Abstract

Low frequency sound and vibration inside aircraft is now attenuated using commercial active control systems. These typically operate using many shakers acting on the structure to modify its vibration and hence reduce excitation of the sound field. As the structure becomes larger, or the excitation frequency becomes higher, the number of actuators and sensors required for effective control rises significantly. Conventional, fully coupled, control systems then become costly in terms of weight and sensitivity to individual failures. An alternative strategy is to distribute the control over multiple local feedback loops, which has been shown to be effective in a number of cases. Recent work will be presented on tuning these local control loops to maximise the power they absorb from the structure, which may allow the mass-production of generic active control modules that include an actuator, sensor and self-tuning controller. The workings of the inner ear also provide a remarkable natural example of distributed active vibration control, whose objective in this case is to enhance the motion within the cochlea. A simple model for this cochlear amplifier, in which each of the outer hair cells act as local control loops, will be described and its use illustrated in predicting the otoacoustic emissions generated by the ear. These emissions are used clinically to screen the hearing of young children and so it is important to understand how they are generated within the cochlea.