Evanescent Waves at the Interface between Ear Canal and Otoacoustic Emission Probe

The measurement of otoacoustic emissions (OAE) allows for an objective examination of the cochlear function. However, the validity of OAE tests is affected negatively by calibration errors, rendering the diagnosis less accurate. In this report, we shed light on the evanescent waves arising at the interface between the OAE probe and the ear canal. For this purpose, finite element models of the ear canal along with the microphone and sound tubes of the OAE probe were created. The impact of evanescent waves on the estimation of the acoustic length was studied. This effect was negligible for an average human ear canal model (8 mm diameter). However, for a 12 mm-diameter ear canal model, an extension of the probe microphone tube by 2 mm was required to counterbalance the evanescent wave effect. Hence, as a preliminary result, we expect that modifying the 12 mm-diameter eartips – by extending the probe microphone tube by about 2 mm – will have a positive effect on the length estimation of large-diameter ear canals.