectrum of the SAMs, the characteristic absorption band of the MC form in the visible region at 555 nm, and the C–O stretching band in the SERS spectrum. Recovery of the initial state of the monolayer was observed both thermally and after irradiation with visible light. Several switching cycles were performed and monitored by SERS spectroscopy, demonstrating the stability of the SAMs during repeated switching between SP and MC states. A key finding in the present study i...

UV/Vis and NIR Light-Responsive Spiropyran Self-Assembled Monolayers

In this paper, a new type one-dimensional (1D) double hetero-structure composite photonic crystal (CPC) for infrared-radar stealth-compatible materials applications was proposed and studied numerically and experimentally. First, based on transfer matrix method of thin-film optical theory, the propagation characteristics of the proposed structure comprising a stack of different alternating micrometer-thick layers of germanium and zinc sulfide were investigated numerically. Calculation results exhibit that this 1D single hetero-structure PC could achieve a flat high reflectivity gradually with increasing the number of the alternating media layers in a single broadband range. Then, based on principles of distributed Bragg reflector micro-cavity, a 1D double hetero-structure CPC comprising four PCs with thickness of 0.797 μm, 0.592 μm, 1.480 μm, and 2.114 μm, respectively, was proposed. Calculation results exhibit that this CPC could achieve a high reflectance of greater than 0.99 in the wavelength ranges of 3–5 μm and 8–14 μm and agreed well with experiment. Further experiments exhibit that the infrared emissivity of the proposed CPC is as low as 0.073 and 0.042 in the wavelength ranges of 3–5 μm and 8–12 μm, respectively. In addition, the proposed CPC can be used to construct infrared-radar stealth-compatible materials due to its high transmittance in radar wave band.

Design and realization of one-dimensional double hetero-structure photonic crystals for infrared-radar stealth-compatible materials applications

Thermochromic vanadium dioxide (VO2) exhibits a semi-conducting to metallic phase transition at about 68°C, involving strong variations in electrical and optical properties A simple method was proposed to prepare VO2 thin films from easily gained V2O5 thin films The detailed thermodynamic calculation was done and the results show that V2O5 will decompose to VO2 when the post annealing temperature reaches 550°C at the atmospheric pressure of less than 006Pa The initial V2O5 films were prepared by sol-gel method on fused-quartz substrates Different post annealing conditions were studied The derived VO2 thin film samples were characterized using X-ray diffraction and X-ray photoelectron spectroscopy The electrical resistance and infrared emissivity of VO2 thin films under different temperatures were measured The results show that the VO2 thin film derived from the V2O5 thin film annealed at 550°C for 10 hours is pure dioxide of vanadium without other valences It was observed that the resistance of VO2 thin film with thickness about 600nm can change by 4 orders of magnitude and the 75-14μm emissivity can change by 06 during the phase transition

Thermochromic VO2 Thin Film Prepared by Post Annealing Treatment of V2O5 Thin Film

Infrared emissivity of capacitive frequency-selective surfaces is affected by many factors, such as metal area, emissivity of medium part, surface roughness, metal oxidation, and surface cleanness, etc. In this paper, the influence of metal area and emissivity of medium part on the emissivity of CFSSs were depicted in detail. Furthermore, a kind of radar and IR compatible stealth sandwich structures, radar absorbing properties of which were calculated by the finite-difference time-domain (FDTD) method, were designed and prepared. We conclude that emissivity of CFSSs will be below 0.3 while metal area is above 80% and radar reflectivity of fabricated sandwich structure will be below -10dB in 8-18GHz.

Infrared Emissivity of Capacitive Frequency-Selective Surfaces and its Application in Radar and IR Compatible Stealth Sandwich Structures

Generally, high thermal conductivity of SiC ceramics is required. However, in some circumstances, low thermal conductivity SiC is also needed, for example, for good thermoelectricity or heat insulation. In this work, the product of pyrolysis of polycarbosilane (PCS) is chosen as raw materials. The microwave sintering process was applied to obtain low thermal conductivity at a relatively low sintering temperature. The microwave sintering processes were performed at 1200 °C under Ar atmosphere with dwelling time of 10, 20 and 30 min. The morphology and phases were analyzed by electric microscopy and X-ray diffraction (XRD), respectively. The thermal diffusivities, specific heat and thermal conductivities were measured by laser-flashed method using a thermal analyzer. The thermal conductivity of samples is within the range from 0.81 to 1.37 W/m•K. The sample with dwelling time of 30 min shows potential for multiple applications, due to its good crystallization in XRD spectra and relatively low thermal conductivity in the considered temperature range. The results also suggest a phase transformation at a dwelling time near 20 min that may have occurred.

Reducing Thermal Conductivity of Polymer Derived SiC Ceramics via Microwave Sintering Processing

A series of polyacrylonitrile-based hollow-porous and solid carbon fibers were prepared by pyrolysis of polyacrylonitrile-based hollow-porous and solid fibers at the same condition. The microstructure, composition, surface electrical conductivity, electromagnetic parameters and reflectivity of carbon fibers were studied. The microwave absorbing properties of two kinds of carbon fibers as microwave absorbents were parallel investigated. Results show that the apparent density of the hollow-porous carbon fibers is lower than that of the solid carbon fibers due to their hollow-porous structure. The surface electrical conductivity of single solid carbon fiber is nearly 10 times that of the hollow-porous carbon fiber. The -10dB bandwidths of solid carbon fiber composites carbonized at 850 and 950°C are both 0GHz, while those of the corresponding hollow-porous carbon fiber composites are up to 3.05 and 2.62GHz, respectively. Results indicate that the microwave absorbing properties of the hollow-porous carbon fiber composites are better than those of solid carbon fiber composites.

Comparison of Hollow-Porous and Solid Carbon Fibers as Microwave Absorbents

The tungsten oxideWO3 thin film was prepared by sol-gel process through peroxotungstic acid (PTA). The crystal phase and surface morphological features change at different annealing temperatures. The WO3 thin film is amorphous at 300 °C. When the annealing temperature is increased to 400 °C, it becomes monoclinic phase. The phase begins to become triclinic at 550 °C. The phase then changes to orthorhombic phase at 750 °C. With the increasing of the annealing temperature, the continuum of the WO3 thin film is broke and the gabs among grains become larger. The WO3 thin film is almost disappear after annealed at 850 °C.

Hai Feng Cheng

Papers

Thermochromic VO2 Thin Film Prepared by Post Annealing Treatment of V2O5 Thin Film

Infrared Emissivity of Capacitive Frequency-Selective Surfaces and its Application in Radar and IR Compatible Stealth Sandwich Structures

Reducing Thermal Conductivity of Polymer Derived SiC Ceramics via Microwave Sintering Processing

Comparison of Hollow-Porous and Solid Carbon Fibers as Microwave Absorbents

The Influences of Annealing Temperature on the Crystal Phase and Microstructure of the WO3 Thin Film