Nagesh Thakur

Optimization Criteria for Optimal Placement of Piezoelectric Sensors and Actuators on a Smart Structure: A Technical Review

This article presents in a unified way, the various optimization criteria used by researchers for optimal placement of piezoelectric sensors and actuators on a smart structure. The article discusses optimal placement of piezoelectric sensors and actuators based upon six criteria: (i) maximizing modal forces/moments applied by piezoelectric actuators, (ii) maximizing deflection of the host structure, (iii) minimizing control effort/maximizing energy dissipated, (iv) maximizing degree of controllability, (v) maximizing degree of observability, and (vi) minimizing spill-over effects. Optimal piezoelectric sensor and actuator locations on beam and plate structures for each criterion and modes of interest are presented in a tabular form. This technical review has two objectives: (i) practicing engineers can pick the most suitable philosophy for their end application and (ii) researchers can come to know about potential gaps in this area.

Superparamagnetic La doped Mn–Zn nano ferrites: dependence on dopant content and crystallite size

Magnetic nanoparticles are found to exhibit exciting and substantially distinct magnetic properties due to high surface-to-volume ratio and several crystal structures in comparison to those discovered in their bulk counterparts. The properties of nanoparticles also largely depend on the route of their synthesis. In the present work, we report the synthesis of superparamagnetic nanoparticles of Mn0.5Zn0.5La x Fe2−x O4 (x = 0, 0.025, 0.050, 0.075, 0.1) ferrites by co-precipitation method. Structural, morphological and elemental study has been performed using x-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), FESEM and EDS. Different structural parameters (crystallite size, interplanar spacing and lattice constant) have been calculated from XRD. Formation of cubical spinel structure has been confirmed from XRD and FTIR. Cation distribution for all the samples has been proposed and used for calculation of various theoretical parameters. Magnetic properties have been investigated using vibrating sample magnetometer at room temperature and show transition between paramagnetic and superparamagnetic behavior. Maximum saturation magnetization and magnetic moment have been obtained at x = 0.050. The results are attributed to the solubility of La in Mn–Zn ferrite and the size of nanoparticles. The samples have also been analyzed for dielectric, electric and optical properties. For x ≤ 0.050, a blue shift in absorbance and photoluminescence measurements has been observed due to quantum confinement.

Resistivity dependent dielectric and magnetic properties of Pb(Fe0.012Ti0.988)O3 nanoparticles

High resistivity in nanostructured Pb(Fe0.012Ti0.988)O3 system prepared by using polyvinyl alcohol (PVA) in chemical route is observed. The PVA acts as a surfactant to limit the particle size. The Fe substitution for Ti controls the chemical stoichiometry and reduces the lattice distortion, i.e., c/a ratio, and hence the transition temperature reduces with Fe content. The phase structure, morphology, particle size, dc resistivity, and dielectric and magnetic properties of Pb(Fe0.012Ti0.988)O3 nanoparticles have been characterized by x-ray diffraction, transmission/scanning electron microscopy, source meter, LCR meter, and vibrating sample magnetometer. The results indicate that the nanosize particles have high resistivity, which improves the dielectric constant at high-frequency region and increases magnetization of the specimens. The observed variable-range-hopping conduction mechanism indicates that Fe doping leads to the occurrence of local defect states in the PbTiO3 lattice. The dispersionless dielec...

Effect of germanium addition on the physical properties of Se–Te glassy semiconductors

The effect of germanium addition on the physical properties, i.e. density, molar volume, compactness, number of lone-pair electrons, average coordination number, heat of atomization, mean bond energy, cohesive energy and glass-transition temperature, of (Se80Te20)100− x Ge x (x = 0, 2, 4, 6) bulk glassy alloys was investigated. The density of the glassy alloys is found to decrease with increasing Ge content. The molar volume and compactness of the structure of the glass were determined from the measured density. The mean bond energy is proportional to the glass-transition temperature. The cohesive energy of the samples has been calculated using a chemical bond approach and is correlated with an increase in the optical energy gap with increase in the Ge content. The heat of atomization was also calculated and correlated with the optical energy gap. The glass-transition temperature has been estimated using different methods and is found to increase with an increase of Ge content.

Optical parameters of ternary Te15(Se100−xBix)85 thin films deposited by thermal evaporation

Thin films of Te15(Se100−xBix)85 (x=0, 1, 2, 3, 4 and 5 at.%) glassy alloys were deposited by thermal evaporation (at 10−4 Pa) from bulk samples. Optical characterization of the films was done by analysing their transmission spectra taken in the spectral range 400–2300 nm. Swanepoels method was used to calculate the refractive index (n) and extinction coefficient (k). It was found that the refractive index increases with an increase in Bi content. The Wemple–DiDomenico single-oscillator approach was used to calculate the average band gap energy (Eo), dispersion energy (Ed) and static refractive index (no). The absorption coefficient (α) and film thickness were calculated from the transmission spectra of the films. The optical band gap (Eg) was estimated using Taucs extrapolation and was found to decrease from 1.37 to 1.21 eV with Bi addition from 0 to 5 at.% in glassy alloys. The decrease in optical band gap is explained on the basis of the decrease in cohesive energy of the samples and the difference of electronegativity of the atoms involved. The real (er) and imaginary parts (ei) of the dielectric constant for the films were also calculated and reported.

An optical study of amorphous (Se80Te20)100?xGex thin films using their transmission spectra

Optical constants (refractive index and extinction coefficient) have been studied for a-(Se80Te20)100−xGex (x = 0, 2, 4, 6) thin films using transmission spectra in the wavelength range 500–2500 nm. It is observed from optical transmission measurements that the optical energy gap (Eg) increases while the refractive index (n) and the extinction coefficient (k) decrease with the incorporation of Ge in the Se–Te system. The increase in the optical energy gap is interpreted by correlating the optical energy gap with the decrease in electronegativity and increase in the heat of atomization (Hs). The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model.

Facile Synthesis and Electrical Conductivity of Carbon Nanotube Reinforced Nanosilver Composite

Metal matrix nanocomposites reinforced with carbon nanotubes (CNTs) have become popular in industrial applications. Due to their excellent thermophysical and mechanical properties, CNTs are considered as attractive filler for the improvement in properties of metals. In the present work, we have synthesized noncovalently functionalized CNT reinforced nanosilver composites by using a modified molecular level mixing method. The structure and morphology of nanocomposites are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. The electrical conductivity of silver-CNT nanocomposites measured by the four-point probe method is found to be more than that of the pure nanosilver. The significant improvement in electrical conductivity of Ag=CNT nanocomposites stems from homogenous and embedded distribution of CNTs in a silver matrix with intact structure resulting from noncovalent functionalization. The low temperature sintering also enhances the electrical conductivity of Ag=CNT nanocomposites.

A non-isothermal crystallization study of Se85Te15 chalcogenide glass using differential scanning calorimetry

The calorimetric parameters of Se85Te15 glass have been investigated using differential scanning calorimetry under non-isothermal conditions at four different heating rates (5, 10, 15 and 20 °C min−1). The glass transition temperature and peak temperature of crystallization are found to increase with increasing heating rate. The apparent activation energy for glass transition and for the crystallization peak has been determined using different empirical approaches. The kinetic parameters are calculated using methods recently developed for non-isothermal conditions. The calculated value of the kinetic exponent indicates one-dimensional growth for Se85Te15 chalcogenide glass. The average values of activation energy for glass transition and crystallization are found to be equal to (267.82±3.9) and (152.13±16.9)  kJ mol−1, respectively. The ease of glass formation and fragility has also been studied.

Dielectric Relaxation Studies of Binary Mixtures of Ethanol and Chlorobenzene in Benzene Solution from Microwave Absorption Data

Dielectric relaxation of different molar concentrations of ethanol (C2H5OH) in binary mixtures of ethanol and chlorobenzene in benzene solutions has been studied at 9.883 GHz by using standard standing microwave techniques and Gopala Krishna’s single frequency concentration variation method at different temperatures (25 °C, 30 °C, 35 °C, and 40 °C). It was found that the dielectric relaxation time varies linearly with variation in the molar concentration of ethanol in the whole concentration range of the binary mixture. Based upon these results the absence of solute-solute and the presence of solute-solvent type of molecular associations could be assumed. The energy parameters for the dielectric relaxation process of binary mixtures containing 50 mol% of ethanol have been calculated at the given temperatures. Comparison has been made with the corresponding energy parameters for viscous flow processes. It was found that the dielectric relaxation process can be treated as the rate process like the viscous flow process.

Impact of Pb content on the physical parameters of Se-Te-Pb system

In the present study, we have investigated the impact of Pb content on the physical parameters in Se-Te-Pb system via average coordination number, constraints, the fraction of floppy modes, cross-linking density, lone pairs electrons, heat of atomization, mean bond energy, cohesive energy and electronegativity. The bulk samples have been prepared by using melt quenching technique. X-ray diffraction pattern of various samples indicates the amorphous nature of investigated glassy alloys. It is observed that average coordination number, average number of constraints and cross-linking density increase with Pb content. However, lone-pair electrons, floppy modes, average heat of atomization, cohesive energy and mean bond energy are found to decrease with Pb atomic percentage.