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 to provide accurate mechanical properties. A method has been developed to simultaneously extract mechanical properties of the polymer film coated on the device. Our design allows for the simultaneous extraction of multiple properties of a single isotropic film to achieve a more complete characterization than capable with a single sensing element. Viscoelastic properties of the polymer film were extracted using these measurements.

Experiments have been conducted by coating > 650 nm of polyisobutylene on the 197 λ 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 while maintaining a constant temperature, the attenuation and phase responses of the three delay paths are measured. Using a perturbation theory based model for the sensor response, these data allowed for extraction of viscoelastic moduli of the polymer film, in good comparison with literature. Data measured at different solvent exposures allowed for testing of theories of viscoelastic behavior that translate solvent and temperature effects to pure polymer viscoelastic properties.

Acknowledgements Support for this work has been provided by NSF grant number DGE-0221681, University of South Florida IDRG, and DoD Grant W81XWH-05-1-0585.