Circular Capacitance Micromachined Ultrasonic Transducer

Capacitance micromachined ultrasonic transducers (CMUTs) have become an attractive alternative to the piezoelectric transducers, especially in air-coupled nondestructive evaluation (NDE) and ultrasound medical imaging flow metering,  micro/nanoelectronics, and industrial cleaning, etc. These are similar to other capacitance transducers as these employ a vibrating membrane to send and receive ultrasound in air and water. This paper describes the theory and design of a circular micromachined ultrasonic transducer which could lead to a CMUT with many advantages, including less loading effect. The software programs (Intellisuite 8.2 and MATLAB 7.0) were used to model a single cell of CMUT. The simulations-based studies of the critical parameters like collapse voltage and snapback voltage, which influence the operation of the CMUTs to a large extent, has been discussed. Small signal equivalent circuit model for the circular CMUT has been discussed and the program (SPICE) has been used for the simulation of the small signal equivalent circuit.Defence Science Journal, 2009, 59(6), pp.627-633, DOI:http://dx.doi.org/10.14429/dsj.59.156

Dihetero double Michael addition in PEG-400: Synthesis of 2,3-dihydro- [2,3-c]-[1,2,4]-triazole scaffold

1586-1592Potassium carbonate in poly (ethylene glycol-400) has been found to be a highly effective and efficient medium for the straight forward, convenient, one pot and green synthesis of diethyl/ethyl cyano-5-[substituted phenyl-2,3-dihydro-[1,3,4]-thiadiazolidino - [2, 3-c] – [1, 2, 4]-triazol -2- yl] – malonate/acetate through intramolecular cyclo- elimination of Michael adducts formed between the reaction of 4-amino-5- substituted phenyl-3-mercapto-1,2,4-triazole 1 with diethyl-2-(ethoxymethylene) malonate and ethyl -2-cyano-3-ethoxyacrylate respectively. The structures of all the new compounds have been elucidated using IR, 1H and 13C NMR, mass spectral data and elemental analyses

Dihetero double Michael addition in PEG-400: Synthesis of 2,3-dihydro- [2,3-c]-[1,2,4]-triazole scaffold

Potassium carbonate in poly (ethylene glycol-400) has been found to be a highly effective and efficient medium for the straight forward, convenient, one pot and green synthesis of diethyl/ethyl cyano-5-[substituted phenyl-2,3-dihydro-[1,3,4]-thiadiazolidino - [2, 3-c] – [1, 2, 4]-triazol -2- yl] – malonate/acetate through intramolecular cyclo- elimination of Michael adducts formed between the reaction of 4-amino-5- substituted phenyl-3-mercapto-1,2,4-triazole 1 with diethyl-2-(ethoxymethylene) malonate and ethyl -2-cyano-3-ethoxyacrylate respectively. The structures of all the new compounds have been elucidated using IR, 1H and 13C NMR, mass spectral data and elemental analyses.

Directing Monolayer Tungsten Disulfide Photoluminescence using a Bent Plasmonic Nanowire on a Mirror Cavity

Designing directional optical antennas without compromising the field enhancement requires specially designed optical cavities. Herein, we report on the experimental observations of directional photoluminescence emission from a monolayer Tungsten Disulfide using a bent-plasmonic nanowire on a mirror cavity. The geometry provides field enhancement and directivity to photoluminescence by sandwiching the monolayer between an extended cavity formed by dropcasting bent silver nanowire and a gold mirror. We image the photoluminescence emission wavevectors by using the Fourier plane imaging technique. The cavity out-couples the emission in a narrow range of wavevectors with a radial and azimuthal spreading of only 11.0{\deg} and 25.1{\deg}, respectively. Furthermore, we performed three dimensional finite difference time domain based numerical calculations to corroborate and understand the experimental results. We envisage that the results presented here will be readily harnessed for on-chip coupling applications and in designing inelastic optical antennas

Mirror-Coupled Microsphere can narrow the Angular distribution of Photoluminescence from WS2 Monolayers

Engineering optical emission from two dimensional, transition metal dichalcogenides (TMDs) materials such as Tungsten disulphide (WS2) has implications in creating and understanding nanophotonic sources. One of the challenges in controlling the optical emission from 2D materials is to achieve narrow angular spread using a simple photonic geometry. In this paper, we study how the photoluminescence of a monolayer WS2 can be controlled when coupled to film coupled microsphere dielectric antenna. Specifically, by employing Fourier plane microscopy and spectroscopic techniques, we quantify the wavevector distribution in the momentum space. As a result, we show beaming of the WS2 photoluminescence with angular divergence of {\theta}1/2 = 4.6{\deg}. Furthermore, the experimental measurements have been supported by three-dimensional numerical simulations. We envisage that the discussed results can be generalized to a variety of nanophotonic 2D materials, and can be harnessed in nonlinear and quantum technology

Directional emission from WS2 monolayer coupled to plasmonic Nanowire-on-Mirror Cavity

Influencing spectral and directional features of exciton emission characteristics from 2D transition metal dichalcogenides by coupling it to plasmonic nano-cavities has emerged as an important prospect in nanophotonics of 2D materials. In this paper we experimentally study the directional photoluminescence emission from Tungsten disulfide (WS2) monolayer sandwiched between a single-crystalline plasmonic silver nanowire (AgNW) waveguide and a gold (Au) mirror, thus forming an AgNW-WS2-Au cavity. By employing polarization-resolved Fourier plane optical microscopy, we quantify the directional emission characteristics from the distal end of the AgNW-WS2-Au cavity. Given that our geometry simultaneously facilitates local field enhancement and waveguiding capability, we envisage its utility in 2D material-based, on-chip nanophotonic signal processing, including nonlinear and quantum optical regimes.Comment: To appear in Advanced Photonics Research (2021

One-pot Michael addition and cyclo-elimination cascade synthesis of thiazolo-[ 4,5- b]pyridin- 6-carbonitrile scaffold

A series of thiazolo [4,5-b]- pyridine-6-carbonitriles scaffold have been synthesized conveniently and smoothly in a single step in good yields. These compounds have been screened for their antibacterial and antifungal activity against different pathogenic strains of bacteria fungi. The minimum inhibitory concentration (MBC) and minimum fungicidal concentration (MFC) have been determined for the test compounds as well as for reference standards. Compounds 3c, 3d, 3e, 3f, 4c, 4d, 4e and 4f have shown good antibacterial as well as antifungal activity