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Basu S.,Indian Institute of Technology Delhi | Singhi M.,Ambedkar Institute of Advanced Communication Technologies and Research | Satapathy B.K.,Indian Institute of Technology Delhi | Fahim M.,University of Delhi
Polymer Composites | Year: 2013

A series of nanographene filled polystyrene (GPS) nanocomposites was prepared by in situ polymerization of styrene in the laboratory. The concentration of graphene was changed in the step of 0.25 wt% and a total of eight composites (including control) were prepared to obtain a threshold concentration of graphene. These composites, prepared by in situ polymerization followed by compression moulding, were characterized for their structural (using XRD), morphological (SEM), thermal (DSC, TGA, DTGA), dielectric behavior (ε′, ε′″) and DC conductivity. It was observed that the thermal stability as well as electrical and rheological properties of graphene-polystyrene nanocomposites significantly improved due to the homogeneous dispersion, intercalation and exfoliation of the graphene layers in the Polystyrene matrix. It was also observed that at room temperature dielectric constant (ε′) decreased with increasing concentration of graphene and reached a minimum at a certain filler concentration of 0.25 wt% (PSG025) when frequency is kept constant. Rheological study showed an improvement in the storage modulus (G′) with incorporation of graphene as nanofiller. Loss modulus (G′) and complex viscosity (η*) also increased with increasing graphene weight percentage. Relaxation time also increased at high graphene loading because of the pseudo-solid like behavior of polymer melt. © 2013 Society of Plastics Engineers. Source


Gautam A.K.,Gb Pant Engineering College | Kr Kanaujia B.,Ambedkar Institute of Advanced Communication Technologies and Research
Microwave and Optical Technology Letters | Year: 2013

A novel dual-band asymmetric slit with defected ground structure microstrip antenna for circular polarization (CP) operation is proposed. In which, the lower resonant band is excited by cutting asymmetric slit on square microstrip antenna, and a new concept of defected ground with truncated corners structure is used to excite upper resonant band. The antenna is practically fabricated and simulated. Measured results show a good agreement with simulated results. Antenna is compact in size and shows a good quality of polarization at both resonant bands. Antenna shows the bandwidth of 7.5% (2.30-2.48 GHz) and 2.94% (3.80-3.9 GHz) at lower and upper bands, respectively. The antenna also shows 40 and 11 MHz, 3-dB axial ratio bandwidth at lower and upper bands, respectively. The return loss and radiation pattern of the proposed antenna remain consistent for both resonant bands. Copyright © 2013 Wiley Periodicals, Inc. Source


Gautam A.K.,Gb Pant Engineering College | Chandel R.,Gb Pant Engineering College | Kr Kanaujia B.,Ambedkar Institute of Advanced Communication Technologies and Research
Microwave and Optical Technology Letters | Year: 2013

A novel CPW-fed hexagonal-shape monopole-like ultrawideband (UWB) antenna is proposed for UWB applications. The proposed antenna posses a method to minimize the monopole antenna by using a hexagonal shape over the conventional monopole patch antenna to lower the height of the antenna. The ground is vertically extended toward two sides of the single radiator. Therefore, the large space around the radiator that is usually wasted can be effectively saved. The antenna is practically fabricated and simulated. Measured results show a good agreement with simulated results. The prototype with very compact overall size of 25 × 23 × 1.6 mm3 achieves good impedance matching, stable radiation patterns, and constant group delay over an operating bandwidth of 2.71-12.61 GHz (9.9 GHz). © 2013 Wiley Periodicals, Inc. Source


Gautam A.K.,G B Pant Engineering College | Yadav S.,G B Pant Engineering College | Kanaujia B.K.,Ambedkar Institute of Advanced Communication Technologies and Research
IEEE Antennas and Wireless Propagation Letters | Year: 2013

A novel coplanar waveguide (CPW)-fed compact ultrawideband (UWB) microstrip antenna is proposed for ultrawideband applications. The proposed antenna posseses a method to minimize the monopole antenna by loading of inverted L-strip over the conventional monopole patch antenna to lower the height of the antenna. The ground was vertically extended toward two sides of the single radiator. Therefore, the large space around the radiator that is usually wasted can be effectively saved. The antenna is practically fabricated and simulated. Measured results show a good agreement with simulated results. The prototype with overall size of 25 × 25 × 1.6 mm3 achieves good impedance matching, constant gain, stable radiation patterns, and constant group delay over an operating bandwidth of 2.6-13.04 GHz (10.44 GHz). © 2013 IEEE. Source


Singhi M.,Ambedkar Institute of Advanced Communication Technologies and Research | Fahim M.,University of Delhi
Polymer Composites | Year: 2012

In this work, a series of polymer composites was prepared by in situ polymerization of methylmethacrylate (MMA) as a monomer and sonicated nanographite particles (∼400 nm) as conductive fillers. The concentration of nanographite particles was changed in the step of 0.25 wt% in the monomer and five composites having a filler concentration of 0.25, 0.50, 0.75, 1, and 1.5 wt% respectively were prepared. The composites were characterized for their morphology, thermal, and dielectric behavior. Room temperature dielectric behavior of the composites was studied at six different frequencies of 100 Hz, 1, 10, 100, 500 kHz, and 1 MHz. Temperature-dependent dielectric properties was studied in the temperature range from 30 to 150°C at the above frequencies. It was interesting to note that at room temperature dielectric constant (ε′) decreased with increasing concentration of nanographite and reached a minimum at a filler concentration of 0.75 wt%. Dielectric relaxation behavior was observed in the temperature versus tan δ curves. The dielectric peak shifted to higher temperatures with increase in frequency and vice-versa. © 2012 Society of Plastics Engineers. Source

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