On measuring the high frequency response of soft viscoelastic materials at finite strains

Abstract

In such applications as repairing damaged vocal folds to restore normal phonation, viscoelastic properties of normal tissues and candidate replacement materials should be measured at phonation frequencies (100-1000 Hz) and at the large strains (up to 30%) that occur during speech and singing. Previously the authors have developed a torsional wave experiment to measure the complex moduli, in shear, for vocal folds subjected to small strains at phonation frequencies. This method has now been extended to finite deformations by sandwiching a thin disk of vocal fold tissue (lamina propria), or replacement material, between two rigid plates. The lower plate is driven by a galvanometer at phonation frequencies and small rotations. A second stiffer material is placed between the upper plate and a third plate attached to an upper galvanometer that oscillates sinusoidally at low frequency and large rotation. At periodic peak rotations of the upper galvanometer, the lower galvanometer superimposes infinitesimal oscillations at a series of higher frequencies. The magnitude and phase of rotation of the middle plate yield the viscoelastic properties of the test specimen for infinitesimal deformations at high frequency superimposed on finite deformations at low frequency. Preliminary results show the potential of the new test.