The aim of this research is to create a miniature acoustic velocity sensor which, when combined with a conventional miniature pressure microphone will enable accurate measurements of otoacoustic emissions and wideband middle-ear reflectance within the human ear canal. These quantities reveal important information about the functional status of the peripheral auditory system. Existing methods of making acoustic measurements within the ear canal using sound pressure microphones suffer from the strong dependence of pressure on the measurement location. This research will enable the detection of acoustic particle velocity simultaneously with sound pressure providing a much more repeatable and reliable measure of otoacoustic emissions than existing methods. Existing methods for measuring physiologically relevant sounds in the ear canal also suffer because these sounds are often very quiet, close to the noise floors of the miniature microphones employed in state-of-the-art systems for measuring otoacoustic emissions. The proposed effort will enable the detection of otoacoustic emissions at levels at least 10 dB lower than currently feasible. Lowering the measurement noise floor will reduce the averaging time necessary to extract these signals from noise and enable the detection of much quieter otoacoustic emissions, which can be important in subjects with hearing loss. Extending our ability to measure these important sounds in the human ear canal will lead to new discoveries of middle and inner ear function and will provide greatly improved clinical tools for the hearing impaired. This research comprises an extension of a recent discovery by the investigators that nanoscale fibers can be driven by viscous forces such that their sound-induced vibrations can be nearly identical to that of the air in a sound field. The motion of air velocity-driven electrodes will be detected using their new approach to capacitive sensing that is appropriate for highly compliant structures such as those used here. The novel acoustic velocity sensor will then be incorporated with a low-noise miniature hearing aid microphone in a measurement device. Acoustic measurements in human ear canals obtained using this low-noise and robust system will then be compared to those obtained using existing methods.
This research will result in a dramatic improvement in our ability to measure sounds within the human ear canal, providing important information about the functional status of the peripheral auditory system. This will greatly improve our ability to identify specific hearing disorders, to monitor effects of therapeutic interventions, and to examine basic physiology of the ear. Extending our ability to measure these important sounds in the human ear canal will lead to new discoveries of middle and inner ear function and will provide greatly improved clinical tools for the hearing impaired.