The self-tuned regenerative electromechanical arametric amplifier: A model for Active amplification in the cochlea

We describe an electromechanical acoustic sensor which we have constructed and tested as a conceptual model for the active process in the mammalian cochlea. The sensor is based on a mechanical resonator - a stretched latex band - which is tonically (tensionally) modulated by an electromechanical actuator. A feedback circuit senses the motion of the resonator, and modulates its tension at twice the frequency of its motion. An amplifier is thereby formed, which is self-tuned to the circuit´s resonance, and which produces gain by regeneration and degenerate parametric pumping. We show that this system is surprisingly simple in structure; is physiologically plausible as a model for the basilar membrane and associated structures; and that it reproduces several well-known features of the cochlear amplifier, such as the variation in center frequency and bandwidth with gain, and a cubic transfer characteristic in open loop.