Thin Film Sensor for Ultra High-Temp Measurement

Glenn's breakthrough technology introduces batch-fabricated, miniature sensors embedded and distributed over a large surface area of a material or product during the manufacturing process. The sensors can be utilized for test instrumentation or as an integrated in-situ monitoring system. This integrated manufacturing approach preserves the structural and mechanical system integrity by eliminating the antiquated plug-in approach, invasive machining, manual insertion, and gluing processes currently required to implant sensors into a material. The sensor ladder network of resistors and capacitors breaks down as result of the thermo-physical effects caused by temperature, shock, radiation, corrosion, or other reactions, causing a change in the electrical properties. A processor interprets these changes in the electrical properties and generates a high-resolution, large-area surface profile. The profile demonstrates the amount or rate of material deterioration and temperature change, and is used to optimize geometric structural design, develop materials, predict performance, and make decisions. These sensors play an important role as industries work to realize material performance and product design. This type of monitoring is ideal for infrastructures, nuclear enclosures, or any system susceptible to surface deterioration.

This technology is a new sensor made up of dielectric materials tuned to accurately measure a variable and wide range of temperatures. The sensor is wireless and is powered by an external magnetic field. As the temperature changes, the dielectric material changes its signature magnetic response and the change is detected by a magnetic field response sensor. Applications for this technology are temperature sensors for non-conductive surfaces where the conditions or operations require a robust and wireless sensor.

These materials, which are composed of highly optically transmissive materials, are engineered to provide near-perfect reflection of the full solar spectrum in space. The materials are finely divided such that they scatter and reflect the incoming radiation from the UV down into the mid-IR and are also coated in some fashion with silver to extend the reflectance down into the far IR region of the solar spectrum. With this near-perfect reflectance of the complete solar spectrum, the scientists envision use of these materials for maintaining cryogenic temperatures for extended periods of time in space. The materials have also been developed into highly flexible, moisture resistant selective surface paint.The use and storage of cryogenics fluids is critical to many space operations, and while there are thermal control coatings in use today for spacecraft, none can provide this near-perfect reflection required for long-term maintenance of cryogenic temperatures.

Advances in new polymers and composites along with growing industrial needs in below-ambient temperature applications have brought about the Macroflash development. Accurate thermal performance information, including effective thermal conductivity data, are needed under relevant end-use conditions. The Macroflash is a practical tool for basic testing of common materials or research evaluation of advanced materials/systems. The Macroflash can test solids, foams, or powders that are homogeneous or layered in composition. Test specimens are typically 75mm in diameter and 6mm in thickness. The cold side is maintained by liquid nitrogen at 77 K while a heater disk maintains a steady warm-side temperature from ambient up to 373 K. The steady boiloff of the liquid nitrogen provides a direct measure of the heat energy transferred through the thickness of the test specimen. Nitrogen or other gas is supplied to the instrument to establish a stable, moisture-free, ambient pressure environment. Different compression loading levels can also be conveniently applied to the test specimen as needed for accurate, field-representative thermal performance data. The Macroflash is calibrated from approximately 10 mW/m-K to 800 mW/m-K using well-characterized materials.

Going farther, faster and hotter in space means innovating how NASA constructs the materials used for heat shields. For HEEET, this results in the use of dual-layer, three-dimensional, woven materials capable of reducing entry loads and lowering the mass of heat shields by up to 40%. The outer layer, exposed to a harsh environment during atmospheric entry, consists of a fine, dense weave using carbon yarns. The inner layer is a low-density, thermally insulating weave consisting of a special yarn that blends together carbon and flame-resistant phenolic materials. Heat shield designers can adjust the thickness of the inner layer to keep temperatures low enough to protect against the extreme heat of entering an atmosphere, allowing the heat shield to be bonded onto the structure of the spacecraft itself. The outer and inner layers are woven together in three dimensions, mechanically interlocking them so they cannot come apart. To create this material, manufacturers employ a 3-D weaving process that is similar to that used to weave a 2-D cloth or a rug. For HEEET, computer-controlled looms precisely place the yarns to make this kind of complex three-dimensional weave possible. The materials are woven into flat panels that are formed to fit the shape of the capsule forebody. Then the panels are infused with a low-density version of phenolic material that holds the yarns together and fills the space between them in the weave, resulting in a sturdy final structure. As the size of each finished piece of HEEET material is limited by the size of the loom used to weave the material, the HEEET heat shield is made out of a series of tiles. At the points where each tile connects, the gaps are filled through inventive designs to bond the tiles together.