Estimation of viscoelastic shear properties of vocal-fold tissues based ontime-temperature superposition

Empirical data on the viscoelastic shear properties of human vocal-fold muc osa (cover) were recently reported at relatively low frequency (0.01-15 Hz) . For the data to become relevant to voice production, attempts have been m ade to parametrize and extrapolate the data to higher frequencies using con stitutive modeling [Chan and Titze, J. Acoust. Soc. Am. 107, 565-580 (2000) ]. This study investigated the feasibility of an alternative approach for d ata extrapolation, namely the principle of time-temperature superposition ( TTS). TTS is a hybrid theoretical-empirical approach widely used by rheolog ists to estimate the viscoelastic properties of polymeric systems at time o r frequency scales not readily accessible experimentally. It is based on th e observation that for many polymers, the molecular configurational changes that occur in a given time scale at a low temperature correspond to those that occur in a shorter time scale at a higher temperature. Using a rotatio nal rheometer. the elastic shear modulus (G') and viscous shear modulus (G" ) of vocal-fold cover (superficial layer of lamina propria) tissue samples were measured at 0.01-15 Hz at relatively low temperatures (5 degrees -37 d egreesC). Data were empirically shifted according to TTS, yielding composit e "master curves" for predicting the magnitude of the shear moduli at highe r frequencies at 37 degreesC. Results showed that TTS may be a feasible app roach for estimating the viscoelastic shear properties of vocal-fold tissue s at frequencies of phonation (on the order of 100-1000 Hz). (C) 2001 Acous tical Society of America.