National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Density field visualization of a Micro-explosion using background-oriented schlieren

Abstract: The determination of flow field properties of large-scale explosions which is necessary for better understanding and flow modeling is rather challenging and difficult. Recent studies show that micro-explosions can be an acceptable substitute. However, quantitative determination of the flow field is still a challenge given the extremely short duration and spatio-temporal evolution of the flow. Determination of shock wave propagation properties from a blast using available flow diagnostic techniques is difficult. The complex nature of the chemical reaction process and spatial and temporally varying flow field imposes serious limitations on applied diagnostics. Most of the earlier works are qualitative in nature (Dewey 2001; Kleine et al. 2003; Klingenberg 1977) where the blast wave properties are derived through Rankine–Hugoniot relations. Sommersel et al. (2008) and Mizukaki et al. (2011) have used the Natural Background Oriented Schlieren technique on large and laboratory scale blasts respectively. They used the BOS technique to get the time-radius relationship of the blast wave; however no direct quantitative density field could be obtained. In this study, density field of a spatial-temporally evolving blast wave generated from a small microexplosion (Obed et al. 2012) is documented using Background Oriented Schlieren (BOS). A preliminary attempt at application of BOS to a micro-explosion was carried out by Suriyanarayanan et al. (2011). In the present study the three dimensional density field was reconstructed using the filtered back projection technique at several instants of time in order to capture the evolution of the density field of the blast wave.

Design of airborne radome using Swastika-shaped metamaterial-element based FSS

Abstract: This paper presents a novel Swastika-shaped metamaterial structure which exhibits metamaterial behavior (μ- and e-negative) in distinct frequency ranges. The EM analysis of metamaterial (MTM) structure is carried out using transmission line transfer matrix method and validated with full-wave method based software package. The proposed structure is observed to exhibit bandpass frequency selective characteristics with very good transmission efficiency in the frequency range of 8.5 GHz–10.3 GHz. Further, a planar multilayered radome wall configuration is designed which consists of a thick Arlon layer embedded with Swastika-shaped MTM FSS as the middle layer backed by two thin quartz-based laminations on each side. Further, the thickness of radome wall is optimized sector wise in view of airborne radome applications.

Improved Corrosion Protection of Magnesium Alloys AZ31B and AZ91 by Cold-Sprayed Aluminum Coatings

Abstract: Magnesium (Mg) alloys have a high strength/weight ratio, high dimensional stability, good machinability, and the ability to be recycled. However, their poor corrosion resistance in humid environments limits their usage for exterior aerospace components. This study aims to improve the corrosion resistance of two Mg alloys (AZ31B and AZ91) by using aluminum coatings. The latter have been deposited by a low pressure and temperature cold spray process. An aluminum powder (60 wt%) with a particle size ranging between 1 and 8 µm and nickel powder (40 wt%) with a particle size of about 70 µm were blended and used as feedstock powder. The coating thickness was about 240 μm. Its densification was achieved by the in-situ hammering effect of the nickel particles. The shot-peening effect also resulted in an enhanced coating hardness. The microstructure, mechanical properties, and corrosion resistance of the coatings have been investigated. They showed that the aluminum had a face centered cubic structure. Potentiodynamic polarization tests were performed along with a combination of materials characterization techniques to assess the corrosion resistance of the coatings when immersed in a 3.5 wt% NaCl solution for long durations. The results revealed that the corrosion resistance increased with the immersion time because of the formation of a protective oxide layer on the surface. These results were supported by elemental and structural analyses. This study shows that cold-sprayed aluminum coatings are a promising candidate for enhancing the corrosion resistance of AZ31B and AZ91Mg alloys compared to other thermal spray processes.

Active Terahertz Metamaterial for Biomedical Applications

Abstract: Terahertz (THz) spectroscopy is gaining momentum as a tool for imaging in the field of biomedical engineering. This increase in popularity is due to the non-invasive, non-ionizing nature of terahertz radiation coupled with its propagation characteristics in water, which allows the operator to obtain high-contrast images of skin cancers, burns, etc. without detrimental effects. In order to tap this huge potential, researchers worldwide are aiming to build highly efficient biomedical imaging systems by introducing terahertz absorbers into biomedical detectors. The biggest challenge faced in the fulfilment of this objective is the lack of naturally occurring dielectrics, which is overcome with the use of artificially engineered resonant materials, viz. the metamaterials. This book describes such a metamaterial-based active absorber. The design has been optimized using particle swarm optimization (PSO), eventually resulting in an ultra-thin active terahertz absorber. The absorber shows near unity absorption for a tuning range of terahertz (THz) application.