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ZnO nanorods were drop-casted over gold inter-digitated electrodes to fabricate chemi-resistive sensors. The response of this sensor to analyte gas Carbon Dioxide was studied as a function of the analyte concentration and sensor operating temperature. The sensing response was continuously logged in an experimental set-up containing a glass-chamber, substrate heater, micro-probes, mass-flow controllers and a datalogger. The resistance measurement was carried out, in the temperature range 100 C–450 degree in steps of 50 C, and in the CO2 concentrations range 460 ppm–2550 ppm. The sensor-response/sensitivity increases linearly with the analyte concentration, for all temperatures. The sensitivity of the sensor increases with temperature.

Titanium dioxide (TiO2) thin films were prepared by radio-frequency (13.56 MHz) reactive sputtering onto glass substrate with different oxygen flow rates while maintaining a constant Ar flow rate. The structural and optical properties of these films were studied with variation in O2 flow rate. X-ray diffraction (XRD) analysis of these films reveals the presence of anatase and rutile phases. The lattice parameters and crystallite size were evaluated from XRD patterns. The optical properties of these films were correlated with their morphological nature. Field emission scanning electron microscopy (FESEM) results show a dense granular morphology and the particle size is found to decrease with increase in oxygen flow rate. The average optical transmittance was observed to be 96% for all the films. The room temperature photoluminescence (PL) spectroscopy revealed a blue shift of the near band edge emission as the oxygen flow rate is increased and defect related emissions is shifted towards red region.

ZnO thin films were deposited on glass substrates by radio-frequency (RF) reactive sputtering under different O2 flow rates, with constant Ar flow rate (50sccm). The dependence of O2 flow rate on s...

A novel, needle array dry electrode consisting of 10 × 10 array of stainless steel (SS) Microtips was developed for electroencephalography (EEG) monitoring. The developed dry electrode uses commercially available, inexpensive, SS acupuncture needles certified for invasive use, to collect the EEG signal. The microtips of the acupuncture needles project out of a flat Teflon base by approximately 150 μm. Mechanical failure analysis was carried out, with theoretical calculations for individual needles and experimental measurements with a universal testing machine (UTM). The theoretically calculated critical load for failure for individual needle was 0.88 N, while the UTM measurements show the failure occurring at 0.95 N; this difference is probably due to the simplified assumptions used in calculations. The UTM measurements of the individual needle applied against a Silicone elastomer reveal that the force required for the penetration of the needle of the electrode into skin maybe as low as 0.01 N. Needle array insertion into silicone elastomer sheet and its optical inspection was carried out to assess the ability of the microneedles to penetrate the skin. The impedance of the electrode, measured in three electrode configuration in 0.9% NaCl solution, was approximately 6.8KΩ at 20 Hz, which is sufficiently low to fulfill the requirements of biopotential measurement. The construction and characteristics of the developed needle array dry electrode show that they are suitable for penetrating the stratum corneum of the skin and acquire the EEG signal directly from the interstitial fluidic layer underneath. The construction of the electrode and its mechanical and electrical characteristics show that it is a promising dry electrode for long duration EEG Monitoring.

Wavelength modulation spectroscopy is a versatile technique for wide range of applications such as determination of gas/chemical concentration, temperature and velocity/flux of gaseous molecules in industrial, biomedical and aerospace industry. A WMS based system/ sensor consists of various sub-systems. One important subsystem is the photo-detection circuit which is used to detect the laser light and condition it in accordance with the signal processing block. This paper presents the design and simulation results of photo-detection circuit using OrCAD Pspice. This design is implementedand tested for the detection of optical signal and is compared with the already established bench model setup of Tunable Diode Laser Absorption Spectroscopy (TDLAS) based oxygen sensor. The simulation results show that the designed circuit is capable of detecting optical signal in 50uV range.

Wavelength Modulation Spectroscopy (WMS) using tunable diode laser is a versatile method for determination of concentration, temperature and velocity of absorbing gaseous molecules. This technique finds major application in industrial and scientific areas. An important component of sensors/systems based on these techniques is the phase sensitive detection for demodulation, in the form of hardware or software based lock-in amplifier. This paper presents the details of (a) a MATLAB based Digital Lock-in amplifier technique for extraction of harmonics (1f & 2f), from the wavelength modulated optical absorption signal, and (b) a MATLAB based program for calculating the oxygen concentration from 1f and 2f harmonics. The oxygen concentration has been measured using MATLAB implemented digital lock-in-amplifier and concentration computation formula. The deviation in the measured Oxygen concentration from the actual Oxygen concentration supplied through the mass flow controllers is less than 1%. The oxygen concentration measured using digital Lock-in amplifier has a deviation within 0.2% as compared to measurement from hardware measuring device.

Tunable Diode Laser Absorption Spectroscopy (TDLAS) based gas sensing technology, has widespread applications, ranging from use in biomedical industry to aerospace applications. An experimental set-up was established to measure concentration of oxygen gas in the range 0–100% using TDLAS technique. The oxygen absorption at 760.241 nm was scanned with a tunable DFB laser, and wavelength modulation spectroscopy was used to obtain the harmonics (1f, 2f, 3f & 4f) of the oxygen absorption signal. The modulation parameters such as the modulation voltage, modulation frequency, reference phase, time constant of lock in amplifier, the tuning voltage, and the tuning frequency were optimized to obtain the harmonics of high amplitude and narrow half width. Keeping the experimental parameters constant, the oxygen concentration measurements were obtained by the following three methodologies, viz, (i) using only the 2nd harmonic, (ii) using the 2nd and 4th harmonics and, (iii) using the 1st and 2nd harmonics. The results of these measurements were compared and the merits and drawbacks of these methods are discussed.

Multiwalled carbon nanotube (CNT) arrays were grown by catalytic thermal decomposition of acetylene, over Fe-catalyst deposited on Si-wafer in the temperature range 700–750 °C. The growth parameters were optimized to obtain dense arrays of multiwalled CNTs of uniform diameter. The vertical cross-section of the grown nanotube arrays reveals a quasi-vertical alignment of the nanotubes. The effect of varying the thickness of the catalyst layer and the effect of increasing the growth duration on the morphology and distribution of the grown nanotubes were studied. A scotch-tape test to check the strength of adhesion of the grown CNTs to the Si-substrate surface reveals a strong adhesion between the grown nanotubes and the substrate surface. Transmission electron microscopy analysis of the grown CNTs shows that the grown CNTs are multiwalled nanotubes with a bamboo structure, and follow the base-growth mechanism.

Growth of Hg1-xCdxTe epitaxial films by a new technique called asymmetric vapour phase epitaxy (ASVPE) has been carried out on CdTe and CZT substrates. The critical problems faced in normal vapour phase epitaxy technique like poor surface morphology, composition gradient and dislocation multiplication have been successfully solved. The epitaxial films have been electrically characterized by using the Hall effect and capacitance-voltage (C-V) measurements.

The liquid phase epitaxial growth of high-quality Hg1−xCdxTe epilayers from Te-rich solution using a modified horizontal slider is described. The horizontal slider has the provisions for (i) the compensation of Hg loss from the growth solution and (ii) an in situ meltback of the substrate surface immediately prior to the layer growth. The two major technological difficulties posed by the low surface tension of Te-solution were overcome to achieve (i) the intact removal of the layer/substrate from the substrate cavity and (ii) a complete wipe-off of the growth solution from the epilayer surface.

The surface morphology of Hg 0.8 Cd 0.2 Te epilayers on (111)±0.5° oriented Cd 0.96 Zn 0.04 Te substrates grown from Te-rich solution by LPE using horizontal slider has been studied. The surface morphology, apart from exhibiting the terrace patterns typical of LPE growth, shows other surface features like pin holes/voids, Hg-evaporation points, slider scratch marks and some long-distance perturbations in the layer thickness visible to the naked eye. Also, discussed are the surface morphology of the layer at edge regions and the effect of non-smooth slide-out of the layer on its surface morphology.

The characteristics of HgCdTe epilayers grown in a modified horizontal slider system, are reported here. The surface morphology of the grown layers, their IR transmission characteristics, depth and lateral compositional uniformity, structural and electrical characteristics are discussed.

Dry electrodes, which have an array of vertically aligned conducting micro-needles over a conducting substrate/base are most suitable for long-term continuous monitoring of EEG-signal, and overcomesthe disadvantages of conventional wet electrodes. A crucial design requirement for thesemicro-needlearrays, is the choice of the needle material with suitable mechanical strength to penetrate the skin without mechanical failure. This paper gives, the results of mechanical failure analysis of different needle materials that have been typically used/proposed for invasive use. A conical needle with 150μ width at the base and 10μ width at the tip, and length in the range 10μ - 200μ was taken up for calculation. The Critical load for failure, falls in the following descending order for the selected materials: viz., Carbon Nanofibre (CNF), Titanium-alloy (Ti 6-4), Single Crystal Silicon, Nickel, Tungsten, Platinum-Iridium (Pt90 percent-Ir10 percent), Stainless Steel (SS304),Poly Methyl Methacrylate (PMMA), Polyimide, Polycarbonate, Gold, Silver, Photoresist-SU8, Polyurethane and Poly DiMethylSiloxane (PDMS).Taking the most accepted value of 0.1N as the penetration force required for needle penetration into skin, it is seen that for a needle length of 100μ, the following materials, Carbon Nanofibre (CNF), Titanium-alloy (Ti 6-4), Single Crystal Silicon, Nickel, Tungsten, Platinum -Iridium (Pt90 percent-Ir10 percent) andStainless Steel (SS304), can penetrate the skin without mechanical failure.

One of the most pressing issues in the growth of high quality single crystal Cd 0.96 Zn 0.04 Te material, is to achieve homogenization of the high axial variation of Zn concentration, caused by the larger than unity segregation coefficient of Zn in CdTe. This is achieved in our crystals (i) by thermal annealing of the CdZnTe crystal, which redistributes the as grown Zn distribution by solid state diffusion of Zn (this solid state diffusion of Zn occurs at three stages (a) during the growth when the solidified crystal is near to the melting point temperature, (b) during the post growth annealing of the crystal at a high temperature and (c) during the cooldown to room temperature) and (ii) by the reduction of Zn segregation during the growth stage by enhanced convective mixing of the melt, through a proper choice of ampoule and furnace dimensions. By adopting suitable growth parameters and sufficient post growth annealing it has been possible to grow Cd 0.96 Zn 0.04 Te crystals, which have nearly 75% of their fraction within 1% Zn concentration variation.

Cathodoluminescence investigations on bulk undoped semi-insulating GaAs samples taken from different sources reveal the presence of a deep level emission at 0.9 eV at 77 K, with a narrow full width at half maximum of 8 meV. The temperature-dependent and beam-parameter-dependent studies indicate that, the probable origin for this emission may be some nanocluster/quantum-dot like structures with a band gap of 0.9 eV, present inside the semi-insulating GaAs crystal lattice. One possibility for such structures in semi-insulating GaAs are clusters/nanoprecipitates of arsenic.

Oxygen Concentration Monitoring is an important requirement in fighter aircrafts. This paper reports the results of performance evaluation of an indigenous Zirconia Oxygen Sensor, which meets the requirements of a fighter aircraft environment. The Oxygen Sensor uses a solid state electrolyte, Zirconia stabilized with 8mol% Yttria, in the form of a Nernst Cell, which when heated above 600°C, develops an emf proportional to the ratio of partial pressures of Oxygen across its two electrodes. The reference gas used is air (21% O 2 ). The sensor performs satisfactorily in a wide range of environments faced in the fighter aircraft, such as altitudes upto 50K feet, the extreme temperatures of −40C to 65C, arrestor-hook shock, etc. These results are presented here.

Tunable Diode Laser Absorption Spectroscopy (TDLAS) based gas sensing technology is a futuristic technology that has wide application in aerospace industry. In this paper we present the preliminary measurements on a TDLAS based Oxygen Sensor. TDLAS bench model setup has been established to measure the 1st and 2nd harmonics of the absorption signal. If-normalized WMS-2 technique is used for calculation of percentage oxygen concentration. The result has been compared with the 2nd harmonic detection technique and observed that the measured oxygen concentration coincides with the actual oxygen concentration using If-normalized WMS-2 technique.

CsCl crystals grown from water solution give a broad fluorescence emission between 340 nm and 500 nm due to the OH- ions embedded in the lattice, which are also responsible for the 267 nm absorption band observed in these crystals. Eu doped CsCl crystals give a prominent emission with maximum at 440 nm, due to the divalent Eu ions. The emission due to OH- ions is also observed in CsCl:Eu crystals.

The optical absorption and TL studies of γ-irradiated CsCl:Eu crystals show the participation of the divalent europium ions in the TL process. The glow curves show new peaks in the higher temperature regions at 418 and 441 K, not observed in pure CsCl.

The TL emission spectra of γ-irradiated CsCl crystals exhibit bands at 407 and 470 nm. These results are correlated with the glow curves and optical absorption, and a mechanism for the TL process in which V-centers are the recombination centers is suggested.

Carbon nanotube based electrodes can overcome the drawbacks posed by the conventional wet electrodes, used for physiological monitoring. Here, multiwalled CNT arrays were grown on highly doped n-type Si-wafers with Fe-catalyst layer, using a thermal CVD system. Acetylene was used as the carbon source gas, while Ammonia was the reducing gas and Argon was the purging inert gas, in these experiments. The thermal annealing of the catalyst layer and the carbon nanotube growth schedule, were optimized to get a dense and uniform multiwalled CNT array. SEM images reveal dense uniform growth of multiwalled carbon nanotubes over the entire catalyst deposited area. The cross-sectional images reveal a quasi-vertical alignment.

The bioelectrical potentials generated within the human body are the result of electrochemical activity in the excitable cells of the nervous, muscular or glandular tissues. The ionic potentials are measured using biopotential electrodes which convert ionic potentials to electronic potentials. The commonly monitored biopotential signals are Electrocardiogram (ECG), Electroencephalogram (EEG) and Electromyogram (EMG). The electrodes used to monitor biopotential signals are Ag-AgCl and gold, which require skin preparation by means of scrubbing to remove the dead cells and application of electrolytic gel to reduce the skin contact resistance. The gels used in biopotential recordings dry out when used for longer durations and add noise to the signals and also prolonged use of gels cause irritations and rashes to skin. Also noises such as motion artifact and baseline wander are added to the biopotential signals as the electrode floats over the electrolytic gel during monitoring. To overcome these drawbacks, dry electrodes are used, where the electrodes are held against the skin surface to establish contact with the skin without the need for electrolytic fluids or gels. The major drawback associated with the dry electrodes is the high skin-electrode impedance in the low frequency range between 0.1-120 Hz, which makes it difficult to acquire clean and noise free biopotential signals. The paper presents the design and development of biopotential data acquisition and processing system to acquire biopotential signals from dry electrodes. The electrode-skin-electrode- impedance (ESEI) measurements was carried out for the dry electrodes by impedance spectroscopy. The biopotential signals are processed using an instrumentation amplifier with high CMRR and high input impedance achieved by boot strapping the input terminals. The signals are band limited by means of a second order Butterworth band pass filters to eliminate noise. The processed biopotential signals are digitized and transmitted wirelessly to a remote monitoring station.

Cathodoluminescence investigations on bulk undoped semi-insulating GaAs (SI GaAs) samples taken from different sources reveal the presence of a sharp, long wavelength emission at 0.9 eV (at 10 K), with a very narrow full-width at half-maximum of 7 meV, which shows a redshift and thermal broadening upon increasing the temperature. At 10 K, the liquid encapsulated Czokralski grown undoped SI GaAs samples show an additional lower energy emission at 0.89 eV, which is absent in the vertical gradient freeze grown undoped SI GaAs samples. Systematic temperature dependent and beam parameter dependent studies indicate that, the probable origin for the 0.9 eV emission maybe some quantum-dot/nano-cluster like structures present inside the SI GaAs crystal lattice.