Under NASA STTR NNK07EA39C, ASR&D developed passive surface acoustic wave (SAW) based hydrogen sensors that utilize Pd nanocluster films on self-assembled siloxane monolayers to provide rapid, reversible room temperature responses to hydrogen exposure. Under NASA SBIR NNX09CE49P ASR&D demonstrated wireless interrogation of SAW RFID sensor-tags. In this project, we propose to combine the results of these two technology development programs to produce wireless, uniquely identifiable SAW-based hydrogen sensors, and to evaluate the sensor response time to low levels of hydrogen exposure (down to 1 ppm). ASR&D will also implement a SAW-based in-situ Pd deposition monitor for enhanced film reproducibility. ASR&D's previous hydrogen work was based on Argonne National Labs work with similar films that demonstrated hydrogen sensing from 25 ppm to over 2% hydrogen, with response times of milliseconds, complete reversibility, and no baseline drift at room temperature. ASR&D demonstrated the ability to measure changes in such films using a SAW sensor, however our ability to test at low hydrogen concentrations and at rates exceeding 1 sample/sec were limited by our experimental test equipment. In the proposed effort, we will utilize an Environics gas dilution system to generate calibrated gas concentrations (for hydrogen and methane) down to 1 ppm, and we will utilize the electronic interrogation system being developed for our RFID work to measure the sensors. This system is capable of measuring sensor responses with a good S/N in 1 msec (or less), overcoming the prior limitations of our testbench equipment. In addition to the hydrogen sensor work, working with Temple University, we propose to evaluate the technical feasibility of producing SAW-based methane sensors using a similar SAW sensor device, but incorporating methane selective supramolecular cryptophane films. Hydrogen sensors will be TRL4 at completion of the proposed effort, and methane sensors will be TRL 3.
