Optical Methods used to Quantify Fluid and Solid Dynamics of Voice Production

Human vocal fold flow-induced vibration is central to the production of sound for voiced speech. This process involves flow, structural, and acoustical dynamics. The primary aim of voice production research is to better understand these tightly-coupled physical phenomena in order to improve the prevention, diagnosis, and treatment of voice disorders.  Synthetic models of the vocal folds that exhibit flow-induced oscillations that are comparable to those of the human vocal folds are commonly used in voice research.  Using these models as test subjects, experiments are conducted to characterize their vibration patterns, radiated sound production, and air flow patterns.  Optics-based methods are among the most common tools used to study their vibratory and flow responses.  Particle image velocimetry (PIV) is a method used to acquire spatially- and temporally-resolved flow velocity data. Micron-sized particles are injected into the flow field. A laser sheet illuminates particles in a plane of interest and a digital camera acquires two successive images of the illuminated particles. By tracking the particles as they move with the fluid (e.g., using cross-correlation methods), the velocity field can be quantified. Recently, we have used eight high-speed cameras synchronized with a high-speed laser to perform three-dimensional PIV (Synthetic Aperture PIV, or SAPIV) to study vocal fold aerodynamics. Digital image correlation (DIC) is used to track the deformation and motion of the solid model during vibration. Its implementation is similar to PIV. The solid is coated with a random speckle pattern, imaged during movement, and tracked using pattern matching algorithms. In this talk, the use of these optics-based measurement techniques in studying vocal fold vibration will be described. Their capabilities and limitations will be discussed, in addition to specific advances that are needed to improve the state of the art.