Nagaraju Jampana

A multifrequency constant current source suitable for Electrical Impedance Tomography (EIT)

Constant current source is essential in Electrical Impedance Tomography (EIT) for injecting a sinusoidal constant current to the phantom boundary. In medical EIT the multifrequency scanning is desired for studying the wide range of tissue conductivity among different type of subjects. A multifrequency constant current source is developed for medical EIT and the boundary data of a practical phantom is studied. A sinusoidal constant crrent is injected to the phantom boundary at different frequency levels and the boundary potentials are measured. Results show that the developed current source efficiently generate constant current with minimal amount of noise at different frequency levels. Boundary data are successfully generated at four different frequencies and found suitable for image reconstruction study in multifrequecy EIT.

Improving the image reconstruction in Electrical Impedance Tomography (EIT) with block matrix-based Multiple Regularization (BMMR): A practical phantom study

Conductivity image reconstruction is studied with a Block Matrix based Multiple Regularization (BMMR) technique in Electrical Impedance Tomography (EIT) using practical phantoms. The response matrix (JTJ) is partitioned into several sub-block matrices and the largest element of each sub-block matrices is taken as regularization parameter for the nodes of the FEM mesh contained by that sub-block. Boundary potential data are collected from practical phantoms with different inhomogeneity configurations and the conductivity images are reconstructed in a Model Based Iterative Image Reconstruction (MoBIIR) algorithm. Conductivity images, reconstructed with BMMR technique, are compared with the images obtained with Single-step Tikhonov Regularization (STR) and modified Levenberg-Marquardt Regularization (LMR) methods. Results show that BMMR technique reduces the reconstruction error and reconstruct the better conductivity images by improving the conductivity profile of the domain under test for all the phantoms. Image analysis showed that the BMMR method improves image contrast parameters, conductivity profiles, and spatial resolution of the reconstructed images.

Molybdenum Microheaters for MEMS-Based Gas Sensor Applications: Fabrication, Electro-Thermo-Mechanical and Response Characterization

In this paper, we present the fabrication and characterization of molybdenum microheaters for high-temperature gas sensing applications. The surface morphology of dc magnetron sputtered molybdenum thin films was characterized by scanning electron microscopy and atomic force microscopy. The suspended membrane microheater consumed 104 mW to reach a maximum temperature of 800°C and showed an absolute thermal resistance of 7.2°C/mW. Thermal distribution patterns over the active heating area were recorded using FLIR camera. It showed a temperature gradient of 1.18 % from the center of the microheater to its periphery. The thermal and mechanical stabilities of the microheater were analyzed, and its membrane failure at higher operating temperatures was prevented. The microheater membrane deformation at different temperatures was characterized using optical profilometer, and its maximum value was found to be

Growth of Polypyrrole–Horseradish Peroxidase Microstructures for

16.25~\mu \text{m}

\hbox{H}_{2}\hbox{O}_{2}

at 800 °C. The microheater response to a pulse, continuous pulse train, and constant dc voltages was characterized. Its response and recovery times are in the order of 19 and 34 ms, respectively. It showed a stable temperature with a negligible resistance drift (0.96%) over a period of 600 h. The TiO2 thin film integrated molybdenum microhotplate-based MEMS gas sensor response for CO (5000 ppb) was measured at different operating temperatures (300 °C-700 °C).

Biosensor

Conducting polymer microstructures for enzymatic biosensors are developed by a facile electrochemical route. Horse radish peroxide entrapped polypyrrole films with bowl shaped microstructures are developed on stainless steel (SS 304) substrates by a single step process. Potentiodynamic scanning/cyclic voltammetry is used for generation of polypyrrole microstructures using electro generated oxygen bubbles stabilized by zwitterionic surfactant/buffer N-2-Hydroxyethyl piperazine N-2-ethane sulfonic acid (HEPES) as soft templates. Scanning electron microscopic images reveal the bowl shaped structures surrounded by cauliflower like fractal polypyrrole films and globular nanostructures. Raman spectroscopy reveals the oxidized nature of the film. Amperometric biosensor responses are good with sensitivity of 1.1µA/(cm2.mM) in 0–10 mM H2O2 concentration range at −0.15 V.

Growth of polypyrrole-horse radish peroxidase microstructures for H 2 O 2 biosensor

Conducting polymer microstructures for enzymatic biosensors are developed by a facile electrochemical route. Horse radish peroxide entrapped polypyrrole films with bowl shaped microstructures are developed on stainless steel (SS 304) substrates by a single step process. Potentiodynamic scanning/cyclic voltammetry is used for generation of polypyrrole microstructures using electro generated oxygen bubbles stabilized by zwitterionic surfactant/buffer N-2-Hydroxyethyl piperazine N-2-ethane sulfonic acid (HEPES) as soft templates. Scanning electron microscopic images reveal the bowl shaped structures surrounded by cauliflower like fractal polypyrrole films and globular nanostructures. Raman spectroscopy reveals the oxidized nature of the film. Amperometric biosensor responses are good with sensitivity of 1.1µA/(cm2.mM) in 0–10 mM H 2 O 2 concentration range at −0.15 V.

Inductively coupled reactive ion etching studies on sputtered yttria stabilized zirconia thin films in SF6, Cl2, and BCl3 chemistries

Downscaling of yttria stabilized zirconia (YSZ) based electrochemical devices and gate oxide layers requires successful pattern transfer on YSZ thin films. Among a number of techniques available to transfer patterns to a material, reactive ion etching has the capability to offer high resolution, easily controllable, tunable anisotropic/isotropic pattern transfer for batch processing. This work reports inductively coupled reactive ion etching studies on sputtered YSZ thin films in fluorine and chlorine based plasmas and their etch chemistry analyses using x-ray photoelectron spectroscopy. Etching in SF6 plasma gives an etch rate of 7 nm/min chiefly through physical etching process. For same process parameters, in Cl-2 and BCl3 plasmas, YSZ etch rate is 17 nm/min and 45 nm/min, respectively. Increased etch rate in BCl3 plasma is attributed to its oxygen scavenging property synergetic with other chemical and physical etch pathways. BCl3 etched YSZ films show residue-free and smooth surface. The surface atomic concentration ratio of Zr/Y in BCl3 etched films is closer to as-annealed YSZ thin films. On the other hand, Cl-2 etched films show surface yttrium enrichment. Selectivity ratio of YSZ over silicon (Si), silicon dioxide (SiO2) and silicon nitride (Si3N4) are 1:2.7, 1:1, and 1:0.75, respectively, in BCl3 plasma. YSZ etch rate increases to 53 nm/min when nonoxygen supplying carrier wafer like Si3N4 is used