Abstract
Our research group has developed a fully implantable artificial cochlea using biomimetics to aid patients with sensorineural hearing loss. An artificial cochlear sensory epithelium that mimics the organ of Corti was fabricated using MEMS technology and realized frequency selectivity ranging from 157 to 277 kHz by the position of maximum amplitude. Unfortunately, multiple peaks of amplitude were observed in the high frequency. This causes the position of peak to overlap at different frequencies. To enhance its frequency selectivity, we turned our attention to the intriguing phenomenon of traveling waves known to occur in the organ of Corti. To investigate this aspect, we employed a full-field optical coherence microscope for precise measurements of oscillation. The use of a heterodyne interferometer in this measurement system allowed us to capture oscillation at low frame rates, utilizing the interference of two lights with slightly different frequencies for improved resolution and shortened measurement times. The results showed that the resonance frequency in the 1st mode was 120 kHz, and in the 2nd mode, it was 200 kHz. One peak was observed in the 1st mode, while two were seen in the 2nd mode. Moreover, the velocity of the traveling wave in the 1st mode measured 102.6 m/s. In contrast, in the 2nd mode, the peak's velocity at the resonance position reached 118.7 m/s, while the other peak exhibited a velocity of 62.1 m/s. We discussed the result by using two-dimensional wave equation in cylindrical coordinate system. This indicated the difference in velocity depend on the wavelength. Present observation demonstrated that the velocity increases at the resonance position, promising possibilities for further enhancement of the frequency selectivity in our cochlear implant.
