Active vibration control

Lueg's 1936 patent [1] is generally cited as the founder of the concept of active control; but we have to agree with A. Roure [2] that, while it's undeniable that "active control works", industrial applications are still few and far between sixty-five years later, despite the advent of digital processors fast enough to implement most applications.

The first industrial applications, however, were mainly acoustic, in particular to control fan noise in ventilation and air-conditioning ducts, leading today to genuine industrial products.

Another field which has seen early industrialization with real success is that of residual noise control in the internal cavity of earmuffs.

Active vibration control is a priori more complex for the following reasons:

• several waves coexist at a given frequency [R 3 140] , with velocities that vary with frequency;

• boundary conditions are of great importance;

• the structures involved are very rarely unidirectional.

Since the mid-1980s, however, a major challenge has been to control the acoustic emissions of submarines carrying the strategic deterrent force, leading to significant R&D investment in active vibration control in France. This was the main impetus behind the development of "plots actifs" or active magnetic bearings. [3] .

Outside France, one of the earliest applications of active vibration control also involved "active studs", this time for aeronautical applications: an active suspension system for the engines of Cessna's Citation X business jet, developed by Lord, an American pioneer in this field. The aim is to attenuate solid-borne noise in the cabin.