Active Vibration Isolation using Smart Structures

Passive techniques for the isolation of structures from vibrating sources of ten have inadequate performance, particuarly in the case of lightweight flexible structures. The use of active control inputs applied directly to the source is one way of dealing with the problem. An alternative procedure is to design a structure integrating the transducers required for the control inputs and the response measurements. The form of the transducers and the optimisation of their performance may then be adapted to deal with particular types of vibration input or modes of response of the structure. In addition the system may be used to control acoustic radiation or transmission as well as isolating vibrations. This paper presents the results obtained on an expeeimental set up simulating this kind of problem where the form and the position of the transducers could be varied. By measuring the response of the structure integrated over a particular area the effects of particular types of mode could be taken into account to deal with specific types of input or limit particular modes of reponse more efficiently. Results are presentend using different modes of vibration excitation of the receiving structure with and without control are presented for particular input frequencies. The problems of optimising the control system to deal with multiple frequency inputs are discussed.