Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties

Purpose: The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency (F[subscript 0]) during anterior-posterior stretching. Method: Three materially linear and 3 materially nonlinear models were created and stretched up to 10 mm in 1-mm increments. Phonation onset pressure (P[subscript on]) and F[subscript 0] at P[subscript on] were recorded for each length. Measurements were repeated as the models were relaxed in 1-mm increments back to their resting lengths, and tensile tests were conducted to determine the stress-strain responses of linear versus nonlinear models. Results: Nonlinear models demonstrated a more substantial frequency response than did linear models and a more predictable pattern of F[subscript 0] increase with respect to increasing length (although range was inconsistent across models). P[subscript on] generally increased with increasing vocal fold length for nonlinear models, whereas for linear models, P[subscript on] decreased with increasing length. Conclusion: Nonlinear synthetic models appear to more accurately represent the human vocal folds than do linear models, especially with respect to F[subscript 0] response.