Experimental measurement of tympanic membrane response for finite element model validation of a human middle ear

Tae-Soo Ahn,Moo-Jin Baek,Dooho Lee

doi:10.1186/2193-1801-2-527

Abstract

The middle ear consists of a tympanic membrane, ligaments, tendons, and three ossicles. An important function of the tympanic membrane is to deliver exterior sound stimulus to the ossicles and inner ear. In this study, the responses of the tympanic membrane in a human ear were measured and compared with those of a finite element model of the middle ear. A laser Doppler vibrometer (LDV) was used to measure the dynamic responses of the tympanic membrane, which had the measurement point on the cone of light of the tympanic membrane. The measured subjects were five Korean male adults and a cadaver. The tympanic membranes were stimulated using pure-tone sine waves at 18 center frequencies of one-third octave band over a frequency range of 200 Hz ~10 kHz with 60 and 80 dB sound pressure levels. The measured responses were converted into the umbo displacement transfer function (UDTF) with a linearity assumption. The measured UDTFs were compared with the calculated UDTFs using a finite element model for the Korean human middle ear. The finite element model of the middle ear consists of three ossicles, a tympanic membrane, ligaments, and tendons. In the finite element model, the umbo displacements were calculated under a unit sound pressure on the tympanic membrane. The UDTF of the finite element model exhibited good agreement with that of the experimental one in low frequency range, whereas in higher frequency band, the two response functions deviated from each other, which demonstrates that the finite element model should be updated with more accurate material properties and/or a frequency dependent material model.

Highlights

The auditory system is a very complex sensory system
It can be seen that the displacements of the tympanic membrane are proportional to the sound pressure level of the cavity, which indicates that the dynamic behavior of the tympanic membrane can be treated as a linear system for those sound input levels
In order to demonstrate the linearity of the tympanic membrane displacement, the umbo displacement transfer function (UDTF), which is defined as the transfer function due to the unit sound pressure on the

Summary

Introduction

The auditory system is a very complex sensory system. It can be categorized into three main parts: the outer ear, middle ear, and inner ear. Wada et al (1992) investigated the dynamic behavior of the human middle ear using an FE model that includes the eardrum and ossicles. Williams et al (Williams and Lesser 1990) developed a finite element model for a human tympanic membrane. They considered the cochlear impedance and stiffness of the annular ligament of the tympanic membrane in the FE model. Researchers (Sun et al 2002; Gan et al 2002; Gan et al 2006; Zhao et al 2009) explored the sound transfer characteristics of the middle ear using finite element models and compared these with previous studies

Methods

Results

Conclusion