Active control of a lumped acoustic source driven by various actuators

This paper studies an acoustic source with a relatively small thickness and high bending stiffness. The high bending stiffness is obtained with a sandwich structure in which the face of the sandwich structure internal to the source is perforated to increase the acoustic compliance. Multiple actuators are used to drive the moving component of the acoustic source. Feedback and feedforward damping control techniques are used to actively obtain a smooth frequency response, especially at low frequencies. Such a compensation scheme generally leads to amplification of the lower frequencies and may result in a significant electrical input power. In addition, a part of the input power is stored in mechanical and acoustical elements of the acoustic source. Voice coil and piezoelectric actuators are compared regarding the ability to recover the stored energy. Piezoelectric actuators are particularly attractive from energy recovery point of view because the acoustic source has to operate in the low frequency, quasi-static regime. The two-way energy ?ow between the actuator and a connected ampli?er is investigated. In particular, the effectiveness of energy recovery from the reactive components of the acoustic source is evaluated to improve the overall radiation ef?ciency. A lumped model is used to represent the acoustic source that is excited by a stacked piezoelectric element. The required power supply and resulting radiation ef?ciency are evaluated when a conventional analogue ampli?er is used. The result is compared to the case in which some parts of the stored power are recovered and sent back to the connected switching amplifier. It was found that approximately 66% of the reactive power stored in the acoustic source can be recovered. The study also reveals a significant increase in overall system ef?ciency and more than 80% decrease in the amount of required input power through recovering the reactive power in the system.