A controlled-strain rheometer for the measurements of vocal fold viscoelasticity at phonatory frequencies
Roger W. Chan, Maritza L. Rodriguez · The Journal of the Acoustical Society of America · 2007
Glottal fluid-structure interactions are critically dictated by the viscoelastic properties of the vocal fold. Viscoelastic shear response of the vocal fold lamina propria has been reported previously, but with torsional rheometers data have only been obtained at low audio frequencies (up to about 80 Hz), necessitating data extrapolation to predict tissue properties in the typical phonatory frequency range. In order to characterize the viscoelastic behavior of vocal fold tissues at higher frequencies, a controlled-strain, linear simple shear rheometer was built based on the linear-motor design of the EnduraTEC ELF 3200 system. A tissue specimen was subjected to simple shear between two rigid rectangular acrylic plates, with the displacement measured by a linear variable displacement transducer (LVDT), and the shear force response detected by a piezoelectric quartz transducer. The frequency responses of the system components were assessed by accelerometers, and the complex shear modulus (G*) of a standard ANSI 2.21 polyurethane material and that of vocal fold specimens were measured. Results showed that the rheometer can provide valid and reliable viscoelastic data of the human vocal fold cover at frequencies of up to 250 Hz. [Work supported by NIH.]