Passive Wireless Hydrogen Sensors Using Orthogonal Frequency Coded Acoustic Wave Devices

This proposal describes the development of passive surface acoustic wave (SAW) based hydrogen sensors for NASA application to distributed wireless hydrogen leak detection systems. Orthogonal Frequency Coded (OFC) SAW devices have been demonstrated as passive wireless temperature sensors in NASA Contract NNK04OA28C, and are being further developed under NNK05OB31C. The proposed hydrogen sensors will use a novel OFC SAW device structure, combined with Palladium nanocluster film elements to produce fast, reversible, highly sensitive hydrogen sensors capable of detecting a wide range of hydrogen concentrations at room temperature. The proposed research will utilize results from Argonne National Labs on the formation of Pd nanocluster films on self-assembled siloxane monolayers on glass. These optimized nanocluster films demonstrated hydrogen sensing from 25 ppm to over 2% hydrogen, with response times of milliseconds, complete reversibility, and no baseline drift at room temperature. The films experience large conductivity changes due to the hydrogen induced lattice expansion of the Pd nanoclusters and the quantum nature of conduction in nanocluster films. The performance of the SAW device will change in response to a change in conductivity of this film. Issues including SAM formation on piezoelectric substrates, nanocluster film deposition, and simulation of device performance will be evaluated.