Pankaj Tripathi

Enhancement of birefringence of liquid crystals with dispersion of poly (n-butyl methacrylate) (PBMA)

In this work, we have reported the temperature dependence of birefringence for pure liquid crystals (LCs) and liquid crystal-polymer composite (LC-PC) systems. The enhancement of the electro-optical performances is higher in LC with poly (n-butyl methacrylate) polymer. The temperature dependence of the birefringence (Δn) were determined from the transmitted intensity. Dielectric study of pure LC system and LC-PC system has also been presented as a function of frequency. The observed results may be attributed to the occurrence of polymeric domains (chains) formed in LCs. The complete study reveals that the use of polymeric materials in nematic LCs is effective to improve the response in phase shifters devices.

Low Temperature Sintering and Characterization of MgO-B2O3-SiO2 Glass-Ceramics for LTCC Substrate Applications

ABSTRACT MgO-B2O3-SiO2 (MBS) glass-ceramics, with and without TiO2 as additive, has been prepared by sintering at 900oC and their structural, thermal and dielectric properties have been studied. The XRD and SEM studies show that the crystallization increases with addition of nucleating agent TiO2. The per cent thermal expansion decreases as TiO2 content increases. The value of dielectric constant increases with increasing wt% of TiO2 in MHz and GHz frequency range. The dielectric constant values lie in between 3 and 5 in the frequency range of 13.5–18 GHz and in between 9 and 11 at 1 MHz frequency. The microwave dielectric constants of the specimen have been found to be strongly dependent on TiO2 content. Due to low dielectric constant and low sintering temperature, this glass-ceramics is an attractive material for low temperature co-fired ceramics (LTCC) application. GRAPHICAL ABSTRACT

Manifestation of strong magneto-electric dipolar coupling in ferromagnetic nanoparticles−FLC composite: evaluation of time-dependent memory effect

ABSTRACT Rod-shaped 5 wt.% copper-doped ZnO (ZnO:Cu2+) ferromagnetic nanoparticles (NPs), prepared by hydrothermal method, were dispersed in ferroelectric liquid crystal (FLC) named Felix 17/100. The effect of ferromagnetic NPs on the physical properties of FLC material (Felix 17/100) has been investigated by dielectric, electro-optical and polarising optical microscopic methods. A noteworthy time-dependent memory has been observed in the NPs-dispersed FLC composite attributed to the coupling of magnetic field associated to NPs with the director orientation of FLC. Improvement in spontaneous polarisation and dielectric susceptibility of FLC material has been ensued with the addition of ferromagnetic NPs. Faster electro-optic response, at lower applied voltage, has also been observed in NPs-dispersed FLC composite. These changes are accredited to the magneto-electric dipolar coupling existing due to the interactions between magnetic-dipole and electric-dipole moments of magnetic NPs and FLC material, respectively. The formation of periodic domains capable to show memory effect has been observed in composite. The observed time-dependent memory was confirmed by dielectric and electro-optical methods. FLC material enriched with the properties of ferromagnetic NPs can be utilised in advanced multifunctional optical devices, time-dependent memory-based security devices and computational purposes. Graphical Abstract

Synthesis and catalytic activity of Cu–Cr–O–TiO2 composites for the thermal decomposition of ammonium per-chlorate: enhanced decomposition rate of fuel for solid rocket motors

This study presents the sol–gel synthesis of Cu–Cr–O·nTiO2 particles calcined at different temperatures and their catalytic effects on thermal decompostion of AP. The study focuses on the impact of crystallite size, shape and concentration of TiO2 in the catalyst composition on the thermal decomposition behaviour of ammonium per-chlorate (AP). During synthesis, the molar ratio of Cu/Cr was kept to 0.7 and TiO2 nanoparticles were added into Cu–Cr–O–citric acid solution at different molar ratios to form three different compositions of the catalyst Cu–Cr–O·nTiO2 (n = 0.5, 0.7 and 0.9 mol%). The effect of temperature on the thermal, structural and spectroscopic properties of the different Cu–Cr–O compositions was also studied by calcining them at two different temperatures, 300 and 1050 °C. Post synthesis characterizations of the prepared catalysts were carried out by using XRD, FT-IR, SEM, EDAX and TEM (with SAED pattern) techniques. The desired qualification of Cu–Cr–O–citric acid (the precursor of the catalyst) and the final compositions of the catalysts were carried out by using thermogravimetric and differential thermal analysis (TG-DTA) techniques. The efficiency of the synthesized catalysts was evaluated on thermal decomposition behaviour of AP using TG-DTA techniques. The Cu–Cr–O·nTiO2 composition with the molar ratio of n = 0.7 was found to be the most efficient catalyst for decomposition of AP; it was much better than other laboratory prepared samples (n = 0.5 and 0.9) as well as the industrial catalyst (i.e. activated copper chromite (ACR); Cu–Cr–O). Further experimental work showed that addition of 10 wt% Cu–Cr–O·0.7TiO2 into AP significantly lowered the AP decomposition temperature to 306 °C from 385 °C and was accompanied by a very sharp exothermic peak indicating a single stage decomposition. The excellent finding of the study was also verified by heat of reaction (i.e. calibrated delta H) values. This study finds potential application due to the remarkable enhancement in the thermal decomposition rate of the AP used as oxidizer in propellant of solid rocket motors (SRMs) and space vehicles (SVs) at lower decomposition temperature. The fast decomposition rate of oxidizer at lower decomposition temperature enhances the efficiency of fuel which ultimately will enhance the efficiency of SRMs and SVs.

Design of rectangular dielectric resonator antenna using glass added Barium Strontium Titanate

A compact aperture-coupled dual segment rectangular dielectric resonator antenna (ACDS-RDRA) is described in this paper. The antenna consists of Teflon (εr = 2.1) as lower segment and liquid phase (glass) sintered Barium Strontium Titanate (BST) namely Ba0.5Sr0.5TiO3 (εr = 27) as upper segment. 10 wt% of PbO-BaO-B2O3-SiO2 glass was added to lower the sintering temperature from 1050 °C to 800 °C and increase the dielectric constant of BST. The input and radiation characteristics of ACDS-RDRA are investigated through simulation using Ansys HFSS software. The antenna provides the simulated input impedance bandwidth of 690 MHz (8.80 - 9.49 GHz) with a simulated peak gain of 6.63 dB at 9.1 GHz. The antenna provides broadside radiation patterns in both E-and H-planes of the antenna with fairly low cross-polarization levels in E-plane were obtained. Such RDRA can find potential applications in radar and satellite communication.

Stacked cylindrical dielectric resonator antenna with metamaterial as a superstrate for enhancing the bandwidth and gain

A dual segment cylindrical dielectric resonator antenna with metamaterial superstrate is presented in this paper. The metamaterial cover acting as a converging lens is sharply increasing the gain of the proposed antenna and is also responsible for increasing the bandwidth. The proposed antenna is having a better impedance matching (less than -10 dB return loss) in a wide frequency band with a bandwidth of 2.12 GHz (8.49-10.61 GHz) and peak gain of 12.86 dB. The proposed antenna is presented with parametric analysis of some key parameters. Broadside radiation pattern is obtained without metamaterial, while directive radiation pattern with narrow beamwidth is obtained with metamaterial using as a superstrate. The gain characteristics of the proposed antenna are also presented.

Dielectric Relaxation Spectroscopy of Liquid Crystal in Nematogenic Mesophase

ABSTRACT In the present study, we report the dielectric behavior of a high temperature nematic liquid crystal (NLC) in both the planar as well as homeotropic alignments. To understand the mechanism of such high temperature NLC, we have performed dielectric spectroscopy in frequency range 100 Hz to 10 MHz. The different dielectric parameters, viz., effective dielectric permittivity and dielectric anisotropy of the sample have been determined with the variation of frequency and temperature. It is found that the dielectric parameters depend on dipole moment and rotation of side chain of molecule. The phase transition of this high temperature NLC has been confirmed by the DSC study.

Compact dual segment cylindrical dielectric resonator antenna for X-band applications

The simulation and experimental studies of a compact dual segment cylindrical dielectric resonator antenna (DRA) for X-band applications are presented in this paper. The antenna consists of Teflon (εr = 2.1) as lower segment and ceramic material (Sr La2 Mg2 W2 O12) of dielectric constant εr = 22 and loss tangent tan δ = 0.0021 as upper segment. The simulation study of the antenna is carried out using Ansofts HFSS software. Parametric study of the antenna has been carried out by varying the Teflon and probe heights. The simulated and measured bandwidths of the proposed antenna are 1.11 GHz and 1.69 GHz respectively whereas corresponding values of average gain are 6.39 dB and 6.43 dB. The broadside radiation patterns are obtained (in both E-and H-planes) in the applicable frequency range with fairly low cross-polarization levels in E-plane. The experimental results are in good agreement with simulated results.

Impact of silica nanoparticles dispersion on the dielectric and electro-optical properties and absorption spectra of host ferroelectric liquid crystal

ABSTRACT The present work concerns with the investigation of the effect of dispersion of Silica (SiO2) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO2 NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO2 NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation Ps and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions. Graphical Abstract

An aperture coupled dual segment RDRA on glassceramic LTCC substrate

In this paper, a dual segment rectangular dielectric resonator antenna (RDRA) designed on an MgO-B2O3-SiO2-TiO2 (MBST) glass-ceramic LTCC substrate is described. The simulation results for the RDRA on MBST substrate is compared with those for RDRA on FR4 substrate. Another section of the simulation study includes the effect of composite substrates i.e. FR4-air (FR4C) and MBST-air (MBSTC) substrates on the antenna performance. From the simulation study of these substrate configurations, it was observed that in case of FR4 uniform substrate, impedance bandwidth of 670 MHz was achieved with E-plane radiation pattern beamwidth of 84° and antenna gain of 6.54 dB. While in case of MBST uniform substrate, impedance bandwidth of 680 MHz is achieved along with E-plane radiation pattern beam width of 90° and same antenna gain of 6.54 dB. Thus similar antenna bandwidth and gain is observed with some increase in E-plane beam width in the later case. When the composite substrates are compared, FR4C provides antenna gain of 6.60 dB at its resonating frequency of 9.06 GHz and MBSTC provides little higher gain of 6.63 dB at its resonating frequency of 8.99 GHz. No changes in the resonant frequency and bandwidth are observed for composite FR4C and MBSTC substrates when compared with the corresponding uniform FR4 and MBST substrates respectively. Since, the proposed MBSTC antenna provides similar antenna performance with reduced material and lower cost, it can be an alternative for conventionally available substrates. The simulation study was performed using Ansys HFSS software.