Bio-inspired Nonlinear Control of Artificial Hair Cells

The human auditory mechanism can detect sound frequencies ranging from 20 Hz to 20 kHz, over a broad pressure range of 0-120 dB SPL due to its nonlinear amplification performed by the cochlea. Sound waves travel through the ear canal, eardrum and the three bones of the middle ear. The last bone of the middle ear (stapes) pushes on the oval window and creates propagating waves in the cochlea. Each of the sound frequency components excites a specific location along the basilar membrane when it travels through the cochlea. These are then coupled to the hair cells, which apply their nonlinear compressibility and amplification behavior to improve sound detection. These functions of the cochlea are the inspiration to design more sensitive and capable sensors. The primary objective of this work is to mimic the nonlinear amplification of cochlea by developing piezoelectric based active artificial hair cells (AHCs). By examining models of the biological cochlea, a nonlinear feedback control law is designed which applies the appropriate forcing conditions to the beam to amplify or suppress vibrations initially induced by an external stimulus. To achieve this goal, a two degree of freedom model of the AHCs is created. Control laws are then applied to the system to mimic the phenomenological active nonlinear functions of the outer hair cells seen in the mammalian cochlea and to improve the ability of a single AHC to work for more than one frequency.