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.

Dielectric, ferroelectric and piezoelectric properties of (1 − x)[Pb0.91La0.09(Zr0.60Ti0.40)O3]–x[Pb(Mg1/3Nb2/3)O3], 0 ≤ x ≤ 1

Abstract: The dielectric, ferroelectric, and piezoelectric properties of ceramic materials of compositions (1 − x)[Pb0.91La0.09(Zr0.60Ti0.40)O3]–x[Pb(Mg1/3Nb2/3)O3], x = (0, 0.2, 0.4, 0.6, 0.8, and 1.0) were studied. The above compositions were prepared by mixing the individual Pb0.91La0.09(Zr0.60Ti0.40)O3 (PLZT) and Pb(Mg1/3Nb2/3)O3 (PMN) powders in order to design materials with different combination of piezo and dielectric properties. The powders were calcined at 850 °C for 4 h. The presence of various phases in the calcined powders was characterized by X-ray diffraction (XRD) technique. The compacts were prepared by uniaxial pressing and were sintered at 1250 °C for 2 h. The sintered compacts were electroded, poled at 2 kV/mm dc voltage and their dielectric, ferroelectric, and piezoelectric properties were measured. In general, it was observed that the dielectric constant, loss factor and the slimness of the ferroelectric curves increase with the PMN content while the remnant polarization, saturation polarization, and the coercive fields were decreased. It is now possible to design materials with a wide combination of d 33, K, and loss factor by varying PLZT and PMN ratio.

Control of vortex shedding from a circular cylinder using imposed transverse magnetic field

Abstract: Purpose – The purpose of this paper is to simulate the flow of a conducting fluid past a circular cylinder placed centrally in a channel subjected to an imposed transverse magnetic field to study the effect of a magnetic field on vortex shedding at different Reynolds numbers varying from 50 to 250.Design/methodology/approach – The two‐dimensional incompressible laminar viscous flow equations are solved using a second‐order implicit unstructured collocated grid finite volume method.Findings – An imposed transverse magnetic field markedly reduces the unsteady lift amplitude indicating a reduction in the strength of the shed vortices. It is observed that the periodic vortex shedding at the higher Reynolds numbers can be completely suppressed if a sufficiently strong magnetic field is imposed. The required magnetic field strength to suppress shedding increases with Reynolds number. The simulation shows that the separated zone behind the cylinder in a steady flow is reduced as the magnetic field strength is in...

Investigation of interface properties of sputter deposited TiN/CrN superlattices by low angle x-ray reflectivity

Abstract: Approximately 1.8 µm thick nanolayered multilayer coatings of TiN/CrN (also known as superlattices) were deposited on silicon (1 0 0) substrates at different modulation wavelengths (4.6–12.8 nm), substrate temperatures (50–400 °C) and substrate bias voltages (−50 to −200 V) using a reactive direct current magnetron sputtering system. The x-ray reflectivity (XRR) technique was employed to determine various properties of the multilayers such as interface roughness, surface roughness, electron density, critical angle and individual layer thicknesses. The modulation wavelengths of the TiN/CrN superlattice coatings were calculated using a modified Bragg's law. Furthermore, the experimental XRR patterns were simulated using theoretically generated patterns and a good fit was obtained for a three layer model, i.e. (1) top surface roughness layer, (2) TiN/CrN multilayer coating (approximately 1.8 µm) and (3) Ti interlayer (~0.5 µm) at the film–substrate interface. For the superlattice coatings prepared at a modulation wavelength of 9.7 nm, a substrate bias of −200 V and a substrate temperature of 400 °C the XRR patterns showed Bragg reflections up to 5th order, indicating well-defined periodicity of the constituent layers and relatively sharp interfaces. The simulation showed that the superlattice coatings prepared under the above conditions exhibited low surface and interface roughnesses. We also present the effect of substrate temperature and substrate bias, which are critical parameters for controlling the superlattice properties, onto the various interface properties of TiN/CrN superlattices.