Chapter 39 High-Speed Digital Holography for Transient Response of the Human Tympanic Membrane I. Dobrev, C. Furlong, J.J. Rosowski, and J.T. Cheng Abstract 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., <50ms) 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. Keywords Acoustic-solid interaction • Digital holography • High-speed cameras • Local phase correlation • Otology 39.1 Introduction Ongoing hearing research efforts to understand the human hearing process are mainly focused on tonal acoustic excitation response of the human ear [1–5]. However, studying the transient response of the human ear, and of the human tympanic membrane (TM) in particular, could expand our understanding of the processes by which acoustical energy transformation and transmission from the TM to the ossicles chain occur [1]. Current state-of-the-art clinical methods to measure the I. Dobrev (*) Center for Holographic Studies and Laser Micro-mechaTronics - CHSLT, 100 Institute Road, Worcester, MA 01609, USA Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA e-mail: ivo_d@wpi.edu C. Furlong Center for Holographic Studies and Laser Micro-mechaTronics - CHSLT, 100 Institute Road, Worcester, MA 01609, USA Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02114, USA J.J. Rosowski • J.T. Cheng Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02114, USA H. Jin et al. (eds.), Advancement of Optical Methods in Experimental Mechanics, Volume 3: Proceedings of the 2014 Annual Conference on Experimental and Applied Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-06986-9_39, #The Society for Experimental Mechanics, Inc. 2015 337
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