Sekhar Ranjan Bhadra Chaudhuri

Bio: Sekhar Ranjan Bhadra Chaudhuri is an academic researcher from Indian Institute of Engineering Science and Technology, Shibpur. The author has contributed to research in topics: Slot antenna & Patch antenna. The author has an hindex of 15, co-authored 69 publications receiving 798 citations. Previous affiliations of Sekhar Ranjan Bhadra Chaudhuri include Indian Association for the Cultivation of Science & Indian Statistical Institute.

Bandgap and optical transitions in thin films from reflectance measurements

Abstract: A new formulation and method are presented for evaluating bandgap, optical transitions and optical constants from the reflectance data for films deposited onto a non-absorbing substrate.

A Compact Dual-Band Dual-Polarized Omnidirectional Antenna for On-Body Applications

Abstract: A compact dual-band dual-polarized wearable antenna for on-body communication in the 2.45 and 5.8 GHz ISM bands is presented. The antenna is linearly polarized (LP) at 2.45 GHz and circularly polarized (CP) with the conical pattern at 5.8 GHz, which is suitable for the multisensor link network. By using the characteristic modal analysis initially, the ground plane has been miniaturized and optimized to radiate an omnidirectional beam in the horizontal plane with the excitation of the $\lambda $ /4 resonant mode. The higher order band at 5.8 GHz has been realized by the excitation of the $3\lambda $ /4 resonant mode of the same L-shaped slot. These two odd-order modes radiate horizontally polarized omnidirectional patterns. The combination of the vertical polarization generated from the top-loaded patch antenna along with the $3\lambda $ /4 mode from the L-shaped slot resulted into omnidirectional CP in the 5.8 GHz band. Furthermore, enhancement in axial ratio bandwidth is achieved with the addition of dielectric superstrate over the feed layer. Bending sensitivity study to emphasize for conformal applications, transmission loss along with specific absorption rate analysis has been performed for on-body characterization. The simulated and measured results are found to be in good agreement.

A Miniaturized Ring Slot Antenna Design With Enhanced Radiation Characteristics

Abstract: The design of a miniaturized CPW-fed ring slot antenna using interdigitated slits is presented. The fundamental resonant frequency of the ring slot antenna was reduced significantly using an interdigitated slit-loaded structure. A further reduction in resonant frequency to 54.46% of the unloaded resonant frequency of the ring slot antenna was also achieved using multiple interdigitated slits inside the ring, causing the antenna to almost reach the electrically small limit. Thereafter, the antenna characteristics of the electrically small antenna is significantly enhanced using a low impedance metamaterial slab design working under normal incidence, leading to a considerable reduction in superstrate height. Particularly, the directivity and efficiency of the electrically small antenna is significantly improved with the incorporation of the low-profile superstrate. In addition, good matching characteristics are obtained for the miniaturized antenna without the necessity of a matching network together with improved bandwidth.

Some aspects of surface roughness in polycrystalline thin films: optical constants and grain distribution

Abstract: A modified formulation and new method have been suggested to derive meaningful information on the optical constants, grain size and grain distribution of polycrystalline thin films where surface roughness plays an important part through the contributions arising out of scattered transmission and diffuse reflection. It was observed that this method successfully described the experimental observations in polycrystalline CuInSe2 and CdSe films.

Compact Circularly Polarized Wide-Beamwidth Fern-Fractal-Shaped Microstrip Antenna for Vehicular Communication

Abstract: A compact circularly polarized wide-beamwidth patch antenna is presented here. The proposed antenna can be used for blind spot detection in the smart vehicle. Miniaturization and beamwidth enhancement of the antenna are the main areas of discussion. The size of the patch becomes 44% smaller than the conventional patch by folding the edge of the radiating patch with loading slots. Due to the small size, it can be placed in the compact aerodynamic wireless devices. The half power beamwidth is enhanced by 100 $ ^{\circ }$ , and the axial ratio beamwidth is maximized by 187 $ ^{\circ }$ with the help of a surrounding dielectric substrate and the metallic block as necessitated by intelligent transportation system applications. The proposed antenna can capture signals from a wide elevation angle and a complete azimuth range to cover the entire blind spot zone. The impedance bandwidth of the antenna is 410 MHz with 90-MHz 3-dB axial ratio bandwidth.

Response to FCC 98-208 notice of inquiry in the matter of revision of part 15 of the commission's rules regarding ultra-wideband transmission systems

Abstract: In general, Micropower Impulse Radar (MIR) depends on Ultra-Wideband (UWB) transmission systems. UWB technology can supply innovative new systems and products that have an obvious value for radar and communications uses. Important applications include bridge-deck inspection systems, ground penetrating radar, mine detection, and precise distance resolution for such things as liquid level measurement. Most of these UWB inspection and measurement methods have some unique qualities, which need to be pursued. Therefore, in considering changes to Part 15 the FCC needs to take into account the unique features of UWB technology. MIR is applicable to two general types of UWB systems: radar systems and communications systems. Currently LLNL and its licensees are focusing on radar or radar type systems. LLNL is evaluating MIR for specialized communication systems. MIR is a relatively low power technology. Therefore, MIR systems seem to have a low potential for causing harmful interference to other users of the spectrum since the transmitted signal is spread over a wide bandwidth, which results in a relatively low spectral power density.

Compound Copper Chalcogenide Nanocrystals

Abstract: This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.