Tunable hybrid phononic crystal lens using thermo-acoustic polymers

Solid phononic crystal (PnC) lenses were made active on infiltration with thermosensitive polymers to produce a thermoactuated hybrid solid lens with variable focusing. Acoustic lenses, both solid state and PnCbased, are passive elements with a fixed focal length. Their focal characteristics are functions of the lens structure or the arrangement of the PnC unit cell. Dispersion effects, liquid-filled membranes, and phase delay in a multi-element emitter have been used for variable focusing. The high thermal, electric, and electromagnetic sensitivity of the elastic properties of poly(vinyl alcohol) (PVA) poly(N-isopropylacrylamide) (PNIPAm)-based hydrogels enable them to operate as tunable solids. However, these solids do not have strong enough contrast with water or well-controlled shape parameters to function as standalone lenses. Here, a tunable hybrid solid ultrasonic lens is realized by combining a PnC lens with PVA-PNIPAm thermoacoustic hydrogel to modify the transmission and dispersion properties of transient acoustic waves. Variable focusing is demonstrated from 40 to 50 mm using the anomalous thermosensitivity of the elasticity and speed of sound of the hydrogel.NS

Coupling of spontaneous emission from GaN/AlN quantum dots into silver surface plasmons

We have demonstrated surface-plasmon induced change in spontaneous emission rate in the ultraviolet regime at ~ 375-380 nm, using AlN/GaN quantum dots (QD). Using time-resolved and continuous-wave photoluminescence measurements, the recombination rate in AlN/GaN QD is shown to be enhanced when spontaneous emission is resonantly coupled to a metal-surface plasmon mode. The exciton recombination process via Ag-surface plasmon modes is observed to be as much as 3-7 times faster than in normal QD spontaneous emission and depends strongly on the emission wavelength and silver thickness.Comment: 11 pages, 4 figure

All-acoustic signal modulation and logic operation via defect induced cavity effects in phononic crystal coupled-resonator acoustic waveguides

A coupled resonant acoustic waveguide (CRAW)in a phononic crystal (PnC)was engineered to manipulate the propagation of ultrasonic waves within a conventional phononic bandgap for wavelength division multiplexing. The PnC device included two, forked, distinct CRAW waveguide channels that exhibited strong frequency and mode selectivity. Each branch was composed of cavities of differing volumes, with each giving rise to deep and shallow‘impurity’states. These states were utilized to select frequency windows where transmission along the channels was suppressed distinctly for each channel. Though completely a linear system, the mode sensitivity of each CRAW waveguide channel produced apparent nonlinear power dependence along each branch. Nonlinearity in the system arises from the combination of the mode sensitivity of each CRAW channel and small variations in the shape of the incident wavefront as a function of input power. The all-acoustic effect was then leveraged to realize an ultrasonic, spatial signal modulator, and logic element operating at 398 and 450 kHz using input power.NS

Radio-Frequency Actuated Polymer-Based Phononic Meta-Materials for Control of Ultrasonic Waves

This article describes the achievement of radio-frequency control of a n ultrasonic phononic crystal by encapsulating it in a composite of high k-10% KF-doped BaTiO₃ dielectric nanoparticles with poly(N-isopropylacrylamide) (PNIP Am)-based hydrogel

Long-range propagation of surface plasmons in a thin metallic film deposited on an anisotropic photonic crystal

This article discusses long-range propagation of surface plasmons in a thin metallic film deposited on an anisotropic photonic crystal

Preservation of Sand and Building Energy Conservation

Due to developmental need of humankind, growing trend of energy generation and consumption results more and more Green House Gas emissions, which contribute significantly to the phenomena of Climate Change and Global Warming. The issue is further compounded by huge ash generation from thermal power plants. Judicious utilization of such waste in a greener way is another challenge. It is estimated that by 2030, 40.8% of Indian population shall be living under Urban environment, and huge no. of dwelling units would be required. Sand, being one of the conventional constituent of Concrete, and also the non-renewable soft mineral, is being mined mindlessly across the Globe. The energy consumed by building sector is around 40% of global energy use. HVAC load is the major contributor in overall energy profile in buildings situated under Hot & Humid climatic zones in tropical countries. Solar heat gain is resulted through building envelope, and the conventional concrete and plastered masonry surfaces contribute significantly to the same. An experimental work has been carried out to produce sustainable energy efficient concrete with Portland Pozzolana Cement, Sand, Coal Ash from Thermal Power Plant, Stone aggregate and water. Test samples are prepared with reducing quantities of Sand and increasing quantities of Coal Ash for a Design Mix Concrete. While characteristic strength of concrete could be achieved with replacement of Sand by Coal Ash, thermal conductivity value of concrete is reduced, while compared with normal concrete of same Mix. (C) 2016 The Authors. Published by Elsevier Ltd

Enhanced UV Light emission from Silicon nanoparticles induced by Au ion implantation

Study of light emitting silicon fabricated by ion implantation.Comment: G-COE Conference - Kyoto 2008 abstrac