An overview of micromachined platforms for thermal sensing and gas detection

Micromachined hotplates, membranes, filaments, and cantilevers have all been used as platforms for thermal sensing and gas detection. Compared with conventional devices, micromachined sensors are characterized by low power consumption, high sensitivity, and fast response time. Much of these gains can be attributed to the size reductions achieved by micromachining. In addition, micromachining permits easy, yet precise tailoring of the heat transfer characteristics of these devices. By simple alterations in device geometry and materials used, the relative magnitudes of radiation, convection and conduction losses and Joule heat gains can be adjusted, and in this way device response can be optimized for specific applications. The free-standing design of micromachined platforms, for example, reduces heat conduction losses to the substrate, thereby making them attractive as low power, fast-response heaters suitable for a number of applications. However, while micromachining solves some of the heat transfer problems typical of conventionally produced devices, it introduces some of its own. These trade-offs will be discussed in the context of several micromachined thermal and gas sensors present in the literature. These include micromachined flow sensors, gas thermal conductivity sensors, pressure sensors, uncooled IR sensors, metal-oxide and catalytic/calorimetric gas sensors. Recent results obtained for a microbridge-based catalytic/calorimetric gas sensor will also be presented as a means of further illustrating the concepts of thermal design in micromachined sensors

Reflectance Infrared Spectroscopy on Operating Surface Acoustic Wave Chemical Sensors During Exposure to Gas-Phase Analytes

We have developed instrumentation to enable the combination of surface acoustic wave (SAW) sensor measurements with direct, in-situ molecular spectroscopic measurements to understand the response of the SAW sensors with respect to the interfacial chemistry of surface-confined sensing films interacting with gas-phase analytes. Specifically, the instrumentation and software was developed to perform in-situ Fourier-transform infrared external-reflectance spectroscopy (FTIR-ERS) on operating SAW devices during dosing of their chemically modified surfaces with analytes. By probing the surface with IR spectroscopy during gas exposure, it is possible to understand in unprecedented detail the interaction processes between the sorptive SAW coatings and the gaseous analyte molecules. In this report, we provide details of this measurement system, and also demonstrate the utility of these combined measurements by characterizing the SAW and FTIR-ERS responses of organic thin-film sensor coatings interacting with gas-phase analytes

The O/OREOS Mission - Astrobiology in Low Earth Orbit

The O/OREOS (Organism/Organic Exposure to Orbital Stresses) nanosatellite is the first science demonstration spacecraft and flight mission of the NASA Astrobiology Small- Payloads Program (ASP). O/OREOS was launched successfully on November 19, 2010, to a high-inclination (72), 650-km Earth orbit aboard a US Air Force Minotaur IV rocket from Kodiak, Alaska. O/OREOS consists of 3 conjoined cubesat (each 1000 cu.cm) modules: (i) a control bus, (ii) the Space Environment Survivability of Living Organisms (SESLO) experiment, and (iii) the Space Environment Viability of Organics (SEVO) experiment. Among the innovative aspects of the O/OREOS mission are a real-time analysis of the photostability of organics and biomarkers and the collection of data on the survival and metabolic activity for micro-organisms at 3 times during the 6-month mission. We will report on the spacecraft characteristics, payload capabilities and first operational phase of the O/OREOS mission. The science and technology rationale of O/OREOS supports NASAs scientific exploration program by investigating the local space environment as well as space biology relevant to Moon and Mars missions. It also serves as precursor for experiments on small satellites, the International Space Station (ISS), future free-flyers and lunar surface exposure facilities

The O/OREOS Mission - Astrobiology in Low Earth Orbit

The O/OREOS (Organism/Organic Exposure to Orbital Stresses) nanosatellite is the first science demonstration spacecraft and flight mission of the NASA Astrobiology Small- Payloads Program (ASP). O/OREOS was launched successfully on November 19, 2010, to a high-inclination (72), 650-km Earth orbit aboard a US Air Force Minotaur IV rocket from Kodiak, Alaska. O/OREOS consists of 3 conjoined cubesat (each 1000 cu.cm) modules: (i) a control bus, (ii) the Space Environment Survivability of Living Organisms (SESLO) experiment, and (iii) the Space Environment Viability of Organics (SEVO) experiment. Among the innovative aspects of the O/OREOS mission are a real-time analysis of the photostability of organics and biomarkers and the collection of data on the survival and metabolic activity for micro-organisms at 3 times during the 6-month mission. We will report on the spacecraft characteristics, payload capabilities and first operational phase of the O/OREOS mission. The science and technology rationale of O/OREOS supports NASAs scientific exploration program by investigating the local space environment as well as space biology relevant to Moon and Mars missions. It also serves as precursor for experiments on small satellites, the International Space Station (ISS), future free-flyers and lunar surface exposure facilities

A forest without trees: Development of high-surface-area materials for enhanced-sensitivity SAW arrays

Chemical sensor arrays are an alternative to the tedious development of highly specific single-analyte detectors. Recent efforts have focused on the chemical and physical diversity of interface materials for SAW sensor arrays. However, the issues of wide dynamic range and high sensitivity must also be addressed for sensor arrays to compete in applications requiring low detection limits. Because SAW devices respond in proportion to change in mass per nominal unit area of the device surface, sensitivity is enhanced by surface modification with high-area, thin-film coating materials: a greater mass of analyte is adsorbed at a given ambient concentration. The authors are exploring several classes of electrochemically prepared high-area films, materials whose formulations and processing are well documented for applications other than chemical sensors. They present results from films formed by anodization, chemical conversion, and electroplating, yielding surface area enhancements as high as 170x

Mass-Transport-Limited Electrodeposition of High-Surface-Area Coatings for Surface Acoustic Wave Sensor Technology

The sensitivity of surface acoustic wave (SAW) sensors has been enhanced by increasing the active surface area of these devices, Electrodepositions of Ni, Pd, and Pt in a mass-transport-limited mode with trace foreign metals yield highly dendritic crystal structures of uniform macroscopic thickness. The concentration of metal ions, supporting electrolyte, agitation, and additives greatly impact the crystal morphology of the deposit. This methodology can be used simply and economically to provide high-area films in selective regions