Department Of Physics

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    X-band Scattering Characteristics of Nickel/Nanocarbon Composites for Anti-tracking Application
    (John Wiley and Sons Inc, 2021-10-16T00:00:00) Alegaonkar, Ashwini P.; Tripathi, Krishna C.; Baskey, Himangshu B.; Pardeshi, Satish K.; Alegaonkar, Prashant S.
    Creating clutter in high resolution seeking trackers is of tactical importance which could be achieved by the electromagnetic interference (EMI) shielding. Herein, we report on X-band (8�12 GHz) scattering performance of nickel/nano-carbon-composites for architecting an effective EMI shield. Composite material is prepared by facile, one step, solid state combustion technique with variable 1�5 Ni % and characterized using x-ray diffractometry, infrared-,uv-visible, energy dispersive x-ray spectroscopic techniques, and scanning electron microscopy. Further, composite, transformed into coaxial and rectangular shaped specimens, are subjected to s-parameter and reflection loss studies, respectively, over 8�12 GHz. In analysis, incorporation of Ni, majorly, forms crystalline NiO (d[111]) and Ni2O3 (d[002]) phases dispersed within the nanocarbon network which are responsible to create asymmetric stretching bond between Ni?O?C ((Formula presented.) ?1130 cm?1). Dispersion facilitates synergistic magneto-dielectric coupling to provide long range ordering of polarization, mainly, via electronic transitions between Ni?3d to O?2p states to engage incident microwave power effectively. At highest Ni inclusion, composite showed>95 % shielding effectiveness with infinite bandwidth and>99 % return loss@8.97 GHz matching frequency. � 2021 Wiley-VCH GmbH
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    Shock wave hydrodynamics of nano-carbons
    (Elsevier Ltd, 2021-02-02T00:00:00) Chinke, Shamal L.; Sandhu, Inperpal S.; Bhave, Tejashree M.; Alegaonkar, Prashant S.
    Dynamic deformation of nano-carbons by shock waves is an important object in technological applications as well as in basic sciences. We report, on hydrodynamic response of two types of nano-carbon systems: graphene nano-flakes (GNF) and carbon nano-spheres (CNS) by subjecting them to the Klosky bar shock test (at strain rate 102�104/s). Data of stress (?), strain (?), and strain rate (?) were obtained with time to analyse the behaviour of constitutive parameter (?�?). In elastic region GNF showed superior stress sensitivity at least by fivefold over CNS, whereas, stress accumulation ability of CNS was found to be ten times better than GNF. In plastic region both the systems were behaved quiet complexly. They comprised of various stages of deformation like inter�particle separation, micro�structure gliding, fracture, and perforation. To obtain hydrodynamic variables a few thermodynamic assumptions like matrix homogeneity, linear volume deformity, negligible temperature rise were made to set up the Lagrange�Rankine�Hugoniot model. Interplay of built�in pressure (P), particle velocity (UP), shock velocity (US), specific volume (V/VO), density (?), shock energy (E), behind and ahead of the shock wavefront led to the establishment of the equation of state for the system. Theoretical shock profile was vis-�-vis compared with the experimentally obtained shock results. Distribution of impulse pressure over the topology of the nano-carbons was examined that exhibited non-uniform shock energy dissipation pattern with peak pressure ~250 N/m2. Our calculations revealed that, almost ~65% shock energy was damped within GNF and ~89% in CNS. Details of the analysis are presented. � 2021 Elsevier B.V.