Dr. Sanjay V. Patel Profile

Dr. Sanjay V. Patel

at Seacoast Science Inc

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Publications (4)

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Proceedings Article | 27 October 2005 Paper

Chemicapacitive microsensors for detection of explosives and TICs

Sanjay Patel, Stephen Hobson, Sabina Cemalovic, Todd Mlsna

Proceedings Volume 5986, 59860M (2005) https://doi.org/10.1117/12.634357

KEYWORDS: Sensors, Polymers, Explosives, Capacitors, Electrodes, Humidity, Toxic industrial chemicals, Capacitance, Explosives detection, Industrial chemicals

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Seacoast Science develops chemical sensors that use polymer-coated micromachined capacitors to measure the dielectric permittivity of an array of selectively absorbing materials. We present recent results demonstrating the sensor technology's capability to detect components in explosives and toxic industrial chemicals. These target chemicals are detected with functionalized polymers or network materials, chosen for their ability to adsorb chemicals. When exposed to vapors or gases, the permittivity of these sorbent materials changes depending on the strength of the vapor-sorbent interaction. Sensor arrays made of ten microcapacitors on a single chip have been previously shown to detect vapors of organic compounds (chemical warfare agents, industrial solvents, fuels) and inorganic gases (SO2, CO2, NO2). Two silicon microcapacitor structures were used, one with parallel electrode plates and the other with interdigitated "finger-like" electrodes. The parallel-plates were approximately 300 μm wide and separated by 750 nm. The interdigitated electrodes were approximately 400 μm long and were elevated above the substrate to provide faster vapor access. Eight to sixteen of these capacitors are fabricated on chips that are 5 x 2 mm and are packaged in less than 50 cm³ with supporting electronics and batteries, all weighing less than 500 grams. The capacitors can be individually coated with different materials creating a small electronic nose that produces different selectivity patterns in response to different chemicals. The resulting system's compact size, low-power consumption and low manufacturing costs make the technology ideal for integration into various systems for numerous applications.

Proceedings Article | 26 February 2001 Paper

Stabilizing the response of Pd/Ni alloy films to hydrogen with Ti adhesion layers

Mark Jenkins, Robert Hughes, Sanjay Patel

Proceedings Volume 4205, (2001) https://doi.org/10.1117/12.417437

KEYWORDS: Hydrogen, Sensors, Resistors, Titanium, Resistance, Transistors, Palladium, Nickel, Field effect transistors, Silicon

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We have studied catalytic thin film resistors made from a Pd and Ni alloy, and propose a method for dramatically reducing the drift of the measured resistance. The resistances of Pd films increase monotonically when exposed to hydrogen, however a stable baseline is difficult to achieve and alpha to beta phase transitions result in hysteresis. It is known that at high hydrogen concentrations, the Pd film cracks and delaminates, however long-term exposures to low concentrations of hydrogen can also result in delaminations. Studies using Pd/Ni alloys show that the phase transition can be suppressed. High temperature anneals in 2 % hydrogen, and the addition of a Ti adhesion layer is shown to reduce drift. Usually long term studies on films are conducted in an ordinary air (oxidizing) atmosphere; however, we report here on studies carried out in a reducing atmosphere of 0.1% hydrogen in nitrogen for 6 months on two sensor structures, field effect transistors (FETs) and resistors. The Sandia Robust Hydrogen Sensor platform containing integrated heaters, temperature sensors, and hydrogen sensitive resistors and FETs was compared to a Sandia Wide Range Sensor containing a 10 atomic percent Ni/Pd (1000Å) alloy resistor with a (100Å) Ti adhesion layer. After six months the two hydrogen sensing resistors on the Robust platform, without an adhesion layer, read a hydrogen concentration of 61% and 2.3%, while the Wide Range Sensor read a hydrogen concentration of 0.102%, which is a dramatic improvement in limiting baseline drift.

Proceedings Article | 22 August 2000 Paper

Integrated chemiresistor array for small sensor platforms

Robert Hughes, Stephen Casalnuovo, Kurt Wessendorf, Dan Savignon, Susan Hietala, Sanjay Patel, Edwin Heller

Proceedings Volume 4038, (2000) https://doi.org/10.1117/12.396280

KEYWORDS: Sensors, Polymers, Resistance, Electrodes, Resistors, Temperature metrology, Particles, Temperature sensors, Composites, Electronics

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Chemiresistors are fabricated from materials that change their electrical a resistance when exposed to certain species. Composites of soluble polymers with metallic particles have shown remarkable sensitivity to many volatile organic chemicals, depending on the ability of the analyte molecules to swell the polymer matrix. These sensor can be made extremely small, operate at ambient temperatures, and require almost no power to read-out. However, the chemiresistors itself is only a part of a more complex sensor system that delivers chemical information to a user who can act on the information. We present the design, fabrication and performance of a chemiresistors array chip with four different chemiresistors materials, heaters and a temperature sensor. We also show the design and fabrication of an integrated chemical sensor array, where the electronics for measuring each chemiresistors' resistance are on the same chi with the chemiresistors films. The circuit was designed to perform several functions to make the sensor data more useful. The integrated chemiresistors' resistance are on the same chip with the chemiresistors films. The circuit was designed to perform several functions to make the senor dat more useful. The integrated chemiresistors array's small size and low power demand makes it ideal for deployment on a Sandia-developed microrobot platform.

Proceedings Article | 6 June 2000 Paper

Automated stromal nerve rejection in corneal confocal images in vivo

Eric Brown, Jon Camp, Sanjay Patel, Jay McLaren, William Bourne, Richard Robb

Proceedings Volume 3979, (2000) https://doi.org/10.1117/12.387625

KEYWORDS: Nerve, Confocal microscopy, Cornea, In vivo imaging, Microscopes, Image segmentation, Binary data, Evolutionary algorithms, Algorithm development, Image processing

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With the advent of corneal confocal microscopy, investigators can determine keratocyte density in the corneal stroma in vivo. We and others have written automated algorithms to measure keratocyte density from human corneal confocal images. Such algorithms are only accurate if they exclude images of stromal nerve bundles (elongated objects) that would otherwise be counted as keratocytes. In this study we devised an algorithm to identify stromal nerve bundles and exclude them from measurements of keratocyte density. Nerve bundles were detected based on their size and aspect ratio, and were then subtracted from images by using a combination of morphology operations and direction calculations. The validity of nerve removal on measurements of keratocyte density was assessed. Keratocyte density was measured from confocal images of three normal human corneas in vivo by using our algorithm with nerve removal. After the same eyes underwent enucleation, density was measured manually from histologic sections. Keratocyte density was also measured from confocal images of 57 normal corneas in vivo (57 subjects) with and without nerve removal. In the three enucleated eyes, there was no significant difference between keratocyte density measured by automated counting with nerve removal and by histologic methods (P equals 0.75). However, in the 57 normal corneas, use of the nerve-removal algorithm reduced estimates of density by 57.0 +/- 164.6 cells/mm³ (mean +/- SD, p < 0.038) in the anterior two-thirds of the stroma.

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