P2I-6 Vapor Discrimination Using a Hexagonal Surface Acoustic Wave Device

We present the design, fabrication, and testing of a hexagonal surface acoustic wave (SAW) array based on YZ lithium niobate for non-destructive evaluation of acoustically thick polymer films. Our design allows for the simultaneous extraction of multiple properties of a single isotropic film to achieve a more complete characterization than is possible with a single delay-line element. Experiments have been conducted by coating >650 nm of polyisobutylene on the 197 lambda delay path of the hexagonal SAW sensor with center frequencies of 107 MHz, 111 MHz, and 112 MHz. By exposing the sensor to different concentrations of organic vapors at constant temperature, phase and attenuation changes of the three delay paths have been measured. These data were evaluated for the capability of this device to discriminate vapors and their concentrations using principal component analysis. Results are found to be encouraging. Preliminary investigations utilizing a perturbation theory for the sensor response to extract multiple physical properties of the sensing film are inconclusive