Passive Wireless Hydrogen Sensors Using Orthogonal Frequency Coded Acoustic Wave Devices

This proposal describes the continued development of passive orthogonal frequency coded (OFC) surface acoustic wave (SAW) based hydrogen sensors for NASA application to distributed wireless hydrogen leak detection systems. These novel sensors use an OFC SAW device structure, combined with Palladium (Pd) nanocluster film elements and hydrophobic self assembled monolayer (SAM) coatings to produce fast, reversible, highly sensitive hydrogen sensors capable of detecting a wide range of hydrogen concentrations at room temperature. The technical feasibility of these sensors was clearly demonstrated in Phase I. The Pd films experience conductivity changes due to the hydrogen induced stretching 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. Rapid (under 1 second) room temperature detection of hydrogen was observed, with complete reversibility of response. Compatibility of film conductivity with acoustic wave propagation and detection of changes in film conductivity using variations on SAW device delay were confirmed. Manufacturing compatible processes for SAM deposition and patterning were developed. The successful elimination of the potential technical risks accomplished in this Phase I effort provides a sound basis for further development of these sensors.