Terahertz Resonances of Di(Pyridin-2-yl)amine: A Detailed Experimental and Computational Study :
Terahertz spectra of a synthesized organic molecule di(pyridine-2-yl)amine have been studied and the vibrational modes are explained using Density Functional Theory simulations. Crystal structure simulation confirms that lower terahertz resonances originate due to intermolecular hydrogen bond vibrations.
Terahertz Spectroscopy of Concrete for Evaluating the Critical Hydration Level :
Concrete, a mixture of cement, coarse aggregate, sand and filler material (if any), is widely used in the construction industry. Cement, mainly composed of Tricalcium Silicate (C3S) and Dicalcium Silicate (C2S) reacts readily with water, a process known as hydration. The hydration process forms a solid material known as hardened cement paste which is mainly composed of Calcium Silicate Hydrate (C-S-H), Calcium Hydroxide and Calcium Carbonate. To quantify the critical hydration level, an accurate and fast technique is highly desired. However, in conventional XRD technique, the peaks of the constituents of anhydrated and hydrated cement cannot be resolved properly, where as Mid-infrared (MIR) spectroscopy has low penetration depth and hence cannot be used to determine the hydration level of thicker concrete samples easily. This work describes a promising approach to quantify the level of water for perfect hardening of hydrated cement using Terahertz (THz) spectroscopy. This technique has been employed to track the time dependent reaction mechanism of the key constituents of cement that react with water and form the products in the hydrated cement, viz., C-S-H, Calcium Hydroxide and Calcium Carbonate.
Terahertz Spectroscopy of Cement Hydration Dynamics :
THz spectroscopy is employed to understand the variation in hydration dynamics when the water-cement ratio is varied. Further to the work by the above authors on the hydration dynamics of cement with water-cement ratio of 0.4, this work concentrates on using THz spectroscopy as a tool to estimate and track the changes in the consumption of C3S/C2S. Moreover, this analysis will help to show variation in the formation of key hydration products for different water-cement ratios (0.3, 0.4, 0.5 and 0.6) during the first 4 weeks of the hydration process. The understanding gained from these studies will help to add optimum amount of filler materials, such as nano silica and fly ash, to the cement mixture at specific times to quicken the hydration process and improving the short term strength and long term durability of the concrete.
Quantitative Analysis of the consumption of cement constituents and formation of key hydration product :
Quantitative analysis shows the variation in consumption of C3S and C2S (459 cm-1 and 520 cm-1) peaks and the formation of a key hydration product, Calcium Hydroxide (Ca(OH)2).
Thickness Measurement of Tablet Coating using Continuous Wave Terahertz Reflection Spectroscopy :
THz rays have higher penetration depth compared to infrared rays and hence can be effectively used to measure tablet coating thickness. In addition, THz wavelength (1 mm – 0.1 mm) provides an optimal depth resolution for the thickness measurement. This method can be non-invasive and hence ideal for inline quality monitoring. Tablet coating thickness is one of the major parameters of interest in Process Analytical Technology (PAT). Reflection mode Continuous Wave (CW) Terahertz (THz) system has been employed to measure the tablet coating thickness. CW system is a low cost and compact system in comparison with the pulsed THz system and hence it can be used for real-time coating measurement in pharmaceutical applications. The above procedure can also be employed for the dissolution studies of the pharmaceutical tablets which is yet another important parameter in PAT.
Design of Novel Organic Molecules with Resonances Below 1 THz :
Novel organic molecules have been designed with resonances below 1 THz. C6-UPh and DPA have been synthesized which show prominent resonances below in this frequency region. Further studies is being done to increase the intensity of the peaks as well a tune the frequency by varying the mass of the atoms, adding/shifting functional groups and synthesizing molecules with hydrogen bonds.
Maskless Interference Lithography :
This is a maskless lithographic technique which uses the interference pattern from multiple beams. This is a highly versatile device which can be used for fabrication of wide variety of structures on a wide class of substrate. These grating structures have a variety application including Solar Concentrators, Biophotonics,etc.
High Efficiency Green Solar Cells :
Dye Sensitized Solar Cells (DSSCs) are third-generation of solar cells whose advantages are low cost production, low energy payback time and flexibility. The sensitizer is the vital component of the DSSC, playing a major role of absorbing light and generating excitons. DSSCs typically use toxic dyes such as metal-based porphyrins or cyanin derivatives and also require complex synthesis. Compared to synthetic dyes, natural dyes which are found in plants can be easily extracted by simple procedures. Moreover, they are non-toxic, inexpensive and completely biodegradable; hence they are being explored as alternative photosensitizers to be used in Green Solar Cells. Natural Photo-Sensitizers are a viable non-toxic, inexpensive and environment friendly option for developing Green Solar Cells suitable for Building Integrated Photovoltaic (BPIV) applications.
Solar Panel Cleaning :
Solar PV modules are generally installed in arid and remote locations which are usually dusty. Dust gets accumulated on the surface of panels decreasing its power generation capability. The output power decreases up to 30% if not cleansed for a month. The project aims to devise both active and passive cleaning procedures to maintain the optimum performance of the solar panel all-round the year. In order to decrease the dust accumulation on the panel, the surface has been made hydrophobic by the application of a nano-coating. Studies have been done to find the suitability of the coating to be applied on the solar panel. A mechanical system cleaning system has been devised to clean the panel each day to maintain the optimum performance of the panel. The project also aims to develop unmanned drones that can inspect the dirty panels and clean them as and when required.
Solar Tree Optimization :
One of the problems which hinder the solar installations in India is the land area requirement. The proposed research work will involve in development of solar tree in which the solar panels will be placed in appropriate positions likes the leaves of a tree. The objective of building a solar tree is to decrease the land area requirement for obtaining equivalent amount of solar output. To avoid the effect of shading, the solar panels can be placed such that the shade of one panel does not affect the other panels. Reflectors can be designed to further increase the productivity. Similar to leaves in trees, the solar panels can be made to automatically realign themselves according to the available irradiance or season.
Non-imaging concentrator based Low Concentrating Photovoltaic Thermal system (LCPVT) :
Silicon based solar PV cells have an efficiency of less than 25%, losing the remaining energy as heat due to band-gap, thermalization and resistive losses. The key idea was to improve the system efficiency by converting the lost heat to low temperature usable heat thereby reducing the overall cost of system and area requirement. The LCPVT system essentially consists of 3 elements viz. solar PVT module, concentrator and mounting structure. The most commonly used concentrator in LCPVT systems is compound parabolic concentrators but these concentrators result in non-uniform radiation on the PV module. The non-uniform illumination results in non-uniform temperature distribution and high local concentration on the solar cell which have been the prime reasons for low system efficiency and poor durability of conventional CPVT systems. Therefore, the design of optical concentrator is the most critical part of the system. A CPC along with a secondary flux homogenizer was designed and optimized to obtain uniform solar radiation flux on the solar cell. Detailed ray tracing simulations have also been performed using Zemax optical simulation to optimize the parameters of homogenizer. A working prototype of a 40 We is developed and is under analysis under outdoor insolation conditions.
Solar ThermoPhotovoltaic System :
A solar thermophotovoltaic system (STPV) is a unique type of system that directly converts both solar and thermal energy (extra kinetic energy from photons and unabsorbed photons by the solar cell) into electricity. Typical STPV systems consist of a thermal emitter and a photovoltaic cell in which there are no moving parts allowing for a compact power generation platform. In theory, STPV systems can convert radiative energy from the thermal emitter to electricity at an efficiency approaching the Carnot limit for monochromatic radiation and can be used for both waste heat and solar energy harvesting.
STPV modules consists of absorber, emitter and receiver. The absorber heats up to a high temperature by absorbing the light and the thermal energy is transferred to the emitter. Most of the materials will absorb with maximum efficiency at particular wavelengths and also emit the absorbed radiation depending on the material properties and temperature. So, we intend at designing a broadband absorbers with high absorptivity and low emissivity. In addition, the emitters typically emit radiation over a broad range of wavelengths. This requires an additional component, a filter to suppress low energy photons below the bandgap and high energy photons well above the bandgap. To avoid using a filter, we would aim at realizing an emitter by leveraging the unique photonic properties of high-contrast grating to emit in a narrow band region. By varying the parameters of the emitter structure such as grating shape, material and dimensions, it is possible to achieve narrow band emission.
Non – Invasive Blood Pressure Monitor :
Preliminary to the actual work of developing a non-invasive Blood Pressure monitor, four prototypes of health monitoring wrist-worn devices have been developed in this lab. The first device measures the wearer’s pulse based on a Photoplethysmography (PPG) sensor. This information is relayed to a smartphone through Bluetooth and is displayed on an app, along with pulse waveforms. The second device displays the calculated pulse on an LCD screen. The third and fourth devices, which can also monitor pulse through PPG sensors, have additional features. The third device monitors the real-time movement of the wearer using an accelerometer and once again this data is displayed on a smartphone. The fourth device monitors the soundness of sleep of the wearer (based on the magnitude of body movements, recorded through an accelerometer) and sends the data to a smartphone in the morning so that the trends in sleep quality can be visualized and analyzed.
UV-Fluorescence Readers :
Fluorescence is the emission of light by a substance that has absorbed light. The emitted light has a longer wavelength (and lower energy), than the wavelength of the absorbed light. When invisible fluorescent inks/ varnishes are lit by UV light they emit light, at a longer wavelength than UV, which falls in the visible light region. The color that is emitted by these flourescent inks, when incident with a known wavelength of UV light, can be made unique and hence can be used in security tags. The aim of this work is to design a device that can detect the colour of the light emitted by the flourescent ink when UV light is incident on it. UV light (of known wavelength) is flashed on a substrate which is coated with invsible flourescent ink. As the UV light is on a digital camera is made to capture an image of the substrate (coated with flourescent ink). This image is then then processed by a processor to detect the colour emitted by the flourescent ink.