The aerodynamic transfer of energy from glottal airflow to vocal fold tissue during phonation was explored using complementary synthetic and numerical vocal fold models. The synthetic model was fabricated using a flexible polyurethane rubber compound. The model size, shape, and material properties were generally similar to corresponding human vocal fold characteristics. Regular, self-sustained oscillations were achieved at a frequency of approximately 120 Hz. The onset pressure was approximately 1.2 kPa. A corresponding two-dimensional finite element model was developed using geometry definitions and material properties based on the synthetic model. The finite element model upstream and downstream pressure boundary conditions were based on experimental values acquired using the synthetic model. An analysis of the fully coupled fluid and solid numerical domains included flow separation and unsteady effects. The numerical results provided detailed flow data that was used to investigate aerodynamic energy transfer mechanisms. The results support the hypothesis that a cyclic variation of the orifice profile from a convergent to a divergent shape leads to a temporal asymmetry in the average wall pressure, which is the key factor for the achievement of self-sustained vocal fold oscillations.

The flow-induced responses of four self-oscillating synthetic vocal fold models are compared. All models were life-sized and fabricated using flexible silicone compounds with material properties comparable to those of human vocal fold tissue. Three of the models had two layers of different stiffness to represent the body–cover grouping of vocal fold tissue. Two of the two-layer models were based on the “M5” geometry [Scherer et al., J. Acoust. Soc. Am. 109, 1616–1630 (2001)], while the third was based on magnetic resonance imaging data. The fourth model included several layers, including a thin epithelial layer, an exceedingly flexible superficial lamina propria layer, a ligament layer that included an anteriorly–posteriorly oriented fiber to restrict vertical motion, and a body layer. Measurements were performed with these models in full larynx and hemilarynx configurations. Data included onset pressure, vibration frequency, glottal flow rate, maximum glottal width, and medial surface motion, the latter two of which were acquired using high-speed imaging techniques. The fourth, multi-layer model exhibited onset pressure, frequency, and medial surface motion traits that are comparable to published human vocal fold data. Importantly, the model featured an alternating convergent–divergent glottal profile and mucosal wave-like motion, characteristics which are important markers of human vocal fold vibration.

A synthetic two-layer, self-oscillating, life-size vocal fold model was used to study the influence of the vocal tract and false folds on the glottal jet. The model vibrated at frequencies, pressures, flow rates, and amplitudes consistent with human phonation, although some differences in behavior between the model and the human vocal folds are noted. High-speed images of model motion and flow visualization were acquired. Phase-locked ensemble-averaged glottal jet velocity measurements using particle image velocimetry (PIV) were acquired with and without an idealized vocal tract, with and without false folds. PIV data were obtained with varying degrees of lateral asymmetric model positioning. Glottal jet velocity magnitudes were consistent with those measured using excised larynges. A starting vortex was observed in all test cases. The false folds interfered with the starting vortex, and in some cases vortex shedding from the false folds was observed. In asymmetric cases without false folds, the glottal jet tended to skew toward the nearest wall; with the false folds, the opposite trend was observed. rms velocity calculations showed the jet shear layer and laminar core. The rms velocities were higher in the vocal tract cases compared to the open jet and false fold cases.

The process of human phonation involves a complex interaction between the physical domains of structural dynamics, fluid flow, and acoustic sound production and radiation. Given the high degree of nonlinearity of these processes, even small anatomical or physiological disturbances can significantly affect the voice signal. In the worst cases, patients can lose their voice and hence the normal mode of speech communication. To improve medical therapies and surgical techniques it is very important to understand better the physics of the human phonation process. Due to the limited experimental access to the human larynx, alternative strategies, including artificial vocal folds, have been developed. The following review gives an overview of experimental investigations of artificial vocal folds within the last 30 years. The models are sorted into three groups: static models, externally driven models, and self-oscillating models. The focus is on the different models of the human vocal folds and on the ways in which they have been applied.

Recent vocal fold vibration studies have used models defined using idealized geometry. Although these models exhibit important similarities with human vocal fold vibration, some aspects of their motion are less than realistic. In this report it is demonstrated that more realistic motion may be obtained when using geometry derived from magnetic resonance imaging (MRI) data. The dynamic response of both idealized and MRI-based synthetic vocal fold models are presented. MRI-based model improvements include evidence of mucosal wave-like motion and less vertical movement. Limitations of the MRI-based model are discussed and suggestions for further synthetic model development are offered.