scispace - formally typeset
Search or ask a question
Author

N. Hema

Other affiliations: VIT University
Bio: N. Hema is an academic researcher from Queen Mary's College. The author has contributed to research in topics: Crystal & Single crystal. The author has an hindex of 3, co-authored 9 publications receiving 20 citations. Previous affiliations of N. Hema include VIT University.

Papers
More filters
Journal ArticleDOI
TL;DR: The proposed algorithm is Minimum Variance Distortionless Response (MVDR) for near field beamforming of broadband data which gives better contrast and resolution compared to conventional Delay and Sum (DAS) beamformers and is implemented in frequency domain.
Abstract: Background/Objectives: The main objective of this proposed work is to investigate the significance of adaptive beamforming technique and to develop an efficient VLSI architecture for broadband MVDR beamformer in the field of medical ultrasound imaging. Methods/Statistical Analysis: The proposed algorithm is Minimum Variance Distortionless Response (MVDR) for near field beamforming of broadband data which gives better contrast and resolution compared to conventional Delay and Sum (DAS) beamformers and is implemented in frequency domain. MVDR beamformer minimizes the output power by allowing the desired signal to pass undistorted with unity gain. The solution for this optimization problem, involves correlation matrix inversion, which is the challenging part of MVDR algorithm. Findings: MVDR algorithm is applied by finding the inverse of correlation matrix which is a complex matrix. Here four elements are used for simplicity. Calculation of inverse complex matrix is the challenging part of MVDR algorithm where different methods are being used. Here QR decomposition is used which follows givens rotation algorithm. The paper demonstrates the formal verification of the proposed work. Final result is compared with the golden reference model which is designed using FIELD II scanner in Matlab. From the results it’s seen that, MVDR beamformer gives a pencil like beamform which shows high resolution and better contrast when compared to DAS. The timing constraints and device utilization parameters are obtained from synthesis report of final architecture designed in FPGA. Conclusion/Improvements: MVDR algorithm gives a pencil like beamformer output with reduced main lobe width and reduced side lobe level. By upgrading number of elements from 4 to 64, it can be made real time.

6 citations

Journal ArticleDOI
TL;DR: Good quality single crystals of organic nonlinear optical material l-proline 2,4-dichlorobenzoic acid (LPDCBA) were synthesized and grown by slow evaporation technique as mentioned in this paper.
Abstract: Good quality single crystals of organic nonlinear optical material l-proline 2,4-dichlorobenzoic acid (LPDCBA) were synthesized and grown by slow evaporation technique. The lattice parameters and space group were determined using single crystal XRD analysis. The optical absorbance and the lower cut-off wavelength of the LPDCBA were identified by UV–VIS–NIR studies. The modes of vibrations of different molecular groups present in the sample were identified by the FTIR spectral analysis. Dielectric measurement of LPDCBA were carried out at different frequencies. Thermal stability of LPDCBA were determined by TGA/DTA measurements. Laser induced damage threshold study was carried out for the grown crystal using Nd:YAG laser. The second harmonic generation efficiency were found to be 1.66 times greater than that of KDP.

5 citations

Journal ArticleDOI
R. Usha1, N. Hema1, V. Revathi Ambika1, D. Shalini1, D. Jayalakshmi1 
TL;DR: In this article, a 4-Methoxy Anilinium 5-Sulfo Salicylate (4MA5SS) was grown with the dimension of 9mm× 6mm × 3mm from ethanol solution by slow evaporation solution growth technique.
Abstract: Quality crystals of 4-Methoxy Anilinium 5-Sulfo Salicylate (4MA5SS) were grown with the dimension of 9 mm × 6 mm × 3 mm from ethanol solution by slow evaporation solution growth technique. The cell parameters and crystal structure studied by single-crystal X-ray diffraction. FTIR spectroscopic studies were carried out to confirm the functional groups and vibrational modes present in the grown crystals. The linear optical properties of the grown crystal were studied from the UV–Vis spectrum. The surface laser damage threshold for the grown crystal was measured using Nd:YAG laser. Further, Vickers micro-hardness study was carried out to analyze the mechanical strength of the grown crystals for various loads. The dielectric measurements of this crystal in the frequency region from 50 Hz to 5 MHz showed that the material can be used for optical application.

4 citations

Journal ArticleDOI
D. Shalini1, S. Kalainathan2, N. Hema1, R. Usha1, D. Jayalakshmi1 
TL;DR: In this paper, a nonlinear optical material 4-methylpyridinium5-sulfosalicylate has been successfully synthesized, and the optical quality single crystals were grown by slow solvent evaporation solution growth technique at room temperature.
Abstract: A nonlinear optical material 4-methylpyridinium5-sulfosalicylate has been successfully synthesized, and the optical quality single crystals were grown by slow solvent evaporation solution growth technique at room temperature. The single crystal XRD analysis indicated that the crystal belongs to the monoclinic system with lattice parameters a = 7.07 A, b = 13.45 A, c = 15.57 A. The presence of various functional groups in the crystal was confirmed by FT-IR spectral analysis. The optical transmission window of the 4MSS has been identified by UV–vis–NIR studies. Broadband dielectric analysis has been studied in the frequency range 10 Hz to 20 MHz at room temperature. It is found that the real (e′) and imaginary (e″) dielectric constant, dielectric loss, dielectric modulus depend on frequency. The third order nonlinear optical properties of the grown crystals were investigated using Z-scan technique. The nonlinear index of refraction and nonlinear absorption coefficient were determined to explore the ...

3 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: The modulation of piezoelectric charge constants in collagen building blocks as the crystal symmetry is lowered and the molecule size increases is mapped, finding strong evidence for amino acid-level barcoding of collagen piezolectricity that can be tuned using very simple chemistry.
Abstract: Collagen piezoelectricity has been the focus of a large number of experimental and theoretical studies for over fifty years. Less is known about the piezoelectric properties of its building blocks, in particular but not limited to, proline and hydroxyproline. Spurred by the recent upsurge of interest in piezoelectricity in organic crystals including our own report of unprecedentedly high piezoelectricity in amino acid glycine, we predict and measure the piezoelectric properties of collagen subcomponents in single crystalline forms and the collagen-like alanine-hydroxyproline-glycine trimer peptide. We map the modulation of piezoelectric charge constants in collagen building blocks as the crystal symmetry is lowered and the molecule size increases, finding strong evidence for amino acid-level barcoding of collagen piezoelectricity that can in turn be tuned using very simple chemistry. The simple addition of an -OH group can increase piezoelectric constants by up to two orders of magnitude (d25 = 25 ± 5 pC N-1) as measured in Y-cut hydroxyproline crystals. The value is similar to that obtained from thermoelectrically poled commercial polyvinylidene di fluoride (PVDF) films. Overall, our findings support a simple block by block approach in which first principles calculations can guide the understanding and re-engineering of piezoelectric biomolecules.

34 citations

Journal ArticleDOI
TL;DR: In this paper, a novel third-order nonlinear optical (NLO) crystal, piperazine-1,4-diium bis(2,4dichlorobenzoate) (abbreviated as PBDCB) was successfully synthesized and grown good quality crystal by slow evaporation solution growth technique by methanol as a solvent at room temperature.

18 citations

Journal ArticleDOI
TL;DR: A single crystal of L-Phenylalanine Fumaric Acid (LPFA) with molecular formula C9H11NO2 was successfully synthesized by slow evaporation solution growth technique as mentioned in this paper.
Abstract: A single crystal of L-Phenylalanine Fumaric Acid (LPFA) with molecular formula C9H11NO2.C4H4O4 was successfully synthesized by slow evaporation solution growth technique. The grown crystal underwent several characterizations. The single crystal X-ray diffraction analysis reveals that the synthesized sample crystallizes in the triclinic system with the space group PI. Using the UV-Vis spectral analysis, it was found that the grown crystal holds good optical quality which indicates that the crystal is transparent in the visible region with lower cut-off wavelength of 223 nm and optical band gap is found to be 5.57 eV. Using the UV-Vis spectrum, the remarkable properties such as extinction coefficient, reflectance, refractive index, electrical conductivity, optical conductivity, and electric susceptibility have been calculated. From Vickers Micro hardness, the mechanical stability of the LPFA crystal and work hardening coefficient is found to be 3.8. By thermogravimetric and differential thermal analysis, it has been analyzed that the grown crystal is having thermal stability up to 206 °C. The electrical properties have been analyzed using the dielectric studies. It has been found that the sample exhibits lower dielectric constant and dielectric loss at high frequencies which indicates good optical quality of the crystal. The antibacterial activity was investigated using four strains such as Escherichia coli, Serratia marcescens, Pseudomonas aeruginosa, and Staphylococcus aureus using Agar disk diffusion test and it has been evaluated that the sample is having strongest activity of 43 mm against Pseudomonas aeruginosa. Hence, the as grown sample is having wide applications in the field of electro-optics, water purification and bio-medicine.

17 citations

Journal ArticleDOI
TL;DR: Diversities of salts formed by 5-sulfosalicylic acid (5-SSA) and isonicotinamide (INA) were obtained by mechanochemical grinding and from solution, including three polymorphs of (5SSA-2H) and (INA-H) as mentioned in this paper.
Abstract: Diversities of salts formed by 5-sulfosalicylic acid (5-SSA) and isonicotinamide (INA) were obtained by mechanochemical grinding and from solution, including three polymorphs of (5-SSA-2H)–·(INA-H)...

8 citations

Journal ArticleDOI
TL;DR: In this article, a single crystal of p-Toluidinium L-Tartrate (PTLT) was harvested via slow solvent evaporation technique, which has a triclinic structure, P1 space group.

8 citations