Problems with AVC

• Since active control system essentially adds energy to the vibrating system, it may also create instability due to erroneous sensors and phase-lag in actuation.
• Active systems are in general quite expensive – since it involves the installation of micro-processors, data acquisition systems, sensors, actuators, signal conditioners and power amplifiers.
• Also, in general, active systems work efficiently within a finite frequency band. If the vibrating system gets excited beyond the range, it could amplify the disturbance. This is also known as ‘water-bed' effect.

Spillover: The biggest problem of AVC

• Many of the vibrating systems are essentially flexible in nature and they are to be modelled as continuous systems.
• The actuation and sensing, however, are traditionally pointed in nature – for example, vibration sensing using accelerometers or actuation using pointed exciters.
• Such finite number of actuators and sensors could not control all the vibrating modes of an infinite dimensional continuous system. Furthermore, the unmodelled modes could always get excited by the finite-actuation system. Hence, eventhough the vibration could be controlled in the desired bandwidth, the actuation energy may spill-over to the unmodelled modes causing severe resonance.
• This problem could, however, be resolved by using distributed sensors and actuators based on smart materials.