Modelling inertial actuators and cochlear micromechanics

Institute of Sound and Vibration Research (ISVR), University of Southampton, UK

Some current research trends in active vibration control are discussed, focusing on the use of many locally-acting modular controllers to reduce the global vibration in large structures. Such modules would contain a single actuator, sensor and controller, together with a self-tuning element to adapt the controller to the environment it finds itself in. If the actuator and sensor are collocated and dual, the global performance of an array of locally acting controllers can be almost as good as a fully centralised controller, but without the design and communication problems. The use of inertial shakers as practical actuators in such systems is considered, together with the stability problems associated with using these devices in local feedback loops. The action of the cochlear amplifier within the inner ear is then discussed in terms of the control of the global vibration behaviour through the action of a large array of locally acting feedback systems, with actuation provided by the outer hair cells in this case. The cochlear amplifier enhances the vibration within the inner ear, by 40-50 dB, greatly improving the sensitivity and selectivity of our hearing. The changes in the basilar membrane dynamics required to amplify a wave propagating along the cochlear are described, and the way in which these changes are achieved is discussed for various micromechanical models of the organ of Corti. It is seen that the kind of lumped parameter model used to understand the action of a feedback loop in the case of an inertial actuator, used to attenuate the vibration in engineering structures, can be used to describe the dynamics of the basilar membrane under feedback control, which amplifies the vibration in the inner ear.

Laboratoire de Mécanique des Structures et des Systèmes Couplés - LMSSC