Faculty Publications

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    Fabrication and characterisation of RF MEMS capacitive switches tuned for X and Ku bands
    (Inderscience Publishers, 2018) Shajahan, E.S.; Bhat, M.S.
    Microelectromechanical systems (MEMS) capacitive switches discussed in this paper employ electrostatic actuation to perform switching. Capacitive switches employ inductive tuning for excellent switching characteristics in X and Ku bands. Employing inductive tuning is found to increase the switch beam inductance by a few tens of pico-henry. This enhances the Q factor and enables tuning of isolation over a narrow band of frequencies. Beam inductance can be extracted from the simulated isolation characteristics of the switch by curve fitting. This paper presents design, fabrication and characterisation of inductive tuned MEMS capacitive switches tuned for X and Ku bands. The devices are fabricated on high resistive (10 KΩ) silicon substrate by a five mask process. The characterisation of the fabricated devices are conducted using Cascade probe station and high frequency Power network analyser. Characterisation results show an actuation voltage of 18.5 volts. The insertion - loss and isolation are better than 0.5 dB and -40 dB respectively in the 8-18 GHz band. © © 2018 Inderscience Enterprises Ltd.
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    Fabrication of single-mode Y-branch waveguides in photosensitive polymer with reduced Y-junction residue
    (2012) Singhal, R.; Satyanarayan, M.N.; Pal, S.
    Single-mode small-core (?2 ?m × 2 ?m) Y-branch waveguide structures in photosensitive polymer have been fabricated. Y-branch waveguides are designed by the beam propagation method and Y-branch waveguides are obtained on development after a cross-linkable negative tone epoxy SU-8 2002 polymer is exposed to UV through a photomask. Optical Adhesive NOA 61 is used as under- and over-clad. The fabrication process is optimized to avoid polymer residue at the Y-junction. The average insertion loss obtained for a 7.2 mm 1 × 2 device at chip-level is ?13 dB at 1550 nm. © 2011 Elsevier GmbH.
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    Reduced graphene oxide derived from used cell graphite and its green fabrication as an eco-friendly supercapacitor
    (Royal Society of Chemistry, 2014) Sudhakar, Y.N.; Muthu, M.; Bhat, D.; Senthil Kumar, S.
    Graphite extracted from a used primary cell was converted into reduced graphene oxide (rGO) using calcium carbonate together with rapid and local Joule heating by microwave irradiation. Electrodes were prepared by ultrasonically dispersing rGO in biodegradable poly(vinylpyrrolidone) (PVP) binder and coating this on recyclable poly(ethyleneterephthalate) (PET) sheet using a low cost screen printing technique. The use of the same polymer (PVP) as a binder, in addition to as the solid polymer electrolyte (SPE), enhances the compatibility and ionic conductivity of the hydrophobic rGO electrode in the supercapacitor system. Further, the phosphoric acid (H3PO4)-doped biodegradable SPE was screen printed for the first time on the rGO electrodes. Ionic conductivity and dielectric studies of the SPE were carried out at different temperatures and different dopant acid concentrations. The morphology, composition and structure of the graphene electrode components were characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. Transmission electron microscopy (TEM) images showed a single layer or a few layers of rGO sheets and selected area electron diffraction showed the presence of slight defects. The fabricated environmentally friendly, industrially favorable and green supercapacitor showed a specific capacitance of 201 F g-1 and cyclic stability with 97% retention of the initial capacitance over 2000 cycles. Furthermore, the performance of this green supercapacitor is comparable to that of those fabricated using rGO synthesized from commercial graphite and in other literature reports. © 2014 The Royal Society of Chemistry.
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    Fabrication of hair and copper fiber reinforced polymethyl methacrylate (pmma) composites and evaluation of their mechanical properties, thermal conductivity and color stability for dental applications
    (Society for Biomaterials and Artificial Organs - India sharmacp@sbaoi.org, 2016) Jayaprakash, K.; Nandish, B.T.; Rijesh, M.; Nayak, J.; Bhat, S.M.; Shetty, K.H.K.; Nityananda Shetty, A.; Prabhu, S.
    The objective of the work was to fabricate and evaluate the impact strength, flexural strength, thermal conductivity and color stability of heat cure Polymethyl methacrylate denture base resin, reinforced with human hair fibers and copper fibers. Specimens were prepared by reinforcing human hair fibers of 2mm length and diameter in the range of 64 -78 ?m, in different quantities with respect to two different age groups and genders, to polymer-monomer mix before dough stage. Same procedure was followed to fabricate specimens with copper fibers (2mm length and 200 ?m diameter) too. The impact strength, transverse strength, thermal conductivity, and color stabilities were measured by using standard equipment's. Scanning electron microscope (SEM) was used to study the fractured surface of the fiber reinforced composites. The impact strength increased three times in hair reinforced and about twice in copper reinforced composites. The transverse strength was slightly decreased and the cause for it was investigated. Copper fiber reinforced composite significantly increased the thermal conduction. The human hair and copper reinforced Polymethyl methacrylate showed significant improvements in its mechanical properties and retained color stability similar to control specimens during storage in various beverages.
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    Fabrication and performance evaluation of hybrid supercapacitor electrodes based on carbon nanotubes and sputtered TiO2
    (Institute of Physics Publishing michael.roberts@iop.org, 2016) Aravinda, L.S.; Nagaraja, K.K.; Nagaraja, H.S.; Bhat, K.U.; Badekai Ramachandra, B.R.
    We report a simple and eco-friendly method for the fabrication of a titanium dioxide/functionalized multiwalled carbon nanotube (TiO2/FMWCNT) composite electrode for use in supercapacitors. The nanocomposite electrodes were formed by depositing titanium dioxide onto FMWCNTs using reactive magnetron sputtering, thus providing a green roue for the formation of the binder-free composite electrode. It is shown that the electrochemical performance of the fabricated electrodes can be altered by tuning the thickness of the titanium dioxide overlayer. The integrated nanocomposite electrode showed an improved specific capacitance of 90 Fg-1 in two-electrode configuration. © 2016 IOP Publishing Ltd.
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    Investigation on the performance of valveless pump for microdelivery of the fluid, fabricated using tool-based micromachining setup
    (World Scientific Publishing Co. Pte Ltd wspc@wspc.com.sg, 2017) Veeresha, R.K.; Rao, M.; Rao, R.; Tauro, A.M.
    Micropump is an integrated part of microfluidic system and is a boon to the field of miniaturization, owing to its helping hand in numerous applications mainly in biomedical, electronic cooling, fuel cells, spacecraft, etc. In this paper, an attempt is made to design and fabricate valveless pump, with active and passive valves. The actuation element used is piezowafer, piezowafer was experimentally tested and compared with simulated values from ANSYS for its peak displacement and these displacements were used to find volume pumped by pump. The pumping volumes found by experimentation are in good agreement with the simulated results. Further fabrication of valveless pump is carried out by using tool-based micromachining center which is a novel type of fabrication technique in micromachining. Through experiments, the optimum frequency of the pump was found to be 60Hz at an actuating voltage of 150V. The maximum head that a pump could pump was found to be 0.051m with pressure of 500.13Pa. The flow rate of the pump had a decreasing trend with increase in head. © 2017 World Scientific Publishing Company.
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    Fabrication of novel PPSU/ZSM-5 ultrafiltration hollow fiber membranes for separation of proteins and hazardous reactive dyes
    (Taiwan Institute of Chemical Engineers, 2018) Nayak, M.C.; Isloor, A.M.; Moslehyani, A.; Ismail, N.; A.F., A.F.
    Polyphenylsulfone (PPSU) based asymmetric hollow fiber membranes were prepared by the addition of different percentages of ZSM-5 particles by diffusion induced phase separation method. Polyvinylpyrrolidone (PVP) was used as a pore forming agent. The fabricated membranes were characterized by Field Emission scanning electron microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), contact angle, water permeability, water uptake and by porosity measurements. Membranes filtration study was performed using different proteins namely bovine serum albumin (BSA), egg albumin (EA) and hazardous dyes like Reactive black 5 (RB-5), Reactive orange 16 (RO-16) in aqueous solutions. It was found that, addition of ZSM-5 in membrane matrix showed better dye removal capacity because of its hydrophilic and adsorptive nature. The membrane (PZ-3) with higher loading of additive exhibited rejection percentages of 100% for BSA, 95.23% for EA proteins and with reactive dyes 90.81% for RB-5 and 82.84% for RO-16 as compared to the pristine HF membrane. © 2017 Taiwan Institute of Chemical Engineers
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    Fabrication of polyetherimide nanocomposite membrane with amine functionalised halloysite nanotubes for effective removal of cationic dye effluents
    (Taiwan Institute of Chemical Engineers, 2018) Hebbar, R.S.; Isloor, A.M.; Siddique, I.; Abdullah, M.S.; A.F., A.F.; Asiri, A.M.
    Naturally, occurring, low cost and eco-friendly halloysite nanotubes were chemically modified and uniformly immobilised into the polyetherimide membrane matrix with the aim of enhancing the properties and possible cationic dye rejection efficacy. The properties of fabricated nanocomposite membranes were examined by means of porosity, hydrophilicity, zeta potential and permeability. Permeation experiments revealed the enhanced water flux up to 195 L/m2h with 4 wt% additive dosage. The dye rejection efficacy of the prepared membranes was determined by using rhodamine B (Rh.B) and methylene blue (MB). The dye rejection studies were executed in terms of pH, contact time and initial dye concentration. The membrane with 4 wt% of nanomaterial dosage, showed rejection of 97% at pH 8 and 94% at pH 7 for MB and Rh.B dyes, respectively. Langmuir adsorption isotherm is the best model to explain interaction between dye molecules and membrane surface, with quantity of dye adsorbed (qmax) was observed to be 20.4 mg/g and 19.6 mg/g for MB and Rh.B, respectively. This approach showed modified membrane has good cationic dye rejection efficacy and can be efficiently employed to remove the dyes from aqueous streams. © 2018 Taiwan Institute of Chemical Engineers
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    Novel polyphenylsulfone (PPSU)/nano tin oxide (SnO2) mixed matrix ultrafiltration hollow fiber membranes: Fabrication, characterization and toxic dyes removal from aqueous solutions
    (Elsevier B.V., 2019) Nayak, M.C.; Isloor, A.M.; Siddique, I.; Balakrishna Prabhu, B.; Ismail, N.I.; Asiri, A.M.
    Novel polyphenylsulfone (PPSU)/nano tin oxide (SnO2) mixed matrix hollow fiber membranes (HFMs) were fabricated by dry-wet spinning via phase separation method. In the current research, reported the contrast between neat PPSU membrane and nanocomposite membranes (PPSU/SnO2), to determine the toxic reactive dyes namely, reactive black-5 (RB-5) and reactive orange-16 (RO-16) removal ability from the aqueous media. Scanning electron microscopy (SEM) was used to observe the HFMs cross-sectional morphological changes and surface roughness parameters of membranes were analyzed using atomic force microscopy (AFM). The surface wettability ability of HFMs was examined with a contact angle, water uptake, and porosity measurements. The cross-flow filter unit was engaged to quantify the water permeability, anti-fouling ability as well as the dye rejection ability of fabricated membranes. With increasing the SnO2 NPs wt% in PPSU polymer matrix the membrane performance was enhanced continuously, it became evident that the incorporated SnO2 NPs plays main role in membrane performance. Added, water-soluble poly (vinylpyrrolidone) (PVP) can also impact the pore morphology in membranes. At the end, PS-3 membrane exhibited lower contact angle (63.7 0), higher water uptake (74.8%), porosity (84.1%), pure water flux 362.9 L/m2 h, and high potential for dyes rejection application, of about >94% for RB-5, and >73% for RO-16 dye, respectively. From the preliminary results, it can be stated that the usage of SnO2 NPs in membrane technology become effective towards wastewater treatment. © 2019 Elsevier B.V.
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    Highly Sensitive and Stable NO2 Gas Sensors Based on SWNTs with Exceptional Recovery Time
    (Institute of Electrical and Electronics Engineers Inc., 2019) Chauhan, S.S.; Kumar, D.; Chaturvedi, P.; Rahman, M.R.
    Room temperature operable and highly sensitive NO2 gas sensors are fabricated based on (i) random and (ii) aligned networks of single-walled carbon nanotubes (SWNTs). The fabricated sensors are very sensitive, stable, and show shorter recovery time in the presence of UV light. Also, the variation of the response and recovery with network density is analyzed. The thin film resistor (TFR) of random network is fabricated by a reliable, cost-effective, and reproducible vacuum filtration method. The aligned network is fabricated using AC di-electrophoresis (DEP) technique. Electrodes spacing is optimized to avoid the chaining effect of aligned and bridged SWNTs between the gold electrode pair to enhance the stability and sensitivity of the sensor. Both the sensors based on random and aligned networks of SWNTs is tested with NO2 at room temperature. It is found that the sensor made of the aligned network shows 3.5 times more sensitivity as compared to the random networks gas sensor but recovery time increases. It is also observed that sensors fabricated by TFR and aligned network techniques are stable and having less than 0.02 % and 0.15 % change in resistance with baseline, respectively. The TFR gas sensors fabricated using as prepared (AP) and purified and low functionality (P2) SWNTs show higher stability but less sensitive compared to the aligned network. The measured complete recovery time of sensors based on random and aligned SWNTs are 50 sec and 124 sec, respectively, for 0.5 ppm NO2. It is also observed that as the network density decreases response improves but the recovery time increases. © 2001-2012 IEEE.