Cochlear amplifier inspired two-channel active artificial hair cells

Abstract

The mammalian auditory system exhibits rich characteristics that has inspired research for decades. Some of these key characteristics include frequency selectivity of the basilar membrane (BM), nonlinear amplification of low-level stimuli, and compressive nonlinearity that enables the ear to sense over a large range of sound pressure levels (0–120 dB in humans). Cochlear outer hair cells (OHCs) play a vital role in the nonlinear amplification and compression of input signals and this behavior is referred to as the cochlear amplifier. Damage to OHCs due to aging, diseases, and environmental conditions often results in a sensorineural hearing loss. As a result, there is a need to develop better hearing prosthesis that transduce sound-induced vibrations to electrical signals by mimicking OHCs. In the present work, active artificial hair cells (AHCs) made of piezoelectric cantilever beams are developed to mimic the nonlinear behavior of the OHCs. In literature, AHC based prosthesis operate over a spectrum by developing an array of AHCs with different fundamental frequencies. The present work extends the frequency bandwidth of each AHC to sense over multiple resonant frequencies, unlike conventional single-channel AHCs. Therefore, a single active multi-frequency resonant AHC is presented to minimize the need for more artificial hair cells to cover the desired bandwidth of interest in an array format. Herein, the response of a 26 mm AHC to a base excitation is controlled by applying a phenomenological feedback control law that tunes the system close to a Hopf bifurcation near the first and second natural frequencies. The experimental results show a power relation of about one-third, between the output and input of the AHC. This is very similar to the compressive nonlinearity seen in the mammalian cochlea. The present effort is a continuation of the authors’ previous studies in bio-inspired nonlinear control of AHCs, which can lead to an implantable cochlear device, acoustic, or flow sensor in future.