High-Speed Digital Holography for Transient Response of the Human Tympanic Membrane

The tympanic membrane (TM; eardrum) transforms sound energy from the ear canal into mechanical vibrations of the ossicles (middle-ear bones), whence energy enters the inner ear and stimulates auditory hair cells for hearing. Our past efforts toward understanding of the energy transformation within the middle-ear has been focused on the TM's response to single tones. In this paper, we report results of the development of high-speed holographic capabilities to measure the transient characteristics of the TM. We have developed a high-speed holographic system (HHS) that incorporates a transient (i.e., >40 kHz) acquisition method to quantify the displacements on the TM surface excited by sharp (i.e., <50 mu s) acoustic clicks. The performance of the HHS is compared with Laser-Doppler Vibrometery (LDV) measurements on both artificial membrane and human cadaveric TM. The instantaneous response of > 100 k data points on the TM surface measured by the HHS can be used to quantify spatially-dependent motion parameters such as modal frequencies, mode shapes, time constants, and acoustic delays. In addition, the local material properties across the surface of the TM can be inferred.