Chakravarthy Venkateswaran - Academia.edu (original) (raw)

Papers by Chakravarthy Venkateswaran

$Research paper thumbnail of Thz Flat Lenses Based on Wide-Angle, Polarization Independent 3-D Negative Refractive Index Metamaterial for Sub-Wavelength Imaging and Self-Collimation Assisted Beam Transfer Applications$

2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring)

Photonic Crystals (PhCs) are the periodic arrangement of dielectrics in one, two or three dimensi... more Photonic Crystals (PhCs) are the periodic arrangement of dielectrics in one, two or three dimensions, which can modulate electromagnetic (e-m) waves in an exotic manner. In this work, a PhC structure formed by Moirè patterns is reported. Moirè patterns are the contours of trigonometric functions, where desired geometric profiles can be arranged in desired 2-D lattices. The calculations of photonic bandstructures, scattering parameters and wave propagation studies of the proposed tiles are carried out numerically. To demonstrate the utility of the proposed tiles, wave confinement in a cavity resonator formed by a PhC consists of asymmetric dielectric shape is reported for both TE and TM polarizations. We anticipate that such light structures can be fruitful for replacing expensive conventional optical components especially in the terahertz frequencies.

Applied Physics Express, 2022

Contours of trigonometric functions form an interesting tessellation known as Non-Moiré (NM) tile... more Contours of trigonometric functions form an interesting tessellation known as Non-Moiré (NM) tiles. We realize that the proposed NM tiles themselves serve as an efficient photonic crystal waveguide, in which some of the eigenmodes are guided modes. The waveguiding mechanism in NM tiles is due to both the photonic bandgap and index guiding. Depending on the electromagnetic source’s position, a combination of several NM tiles emulates various beam steering functionalities including multi-channel waveguiding, beam-splitting, and Mach–Zehnder type beam-combining applications. The reported tiles are scalable to all electromagnetic frequencies so that one can realize design-free waveguides for engineering the light path in photonic circuits.

DAE SOLID STATE PHYSICS SYMPOSIUM 2019, 2020

Journal of Magnetism and Magnetic Materials, 2015

BaMg 1 À x Mn x F 4 (0 rx r 0.07) samples were prepared by hydrothermal method which have heterog... more BaMg 1 À x Mn x F 4 (0 rx r 0.07) samples were prepared by hydrothermal method which have heterogeneous particle size distribution with combined hexagonal and rectangular shapes. An isovalent Mn ion at Mg site induces antiferromagnetism at room temperature and the antiferromagnetic nature is confirmed by Arrott-Belov-Kouvel plot. Magnetization values taken at 15 kOe initially increases and then decreases with increase in the Mn concentrations. Undoped and doped samples show unsaturated ferroelectric loops with lossy nature and the lossy nature is found to decrease with increase in doping concentration. BaMg 0.95 Mn 0.05 F 4 exhibits a stable resistivity behavior over the temperature range 350-650 K. Almost a flat response in dielectric properties is observed for all the samples at 100 kHz in the measured temperature range. The probable origin of magneto-dielectric effect is discussed based on the study at a frequency of 1 kHz at room temperature.

Journal of Atomic, Molecular, and Optical Physics, 2011

Bulk Zn0.95TM0.05O (TM=Cr, Mn, Fe, Co, and Ni) were synthesized by the standard ceramic method an... more Bulk Zn0.95TM0.05O (TM=Cr, Mn, Fe, Co, and Ni) were synthesized by the standard ceramic method and explored for variation in their band gap energies using Diffuse Reflectance Spectroscopy in the ultraviolet-visible region. Phase quantification and compositional studies were performed using Rietveld analysis of the X-Ray Diffraction patterns, Scanning Electron microscopy, and Energy Dispersive X-Ray Analysis. Due to 3d transition ion doping, the samples have brilliant colors, and the absorption edge of Zn0.95TM0.05O was found to shift towards the visible and ultraviolet-visible region. The blue and red shifts in band gaps observed for various transition metal ion-doped ZnO are discussed.

Phys. Chem. Chem. Phys., 2015

Oxygen vacancy created an intrinsic magneto-dielectric effect in Lu3Fe5O12.

AIP Conference Proceedings, 2014

ABSTRACT Magnesium ferrite (MgFe2O4) is one of the important and versatile spinel ferrite (usuall... more ABSTRACT Magnesium ferrite (MgFe2O4) is one of the important and versatile spinel ferrite (usually written as (Mg1-xFex)[MgxFe2-x]O4) having low saturation magnetization value, high resistivity and reproducible characteristics. The stoichiometric phase of MgFe2O4 was successfully prepared by ball milling assisted sintering process. XRD pattern of the sample shows the formation of stoichiometric MgFe2O4 phase. The HRSEM image shows a distribution of particle size. Vibrating Sample Magnetometer study at room temperature shows a hysteresis loop behavior with a low saturation magnetization of about 20 emu/g and a small coercivity value. The temperature versus magnetization curve shows the ferromagnetic to paramagnetic transition.

AIP Conference Proceedings, 2012

ABSTRACT Polycrystalline Lu3Fe5O12 ceramics 'having garnet structure' had been pr... more ABSTRACT Polycrystalline Lu3Fe5O12 ceramics 'having garnet structure' had been prepared by the solid state reaction method. X-ray diffraction study confirms the single phase nature. HRSEM image shows densely formed micron sized flakes. Magnetization studies show a clear hysteresis behavior at room temperature with a high saturation magnetization of 77 emu/ g at a relatively low applied magnetic field of 1500 Oe. The material also possesses a high dielectric constant of the order of 105. These results confirm that Lu3Fe5O12 has a very good magnetodielectric response even for a small applied field.

Review of Scientific Instruments, 1997

A modified belt-type high pressure, high temperature apparatus without tungsten carbide has been ... more A modified belt-type high pressure, high temperature apparatus without tungsten carbide has been designed and constructed based on the theory of multilayered pressure vessels. The calculated interferences seem to give adequate support for reaching a high pressure of 10 GPa and simultaneously temperatures up to 1400°C. We estimate the highest pressure reached in our experiment to be ϳ17 GPa in the sample region, based on the load versus pressure curve calibrated in bismuth, tin, and lead. Talc gaskets were used along with a tubular graphite furnace for high temperatures. This represents a relatively simple and inexpensive device for material synthesis and phase transformation studies.

physica status solidi (a), 2011

ABSTRACT Chalcopyrites are a versatile class of semiconductors known for their potential in photo... more ABSTRACT Chalcopyrites are a versatile class of semiconductors known for their potential in photovoltaic applications. Considering the well established CuInSe2 as a prototype system, a new compound of the chalcopyrite type, Cu1–xZn1–ySe2–δ, by replacing In with Zn, has been prepared (both undoped and 2% Cr doped) by the metallurgical method. Thin films have been deposited by the thermal evaporation technique using the stabilized polycrystalline compounds as charge. Structural, compositional, morphological, and optical properties of the films are analyzed and reported. Use of these films as electrodes in dye sensitized solar cell (DSSC) is demonstrated.

Physica B: Condensed Matter, 2014

ceramics (LFO) with garnet structure were prepared by solid-state reaction method and a part of t... more ceramics (LFO) with garnet structure were prepared by solid-state reaction method and a part of the sample was ball milled for 15 h (LFO15h) using a high energy ball mill to study the grain size effect. The cubic garnet phase was confirmed for both LFO and LFO15h samples by X-ray diffraction analysis. The magnetic behavior was studied using a Vibrating Sample Magnetometer and it shows a clear hysteresis loop with ferrimagnetic ordering at room temperature for both LFO and LFO15h samples. X-ray photoelectron spectra reveal the presence of single valence state of Fe ions (Fe 3 þ) in the unmilled sample and mixed valence state of Fe ions (i.e., Fe 2 þ and Fe 3 þ) in the 15 h ball milled sample. Magneto-dielectric (MD) studies that have been carried out using an indigenous magneto-impedance setup show large MD coupling at room temperature for the LFO15 h in comparison to the LFO sample, making it a candidate explorable for applications in magneto dielectric devices.

Modern Physics Letters B, 1993

Synthesis of air-quenched high-T c superconductors Y 0.8 Sr 0.2 Ba 2 Cu 3 O 6+x and Y 0.8 Ba 2.2 ... more Synthesis of air-quenched high-T c superconductors Y 0.8 Sr 0.2 Ba 2 Cu 3 O 6+x and Y 0.8 Ba 2.2 Cu 3 O 6+x exhibiting transition temperatures of 90 K and 88 K respectively and the variation of their electrical resistivity at high pressure are reported here. X-ray powder diffraction of the above systems reveal tetragonal structure.

Modern Physics Letters B, 1999

High pressure synthesis and structural studies on the reported high pressure phase compound ( Ca ... more High pressure synthesis and structural studies on the reported high pressure phase compound ( Ca 0.3 Sr 0.7)0.9 CuO 2 have been carried out using zinc. Substitution of zinc seriously affects the superconducting transition temperature T c , which gets lowered to around 60 K for the x=0.1 compound. Further increase in zinc concentration destroys superconductivity. All the compounds could be well indexed to the tetragonal system with little variation in lattice parameters showing structural phase stability.

Materials Letters, 2005

ZnO substituted with transitional metal ions at the cationic site presents interesting magnetic p... more ZnO substituted with transitional metal ions at the cationic site presents interesting magnetic properties arising due to the strong sp-d exchange interaction. They are intensively explored for spintronics applications. The preparation route plays a vital role in the synthesis of single phase oxide Diluted Magnetic Semiconductor (DMS). Single phase Zn 0.95 Mn 0.05 O prepared by co-precipitation and standard ceramic methods was confirmed by powder X-ray diffraction measurements. The sample prepared by co-precipitation method was pelleted and examined for its magnetic property using Vibrating Sample Magnetometer (VSM) indicated ferromagnetic-like behavior at 300 K. Spin-glass state was observed at 77 K. Mn substitution in ZnO affects the transparency considerably in the visible region. Comparing the results of measurements performed on samples prepared by both the methods we conclude co-precipitation method to be more effective than ceramic method in obtaining single phase compound with desirable properties.

Materials Chemistry and Physics, 2009

'3d' transition metal ion doped oxide semiconductors are widely studied for utilization in Spintr... more '3d' transition metal ion doped oxide semiconductors are widely studied for utilization in Spintronics. CuO, a p-type semiconductor with a band gap of 1.2 eV was explored for ferromagnetic ordering by doping with Mn. Cu 0.95 Mn 0.05 O samples prepared by the standard ceramic and co-precipitation methods were analyzed using X-ray diffraction-Rietveld analysis, differential thermal analysis, scanning electron microscopy and energy dispersive X-ray analysis, respectively. Magnetic measurements using vibrating sample magnetometer on samples prepared by both the methods show possible ferromagnetic behavior at 77 K.

Materials Characterization, 2008

... Dr. A. Narayanasamy, Prof. Dr. PR Subramanian and all the technical staff of their department... more ... Dr. A. Narayanasamy, Prof. Dr. PR Subramanian and all the technical staff of their department for their support. ... [3] D. Paul Joseph, S. Naveenkumar, N ... [8] DH Yoon, JH Yu and GM Choi, CO gas sensing properties of ZnOCuO composite, Sens Actuators B46 (1998), p. 15. ...

Journal of Power Sources, 2006

LiNi 0.5 Fe 0.5 O 2 is prepared by a sol-gel method and the sample is heat-treated to various tem... more LiNi 0.5 Fe 0.5 O 2 is prepared by a sol-gel method and the sample is heat-treated to various temperatures to characterize its physico-chemical properties. Calcination of the precursor at 673 K produces powders of tetragonal and hexagonal phases. Subsequent heat treatment at 873, 1073 and 1273 K results in a pure hexagonal phase. Vibrating sample magnetometer (VSM) studies show that the tetragonal phase is magnetically stronger than the hexogonal phase. Room-temperature Mössbauer studies reveal magnetic ordering for the tetragonal phase and the paramagnetic nature of the hexagonal phase. The hexagonal phase is magnetically ordered at 77 K. By comparing the value of the hyperfine field with the bulk magnetization value at 77 K obtained from VSM, it is concluded that the magnetic ordering cannot be ferromagnetic but should be antiferromagnetic.