Novel Solid-State Humidity Sensor

Sensors
Novel Solid-State Humidity Sensor (MFS-TOPS-80)
Unparalleled sensitivity, response, recovery time, and robustness
Overview
NASAs Marshall Space Flight Center has developed a humidity sensor that offers high sensitivity and extremely fast response and recovery across a range of humidity levels. The sensor is based on a novel ceramic dielectric material that exhibits rapid and large changes in capacitance and resistance with very small changes in water vapor concentration; making it ideal for humidity, dew point, or water vapor concentration sensing applications. The dielectric sensing element is low-cost and can easily be made using standard printed electronics processing and packaging methods. The finished sensor is small and robust, and can be used to for rapid measurements of very small changes in humidity across a range of humidity levels, temperatures and chemical environments. The humidity sensor technology is particularly well suited for market applications requiring extremely high sensitivity, fast response times, and/or use in challenging environments. NASA is currently seeking partners to bring this novel sensor technology to the marketplace.

The Technology
NASAs novel ceramic dielectric material enables extremely high-sensitivity humidity sensing. The ceramic sensing element is robust, can be manufactured using printing processes, and exhibits fast response and recovery speeds with large capacitance and resistance response/change per relative humidity unit change across a wide range of humidity levels in a log-linear response. Preliminary test data conducted in a humidity test chamber show a log-linear measured response in capacitance from 5 nanofarads (at 30% relative humidity, room temperature) to 0.2 millifarads (at 90% relative humidity, room temperature). The inventors discovered the humidity sensing element technology during their efforts to develop next-generation energy storage materials and devices for NASA. The inventors were initially puzzled by large swings in capacitance observed over the course of any given day in one particular dielectric composition, and, ultimately, they were able to trace these unexpected changes in capacitance back to corresponding changes in ambient humidity, even those occurring from breathing and exhalation. The sensor element can be formed using a dielectric ink or paste formulation, also developed by NASA, via traditional screen printing or advanced ink jet, aerosol, or 3D printing methods. The printed sensor element can be very thin, on the order of microns in thickness, with a small footprint, one square centimeter or less.
FIGURE - (left) Sensor shows similar response at 25C and 85C for easy calibration (right) Three curves showing complete data from sensors of different sizes repeatedly cycled up and down from 25 - 95% RH, demonstrating perfect repeatability for each sensor without any hysteresis effects.
Benefits
  • Very high sensitivity to small changes in relative humidity, dew point, and water vapor concentration
  • Nearly instantaneous response and recovery speeds
  • Robust solid-state sensor can operate in challenging temperature, humidity and chemical conditions
  • Low voltage and power operation
  • Small form factor
  • Flexibility in dielectric ceramic powder formulation that enables the use of a variety of thick film and advanced printed electronics manufacturing methods

Applications
  • Aerospace
  • Automotive
  • Industrial
  • Health care
  • Marine
  • Consumer
  • Defense
Technology Details

Sensors
MFS-TOPS-80
MFS-33214-1
9,987,658
-Hanekom, K. R., and T. D. Rolin. "Fabrication and Testing of a Novel Ceramic-Based Additively Manufactured Humidity Sensor." (2022)
Similar Results
Collage of cryogenic humid environments
Enhanced Fabrication Improves Temperature Sensing in Cryogenic Humid Environments
This technology was developed to improve Armstrong's multi-patented FOSS system, which has long been used to measure temperature and liquid levels in cryogenic environments. When the sensing system's fibers trapped humidity from the surrounding environment before their submersion into cryogenic liquids, the moisture adversely affected outputs. A new manufacturing process solves this problem, increasing reliability and accuracy not only of NASA's FOSS but also any fiber optic sensing system. How It Works Armstrong has developed a two-step process to assemble the sensors. First, the bare sensor fiber is inserted into an oven to expel all moisture from the fiber coating. Then, the moisture-free fiber is placed inside a humidity-controlled glove box to prevent it from absorbing any new moisture. While inside the glove box, the fiber is inserted into a loose barrier tubing that isolates the fiber yet is still thin enough to provide adequate thermal transfer. The tubing can be further purged with various gases while it is inside the glove box to provide additional moisture isolation. This innovation is particularly useful for fiber optic systems that measure temperature and that identify any temperature stratifications within cryogenic liquids. Why It Is Better This process seals sensor fibers from environmental moisture, enabling fiber optic sensing systems to operate reliably in humid environments. The innovation eliminates erroneous readings that can occur due to moisture collection on the fiber sensors. For more information about the full portfolio of FOSS technologies, see DRC-TOPS-37 or visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing
Sansec Sensors
Wireless Temperature Sensor Having No Electrical Connections
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.
Front page image provided by inventor
Optical concentration sensor for liquid solution
Typical concentration sensors, like the one initially used in the UWMS, rely on changes in electrical conductivity to measure the concentration of a solution. These measurements using conductivity are prone to voltage drift over time, leading to unreliable measurements as the sensor ages. The optical sensor developed here uses light scattering to measure the solution concentration without the issue of voltage drift. In this sensor, light from a green LED is passed into the sensor housing where it hits a first detector (i.e., a photodiode) to establish a reference of the amount of light before scattering. Simultaneously, the light from the LED scatters through the pretreat solution and then hits a second photodiode to measure the amount of light after scattering. The difference between the amount of light measured by the two detectors is used to calculate the concentration of the pretreat solution (based upon Beer’s Law). The optical concentration sensor has been demonstrated to effectively measure pretreat concentrations in both still and flowing liquid conditions and is resistant to contamination issues as necessitated by the UWMS. The optical pretreat concentration sensor is at technology readiness level (TRL) 4 (component and/or breadboard validation in laboratory environment) and is available for patent licensing.
Sensor
Solid State Carbon Dioxide (CO2) Sensor
The technology is a solid state, Carbon Dioxide (CO2) sensor configured for sensitive detection of CO2 having a concentration within the range of about 100 Parts per Million (ppm) and 10,000 ppm in both dry conditions and high humidity conditions (e.g., > 80% relative humidity). The solid state CO2 sensor achieves detection of high concentrations of CO2 without saturation and in both dynamic flow mode and static diffusion mode conditions. The composite sensing material comprises Oxidized Multi-Walled Carbon Nanotubes (O-MWCNT) and a metal oxide, for example O-MWCNT and iron oxide (Fe2O3) nanoparticles. The composite sensing material has an inherent resistance and corresponding conductivity that is chemically modulated as the level of CO2 increases. The CO2 gas molecules absorbed into the carbon nanotube composites cause charge-transfer and changes in the conductive pathway such that the conductivity of the composite sensing material is changed. This change in conductivity provides a sensor response for the CO2 detection. The solid state CO2 sensor is well suited for automated manufacturing using robotics and software controlled operations. The solid state CO2 sensor does not utilize consumable components or materials and does not require calibration as often as conventional CO2 sensors. Since the technology can be easily integrated into existing programmable electronic systems or hardware systems, the calibration of the CO2 sensor can be automated.
hazmat suits, bridge, airplane wing
Damage and Tamper Detection Sensor System
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