Friedrich-Alexander-Universität Erlangen-Nürnberg

Optical Methods for Quantifying Fluid and Solid Dynamics of Biological Systems

Optical Methods for Quantifying Fluid and Solid Dynamics of Biological Systems

Human vocal fold flow-induced vibration is central to the production of sound for voiced speech.  This process involves flow, structure, and acoustic dynamics.  One of the primary aims of voice production research is to better understand these tightly-coupled physical phenomena in order to improve clinical treatment of voice disorders.  The focus of this SAOT-sponsored research is the use of optics-based experimental methods, complemented by computational models, to study the physics of vocal fold fluid-structure interactions.  The two primary experimental approaches are particle image velocimetry (PIV) and 3D high-speed digital image correlation (DIC), each of which is summarized below.

PIV is a method of acquiring 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. Fig. 1 shows PIV implemented to analyze the flow through a synthetic human vocal fold model [Ref. 1; see also Ref. 2].  Additionally, matched index of refraction methods can be used to acquire PIV data in liquid-based flows in human vocal tract models with complex geometry [Ref. 3].

FIG. 1. Left: Sample PIV image. Particles are visible, and a flow vortex can be seen. Right: Velocity field shows jet evolution. Colors denote velocity magnitude

DIC is a method for tracking the deformation and motion of solids. Its implementation is similar to PIV. The solid is coated with a random speckle pattern, imaged during movement, and the pattern is tracked using cross-correlation methods. Three-dimensional DIC can be used to track the surface of a vibrating synthetic vocal fold model. DIC is used to correlate surface patterns and a direct linear transformation (DLT) procedure is used to determine 3D surface position. Fig. 2 shows a typical image pair and corresponding surface reconstruction (right).  In this manner, multi-view high-speed imaging is used to characterize the surface dynamics of vocal fold models.

FIG. 2. Left: Snapshot from high-speed video of vocal fold model. Two views obtained in single image using prism. Right: Reconstructed surface.



  1. Drechsel JS, Thomson SL. 2008. Influence of supraglottal structures on the glottal jet exiting a two-layer synthetic, self-oscillating vocal fold model. Journal of the Acoustical Society of America 123(6):4434-4445.
  2. Pickup BA, Thomson SL. 2009. Influence of asymmetric stiffness on the structural and aerodynamic response of synthetic vocal fold models. Journal of Biomechanics 42(14):2219-2225.
  3. Farley J, Thomson SL. 2011. Acquisition of detailed laryngeal flow measurements in geometrically realistic models. Journal of the Acoustical Society of America 130(2):EL82-EL86.


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Optical Metrology
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