Microwave preparation and sintering of industrially important perovskite oxides: LaMO3 (M = Cr, Co, Ni)

Perovskite oxides LaMO3 (M = Cr, Co, Ni), have been successfully prepared using microwaves of 2.45 GHz. Microwave preparation is rapid, clean and energy efficient. Preparation of LaCrO3, LaCoO3 and LaNiO3 has been achieved in 3 min, 5 min and 10 min respectively. Direct reaction between component oxides is used for the preparation of LaCrO3 and LaCoO3, whereas nitrates are used as starting materials for LaNiO3 preparation. Products have been characterized using XRD, IR spectroscopy and SEM. Their dc electrical conductivity has also been studied and their fracture behaviour has been examined. All three microwave prepared oxide powders are of submicron size. These perovskite oxides have been sintered to very high densities using microwaves. Possible mechanisms of the microwave-material interaction both during preparation and during sintering have been discussed.

Comparative Analysis of Pilot-Assisted Distributed Cophasing Approaches in Wireless Sensor Networks

This paper compares and analyzes the performance of distributed cophasing techniques for uplink transmission over wireless sensor networks. We focus on a time-division duplexing approach, and exploit the channel reciprocity to reduce the channel feedback requirement. We consider periodic broadcast of known pilot symbols by the fusion center (FC), and maximum likelihood estimation of the channel by the sensor nodes for the subsequent uplink cophasing transmission. We assume carrier and phase synchronization across the participating nodes for analytical tractability. We study binary signaling over frequency-flat fading channels, and quantify the system performance such as the expected gains in the received signal-to-noise ratio (SNR) and the average probability of error at the FC, as a function of the number of sensor nodes and the pilot overhead. Our results show that a modest amount of accumulated pilot SNR is sufficient to realize a large fraction of the maximum possible beamforming gain. We also investigate the performance gains obtained by censoring transmission at the sensors based on the estimated channel state, and the benefits obtained by using maximum ratio transmission (MRT) and truncated channel inversion (TCI) at the sensors in addition to cophasing transmission. Simulation results corroborate the theoretical expressions and show the relative performance benefits offered by the various schemes.

Photo-Defined Electrically Assisted Etching Method for Metal Stencil Fabrication

Metal stencils are well known in electronics printing application such as for dispensing solder paste for surface mounting, printing embedded passive elements in multilayer structures, etc. For microprinting applications using stencils, the print quality depends on the smoothness of the stencil aperture and its dimensional accuracy, which in turn are invariably related to the method used to manufacture the stencils. In this paper, fabrication of metal stencils using a photo-defined electrically assisted etching method is described. Apertures in the stencil were made in neutral electrolyte using three different types of impressed current, namely, dc, pulsed dc, and periodic pulse reverse (PPR). Dimensional accuracy and wall smoothness of the etched apertures in each of the current waveforms were compared. Finally, paste transfer efficiency of the stencil obtained using PPR was calculated and compared with those of a laser-cut electropolished stencil. It is observed that the stencil fabricated using current in PPR waveform has better dimensional accuracy and aperture wall smoothness than those obtained with dc and pulsed dc. From the paste transfer efficiency experiment, it is concluded that photo-defined electrically assisted etching method can provide an alternate route for fabrication of metal stencils for future microelectronics printing applications.

Impact of satellite observed microwave SST on the simulation of tropical cyclones

The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold's SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold's and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial resolution showed sharper gradient when compared to the Reynold's SST. The use of TMI SST improved the WRF cyclone intensity prediction when compared to that using Reynold's SST for both the cases studied. The improvements in intensity were mainly due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold's SST improved cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification and movement of tropical cyclones over the Indian Ocean.

Microwave spectrum and structure of C(6)H(5)CCH center dot center dot center dot H(2)S complex

Rotational spectra of C(6)H(5)CCH center dot center dot center dot H(2)S, C(6)H(5)CCH center dot center dot center dot H(2)(34)S, C(6)H(5)CCH center dot center dot center dot HDS, C(6)H(5)CCH center dot center dot center dot D(2)S and C(6) H(5)CCD center dot center dot center dot H(2)S complexes have been observed using a pulsed nozzle Fourier transform microwave spectrometer. The observed spectrum is consistent with a structure in which hydrogen sulfide is located over the phenyl ring pi cloud and the distance between the centers of masses of the two monomers is 3.74 +/- 0.01 angstrom. In the complex, the H(2)S unit is shifted from the phenyl ring center towards the acetylene group. The vibrationally averaged structure has an effective Cs symmetry. Ab initio calculations were performed at MP2/aug-cc-pVDZ level of theory to locate the possible geometries of the complex. The calculations reveal the experimentally observed structure to be more stable than a coplanar arrangement of the monomers, which was observed for the C(6)H(5)CCH center dot center dot center dot H(2)O complex. Atoms in molecule theoretical analysis shows the presence of S-H center dot center dot center dot pi hydrogen bond. For the parent isotopologue, each transition frequency was found to split into two resulting from an interchange of the equivalent hydrogens of H(2)S unit in the complex. (C) 2011 Elsevier Inc. All rights reserved.

Compiler Assisted Leakage Energy Optimization for Clustered VLIW Architectures

Miniaturization of devices and the ensuing decrease in the threshold voltage has led to a substantial increase in the leakage component of the total processor energy consumption. Relatively simpler issue logic and the presence of a large number of function units in the VLIW and the clustered VLIW architectures attribute a large fraction of this leakage energy consumption in the functional units. However, functional units are not fully utilized in the VLIW architectures because of the inherent variations in the ILP of the programs. This underutilization is even more pronounced in the context of clustered VLIW architectures because of the contentions for the limited number of slow intercluster communication channels which lead to many short idle cycles.In the past, some architectural schemes have been proposed to obtain leakage energy bene .ts by aggressively exploiting the idleness of functional units. However, presence of many short idle cycles cause frequent transitions from the active mode to the sleep mode and vice-versa and adversely a ffects the energy benefits of a purely hardware based scheme. In this paper, we propose and evaluate a compiler instruction scheduling algorithm that assist such a hardware based scheme in the context of VLIW and clustered VLIW architectures. The proposed scheme exploits the scheduling slacks of instructions to orchestrate the functional unit mapping with the objective of reducing the number of transitions in functional units thereby keeping them off for a longer duration. The proposed compiler-assisted scheme obtains a further 12% reduction of energy consumption of functional units with negligible performance degradation over a hardware-only scheme for a VLIW architecture. The benefits are 15% and 17% in the context of a 2-clustered and a 4-clustered VLIW architecture respectively. Our test bed uses the Trimaran compiler infrastructure.

A low cost approach for the fabrication of microwave phase shifter on laminates

This paper presents a simple and low cost fabrication approach using extended printed circuit board processing techniques for an electrostatically actuated phase shifter on a common microwave laminate. This approach uses 15 mu m thin copper foils for realizing the bridge structures as well as for a spacer. A polymeric thin film deposited by spin coating and patterned using lithographic process is used as a dielectric layer to improve the reliability of the device. The prototype of the phase shifter for X-band operation is fabricated and tested for electrical and electromechanical performance parameters. The realized devices have a figure of merit of 70 degrees/dB for a maximum applied bias potential of 85 V. Since these phase shifters can be conveniently fabricated directly on microwave substrates used for feed distribution networks of phased arrays, the overall addition in cost, dimensions and processing for including these phase shifters in these arrays is minimal.

Influence of substrate temperature on the properties of oxygen‐ion‐assisted deposited CeO2 films

Substrate temperature and ion bombardment during deposition have been observed to modify significantly the optical and structural properties of dielectric thin films. Single‐layer films of CeO2 have been deposited by electron beam evaporation with simultaneous oxygen‐ion bombardment using a Kaufman broad beam ion source and maintaining the substrates at elevated temperature. A systematic study has been made on the influence of (a) substrate temperature in the range ambient to 300 °C, (b) ion energy in the range 300–700 eV, and (c) ion current density 100–220 μA/cm2 on optical properties such as refractive index, extinction coefficient, inhomogeneity, packing density, and structural properties. The refractive index increased with in increase in substrate temperature: ion energy up to 600 eV and ion current density. Homogeneous, absorption free and high index (2.48) films have been obtained at 600 eV, 220 μA/cm2 and at substrate temperature of 300 °C. The packing density of the films was observed to be unity for the same deposition conditions. Substrate temperature with simultaneous ion bombardment modified the structure of the films from highly ordered to fine grain structure.

Improved microwave dielectric properties of (Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics

Phase-singular solids of the composition, (Mg1−(x+y) Cax Lay)(Ti1−yAly)O3 (x = 0 to 0.88; y = 0.05 to 0.35) having the cubic perovskite-type structure were prepared by the substitution of La3+ and Al3+ in equivalent quantities which brought about complete miscibility between MgTiO3 and CaTiO3. These ceramics showed relative permittivities of 16.5 to 50 (at 6 GHz) with increasing Ca content, high Q values of 10 000 to 30 000 and retained near-zero temperature coefficients in permittivity at optimum y values. Their dielectric characteristics are better accountable in terms of the positional disorder rather than the tolerance factor of perovskite structure.

Microwave cavity resonators. Some perturbation effects and their applications

Lagrange's equation is utilized to show the analogy of a lossless microwave cavity resonator with the conventional LC network. A brief discussion on the resonant frequencies of a microwave cavity resonator and the two degenerate companion modes H01 and E11 appearing in a cavity is given. The first order perturbation theory of a small deformation of the wall of a cavity is discussed. The effects of perturbation, such as the change in the resonant frequency and the Q of a cavity, the change in the electromagnetic field configurations and hence mixing of modes are also discussed. An expression for the coupling coefficient between the two degenerate modes H01 and E11 is derived with the help of the field equations. Results indicate that in the absence of perturbation the above two degenerate modes can co-exist without losing their individual identities. Several applications of the perturbation theory, such as the measurement of the dielectric properties of matter, study of ferromagnetic resonance, etc., are described.