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Publications (45)11.42 Total impact

  • Tushar Kanti Bera, J. Nagaraju
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    ABSTRACT: Surface electrodes are essentially required to be switched by analogue multiplexers operating with a set of parallel digital data for boundary data collection in electrical impedance tomography EIT. A 16 electrode EIT system needs 16-bit parallel digital data to operate the multiplexers. More electrodes in an EIT system require more digital data bits. In this paper, a common ground current injection method is proposed for a 16 electrodes EIT system to switch the electrodes with reduced number of digital data. Common ground method needs only two 16:1 multiplexers operating with only 8-bit parallel digital data. Boundary data are collected from practical phantoms by injecting a constant current using common ground method. Resistivity images are reconstructed in EIDORS and the results are compared with the images obtained in opposite current pattern. Reconstructed images obtained with common ground method are found similar to the images obtained with the conventional opposite current pattern.
    International Journal of Communication Networks and Distributed Systems 11/2014; 12(1):47-68.
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    ABSTRACT: Chalcopyrite Cu(In,Al)Se2 (CIAS) thin films are grown on stainless steel substrate through one-step electrodeposition at room temperature. Indium is partially replaced with aluminum to increase the band gap of CuInSe2 without creating significant change in the original structure. The deposition potential is optimized at − 0.8 V (vs. SCE) and annealing of the films is performed in vacuum to remove binary phases present in the as-deposited films. In/Al ratio is varied from 1/9 to 8/2, to find the suitability for solar cell fabrication. For In/Al ratio of less than 8/2, CuAlSe2 phase is formed in the film in addition to the CIAS phase. Depth profile X-ray photoelectron spectroscopy analysis of the CIAS sample prepared with In/Al ratio of 8/2 in the precursor solution confirmed the existence of single phase CIAS throughout the film. This film showed p-type conductivity while the rest of the samples with In/Al ratio less than 8/2 showed n-type conductivity. The band gap of the film varied from 1.06 to 1.45 eV, with variation in deposition potential. Structural, optical, morphological, compositional and electrical characterizations are carried out to establish the suitability of this film for solar cell fabrication.
    Thin Solid Films 01/2014; 551:1–7. · 1.87 Impact Factor
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    ABSTRACT: A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve the image quality in Electrical Impedance Tomography (EIT). PEPR method defines the regularization parameter as a function of the projection error developed by difference between experimental measurements and calculated data. The regularization parameter in the reconstruction algorithm gets modified automatically according to the noise level in measured data and ill-posedness of the Hessian matrix. Resistivity imaging of practical phantoms in a Model Based Iterative Image Reconstruction (MoBIIR) algorithm as well as with Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS) with PEPR. The effect of PEPR method is also studied with phantoms with different configurations and with different current injection methods. All the resistivity images reconstructed with PEPR method are compared with the single step regularization (STR) and Modified Levenberg Regularization (LMR) techniques. The results show that, the PEPR technique reduces the projection error and solution error in each iterations both for simulated and experimental data in both the algorithms and improves the reconstructed images with better contrast to noise ratio (CNR), percentage of contrast recovery (PCR), coefficient of contrast (COC) and diametric resistivity profile (DRP).
    Measurement. 01/2014; 49:329–350.
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    ABSTRACT: Silver Indium Di-sulfide (AgInS2) thin films are deposited using ultrasonic spray pyrolysis technique and the effect of substrate temperature (Ts) on film growth is studied by varying the temperature from 250 to 400 °C. From the structural analysis, orthorhombic AgInS2 phase is identified with preferential orientation along (002) plane. Further analysis with Raman revealed the coexistence of Cu–Au ordered and chalcopyrite structures in the films. Stoichiometric films are obtained at Ts of 300 °C. Above 300 °C, the film conductivity changed from p to n-type and the grain size decreased. The band gap of AgInS2 films varied from 1.55 to 1.89 eV and absorption coefficient is found to be > 104 cm− 1. The films have sheet resistance in the range of 0.05 to 1300 Ω/□. Both p and n type films are prepared through this technique without any external doping.
    Thin Solid Films 01/2014; 550:71–75. · 1.87 Impact Factor
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    Tushar Kanti Bera, J. Nagaraju
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    ABSTRACT: Practical phantoms are essential to assess the electrical impedance tomography (EIT) systems for their validation, calibration and comparison purposes. Metal surface electrodes are generally used in practical phantoms which reduce the SNR of the boundary data due to their design and development errors. Novel flexible and biocompatible gold electrode arrays of high geometric precision are proposed to improve the boundary data quality in EIT. The flexible gold electrode arrays are developed on flexible FR4 sheets using thin film technology and practical gold electrode phantoms are developed with different configurations. Injecting a constant current to the phantom boundary the surface potentials are measured by a LabVIEW based data acquisition system and the resistivity images are reconstructed in EIDORS. Boundary data profile and the resistivity images obtained from the gold electrode phantoms are compared with identical phantoms developed with stainless steel electrodes. Surface profilometry, microscopy and the impedance spectroscopy show that the gold electrode arrays are smooth, geometrically precised and less resistive. Results show that the boundary data accuracy and image quality are improved with gold electrode arrays. Results show that the diametric resistivity plot (DRP), contrast to noise ratio (CNR), percentage of contrast recovery (PCR) and coefficient of contrast (COC) of reconstructed images are improved in gold electrode phantoms.
    Measurement 01/2014; 47:264–286. · 1.13 Impact Factor
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    ABSTRACT: Electrical Impedance Tomography (EIT) is a computerized medical imaging technique which reconstructs the electrical impedance images of a domain under test from the boundary voltage–current data measured by an EIT electronic instrumentation using an image reconstruction algorithm. Being a computed tomography technique, EIT injects a constant current to the patient's body through the surface electrodes surrounding the domain to be imaged ( ) and tries to calculate the spatial distribution of electrical conductivity or resistivity of the closed conducting domain using the potentials developed at the domain boundary ( ). Practical phantoms are essentially required to study, test and calibrate a medical EIT system for certifying the system before applying it on patients for diagnostic imaging. Therefore, the EIT phantoms are essentially required to generate boundary data for studying and assessing the instrumentation and inverse solvers a in EIT. For proper assessment of an inverse solver of a 2D EIT system, a perfect 2D practical phantom is required. As the practical phantoms are the assemblies of the objects with 3D geometries, the developing of a practical 2D-phantom is a great challenge and therefore, the boundary data generated from the practical phantoms with 3D geometry are found inappropriate for assessing a 2D inverse solver. Furthermore, the boundary data errors contributed by the instrumentation are also difficult to separate from the errors developed by the 3D phantoms. Hence, the errorless boundary data are found essential to assess the inverse solver in 2D EIT. In this direction, a MatLAB-based Virtual Phantom for 2D EIT (MatVP2DEIT) is developed to generate accurate boundary data for assessing the 2D-EIT inverse solvers and the image reconstruction accuracy. MatVP2DEIT is a MatLAB-based computer program which simulates a phantom in computer and generates the boundary potential data as the outputs by using the combinations of different phantom parameters as the inputs to the program. Phantom diameter, inhomogeneity geometry (shape, size and position), number of inhomogeneities, applied current magnitude, background resistivity, inhomogeneity resistivity all are set as the phantom variables which are provided as the input parameters to the MatVP2DEIT for simulating different phantom configurations. A constant current injection is simulated at the phantom boundary with different current injection protocols and boundary potential data are calculated. Boundary data sets are generated with different phantom configurations obtained with the different combinations of the phantom variables and the resistivity images are reconstructed using EIDORS. Boundary data of the virtual phantoms, containing inhomogeneities with complex geometries, are also generated for different current injection patterns using MatVP2DEIT and the resistivity imaging is studied. The effect of regularization method on the image reconstruction is also studied with the data generated by MatVP2DEIT. Resistivity images are evaluated by studying the resistivity parameters and contrast parameters estimated from the elemental resistivity profiles of the reconstructed phantom domain. Results show that the MatVP2DEIT generates accurate boundary data for different types of single or multiple objects which are efficient and accurate enough to reconstruct the resistivity images in EIDORS. The spatial resolution studies show that, the resistivity imaging conducted with the boundary data generated by MatVP2DEIT with 2048 elements, can reconstruct two circular inhomogeneities placed with a minimum distance (boundary to boundary) of 2 mm. It is also observed that, in MatVP2DEIT with 2048 elements, the boundary data generated for a phantom with a circular inhomogeneity of a diameter less than 7% of that of the phantom domain can produce resistivity images in EIDORS with a 1968 element mesh. Results also show that the MatVP2DEIT accurately generates the boundary data for neighbouring, opposite reference and trigonometric current patterns which are very suitable for resistivity reconstruction studies. MatVP2DEIT generated data are also found suitable for studying the effect of the different regularization methods on reconstruction process. Comparing the reconstructed image with an original geometry made in MatVP2DEIT, it would be easier to study the resistivity imaging procedures as well as the inverse solver performance. Using the proposed MatVP2DEIT software with modified domains, the cross sectional anatomy of a number of body parts can be simulated in PC and the impedance image reconstruction of human anatomy can be studied.
    Journal of Medical Imaging and Health Informatics 01/2014; 4(2). · 0.64 Impact Factor
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    ABSTRACT: A constant current source is essential for impedance measurement techniques in several biomedical applications. The impedance measurement studies in biomedical applications such as bioelectrical impedance analysis (BIA), electrical impedance plethysmography (IPG), electrical impedance myography (EIM), electrical impedance cardiography (ICG), electrical impedance spectroscopy (EIS), electrical impedance tomography (EIT) all need a high precision impedance measurement circuit with high signal to noise ratio (SNR). Moreover the impedance measurement circuit applied to the biomedical, clinical or medical applications such as human subject studies should have a better patient safety. In this direction a Battery-based Constant Current Source (Bb-CCS) is developed for biomedical applications. The Bb-CCS is developed with a modified Howland current source (MHCS) fed by a battery based power supply (BBPS). The current amplitude, frequency and waveforms are set as the circuit variables which are found as adjustable as per the requirements. The frequency responses, load response, Fast Fourier Transform (FFT) of the Bb-CCS are studied and results show that the Bb-CCS can be suitably used for multifrequency impedance measurement methods in biomedical applications.
    Computing, Communications and Networking Technologies (ICCCNT),2013 Fourth International Conference on, Tiruchengode; 07/2013
  • Tushar Kanti Bera, J. Nagaraju
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    ABSTRACT: Studying of elemental resistivity profile of reconstructed images in Electrical Impedance Tomography (EIT) is essential to assess its image quality, reconstruction process and the systems performance. Visual assess- ment of the impedance images must not be accepted as the ultimate and sufficient judgment criteria for reconstruction efficiency of the tomograph. To identify the better image contrast and better image quality in 2D EIT, resistivity images are studied with image parameters calculate from the elemental resistivity profiles. Boundary potential data are simulated for different phantom configurations and the resistivity images are reconstructed using Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS). Images obtained at different iterations for all the phantom configurations are studied with image contrast parameters calculated from the elemental resistivity matrices obtained for each image. Mean Inhomogeneity Resistivity (IRMean), mean Background Resistivity (BRMean), Contrast to Noise Ratio (CNR), Percentage of Contrast Recovery (PCR) and Diametric Resistivity Profiles (DRP) are calculated from the elemental resistivity matrices and the images elemental resistivity profiles are analyzed. Image analyzing parameters are found essential to assess the contrast and quality of the reconstructed images more technically, qualita- tively and quantitatively.
    International Journal of Information Processing. 01/2013; 7(1):1-14.
  • Tushar Kanti Bera, J. Nagaraju
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    ABSTRACT: Phantoms are essentially required to generate boundary data for studying the inverse solver performance in electrical impedance tomography (EIT). A MATLAB-based boundary data simulator (BDS) is developed to generate accurate boundary data using neighbouring current pattern for assessing the EIT inverse solvers. Domain diameter, inhomogeneity number, inhomogeneity geometry (shape, size, and position), background conductivity, and inhomogeneity conductivity are all set as BDS input variables. Different sets of boundary data are generated by changing the input variables of the BDS, and resistivity images are reconstructed using electrical impedance tomography and diffuse optical tomography reconstruction software (EIDORS). Results show that the BDS generates accurate boundary data for different types of single or multiple objects which are efficient enough to reconstruct the resistivity images for assessing the inverse solver. It is noticed that for the BDS with 2048 elements, the boundary data for all inhomogeneities with a diameter larger than 13.3% of that of the phantom are accurate enough to reconstruct the resistivity images in EIDORS-2D. By comparing the reconstructed image with an original geometry made in BDS, it would be easier to study the inverse solver performance and the origin of the boundary data error can be identified.
    Journal of Medical Engineering. 01/2013; 2013(Article ID 193578):15 pages.
  • K.G. Deepa, J. Nagaraju
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    ABSTRACT: Tin sulphide (SnS) quantum dots of size ranging from 2.4 to 14.4 nm are prepared by chemical precipitation method in aqueous media. Growth of the SnS particles is monitored by controlling the deposition time. Both XRD and SAED patterns confirm that the particles possess orthorhombic structure. The uncapped SnS particles showed secondary phases like Sn2S3 and SnS2 which is visible in the SAED pattern. From the electrochemical characterization, HOMO–LUMO levels of both TiO2 and SnS are determined and the band alignment is found to be favorable for electron transfer from SnS to TiO2. Moreover, the HOMO–LUMO levels varied for different particle sizes. Solar cell is fabricated by sensitizing porous TiO2 thin film with SnS QDs. Cell structure is characterized with and without buffer layer between FTO and TiO2. Without the buffer layer, cell showed an open circuit voltage (Voc) of 504 mV and short circuit current density (Jsc) of 2.3 mA/cm2 under AM1.5 condition. The low fill factor of this structure (15%) is seen to be increased drastically to 51%, on the incorporation of the buffer layer. The cell characteristics are analyzed using two different size quantum dots.
    Materials Science and Engineering: B. 08/2012; 177(13):1023–1028.
  • Tushar Kanti Bera, J. Nagaraju
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    ABSTRACT: A current injection pattern in Electrical Impedance Tomography (EIT) has its own current distribution profile within the domain under test. Hence, different current patterns have different sensitivity, spatial resolution and distinguishability. Image reconstruction studies with practical phantoms are essential to assess the performance of EIT systems for their validation, calibration and comparison purposes. Impedance imaging of real tissue phantoms with different current injection methods is also essential for better assessment of the biomedical EIT systems. Chicken tissue paste phantoms and chicken tissue block phantoms are developed and the resistivity image reconstruction is studied with different current injection methods. A 16-electrode array is placed inside the phantom tank and the tank is filled with chicken muscle tissue paste or chicken tissue blocks as the background mediums. Chicken fat tissue, chicken bone, air hole and nylon cylinders are used as the inhomogeneity to obtained different phantom configurations. A low magnitude low frequency constant sinusoidal current is injected at the phantom boundary with opposite and neighboring current patterns and the boundary potentials are measured. Resistivity images are reconstructed from the boundary data using EIDORS and the reconstructed images are analyzed with the contrast parameters calculated from their elemental resistivity profiles. Results show that the resistivity profiles of all the phantom domains are successfully reconstructed with a proper background resistivity and high inhomogeneity resistivity for both the current injection methods. Reconstructed images show that, for all the chicken tissue phantoms, the inhomogeneities are suitably reconstructed with both the current injection protocols though the chicken tissue block phantom and opposite method are found more suitable. It is observed that the boundary potentials of the chicken tissue block phantoms are higher than the chicken tissue paste phantom. SNR of the chicken tissue block phantoms are found comparatively more and hence the chicken tissue block phantom is found more suitable for its lower noise performance. The background noise is found less in opposite method for all the phantom configurations which yields the better resistivity images with high PCR and COC and proper IRMean and IRMax neighboring method showed higher noise level for both the chicken tissue paste phantoms and chicken tissue block phantoms with all the inhomogeneities. Opposite method is found more suitable for both the chicken tissue phantoms, and also, chicken tissue block phantoms are found more suitable compared to the chicken tissue paste phantom.
    Measurement 05/2012; 45(4):663–682. · 1.13 Impact Factor
  • K.G. Deepa, M.A. Sunil, J. Nagaraju
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    ABSTRACT: Different size SnS quantum dots are prepared by chemical bath deposition. size of the particles are varied from 2.4 to 14.4 nm by varying the deposition time from 30 to 120 min. solar cells are fabricated with these quantum dots. Cu2S coated FTO is used as counter electrode instead of the conventional platinum electrode and Na2S as electrolyte. Cu2S acts as a good catalyst for the polysulfide electrolyte. on comparing with a cell having platinum counter electrode and iodine based electrolyte, Cu2S -polysulfide combination found to improve both the short circuit current and fill factor of the solar cell.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
  • M.A. Sunil, K.G. Deepa, J. Nagaraju
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    ABSTRACT: AgInS2 thin films are deposited by chemical spray pyrolysis technique. Aqueous solution of Silver Nitrate (AgNO3), Indium Chloride (InCl3), and Thiourea (CS (NH2)2) are used as the precursors and substrate temperature is kept at 3500C. Effect of variation in sulfur concentration was studied by varying the [S2-]/ [In3+] ratio. Orthorhombic structured AgInS2 with preferred orientation along (0 0 2) plane is identified using XRD. Even though the crystallinity decreased with increase in sulfur concentration, Ag2O3 phase which was observed in the sulfur poor sample was found to be disappeared for higher Sulfur concentration. EDAX data revealed nearly stoichiometric films for [S2-]/ [In3+] ratio 5, with atomic percentage of 26.69, 23.80, 49.81 for Ag, In, S respectively. SEM images show a gradual change from non-spherical to spherical grains with increase in sulfur concentration. Band gap measured was in the range 1.85 to 2.03 eV.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
  • Tushar Kanti Bera, J. Nagaraju
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    ABSTRACT: Multifrequency Electrical Impedance Tomography (EIT) is preferred for imaging of biomedical objects to study their wide range of tissue conductivity profiles among different type of subjects under test. In this direction, a multifrequency EIT system is developed for biomedical imaging and the resistivity imaging of a practical phantom is studied at different frequencies. Practical biological phantoms are developed with NaCl solution as the bathing medium and vegetable tissue cylinders as the inhomogeneity. A sinusoidal constant current is injected to the boundary of the practical phantoms at different frequency levels and the surface potentials are measured. Resistivity images are reconstructed from the boundary potential data using EIDORS and images are analyzed with image contrast parameters. Results show that the instrumentation part of the developed EIT system injects constant current at different frequency levels and measures the boundary potential data. Boundary data are successfully generated for all the frequencies and found suitable for image reconstruction. CNR, PCR and COC of the resistivity images show that the resistivity images are efficiently reconstructed from the boundary data acquired from the multifrequency EIT system.
    IEEE International Conference on Signal Processing and Communications (SPCOM 2012), Bangalore, India; 01/2012
  • Tushar Kanti Bera, J. Nagaraju
    International conference on soft computing for problem solving (SocProS 2012), Jaipur, India; 01/2012
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    Journal of Electrical Bioimpedance. 03/2011; 2:2-12.
  • Journal of Electrical Bioimpedance. 03/2011; 2:33-47.
  • Tushar Kanti Bera, Jampana Nagaraju
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    ABSTRACT: Resistivity imaging of a reconfigurable phantom with circular inhomogeneities is studied with a simple instrumentation and data acquisition system for Electrical Impedance Tomography. The reconfigurable phantom is developed with stainless steel electrodes and a sinusoidal current of constant amplitude is injected to the phantom boundary using opposite current injection protocol. Nylon and polypropylene cylinders with different cross sectional areas are kept inside the phantom and the boundary potential data are collected. The instrumentation and the data acquisition system with a DIP switch-based multiplexer board are used to inject a constant current of desired amplitude and frequency. Voltage data for the first eight current patterns (128 voltage data) are found to be sufficient to reconstruct the inhomogeneities and hence the acquisition time is reduced. Resistivity images are reconstructed from the boundary data for different inhomogeneity positions using EIDORS-2D. The results show that the shape and resistivity of the inhomogeneity as well as the background resistivity are successfully reconstructed from the potential data for single or double inhomogeneity phantoms. The resistivity images obtained from the single and double inhomogeneity phantom clearly indicate the inhomogeneity as the high resistive material. Contrast to noise ratio (CNR) and contrast recovery (CR) of the reconstructed images are found high for the inhomogeneities near all the electrodes arbitrarily chosen for the entire study. (C) 2010 Elsevier Ltd. All rights reserved.
    Measurement 01/2011; · 1.13 Impact Factor
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    Tushar Kanti Bera, J. Nagaraju
    Journal of Electrical Bioimpedance. 01/2011; 2:48-63.
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    ABSTRACT: Experimental studies conducted on oxygen-free high conductivity (OFHC) Cu contacts are presented in this paper. Effect of normal force, surface roughness, initial run-in, sliding speed, and liquid lubricants on ECR and COF is studied. Experiments are conducted with the help of indigenously developed test setup, consisting of a reciprocating pin-on-flat sliding arrangement. All contacts showed a decrease in ECR with increase in normal force. At small speeds (≤1.0mm/s), both ECR and COF are found to be independent of sliding speed. A significant decrease in ECR and COF is observed with progressive sliding during the initial cycles. Roughness of the flat sample is found to have significant effect on ECR and COF, especially during initial sliding cycles. Contacts exhibited an inverse relationship between ECR and COF in the mild wear regime (0.2 < COF ≤ 0.4). Liquid lubricants having low viscosity exhibited reasonably low values of ECR and COF for prolonged sliding duration. Presence of wear debris at the sliding zone is found to have significant effect on both ECR and COF. Wear of the sliding surfaces is analyzed using scanning electron microscopy (SEM) and correlated with the observed behavior of ECR and COF.
    01/2011;