Polarization Independent Dual-band Metamaterial Based Radar Absorbing Structure (RAS) for MillimeterWave Applications

The EM analysis of multi-layered metamaterial based radar absorbing structure (RAS) with dual-band characteristics in millimeter wave frequency regime has been carried out in this paper using transmission line transfer matrix (TLTM) method for TE and TM polarizations. The proposed metamaterial-based RAS exhibits dual-band characteristics at centre frequencies 120 GHz and 175 GHz with very low power reflection. It absorbs more than 90% power of incidence wave over the frequency range from 111-131 GHz at first resonance and from 164.5-185 GHz at second resonance without metal backing plate, which is desirable for stealth applications. It also showed very low (< 1.6%) transmission over the frequency of interest for both TE and TM polarizations. The proposed metamaterial-RAS has potential applications in the design of multi-band sensor systems and RCS reduction in millimeter wave frequency regime.     

Electromagnetic Performance Analysis of Novel Multi-band Metamaterial FSS for Millimeter Wave Radome Applications

The electromagnetic design and performance analysis of dual/ multi-band metamaterial frequency selective surface (FSS) structures have been carried out for radome applications in microwave and millimeter wave frequency regimes. The proposed metamaterial FSS structure, consisting of cascaded MNG (mu-nega -tive) and DPS (double positive) layers, exhibits dual-band transmission responses at V-band and W-band. Excellent transmission efficiency (more than 95%) has been obtained over the frequency range 45.8-53.1 GHz at first resonance, and from 93.0-97.1 GHz at second resonance. The incorporation of additional DPS layer to the proposed metamaterial-FSS structure facilitates multiband bandpass characteristics at 30 GHz (in Ka-band), 64 GHz (in V-band), and 93.6 GHz (in W-band). The reflection and insertion phase delay characteristics are also analyzed at high incidence angles in view of streamlined airborne nosecone radome applications.     

Oxidative control of surface plasmon resonance of bismuth nanometal in bismuth glass nanocomposites

We demonstrate here a novel oxidative process to control the metallic bismuth (Bi°) nanoparticles (NPs) formation in bismuth glass nanocomposites by using KClO₄ and KNO₃ as oxidant instead of usual reducing technique. The formation of Bi° NPs has been monitored by its distinctive surface plasmon resonance (SPR) band at 460 nm in the UV–vis absorption spectra. It is further confirmed by the TEM images of Bi° NPs using KNO₃ and KClO₄ which show the formation of spherical Bi° NPs of 2–15 nm sizes and the SAED pattern reveals their crystalline rhombohedral phase. Using this technique it is possible to control the SPR band of nanobismuth (Bi°) in bismuth glasses.     

Effects of SiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript> fillers on thermal and dielectric properties of eco-friendly bismuth glass microcomposites of plasma display panels

The effects of SiO₂ (amorphous) and TiO₂ (crystalline, rutile) fillers on softening point (T _s), glass transition temperature (T _g), coefficient of thermal expansion (CTE), and dielectric constant (ɛ) of zinc bismuth borate, ZnO-Bi₂O₃-B₂O₃ (ZBIB) glass microcomposites have been investigated with a view to its use as the white back (rear glass dielectric layer) of plasma display panels (PDPs). The experimentally measured properties have also been compared with those of theoretically predicted values. Both the experimental and theoretical trends of these properties with added filler contents correlate very well. The interaction of fillers with glass which occurred during sintering at 560°C has also been monitored by XRD and FTIR spectroscopic analyses. The microstructures and distribution of fillers in the glass matrix have been analyzed by SEM images. It is observed that the fillers have partially dissolved in the glass at the firing temperature leaving some unreacted filler as residue which results in ceramic-glass microcomposites. In consideration of the desired properties of white back of PDPs, the addition of TiO₂ filler to ZBIB glass is found to be more preferable than SiO₂ filler. The addition of 10 wt% TiO₂ filler yielded T _s, T _g, CTE and ɛ values of 560°C, 480°C, 82 × 10⁻⁷/K and 14·6 which are found to meet the desired values of <580°C, <500°C, <83 × 10⁻⁷/K and <15, respectively with respect to use of PD200 glass as substrate in PDP technology.     

Crystallization,mechanical, and optical properties of transparent,nanocrystalline gahnite glass‐ceramics

This paper describes the preparation of a transparent glass‐ceramic from the SiO₂‐K₂O‐ZnO‐Al₂O₃‐TiO₂ system containing a single crystalline phase, gahnite (ZnAl₂O₄). TiO₂ was used as a nucleating agent for the heat‐induced precipitation of gahnite crystals of 5‐10 nm. The evolution of the ZnAl₂O₄ spinel structure through the gradual formation of Al‐O bonds was examined by infrared spectroscopy. The dark brown color of the transparent precursor glass and glass‐ceramic was eliminated using CeO₂. The increase in transparency of the CeO₂‐doped glass and glass‐ceramics was demonstrated by UV‐visible absorption spectroscopy. EPR measurements confirmed the presence of Ce³⁺ ions, indicating that CeO₂ was effective in eliminating the brown color introduced by Ti³⁺ ions via oxidation to Ti⁺⁴. The hardness of the glass‐ceramic was 30% higher than that of the as‐prepared glasses. This work offers key guidelines to produce hard, transparent glass‐ceramics which may be potential candidates for a variety of technological applications, such as armor and display panels.     

A Block-Level Image Tamper Detection Scheme Using Modulus Function Based Fragile Watermarking

Intentional illegitimate modification in any digital image data is one of the general malversations in the existing digital domain. Therefore in this work, the authors have devised a fragile watermarking technique for the localization of illegitimate modifications in the digital image content effectually. The proposed technique detects forged digital image content strongly in the block-level of two successive pixels. This scheme is performed at the block level, where the actual image is partitioned into non-overlapping blocks of size (1?×?2) pixels. Afterward, the block-level authentication code is generated from the MSB of two successive pixels of each block using averaging and modulus operations. The generated authentication code/watermark is encrypted using a logistic-map-based chaotic key series. The encrypted authentication code is embedded into two successive pixels of the corresponding block. Further, any form of forgery in the watermarked image can be detected by comparing its extracted authentication code and regenerated authentication code. The proposed procedure is successfully experienced on a variety of grayscale images, and the experimental results exhibit that watermarked images generated by this scheme are of considerably high quality in terms of PSNR, IF, and SSIM. The proposed method is capable of efficient forgery detection by achieving very high accuracy, NC, and true positive rate while maintaining considerably low false-positive and false-negative rates.

     

Mica (KMg3AlSi3O10F2) based glass-ceramic composite sealant with thermal stability for SOFC application

In this work, pre-synthesized fluorophlogopite mica (KMg₃AlSi₃O₁₀F₂) crystalline powder was added into potassium-magnesium boro-alumino-silicate (K₂O–MgO–B₂O₃–Al₂O₃–SiO₂) glass powder to synthesize glass-ceramic composite (GCC) sealant for solid oxide fuel cell (SOFC) application. The basic purpose was to report the influence of KMg₃AlSi₃O₁₀F₂ on microstructure, thermal expansion and volume shrinkage behavior of GCCs in terms of their SOFC sealing ability. The predominant crystalline phase was also identified as fluorophlogopite mica (KMg₃AlSi₃O₁₀F₂) by X-ray diffraction in the GCCs heat-treated at 900 °C (for 2 h) followed by 800 °C (for 10 h). Higher thermal expansion (10.65–10.81 × 10^?6/K at 50–800 °C) compatible with SOFC components (metallic electrode/interconnect, ceramic electrolyte) was realized for 5–10 wt % mica containing GCC. However, it was found decreased linearly with adding further KMg₃AlSi₃O₁₀F₂ content (20–40 wt%) in the composites. GCC with 5 wt % of mica was stable under thermal cycling testing and no significant degradation was observed in thermal expansion till 10 cycles. Field emission scanning electron microscopy revealed the spherical shaped nanocrystallites morphology of those GCCs and that was ascribed for their compact bonding with SOFC components. Heating stage microscopy (HSM) ensured the lower softening temperature (752 ± 7 °C) for 5 wt % mica containing GCC which furthermore showed 11–13% volume shrinkage (to ensure the self-healing) in SOFC operating temperature. In a summary, the above factors confirmed the suitability of 5 wt % mica (KMg₃AlSi₃O₁₀F₂) containing K₂O–MgO–B₂O₃–Al₂O₃–SiO₂ system (GCC) for SOFC sealant application.