Towards an intermediate water wave model of vocal fold vibration: Evidence from vocal-fold dynamic sonography

A simplified water wave model was developed for predicting the global vibration of human vocal folds. As the depth of the liquids in the lamina propria is 1/2–1/20 of the wavelength, they were analogized to intermediate waters. The water wave model predicted elliptic orbits of the tissue particles with the major axis parallel to the surface, and these ellipses flattened with depth. This vibration behavior was verified by ultrasound imaging of the vocal fold during modal phonation. The possible mechanical roles of different layers of the vocal fold were discussed in the light of the water wave model. The epithelium may provide the restoring forces of the water waves, whereas the vocal ligament may serve as a wave damper, an impedance matcher, and an energy saver. The liquids in Reinke’s space play a key role in the conversion between the circular motion on the vocal-fold surface to the tangential motion in the vocal ligament. This water wave model may be viewed as a start point of the poroelasticity model of vocal fold vibration.